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HYDROELECTRIC
POWER STATIONS
BY
ERIC A. JjOF
t •
AND
DAVID B. RUSHMORE
FIHST EDITION
NEW YORK:
JOHN WILEY & SONS, Inc.
London: CHAPMAN A HALL, Limitbd
1917
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Copyright, 1917
BY
ERIC A. LOF AND DAVID B. RUSHMORE
P<?CSB Of
BRAUNWORTH & CO.
Bi»OK MANUFACTUREH8
BROOKLYN, N. Y.
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PREFACE
Increased activity in the development of our water-power
resources is certain to take place in the near future, because
of the rapid and general increase in power demands on the central
station systems, and because of the increased cost and shortage of
fuel. A book, therefore, dealing with the many phases of this
subject from a practical and up-to-date engineering standpoint,
will be of great benefit, not only to those who have been actively
engaged in such development work, but also to those who may
desire to enter it in the future.
The work of planning, building, operating a hydro-electric
power development requires a full understanding of the economic
factors which enter into the problem, and a thorough knowledge
of both the hydraulic and the electrical engineering sides of the
subject. Any book to be complete, must, of necessity, cover all
these branches. Limited space, however, makes it impossible to
deal with minor details, and the book is not intended as a treatise
on the design of individual structures, machinery and apparatus
which go into the makeup of a power station. Many books have
been written dealing with such detailed desig^ns, and manufac--
turers should be freely consulted. This book deals with and
explains the problems which must be solved in connection with
the construction and management of a hydro-electric power'
station, so that the manager or engineer may select power equip-
ment and fully understand the economic factors which enter into
each individual situation. The authors have endeavored to
describe the most recent engineering practice and they have
included a considerable amount of information not available
hitherto.
This is an educational treatise for the student and operating
man and the manuscript has been submitted to experts in the
various branches of the subjects treated.
It is believed that a study of this volume will result in improving
the service and operating eflBciency of many systems.
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vi PREFACE
The authors also wish to take this opportunity to express
their appreciation and thanks to those who have so kindly and
wiUingly assisted in the preparation of this work with their
suggestions and advice. Among these may especially be men-
tioned, Mr. Lewis F. Moody of the I. P. Morris Company; Mr.
Chester W. Larner of the Wellman-Seaver-Morgan Company;
Mr. W. A. Doble of the Pelton Water Wheel Company; Mr. A.
V. Garratt of the Lombard Governor Company; Mr. J. H. Man-
ning of the Stone & Webster Company; and Mr. A. S. Crane of
the J. G. White Company.
Eric A. Lof
David B. Rushmore
Schenectady,
October, 1917.
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CONTENTS
PAOB
I. General Introduction 1
History of Water Power and Electrical Developments.
Conservation of Natural Fuel Resources. Available and
Developed Water Power in United States. Power from
Inland Waterways. Primary Power and Its Uses. CJonv-
mercial Possibilities for Hydro-Electric Power.
II. Htdboloqt 39
1. Properties of Water 39
Weight. Volume. Critical Temperatures. Latent Heat.
Specific Heat. Effect of Atmospheric Pressure. Measure-
ments.
2. Rainfall 44
Source of Water Supply. Variation in Rainfall. Rainfall
Records.
3. Disposal of Rainfall 47
Evaporation. Absorption. Run-off.
4. Stream-flow 63
Definition of Terms. Variation in Stream-flow. Factors
Affecting Stream-flow. Measurements of Stream-flow.
Government Records.
6. Energy of Flowing Water . ." 66 >
Potential Energy. Kinetic ,Energy. Head. Velocity.
Quantity. Horse-power.
6. Convenient Equivalents 68
Second-feet per square mile vs. run-off in inches. Second-
feet vs. run-off in acre-feet. Miner's inch, etc.
III. CXiASSmCATIGN OP DEVELOPlfENTS 70
Low-head Developments. Medium and High-head De-
velopments.
IV. Dams and Headworks 74
1. Dams 74
Classification. Location. Timber Crib Dams. Earth-fiU
Dams. Rock-fill Dams. Masonry Dams — Gravity — But-
tressed— ^Arched. Rules Governing Design.
2. Flashboards 91 /
Stationary Boards. Sliding Gates. Tilting Gates. Tain-
ter Gates. Rolling Gates,
vii
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viii CONTENTS
CHAPTER PAGE
3. Fishways 99
4. Intakes 100
Trash Racks. Low-head Installations. High-head Instal-
lations. Influence of Ice.
V. Water Conductors and Accessories 1C4
1. Water Conductors iv/4
Classification. Canals. Flumes. Tunnels. Pipe Lines —
Head — Loss of Head — Hydraulic Gradient — Size of Pipe
Line — Steel Pipe — Wooden Stave Pipe — Concrete Pipe.
2. Water Hammer and Surge Tanks 138
Water Hammer. Surge Tanks — Simple — Differential.
3. Gates and Valves 144
Requirements. Sluice Gates. Tainter Gates. Gate
Valves. Operation and Control. Pivot Valve. Johnson's
Hydraulic Valve. Air Valves.
VI. Storage Reservoirs 169
Storage and Pondage. Limitation to Storage. Location of
Reservoir. Intakes. Seepage and Evaporation.
VII. Power-house Design 165
1. Building 165
General Design. Basement43. Foundations. Floors.
Walls. Roof. Windows. Doors. Traveling Crane. Venti-
lation. Illumination. Heating. Miscellaneous.
2. Arrangement of Apparatus 175
General Considerations. Turbines. Governors. Gen-
erators. Exciters. Transformers. Current Limiting Reac-
tors. Switchboards. Oil Circuit Breakers. Lighting Ar-
resters. Outdoor Apparatus.
3. Transportation and Erection 193
Transportation. Unloading. Apparatus Storage. Sched-
ule of Erection. Crane Service. Protective Features. Co-
operation.
4. Starting Up 198
General Precautions. Drying-out. Insulation Resistaiice.
VIII. Hydraulic Equipment 202
1. Turbines 202
Reaction Turbines. Impulse Turbines. Selection of Tur-
binet:. Specific Speed. Actual Speed. Characteristic
Curves. Speed Regulation. Overspeed. Mechanical De-
signs. Reaction Type — Horizontal — Vertical — Runners —
Gate Mechanism — Speed Rings — Casings — Draft Tubes —
Bearings. Impulse Type — Horizontal and Vertical — Runners
— Arrangement of Runners — Nozzles — Housings.
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CONTENTS ix
CBAPTKB PAOB
2. Governors 246
Factors affecting Speed Regulation. Action of Governor.
Pipe-line Pressure caused by Governor Action. Energy
Output. Arrangement and Operation. Methods of Con-
trol. Typical Designs.
3. Pressure Regulators or Relief Valves 258
Governor-operated. Pressure-operated.
4. Water-flow Meters 262
Venturi Meter — ^Register — Manometer.
5. Water Stage Registers 266
Printing — ^Recording.
IX. Electrical EgtriPMENT '. 270
1. General Considerations 270
Voltage. Frequency.
2. Ssmchronous Generators 280
General Description. Induced E.M.F. Effect of Power
Factor on Operation. Field Excitation. Regulation. Short-
circuit Current. Armature Connections. Wave Shape.
Grounding of Generator Neutral. Rating. Efficiency.
Speed. Voltage. Parallel Operation. Mechanical Design.
Lubrication. Ventilation. Brakes.
3. Induction Generators 348
Output and Excitation. Comparative Capacity of In-
duction and Synchronous Generators. Operation. Places
of Utilization. General Construction.
4. Exciters 350
Separate Excitation. Capacity and Rating. Voltage.
Characteristics. Shunt vs. Compound Wound. Speed.
Method of Drive. Mechanical Design. Arrangement and
Connections. Exciter Batteries.
5. Voltage Regulation 363
Hand Regulation. T.A. Regulator — Method of Opera-
tion— Cycle of Operation — Regulator Arrangements. Line-
drop Compensation. KR-System of Regulation. High
Voltage — High Current Relays. Synchronous Condenser
Regulation.
6. Transformers 373
Fundamental Principles. Induced E.M.F. Ratio. Mag-
netizing Current. Reactance. Regulation. Core and Shell
Type. Method of Cooling. Single and Polyphase. Rating.
Efficiency. Voltage. Taps. Number and Size of Units.
Connections. Parallel Operation. Mechanical Design. Oil.
Drying Transformers. Drying Oil. Testing Oil. Operation.
Oil Supply System. Cooling Water System.
7. Current Limiting Reactors 458
Purpose of Reactors. Rating. Rating as Affected by Fre-
quency, Voltage and Current. Effect of Reactance on Power
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X CONTENTS
CBAPTSB PAOa
Factor and Regulation. Lones. Inductance. Location.
Number of Reactors. Size of Reactor and Determination
of Three-phase or Balanced Short-circuit Currents. Single-
phase Short-circuit Currents. Mechanical Design.
8. Switching Equipment 485
System of Connection and Relay Protection. Oil Circuit
Breakers. Relays. Switchboards. Instrument Equipment.
Current and Potential Transformers. Exciter and Field
Control. Voltmeter and Synchronizing Receptacles. Am-
meter Transfer Switches. Throw-over Switches. Calibrat-
ing Terminals. Control Switches. Mimic Buses. Bus and
Switch Structures. Disconnecting Switches. Signal Systems.
Multi-recorder. Oil Circuit Breaker Batteries.
9. Over-voltage Protection 503
Classification of Over-voltages. Lightning Arresters.
Arcing Ground Suppressor. Short Circuit Suppressor. Pro-
tection of Telephone Lines.
10. Station Wiring 625
Insulation. Open Wiring. Cables in Ducts or Conduits.
Single vs. Multiple Conductors. General Practice. Size of
Cables. Corona limit of Voltage. Economical Considera-
tions. Voltage Drop. Resistance and Reactance Tables.
X. Economical Aspects 644 /
Preliminary Considerations. Guide for Preparing Water
Power Reports. Amount of Energy Available. Power De-
mand. Load and Diversity Factor. Primary and Second-
ary Power. Water Storage. Auxiliary Stations. Intercon-
nection of Systems. Investigating an Enterprise. Cost of
Hydro-Electric Power Plants. Cost of Power.
XI. Organization and Operation 746
Management. Operating Force. Operating Records.
Operating and Maintenance Instructions.
Appendix:
I. References to Descriptions of Plan)» 757
II. Principal Data on Transmission Systems Operating at 70,000
volts and above 783
■ III. Turbine Testing Code 788
Index 803
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HYDEO-ELECTKIC POWEfi STATIONS
CHAPTER I
GENERAL INTRODUCTION
HISTORY OF WATER POWER AND ELECTRICAL DEVELOPMENTS
The use of water power for industrial purposes dates back to
very ancient times. The crude current wheels were familiar
to the Chinese on the Yellow River and the Hamites on the Nile
and Euphrates fully three thousand years ago. These wheels
operated entirely by the kinetic energy of the moving water, and
the power thus obtained was utilized for raising the water of the
rivers for irrigating the arid land and also for grinding of corn
and other simple applications. Similar current wheels, although
necessarily of improved design, have been most widely utiUzed
and, while very inefficient, they are still used for minor irrigation
and other purposes in many countries.
The first radical change in the art was the use of channels,
by which the water could be conducted and directly applied to
undershot wheels. This improvement resulted in the utilization
of some 30 per cent of the theoretical water power, and the system
maintained its prominence imtil almost the middle of the eigh-
teenth century, when the overshot wheel was invented by John
Smeaton, who showed that if the bucket wheel was changed into
an overshot form, its useful efficiency would be increased to over
6Q per cent. In this type of wheel the energy of the water was
applied directly through its weight by the action of gravity and
3delded a very high efficiency. Overshot wheels were formerly
built of great size. One at Laxey, Isle of Man, constructed about
1865 and is said to be still in operation, is 72 feet 6 inches in
diameter and develops 150 horse-power. A number of overshot
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2 GENERAL INTRODUCTION
wheels are also in use at old mills in the Catskill Mountains
in New York State.
The breast wheel, which followed the overshot wheel, was de-
veloped in England during the latter part of the eighteenth
century and was used for a long number of years. It consisted
of a circular drum, having on its periphery a series of buckets,
the sheathing of the drum forming their bottom. They were
operated partly by gravity and partly by kinetic energy, and
the water was appUed through a fliune and controlled by gates.
Below these was located the " breast " which consisted of a con-
cave cylindrical surface of planking concentric with the wheel.
The clearance was very small, thus preventing the water 'from
spilling out of the buckets until it had reached the lower
level. This type of wheel gave an eflSciency of about 70 per
cent.
The wheel types described above have, nowever, now been
almost entirely superseded by the turbine, and are therefore
so nearly obsolete that they may be considered as of historical
interest only. While the fundamental principles of the turbine
may be distinguished in wheels used in the sixteenth century,
the principal developments were made during the last century.
In the turbine the water acts mainly by impulse or reaction or
both, and the velocity has a definite relation to the head.
In 1823 M. Fourneyron began his experiments on the radial
outward-flow turbine, the first of which was installed at Pont
Sur rOgnon in France in 1827. Its principle consisted in an out-
ward discharge from a pipe to a wheel with curved buckets placed
outside of the apertures of discharge. The buckets, revolving
from the action of the water, finally discharged it at the circum-
ference with its force exhausted. The tube which supplied the
water was closed at the bottom by a concave cone surrounding the
wheel shaft, which passed up through it in a pipe, so as not to be
exposed to the water. This cone was surrounded by a number of
guide plates, which directed the water to the buckets in the proper
tangential direction.
The axial discharge turbine was first built by Henschel & Son in
Germany in 1837. There has always been doubt as to whether
this turbine should be attributed to Jonval or to Henschel. Jon-
val thoroughly described the basic idea in a patent dated 1841 and
it is quite possible that he was working on the proposition as early
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WATER POWER AND ELECTRICAL DEVELOPMENTS 3
as Henschel. It proved to be far superior to the outward dis-
charge type in that it ahnost entirely eliminated the latter.
The inward-flow wheel, in which the action of the Foumeyron
turbine is reversed, was patented by S. B. Howd, of Geneva, N. Y.,
in 1836, and seems to have been the origin of the American type of
turbine. Very great improvements were, however, made in the
construction by James B. Francis about 1847, and many regard
him as the originator. The Francis turbine of to-day has dis-
placed all other types of reaction turbines, and with its rapid
development, radical departures have been made from the strictly
radial inward-flow, so that the Francis turbine of to-day is of a
combined radial or diagonal inward discharge type.
The impulse wheels were among the earliest forms used. Thus
the rovet volant or flutter wheels were used for centuries in
India, Egypt, Syria and Southern France. They consisted of flat,
vertical vanes projecting radially from a vertical wooden shaft,
the water jet from the feeding spout striking the vanes tan-
gentially near their ends. It was not, however, until 1853 that
this type of wheel was given a scientific consideration in this
country by Jearum Atkins, while its practical development must be
credited to Lester A. Pelton, who, in 1882, and following years,
made radical improvements in its design. This type of wheel is
now extensively used in the West, where the high heads made such
a wheel necessary. '^
The first great water power developments were made in the
New England States. The textile industry was destined to
expand rapidly and the water power of the streams was its sup-
porting ally. Under this influence the first great water power
was developed on the Merrimac River, in 1822, where subse-
quently the City of Lowell became a great cotton manufacturing
center. Near Lowell there were soon developed the equally
prominent water powers on the Merrimac River at Manchester,
in New Hampshire, and Lawrence, Mass. These developments
had each capacities of 10,000 to 12,000 horse-power,* and each
was chiefly devoted to the manufacture of cotton goods, as were
the water powers of Cohoes (1828) in New York, and Lewiston
(1849) in Maine. The Connecticut River water power at Hol-
yoke (1848) was largely devoted to the manufacture of paper, as,
later, were the Fox River powers in Wisconsin. The water pow-
ers on the Genesee River at Rochester, N. Y. (1856), and on the
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4 GENERAL INTRODUCTION
Mississippi River at Minneapolis (1857), were largely devoted to
the manufacture of flour.
In 1861 the development of the mighty power of Niagara Falls
was begun, a canal being built through the town to a power-
house at the edge of the gorge below the falls. The Niagara Falls
Hydraulic Power & Manufacturing Company was formed in
1872, and during the first years its operation consisted in fur-
nishing water to numerous water wheels of different manufactur-
ing enterprises. The inefficiency of this method, however, soon
became apparent, and a central power-house was built in 1881 »
the energy being transmitted to the factories along the edge of the
cliff by means of ropes, belts and shafts.
Different opinions exist as to the time at which the first trans-
mission of electricity took place. Its possibility was pointed
out as early as 1850 and possibly earlier, and it is claimed that in
1858 electricity was, for the first time, utilized for driving a com-
mercial machine. This was in the artillery works of St. Thomas
d'Aquin, France, where a dividing machine was driven by an
electric motor, which derived its current from an adjacent bat-
tery. Though the electric motor existed long before the dynamo,
it attained no prominence until after the practical demonstration
of the latter. As long as the galvanic battery constituted the
source of power, the application was naturally restricted. Another
reason was the defective construction of the earlier motors, their
counter E.M.F. being comparatively weak, and hence the work
which could be obtained from them was small in comparison with
the power expended and their size.
While the principle of the reversibility of the electric motor
seems to have been known as early as 1850, it was the practical
experiments carried out by Gramme at the Vienna Exposition in
1873 that clearly demonstrated the practical importance of this
property. Gramme is, therefore, generally given the credit as
being the one who first practically demonstrated the possibility
of employing the electric current for transmitting energy from one
place to another. His experiments at this Exposition consisted
in transmitting current from a machine working as a generator
to a second machine about 550 yards distant, working as a
motor driving a pump.
In 1878 a motor was installed at the sugar works at Sermaize,
France. It was used to operate a hoist and derived its current
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WATER POWER AND ELECTRICAL DEVELOPMENTS 5
from a steam-driven Gramme generator. The application of
water power for driving dynamos followed shortly, and the same
year a water-wheel-driven generator was installed at the Shaw
Chemical Works, Eng., and power supplied to a motor 150 yards
distant for driving miscellaneous tools. In 1882 the first com-
mercial central stations for lighting began operation in London
and New York, and the same year marked the building of the first
hydro-electric central station in the United States at Appleton,
Wis., Rgs. 1 and 2.
In the above systems, and several others, the electric current
was transmitted for very short distances only but in 1882 Marcel
Deprez bxiilt the first long-distance transmission line from Mies-
bach to Munich, a distance of 37 miles. It was built purely for
experimental and demonstration piurposes, 2400-volt direct-
current being used. The results proved to be very encouraging
and financial support was obtained for a larger project. Thus,
in 1884, Deprez began preparations for the Criel-Paris trans-
mission, which was completed in 1886. In this 20 amperes direct-
ciurent was transmitted the 25-mile distance at a potential of
7500 volts, the transmission efficiency obtained being about 32
per cent.
The first A.C. transmission system was the one at Cerchi,
Italy, made in 1886 and known as the " Cerchi Tivoli-Rome
Plant." The equipment of this station consisted of two 150 H.P.
steam-driven, single-phase Ganz generators designed to operate at
112 volts. Transformers having a ratio of 1 : 18 were used to
step from this voltage up to 2000, at which voltage energy was
transmitted to Rome, a distance of 17 miles. In 1889 the capac-
ity of this steam plant was increased to 2700 H.P.
In 1887 Tesla, Ferraris and Bradley pointed out the advan-
tages of the three-phase over the single-phase system, but it
was not until 1891 that the first commercial three-phase trans-
mission line was put into operation. This was the 112-mile
Laufifen-Frankfort Une supplying a Ughting load to the City of
Frankfort. The power-house installation consisted of one 225
Kw. three-phase generator, direct connected to a water wheel
operating under a head of 10 feet. The line voltage was 12,000.
In the United States the first A.C. hydro-electric installation
was the one at Oregon City by the Willamette Falls Electric
Conipany, now owned by the Portland Railway, Light and Power
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6
GENERAL INTRODUCTION
Fio. 1. — Exterior View of First Hydro-Electric Central Station in United
States at Appleton, Wisconsin. Installed in 1882. Capacity 250 lights.
|ii^^
Fig. 2. — Interior View of First Hydro-Electric Central Station in United
States at Appleton, Wisconsin.
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WATER POWER AND ELECTRICAL DEVELOPMENTS 7
Company. This installation took place in 1889 and consisted of
two 300-H,P. Victor wheels belted to 4000-volt single-phase gen-
erators, the power being transmitted to Portland, 13 miles distant.
In 1890, shortly after the Willamette Falls Electric Company
had completed their installation, the Telluride Power Company
installed at Ames, Col., two 150-Kw. single-phase generators
directly connected to Pelton water wheels operating under a head
Fig. 3. — Power House, Mississippi River Power Company, Keokuk, Iowa.
of 500 feet. Power was transmitted to Telluride^ a distance of
5 miles, at 3000 volts.
In 1892 another single-phase transmission plant was installed
in CaUfomia and deUvered power to Pomona, approximately 13
miles distant, and about 29 miles to San Bernardino. The voltage
at the beginning of operation was 5000, which was higher than
any previously used commercially, but on February 16, 1893,
this was raised to 10,000 volts, and on May 2, 1893, by connecting
their transmission Unes all in series, 120 kw. was carried 42 miles
with a transmission efficiency of 60 per cent, at that time a great
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8
GENERAL INTRODUCTION
achievement and an indication of the possibilities of electric trans-
mission of power.
To Southern Califomia also belongs the distinction of having
the first commercial pol3^hase transmission system installed and
operated in the United States. In 1893 a generating station was
—
—
—
—
—
—
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—
•~
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■"
ISO^OOO
140,000
180,000
10,000
110,000 -
8
100,000 1
90,000^
80,000 3
70,000 3
__
80,000 1
a
Mazi
40,000
90,000
SQlQOO
10,000
Yeat>
Fig. 4. — Commercial Transmission Voltages.
built by the Redlands Electric Light & Power Company (now the
Southern Califomia Edison Company), at the mouth of Mill
Creek Canyon. The plant consisted originally of two 250-Kw.,
2400-volt, three-phase, Y-connected generators, running at
600 R.P.M., and driven by Pelton water wheels under a head of
295 feet. The power was transmitted for a distance of 7§ miles
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WATER POWER AND ELECTRICAL DEVELOPMENTS 9
to Redlands and there used for lighting and industrial motor
applications.
Before the end of the same year another polyphase plant was
installed at Hartford, Conn., where 400 Kw. was transmitted
11 miles at 5000 volts. This plant replaced a single-phase in-
stallation which had been delivering power for lighting over the
same line since 1891.
With these plants began the era of hydro-electric power trana-
mission in the country, and statistics show that nearly three
hundred plants were in actual operation about 1896. It would be
almost impossible to tabulate all the thousands of plants and
systems now in operation. Single plants with capacities of one-,
quarter million horse-power have been built, Fig. 3, and power
is now being commercially transmitted for distances of nearly
250 miles at potentials of 150,000 volts, Fig. 4. As yet the limit
is not in sight, but one thing is certain, that the introduction of
the electric system and the evolution in the design of apparatus
have made possible the concentration of such enormous amounts
of power which are now generated in modem stations and its
transmission for long distances to centers where an economical
market can be found.
HISTORICAL REVIEW OF WATER-WHEEL DEVELOPMENT
7
1740 Barker's Mill, the simplest t3rpe of tangential outflow turbines, was
invented. It had radial arms and operated purely by reaction.
1823 M. Foumeyron began his experiments with the radial outward-flow
turbine.
1826 A radial inward-flow turbine waa proposed by Ponoelet.
1827 The first Fourneyron turbine was erected at Pont Sur TOgnon, France.
1836 Samuel B. Howd of Geneva, N. Y,, obtained a patent on an inward-
flow turbine.
1837 Foumeyron erected a turbine at St. Blaise, Switzerland, which oper-
ated under a head of 354 feet.
1837 O. Henschel, of Cassel, Germany, invented the downward axial-dis-
charge turbine, later known by the name of Jonval or Koechlin.
1841 The first axial-discharge wheel was introduced into practice by the
French engineer, Jonval.
1842 James Whitelaw, of Paisley, developed an improved type of Barker's
Mill which was erected on Chard Canal. This wheel had spiral
tapering arms so curved that the water flowed radially when the wheel
was running at proper speed.
1844 A Foumeyron turbine, constmcted by Uriah A. Boyden, was erected
at Appleton Company's cotton mills in Lowell, Mass.
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10 GENERAL INTRODUCTION
1847 James B. Francis made radical improvements in the inward-flow tur-
bine.
1850 About this time the Jonval turbine was introduced in America by
Elwood and Emile Geyelin, of Philadelphia.
1853 Jearum Atkins was the first scientifically to consider the impulse wheel
in this country.
1859 The " American " or mixed-flow turbine was designed.
1882. Lester A. Pelton made radical improvements in this type of wheel.
HISTORICAL REVIEW OF THE PROGRESS OF ELECTRIC POWER
TRANSMISSION
1820 A. M. Ampere announced his discovery of the dynamical action between
conductors conveying electric currents; currents flowing in the same
directions attracting and in opposite directions repelling.
1821 Michael Faraday discovered the electro-magnetic rotation in causing
a wire conveying a voltaic current to rotate continuously around the
pole of a permanent magnet.
1831 Faraday discovered the principles of electro-magnetic induction and
laid the foundation for all subsequent inventions which finally led
to the production of electro-magnetic or d3mamo-electric machines.
1832 H. Pixii built a magneto-electric machine consisting of a fixed horse-
shoe armature, wound over with insulated copper wire, in front of
which revolved about a vertical axis a horse-shoe magnet.
1832 H. Pixii invented the spfit-tube commutator for converting the alter-
nating current into continuous current.
1840 Henry Pinkus proposed and patented the principle of transmitting
electric energy through wires to an electric motor on a railway
car.
1841 Prof. Francois Nolle t, Brussels, proposed the electrical utilization of
water and wind power for driving dynamos.
1850 Jacobi claimed that an electro-magnetic machine could also be worked
as a magneto-electric machine and vice versa.
1851 Dr. Sinsteden suggested the use of currents produced by magneto-
electric machines for driving electric motors.
1855 Bessolo, Italy, suggested and patented a scheme for the electrical
utilization of natural forces, and long-distance transmission of elec-
trical energy for power purposes.
1857 E. W. Siemens invented the drum-wound armature and improvement
in the shape of field magnets.
1858 Beams of intense electric light obtained from the volataic arc by
Faraday.
1858 Eugene Regnault worked a Froment electrical motor by the current
from a Clarke magneto-electric machine, driven itself by a mechan-
ical motor.
1858 A dividing machine was driven by an electric motor at the Artillery
Works of St. Thomas d'Aquin, France. Current was obtained from
a battery.
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WATER POWER AND ELECTRICAL DEVELOPMENTS 11
1864 Cazel obtains a French patent on an electric railway system in which
one or more magneto-electric machines are to be driven by hydraulic
or wind motors, and the current generated conveyed to a rotary
car motor by wires and the track rails.
1866 Dynamos according to Siemens' principle began to be built commerci-
ally and were employed for producing electric light.
1866 Felice Marco, Italy, was granted an Italian patent for the electrical
utilization of water power.
1867 Prof. Pfaundler, of Innsbruck, experimented with a Kravogl electric
motor exhibited at the Paris Exposition, and found %at it could
also be used for generating electric currents.
1870 The Gramme ring dynamo was invented.
1870 Jacobi works an electric motor by means of a secondary battery.
1873 Gramme and Fountaine discovered the reversible action of the dynamo
and made the first public demonstration of power transmission at
the Vienna Exposition. Current was transmitted from a machine .
working as a generator to a second machine 550 yards distant,
working as a motor and driving a pump.
1875 Alcide Girin was granted a French patent for the combination of elec-
tro-magnetic inductive apparatmi and a certain number of induction
coils in order to obtain in the secondary circuits a lower tension and
a higher intensity than in the primary circiUts.
1876 Jablochkofif's arc lamp invented.
1876 WaUaoe-Farmer dynamo at the Philadelphia Centennial Exposition.
1878 A motor was installed in the sugar works at Sermaize, France, for oper-
ating a hoist. Current was obtained from a steam-driven Gramme
generator.
1879 First commercial arc lamp system (Brush) installed in Cleveland.
1879 Edison incandescent lamp invented and first complete system of
incandescent lighting installed at Menlo Park.
1879 Siemens and Halske install the first electric railway in which current
was generated by dynamos. It was at the Berlin Exposition that
a line of 550 yards was laid down upon which a small locomotive
drew passenger cars merely as a novelty.
1881 Carpentier and Deprez were granted a patent for a system of trans-
porting electricity to a distance and transforming it.
1882 Gaulard and Gibbs suggested the transformer for practical operation.
1882 Marcel Deprez built the first long-distance experimental line from
Miesbach to the Exposition in Munich, a distance of about 37
miles. He transmitted one-half horse-power direct current at a
pressure of 2400 volts.
1882 First hydro-electric central station installed at Appleton, Wis. Ca-
pacity 250 lights.
1882 First 'commercial central station for incandescent lighting began oper-
ation in London.
1882 Pearl Street Station of Edison Electric Illuminating Company began
operation in New York.
1883 " Feeder and Main " system first used.
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12 GENERAL INTRODUCTION
1883 " Thiee-wire " system first used.
1884 Dr. J. Hopkinson clearly established the fact that similar alternators
could be run as generators and motors. First practically demon-
strated in 1889 by Mordey.
1884 American Institute of Electrical Engineers was organized.
1885 First transformer built in this country by Wm. Stanley at Great
Barrington, Mass.
1885-88 Nicola Tesla and Galileo Ferraris invented independently the poly-
phase induction motor and pointed out the advantages of the three-
ph|pe system.
1885 National Electric Light Association was organized in Chicago.
1886 First regular 133-cycle, single-phase lighting plant was installed in
Buffalo.
1886 Criel-Paris transmission was completed. Twenty amperes direct-
current was transmitted for a distance of 25 miles at a potential of
7600 volts.
1886 Sprague installed the first electric street railway in this country at
Richmond, Va.
1886 The first A.C. transmission system was installed at Cerchi, Italy,
150 H.P being transmitted for 17 miles at 2000 volts single phase.
1887 Tesla, Ferraris and Bradley pointed out the advantages of the three-
phase system.
1888 Rotating field principle of alternating-current generators was invented.
1889 The first A.C hydro-electric installation in the United States was
installed by the Willamette Falls Electric Co., 300 H.P. being trans-
mitted for 13 miles at 4000 volts single phase.
1891 Lauffen-Frankfort Transmission. 110 H.P. was transmitted from
Lauffen to the Exposition at Frankfort, a distance of 112 miles at
12,000 volta, three phase.
1891 Sixty cycles introduced in United States.
1892 The first long-distance transmission in United States at San Antonio,
Cal. 800 H.P. was transmitted 28 miles at 10,000 volts single phase.
1893 Twenty-five cycles introduced.
1893 The first three-phase hydro-electric plant in United States was in-
stalled at Redlands, Cal.
1895 The first 5000-H.P. generators were installed at the Niagara Falls
Power Company.
1896 25,000-volt S3rstem of the Pioneer Electric Power Company, Utah.
1903 60,000-volt system of the Guanajuato Power and Electric Co., Mexico.
1908 110,000-volt system of Au Sable Electric Company, Grand Rapids,
Mich.
1913 150,000-volt system of the Pacific Light and Power Co., Los Angeles,
Cal,
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CONSERVATION OF NATURAL FUEL RESOURCES
13
WATER POWERS OF THE WORLD
The following Table is based on the area of the different
continents and on the assumption that the water power per
square mile is approximately 14 H.P. This value has been
found to be the average of a number of investigations in Euro-
pean countries. For Australia, however, this value is entirely
too high, and 3 H.P. per square mile has been assumed.
TABLE I
Watbb Powbbs of the World
Continent.
Area in
Square Miles.
Horse-power.
Africa
America, North .
America, South .
Ada
Australia. . .
Europe
11,613,679
8,037,714
6,g61,306
17,057,666
3,466,290
3,764,282
Total.
161,190,116
112,627,996
96,918,284
238,807,324
10,368,870
62,669,948
671,372,638
It is thus seen that the total water powers of the world rep-
resent about 700 miUion horse-power. This vast amount can,
however, not be economically developed at the present time, but
the tabulation merely shows the possibilities that may, in the
future, be derived from this natural source.
CONSERVATION OF NATURAL FUEL RESOURCES
One of the most important questions of the present time is the*
one relating to the conservation of our natural fuel resources.
While in 1880 the yearly coal consumption in this country was,
only approximately 70 million tons, in 1913 it amounted to about
575 million tons, Fig. 5. The output of our oil fields has, during
the same time, also increased at the same astonishing rate, while
the growth of our population during this period was only about
85 per cent, or about one-seventh the rate at which the fuel
consumption increased. It is easily realized what a tremendous
drain this consumption has been on our natural fuel resources,
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14
GENERAL INTRODUCTION
TABLE II
Land and Water, and Population op the States op the United States
Square Miles.
State or Territory.
Alabama
Arizona
Arkansas
California
Colorado
Connecticut
Delaware
District of Columbia. . . .
Florida
Georgia
Idaho
lUinois
Indiana
Iowa
Kansas
Kentucky
Louisiana
Maine
Maryland
Massachusetts
Michigan
Minnesota
Mississippi
Missouri
Montana
Nebraska
Nevada
New Hampshire
New Jersey
New Mexico
New York
North Carolina
North Dakota
Ohio
Oklahoma
Oregon
Pennsylvania
Rhode Island
South Carolina
South Dakota
Tennessee
Texas
Utah
Vermont
Virginia
Washington
West Virginia
Wisconsin
Wyoming
Totals and averages
Gross Area.
52,250
113,020
53.850
158,360
103.925
4,990
2.050
70
58.680
69.475
84.800
56.650
36,350
56,025
82.080
40,400
48.720
33.040
12.210
8.315
58.915
83.365
46.810
69.415
146.080
77.510
110.700
9,305
7,815
122,580
49,170
52.250
70.795
41.060
70,430
96.030
45.215
1.250
30,570
77.650
42.050
265,780
84,970
9,565
42.450
69,180
24,780
56.040
97.890
3.025.880
Water.
710
100
805
2.380
280
145
90
10
4.440
495
510
650
440
550
380
400
3,300
3.145
2.350
275
1.485
4.160
470
680
770
670
960
300
290
120
1.550
3.670
600
300
600
1.470
230
197
400
800
300
3,490
2.780
430
2.325
2.300
135
1,590
315
54,842
Land.
61.540
112.920
53.045
155.980
103.645
4.845
1.960
60
54.240
58.980
84.290
56.000
35.910
55.475
81,700
40.000
45,420
29,895
9,860
9.040
67.430
79.205
46.340
68.735
145.310
76.840
109.740
9.005
7,525
122.460
47.620
48.580
70.195
40,760
69.830
94,560
44,985
1.053
30,170
76,850
41,750
262,290
82,190
9,135
40.125
66.880
24.645
54.450
97.575
2.971.0.38
Population
1915.
2.301,277
247.299
1,713.102
2,848.275
935.799
1.223.583
211.598
358.679
870.802
2.816.289
411.996
6,069.519
2.798.142
2.221.038
1.807.221
2.365.185
1,801.306
767,638
1.351.941
3.662.339
3.015.442
2.246.761
1,926.778
3.391.789
446.054
1.258.624
102.730
440.584
2.881.840
396.917
10,086.568
2.371.095
713.083
5.088.627
2.114.307
809.490
8.383.992
602.765
1.607.745
680.046
2.271.379
4.343.710
424.300
362,452
2.171,014
1,471.048
1,359,474
2.473,533
174.148
100.399.318
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CONSERVATION OF NATURAL FUEL RESOURCES 15
Oil ProducUo
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FiQ. 5. — Yearly Coal and Oil Production in United States.
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16 GENERAL INTRODUCTION
and in justice to the welfare of the nation and of coming genera-
tions every practicable means should be employed for reduc-
ing it.
A material saving has been effected by the introduction of more
efficient apparatus and improved systems of operation. In the
modern central station, very great economies have been the result
from the substitution of a few large and highly efficient boilers
and steam turbines for a large number of relatively small and
uneconomical units, and from the introduction of plant economics
and skill not attainable in the smaller plants. The fuel economy
of the gas and oil engine is well appreciated. While their devel-
opment has been slow, a number of large gas-engine plants have
been built during the last few years, and it is quite possible that
the gas or oil engine will in the future be used to a great extent
for the production of power. The application of the power directly
to the work through electric motors instead of indirectly through
inefficient countershafting and belting has also resulted in a very
material increase in economy.
Beyond the above gains, which may be considered well within
the limits of possible attainment by our present knowledge, it is
reasonable to assume that the efficiency of our fuel engines will
not be increased very materially in the near future, and the only
safe course of accomplishing a reduction in the consiunption of
our natural fuel resources is to utihze the enormous energy of the
numerous water powers which is now going to waste.
Based on the Census Report the developed water powers of
this country may be taken as approximately 6 million horse-power.
Assuming that one hydraulic horse-power corresponds to an
annual coal consumption of 8 tons, it follows that the utilization
of this water power means a yearly saving in the coal consumption
of 48 million tons.
In the recent Report of the Bureau of Corporations the min-
imum water power in this country which can be readily developed
is placed at 31 million horse-power. This enormous power,
which is now entirely going to waste, could, if developed, effect
a yearly saving of 250 million tons of coal, besides releasing about
750,000 men for other work, and in addition dispense with the
tremendous railroad equipment required for its transportation.
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AVAILABLE AND DEVELOPED WATER POWERS
17
AVAILABLE AND DEVELOPED WATER POWERS IN UNITED STATES
The surveys and examinations necessary to a thorough and
ccurate report of the water-power resources of the United States
have never been completed. While in certain parts of the coun-
try they are fairly well known, in other parts, however, the infor-
mation is very fragmentary, and, therefore, an estimate of the
available water powers, such as given in Table III, must neces-
sarily be considered approximate.
TABLE III
Estimated Available Water Power in UNrrED States
Drainage
Area in
Square
MUes.
Flow per
Annum in
Billion
Cu.ft.
Horse
-POWBB.
Principal Drainaeres.
Minimum.
Assumed
Maximum
Develop-
ment.
North AtUntlc to Cape Henry. Va. . .
Southern Atlantic to Cape Sable, Fla .
Eastern Qulf of Mexico to MissiBsippi
River
159.879
123.920
142.220
433.700
333,600
905.200
299.720
225.000
70.700
290.400
223,000
62.150
8.942
5,560
6,867
2.232
12.360
9.580
8.583
521
2.193
15.220
614
1.761,000
1,050.000
466,000
362.000
2.180,000
3,300,000
5.570,000
2,425.000
2.680.000
10.750,000
433,000
63.000
3,481.000
1,630,000
803,000
Western Gulf of Mexico west of Ver-
million River
686.000
Miasiasippi River (tributaries from east)
Mississippi River (tributaries from
west, including Vermillion River). . .
St. Lawrence River to Canadian line. .
Colorado River above Yuma, Ariz ....
Southern Pacific to Point BoniU. Calif.
Northern Pacific
4,450.000
5.900,000
6.740.000
4.610.000
6.500.000
20,500,000
Great Basin
670.000
Hudson Bay
175,000
Total
3,260,490
72,672
31.040,000
56,146.000
These values are based on estimates prepared by the United
States Geolc^cal Survey for the National Conservation Com-
mission, 1908. With some revision, owing to lack of data avail-
able at that time, these estimates would place the minimum water
power of the country at approximately 31 milUon horse-power
and the maximum at 56 millions.
In arriving at this minimum horse-power, the minimum flow for
the two lowest seven-day periods in each year for seven years was
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18 GENERAL INTRODUCTION
determined and the mean of these values for the period of record
was taken as the minimum flow. It is obvious that this is some-
what higher than the absolute minimum, but the latter is usually
of so short duration that it would not be practicable or profit-
able to develop a site on this basis. The efficiency of the hydro-
electric equipment has been assumed to be 75 per cent.
The assumed maximum power has been based upon the con-
tinuous power indicated by the flow of a stream for the six months
of the year showing the highest flow. The average flow for the
lowest week of the lowest month of these six highest months was
then taken as the assumed maximum for the year. The yearly
averages thus obtained were then themselves averaged for a
series of years. It is, however, common practice to estimate on
the continuous power for nine months instead of six, which would,
of course, reduce the amount of maximum power available.
The above estimates do not include any storage possibilities
and a commercial development of the maximum power would
have to be based on the assumption that it would be profitable to
install auxiliary fuel plants to supplement the deficiencies during
the remaining six months of the year.
An endeavor has been made to determine the maximum power
that might be produced if all the practicable storage facilities on
the drainage areas were utilized. Surveys on many of the basins
make possible a fairly close estimate, but inasmuch as fully three-
fourths of the country has not been surveyed in a manner suitable
for this purpose, only rough estimates can be given for the entire
area. It may, however, be assumed with confidence with all
practicable storage sites utilized and the water properly applied,
there might be established eventually in the country a total water-
power installation of at least ICO million horse-power and possibly
more. It should, however, not be assumed that all this power is
economically available to-day. Much of it, indeed, would be too
costly in development to render it of commercial importance under
the present condition of the market and the price of fuel power. It
represents, on the other hand, the maximum possibilities in the
day when our fuel shall have become so exhausted that the price
thereof for production of power is prohibitive, and the people of
the country shall be driven to the use of all the water power that
can reasonably be produced by the streams.
The total developed water power of the United States, exclud-
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AVAILABLE AND DEVELOPED WATER POWERS 19
ing developments of less than 1000 H.P. each, as computed by the
Bureau of Corporations and given in Table IV, is 4,016,127 H.P.
Of this, 2,961,549 H.P. is classed as " commercial " power, and
1,054,578 H.P. as "manufacturing" power. Adding 2,000,000
H.P. to represent the power of developments of less than 1000
H.P. each, gives a grand total, in roimd numbers, of at least
6,000,000 H.P. and possibly 6,500,000 as the total water power of
the United States developed and under construction.
There is a marked geographical concentration of developed
water power. Thus, nearly 50 per cent of the developed " com-
mercial " water power of the coimtry is located in five States as
follows:
Per Cent
California 14
New York 13
Washington 10
Pennsylvania 6
South Carolina 6
Total 48
An even more marked concentration of developed water power
employed in manufacturing is shown by the following summary.
Per Cent
New York 30
New England States 36
Minnesota and Wisconsin 17
South Carolina 6
Total 88
The accompanying map, Fig. 6, shows the location of water-
power developments and power sections of streams in the United
States.
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20
GENERAL INTRODUCTION
TABLE IV
Developed Water Power in the United States of Concerns Havino
1000 H.P. or Over (Including Undeveloped Power), by States
(Compiled by Bureau of Corporations. 1912)
State.
Developed and
under constbuction.
Commer-
cial.
Manufac-
turing.
Undevel-
oped.«
Total
United States
North Atlantic States:
Maine
New Hampshire
Vermont
Massachusetts
Connecticut
New York
New Jersey
Pennsylvania
South Atlantic States:
Virginia
West Virginia
North Carolina
South Carolina
Georgia
Florida
North Central States:
Ohio
Indiana
Illinois
Michigan
Wisconsin
Minnesota
Iowa
South Dakota
Kansas
South Central States:
Tennessee
Alabama
Western States:
Montana
Idaho
Colorado
Arizona
Utah
Nevada
Washington
Oregon
California
Other States, not enumerated ^
Summary.
North Atlantic States
South Atlantic States
North Central States
South Central States
Western States
Other States, not enumerated «.
H.P.
2.061.549
H.P».
1.064.678
H.P.
2.638.528
H.P.
6.664.656
66.360
16.450
63.648
76.697
32,000
398.058
7.200
169,632
33.700
5.260
82.960
135.040
126.927
6.000
4.026
10.425
38.460
102.682
96.790
95.815
161.400
6.000
6.800
62.000
6.000
139.260
52,100
69.690
16.200
52.700
14.300
300.510
95.777
429.467
4.317
819.045
388.877
511.406
68.000
,169.904
4.317
168,338
103.658
40.197
53.922
16,519
316.313
17.620
16,160
14.050
47,467
12.360
4.260
12,751
30.420
106.153
72,200
10.450
6.000
7.780
696.947
107.627
225.774
10.450
6,000
7.780
100.000
13,600
44,460
14,620
4,000
103.093
i3!i43
44,800
1.260
61,426
96,686
286.360
6,676
1,000
62,100
117,660
91,400
101.600
161,000
8,167
200
3.862
105.700
42,300
59.000
2,600
24,000
116,700
143.600
732.749
2.000
382.815
489.410
634.792
3.862
1.225.649
2,000
333.608
133.608
138.305
146.239
61,619
906,464
7,200
182.774
96.120
22.660
168,436
278.082
425.627
6.000
10.700
15.675
113.311
260.762
294.352
269,616
302,400
8.167
7.000
65.862
16,460
244.960
94.400
128,690
16.200
66.300
38,200
416,210
230.377
1,168.216
14.097
1,808.807
086,014
1.271,072
82.313
2.401.663
14.007
> Ownership of less than 1000 H.P. excluded. States omitted from this table had
no concerns reporting developed water powers of 1000 H.P. or over, except as Indicated
in note 1. p. 63.
9 Embracing one concern in Missouri and four each in Maryland and Rhode Island
s The Census Report for 1910 gives the total water power used in manufacturing
•8 1.822.593 H.P.
< Sites on which expenditures have been made.
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AVAILABLE AND DEVELOPED WATER POWERS
21
ai
P
a
S
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22 GENERAL INTRODUCTION
POWER FROM INLAND WATERWAYS
There are great possibilities of hydro-electric power develop-
ments in connection with inland waterways, and this subject
should be given careful consideration when improvements or
new projects are contemplated. The advantages to conmiuni-
ties through the development of such water powers would be,
besides the benefit of cheap electric power, the prevention of floods
and increased efficiency of river navigation.
The low water in many rivers during the dry season would
absolutely prevent navigation unless dams with locks were
provided for raising the water level, while on the other hand
there are a very large number of streams that are not now navi-
gable at all, but which could easily J^e converted into streams of
great commercial value.
When a dam is to be built for improving the navigation of a
river, consideration should, therefore, always be given to the fact
that every dam not used for the development of electrical energy
means just so much loss of income. Such dams should, therefore,
be built of adequate height for possible hydro-electric develop-
ment.
The prevention of floods is also of the utmost importance.
In the United States alone the yearly flood loss has for a number
of years exceeded several hundred milUon dollars.
Storage and levee systems appear to be the only practical
.solution for flood prevention. Storage of flood waters is effected
by forests and similar surface vegetation and by artificial reser-
voirs. The amount stored by forests is and probably will be for
a long time to come indeterminate, since the forest is merely an
agent in assisting the ground to absorb the water. This is, there-
fore, essentially a ground storage, and the ability of the forest to
enhance this is dependent absolutely on the soil beneath the forest.
The extent to which flood waters could be stored by reservoirs
depends on the available reservoir capacity in the several river
basins. As a rule, the more diversified the character of the
basins, especially in contour, the greater facilities they afford for
reservoir storage. Large portions of many rivers are not subject
to correction by reservoirs, as in the Mississippi Vallej'^ for example.
It is, therefore, probable that streams draining one-third of the
area of the United States must forever be subject to floods, and the
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POWER FROM INLAND WATERWAYS 23
only treatment that now appears feasible for these streams is the
construction of levee systems. For the remaining two-thirds of
the United States, investigations made indicate that from 55 to
60 per cent of the flood waters can be saved by the utiUzation of
maximum storage capacity. Although the cost of such construc-
tion would be enormous in the aggregate, it is apparent that the
saving that would accrue for relief from flood damages alone would
soon return the entire investment.
In addition, the construction of storage reservoirs will natur-
ally have a very great bearing on the possibiUties of power devel-
opments. The stream can be regulated and the flows equaUzed
by storing the water dming the wet season and using the same to
increase the volume of the stream through the dry season. This
means a consequent increase in the power value of the stream due
to augmenting the low-water flow. It is thus estimated that in
this manner the economical water-power possibilities of the United
States would be increased to about 60 million horse-power.
Striking examples of what may be accomplished by an eflScient
regulation of navigable rivers is shown at Keokuk on the Mississippi
River, and at Hale's Bar on the Tennessee River. In both cases
Federal grants were given to private companies for constructing
a dam across a large navigable river, the result being a com-
bined river improvement and a power development of immense
size.
The Sanitary District's Canal, at Chicago, with its 50,000 H.P.
power development at Lockport, 111., clearly illustrates the great
possibilities in connection with canals. This subject has also been
given careful consideration in connection with the Barge Canal in
the State of New York, and the principal water powers created
by this canal are given in Table V. From this it is seen that the
increased power possibilities attributable to it will amount to
about 40,000 H.P.
The possibilities of power developments in connection with
water supply systems is, on the other hand, illustrated by the
Lob Angeles Aqueduct. This has a length of about 250 miles and
a capacity of 258 million gallons of water every twenty-four hours.
The flow of this water will be utiUzed for generating a total of
90,000 Kw. of electric energy at a number of power stations along
the route, from where it will be transmitted to Los Angeles. It is
estimated that the sale of this energy will take care of all the bonds
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24
GENERAL INTRODUCTION
TABLE V
Summary of Principal Water Powers Created by Barge Canal *
Location.
DiSTBXBUTBD HtDBAUUC HoBSE-POWKB
WITH ECONOMICAI. DeVBLOPMXNT
Before Canal. With Barge Canal.
Lockport
Rochester
Baldwinsville . .
Oswego River. .
Vischers Ferry .
Crescent
Waterford
1,700
2,452
33,960
4,530
9,732
2,640
41,640
6,530
6,980
6,506
> From Sixth Annual Report of N. Y. State Water Supply Commission.
and interest charges upon both the aqueduct system and the
entire hydro-electric installation.
PRIMARY POWER AND ITS USES
Statistics have never been compiled giving accurately the
total mechanical horse-power used in the United States. The
following estimate may, however, be considered to be fairly close
to the actual conditions, and it is safe to place the present value
at approximately 180 milUon horse-power, or nearly two horse-
power per capita for the entire population.
TABLE VI
Primary Power in UNrrED States
H.P.
Manufacturers 26,000,000
Central, stations 8,500,000
Isolated plants 4,500,000
Street and electric railways 4,000,000
Steam railroads 50,000,000
Steam and naval vessels 5,000,000
Mines and quarries 6,000,000
Flour, grist and saw mills 1,500,000
Irrigation 500,000
Automobiles 50,000,000
Horses and mules 25,000.000
Total 180,000,000
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PRIMARY POWER AND ITS USES
25.
The rapid growth in central electric Ught and power stations,
as taken from the latest Census Report, is shown in Table VII.
TABLE VII
Central Electric Light and Power Stations
Per Cent
•
1912
1907
1902
of
increase:
1902-1912
Number of stations ^
5.221
4,714
3,620
44.2
Commercial
3.659
1.562
3,462
1,252
2.805
815
30.4
Municipal
91.7
Total income
$302,115,599
$175,642,338
$85,700,605
252.5
Light, heat, and power.
including free service .
$286,980,858
$169,614,691
$84,186,605
240.9
All other sources
$15,134,741
$6,027,647
$1,514,000
899.7
Total expenses, including
salaries and wages
$234,419,478
$134,196,911
$68,081,375
244.3
Total number of persons em-
ployed
79,335
47,632
30.326
161.6
Total horse-power
7,528.648
4.098,188
1,845,048
308.0
Steam engines and
steam turbines:
Number
7,844
4.946.532
8.054
2,693,273
6,295
1,394.395
24.6
Horse-power
254.6
Water wheels
Number
2.933
2,471,081
2.481
1,349,087
1.390
438.472
111.0
Horse-power
463.6
Gas and oil engines:
Number
1,116
111,036
463
55.828
165
12.181
576.4
Horse-power
811.5
Kw. capacity of dynamos. . .
5,134.689
2,709,225
1,212.235
323.6
Kw. capacity per station . . .
983
574
334
194.3
Cost of construction and
equipment
$2,175,678,266
$1,096,913,622
$504,740,352
331.4
Cost per kilowatt capacity. .
$425
$404
$416
Output of stations, kw.-hrs .
11,602,963,006
5,«62,276,737
2,507,051.115
358.8
Estimated number of lamps
for service:
Arc
505,395
562,795
385.698
31.0
Incandescent and other
varieties
76,507,142
41,876,332
18.194.044
320.5
Stationary motors served :
Number
435,473
167,184
101.064
330.9
Horse-power capacity
4.130,619
1.649.026
438,005
843.1
> The term " station " as here used may represent a single electric station or a
number of stations operated under the same ownership.
The statistics represent all central stations which furnish elec-
trical energy for Ught, power and heat; for manufacturing, mining
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•26 GENERAL INTRODUCTION
and other commercial enterprises; for private dwellings; and for
public uses such as lighting streets, parks, etc. They do not
include electric plants operated by factories, hotels, etc., which
consume the current generated; those operated by the Federal
Government and State institutions; or plants that were idle or
in course of construction.
Aside from the growth in the number of stations the striking
features of the above table are the relatively larger increase in
the kilowatt capacity per station, while the cost of construction
and equipment remains practically the same. That this cost
has not been materially reduced is no doubt due to the increased
cost of the distributing and transmission lines, which form an
important part of the total cost of the system.
It is also of interest to note that the percentage increase in
the use of water power for the period of 1902 to 1912 was 463 per
cent, as compared to 264 per cent for steam power. On the
other hand, gas power increased 811 per cent, but this is not
of any great importance, as the horse-power capacity of the
gas engines installed at the beginning of above period was very
small.
Water power was used more extensively than steam in the
manufacturing industry prior to 1870. Since that time, however,
it declined steadily, while the use of steam power increased,
reaching a maximum of about 87 per cent in 1900. There has
since been a marked falling off in the percentage of directly applied
steam power and this has been due to the rapid introduction of
electric power. The increased use of the electric motor for driving
industrial machinery has been phenomenal and this is again best
illustrated by a reference to the Census Report.
Table VIII shows for all industries combined the horse-
power of engines and motors employed by manufacturing con-
cerns for the period from 1870 to 1909. The figures for the total
primary power exclude duplication and represent the primary
power of engines, water wheels, etc., owned by the manufacturing
establishments themselves plus the electric and other power pur-
chased from outside concerns. Especially striking is the increased
use of electric motor applications during this period. While the
primary power increased about 85 per cent, the application of
electric motors for manufacturing industries alone increased close
to 900 per cent.
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PRIMARY POWER AND ITS USES
27
TABLE VIII
Power Used in Manufacturing Industries
Primary i>ower, total.
Owned, total
Steam
Gan
Water
Other
Rented, total
Electric
Other
Electric motors, total.
Run by own power . .
Run by rented power.
1870
2,346.142
1,215,711
1.130.431
1880
3.410,83;
2.185,468
1,225.370
1890
5.939,086
5,850.516
4.681,596
8.930
1.255,206
4,784
88.571
88.571
15.569
1899
10,097,
9.778,
8.139,
134,
1.464,
49,
319,
182,
136,
492,
310,
182,
,893
,418
,579
,742
,112
,986
.475
,662
,913
,936
,374
,562
1904
,487.707
,854,806
,825,348
289.423
.647,880
92.154
632.902
441.589
191.313
.592.475
.150.886
441,689
1909
18.680,776
16.808.106
14.202,137
754.083
1,822.593
29.293
1,872,670
1.749.031
123.639
4.817,140
3.068.109
1.749.031
i
,
^^
Ste
am
Poi
or
—
—
—
...
^
1 '
1
-
—
--
I
—
--
--
^
1
'
Vati
rP
>we
r
—
— "
~
U-*
•
'_
Oas
Power
^__
^_
^_
—
-^
—
*— '
L— J
.^m-J
^^
1.— 1
L— 1
1— — 1
L— 1
L— J
1— ^
L_J
1 1
^—1
L_J
1 1
1900
1904
Year
1906
1912
100
00
80
70
60
30
40
30
20
10
a
s
£
FiQ. 7.— Relation of Steam, Water and Gas Power.
The curves in Fig. 7 show the approximate percentage relation
that steam, water and gas power bear to the total in the three
principal industries — Central Stations, Electric Railways and
Manufacturing.
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28
GENERAL INTRODUCTION
COMMERCIAL OPPORTUNITIES FOR HYDRO-ELECTRIC POWER
During recent years there has been a very large increase in the
number and variety of electric power applications, and this has a
very important bearing in stimulating the development of water
powers. Among the more important industries affected may be
mentioned: Agricultural work, including irrigation, textile mills,
mining, electrochemical work, railroad electrifications, etc.
Agricultural Work. The possibiUties of the use of hydro-
electric power in connection with farming and agricultural work
Fig. 8.— Operating Thresher at Night with Portable Motor Outfit.
are many and offer one of the most promising fields of the future.
The unqualified success that the appUcation of electric power
has had in this line of work indicates that it has become a factor
of such importance that it must now be seriously considered as
affecting both the cost and quality of the products of the modem
farm. Compared to other forms of applied power, the chief
advantages of electricity are reliability, safety, cleanliness and
flexibility in application. Power can be readily and economically
distributed to the scattered location of the various buildings where
the cost of providing separate engines would be practically pro-
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COMMERCIAL OPPORTUNITIES
29
hibitive. Fire risk is reduced to a minimum, which is of greatest
importance on isolated farms, where fire-fighting appliances are
limited, Fig. 8. With a number of motors installed for the various
classes of service, the operating periods can be so arranged as to
secure a very good load-factor, thus minimizing the cost of power.
The power supply may be obtained from the extensive net-
works of high-tension transmission lines which are now being
erected in so many sections of the country, and which are con-
tinuously being extended at a very rapid rate. While this supply
without doubt oflFers the simplest and cheapest source of power,
there are thousands of small streams whose wasted energy might
readily be transformed and appUed to useful work on farms by
the installation of small and inexpensive water-power plants.
The following tables show some of the more important appli-
catioDS of electric drive for farm machinery and power required.
TABLE IX
Motors for Farm Machinert
Machines.
Horse-power of Motor.
Minimum.
Maximum.
Size Most
Commonly
Used on Aver-
Kge Farms.
Feed grinders (small)
Feed grinders (large)
Ensilage cutters
Shredders and buskers
Threshers, 19-inch cylinder .
Threshers, 32-inch cylinder .
Com sheilers, single hole . . .
Power shellers
Fanning wnilla
Grain graders
Grain elevators
Concrete mixers
Groomer, vacuum system. . .
Groomer, revolving system .
Hay hoists
Root cutters
Cord wood saws
Wood splitters
Hay balers
Oat crushers
3
10
10
10
12
30
i
10
10
30
25
20
18
50
IJ
15
li
2
1
1
3
1
3
1
3
2
5
10
3
2
15
5
10
4
10
10
5
15
15-20
15
15
40
1
15
i
i
3
5
2
1
5
2
5
2
7i
5
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30
GENERAL INTRODUCTION
TABLE X
Power Required to Thresh a Bushel op Grain
Kind of
Grain.
No. of
Tests
Made.
Yield Per Acre.
Kw.-hr.
to Thresh
1 Ton.
Kw.-hr.
to Thresh
1 Bushel.
Cost or Powek
AT 5 Cents Per
KW.-HB.
Tons of
Grain
and
Straw.
Bushels
of Grain.
Per Ton.
Per
Bushel.
Oats
Barley. . .
Wheat. ..
31
5
10
1.99
2.27
1.97
73.6
49.9
27.9
2.62
2.36
2.27
0.070
0.108
0.160
$0.13
0.128
0.113
$0.0035
0.005
0.008
TABLE XI
Power Required for Grinding
Operation.
Capacity of
Machine
per Hour
in Bushels.
H.P. of
Motor
Kw.-hr.
Required
Required.
per
Bushel.
20
0.411
3
0.37
2
0.045
15
0.272
7.5
0.086
Power Cost
per Bushel
with Electric-
ity Costing
5 Cents per
Kw.-hr.
Grinding corn on the cob . .
Grinding oats
Crushing oats
Grinding shelled com
Cracking corn
41
5.7
50
41.5
65.8
$0.0205
0.0185
0.0022
0.0136
0.0043
Inigation. Water is a necessity for the growth of every crop.
In the Western States, the rainfall is, as a rule, insufficient to sup-
port even a scant growth of vegetation, but in the Central and
Eastern States the average rainfall during the growing season is
ordinarily considered sufficient. However, in the latter sections
of the country hardly a year passes without some particular
section being badly in need of rain.
As rains, to be beneficial, must come at such times and in such
amounts as will properly moisten the soil and produce growth, a
check in this supply of soil moisture at any stage of the growth
affects both the quality and quantity of the yield and may greatly
reduce the profits of the grower. The real test of the necessity of
irrigation is not the total annual rainfall, but the monthly, and,
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COMMERCIAL OPPORTUNITIES
31
in the case of most crops, the weekly amount of precipitation
throughout the growing season. Under average conditions, it is
safe to say that a drought occurs whenever the rainfall totals less
than one inch in any fifteen-day period and crops will usually
suffer if they do not receive more than this amount of rain, espe-
cially during the spring and early summer months.
Prof. F. H. King in his book on irrigation and drainage fur-
nishes the following data as to the highest probable duty of water
per acre for different yields of different crops:
TABLE XII
Duty op Water por Different Crops
Bushels per acre.
15
20
30
40
50
60
Least Number of Acre-inches of Water.
Wheat
Barley
Oats
Maize (com).
Potatoes
4.5
3.2
2.3
2.5
Tons per Acre.
6.0
4.3
3.1
3.3
0.4
9.0.
6.4
6.7
5.0
0.6
12.0
8.5
6.3
6.7
0.8
15.0
10.7
7.8
8.4
1.0
6
18.0
12.8
9.4
10.0
1.2
8
Clover hay . .
Com (green).
4.4
2.1
8.8
4.2
13.3
6.2
17.7
8.3
26.5
12.5
35.0
16.6
Some artificial means of supplying water to the land is there-
fore a necessity in the western section of the coimtry, and would
be excellent insurance to the central and eastern parts as well.
Two general methods of supplying this water are now in use:
The ordinary gravity flow, such as that of taking water from a
reservoir or ditch; and the mechanical lift, such as pumping water
from a well, pond, river or lake. Of the two, the development
of the mechanical lift has been far more rapid. There are two
reasons for this: First, because the land which can be econom-
ically irrigated by the gravity method has been practically all
taken up; and, second, because the farmer can pump water to
almost any elevation, and in this way he is enabled to irrigate
land which is above his source of water supply. This is impos-
sible when the gravity system is used.
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32 GENERAL INTRODUCTION
Irrigation pumping, from, the farmer's point of view, has
many advantages, in that a pmnping plant will give him water
just at the time he wants it, and this is a more important factor
to him than the saving of the money effected. It is exceptional
to be able to get water just at the time when it is wanted, when
irrigating from a ditch, as ditch riders and water superintendents
must serve all alike. Not only this, but when water is turned
into a ditch, it must run in quantities in order to secure economy,
and it is not possible that every man along a ditch will be similarly
situated with regard to the progress of his work so that all will
require water at any one time.
If water is to be pumped, some kind of power is necessary to
operate the pump. Among the more important sources of power
are the gasolene engine, steam engine, and electric motor. The
latter, however, is rapidly displacing the other two wherever
electric power is available, just as it has already done in the city.
The principal advantage of the electric motor is that its power is
instantaneously available and it will always run when wanted.
Furthermore it can be rim for months at a time without shut-
ting down the plant, and there are thousands of electric pump-
ing installations in the Far West which run twenty-four hours a
day for six months at a time; this being entirely feasible as the
only attendance that is required for electrical equipment is an
occasional oiling of the motor bearings. The steam engine, on
the other hand, requires the constant attendance of a Ucensed
engineer, while the gasolene engine has a large number of moving
parts, which must necessarily be adjusted from time to time. It is
practically impossible to operate a gasolene engine for six months
at a time without extensive repairs at the end of the period. Being
able to run the electric motor all the time is, therefore, a distinct
advantage, in that a small reservoir can be used to store the water
pumped during the night, and in this way a much smaller equip-
ment can be used than would otherwise be required. The electric
motor has the added advantage of remote control, the fanner
being able to stop and start it even if he is several miles away.
The advantages of electric power for irrigation purposes have
been clearly demonstrated by the excellent work which is being
done by the United States Reclamation Service, the United States
Indian Service, and numerous cooperative and individual enter-
prises. The Salt River project in Arizona, when completed, will
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COMMERCIAL OPPORTUNITIES 33
furnish irrigation to over one-quarter million acres of arid lands
in the Southwest, and the Minidoka project in Southern Idaho
will be capable of irrigating approximately fifty thousand acres.
In connection with these projects, electricity plays an important
part. Hydro-electric power is generated on the nearest available
river and the energy is transmitted over high-tension trans-
mission lines to piunping stations scattered over the territory
to be irrigated. Besides these, there are numerous other projects
where hydro-electric power is similarly used for irrigating the land.
Mining. The advantage of using electric power for mining
operations is now fully recognized, almost all new mines being
equipped for electric drive, and a very large number of old ones
changing over to this system. Not only does this reduce the cost
of working, but it also offers a much safer and more reUable oper-
ation. The economy of electric-p)ower distribution to the various
points in a mine surpasses all other methods. The electric
system eliminates long and expensive steam and air lines, with
which the danger of breakdown and the difficulty of keeping up
the necessary working pressure increase with every extension to
the service. Electric distribution, on the other hand, is most
simple and flexible. Very large districts can be efliciently sup-
plied and additions or alterations can at all times be made without
the least difliculty.
A most eflScient appUcation of motors to the many forms of
mining machines is readily accomplished. They can be direct
connected, or geared to the driving shafts, thus reducing the fric-
tion losses and repair charges to a considerable extent, while,
on the other hand, the cost of belting and coimtershafts is entirely
eliminated. Individual motors can be substituted for driving
conveyors, scrapers and other machinery in breakers and tipples,
which formerly were equipped for group operation by means of
inefficient engines. In motor-driven breakers, the saving in belt-
ing alone is considerable.
Operation with the electric system is very simple, and results
in a materially increased output of a mine. Perfect control is at
all times possible. Simple, automatic, safety devices can be
installed, and indicating or recording meters can be provided in
the several circuits as desired, and the performance of every
individual machine ascertained. This is a very important point,
as it is possible to maintain the machinery in the best possible
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34 GENERAL INTRODUCTION
condition. Any excess consumption of power can at once be
detected and the defect remedied, while also an accurate record
can be kept of the cost of the different operations.
Power may be purchased from nearby existing hydro-electric
transmission companies, or available water powers may be devel-
oped and the energy transmitted to the mines. That water
powers may, in some instances, compete with very cheap steam
power is also illustrated by the system of the Appalachian Power
Company, which furnishes a considerable amoimt of power from
its hydro-electric plants on the New River in Virginia to the
Pocahontas coal fields, a distance of about 50 miles.
Electro-chemical Industries. The industrial processes foimded
upon electro-chemistry have a large and important part in the
manufacture of a very wide range of commercial products, such as
fertilizers, explosives, paper, wood pulp and numerous electro-
chemicals among which may be mentioned: aluminimi, carbo-
rundum, alimdum, silicon, graphite, calcium carbide, cyanamid,
ferroHsilicon, ferro-chromium, ferro-manganese, caustic soda,
sodium, chlorine, chlorate, chloroform, carbon tetrachloride, etc.
Table XIII, taken from the Report of the Bureau of Census,
gives comparative statistics for 1914 and 1909 of the production
of chemicals and allied commodities by means of electricity.
I The question of cheap water power is vital in connection with
electro-chemical industries, but, on the other hand, the location
of raw materials and the transportation facilities of the product
to the market centers is also of the greatest importance, and this
latter point has to a great extent been detrimental to a much
greater development of our western water powers for electro-
chemical products. Niagara Falls, on the other hand, forms an
ideal example of what cheap water power has done for this industry.
At this point are now situated the greatest electro-chemical indus-
tries in the world, not one of which was in existence when the
Niagara Falls Power Company began to take water from the
Niagara River to generate electricity. In the treaty of 1910
between the United States and Great Britain it was stipulated that
the volume to be diverted on the American side should be limited
to 20,000 cubic feet per second and on the Canadian side to 36,000
cubic feet per second. The volume of the water that can be
diverted at the Falls is thus limited to 56,000 cubic feet per second
until such time as the two Governments may determine to increase
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COMMERCIAL OPPORTUNITIES
35
TABLE XIII
Chemicals Made by Electricitt
1914
1909
Number of establishments
Products —
Total value
Chlorates:
Number of establishments
Tons
Value
Hypochlorites:
Number of establishments
Tons
Value
Caustic soda, caustic potash, and lye:
Number of establishments
Tons
Value
Ferro and other alloys:
Number of establishments
Value
Oxygen and hydrogen:
Number of establishments
Value
All other, names in order of value — aluminum,
calcium carbide, abrasives, electrodes,
sodium and sodium peroxide, phosphorus,
silicon chlorine, carbon bisulphide, and
muriatic acid:
Number of establishments
Value
36
129,661,649
5
8,304
11,131,316
4
73,197
$1,714,837
51
48,663
12,309,511
7
12,859,482
5
$68,441
34
$18,451,461
5
6,785
$904,550
5
45,970
$1,506,831
17
$21,578,062
$16,040,080
the amount. This is approximately 25 per cent of the total flow^f
the river, as computed by Government engineers. It is, however,
not sufficient to allow for any further expansion of these electro-
chemical industries, some of the largest and most important of
which are now compelled to go to Norway or other fields where
abimdant water power can be had cheaply; this, in spite of the
fact that at least one million horse-power additionally could be
developed at Niagara Falls without seriously interfering with the
scenic beauty of the Falls. On the other hand, the shortage of
power was responsible for the recent installation of the mammoth
steam plant almost within the shadow of the Falls.
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36
GENERAL INTRODUCTION
Another great need for the unmediate development of addi-
tional water power is the imperative necessity of increasing our
nitrate supply and making it independent of foreign deposits.
Fixed nitrogen is the most important constituent of plant food and
absolutely indispensable in the manufacture of explosives. Europe
Fig. 9.— Rjukan II Power and Furnace House for Nitrogen Fixation in Nor-
way. Capacity 120,000 horse-power.
uses per acre (rf cultivated land 200 pounds of fertilizer; the
United States 28 pounds. Germany, in twenty years, by the use
of fertilizers, has increased the average yield of all crops grown
three and one-half times as much per acre as America, the yield
per acre in bushels for various crops being as follows:
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COMMERCIAL OPPORTUNITIES
.37
TABLE XIV
Crop Yields
Wheat.
Oat3.
Barley.
Rye.
Potatoes.
Europe
United States.
32
15
47
29
38
25
30
16
158
96
As a measure of preparedness our reserve stock of nitrates is
insif^nificant and our nation would be powerless if our navy were
not strong enough to protect our import from Chile. Fortunately
enough, nitrates can readily be extracted from the atmosphere and
fixed as a compound by the utilization of electric energy. The
possibilities of this have never been more clearly demonstrated
than during the European war, when Germany's entire supply was
obtained in this way. In Norway, with its cheap wat<er powers,
the industry has long been established, about 350,000 horse-
power being at present utilized by one company alone for the
fixation of nitrogen by the arc process. Fig. 9 shows one of its
power-houses and factories, with a capacity of 120,000 horse-
power.
The power requirements vary widely for the different electro-
chemical products as seen from Table XV, and in many instances
it is a large item in the cost sheet of the product.
TABLE XV
Tower Consumption op Electro-chemical Frocessbs Per Ton
OP 2000 Pounds
Kw.-hra.
Refining of lead 120
Refining of copper 300
Refining of steel 600-1,000
Refining of nickel 3,000
Refining of zinc 3,500
Reduction of calcium carbide 4,000
Reduction of ferro-alloys 4,000-12,000
Reduction of abrasives 7,500
Reduction of aluminum 30,000
Pig iron from ore 2,000-3,000
Brass melting 220-280
Nitrogen (fixed) 15,000-60,000
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38
GENERAL INTRODUCTION
Railroad Electrification. Hydro-electric power will undoubt-
edly play an important part in connection with future railroad
electrifications, especially in the western mountainous States.
440 miles of the main line of the Chicago, Milwaukee & St.
Paul Railroad haVe now been equipped for operation by elec-
tricity, power being supplied' by nearby hydro-electric develop-
ments, Fig. 10. In view of the economical success of this elec-
FiG. 10. — Electric Trains at the Entrance to Silver Bow Canyon on the
Chicago, Milwaukee & St. Paul and the Butte, Anaconda & Pacific
Railways.
trification, it is almost certain that within the next ten years a
majority of the railroads operating through the mountainous
country of the Far West, where hydro-electric power can be
developed cheaply, will adopt electricity as a motive power. It
is estimated that five million horse-power would be required to
electrify the 50,000 miles of railroad in the western States, or
one-ninth of the total hydro-electric power possible to develop in
the territory traversed by these railroads.
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CHAPTER n
HYDROLOGY
1. PROPERTIES OF WATER
Weight The weight and specific gravity of water vary
somewhat, depending on its temperature and on the variou
impurities which it contains in solution or carries in suspension.
For pure water the weight may be considered practically constant,
as the maximum variation has been found to be so inconsiderable,
being only about 0.05 of 1 per cent. Its weight is now generally
assumed to be 62.355 pounds per cubic foot at a temperature of
62° F., although authorities differ somewhat about the exact
figure. Water of lakes and rivers will, under •ordinary circum-
stances vary between 62.3 and 62.5 pounds, depending on the
impurities. Table XVI, however, shows that a considerable
variation may be expected under unusual conditions, as for exam-
ple, the Great Salt Lake, where the water, due to the large amount
which it contains, weighs nearly 73 pounds per cubic foot.
TABLE XVI
Weights and Specific Gravity op Water
Weight per
Cubic Foot
62*» Fah.
Specific Gravity.
Pure water
Atlantic Ocean
Lake Michigan
Great Salt Lake, Utah
Mono Lake, Cal
Mississippi River
Delaware River
62.355
64.043
62.336
72.925
65.134
62.333
62.333
1.00000
1.0275
1.0011
1.17
1.045
1.00006
1.00006
While sometimes invisible, all natural waters always contain
in solution more or less of the substances which they have come in
39
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40 HYDROLOGY
contact with in their course. These substances may be either
solidSy liquids or gases. The quantity of a solid which may be
dissolved by a liquid is fixed and limited, and is always the same
for the same temperature, the solubility however, generally
increasing with the temperature. The same quantity of gas will
also be dissolved by a liquid if the temperature and the pressure
remains the same, the volume of gas dissolved being proportional
to the atmospheric pressure. Rain water always contains in
solution a certain amoimt of the natural gases of the atmosphere.
These are, however, not dissolved in proportion to their occur-
rence in the atmosphere, but more nearly to the solubility of the
gases. Deep waters and waters of springs which have been under
pressure carry in solution larger percentages of carbonic acid
gas than natural waters.
There is a distinct difference between substances in solution
and in suspension. When in suspension the substance still retains
its ph3rsical identity, although it may be held in an exceedingly
finely divided state and thus be carried in suspension for indefinite
periods. When <he water is at rest the heavier suspended par-
ticles are soon deposited.
Volume. For all practical purposes water may be considered
non-compressible. The coefficient of compressibility ranges from
0.00004 to 0.00005 per atmosphere at ordinary temperature the
coefficient decreasing as the temperature increases.
Table XVII gives the relative volume and weight of pure
water at various temperatures, as compared with its volume at
39.2° F.
Critical Temperatures. There are four temperatures of water
which are often used in physical calculations and which should be
kept in mind, viz.: 32® F. or 0® C, at which pure water freezes at
one atmosphere pressure (sea level). The weight of ice is 57.5
pounds per cubic foot, and when floating in pure water 92 per cent
of its mass is submerged, while in sea water about 89 per cent.
39.2** F. or 4** C, which is the approximate point of maximum
density of pure water.
62"* F. or le.e?"* C, which is the British Standard tempera-
ture, and which is used as a basis in calculating the specific gravity
of bodies in England and United States.
212® F. or 100° C. is the boiUng point of piure water at atmos-
pheric pressure.
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PROPERTIES OF WATER 41
TABLE XVII
VOLUMB AND WbIQHT OF PURB WaTER AT VaBIOUS TeMFESATUBBB
(From Marks and Davis)
Temperature
in deg. Fah.
Relative Volume.
Weight per Cu.ft.
in Pounds.
32
1.000176
62.42
39.2
1.000000
62.43
40
1.000004
62.43
50
1.00027
62.42
60
1.00096
62.37
70
1.00201
62.30
80
1.00338
62.22
90
1.00504
62.11
100
1.00698
62.00
110
1.00915
61.86
120
1.01157
61.71
130
1.01420
61.55
140
1.01705
61.38
150
1.02011
61.20
160
1.02337
61.00
170
1.02682
60.80
180
1.03047
60.58
190
1.03431
60.36
200
1.03835
60.12
210
1.04256
59.88
212
1.04343
59.83
Latent Heat This is the heat which apparently disappears
in producing some change in the conditions of a body without
increasing its temperature. To transform ice water and vapor
or steam from one state to the other, it is only necessary to supply
a certain quantity of heat energy, —460® F. being the absolute
zero of temperature.
Thus in melting 1 poimd of ice into water at 32® F., about 142
heat-units are absorbed and become latent, while in freezing one
pound of water into ice a like quantity of heat is given out to the
surrounding medium.
Latent heat is not lost, but reappears whenever the substances
pass through a reverse cycle, from a gaseous to a liquid, or from a
liquid to a soUd state. It may, therefore, be considered as the
heat which apparently disappears, or is lost to the thermometric
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42
HYDROLOGY
measurement, when the molecular constitution of a body is being
changed.
Specific Heat The specific heat of water is greater than all
known substances with the exception of bromine and hydrogen,
and it is the basis for measurement of the capacity of heat absorp-
tion of all other substances. Its value varies with the tempera-
ture of the water, being lowest near 40® C, after which it increases
up to and beyond the boiling-point. The generally accepted
values as determined by Peabody are given in Table XVIII.
TABLE XVIII
Specific Heat of Water at Various Temperatures
Temperaturb.
Specific Heat.
1
Deg. C.
Deg. F.
0
32
1.0094
5
41
1.0053
10
50
1.0023
15
59
1.0003
16.11
61
1.000
20
68
0.9990
25
77
0.9981
30
86
0.9976
35
95
0.9974
40
104
0.9974
45
113
0.9976
50
122
0.9980
55
131
0.9985
60
140
0.9994
65
149
1.0004
70
158
1.0015
75
167
1.0028
80
176
1.0042
85
185
1.0056
90
194
1.0071
95
203
1.0086
100
212
1.0101
Effect of Atmospheric Pressure. At sea level the average
atmospheric pressure is 14.72 pounds per square inch, but it
decreases as the height above sea level increases. With water
weighing 62.4 pounds per cubic foot, the weight of a column having
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PROPERTIES OF WATER
43
a cross-section of 1 square inch and a height of 1 foot will equal
62 4 . •
-T^ or 0.43 poimd, so that at sea level water will rise to an aver-
144
14 72
age height of ' or 33.9 feet in vacuum.
The barometric pressure in inches is equal to the pressiure per
square inch divided by 0.4908.
In Table XIX are given the relations of altitude to barometer
and atmospheric pressure.
TABLE XIX
Relations of Elevation to Barometer and Atmospheric Pressure
Height aboye
Average Height
Barometer in
Average Pressure
in Pounds per
Average Height to
which Water WUl
Sea Level.
Inches of Mercury.
Square Inch.
Rise in an Ex-
hausted Tube.
0
30.00
14.72
33.96
100
29.89
14.67
33.84
200
29.78 .
14.62
33.72
300
29.68
14.57
33.60
400
29.57
14.51
33.48
£00
29.47
14.46
33.35
600
29.36
14.41
33.23
700
29.25
14.36
33.11
800
29.15
14.30
32.99
900
29.04
14.25
32.87
1,000
28.94
14.20
32.76
1,250
28.67
14.07
32.47
1,500
28.42
13.95
32.19
2,000
27.92
13.70
31.61
2,500
,27.40
13.45
31.04
3,000
26.93
13.21
30.49
3,500
26.43
12.98
29.94
4,000
25.98
12.74
29.41
4,500
25.51
12.51
28.89
5,000
25.06
12.29
28.37
6,000
24.18
11.85
27.37
7,000
23.32
11.43
* 26.40
8,000
22.50
11.04
25.47
9,000
21.70
10.65
24.57
10,000
20.93
10.28
23.70
Measurements. Conversion Table XX gives the most com-
mon units in which water is measured.
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44
HYDROLOGY
TABLE XX
Equiyalent Mbasubbs akd Weights of Water at 4* Centiqbade, 39.2''
Fahrenheit
U. B.
GaUoDB.
Liters.
Cubic
Metera.
PoundB.
Cubic
Feet.
Cubic
Inches.
1.
3.7853
.0037853
8.34112
.13368
231.
1.20017
4.54303
.004543
10.0108
.160439
277.274
.264179
1.
.001
2.20355
.035316
61.0254
264.179
1000.
1.
2203.55
35.31563
61025.4
.119888
.453813
.0004538
1.
.0160266
27.694
7.48055
28.3161
.0283161
62.3961
1.
1728.
.004329
.0163866
.0000164
.0361089
.0005787
1.
.0408
.1544306
.0001544
.340008
.005454
9.4224
2. RAINFALL
Source of Water Supply. The ultimate source of our water
supply is the precipitation in the form of rain or snow which
reaches the earth. For the United States the chief source of this
is the evaporation from the Pacific Ocean which by westerly winds
is carried eastward in diminishing quantities. In the Mississippi
Valley the small supply of moisture still remaining is augmented
by a generous contribution from the Gulf of Mexico, from where
it is carried inland by southerly and southwesterly winds. East
of the Appalachian Moimtains the precipitation is mainly derived
from the Atlantic Ocean.
Rain is formed whenever the air is cooled below the point of
satm-ation. This cooling may be caused by the air currents
being forced upward, as when they strike mountain ranges, or
they may be intermingled with other colder air currents, or come
into contact with a cold land.
Variation in Rainfall. The rainfall varies greatly in different
parts of the country and is governed quite largely by the geo-
graphic or topographic relations. It is usually given in either
total inches of rain per year or per month, while the daily maps of
the Weather Bureau show the variations from day to day. A
map of the United States giving the average annual rainfall in
inches for the different sections is shown in Fig. 11, the mean
annual precipitation for the whole coimtry being 29.4 inches.
Table XXI also gives some typical values of rainfall in different
parts of the coimtry.
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RAINFALL
45
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46
HYDROLOGY
TABLE XXI
Typical Averages of Rainfall
Inchee Annual
RalnfaU.
Approximate
Mean Annual
Run-off. Inchei.
North Atlantic States.
Gulf States
Lake Region
Mississippi Valley ....
Mountain Region
Plains
Pacific Coast, north. . .
Pacific Coast, south. . .
40-60
50-60
30-40
30-60
10-20
0-10
40-60
10-^
Over 20
Over 20
10-20
10-20
2- 5
0- 2
10— Over 20
2-10
State.
Spring.
Summer.
Autumn.
winter.
11.6
11.4
11.9
11.7
12.4
15.6
10.7
12.7
7.9
9.7
9.2
7.0
10.0
12.0
9.1
6.5
4.2
5.5
2.8
2.3
2.3
0.8
1.3
3.2
9.8
2.7
10.5
21.0
6.2
0.3
3.5
11.9
Total.
Massachusetts .
Georgia
Michigan
Missouri
Colorado
Nevada
Oregon
California. . . . .
46.6
51.4
33.8
38.0
14.8
7.6
44.0
21.9
The annual as well as the monthly rainfall varies irregularly
from year to year, and the amount of these variations is greater
in some localities than other. While they may remain within
certain Umits, the totals are made up of still greater variations in
individual storms.
The rainfalls to be considered for practical purposes are the
average monthly and the montiily of the driest year, both of
which affect the supply, while a knowledge of the maximum rainfall
is essential for determining the discharge.
Rainfall Record. The United States Weather Bureau main-
tains several thousand stations for recording the rainfall of the
coimtry and the number of points at which such observations
is increasing from year to year. There are some places where
observations have extended for over fifty j-ears and suflScient
information can therefore usually be obtained from the bulletins
of the Weather Bureau. Where small watersheds are under in-
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DISPOSAL OF RAINFALL
vestigation it may, however, often
be found necessary to make indi-
vidual rainfall measurements.
Diagrams, Figs. 12 and 13, repre-
sent a 75-year rainfall record at
St. Paul, as reported by the Minne-
sota Board of Water Commis-
sioners.
3. DISPOSAL OF RAINFALL
Of the rainfall a portion evap-
orates, a portion enters the soil and
is either absorbed by plant growth
or by ground flow reaches the rivers
or lakes, while the third portion
finds its way into streams as surface
flow or run-off.
Evaporation. Of the tremendous
losses due to evaporation from the
ground surface comparatively little
is known. It is impossible to arrive
at such losses by taking the differ-
ence between rainfall and run-off,
as in this there would also be in-
cluded the losses due to absorption
by the soil and by vegetation, and
again the rate of run-off does not
altogether depend upon the rainfall.
The rate of evaporation or the
proportion of the rainfall to the air
varies greatly under different con-
ditions and is affected by atmos-
pheric conditions as well as by the
character of the soil. The capacity
of the atmosphere to take up and
dissipate the moisture depends in
turn on the temperature, the wind,
ahd how saturated it already is.
Wind increases the evaporation to
a great extent, especially from ex-
FiG. 12. — Annual Precipitation at
St. Paul, Minn., 1837-1912.
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48
HYDROLOGY
posed water surfaces, as the saturated air in contact with such
surfaces is rapidly removed and continually replaced by fresh.
In cool climates with light breezes the evaporation is considerably
lower than in warm climates with strong winds.
The natiu*e of the earth's surface, on the other hand, deter-
mines the rate at which moisture is supplied. Thus, a ver}*
large evaporation takes place from exposed water surfaces such
as lakes, swamp lands, etc., and the amount may, in certain
instances, equal the actual rainfall itself. They tend, however,
8
n u h II 11 i§ i§ II II li 11 t
n
n n
%
"1
_-
^ ^
^
^ >
^
^ ^
V ^ ^ 5
Jan. Feb. Mu. Ajydl May Jane July Aug. Sept. Oct Not. Dec
FiQ. 13. — Monthly Variation in Precipitation at St. Paul. Minn. From
Records 1837-1912.
as a storage of flood waters and add, therefore, materially to the
regulation of the stream flow.
The depth to the water in the soil and its capillary action in
bringing the water to the surface also naturally affect the evapo-
ration. A light rain falling on an impervious rock surface may
simply wet the surface and quickly disappear as vapor, while
saturated surface layers of the soil, such as after heavy rains, will
also cause considerable evaporation.
A large amount of water is necessarily taken up by the vege-
tation and evaporated, while the effects of forests are to greatly
reduce the evaporation as compared to open fields.
A more complete study has been made of the evaporation from
the water surface of lakes and rivers, the greatest use of such
studies being in the investigation of storage and the losses which
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DISPOSAL OF RAINFALL 49
are likely to occur on such reservoirs through evaporation. That
the losses on lake areas are very great, and often of greater extent
than precipitation, is well known.
The map in Fig. 14 shows the mean average evaporation in the
United States from open waters. It is compiled from observa-
tions of the United States Weather Bureau in 1887 and 1888.^
Absorption. A considerable part of the rain which falls on
the earth is absorbed by the groimd. > The amoimt varies, how-
ever, greatly, depending on the rate of precipitation, texture of
soil, slope of drainage surface, temperature and vegetation.
A light shower will usually be quickly evaporated, while a
heavier rain may be absorbed, and if lasting for some time there
will be an excess amount of water which will run off to the nearby
stream. On the other hand, less may be absorbed during a heavy
rain than during a light, gentle rain, because each type of soil has
a certain rate of absorption due to its porosity, and if the water is
supplied more rapidly than it can be taken up, the excess runs off.
A deep, porous, sandy soil naturally will absorb and hold water
more than a compact, shallow one, such as a clayey soil.
If the slope of the watershed is very steep, the water may
drain off before any can be absorbed by the soil, and if the slopes
are rocky practically no water is absorbed.
Temperature necessarily also affects absorption. A high tem-
perature increases it while the opposite is the case at low tem-
peratures as when the ground is frozen.
On slopes, vegetation and forest are of the greatest importance
in that they retard part of the drainage water during heavy rains,
which gives the soil time to absorb the same. They are, there-
fore, of great value in reducing the intensity of floods after severe
storms. The absorbed water seeps into the ground, which it sat-
urates, and some of it percolates still further into the pores and
fissures and trickles slowly toward the stream.
These groimd waters have a most important bearing on the
stream flow. Areas of Uttle or no underground flow are subject
to violent floods and extreme droughts, while areas with a large
proportion of underground storage are comparatively free from
floods. The greater part of the low-water of streams having no
lakes or swamps in their watershed is also supplied by this under-
ground flow.
1 Monthly Weather Review, September, 1888.
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50
HYDROLOGY
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DISPOSAL OF RAINFALL 5.1
A detennination of the exact quantity of underground waters
is a very diflScult problem. Numerous papers have been pre-
pared on the subject by different authors. Water Supply and
Irrigation Paper No. 163 of the United States Geological Survey
contains a bibliographic review and index of underground-water
literature published in the United States up to and including the
year 1905.
Run-off. The run-off is that part of the rainfall which drains
off the surface of the watershed in visible streams. It is that part
of the rainfall which remains after nature's need of moistiu*e has
been supplied in the form of evaporation and absorption.
The close relation between these three subdivisions of rain-
fall has been referred to in the above, and it follows that the run-
off is affected, both directly and indirectly, by the same factors
that govern the rate of evaporation and absorption.
It is often important to know the relation between rainfall
and run-off, as this may in many instances be the only way to
ascertain the flow of a stream. Rainfall observations have been
made for many years and it may be possible by knowing the ratio
between run-off and rainfall for a certain <irainage area, to apply
this value to a watershed in another place. It is, of course, of
the greatest importance in such comparisons that the areas from
which the deductions are made must be of similar character.
Also that they are of approximately the same size, because smaller
drainage areas usually have a wider variation between maximiun
and minimum run-off than large ones.'
It is apparent that there can be no constant relation between
the rainfall and the run-off for the whole country, although in this
respect the ratio for the Eastern States is much more constant than
for the Western States. There are also great variations in the
yearly as well as the monthly and daily run-off, and it is very
diflScult to make accurate estimates as to what the two latter may
be expected to be; the daily being, of course, almost impossible to
foretell. The yearly run-off, however, bears a more nearly uni-
form ratio to the rainfall, so that with a good knowledge of the
presence of forests, character of soil, climate, etc., a fairly accurate
estimate of the yearly nm-off may be made, based on known
values under similar conditions.
As for rainfall, run-off is also usually expressed in inches, and
the map in Fig. 15 shows approximately the mean annual run-off
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HYDROLOGY
1 I
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STREAM-FLOW 53
for the country. By comparing this map with that of rainfall
in Fig. 11, a fairly good idea of the relation between rainfall and
nin-oflf may be had. Table XXII furthermore gives the run-oflf
for various watersheds in the United States.
4. STREAM-FLOW
Definition of Tenns. The voliune of water flowing in a river
IS generally defined as " stream-flow " and is expressed in various
terms depending upon the particular class of work for which it is
to be used. The term used in the reports of the U. S. Geological
Survey are: Second-feet, second-feet per square mile, acre-feet
and depth in inches. Of these the first two represent the rate of
flow only, while the two latter represent the actual quantity of
water. They are defined in the Survey Reports as follows:
" Second-foot " is an abbreviation for cubic foot per second
and is the imit for the rate of discharge of water flowing in a stream
1 foot wide, 1 foot deep, at a rate of 1 foot a second. It is gen-
erally used as a fundamental imit from which others are com-
puted by the use of the factors given in the following table of
equivalents.
" Second-feet per square mile " is the average number of cubic
feet of water flowing per second from each square mile of area
drained, on the assumption that the run-off is distributed xmi-
formly both as regards time and area.
" Depth in inches " is the depth to which the drainage area
would be covered if all the water flowing from it in a given period
were conserved and imiformly distributed on the surface. It is
used for comparing run-off with rainfall, which is usually expressed
in depth in inches.
An " acre-foot " is equivalent to 43,560 cubic feet, and is the
quantity required to cover an acre to the depth of 1 foot. The
term is commonly used in connection with storage for irrigation.
The direct course of stream-flow is the visible run-off from the
watershed and that part of the rain-fall which was absorbed by
the soil and which slowly finds its way to the stream bed in the
form of an underground flow.
Variation in Stream Flow. There is a very considerable vari-
ation in the flow of rivers not only dm-ing the various months of
the year, but from year to year as well, and the variation is greater
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HYDROLOGY
TABLE XXII
Mean Amkual Run-off for Various Watersheds in Unttbd States *
River.
Point of Measurement.
Drainage
Area
Square
MUes.
Period.
Run-off in
Depth in
Inches on
Draina^
Area.
Kern
San Joaquin . .
Kings
Sacramento. . .
UmatiUa
Willamette. .
Boise.
Green.
Laramie
Red
Rio Grande . .
Animas
South Platte .
Green.
Logan. .,
Carson
Truckee
Humboldt . . .
Colorado ....
St. Croix . . .
Menominee.
liilnois . . .
Maumee .
Scioto. . . .
Duck . . . .
Tennessee ....
Tombigbee. . .
Black Warrior.
Alabama
Savannah ....
Catawba
Tar
Roanoke
Potomac
Oswego
Delaware
Susquehanna. .
Hudson
Mohawk
Bakersfleld. Cal.
Herndon, Cal. . .
Sanger, Cal ....
Red Bluff, Cal. . .
Umatilla, Ore. . .
Albany, Ore.
Boise, Idaho
Green River, Wyo. .
Uva, Wyo
Grand Forks, N. Dak.
Rio Grande, N. Mex.
Durango, Cal..
Denver. Col. . ,
Greenriver, Utah .
Logan, Utah
Empire. Nev
Vista. Nev
Orleans. Nev.
Yuma, Ariz .
St. Croix Falls Wis. .
Iron Mountain, Mich.
Peoria, 111.
Waterville, Ohio.
Columbus, Ohio .
Columbia, Tenn.
Chattanooga. Tenn . . .
Columbus, Miss
Cordova, Ala
Selma, Ala
Augusta, Ga
Rock Hill, S. C
Tarboro, N. C
Randolph, Va
Pt. of Rocks, Va
Oswego. N. Y
Port Jarvis. N. Y
Binghamton, N. Y. . . .
Mechanicsville, N. Y. .
Dunsbarh Ferry, N. Y.
2.340
1,640
1.740
4,300
2.130
4.860
2,610
7.460
3.180
25.100
14.000
812
3.840
38.200
218
988
1.620
13.800
225,000
6,370
2,420
13,200
6,110
1,050
1.260
21,400
4.440
1,000
15,400
7,300
2,990
2,290
3,080
9,650
5,000
3.250
2.400
4.500
3.440
1896-1905
1896-1901
1897-1906
1902-1906
Nov. 1, 1900, to
Dec. 31. 1900
Jan. 1, 1899, to
Dec. 31, 1908
1895-1904
May 1, 1896, to
Oct. 31, 1906
May. 1895, to
Oct.. 1903
Sept., 1902, to
Sept.. 1908
Jan. 1, 1896. to
Dec. 31, 1906
July, 1895, to
Dec., 1905
Jan. 1, 1896, to
Nov. 30, 1906
Jan.. 1895. to
Dec., 1908
1896-1900
1904-1906
Nov.. 1900. to
Dec.. 1906
Sept.. 1899. to
Dec., 1906
Jan.. 1897, to
Dec., 1906
Jan.. 1902, to
Dec., 1906
1902-1904
Sept., 1902. to
Sept., 1906
Apr. 1, 1903, to
Jan. 30, 1906
Dec., 1898, to
Jan., 1902
1899 to
July. 1906
Nov. 1, 1904. to
Dec. 31, 1908
1899-1908
1905-1908
1900-1908
1900-1908
1899-1908
1895-1903
1896-1900
1901-1905
1895-1906
1897-1901
1904-1908
1901-1906
1891-1900
1898-1907
4.36
20.47
20.38
24.06
3.94
46.62
16.60
4.81
1.10
2.08
1.46
14.86
1.44
3.17
21.18
6.26
0.18
0.25
1.16
10.60
18.92
14.11
13.61
10.43
18.87
23.63
15.48
19.37
24.01
22.29
25.21
13.89
18.86
14.40
11.60
22.20
28.88
22.06
23.28
1 Prepared by Newell and Murphy from U. S. Geological Survey Records.
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STREAM-FLOW
55
in some regions than in others. In Fig. 16 are shown some t3rpical
hydrograph records of New York streams, which clearly illustrate
what may be expected in the way of variations in stream flows.
OSWEGO RIVER
BATTLE ISLAND
UNUSUALLY STEADY STREAM
.1
GENESEE RIVER
MOUNT MORRIS
UNUSUALLY FLASHY STREAM
Fiu. 16. — ^Hydrographs Showing Natural Fluctuations of Flow of New York
York State Streams.
While of entirely different characteristics it can be seen that
there are certain common features in that the flows are heaviest
during the spring and early summer and lowest in autunm.
This irregularity of flow is a very important factor in any water-
power development and one that compels the reckoning with the
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56 HYDROLOGY
minimiim flow and the possibilities of storage for increasing the
same in order to safely develop the enterprise.
Factors A£fecting Stream Flow. It was previously shown how
absorption and the natural storage of underground waters had a
very important bearing on the regularity of the stream flow, these
waters being the main source of supply during the dry season.
It was also shown how vegetation and heavy forests will inter-
pose an appreciable time element in the run-off. In addition
there are several other factors which may delay the same. So
for example, where snow and ice form to considerable depths, a
large part of the precipitation may be stored for weeks or months.
On the other hand, the effect of an abnormally dry or wet season
may extend beyond a single year; since it somewhat affects the
conditions of the ground during the next year, so that a succession
of dry or wet years may disturb the expected relations of run-off to
rainfall producing imexpected drought or flood.
Most watersheds have some natural storage features tending
to equalize the stream-flow as compared with the rainfall. In the
northern part of the United States most watersheds have distinct
periods in the water year as distinguished from the calendar year.
These are usually classified into istoring, growing and replenishing.
Beginning about the first of December water begins to accumulate
in the form of snow, ice, or in the soil, and for months there is an
increasing storage. With the beginning of spring the storage
period terminates, and the growing period begins, during which
moisture is absorbed. By harvest time vegetation has ceased
to absorb moisture and it usually tends to replenish the ground
until the end of the fall. That these periods have great effects on
run-off can readily be appreciated and how great the effects may
be can well be judged from the typical figures in table XXIII.
The curves in Fig. 17 indicate graphically the approximate
relations for this area, and will show that for the same watershed
the percentage run-off increases with increasing rainfall.
Lakes, ponds and swamps are, of course, of great value in
regulating the stream-flow, and very frequently broad rivers have
storage possibilities not readily appreciated at first. In localities
where there is a pronounced dry season extending over several
months' time, water-power plants have been built in which it is
regularly proposed to store water for six months at a time, thus
enabling the average daily output of the plant to be increased
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STREAM-FLOW
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TABLE XXin
Hudson Riveb, 1888-1901
Catchment Area, 4500 Square Miles
Mean Values
Period.
Rainfall
in Inches.
Run-off
in Inches.
Evaporation
in Inches.
Per Cent Run-
off to Rainfall.
Storage
20.6
12.7
10.9
44.2
16.1
3.5
3.7
23.3
4.5
9.2
7.2
20.9
78 2
Growingr .....,.,..
27 6
Replenishing
34.0
62.7
80
/
/
/
/
/
i
/
J
/
1
7
J
M
r
y
^
y
y
'/
r
y
/
^
^
y
10
/
r
€\
Z
A
y
^
y
y
^
^r
y
^
y^
y^
y
^-
^
;^
^
»,
)
^
•^
1
0
'A
0
80
Inches Precipitation
FiQ. 17. — Curves Showing Mean Rainfall and Run-off on Upper
Hudson River.
several fold. This occurs usually in high-head plants where the
quantity of water is relatively small and the rough character of
the country permits the construction of deep reservoirs, but there
are some low head plants with short periods of low water where
the storage of some important tributary stream will, at reasonable
expense, greatly increase the minimum average daily output.
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58 HYDROLOGY
The diagrams S shown in Fig. 18, represent the ideal regula-
tion of the Hudson River, and was based on a proposed extensive
reservoir system and the stream-flows for the years 1908-09.
Other stream-flow records would, of course, modify the result,
while, on the other hand, such ideal flow can seldom be obtained
at a cost which would be commercially possible.
From the above it can readily be seen that usually very careful
measiu^ments of stream-flow extending over many years' time are
necessary to enable good .estimates of available power to be made,
particularly where the contemplated development has no storage
facilities.
Measurements of Stream-flow. The methods by which the
records of stream discharge are made differ according to the nature
and importance of the work. The simplest and most accurate
method for a small stream is by means of a weir. This consists
of a dam extending across and at right angles to the stream, and
having a rectangular notch cut in the top plank, with both side
edges and bottom sharply beveled toward the intake, as shown in
Fig. 19. The bottom of the notch, which is called the " crest "
of the weir, should be perfectly level and the sides vertical.
There are certain proportions which must be observed in the
dimensions of this notch. Its length, or width, should be between
four and eight times the depth of water flowing over the crest of
the weir. The pond back of the weir should be at least 50
per cent wider than the notch and of suflScient width and
depth that the velocity of flow or approach be not over 1 foot per
second.
On the up-stream side in the pond a stake is then driven down
in the bottom near the bank, so that its top is level with the bot-
tom edge of the notch, this level being easily found when the water
is beginning to spill over the crest. The stake should be placed
several feet from the board and at least not nearer than the length
of the notch.
By means of a rule, as shown in the illustration, the depth of
water over the top of the submerged stake is measured, allow-
ance being made for the capillary attraction of the water against
the sides of the weir. Having ascertained this depth, the
amoimt of water flowing the weir may be readily found from
Table XXIV.
» D. W. Mead, " Flow of Streams."
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STREAM-FLOW
59
IndiottM Wauc 8t(md darinff the Flood SeMoa added to the Row la the Dry fi
lllllllll Indicates IVatonl Ilactiiatioiia of Flow ndiuive oC Flood Waten.
3 Indioatc* Flood Waten which coold he stored ia PropoMd ReeerrtilEW'
IHI^I Indicates Hood Waters UaaYoidabljr wasted.
Fig. 18. — Diagrams Illustrating Typical Regulating Effect of Proposed
Reservoirs on the Flow of the Hudson River.
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HYDROLOGY
Fig. 19. — ^Weir for Measuring Flow of Water.
TABLE XXIV
Table for Weir Measureicent
Giving cubic feet of water per minute, that will flow over a weir 1 inch long
and from | to 20J inches deep.
Depth,
Inches.
i
i
f
i
f
}
{
0
.00
.01
.05
.09
.14
.19
.26
.32
1
.40
.47
.55
.64
.73
.82
.92
1.02
2
1.13
1.23
1.35
1.46
1.58
1.70
1.82
1.95
3
2.07
2.21
2.34
2.48
2.61
2.76
2.90
3.05
4
3.20
3.35
3.50
3.66
3.81
3.97
4.14
4.30
5
4.47
4.64
4.81
4.98
5.15
5.33
5.51
5.69
6
5.87
6.06
6.25
6.44
6.62
6.82
7.01
7.21
7
7.40
7.60
7.80
8.01
8.21
8.42
8.63
8.83
8
9.05
9.26
9.47
9.69
9.91
10.13
10.35
10.57
9
10.80
11.02
11.25
11.48
11.71
11.94
12.17
12.41
10
12.64
12.88
13.12
13.36
13.60
13.85
14.09
14.34
11
14.59
14.84
15.09
15.34
15.59
15.85
16.11
16.36
12
16.62
16.88
17.15
17.41
17.67
17.94
18.21
18.47
13
18.74
19.01
19.29
19.56
19.84
20.11
20.39
20.67
14
20.95
21.23
21.51
21.80
22.08
22.37
22.65
22.94
15
23.23
23.52
23.82
24.11
24.40
24.70
25.00
25.30
16
25.60
25.90
26.20
26.50
26.80
27.11
27.42
27.72
17
28.03
28.34
28.65
28.97
29.28
29.59
29.91
30.22
18
30.54
30.86
31.18
31.50
31.82
32.15
32.47
32.80
19
33.12
33.45
33.78
34.11
34.44
34.77
35.10
35.44
20
35.77
36.11
36.45
36.78
37.12
37.46
37.80
38.15
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For example: Suppose the weir to be 72 inches long^ and the
depth of water over the stake to be 1 If inches. Follow down the
left-hand column of the figures in the table until you come to
11 inches. Then run across the table on a line with the 11, until
under f on top line, you will find 15.85. This multiplied by 72,
the length of weir, gives 1141.2, the
number of cubic feet of water passing
per minute.
The above table will give results
sufficiently close for all practical pur-
poses, but if extreme accuracy is
essential the following formula ^
might be used, in connection with
measurements obtained from the
method previously described:
Q = 3.33(L-.2H)«'/*.
In the above L= length of weir
in feet, H=hesd or depth of flow in
feet over weir, as measured on the
stake; Q= cubic feet of water per
second.
The Gurley Hook Gauge, Fig. 20,
is a very useful device for measuring
the depth of the water passing over a
weir. Its arrangement is such that
the readings can be taken by the
observer with the greatest possible
convenience and at some distance
from the surface of the stream being
measured.
This gauge is used in a box attached to a flume at any con-
venient point near the weir, the water from the flume being con-
veyed to the box by rubber or lead pipes, thus indicating the pre-
cise level of the water in the flume, the surface of the water in the
box being at rest. The exact level of the crest of the weir should
be taken by a leveling instrument and rod, and marked by a line
drawn in the still water box at the surface of the water. The
1 Pelton Water Wheel Ck).
Fig. 20.— Gurley Hook Gauge.
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HYDROLOGY
scale of the gauge being previously set at zero wth the vernier,
the base ia fastened to the box above the water in a vertical posi-
tion and at such a height that the point of the hook is at the same
level as the crest of the weir, the precise point being secured
by moving the hook in the tube. The point of the hook
will, of course, be under water and level with the crest of the
weir.
The depth of water flowing over the weir is the distance between
the point of the hook in the position named and the exact surface
of the water. To ascertain this, the hook is raised by turning the
milled head nut imtil the point of the hook, appearing a Uttle
Fig. 21. — ^Typical Gauging Station with Automatic Gauge.
above the surface, causes a distortion in the reflection of the light
from the surface of the water. A slight movement of the hook in
the opposite direction will cause the distortion to disappear, and
will indicate the surface with precision. The reading of the scale
will then give the depth of water passing over the weir, in thou-
sandths of a foot.
Where measurement by weir is impracticable the amount of
water can be calculated by ascertaining the average velocity of
the water and the cross-section of the stream, the quantity being
the product of these two factors. The mean velocity is the func-
tion of the cross-section, surface slope, wetted perimeter, and
roughness of the bed, while the cross-sectional area dep)ends on
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STREAM-FLOW
63
the permanency of the bed and the fluctuations of the surface^
which govern the depth.
Gauging stations should be located at places where the record
of flow is to be made. Bridge locations are preferable, as from
them the measurements can be easily made, with the least expense.
If the channel conditions are not satisfactory at such points it is
necessary to use boats or erect a cable station. Fig. 21 showing a
Fig. 22.— Typical Gauging Station for Bridge Measurement.
typical station used by the U. S. Geological Survey. The location
should also be preferable where the channel is straight and without
cross-currents, both above and below the station, and the bed
should be as free from obstructions as possible.
The methods by which the measxu^ments are made are in
general those in common use by the U. S. Survey. An arbitrary
number of points are laid off perpendicular to the thread of the
stream, Fig. 22. They are known as measuring points and divide
the gauging section into strips. The area for each strip is cal-
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64
HYDROLOGY
culated from careful soundings and the mean velocity ascertained
by making measurements at different depths. By multiplying
the area and the velocity for each^strip, its discharge value ia
determined independently of the other, and by adding them
together the total is arrived at in the most accurate manner.
Fig. 23. — Price Electric Current Meter with Telephone Sounder,
factured by W. & L. E. Gurley, Troy, N. Y.)
(Manu-
The greatest error in these estimates is generally due to inac-
curate determination of the mean daily gauge heights, ordinarily
secured from a few observations during the day or even more
infrequently. This has led to the introduction of automatic
water stage registers (see page 265), by which the varying height
of water may be accurately gauged and a dependable, continuous
record obtained.
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STREAM-FLOW
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For measuring the velocity the current meter is jiow most
generally used. This meter is primarily an instrument for
measuring the velocity of moving water, and consists essentially
of a wheel with vanes, which may be shaped like those of a wind-
mill or of a screw, or with caps like those of an anemometer, the
necessary qualification being that the moving water shall easily
cause the wheel of the meter to revolve. The velocity of the
water is then determined from the revolutions of the meter in
unit time. The meter which has been adapted by the U. S.
D UOOO IMOO 16000 18000 20000 S9000 SiOOO 9
Dtscharge tn Second Feel
Fig. 24.— Discharge, Mean Velocity, and Area Curves for James River at
Cartersville, Va.
Geological Survey after years of experience and improvements is
the Price Current Meter, which is manufactured by W. & L. R
Gurley. It is illustrated in Fig. 23.
The curves in Fig. 24 show a method of plotting the values
of discharge, mean velocity and area in relation to the gauge
height.
Where a current meter is not available or its expense not jus-
tified as in minor preliminary investigations, the float method may
be used for approximately determining the velocity. This may
be done by .laying off 100 feet of the bank and throw a float into
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66 HYDROLOGY
the middle of the stream, noting the tune it takes for the same to
pass over this 100-foot stretch. This is repeated a number of
times and the average taken. As the stream-flow at the swf ace is
greater than at the bottom, the average must be taken which is
about 83 per cent of the surface velocity. It is, therefore, con-
venient to lay o£f the distance as 120 feet and reckon it as 100 feet,
using the surface velocity.
Government Records. The Water Supply and Irrigation
papers of the United States Geological Survey furnishes the chief
source of information relating to stream-flow measurements, and
a complete list on these may be had by applying to the Director,
U. S. Geological Survey, Washington, D. C.
The U. S. Weather Bureau also issues annual reports on the
flow of the principal rivers of the country, while the War Depart-
ment from time to time issues reports dealing with special investi-
gations undertaken by ^the engineers for determining the navi-
gation faciUties of certain rivers and the possibilities of their
improvement.
In addition to the above Federal Reports, numerous investi-
gations are also made every year by different States and these can,
as a rule, be obtained from the Geological Survey Departments
of these States.
It is thus seen that there is an abundant amount of data on
stream-flows in the different sections of the country. These
records are, however, scattered around in so many different publi-
cations, that it is a difficult matter to find the desired information.
An excellent system of indexing such data on stream-flow and
rainfall has been devised and is used by H. M. Byllesby A Co.,
Chicago. It is described in Engineering Record for January 31,
1914.
6. ENERGY OF FLOWmO WATER
The energy of flowing water is entirely due to its position, or
head. It follows in general the same laws as falling bodies so
that, assuming a 100 per cent efficiency, its potential energy
depending on the position must be equal to its kinetic energy
depending on the velocity. That is
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where
thus
and
ENERGY OF FLOWING WATER 67
w
m=iiia8s=-,
9
(/= gravity acceleration « 32. 16,
A^heady
»= velocity,
w = weight of water = 62.4 lb. per cu. ft. ;
v^y/2gh.
The quantity of flowing water expressed by the formula:
where
9= quantity;
»= velocity;
a = area of stream.
From the above the following formula for calculating the gross
horse-power of a stream or body of flowing water may be computed :
^p_QXgX62.4.
^•^' 550 '
in which
H.P. = gross horse-power ;
Q= discharge of water in cubic feet per sec;
£f= gross head in feet.
The above values are, however, only theoretical and never realised
in practice. This is caused by the loss in head due to friction in
the water conductors, the nature and value of which will be
dealt with under the section on Water Conductors.
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HYDROLOGY
6. CONVENIENT EQUIVALENTS
The following is a list of convenient equivalents for use in
hydraulic computations:
TABLE XXV
Table for oonyertmg discharge in second-feet per square mile into run-o£F
in depth in inches over the area.
Discharge in
Becond-feet per
Run-off
(Depth in
Inches).
Square Mile.
1 Day.
28 Days.
20 Days.
30 Days.
31 Days.
1
0.03719
1.041
1.079
1,116
1.153
2
.07438
2.083
2.167
2.231
2.306
3
.11167
3.124
3.236
3.347
3.459
4
.14876
4.165
4.314
4.463
4.612
5
.18696
6.207
5.393
5.687
5.764
6
,22314
6.248
6.471
6.694
6.917
7
.26033
7.289
7.660
7.810
8.070
8
.29752
8.331
8.628
8.926
9.223
9
.33471
9.372
9.707
10.041
10.376
Note — For partial month multiply the values for one day by the number of dasrs.
TABLE XXVI
Table for converting discharge in second-feet into run ofif in acre-feet.
Run-off in Acre-
FEET.
Discharge in
Second-feet.
IDay.
28 Days.
29 Days.
30 Days.
31 Days.
1
1.983
65.64
67.60
59.60
61.49
2
3.967
111.1
116.0
119.0
123.0
3
6.960
166.6
172.6
178.5
184.6
4
7.934
222.1
230.1
238.0
246.0
5
9.917
277.7
287.6
297.5
307.4
6
11.90
333.2
345.1
367.0
368.9
7
13.88
388.8
402.6
416. ^
430.4
8
16.87
444.3
460.2
476. J
491.9
9
17.86
499.8
617.7
635.6
663.4
Note. — For partial month multiply the values for one day by the number of days.
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CONVENIENT EQUIVALENTS 69
1 Beoond-foot equals 40 California miner's inches (Law March 23, 1001).
1 second-foot equals 38.4 Colorado miner's inches.
1 second-foot equals 40 Arizona miner's inches.
1 second-foot equals 7.48 United States gallons per second; equals 448.8
gallons per minute; equals 646,317 gallons for one day.
1 second-foot for one year covers 1 square mile 1.131 feet or 13.572 inches
deep.
1 second-foot for one year equals 31,536,000 cubic feet.
1 second-foot for one day equals 86,400 cubic feet. .
1 second-foot equals about 1 acre-inch per hour.
1,000,000,000 (1 United States billion) cubic feet equals 11,570 second-feet
for one day.
1,000,000,000 cubic feet equals 414 second-feet for one 28-day month.
1,000,000,000 cubic feet equals 399 second-feet for one 29-day month.
1,000,000,000 cubic feet equals 386 second-feet for one 30Kiay month.
1,000,000,000 cubic feet equals 373 second-feet for one 31-day month.
100 California miner's inches equals 18.7 United States gallons per second.
100 California miner's inches for one day equals 4.96 acre-feet.
100 Colorado miner's inches equals 2.60 second-feet.
100 Colorado miner's inches equals 19.5 United States gallons per second.
100 Colorado miner's inches for one day equals 5.17 acre-feet.
100 United States gallons per minute equids 0.223 second-foot.
100 United States gallons per minute for one day equals 0.442 acre-foot.
1,000,000 United States gallons per day equals 1.55 second-feet.
1,000,000 United States gallons equals 3.07 acre-feet.
1,000,000 cubic feet equals 22.95 acre-feet.
1 acre-foot equals 325,850 gallons.
1 inch deep on 1 square mile equals 2,323,200 cubic feet.
1 inch deep on 1 square mile equals 0.0737 second-ioot per year.
1 foot equals 0.3048 meter.
1 mile equals 1.60935 kilometers.
1 mile equals 5,280 feet.
1 acre equals 0.4047 hectare.
1 acre equals 43,560 square feet.
1 acre equals 209 feet square, nearly.
1 square nule equals 2.59 square kilometers.
1 cubic foot equals 0.0283 cubic meter.
1 cubic foot of water weighs 62.4 pounds approx.
1 cubic meter per minute equals 0.5886 second-foot.
1 horse-power equals 550 foot-pounds per second.
1 horse-power equals 76 kilogram-meters per second.
1 horse-power equals 746 watts.
1 horse-power equals 1 second-foot falling 8.80 feet.
IJ horse-power equals about 1 kilowatt. ..,,.►
^ , , ^ X . ,, sec.-ft.Xfallin feet ^ .
To calculate water power qmckly: — =iiet horse-power on
water wheel realizing 80 per cent of theoretical power,
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CHAPTER III
CLASSIFICATION OF DEVELOPMENTS
LOW-HEAD DEVELOPMENTS
Water-poweb developments may be divided in two broad
classes: First, low-head and second, inedimn and high-head.
To the former class belong those plants which consist of a dam
which creates pondage at the point where the water is to be utilized,
so that the water passages to the turbine luits will be compara-
tively short while the quantity is large. The chief items com-
Fio. 26. — Map Showing General Lay-out of Pennsylvania Water and Power
Companies, Development at Holtwood, Pa.
prising the headworks of such a development are: The dam with
its spillway, the forebay, the intake and the taUrace.
Typical plants of this kind are shown in Figs. 25 and 26.
A dam extends across the river and impounds a large body of
water above it. It is built with a spillway section for the entire
length, this being necessary on accoimt of the large flood dis-
70
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LOW-HEAD DEVELOPMENTS
71
charges. The pondage may also be materially increased by
placing flashboards on top of the dam, and by this means an addi-
tional head is also gained.
Precautions must alwa3rs be taken to guard against floating
1<^8, debris, ice, etc., and for this a wing dam, having submerged
arches through which the water enters the forebay, has been built
at right angles to the main dam, between which and a rock-fiU
Fig. 26. — SectioDal Elevation of Power House, Cedars Rapids Mfg. and
Power Company.
above there are floating booms, which serves to deflect such ice,
etc., which is carried towards the forebay. Care should be taken
that the arches of the wing dam are submerged at least two feet
when the water level is at its lowest.
Any ice which enters the forebay despite these safeguards, as
weD as ice which may be formed there, can be diverted by provid-
ing ice chutes from the forebay toward the tailrace. The crests
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CLASSIFICATION OF DEVELOPMENTS
of these should be of the same elevation as the crest of the main
spillway.
MEDIUM AND HIGH-HEAD DEVELPMENTS
To this class belong those plants which consist of a diversion
dam with an intake at the head waters from where the flow is led
through tunnels, open canals or flumes to a forebay pond. This
is usually located on the hillside above the power-house and pipe
lines carry the water from the same to the turbines. In other
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LOW-HEAD DEVELOPMENTS 73
instances the entire water conductor from the diversion dam to
the wheels may be of enclosed pressm^ type. The quantity of
water is usually much smaller than in low-head plants.
High-head developments are characteristic of the California
water powers where the high mountain storage of the wiuter
flood waters can be used during that part of the year when the
run-off is a Tninimnm.
A typical high-head installation is shown in Fig. 27. It con-
sists of a diversion dam with spillway for impounding the waters
of the river, thus forming a reservoir of considerable size. The
intake is located at right angles to the dam, thus lessening the
accumulation of ice, logs, trees and other floating debris in front
of the intake trash racks.
The water conductor connecting the intake and the turbines
in the power-house consists of five sections; a reinforced concrete-
lined tunnel blasted through rock, a woodnstave pipe, a steel
pipe, a distributor and finally the steel penstocks.
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CHAPTER IV
DAMS AND HEADWORKS
1. DAMS
Classification. Dams may be classified according to the
material used in their construction, as:
. Timber crib dams.
Earth-fill dams.
Rock-fill dams.
Masonry dams.
The choice of type is generally dictated by natural conditions.
Sohd rock foimdations usually mean masonry dams, whether of
overflow type or not. Absence of rock foundations, however,
usually means the choice of crib, earth or rock-fill dams, and which
of these is chosen is generally determined by local conditions,
such as available construction material, etc.
Location. Before a final decision can be reached as to the
exact location of a dam there are niunerous points which must be
carefully investigated. For example, with low-head developments,
the area which will be flooded must be ascertained as this will
determine the available head. It is, therefore, evident that, from
this point of view, a dam would be preferable at a point where the
river banks are steep so that a sufficient pondage and head could
be obtained without causing a flooding of too much adjacent land.
The character of the soil is also of the utmost importance, and
governs, as previously stated, the type of dam which is to be
selected. It should be impervious and able to withstand the load
of the dam. It is alwa3rs advisable, especially where a sohd rock
foundation is not to be had, to dig or drill a number of test holes,
from which the character of the underlying strata may be ascer-
tained. It may then be found that one site will require a very
deep foundation but a smaller dam structure, while at another
site the reverse may be true.
Available material for construction, such as rock, sand, etc.,
74
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DAMS 76
are also deciding factors, as are also the facilities for spillways to
take care of the overflow.
It is, therefore, evident that the location can only be deter-
mined after a careful consideration of all the above facts, and com-
parative estimates are often required for a number of sites before
the problem can be intelligently solved, both from a technical
and economical standpoint.
Timber Crib Dams. These dams are only used for low heads
of about 30 feet and less and in locations where timber is plentiful
and cheap. They are generally used for diversion purposes and
Pig. 28. — ^Timber Crib Dam, Montana Power Company.
mostly entirely submerged, which gives them a long life. They
are, however, often used for temporary structures or when the
cost of other t3rpes would be prohibitive for the development in
question.
They consist of a crib or framework of logs or sawed timbers
bolted or otherwise fastened together, the structure being filled
with rock, gravel, earth, etc., and the sloping sides are faced with
planks to prevent leakage.
Almost any kind of foundation may be used if the proper pre-
cautions are taken. With solid rock the framework should be
securely bolted thereto to obviate any tendency of the dam to slide.
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76
DAMS AND HEADWORKS
Soft foundations usually require a dam with wider base, and
it may be necessary to first fill in with rock or gravel, while if the
soil is pervious piling may also be required. Undermining should
also be guarded against by extejiding the facing at the toe.
Figs. 28 and 29 show a rock-filled crib dam of modem design.
The up-stream side has been given such a slope that the stability
of the dam is assured even under the greatest floods, the weight
itf^t nnik. ITM i^i h* ^ «•*' tr
Fig. 29. — Cross-section of Timber Crib Dam Shown in Pig. 28.
of the water acting to hold it down, so that the higher the flood
the greater the stabihty. The down-stream side is also sloping
and tapers off into a long apron so designed as to take care of the
overflow without shock or commotion. A sluiceway is provided
at one end of the dam, and at the other there is a concrete cham-
ber or forebay serving as intake to the pipe lines supplying the
plant. The openings to this forebay are controlled by gates and
are provided with the usual screens for the exclusion of trash.
Earth-fill Dams. This type of dam generally has a trapezoidal
cross-section and consists, as the name impUes, of an earth-fill
faced with some harder material. It cannot be overturned and its
stabihty depends on the imperviousness of the material used in its
construction. It is not intended to be used as a weir, and in case
of overflow is liable to be disintegrated and washed away. For
this reason, earth-fill dams must be provided with spillwa3n3 if
there is danger of fiood-waters passing over the crest. They are
not intended for very high structures, and while dams of this type
have been built for heights above 100 feet, about 50 and 75 feet
is more common. There are no definite rules laid down for cal-
culating the dimensions, but it is considered good practice not to
let the slope of the wetted side exceed 1 in 3, while the outside
slope may be 1 in 2. The height should be at least 10 feet higher
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DAMS
77
than the high-water level and the width of the crest varies any-
where from 8 to 10 feet for low dams, to 20 or more for the highest
one.
One of the most important things in its construction is to secure
a water-tight foundation. Hardpan and clay are good founda-
tions while soft soil and rocks with fissures are very bad. The
site must be cleared of tree stumps, roots, etc., and it is always
necessary to remove the soil for a depth of 1 to 2 feet. One or
— JWl
Fig. 30.— Earth-Fm Dam with Puddle Core.
OattiiL? 9urf a« to b* Drwed
FUSia vlth SoU ii*il S
<. friw'i nJil tj r • I 'J '. J - ■ ' r
Fig. 31. — ^Earth-Fill Dam with Impervious Puddle Core.
more trenches are dug parallel to the axis of the structure, to hold
the material, and if the soil is pervious it may be necessary to
provide a puddle core, as shown in Fig. 30, in order to prevent the
water from seeping under the dam, or piling may have to be
driven down to bedrock.
The material which goes into the structiure must be found near
the dam site, and its character, therefore, determines the method
of construction to a great extent. The best material is a mixture
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78 DAMS AND HEADWORKS
of gravel, sand and clay, and if this is readily obtained, the struc--
tiire is generally built homogeneous, as in Fig. 31.
There are many different methods of placing the material,
such as providing trestles and dump-cars, cable ways, etc. If the
material is taken from a higher elevation than the dam, and water
is plentiful, the hydraulic method of filling may be used and is
generally found very economical.
If good material is not to be foimd near the site, puddle or
concrete cores must be built to insure an impervious structiure, as
shown in Fig. 31.
Such a puddle core is pri^ferably made of a mixture of clay and
gravel, this being considered superior to clay alone. It is placed
in the center, with the finer material next and the coarser outside.
It should be protected from becoming dry, in which case it would
crack and permit the water to se^p through. Enough water is,
however, generally percolating through the structure to keep it
moist. The fill towards the outside surface should, however, be
kept as dry as possible to keep it from disintegrating, and it is,
therefore, advisable to install an efficient drainage 83^tem on this
side.
To protect the wetted side from the effect of the water it is
usually constructed with a rip-rap, and sometimes a concrete
facing may be advisable to prevent seepage. The other side
should also have a covering of rip-rap or gravel, or it should, at
least, be sodded.
Rock-fill Dams. A typical construction of this type of dam
is shown in Fig. 32, the essential difference between the same and
E1.4SdO
8p{lliini7 El. 48 W ^H.W. El. 4m
Fig. 32.— Rock-FiU Dam.
an earth-filled dam being the rock-filled part which forms the
down-stream section, while the other side is filled with earth and
gravel.
The rock-fill serves as a support for the earth-fill, which makes
the dam impervious, and it is, therefore, evident that this type
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DAMS
79
is superior to the plain earth-filled t3rpe, in that less damage would
be caused by an overflow.
If only poor material can be obtained for the earth-fiU, it is
necessary to provide a puddle or concrete core, the same as with
the previous construction, and the wetted surface should also be
protected by a rip-rap or concrete facing.
Masonry Dams. Masonry dams may, according to their
design, be divided in two general classes, gravity dams and arched
dams, and these further into solid or buttressed structures.
Gravity Dams. Gravity dams must resist any tendency
toward sliding or overturning.
Assimie a dam structiure of a trapezoidal crossHsection and
with the water surface level with the crest, as in Fig. 33. Then
the pressure in poimds
acting on the up-stream
side of the dam per foot
length is equal to
P= rj X sec e.
Where
/f=Head in feet;
(?= angle of dam sur-
face with the
vertical;
62.4 = weight of 1 cubic
foot of water.
Fig. 33. — Crofis-section of Gravity Dam
(Water same level as crest).
This pressure acts perpendicularly to the surface be at a point
two-thirds the height of the dam, figured from the top. The
leverage with which this force tends to overturn the structure
about point d is equal to the perpendicular distance between this
point d and the continuation of the pressure line P, i.e., dk. The
overturning force is, therefore, equal to Pxdk foot-pounds.
The overturning force must be coimterbalanced by the weight
of the structure. This is equal to W and it acts perpendicularly
from the center of gravity. Its leverage about the point d is equal
to di and the resisting force is, therefore, equal to WXdi foot-
pounds.
The center of gravity of a trapezoid may graphically be found
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80
DAMS AND HEADWORKS
as follows: Draw af equal to cd and ec equal to ab. Divide ab
and cd in two equal parts and connect the dividing points. Cour
nect e and fy and the point where these two lines intersect is the
center of gravity. It may also be calculated from the following
formula:
. H H/cd-abX
cd+abj'
The cross-section A of the dam can be figured from the
formula:
and by multiplying this by the weight of masonry, 150 lbs. per
cu. ft., the weight of the dam per foot length is obtained.
The factor of safety
1 witwLtTfi against overturning S of
the structure is:
-^ WXdi
5 =
PXdk'
Fig. 34. — Croas-section of Gravity Dam
(Water overflowing).
34. In this case the pressiure P is equal to
It is seen that the greater
the inclines of the sur-
faces the more stable
will the structure be.
In the above it was
assimied that the water
was level with the crest
of the dam. Suppose
now that the water is
flowing over, as in Fig.
^=62.4/^^Vff-^
P=62.4r-lJ_*ViJ-A)xsec 6
M^)
sec d pounds.
This pressure is, however, not appUed at a point \H from the top,
as in the previous case, but at a point x from the top, this distance
being equal to
-i"-!^^-
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DAMS
81
The resisting mpment due to the weight of the structure is
figured as in the previous case, except that the weight of the water
should also be considered. The factor of safety, S, is found from
the same formula as before, i.e..
S=
WXdi
PXdk'
It is also a common method to ascertain if the design is safe
by completing the pressure diagram, as in Fig. 35. The two
forces P and W are scaled off from the intersection point X, and
if their resultant Pi falls
inside the middle third of
the base, the dam will
safely withstand the over-
turning moment.
It is, however, not sufloi-
cient to determine the over-
turning moment for the full
cross-section about the toe.
It must be figured for sev-
eral sections such as a, b, c,
d; a, b, e, /, etc., Fig. 35,
and the calculations must
show that every part of the
structure is sufficiently thick
to withstand the pressiure.
Besides the above there are other stresses which must be given
due consideration, such as ice thrust, uplift caused by seepage
waters and internal stresses due to varjring temperature condi-
tions.
According to Mr. A. C. Beardsley, masonry dam design should
be governed by the following rules:
1. Design the crest and apron so that vacuums cannot form.
2. Underdrain the dam to eliminate all uplift.
3. Design the toe of the dam so there will be no imcertainty
as to the exact location of the tipping edge.
4. Allow for the effect of floating due to tail-water.
5. Allow for ice expansion and use the maximum crushing
strength of ice instead of average values.
6. Take care of expansion and contraction stresses.
Fia. 35. — Graphical Determination of
Safety of Grarvity Dams (Middle-third
method).
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DAMS AND HEADWORKS
7. Allow for wave action.
8. Where necessary, reinforce the dam with steel.
On account of their great weight, gravity dams should neces-
sarily be placed on bedrock foundations, and the materials should
be carefully tested as to their bearing power. The fact should
also be kept in mind that the pressure is not uniform over the
entire base but varies according to the water level back of the dam.
For example, with the reservoir full, the pressure is, of course, a
maximum at the toe and decreases toward the other side. All
Fig. 36. — ^Typical Masonry Dam of the Gravity Type.
Company.
Appalachian Power
tendency of seepage should be prevented by sealing all fissures,
and drains should be provided for carrying any waters that may
reach the base or enter the structure.
The material of which gravity dams are built consists either
of concrete or rubble masonry. With the former the rocks are
crushed to a uniform size making an even mixture, while with the
rubble masonry, or cyclopean concrete construction, as it is also
termed, large stones, weighing up to ten tons, are used. These
are carefully placed in position and the spaces between them
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DAMS
83
filled with smaller stones and cement mortar, forming a very
strong structure.
In most low- and medium-head developments where large flood
discharges must be passed, the entire dam or a large part of it
must be built in the form of a spillway. It is important that its
size be sufficient to take care of the largest known floods, and in
flW<iirm)aaJ til n«t\i
HoUu-In ealonlafing pressures
Concrete assumed to weight
8m assumed to weigh 115 Vm.
per en. ft.
Dm^Qb unJfft toe Qi l>offl t€ b&
Fig. 37. — Cross-section of Masonry Gravity Dam Shown in Fig. 36.
order to be on the safe side it is in many instances designed for
10 to 15 per cent greater discharge capacity than any previous
record would show to have taken place. The downstream face
should be curved so that the water will follow the surface and
prevent vacuum from forming, and also so that it is discharged in a
horizontal direction, protecting the bed of the stream against
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DAMS AND HEADWORKS
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DAMS 85
undercutting and erosion at the lower end of the toe when passing
severe floods, and permitting a quiet discharge without subjecting
the masonry structure to dangers from vibrations.
The illustrations in Fig. 36 and 37 show a typical design of a
masonry dam of the straight gravity tjrpe.
Buttressed Dams. This type of gravity dam has been devised
with a view of utilizing the material more economically than is
possible in a gravity structure, a typical design being illustrated in
Fig. 38. As seen, it is a hollow structure consisting of a concrete
deck supported at stated intervals by buttresses or piers per-
pendicular to the axis of the dam. As the downward pressure
of the water is relied on to a great extent to give the structme
stability, the upstream face should have an incline of not more
than 45^ with the horizontal. The thickness of the deck should
be proportioned in accordance with the hydrostatic pressure, and
it should vary uniformly from the base to the top, being some-
times reinforced with steel to increase its strength. Careful
precautions should be taken to make the structure water-tight,
and drains should be provided as well as passageways for interior
inspection.
This type of dam requires very good foimdations. As the
entire pressure must be withstood by the buttresses alone, it is
evident that the base width of these at right angles to the axis
will have to be considerably greater than for a gravity type struc-
ture.
Arched Dams. These may be either of solid or buttressed
design, curved in a horizontal arch with the abutments braced in
the rock on the sides of the gorge or canyon, thus giving greatly
increased stability. It is not considered good practice, however,
to rely entirely on the arch action and dams of this class are,
therefore, as a rule designed as a combined arch and gravity type.
In fact, the dam is often designed purely as a gravity structure,
and the added strength given by its curved form is simply assiuned
to increase its safety to that extent.
It has been the general practice to build these dams in one con-
tinuous arch, and Jorgensen in "Journal of Electricity" states that
for spans less than 600 feet a curved dam of this type requires less
material for the same factor of safety than a straight gravity dam.
If the gap to be closed is over 600 feet, the cross-sectional area of
the arch becomes nearly as great as the cross-sectional area of a
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DAMS AND HEADWORKS
Fig. 39.— Arched Dam. Orland Project, California.
.■>... -7^///"^ ' Confflonienite
Fig. 40. — Cross-section of Arched Dam Shown in Fig. 39.
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DAMS
87
FiQ. 41. — Multiple-Arched Dam. Umatilla Project, Oregon.
FiQ. 42. — CrofiSHsection of Multiple-Arched Dam.
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88 DAMS AND HEADWOKKS
gravity dam for equal stresses, and when it is considered that the
arch is alwa3rs longer than the chord, it is evident that the limit
of economy for a single arch span has been reached, if special
conditions are not present.
Recently the multiple-arch type of dam has come into exist-
ence and gives promise of allowing big reductions in the quan-
tity of material required for structures safely spanning gaps of
any width.
Figs. 39 and 40 illustrate an arched dam and Figs. 41 and 42 a
dam of the multiple-arched type.
General Rules Governing Design of Dams. The foDowing
regulations governing the design and construction of dams were
recently issued by the New York State Conservation Commission.
" Complete plans, elevations and sections of all proposed
dams must be submitted and approved of by this commission
before any work on the dam can be commenced, and the site must
be examined and approved of by this commission, both before
and after it has been prepared.
** Foundation Bei: Dams must be built upon a firm, compact,
impervious and natural foundation bed, from which all perish-
able material has been removed. Earth foundation beds must be
ploughed or trenched. Masonry must be carried into solid rock
at the base and sides, wherever practicable, and also have channels
cut into the rock bed sufficient to afford a firm hold for the dam.
Rock foundations must have all loose material removed; the
crevices for 200 feet above and for 100 feet below the dam, must
be thoroughly filled with concrete or grout, and the whole surface
under the dam thoroughly washed. Masonry dams over 36 feet
in height must have the rock bed drilled for hidden fissures and
tested by compressed air; these holes must be filled with grout
under a pressure equal to the maximimi ultimate pressure.
'' CoLcvlations: Dams must be stable at any section and under
all conditions. The compression upon masonry on the upstream
face shall be 10, 14 and 18 tons per square foot and for the down-
stream face 8, 10 and 14 tons per square foot, depending on the
mass; the first for walls less than 12 feet thick and buttressed
dams, and the last for solid masonry dams over 150 feet in height
with the best of work done under the inspection of a competent
engineer approved by this commission.
" All cement must be Portland and up to the standard of the
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DAMS 89
New York City Building Law, tested as prescribed by the Amer-
ican Society of Civil Engineers, and must more than fill the voids
of sand and stone mixed in the proportions as used. The sand
and stone used for masonry must be sound and permanent, clean,
hard, and not easily sheared or split.
" OvUeU: All dams must be provided with approved outlets
of sufficient size, and so located as to completely allow the im-
pounded water to be released when desired or necessary, and
precautions must be made to prevent leakage along the outlets.
" Ice Pressure: From Dec. 1 to March 15 no dam shall have
the water higher than two-thirds the height of the dam, unless
permission is granted by the Conservation Commission to keep
the water above at a higher level. Dams Uable to be full during
the above period must be built strong enough to resist any possible
ice pressure in addition to the water pressure, and dams not so
designed must have an outlet at two-thirds the height of the dam.
" Aprons: Spillways of all dams must be provided with aprons
or other provision on the downstream side to prevent the under-
mining of the dam by the falling waters.
" Wooden Dams: Wooden dams may be used for temporary
purposes, or where the reach of the water impounded above the
dam is not over 300 feet or its depth more than 10 feet. The
timber of the dam must be removed at the end of five years,
unless express permission is granted by the Conservation Com-
mission for a longer period.
" The crib work of wooden dams shall be built in pockets not
more than 8 feet square, well fastened together with at least
f-inch spikes or bolts, long enough to pass through three timbers,
and the pockets soUdly packed with stone. The upstream face is
to be built at an angle of three horizontal to one vertical, covered
with plank, on which is to be laid a good layer of gravel. If the
foundation is rock, the bottom timbers must be anchored to the
rock.
" Earth Dams: The upstream half of earth dams shall be
composed of gravelly earth with about 15 per cent of clay, with
no stones over 4 inches near the upstream face, or, if there be a
core, next to the core on the upstream side. The earth is to be
moist, not wet, well rolled in 12-inch layers slightly sloping down
to the middle of the dam. The downstream half, or part below
the core, may be composed of coarser materials and stones. The
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90 DAMS AND HEADWORKS
»'-■
top should be slightly convexed and of a minimum width of 8 feet
plus 1 foot in width for every 5 feet over 15 feet in height. The
slop)es should be two horizontal to one vertical, except if stone is
used on the downstream half it may be one and one-half horizontal
tc one vertical. If the upstream part is of very fine material, the
slope must be less. A berm, or horizontal surface, which shall
be not less than 4 feet wide, shall be constructed on the slopes at
every 20 feet horizontally from the top. On the downstream
face these berms shall be provided with paved gutters. The up-
stream face shall have an 18-inch stone pavement laid in broken
stone or gravel from the top to the upper berm, and below shall
have a pavement of rip-rap. The downstream face is to be sodded
or covered with 12 inches of gravel or rip-rap.
" Every earth dam must be provided with a masonry spillway
of sufficient unobstructed area to take the high flow, and built
with the same requirements as for masonry dams. The height
of the dam shall be at least 3 feet above high flow, plus 3 feet for
a reach, or expanse of water upstream, of one mile, plus 8 feet for
a reach of two miles, and proportional for an intermediate reach.
" Earth dams of over 10 feet in height shall be provided with
a masonry core in the middle, the top to be not more than 2 feet
below the top of the dam, and a top width of not less than 2 feet
with a batter of 1 horizontal to 24 vertical on each side. Or, the
core may be placed on the upstream side, in which case the width
of the core at any point must be equal to half of the depth. Or,
the core may be omitted and the dam made 5 feet wider and 3 feet
higher than above specified; in this case the hydraulic process of
construction may be employed.
" Masonry Dams: The least width of masonry dams shall be
one-tenth of the height, with a minimum of 4 feet. The mini-
mum width at any depth shall be two-thirds the depth below the
highest water level.
" The masonry must be built up in horizontal sections with
center grooves in the top and sides for bonding, formed by cm-
bedding beveled timbers in the concrete. Concrete masonry
shall have vertical cast-iron bars in the upstream face, placed at
least 2 feet apart and of sufficient length to protect the masonry
against ice and floating bodies.
''Reinforced Buttressed Dams: The buttresses shall not be
over 20 feet apart for dams over 100 feet high on rock foundations,
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FLASHBOARDS 91
and nearer for others, with the necessary cross stiflfening girders.
The upstream face shall be at an angle of not over 45° with the
horizontal and the downstream face not over 60°. No part of
the dam shall be less than 12 inches thick.
*' If the dam is on rock foundations, the front face must have a
heavy cut-oflf wall built into the rock. If on gravel and clay foun-
dations both faces must have deep cut-oflf walls and a heavy rein-
forced flooring with weep holes to relieve the water pressure under
the flooring. Drainage must be provided in interior pockets for
seepage waters, and, if practical, the interior must be made acces-
sible to allow for inspection.
" The crest of the spillway, and for 3 feet below, must be thick-
ened and heavily reinforced, and the entire dam and bulkheads
protected from ice and floating bodies the same as masonry dams.
The dam must be well anchored to the bulkheads."
2. FLASHBOARDS
The maintaining of a constant water level above the dam is
naturally very desirable. This water surface fluctuates con-
siderably during the diflferent seasons of the year, depending on
the flow, and it was previously shown that the spillway must be of
ample capacity to discharge the flood waters and prevent the
water above the dam from flooding such land as has not been
included in the flowage area. It is furthermore desii*able to keep
the surface at approximately the same level during the low-
water periods and thus maintain a constant head. This is accom-
plished by providing flashboards, which are placed on the top of
the dam, and arranged to be raised or lowered with the variation
in the water level. It has also been found that for installations
with steam reserve plants the operating arrangement that will
insure the most efficient use of the river flow is to maintain the
level in the storage reservoir at nearly the crest of the flashboards,
carrying by the auxiliary plant any excess load until such time as
reports from the watershed above indicate a freshet. Then the
stream plant is shut down and the water drawn down in the reser-
voir to such an extent as to allow it to be filled by the anticipated
freshet.
There are numerous designs of such flashboards, the most
common being as follows:
1. Stationary flashboards.
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92
DAMS AND HEADWOKKS
2. Sliding gates.
3. Tilting gates.
4. Tainter gates.
5. Rolling gates.
All cf these with the exception of the first class require that piers
be provided on the crest of the dam, between which they may be
supported. The number of these piers and spillway sections
depends then on the maximum length to which the gates can be
successfully built.
Stationary Flashboards. This arrangement simply consists
in placing a row of wooden panels on top of the dam crest, and
supporting them by iron pins which are set vertically in holes
np>8tream Bide
-GnwaPIiiB
Fia. 43. — Stationary Flash-board Design.
previously provided in the concrete structure, as shown in Fig. 43.
These pins are so dimensioned that when the water reaches a
certain elevation they will give way and readily release the boards.
R. MuUer (" Engineering Record," August 22, 1908), gives the
following formula for calculating the head of water that will
cause the iron pins to bend. It is based on Wa3me iron pins:
y_18.12(P 2.
in which
X = height of water in feet above the dam crest when pins
begin to bend;
d= diameter of pins in inches;
jS= spacing of pins in feet;
A = height of flashboard in feet.
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FLASHBOARDS
93
The ends of the different sections overlap each other, as seen
in the illustration, and a fairly water-tight joint is thus provided by
utiUzing the water pressure itself. For sealing the joint between
the lower edge of the boards and the masonry it has been found
that a composition of cinders and straw, well mixed before appli-
cation, is very satisfactory. In it the cinders form the body, while
the straw is the elastic tightening medium.
While the pins are ordinarily removed once a year, the flash-
boards are Ukely to be taken up a number of times each season,
and speed and economy in their handling is, therefore, of impor-
tance. For wide streams the usual method of handling them is by
means of a scow provided with a steam-driven derrick, while for
narrower streams specially designed cableways with chain hoist
have been used with very great success.
Sliding Gates. These may be either of the plain friction type
or they may be provided with roller guides to make their operation
easier.
The gates used by the Mississippi River Power Company at
Keokuk, Iowa, shown in Fig. 44, indicate probably the maximum
^ r rn 1 n
^t£i»
Fia. 44. — Spillway Gates. Mississippi River Power CJompany,
Keokuk, Iowa.
size to which the friction type can be built. They are 11 feet
high and 32 feet long over all. Each gate consists of a frame-
work of 18-inch I-beams, covered with |-inch steel plate on the
upstream side. The edges are milled to make a water-tight joint
with the iron sill plates against which they fit, and the gates are
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94
DAMS AND HEADWORKS
operated by an electrically driven crane running along the bridge,
which forms the top of the dam.
For smaller installations a much simpler structure can, of
course, be used, such as an ordinary hand-operated sluice gate.
(See section on " Gates and Valves.")
A good example of the enormous size to which sliding gates
with roller guides can be built is that of the Gatim spillway of the
Panama Canal, as. shown in Figs. 45 and 46. Each of these
gates has a height of 19 feet and an over-all length of 47 feet. The
Fio. 45. — Gatun Spillway, Panama, Showing Spillway Gates.
operating machinery is designed to raise or lower the gates in
approximately ten minutes. It consists essentially of two
counterweights, one at each end of the gate, which practically
balance the weight of the gate, so that the machine has to over-
come only the resistance to movement of the gate due to the
water pressure. These counterweights are connected to the
gate by a screw and chain, the screw being moved vertically by
means of a worm nut, which is motor driven by a worm. The
two screws at the gate ends are driven simultaneously through a
driving shaft which is provided with a worm at each end for
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FLASHBOARDS
95
tf%\::^' 15(2 / y y^^
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96
DAMS AND HEADWORKS
El.lSl4-0f>?
ILISSM.
operating the wonn nuts. The screws are held m a vertical posi-
tion and the hoisting chains pass over sheaves at the tops of the
gate piers. A machinery tunnel extends the full length of the
spillway, a distance of approximately 800 feet, and is built within
the dam and contains all the operating machinery. Limit switches
are provided to prevent overtravel by cutting oflf the current from
the motor at the proper instant.
Tilting Gates. This type of flood gate generally consists of a
flaishboard which is hinged at its lower edge to the crest of the
spillway, the other edge
being free to move from
a more or less vertical to
a horizontal position. It
maintains its upright posi-
tion imtil the water level
above the dam reaches
the normal level. As the
water continues to rise the
additional pressure on the
gate will cause it to tilt
over further until it finally
rests in a horizontal posi-
tion on the dam crest.
As the water subsides the
gate will automatically
rise until the normal water
level in the pond is
reached.
Many different devices
have been used for accom-
plishing the coimterbal-
ancing effect, one of the
latest being that shown in
Fig. 47. This particular installation is designed to operate with
a maximum fluctuation in water level of three inches.
Each flashboard consists of a steel-reinforced timber panel
hinged at the bottom and connected at the top to a 17-ton con-
crete roller counterweight by two steel cables, which are wound
in grooves around each end of the roller. These rollers travel on
inclined tracks, each end being provided with a geared drum which
ELiaaLo.
Fig. 47.— Tilting Spillway Gate with
Counter Weight.
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FLASHBOARDS
97
£t un.&
engages a rack to prevent slipping. The principle of operation is
simply a balancing of the moments of force. The pressure on the
flashboards is transmitted to the dnmis through the cables which
act to roll the coimterweight up the track, while its dead weight
tends to roll it down; the two forces balancing each other when
the water level is at the fixed elevation. Hand-operated winches
are also provided, and their general construction is clearly shown in
the illustration.
The above dam consists of 10 spillway openings, 6 of which are
provided with these automatic spillway gates. The other 4
openings, which are located towards the intake side, are pro-
vided with flashboards of the ordinary stationary construction,
and are so designed that if the water in the pond rises 1 foot
above the normal level, the boards will give away.
Trainter Gates. This type of gate is generally built of steel
throughout, its general construction being clearly shown in Fig. 48.
In order to make it water- c ' - a
tight the bottom of the * — laV. JL; Igkitga
gate may be fitted with a
sill block of oak, which
takes a bearing on a steel
plate set in the top of the
concrete sill. Along the
ends may also be fitted
rubber strips for making a
tight joint with the side
walls.
The gates are usually
raised and lowered by '
chains attached to the
bottom edge of the gate
and wound upon drums on a shaft above,
hand- or motor-operated.
Rolling Gates. The principle of these gates is impUed in the
name, that is, the weir body is moved away from its closed posi-
tion by rolling on an inclined track. In the simplest form it con-
sists of a large hollow cylinder of a diameter corresponding to the
height to which it is desired to raise the water, and of a length
equal to the width of the opening to be closed. This cylinder is
built up of boiler plate, substantially braced to withstand the
Fig. 48.— TaiDter Gate.
They may be either
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98 DAMS AND HEADWORKS
•
strains to which it is subjected. At each end the cylinder is pro-
vided with a specially designed gear engaging a rack laid in an
inclined recess in the abutment or pier. By means of a sprocket
chain wrapped around one end of the cylinder and connecting with
1
S
I
I
(5
the operating mechanism the dam can be rolled up or down as
desired, see Figs. 49 and 49A.
For larger lifts and moderate spans, the cylindrical part of the
weir is often much smaller in diameter than the height of the weir,
the upstream side of the gate being provided with a metal shield
connected by strong braces to the cylindrical body.
This type of gate is a comparatively new invention and, while
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FISHWAYS
99
it has been used in Europe to a considerable extent, there are only
a few installations in this country. It possesses many advantages
Pig. 49a. — ^Dam of Wasmngton Water Power Company, Showing Arrange-
ment of Rolling Gates.
over other types of flood gates on account of the larger size in
which it can be built. For example, rolling dams have been built
in Europe with lengths up to 115 feet and depths of 28 feet.
8. FISHWAYS
In many States the law demands that dams be provided with
means whereby fish can easily ascend and descend according to
their natural habits in search of spawning grounds and of food.
Many different designs, of more or less value, are in use,
the illustrations in Fig. 50 showing fishway recommended by the
New York State Conservation Commission. This type is termed
the Improved Coil Fishway, and consists of a niunber of compart-
ments arranged in steps and separated by cross-partitions. These
are provided with orifices, alternating from side to side, through
which the fish may pass from compartment to compartment,
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100
DAMS AND HEADWORKS
LOHGITUDINAL SECTION
ELEVATION OF INTAKE
Fig. 50.— Fishway.
or they may leap over the cross-partitions, according to their
habit.
4. INTAKES
Intakes of many kinds are employed, and their design and
location is to a great extent governed by local conditions.
Trash Racks. An essential feature common to all types and
which has a bearing on the economic use of water, is the trash
rack and its design. These racks should be so constructed as
to give sufficient area for passing the desired quantity of water
without excessive loss in head. This is especially important in
low-head developments, where large quantities of water are
utilized. Considerable loss of efficiency may result from restricted
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INTAKES 101
water passages through racks, and in the design allowance should
be made for the accumulation of trash as a factor in the restriction
of water passage.
Low-head Installations. With low-head plants the intake
generally forms a part of the dam or power-house, as shown in
Fig. 26 imder section " Low-head Developments." The up-
stream bay comprises the gate room, and by thus installing the
gates and screens indoors, there is less danger from ice forming
therein during cold weather. In certain stations arrangements
are also made whereby the heated air from the generators can be
led to the gatehouse for preventing the formation of ice.
The water from the forebay enters the gatehouse through
arches in the front wall, and by submerging these below the low-
water level certain floating material will be prevented from
entering.
High-head Installations. For high-head plants the intakes
are often built as independent structures, and where overflow
diversion dams are used, they should preferably be located at a
right angle to the dam. This arrangement has several advantages,
among which are the ease with which logs, trees and other float-
ing debris can be cleared away by simply opening one or two of
the nearest flashboards.
The intake shown in Figs. 51 and 52 represents a typical
installation of the latest design. It is a caisson-like, self-contained
structure, divided by partitions into five sections in order to resist
the stresses on the outside walls due to the hydrostatic pressure
when the intake is empty and the water in the pond is at its
maximum elevation. At the rear of each division wall there is an
opening which allows the water to pass to the timnel entrance
located at the center and bottom of the rear wall.
There are two sets of racks, a coarse set consisting of |-inch
round iron rods spaced 4 inches apart, being placed in front of the
head gates to prevent large debris from interfering with their
operation. In addition, there is a fine set mounted in an inclined
position in each of the intake chambers. These racks are made
of 4X|-inch flat iron bars, spaced IJ inches apart. They are
pro\aded with a rack cleaner, each rack section being cleaned by
three rakes placed in a staggered position and operated at a
speed of 3 feet per minute by means of link chains from a motor-
driven coimtershaft located on top of the structure. At the
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DAMS AND HEADWORKS
FiQ. Sl.^Tunnel Intake, Showing Its Relation to the Diversion Dam.
Fig. 62. — Cross-section of Tunnel Intake Shown in Fig. 51, Illustrating Racks,
Rack-cleaners and Gates.
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INTAKES 103
top of each bay an adjustable iron comb catches the debris col-
lected by the rakes and drops it on the floor.
Influeoce of Ice. In cold climates, where it is impracticable
to reduce the entering velocity of water to a sufficient extent to
allow the surface to freeze over, and where considerable quan-
tities of anchor or frazil ice are likely to be swept against the racks,
adherence to the racks may be reduced either by maintaining the
portion of. the racks above the water surface at a temperature
above freezing by housing or otherwise, or by constructing the
exposed portions of the racks of wood, concrete or other non-
conductors of heat, the portion below the water being of steel.
Electric heaters have been used in some cases for the piurpose of
preventing clogging of the racks, and it has also been proposed to
so arrange the bars composing the rack that a low-voltage electric
current may be sent through them in series, thus heating them
sufficiently to prevent the adherence of ice.
In order to prevent trouble from ice in the wheel casings, it is
essential that effective waternseals be provided in the tailrace
discharge to prevent the entrance of cold air.
For further information on precautions to be taken against ice
troubles, the reader is refered to the N.E.L.A. Prime Mover
Committee's Report for 1917.
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CHAPTER V
WATER CONDUCTORS AND ACCESSORIES
1. WATER CONDUCTORS
Classification of Water Conductors. As in the case of dams,
there is a great variety of types of water conductors, the par-
ticular kind to be used being entirely governed by the nature of
the development as well as by economy. Where the power-house
is located near the dam, there may be no need for conduits at all, as
in low-head plants, or they may simply consist of very short pipes.
For medium- and high-head developments, however, a more
elaborate system of conduits must as a rule be provided, as the
water must in many such instances be diverted for miles, before
it finally reaches the power-house.
The different kinds of water conductors in general use may be
divided into two classes, open or closed, the closed construction
being either of the low- or high-pressure type.
Classification op Water CoNDUcroBa
Open.
Canals: lined or unlined.
Flumes: wood, concrete or steel.
Closed.
Low-pressure.
Tunnels.
Pipe: wood, concrete or steel.
High-pressure.
Pipe: steel.
Open canals and flumes are often used for carrying the water
from the point of diversion to the beginning of the pressure lines.
This method was extensively used in earUer developments, and
while it may in many cases be the cheapest, a higher efficiency can
be obtained by a closed system of tunnels and pipes, in that the
total head will be greater. Where the contour of the country is
very irregular the cost of excavating for canals and of building
high trestles for the flumes may be very high, and in such instances
104
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WATER CONDUCTOBfl
105
TABLE XXVII
Table of n for Kutter'b Formxtla
Surface.
Perfect.
Good.
Fair.
Had.
pipe
Uncoated c.-i. pipe
Coated c.-i. pipe
Commercial w.-i. pipe, black
Commercial w.-i. pipe, galv
Smooth brass and glass pipe
Smooth lockbar and welded " OD
Riveted and spiral steel pipe
Vitrified sewer pipe
Glazed brickwork
Brick in cement mortar; brick sewers.
Neat cement surfaces
Cement mortar surfaces
Concrete pipe
Wood-etave pipe
Plank Flumes:
Planed
Unplaned
With battens
Concrete-lined channels
Cement-rubble surface
Dry-rubble surface
Dressed-ashlar surface
Semicircular metal flumes, smooth. . . .
Semicircular metal flumes, corrugated.
Canals and Ditches:
Earth, straight and uniform
Rock cuts, smooth and uniform ....
Rock cuts, jag^d and irregular. . . .
Winding sluggish canals
Dredgea earth channels
Canals with rough stony beds, weeds
on earth banks
Earth bottom, rubble sides .
Natural Stream Channels:
(1) Clean, straight bank, full stage, no
rifts or deep pools
(2) Same as (1), but some weeds and
stones
(3) Winding, some pools and shoals,
dean
(4) Same as (3), lower stages, more in-
effective slope and sections
(5) Same as (3). some weeds and stones
(6) Same as (4), stony sections
(7) Sluggish nver reaches, rather
weedy or with very deep pools
(8) Very weedy reaches
0.012
0.011
0.012
0.013
0.009
0.010
0.013
0.010 \
0.011/
0.011
0.012
0.010
0.011
0.012
0.010
0.010
0.011
0.012
0.012
0.017
0.025
0.013
0.011
0.0225
0.017
0.025
0.035
0.0225
0.025
0.025
0.028
0.025
0.030
0.035
0.040
0.033
0.045
0.050
0.075
0.013
0.012*
0.013
0.014
0.010
0.011*
0.016*
0.013*
0.012
0.013
0.011
0.012
0.013
0.011
0.012*
0.013*
0.015*
0.014*
0.020
0.030
0.014
0.012
0.025
0.014
0.013*
0.014
0.015
0.011
0.013*
0.017*
0.015
0.013*
0.015*
0.012
0.013*
0.015
0.012
0.013
0.014
0.016
0.016*
0.025
0.033
0.015
0.013
0.0275
0.020
0.030
0.040
0.025*
0.0275*
0.0225*
0.033*
0.045
0.0275
0.030
0.030
0.030*
0.035*
0.033*
0.0275
0.030
0.033
0.035
0.040
0.045
0.045
0.035
0.050
0.050
0.040
0.055
0.060
0.100
0.070
0.126
0.015
0.015
0.017
0.013
0.017
0.015
0.017
0.013
0.016
0.016
0.013
0.014
0.016
0.018
0.030
0.036
0.017
0.016
0.030
0.026
0.036
0.030
0.033
0.040
0.036
0.033
0.040
0.050
0.056
0.045
0.060
0.080
0.160
* Values commonly uaed in deaigninc.
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106 WATER CX)NDUCTORS AND ACCESSORIES
the closed construction generally becomes more economical, in
that tmmels may be built and the pipes follow more or less the
contour of the country. The selection of the particular type of
conduit construction is, therefore, an engineering problem of
considerable importance, and has to do with the economic oper-
ating features of the development.
Canals. The velocity of water in a canal is affected by the
roughness of the bed, by the wetted surface of the form of the
crossHsection, and finally by the grade. According to Chesy's
formula it is equal to:
where i;= velocity in feet per second ;
c» coefficient;
r»hydraulic radius in feet;
«» grade or hydraulic slope,
the values of c may be obtained from the following two formula,
both of which are in. common use.
Kutter's formula:
n 8
where n is the coefficient of roughness, the values of which are
given in table XXVIL*
Bazin's Formula:
87
c= .
0.662+^
Vr
TABLE XXVIII
Values of m
Smooth cement and planed boards 0.06
Planks and bricks 0. 16
Rubble masonry 0.46
Earth canab in excellent condition 0.85
Earth canab in fair condition 1 .30
Earth canab in bad condition 1 .75
* R. E. Horton, " Engineering News," February 24, 1916.
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WATER CONDUCTORS 107
on. u J 1- J- Area of Croes-fiection ., , . ,
The hydraubc radius, r= „^ - , ^ . — i — , the wetted per-
Wetted Perimeter "^
imeter of the croes-Bection of a channel being that part which is
in contact with the water.
For an open canal, the grade or slope, a, is the ratio of the fall to
the length in which the fall occurs. For a closed penstock under
pressure, it is the ratio between the loss in head due to friction
to the length. (See also pag^ 117.)
The velocity of the water in a canal should be kept below that
which would cause erosion of the bed. It should, however, be
large enough to prevent vegetable growth from forming or silt
from being deposited. Assuming the bottom velocity to be
about 75 per cent of the mean velocity, the figures in Table XXIX
represent the safe values which are widely used in determining the
permissible velocities of water in open canals.
TABLE XXIX
Safb Mean Velocitibs *
Very fine sandy soil or loose silt 0.50
Pure sand. 1.00
light sandy soil, 15 per cent clay 1 .20
light sandy loam, 40 per cent clay 1 .80-2.00
Coarse sand 1.50-2. 00
Loose gravelly soil 2.60
Ordinary loam 2.60
Ordinary firm soil or loam, 65 per cent clay. ... 3 .00
Stiff clay loam 4.00
Firm gravelly clay soil 5.00-7.00
Stiff day 6.00
Conglomerates, soft slate 6.60
Stratified rocks 8.00
Small botdders 8.00-15.00
Hard rock 13.33
Concrete 16.00-20.00
• B. A. Etcheverry, " Journal of Electricity » Power and Gas."
The most advantageous cross-section to use, from the hydraulic
point of view, would be that which gives the smallest wetted per-
imeter or the largest value of the hydraulic radius. This would
meari a semicircular section, but it is' seldom used on account of
the difficulties in building. A trapesoidal section is, however,
generally used, and by letting the bottom and sides be tangents
to an inscribed semicircle, as in Fig. 53, the best hydrauUc results
will be obtained; the slope, i.e., the angle 6, being 60^
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108
WATER CONDUCTORS AND ACCESSORIES
The ideal croesHsection from the hydraulic point of view is,
however, not always the best to adopt. There are other factors
which must be considered, such as the cost of construetion,
whether lined or unlined,
the character of the soil,
seepage, safety, grade, and
velocity. No specific rules
can be laid down to cover
all cases and each installa-
tion must be treated indi-
vidually.
A concrete-lined canal having the least wetted perimeter will
require the smallest amoxmt of material, while the steeper sides
mean less excavation. Such a canal can furthermore be given a
steeper grade, if sufficient fall is available, and thus a higher
velocity, so that the cross-section can be small for a given quan-
Fia. 53. — Cross-section of Canal.
ITola:-
Approx. 4}^ en. ft. of.o
per fool leairth of ditdu
Bnrf »ee of concrete on Inaide of
diteh to be made frnooth
Fig. 54. — Open Concrete-lined Canal.
tity of water. This fe advantageous especially on hillsides, and, if
the soil is hard and the excavation difficult, a concrete-lined canal
may be cheaper than an unlined one. In other instances the sofl
may be of such a porous nature that lining is essential to prevent
excessive seepage. (See Figs. 64 and 55.)
Note.— For " Flow of Water in Channeb," see Bulletin No. 194 U. S.
Dept. of Agriculture.
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WATER C0NDUC5S0HS
109.
f"
Fig. 55. — Concrete-lined Canal.
From the standpoint of safety a shallow canal is better than a
deep one. The pressure on the banks increases with the depth of water
and may cause breaks, especially where canals are built on side
hills, and where the banks may have been weakened due to erosion.
The slopes should, therefore, in the first place be such that
they will withstand such erosion of the water, the values given in
Table XXX being representative of actual practice.
TABLE XXX
Side Slopes
Solid rock or cement
Hardpan and very firm soil
Ordinary firm soil
Ordinary sandy loam
Loose sandy soil
Vertical.
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no WATER CONDUC?rORS AND ACCESSORIES
Evaporation is small as compared with seepage, which increases
with the depth of the water and with the wetted perimeter, but
decreases with an increase in velocity. While evaporation, there-
fore, can be neglected, the e£fect of seepage must usually be con-
sidered in determining the capacity of a canal.
The velocity decreases with an increase in the wetted perim-
eter, and when the fall is great it may be advisable to use a
shallower section to reduce the velocity, or vice versa. If the
actual slope of the country is so great that the corresponding
velocities would cause erosion, it is necessary to limit the grade to
a value which would not give an excessive velocity, and to con-
centrate the excess fall at suitable drops along the canal.
Flumes. Where the contour of the country is very irregular
or the soil very hard and difficult to excavate, flumes are some-
times used for diverting the water. While the first cost of such
structures may be very low where timber is cheap, their upkeep is,
however, usually much higher than for a canal, and every pre-
caution must, therefore, be taken in their design and construction.
The velocity of the water, which can be foimd from the for-
mulae given in the previous section, may be much higher than for
unlined canals, and the higher the velocity the smaller cross-section
is required. When the water, therefore, enters a flume from a
canal, it becomes necessary to provide a sufficient drop in the upper
end of the fliune for the increased velocity head. This may be
found from the formula:
wbere
/I = drop necessary to increase the velocity in feet;
v\ » velocity of flow in flume in feet per second;
V2 = velocity of flow in canal in feet per second;
(7= acceleration of gravity =32. 16.
Similarly there should be a gain in head when the water again
enters a canal from a flume, although this is not reaUzed to a very
great extent and can be neglected.
Flumes may be classified according to the material of which
they are built, into:
Rectangular wooden flumes.
Semi-circular wood-stave flumes.
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WATER CX)NDUCTORS
111
Reinforced concrete flumes.
Steel.
Also,- according to their general design, into bench flumes and
trestle flumes.
A t3rpical design of a rectangular wooden flume of the bench
t3rpe is shown in Fig. 56, the width being from 1^ to 2 times the
depth of the water. The illustration clearly shows the detail of
construction and this type is used on hillsides or places where it
may be located directly on the ground. When crossing depressions
it is supported on trestles. Careful consideration must be given
to the construction of the foundations, and precautions taken so
alk Bowd iW'x U'z le'o"
C*p2"x8"xlf0"
BBoanb Ik's 111
J^xY'Batten/
I Bottom Boards | li^'x IS'x liVi
Sill e"i
*p-joloted)r
Fig. 66. — ^Rectangular Wooden Flume.
that floods will not undermine the same. Drains should, there-
fore, be provided if there is any such danger. Spillways for dis-
charging any overflow should also be installed at points where
the water can be readily disposed of. This refers to canals as
well as flumes.
Fig. 57 shows the design of a semicircular woodnstave flume.
This section is, as before stated, very advantageous from the
hydrauUc point of view. It is easily adjusted to curves, and it
can be kept water-tight by screwing up the nuts above the tie-
beams at the ends of each threaded band.
Reinforced concrete flumes have been used in some installations
of late, Fig. 58 showing such a design. While the first cost is
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112
WATER CONDUCTORS AND ACCESSORIES
usually much higher than that of a wooden flume, its life is so
much longer and the maintenance cost so much lower, that it may
prove more economical in the long run. There is further one
advantage of such flumes and that is the omission of crosspieces
over the top, which makes cleaning very easy. This point should
be carefully considered for waters which are prolific in moss and
vegetable matters.
Steel flumes are generally semicircular in crossHsection, similar
to Fig. 67. There are several makes of such flumes but their
7 X 14 X SS
r 11 ■£ Wr stringer*
ThoM.' ., _ - , ,
Fig. 57. — Semi-Circular Wood-Stave Flume.
V8q.lMBtB«4
Fig. 58. — Concrete Flimie.
construction does not differ materially. They consist of curved
metal sheets with a bead or corrugated groove rolled in each edge
of the sheet. The sheets are put together by means of an inter-
locking joint formed by overlapping the edges, which fit over
each other. The joint is made tight by means of a curved rod
which fits on the outside of the corrugated groove and a curved
beveled bar or small channel on the inside. The steel rods carry
the weight of the flume, and their ends are threaded for nuts
and pass through a carrier or tie-beam which is supported on
stringers about 16 feet long.
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WATER CONDUCTORS 113
As the use of flumes becomes less and less as hydro-electric
work becomes more permanent in character, it is suggested that
for preliminary estimating purposes the cost of low-pressure pipe
lines be used instead of using the presumably lower cost of flume
construction.
Tunnels. Where the proposed route of the waterway encoun-
ters mountain ridges it is often advantageous if not absolutely
necessary to go through these by means of tunnels rather than to
Are* of waterway IBI aq. ft.
W»t(«d pmimetor 45 ft.
Hydimalla hmIIm SLS
FMetioB ooaffielant .014
Ormdo .00*
C. 130
Fia. 59. — Typical Tunnel Section.
excavate deep cuts or go around. The question as to which method
should be chosen is one of first cost as well as of maintensmce.
Tunnels are, of course, safer and their upkeep is usually low as
compared with open canals, especially if these are built on the
hillsides where they are exposed to dangers from boulders striking
them, undermining, etc.
Tunnels may be either of the pressure or non-pressure type.
When of considerable length they are usually of the former type
so that the drop may be utilized as useful head. They are almost
always lined with concrete, the thickness of the lining varying from
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114 WATER CONDUCTORS AND ACCESSORIES
4 to 12 inches depending on the grade and the pressure of the water.
A lining serves several purposes. It holds the rocky material in
place; it prevents seepage if the rock is porous; and finally it de-
creases the friction which is of greatest importance in tunnel work,
as it permits a higher velocity with a correspondingly reduced sec-
tion. The velocity may be obtained from Kutter's formula, and the
values for n may be taken as 0.014 for lined tunnels and 0.028
for unlined. The safe velocity is from 10 to 15 feet per second.
While the circular cross-section would be most advantageous
from the hydraulic point of view, it is usually given a horseshoe
shape (see Fig. 59) as this has been found to be the easiest to
excavate. In order to permit quick construction, especially of
long timnels, one or more adits or openings are usually provided
at certain intervals so that the work can proceed from several
headings at the same time.
Pipe Lines. Pressure pipes must be used for conveying the
water from the upper level at the forebay or dam to the wheels at
the power-house. These may be constructed of steel, wood, and
sometimes, although rarely, of concrete. The particular kind
to use depends upon the head and the corresponding pressiue.
Head, The total or gross head, as ordinarily understood,
is the difference between the elevation of the water in the fore-
bay and the tailrace. It must be distinguished from the net or
effective head acting on the turbine, the difference between the
two being equal to the head lost on account of friction in the
penstock, etc.
The net or effective head at any point on the pipe line is
equal to the sum of the pressure head at the point considered,
plus the elevation head at the point above a datum plane plus
the velocity head in the pipe. Thus
where
A = effective or net head in feet;
p = pressure head, this being equal to the pressure in pounds
per square foot, at the point in consideration, divided
by 62.4;
2 = the elevation of the point above any arbitrary datum
plane, in feet;
V = velocity at the point in feet per second.
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WATER CONDUCTORS 115
The efifective head at one point in a pipe will differ from
that at another point upstream or downstream from it, by an
amomit corresponding to the losses and, of course, to any work
done or received between the two points when a machine, such
as a turbine or pump, is placed in the pipe line. Considering
only the losses, it follows that the effective head must decrease
in the direction of the flow by an amount equal to the head lost.
Therefore, although either the pressure, elevation, or velocity
may increase in the direction of the flow, the sum of them must
continually decrease so that an increase in one of these items
must always be accompanied by a corersponding decrease in
on 3 or both of the others.
In regard to the head to be used in computing the efficiency
of an installation or a turbine, the turbine testing code of the
turbine builders specifies the following:
"For the purpose of computing the plant efficiency the
total or gross head acting on the plant is to be used, and is to
be taken as the difference in elevation between the equivalent
still-water siuf ace before the water has passed through the racks,
to the equivalent still-water surface in the tailrace after dis-
charge from the draft tube. When the water in the forebay in
advance of the racks flows with sufficient velocity to make its
velocity head an appreciable quantity, the actual elevation
of the water surface shall be increased by the amount of this
velocity head. The same process shall apply to the point of meas-
urement in the tailrace; that is, the velocity head at the point
of measurement in the tailrace shaU be added to the actual ele-
vation of the surface, the sum being considered the equivalent
still-water elevation.
" In computing the efficiency of the turbine, the losses through
racks, in the intake to the penstocks, and in the penstocks shall
not be charged against the turbine; nor shall the head necessary
to set up the velocity required to discharge the water from the
end of the draft tube be charged against the tiurbine.
" The net or effective head acting on turbines equipped with
casings is to be taken as the difference between the elevation
corresponding to the pressure in the penstock near the entrance
to the turbine casing, and the elevation of the tail water at the
highest point attained by the discharge from the unit under test,
the above difference being corrected by adding the velocity
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116 WATER CONDUCTORS AND ACCESSORIES
head in the penstock at the point of measurement and subtract-
ing the residual velocity head at the end of the draft tube. The
velocity head in the penstock shall be taken as the square of the
mean velocity at the point of measurement, divided by 2g; the
mean velocity being equal to the quantity of water flowing in
cubic feet per second, divided by the cross-Bectional area of the
penstock at the point of measurement in square feet. The residual
velocity head at the end of the draft tube shall be taken as the
square of the mesm velocity at the end of the draft tube, divided
by 2g, the mean velocity being equal to the quantity flowing
in cubic feet per second, divided by the final cross-sectional
discharge area of the closed or submerged portion of the draft
tube in square feet."
The loss of head is due to the loss in the entrance of the pen-
stock, to the friction of the interior surface, to curvature, and to
various other obstructions such as headgates, racks, and valves.
In the case of impulse turbines, there is a further loss caused by
the necessity of placing the wheel clear of tailwater so that after
leaving the wheel the water drops freely through the vertical
height between the wheel and the tailwater surface, and fails to
utilize the head corresponding to this free fall. It is customary
in computing the efiiciency of impulse turbines to charge against
the wheel only the net head with reference to the elevation of
the center of the nozzle taken as datum.
Loss of Head in Entrance. This loss of head is probably
due to internal friction of the particles of water against each
other when they converge towards the contracted entrance. The
loss depends on the shape of the intake, but for ordinary purposes
it may be obtained from the formula
Loss of Head in Friction. For determining the loss of fric-
tion in pipe lines there are two formulas in very general use:
Chezy formula:
V = cVrs (for values of c see page 106).
Williams and Hazen formula:
t;=1.32 cr""
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WATER CONDUCTORS 117
where
»= velocity in feet per second;
r = hydraulic radius = - for circular pipes, d being the diameter
in feet;
hf
«= hydraulic slope =y, where A/ represents the loss in head
due to friction and I the length of pipe, both in feet;
c= friction coefficient.
In using the latter (Williams ond Hazen) formula, the folloT^ing
values of the friction coefficient are recommended:
For cast-iron pipe c = 120-110
For riveted steel pipe c = 105-100
For wood-stave pipe c = 130-120
To facilitate the calculations when using their formula,
Williflms and Hazen have published a book entitled " HydrauUc
Tables," which contains a series of tables giving the values of
friction losses for pipes of different materials and sizes, and also
different degrees of roughness and for various velocities. This
book is very useful, and may be obtained from John Wiley &
Sons, Inc.
Merriam in his " Treatise on HydrauUcs " states the following
in regard to the friction loss:
1. The loss of head in friction is directly proportional to the
length of the pipe.
2. It is inversely proportional to the diameter of the pipe.
3. It increases nearly as the square of the velocity.
4. It is independent of the pressure of the water.
5. It increases with the roughness of the interior surface.
Thus
The friction factor, /, depends upon the degree of roughness
of the surface, the values given in Table XXXI being apphcable
to clean cast-iron or wrought-iron pipes.
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118
WATER CONDUCTORS AND ACCESSORIES
TABLE XXXI
Fbiction Factors for Clean Iron Pipes
Diameter
V«LOCITT
m Fbbt p«b Second.
in
Feet.
1
2
3
4
6
10
15
0.05
0.047
0.041
0.037
0.034
0.031
0.029
0.028
0.1
0.038
0.032
0.030
0.028
0.026
0.024
0.023
0.25
0.032
0.028
0.026
0.025
0.024
0.022
0.021
0.5
0.028
0.026
0.025
0.023
0.022
0.020
0.019
0.75
0.026
0.025
0.024
0.022
0.021
0.019
0.018
1.
0.025
0.024
0.023
0.022
0.020
0.018
0.017
1.25
0.024
0.023
0.022
0.021
0.019
0.017
0.016
1.5
0.023
0.022
0.021
0.020
0.018
0.016
0.015
1.75
0.022
0.021
0.020
0.018
0.017
0.016
0.014
2.
0.021
0.020
0.019
0.017
0.016
0.014
0.013
2.5
0.020
0.019
0.018
0.016
0.015
0.013
0.012
3.
0.019
0.018
0.017
0.015
0.014
0.013
0.012
3.5
0.018
0.017
0.016
0.014
0.013
0.012
4.
0.017
0.016
0.015
0.013
0.012
0.011
5.
0.016
0.015
0.014
0.013
0.012
6.
0.015
0.014
0.013
0.012
0.011
Table XXXII * gives the loss in head in each 100 feet of
riveted steel pipe for diameters from 2 to 12 feet and for veloci-
ties up to 12 feet per second.
Loss of Head in Bends. This may be obtained from the
formula:
where /i is the curve factor. The values for the same, given in
the following, were determined by Williams, Hubbell and Fen-
kell by experiments made on a 30-inch cast-iron water main,
with 90 deg. bends.
Let R be the radius of the circle in which the center line of
the pipe is laid and d the diameter, then:
For 1= 24
16
10
6
4
2.4
/i= 0.036
0.037
0.047
0.060
0.062
0.072
^S. Morgan Smith Co.'s Bulletin No. 104.
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WATER CONDUCTORS
119
Hydraulic Gradient. The hydraulic gradient is, strictly
speaking, a line representing atmospheric pressure conditions,
although it may also conveniently be used as a graphical repre-
sentation of the internal pressures in a pipe line at any point.
It may also be defined as the line, the vertical distance between
which and the center of the pipe gives the pressure heads at
the respective points. For example, referring to Fig. 59A, the
hydraulic gradient or grade line is a line through the points to
Pig. 59a. — Hydraulic Gradient.
which the water levels would rise if piezometer tubes were inserted
along the pipe, as shown. The line will be approximately straight
when the head is lost uniformly along the pipe, that is, if the
size and surface of the entire length of pipe is the same.
The grade line should be drawn from a point A near the upper
water-level, the distance AB being equal to the velocity head
plus the entrance head, to a point at the end of the pipe. For
a pipe discharging freely in the air this would be the center of
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120 WATER CX)NDUCTORS AND A(XESSORIES
its outlet, but for a pipe with submerged discharge it would be
the lower water level instead of the point of discharge.
The slope or drop in elevation along the pipe corresponds
to the friction loss, so that, for example, the vertical distance
between D and E would be equal to the head lost on account of
friction between these two points.
If the pipe is laid so that it rises above the hydraulic gradi-
ent ACj as at F, the pr^ure in the pipe at this point will
be less than that of the atmosphere by a head corresponding to
FG; thus negative. If no air could enter the pipe it would act
as a siphon and the flow would continue as usual, provided the
distance FG- did not exceed about 25 feet, the theoretical limit
of vacuum being 34 feet.
Air is, however, always present in the water and will collect
at the smnmit near F and the pressure will approach atmospheric,
in which case the gradient would shift to AF and the discharge
would only be that due to the vertical head between B and F
instead of between B and C. The remainder of the pipe from F
to C would merely act as a channel to deliver the flow.
From the above it is evident that the pipe line should be laid
well below the hydraulic gradient, and much trouble may be
avoided, if from the outset a profile of the proposed route is
prepared and the hydraulic gradient carefully calculated and
drawn in.
Size of Pipe Line: In determining the size of a pipe line or
penstock the first thing to consider is the number of pipes and
necessarily also the amoimt of water which each must be able to
carry. As to the number, this should preferably be equal to the
turbine units, as this secures a greater flexibility in the operation
of the plant. It further does away with the large Y-distributing
joints at the bottom of the penstocks, as well as with large size
gate valves and heavy plate thicknesses.
In determining the most economical pip>e-line installation for a
hydro-electric plant, several factors in addition to the primary
consideration of the grade or route must be studied. In general,
these must have direct relation to the earning capacity with
resp)ect to the first cost. Usually the pip)e-line investment repre-
sents one of the principal items of the initial cost of the generating
station. Elspecially is this apparent in connection with those
installations where the pij^e line is long and subject to high pres-
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WATER CONDUCTORS 121
sure. Because of its initial high relative cost and consequent
interest charge, a careful consideration of the pipe line must be
made; otherwise, an injudicious monetary expenditure may result.
It is obvious that for a given water quantity, the size of the
pipe is determined by the velocity at which the water is allowed
to run. This is the difficult point to settle, and varies anywhere
from 6 to 12 feet per second, the average probably being around 9
feet. A high velocity entails a considerable friction loss, while a
low velocity necessitates a larger pipe and thus increases the cost
of construction. For a low-head development a rather low veloc-
ity should be used, because the loss of head will then form a much
larger percentage of the total head than where a high head is
available. In high-head pipe lines of some length it is, of course,
also more economical to use smaller diameter and larger velocity
at the bottom, where the pressure is higher and thicker pipe is
required. 1
Consideration must also be given to the load factor at which
the turbine is running, i.e., the average amount of water which the
pipe line is to carry. Some plants require that the turbines are
run continuously at full gate opening, while in other instances
they may operate normally at half gate, only opening up occa-
sionally to full gate to take care of momentary peak loads. In
such a case the friction loss should naturally be based on the water
conveyed when the wheels are operating at half gate op>ening.
Theoretically, therefore, the economical diameter of a pipe
line for a water-power development should be such that any
increase in the diameter of the pip)e would cost more than the
value of the power which could be obtained from the decrease in
loss of head due to friction from such increase in diameter. Or,
stated in other words; the size of pipe should be such that the
value of the power annually lost in friction plus the annual interest,
profit and depreciation charges on the pip)e line should be a min-
imum. For a steel pipe this leads to the following formula:^
^4
\S20XYXX^X(^Xe
Where ' if^XtXmXiXc^
d= economic diameter in feet for thickness t;
y= weight of water in poimds per cubic foot =62.4;
» By courtesy of J. G. White & Co.
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122 WATER (CONDUCTORS AND ACCESSORIES
«= thickness of pipe in feet;
m^: weight of material in pipe line in pounds per cubic foot
=490.
g= average flow of water through pipe during twenty-four
hours, expressed in cubic feet per second.
c=sale value of 1 foot-pound per second for one year, meas-
ured in water l^efore delivery to turbine.
t = annual interest, profit and depreciation charge on 1 pound
of material in pipe line in place, expressed as a ratio.
This value should be multiplied by whatever factor is
necessary to make allowance for excess of actual
weight of pip)e line over theoretical weight due to lap,
rivets, etc.
c= friction coefficient. (See page 106.)
The factor X for a 50 per cent load factor will generally vary
from 1.3 to 1.5. It may be figured from the formula:
Average of the cubes of load curve ordinates
Cube of the average of load curve ordinates '
This means that the load cwrve may be divided into as many
sections as desired for accuracy, and the mean ordinate of each
section used in the formula.
Having determined the economic diameter for a given thick-
ness, that for any other thickness, all other conditions remaining
the same, varies inversely as the sixth root of the thickness.^
Speed regulation must also be considered in determining the
size of a pipe line, and this point is probably of more importance
than the economical consideration. Load changes on the tur-
bine cause the governor to open or close the turbine gates rapidly,
thus causing pressure changes in the penstock. These pressure
changes are due to the acceleration or deceleration of the water
column in the pipe line, and the magnitude of the same depends
upon both the length of the penstock and the change of velocity
in same.
The pressure changes always act in opposition to the action
of the governor; thus, when a load suddenly goes oflF the gener-
»See also "Economical Penstock Size" by M. Warren A.S.C.E.,
Dec. 2, 1914.
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WATER CONDUCTORS
123
TABLE XXXII
Loss IN Head in Each 100 Feet Length op Pipe at Different Velocities
PaicTioM llEAti iitr Fekt fo« Prffjft 100 Frist Long rnoM
**
2 Toe
hKisv DiAMKT«n Inci.tj»ive with Ciimc FfcET
a
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A ROB ^K:B
MjVUTE I1hl*fc*l ViHiOClTJEfl FROM
5
1^
^i.
1
tu 12 Fekt Inclijhivi£ i*wu S
eCOKD,
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it
i-^%.
3S£
2' DIam.
3* Dlam.
r Dlarn.
5" Dlam,
6' Diam.
3
II
11
||
II
ii
1=:
1^
>
m
^
u^
u
El.
O
£
O
ki
o
ii.
U
1 Q
.015.^2
00776
.024
188
.015
424
754
IJ78
L696
1 2
02336
oniet
.033
226
022
509
016
905
013
K414
oil
2,036
1 4
1 fl'
03043
01521
043
264
.029
504
.021
10. "iO
017
1,649
Ot4
2.375
.03975
.01087
055
303
036
670
.027
1206
022
1,885
018
2,714
1 S
06031
02515
068
330
045
703
.034
1357
027
2,120
022
3,054
2 0
06211
03105
.082
377
054
848
.041
1508
032
2,356
027
3,393
2 2
,07515
03 787
097
415
064
033
048
16.^*9
039
2,. 592
032
3,732
2 4
.O»044
04473
lU
453
075
1018
057
t8lO
045
2,H27
037
4,071
2 6
104M
05248
131
400
.087
1 1 03
065
1960
(t52
3,063
043
4.411
2 n
.12173
0608fi
150
528
.09'.J
1 18K
075
2111
. 060
3,299
049
4.750
3.0
13075
0^087
.169
565
112
1272
.084
2262
067
3,534
056
5,080
3 2
,15»
0795
190
603
I2ri
13.'->7
O05
2413
076
3.770
063
5,420
3 4
I7i>5
8975
.212
641
.141
1442
106
2563
085
4,006
070
5,768
a e
20124
.ICM>62
,235
679
.i.^>e
1 r.27
117
2714
094' 4.241
078
6,107
as
22422
lun
.260
716
173
1612
.130
2H65
104: 4.477
OH 6
0.446
4 0
24^44
.12422
,285
754
IKO
1607
T42
3016
114
4.712
004
6,78©
4 2
.27^91
.13695
.311
791
207
17X1
155
3167
124
4MAH
103
7J2S
4 4
30062
.15031
339
829
226
1B66
169
3317
t:^.'
5, 1 84
112
7.464
4 6
328SB
16444
368
867
245
1051
184
3468
147
5.410
122
7 804
4 B
35770
I7fi88
307
0O5
264
2036
198
3619
159
5.655
132
N.I 43
5 0
38«19
19400
.428
042
285
2121
214
3770
171
5.801
142
8,482
S Z
4I9&7
20993
46
080
.300
2205
230
3921
1H4
6 J 26
1 53
8.821
5 4
.45270
22630
403
1018
328
2290
246
4071
107
6,362
164
0.1 6t
5 «
.411605
24347
,527
1050
351
2375
263
4222
210
6.507
^fi
O.-^iOO
S R
..V2235
26117
654
1003
.374
2460
2S1
4373
224
0.833
187
9.830
B 0
.559
279
59ft
1131
308
2545
209
4524
239
7.060
101»
19,179
6 2
,50SS9
20844
.035
nfio
423
2630
317
4675
254
7.304
211
i(r.5tft
6 4
63602
.31801
,673
1206
448
2714
336
4P25
269
7.540
224
10,8,57
e 6
67639
.33819
.712
1244
474
^70^(
356
4076
285
7.775
237
1L107
fl 8
7I80I
.35000
753
1282
.501
21^84
376
5127
301
8,0 n
250
( 1 .536
7 0
760B6
38043
794
1319
529
2960
.397
5278
317
8,247
264
n.N7S
7 2
S04ti6
.40248
836
1357
h557
3054
.418
5420
334
8.482
278
J 2.2 14
7 4
.85031
.42515
. mt)
1395
586
3138
440
5570
352
8,7 IH
293
rj,5,'i4
7 0
.89689
44844
024
U33
616
3223
462
5830
:^60
8,954
307
Ili.MJS
7 ft
94472
.47236
070
1470
646
3.H08
,485
5881
38J^
0,1 SO
32;i
13,232
& 0
09378
.49380
1.01
1 508
67"
3393
.'iOrt
6032
406
9.425
33 h
l;i,572
S 2
1 G44DO
62204
i.oe
1546
709
3478
532
6182
425
9.660
3^4
13.011
» 4
1 mm^
54782
1. 11
1583
741
3563
556
6333
445' 0.fi96:
370
14.2.-10
R a
1 14S44
57422
1 16
1621
774
>647
58 J
6484 ,
465 10.132
387
14.580
IB
1 2024«
60124
1 2]
1650
808
3732
606
6635
485
10,367
404
1 i ,929
ft 0
1 25776
62888
1 26
1606
843
3817
632
6786
506
10.603
421
1 5.268
t a
J 31428
65714
1.31
1734
,878
3002
65 K
6036
527
10,830
439
1 5,607
9 4
1 372,^
68602
1.37
1772
.013
3087
685
7087
548
11.0741
456 15.947
& fl
I 43lO/i
71552
1.42
1809
050
4072
713
7238
570
11,310
475 I6.2H6
« S
149190
74565
t 48
1847
om:
4156
741
7389
502
11.545
493| Hi025
10 0
1 55279
77630
1 53
1885
I 02
424 J
76n
7540
615
11,7S1
512 16,964
10 2
I 61552
. 80776
1 59
1923
I 06
4326
798
7600
638
12,017
532 17.304
10 4
1 6795
S3975
1 65
1060
I 10
4411
.827
7841
662
12.252
551
17.043
10 6
1 74472
.87236
1,71
1008
1 14
4496
.857
7002
686
12,488
571
17,082
m 8
1 8U18
90559
1.77
2036
1 18
4580
8143
710
12,733
592
JH.322
11 0
1 87Sft8
,93044
1 83
2073
1 22
4R65
919
fii2a4
735
12,959
612
18,661
H 2
1 947R2
073fll
1.90
2111
I 26
4750
950
H444
760
13.195
633
1 9,000
n 4
2 OlMOl
I 009
1 06
2149
1 31
483.=^'
082
8505
786
13,430
655 («t,:^J9
iL e
2 08944
1.04473
2 02
2187
1 35
4920
1 01
h746
811 13,6661
67r (1L*;79
u &
2 I62n
I 08105.
2,09
2224
1 30
5005
1 04
88r^7 1
838 13.9021 HUK 2il,018
ta Q
2 23602
IIKOI-
2 16
2262
1 44
5089
1 ow
0048 1
Kr;5
I4,3:i7'
72<s.
^o,;ri7
Digitized by
Google
124
WATER (CONDUCTORS AND ACCESSORIES
TABLE XXXIL— Con^inueei
FmcTirm Head in J-'kkt won Pipe« 100 Fbet Lotto rmov
**
7 TO 12 Feet Diauktkr Incluhivb with Cubic Fk«t
m
D[0CK\HI1E PRtt MiMtTTK UfWl»E» VKLOClTlEfl rHOM
s
B&
1 TO 12 Feet Imclubivic peh Beconp.
Pi
3|£
|4S
7' DIara,
8' Diftiii.
0' Diam.
10' Dlftm.
12' Dt»ni.
1^
it
II
-1
H
|l
II
II
11
1^
|l
>
X
m
bk
u
u*
0
U4
U
Urn
0
ta
U
1.0
.01553
00776
2,309
3,016
3.817
4.712
6,786
1.2
.03236
oni8
2.771
3,619
4.580
6.655
S.I 43
1.4
.03043
01521
.012
3.233
4,222
5,344
6,. 597
9.500
16
.0397.^
oiasr
015
3,695
013
4,825
012
6,107
oii
7.540
10,858
1.8
.05031
02515
019
4,156
017
5.429
015
6.871
013
8,482
.011
12.215
2 0
.062U
03105
023
4,618
020
6,032
018
T,634
016
9,425
013
13.572
2 2
.07-51.5
,03757
027
5,080
024
6.635
021
8.397
019
10.367
.016
14.929
2 4
.08944
.04472
032
5.542
028
7.238
025
&,161
022
11,310
018
16.2S6
2ft
. 10496
05248
037
6,004
032
7,841
029
9.924
026
1 2.252
.021
17,644
2 8
12173
.06086
042
ft. 465
039
8,445
033
10.688
,030
13.195
034
19.001
3 0
13975
06987
04 H
6.927
042
9.048
.037
11,451
033
14.137
.028
20.358
3 2
159
J>7H"i ■ O.M
7,389
047
9,651
043
12.214
038
15,080
031
21,715
3 4
t79->
O.H'.i7.-.
4HpO
7,851
053
10,254
047
12,978
043
16.022
035
23,072
3ft
20124
, HHH]2
007
8,313
0.58
10.857
052
13,741
047
16.965
039
24,430
3 8
22423
112M
074
8.775
065
11.460
057
14„5fl5
053
17.907
.043
25.787
4 0
,24ft44
12423
081
9p236
071
1 2,064
063
15.368
057
18.850
.047
27,144
4.2
27391
.13605
088
9.698
077
12,667
069
16.031
062
19.793
051
28,501
4 4
.30062
L^31
097
ID, 160
OM
13,370
075
16.795
067
20,735
056
29*S5S
4 d
32S»S
.16444
,105
10,622
092
1 3,873
081
17,558
073
21.677
061
21.216
4.g
.35776
178SS
113
11.084
099,
14,476
088
18.323
079
22.620
066
32.573
5 0
3smu
. 11*409
133
11,54ft
197
1 5.080
095
19.08,^1
085
23.502
071
33.930
5 2
.41987
,30nP3
131
1 2.007
115
15.683
.102
19,^49
092
24„^4
076
35.287
5.4
. 45279,
2263i)|
140
12,4fl9
.123
1 6,286
,109
20,612
098
25,447
032
36.664
5 6
.48095
.24347
.150
12.931
131
1 6,889
117
21,375
.105
26.389
.087
38,003
6 8
. 52235
.26117
160
13,393
140
17.492
.124
22,139
112
27,332
.093
39,^59
6 0
559
.2795
170
13,855
149
I8,6t»5
.132
22.902
.119
28,274
.099
40.716
d.2
. Bumv
2W844
181
14,316
. 158
18,699
.141
23,666
127
29.317
.105
42.073
6.4
636*12
.31801
192
14,778
168
19,302
.149
24,439
.134
30,1,'>&
U2
43.430
6 e
. 6763W
.33810
203
15.340
178
19.905
.158
25,192
142
31.102
AIS
44.788
6.8,
.71«01
3590
215
15,702
188
20,.50S
.167
25 .9 ,"16
ITjO
32.044
.125
46.145
7.0
.7608ft
3843
226
16.164
198
21.111
.175
26,719
158
32,987
.132
47,502
7.2
.804Ua
40248
238
16,626
209
21,714
\S:t
i;7.483
,167
33.929
139
48.859
7.4
.85031
42515
251
17.087
220
22.318
1 '15
2N,246
176
34.872
.146
50«3I6
7.6
.8§6S©
44844
264
17„^49
231
22.921
. 2U.-»
29,009
.184
3.5,814
154
51.fi74
7,8
.94472
47236
277
18.011
242
23,524
2 I 5
29,773
194
36.757
lil
53,931
8 0
.99.178
49689
290
18.473
254
24.137
, 235
30,536
203
37,699
169
54,288
8.2
1 04100
.52204
303
18,U35
266
24,730
.2.36
31,300
.212
38.642
.177
55,645
8.4
1.09561
547h;j
317
19,396
278
35,334
.247
:i2.nfi3
222
39.584
ISfi
57.002
8 6
1 14844
. 57422
332
19,858
290
25JI37
•jr.^
Hl!,H2fi
2,33
40.527
,193
58,300
g.o
1 20248
1 2577H
60 11^4
.62HH8
34 rt
361
20.320
20,782
303
310
36.540
27,143
:{H..-,90
:i-l,353
.242
253
41.469
43.412
.202
.210
&9,717
61,074
a 2
1,31428
65714
376
21,2^4
.329
27,74fi
2*J2
35,117
263
43.354
.319
62,431
9 4
1 37204
.68002
.391
2K7tl6
342
2^,349
AiU
35.880
274
44.207
.22fi
.237
163.788
9 6
1 43105
. 7 1 552
407
22,167
'A 5fl
2s,9,'i'i
3 1 ()
36,643
2S5
45.230
65,146
© 8
I 4B130
745f>5
423
22,62a
370
2il,556
339
37.407
296
4ft. 182
.247
66,. 503
10 0
1 . 5527il
77tt39
4^19
23,091
384
30,159
341
38,170
307
47,124
.3.56
67.860
10 2
1 61552
807 7 1>
455
23.,553
399
30,762
354
38.943
319
48,066
.266
69.217
10,4
1 67115
S3 97 5
472
24.015
413
31.365
307
39.697
331
49.009
.275
70.574
10.6
1.74172
S7336
490 24.4 7ft
428
31,9H9
381 4O.-lfi0
343
49,951
285
71.932
10 8
1 81118
905511
507 24, 93s
444
32,575
394
41.224
355
50,894
.296
73,289
11.0
1.87888
l^mAi
525 25.400
459
33,175
4 OK
4 1 .987
387
51.836
306
74.646
11 2
J 94782
517391
543 2.5,862
475
33.778
43^:
42,751
,380
52,779
316
76,003
11 4
2 0I8U1
1 000
561 26,324
491
34,381
4M\
43,514
393
53,721
327
77,360
lie
2,08944
1 01472
r,7\t ztii^n
507
34.9S1
\r,ii
44,277
.406
54,ft64
33a
78,718
11. s
2 16211
1 OKI 05 ftiP^' 27 247'
5:>4
:{.^^,^h.^
hfiFi
45.04 1
419
5£i<IOft
,349
§0.075
12.0
2 33602
I MMDI tAl 27. 7139 j
540
3rtj-ji
4. SO
I
15,804
432
5&,4S9
.300
§1,432
Digitized by CjOOQ IC
WATER CONDUCTORS 125
ator and the turbine gates close, there is an increase in pressure
in the penstock which tends to develop more horse-power, and
vice versa, when a load comes on the generator and the turbine
gates op)en, there is a drop in pressure in the penstock, tending
to decrease the output of the turbine. As the length of the p)en-
stock for any particular installation is fixed, it is necessary to Umit
the changes in velocity in the penstock, in order to give reasonably
good speed regulations.
Excessive rises in pressure may be eliminated by the use of
pressure regulators, by-pass relief valves or surge tanks. After
the size of the penstock has been tentatively settled as most suit-
able for economical considerations, it must then be investigated
for speed regulation, and this may indicate that a larger pipe may
have to be used than consistent with the highest economy. (See
also Surge Tanks and Pressure Regulators.)
Steel Pipe. These may be made of rolled steel plates, riveted
together. Fig. 60, or lap-welded, the latter only being used for
very high heads where the pressure is excessive and where the use
of the riveted construction would greatly increase the thickness of
the plate. In figuring the thickness of the plate, this should be
based not only on the pressure due to the net head but also on
the additional pressure caused by the water hanmier.
The formula for the strength of riveted steel pipe is
Pdf
2Te'
where
^ = thickness of plate in inches;
P= pressure in pounds p)er square inch;
d= diameter of pipe in inches;
/= factor of safety, based on the ultimate tensile strength. 4
is a factor generally used in this country.
T=tensUe strength = 50,000 for mild steel;
=60,000 for wrought iron;
e=efl5ciency of riveted joint = approximately 0.60 for single
rivets and 0.70 for double rivets.
Table XXXIII ^ gives the safe working heads and weights of
riveted steel pipes.
» Pelton Water Wheel Company.
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126
WATER CONDUCTORS AND ACCESSORIES
It would seem advisable in proportioning the thickness of
penstocks to provide in addition to the thickness computed by the
above formula, an allowance for corrosion, that is, the addition
Fig. 60.— Ten Five-foot Riveted Steel Penstocks.
of a constant term to the thickness, say | inch or whatever is con-
sidered advisable under the conditions of installation.
Another point which must be given very careful consideration
in connection with the calculation of pipe-line sizes and thicknesses
is their safety from collapsing, due to sudden drop in pressure.
The following formula gives the maximum difference between
the external and the internal pressures which a circular steel pipe
can withstand:
p = 50,200,000Hy.
Where
p = pressure difference in pounds per square inch;
i = thickness of plate in inches;
d= diameter of pipe in inches.
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WATER CONDUCTORS
127
TABLE XXXIII
Safb Wobkinq Heads and Weights of Riveted Steel Pipes
Heavy-face figures -weight per foot.
Light-lace figures -safe head in feet.
Safety factor -4.
Tensile strength -55,000 pounds i>er square inch.
EfBciency of riveted joint -70 per cent.
Platb Thickness
Diam-
Diam-
eter.
In.
No.
18
No.
10
No.
8
A"
i"
A"
1"
A"
*"
A"
1"
eter.
In.
10
15.8
483
18.8
592
88.3
730
10
IS
17.9
401
11.1
493
16.5
607
31.0
600
44.6
921
U
14
10.6
343
15.8
423
81.6
511
86.7
592
49.4
790
14
16
83.8
300
18.9
368
85.8
456
41.4
518
66.0
692
16
18
16.0
268
31.1
320
40.0
405
46.1
460
68.1
615
78.3
768
18
10
18.6
85.3
44.0
50.6
68.5
86.4
104.3
10
240
206
365
414
553
691
830
tt
81.4
88.9
48.1
65.6
74.9
94.9
114.9
135.8
154.9
11
218
269
331
377
503
630
755
880
1006
M
84.1
41.1
58.3
60.8
81.1
101.9
114.3
146.4
168.6
14
201
247
303
346
461
576
602
807
922
S6
86.8
45.3
56.4
64.9
87.5
110.7
184.0
160.0
185.9
M
184
228
280
320
426
534
640
748
856
»
89.6
48.7
60.4
69.8
93.9
119.0
143.7
170.8
197.8
114.0
150.0
18
172
211
260
296
395
494
593
692
790
873
988
ao
41.8
58.1
64.6
74.6
99.1
116.8
153.4
181.4
111.3
839.4
166.8
30
161
197
243
276
368
461
553
645
738
830
922
n
45.0
55.5
68.7
79.1
106.4
134.7
168.9
191.1
119.7
851.3
183.0
31
150
184
228
250
346
432
519
605
692
777
865
34
47.8
58.8
71.9
83.9
111.9
141.7
171.5
104.1
186.0
167.8
199.1
84
141
173
214
243
325
406
488
569
651
731
813
86
50.6
68.0
76.9
88.8
U8.1
149.6
181.0
813.0
147.1
181.0
314.8
86
133
164
202
230
307
384
461
538
615
692
768
88
66.8
81.0
91.3
115.1
167.0
189.0
114.0
159.0
193.8
818 6
88
155
191
217
289
362
435
507
578
652
725
10
68.7
86.1
98.1
131.8
167.0
199.1
135.9
171.9
310.1
347.9
40
148
182
206
276
346
414
484
553
622
691
48
71.0
89.3
101.8
138.0
173.1
108.1
146.0
183.7
384.0
364.1
41
140
173
197
263
329
396
461
517
593
658
44
98.4
107.4
144.1
180.9
117.3
157.8
197.8
339.1
880.0
44
164
188
250
314
377
439
502
565
628
46
97.6
111.0
150.8
188.3
816.5
168.8
810.8
353.6
896.4
48
158
181
239
300
360
420
480
541
601
48
101.6
117.1
158.1
196.4
135.1
179.1
813.5
366.5
410.0
49
151
173
230
288
346
403
461
519
576
60
111.7
168.6
104.1
146.1
190.1
334.5
881.6
418.5
50
165
220
276
331
386
442
497
552
88
116.6
169.7
111.6
155.6
308.8
350.8
398.1
445.1
51
159
212
265
318
371
424
477
531
64
131.8
176.1
110.8
166.1
313.5
361.0
411.1
468.0
54
153
205
256
307
358
410
461
512
66
136.1
188.4
816 6
176 0
316.1
377.8
416.1
477.6
56
149
198
249
298
348
398
447
498
No.
11
No.
10
No.
8
A"
i"
A"
r
A"
i"
A"
1'
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128 WATER CONDUCTORS AND ACCESSORIES
A study must be made of the entire penstock from the head-
gates to the turbine casing, and the exact drop in pressure cal-
culated at each section imder the most severe conditions, which
possibly would occur when a turbine unit is running light, and a
short circuit occurs on the generator, in which case the turbine
gates open wide very quickly, and there is a tendency to accelerate
the water in the various sections of the pipe line.
There may be some section in a long penstock where the
water colmnn below this section has sufficient head to accelerate
the lower column quicker than the water colunm above may be
accelerated. This may cause a break in the water coltmin at the
section in question, and a considerable vacuum, which is very
likely to collapse the penstock. To prevent this air vents (see
page 157) may be provided at the points along the pipe line where
dangers are expected, as whenever the pipe greatly increases its
slope or rate of fall. The amoimt of air which must be admitted
to keep the pressure from going below a certain given value must
be such as will, at the given pressure, replace the water which
has run away from the section.
On account of the imcertainty of the calculation of the col-
lapsing strength of a riveted steel pipe, and in order to provide a
margin of safety, it would seem to be the best practice to pro-
vide against any excess of external over the internal pressure
at any point in the pipe line, rather than attempt to compute
the collapsing pressure. . The critical points subject to a deficient
internal pressure can best be located by drawing a hydraulic
gradient under conditions of accelerated or retarded flow in the
pipe line. ,
For a more complete treatise on this important subject, the
reader is referred to an article by Enger and Seely, in "Engineering
Record^' for May 23, 1914.
Expansion joints are not usually employed in this country, and
if the pipe is carefully laid and buried or kept with water flowing
at all times, are not required except in special cases. Whether
the pipes are buried or not, they should be carried on concrete
piers. Heavy anchorage blocks should be inserted at all vertical
and horizontal bends, and with considerable temperature varia-
tions, expansion joints should in such instances be provided to
take care of the expansion and contraction of the pipe. While the
stress may be well within the elastic limit of the pipe material.
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WATER CONDUCTORS
129
and would have little influence on the pipe itself, the thrust
caused by the expansion may throw a very high stress on the
anchorage blocks. By pro-
viding expansion joints a
material saving can often
be effected in the cost of
anchorage blocks and piers,
esp)ecially where their con-
struction involves difiicul-
ties owing to the steepness
of the grade and lack of
handling faciUties. A de- Fig. 61. — Pipe Line Expansion Joint,
tail design of an expansion
joint is shown in Fig. 61 and in Figs. 62 and 63 are shown a typical
penstock installation and details of supporting and anchoring pier&
Fio. 62. — Large Hydro-Electric Power Station at Rjukan, Norway, Showing
Ten Five-foot Penstocks and Method of Anchoring Same.
In order to prevent freezing it is often essential to know the
amount of water necessary to pass through the penstock, as for
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130
WATER CONDUCTORS AND ACX!ESSORIES
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WATER CONDUCTORS 131
example during the shut-down of a unit. This may be obtained
from the following formula by Boucher: .
T
rp -^ to
Where
Q= Water discharge in cubic meters p)er hour;
Ta = Lowest air temperature in degrees Centigrade; without
negative sign;
T«,= Water temperature in degrees Centigrade* (may be taken
as rC);
S= Exposed surface of penstock in square meters.
Wooden-stave Pipe} This kind of pipe is extensively used
in the West where redwood or fir is cheap and plentiful. It is
admirably adapted for heads up to about 200 feet, and for high-
head developments it is often used for the upper sections. For
heads above 200 feet, steel pipe is preferable, as the spacing of
the bands for wooden-fitave pip)e becomes so close that the cost
of the pip)e may equal or exceed that of steel.
Woodennstave pipe. has a greater carrying capacity than steel
pipe on account of the smooth surface of the planed wood, and its
carrying capacity will not decrease with age, as deposits will not
adhere to the inside of the pipe.
A woodennstave pipe should always be in use so that the staves
are thoroughly saturated. Under these conditions they will not
decay and leakages are prevented. Provisions are, however,
made so that the staves may readily be drawn firmly together by
tightening the bands.
Continuous woodnstave pipe is constructed in place and
should preferably be located above ground and free from all
contact with it, cracHes being provided at certain intervals for
the support (Figs. ^ and 65).
In erecting the pipe the staves are assembled and put together
to form a circle of the diameter of the pipe and the bands put
around the outside and tightened to hold the staves together.
The end joints in the staves should be broken by a lap of not less
1 An excellent treatise on wood-stave pipe is found in Bulletins Nos. 155
and 376 U. S. Dept. of Agriculture.
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132
WATER (CONDUCTORS AND ACCESSORIES
than 1 foot, and they can be made tight by inserting a metal
tongue or plate in the saw kerf cut in the ends of the staves.
Fig. 64. — Wooden-Stave Pipe Showing Method of Installation in Difficult
Territory.
Fig. 65. — Montana Power Company. Dam and Wooden Penstocks for
Madison No. 2 Plant.
After the pipe is completed and before the water is turned on, the
bands should be tightened imiformly so as to give tension on all
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WATER CONDUCTORS 133
the bands. When the pipe is filled with water the staves swell
sufficiently to bed the bands slightly into the wood and make
the longitudinal joints water-tight.
The size of the bands and the spacing are naturally related,
and when properly designed they should be strained to their safe
resisting value, and the bearing pressure on the stave must not be
greater than the safe bearing value of the wood. It has been
found from actual experience that the width of contact between
the band and pipe is equal to about the radius of the band before
the fibers of the wood are crushed beyond safety. The safe
crushing stress for wood is generally taken as 650 pounds per square
inch, and putting the safe stress in the band equal to the safe-
bearing pressure, we get
irr^« = (/J+0650r,
or
^(fl+0650
Where
r= radius of band in inches;
£== internal radius of pipe in inches;
(= thickness of stave in inches;
8 = safe tensile strength of band. Taking the ultimate strength
of steel as 60,000 poimds, and assuming a factor of
safety of 4, the safe strength is 15,000 pounds per
square inch.
The number and thus the spacing of the bands depends on the
stresses due to the water pressiure and to the swelling of the wood.
The sum of these two stresses should be equal to the safe strength
of the band, as determined by the previous formula.
Thus
7n^8==j)dR+tdE,
suid
"pR+tE'
where
d== spacing of bands in inches;
p= water pressure in pounds per square inch;
£= swelling force of wood per square inch. This is usually
assumed to be approximately equal to 100.
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134
WATER CONDUCTORS AND ACCESSORIES
TABLE XXXIV
Flow of Water through Wooden-stavb Pipe
2 Feet Diameter.
3 Feet Diameter.
4 Feet Diametes.
Dis-
charsre,
Cu.ft.
per
Sec.
Veloc-
ity.
Feet
per
Sec.
Loss of
Head in
Feet per
100 Feet
of Pipe.
Dis-
charge,
Cu.ft.
per
Sec.
Veloc-
ity.
Feet
per
Sec.
Loss of
Head in
Feet per
100 Feet
of Pipe.
Dis-
charge,
Cu.ft.
per
Sec.
Veloc-
ity.
Feet
per
Sec.
Loss of
Head in
Feet per
100 Feet
of Pipe.
1.6
0.48
0.003
4
0.57
0.003
6
0.48
0.002
3.0
0.95
0.012
8
1.13
0.010
12
0.95
0.006
4.5
1.43
0.025
12
1.70
0.021
18
1.43
0.011
6.0
1.91
0.042
16
2.26
0.035
24
1.91
0.018
7.5
2.39
0.064
20
2.83
0.054
30
2.39
0.028
9.0
2.86
0.090
24
3.40
0.077
36
2.86
0.040
10.5
3.34
0.122
28
3.96
0.105
42
3.34
0.054
12.0
3.82
0.159
32
4.53
0.137
48
3.82
0.070
13.5
4.30
0.201
36
5.09
0.173
54
4.30
0.088
15.0
4.77
0.248
40
5.66
0.213
60
4.77
0.108
16.6
5.25
0.300
44
6.22
0.258
66
5.25
0.131
18.0
5.73
0.356
48
6.79
0.306
72
5.73
0.156
19.6
6.21
0.416
52
7.36
0.358
78"
6.21
0.183
21.0
6.68
0.482
56
7.92
0.415
84
6.68
0.212
22.6
7.16
0.553
60
8.49
0.476
90
7.16
0.243
24.0
7.64
0.629
64
9.05
0.542
96
7.64
0.276
26.5
8.12
0.709
68
9.62
0.613
102
8.12
0.311
27.0
8.59
0.793
72
10; 19
0.687
108
8.59
0.349
28.5
9.07
0.881
76
10.75
0.764
114
9.07
0.389
30.0
9.55
0.974
80
11.32
0.846
120
9.55
0.431
31.5
10.03
1.073
84
11.88
0.933
126
10.03
0.475
33.0
10.50
1.178
88
12.45
1.024
132
10.50
0.521
34.5
10.98
1.287
92
13.02
1.118
138
10.98
0.569
36.0
11.46
1.400
96
13.58
1.216
144
11.46
0.619
37.5
11.94
1.519
100
14.15
1.319
150
11.94
0.671
39.0.
12.41
1.643
104
14.71
1.427
156
12.41
0.725
40.5
12.89
1.772
108
15.28
1.539
162
12.89
0.781
42.0
13.37
1.907
112
15.85
1.655
168
13.37
0.840
43.5
13.85
2.046
116
16.41
1.775
174
13.85
0.901
45.0
14.32
2.189
1
120
16.98
1.900
180
14.32
0.965
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WATER CONDUCTORS
TABLE XXXIW— Continued
135
5 Fbkt Diamxtbb.
6 Fbbt Diambtbb.
7 Fbbt Diambtbb.
Dis-
charge.
Cu.ft.
per
Sec.
Veloc-
ity.
Feet
per
Sec.
Loss of
Head in
Feet per
100 Feet
of Pipe.
Dis-
charge,
Cu.ft.
per
Sec.
Veloc-
ity.
Feet
Loss of
Head in
Feet per
100 Feet
of Pipe.
Dis-
charge,
Cu.ft.
per
Sec.
Veloc-
ity.
Feet
per
Sec.
Loss of
Head in
Feet per
100 Feet
of Pipe.
10
0.51
0.001
15
0.63
0.001
20
0.52
0.002
20
1.02
0.004
30
1.06
0.004
40
1.04
0.004
30
1.53
0.009
45
1.59
0.008
60
1.56
0.007
40
2.04
0.016
60
2.12
0.014
80
2.08
0.012
50
2.55
0.025
75
2.65
0.022
100
2.60
0.018
60
3.06
0.036
90
3.18
0.032
120
3.12
0.026
70
3.57
0.048
105
3.71
0.043
140
3.64
0.035
80
4.07
0.062
120
4.24
0.056
160
4.16
0.045
90
4.58
0.078
135
4.77
0.070
iro
4.68
0.057
100
5.09
0.096
150
5.31
0.086
200
5.20
.0.070
110
5.60
0.116
165
5.84
0.104
220
5.72
0.085
120
6.11
0.138
170
6.37
0.124
240
6.24
0.102
130
6.62
0.162
195
6.90
0.145
260
6.76
0.120
140
7.13
0.188
210
7.43
0.168
280
7.28
0.139
150
7.64
0.216
225
7.96
0.193
300
7.80
0.169
160
8.15
0.246
240
8.49
0.219
320
8.32
0.180
170
8.66
0.277
255
9.02
0.247
340
8.83
0.203
180
9.17
0.310
270
9.55
0.276
360
9.35
0.227
190
9.68
0.345
285
10.08
0.307
380
9.87
0.263
200
10.19
0.882
300
10.61
0.340
400
10.39
0.280
210
10.70
0.421
315
11.14
0.375
420
10.91
0.308
220
11.20
0.462
330
11.67
0.412
440
11.43
0.337
230
11.71
0.505
345
12.20
0.451
460
11.96
0.368
240
12.22
0.550
360
12.73
0.491
480
12.47
0.401
250
12.73
0.597
375
13.26
0.532
600
12.99
0.436
260
13.24
0.646
390
13.79
0.575
520
13.51
0.472
270
13.75
0.696
405
14.32
0.620
540
14.03
0.509
280
14.26
0.748
420
14.85
0.666
560
14.55
0.548
290
14.77
0.802
435
15.38
0.714
580
15.07
0.588
300
15.28
0.858
450
15.92
0.7C4
600
15.59
0.629
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136 WATER CONDUCTORS AND ACCESSORIES
TABLE XXXIV— Ccm/iniied
8 FbbT DiAlCSTBB.
10 Fbbt Diambteb.
Dis-
charge.
Cu.ft.
per
Sec.
Veloc-
ity.
Feet
per
Sec.
Loss of
Head in
Feet per
100 Feet
of Pipe.
Dis-
charge,
Cu.ft.
per
Sec.
Veloc-
ity.
Feet
per
Sec.
Loss of
Head in
Feet per
100 Feet
of Pipe.
Dis-
charge,
Cu.ft.
per
Sec.
Veloc-
ity.
Feet
per
Sec.
Lose of
Head in
Feet per
100 Feet
of Pipe.
30
0.60
0.001
30
0.47
0.001
40
0.51
0.001
60
1.19
0.004
60
0.94
0.002
80
1.02
0.002
90
1.79
0.008
90
1.41
0.004
120
1.63
0.004
120
2.39
0.014
120
1.89
0.008
160
2.04
0.008
150
2.98
0.021
150
2.36
0.012
200
2.55
0.013
180
3.58
0.030
180
2.83
0.017
240
3.06
0.018
210
4.18
0.041
210
3.30
0.023
280
3.57
0.024
240
4.77
0.053
240
3.77
0.030
320
4.07
0.032
270
5.37
0.067
270
4.24
0.038
360
4.58
0.040
306
5.97
0.083
300
4.72
0.046
400
5.09
0.049
330
6.56
0.100
330
5.19
0.056
440
5.60
0.059
360
7.16
0.119
360
5.66
0.067
480
6.11
0.070
390
7.76
0.139
390
6.13
0.078
520
6.62
0.082
420
8.36
0.161
420
6.90
0.090
560
7.13
0.095
450
8.95
0.185
450
7.07
0.104
600
7.64
0.109
480
9.55
0.211
480
7.55
0.118
640
8.15
0.124
510
10.15
0.238
510
8.02
0.133
680
8.66
0.140
540
10.74
0.267
540
8.49
0.149
720
9.17
0.157
570
11.34
0.297
570
8.96
0.165
760
9.68
0.175
600
11.94
0.329
600
9.43
0.183
800
10.19
0.194
630
12.53
0.362
630
9.90
0.202
840
10.70.
0.214
660
13.13
0.397
660
10.38
0.222
880
11.20
0.235
690
13.73
0.434
690
10.85
0.243
920
11.71
0.257
720
14.32
0.437
726
11.32
0.264
960
12.22
0.280
750
14.92
0.514
750
11.79
0.286
1000
12.73
0.303
780
15.52
0.556
780
12.26
0.309
1040
13.24
0.328
810
16.11
0.599
810
12.73
0.333
1080
13.75
0.364
840
16.71
0.644
840
13.20
0.358
1120
14.20
0.381
870
17.31
0.690
870
13.68
0.385
1160
14.77
0.408
900
17.90
0.738
900
14.15
0.413
1200
15.28
0.437
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WATER CONDUCTORS
137
For large size pipes and high pressures the stress due to the
swelling action is relatively small and may be neglected, in which
case the equation can be written,
d=
The friction losses may be obtained from Hazen and Williams'
formula on page 116, and the Table XXXIV ^ gives the discharge,
velocity and loss of head per 100 feet for pipes of different di-
ameters.
Concrete Pipe. Reinforced concrete pipes (Figs. 66 and 67)
for power work are used to a limited extent for low-pressure con-
PiG. 66.— Concrete Pipe, Showing Steel Forms for Pouring.
duits, but there is every indication that they may in the future
be extensively used in place of open flumes and canals. This will
not only tend to increase the total head of the plant, but it will
prevent leaves, branches, etc., from falling into the conduit, which
is often the case when they are of the open type.
* As given by Washington Pipe and Foundry Company.
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138
WATER CONDUCTORS AND ACCESSORIES
Concrete pipes are in use for heads up to 150 feet. They are
very smooth, being in this respect nearly on a par with wooden-
stave pipe, and thus offer Httle resistance to the flow of water.
Fig. 67. — Cross-section of Concrete Pipe.
They are especially adapted for use where raw material such as
sand, stone or gravel and cement are available locally, in which
case the pipes are generally manufactured on the job where they
are used.
2. WATERHAMMER AND SURGE TANKS ^
Waterhammer. When the gates at the lower end of a pen-
stock are closed and the water column suddenly checked, the
pressure immediately rises and may reach very high and destruc-*
tive values if not provided for or prevented. This rise of pressure
is known imder the name of " waterhammer."
When the gate begins to close the pressure rises first at this
point, and a pressure wave or vibriEttion begins to travel towards
the upper end of the pipe. If the pipe is absolutely rigid, the
velocity at which it would travel would have been about 4650 feet
per second, or the same as that of sound. On account of the
* See also sections on " Water Conductors " and ** Governors."
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WATERHAMMER AND SURGE TANKS 139
flexibility of the penstock walls, however, the velocity is reduced
and may be computed from the following formula:
'idk
Where
a = velocity of pressure wave or vibration in feet per second;
g= acceleration of gravity =32.16;
l/= specific weight of water = 62.4 pounds per cu. ft.;
A: = elasticity of water in compression =42,000,000 poxmds per
sq. ft.
d= inside diameter of penstock in inches;
<= thickness of plate in inches;
J? = elasticity of penstock material in tension:
For steel plate =4,032,000,000 lbs. per sq. ft.=
(28,000,000 lbs. per sq. in.);
For cast iron =2,160,000,000 lbs. per sq. ft.=
(15,000,000 lbs. per sq. in.)
The value of a varies from 2500 to 4000 feet per second as the
size of pipe decreases, and the time required for the pressure wave
to reach the top of the penstock and return is evidently equal to
m 2L
a
Where
Ti =time required for round trip of pressure wave in seconds;
L = Length of penstock in feet.
If now the gate is closed instantaneously, or, in a time T, which
or
is equal to or less than — , i.e.^ before the reflected pressure wave
has had time to return to the gate and reduce the pressure there,
we obtain a maximum excess pressure head which is equal to
while the total pressure will be equal to the above plus that caused
by the static head, or
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140 WATER CONDUCTORS AND ACCESSORIES
where
Hmax=i^eB,d corresponding to maximum pressure;
t;= velocity of water in penstock in feet per second, cor-
responding to the normal water flow;
Ao= static head in feet.
It is impossible for the pressure to rise above this value, Hum.
2L
The time — , therefore, represents the critical time in which the
a
turbine gates may be closed, and it is evident that the time of
2L
closure should always be greater than — , in which case the water-
hanmier can never reach a maximum value.
or
When the time is greater than — , the excess pressure head
may be calculated from the following formula by Warren:^
, Lv
and the total pressure head becomes:
The above pressure will also be obtained if the gate is only
closed partially, as long as the closing is at such a rate that T is
the time which it would require to completely close it.
Example: Assume a steel pipe line having a length of 1000 feet,
a diameter of 4 feet and a plate thickness of J inch. The water
velocity is 6 feet per second and the net head 100 feet. What is
the minimum time in which the turbine gates may be closed, in
order that the excess pressiure due to waterhammer shall not exceed
50 per cent of the normal pressure due to the net head?
The first thing is to ascertain the velocity of the pressure wave
which is computed as follows:
°= // 1 "^'^ 48' y^"^-
' ^^•*42,00O,O0O''"iX4,O32,00O,000J
' For derivation of formula see Transactions Am. Soc. Civil Engre.,
Vol. 79, 1915, page 238.
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WATERHAMMER AND SURGE TANKS 141
The permissible excess pressure is equal to
^X100=50feet;
and thus
1000X6
50=
T=4.1 seconds.
An extensively used formula for calculating waterhammer is
also the following one, derived by L. Allievi:
»..5^«+sf^.
where
This formula is applicable for a slow closing of the valve when
2Z/
T is considerably greater than — , but may be incorrect for a
a
or
quick closing as when the value of T is close to — .
Surge Tanks. In plants with long pipe lines under medium
and high heads it is often foimd that not only the pressure rise,
but also the pressure drop will be excessive, and in such cases
it may be necessary to provide both a relief valve and a surge
tank to equalize the pressure variation. Synchronous relief
valves (see page 258) are, of course, only of use against a pressure
rise when the load is going off and not when the load is coming on,
because they cannot supply to the moving water colunm the
kinetic energy which it has lost and which it must regain before it
can flow at the higher velocity required by an increase of load.
To accomplish this, surge tanks, or standpipes as they are also
conmionly termed, must be used.
There are two kinds of surge tanks, the simple and the differ-
ential. The former consists of an open standpipe or storage tank
placed at the downstream end of the pipe line (Fig. 68). When
the gates are closed the inertia of the water column in the penstock
causes a rise of the water in the standpipe, and the velocity is
thus gradually reduced. On the other hand, when the load comes
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WATER CONDUCTORS AND ACCESSORIES
on suddenly, the standpipe furnishes the water quickly without
waiting for the velocity in the long pipe line to pick up, and thus
greatly aids the regulation.
To be most efficient, the surge tank should be located as near
the power-house as possible, and if operating under atmospheric
pressure, its height should evidently be above that of the high-
water level in the forebay or storage pond. It is obvious, however.
Fig. 68. — Pressure Variations with Stand Pipe.
that such an open design would not be feasible for high-head devel-
opments, and in such cases a closed standpipe is usually provided,
the increased air pressure being obtained by the static head. In
many plants both open and closed surge tanks are provided, the
open type being installed at the upper end of the pipe line, where it
passes over the brow of the hill above the power-house, while
closed air chambers^ are installed just outeide the power-house.
For pipe lines several miles in length it is also advisable to provide
equalizing reservoirs at intervals along the pipe line, so that changes
in the velocity of the water coliunn will be as gradual as possible.
The differential surge tank consists of a standpipe of about the
same diameter as the conduit, freely connected to it, and a storage
tank of larger dimensions, surrounding the standpipe and con-
nected to the conduit by a properly restricted passage. In a
simple tank, the level of the stored water, following a demand for
more power, represents the accelerating level which is urging more
water from the forebay, and measures the head acting on the
water wheel. In the differential type, owing to the resistance
^ For the use of air tanks for pipe line regulating purposes, nee Proceed-
ings American Society of Civil Engineers for August, 1917.
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WATERHAMMER AND SURGE TANKS 143
interposed between tank and ponduit, the level of the stored
water is quite independent of the acceleration, and does not affect
the waterwheel governor directly. The water in the standpipe
takes care of these things, and acts Uke a simple tank of small
dimensions which is supplemented by the steadying action of the
stored water, fed into the system in an independent, nonnsyn-
chronous manner, meeting all demands for water without causing
the unstable pendulum-like behavior which is so characteristic
of the simple surge tank.
Mr. R. D. Johnson^ has derived the following equation for
determining the maximum surge in simple surge tanks:
^-4
^^^,,.
Ag
where
5ni»x = maximum surge up or down, in feet, measured in starting,
from reservoir or head-water level, and, jn stopping,
from a distance below this equal to the friction head, h/;
P = cross-sectional area of pipe Une, in square feet;
L= length of pipe Une in feet; •
r= velocity of water in pipe, in feet per second;
A = cross-section area of surge tank, in square feet;
flf = acceleration of gravity;
A/ = total feet of head lost due to friction in pipe between res-
ervoir and siurge tank.
Fig. 68 illustrates the pressure variations with simple surge
tanks, the upper curve to the right illustrating the rise in pressure
with the closing of the gates and the lower curve, the drop in
pressure due to the opening thereof.
Figs. 69 and 27 show the design and arrangement of a large
differential surge tank. This particular tank consists of a cylin-
drical shell, 50 feet in diameter and 80 feet high, with a hemi-
spherical bottom which adds 25 feet to the height, and its capacity
is, therefore, 1,400,000 gallons. The tank is supported on ten
colunms with heavy concrete footings. It and the riser are housed
in with a frame wooden structure providing a surrounding air
space which can be heated when necessary from a small house*
below. The top of the roof of this structure is 205 feet above the
^ American Society of Civil Engineers, Vol. 79, 1915, p. 265.
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144
WATER CONDUCTORS AND ACCESSORIES
ground, and the top of the tank is high enough above the crest
of the dam so that if the flow of the water in the pipe hne were
FiQ. 69. — Cross-section of Salmoo River Power Company's Development.
suddenly interrupted its energy would be absorbed by the rise
in level in the tank without overflow.
A complete treatise of the surge tank problem is to be found
in two excellent papers by Messrs. R. D. Johnson and M. M.
Warren in the Transactions of the American Society of Civil
Engineers, Vols. 78 and 79, 1915.
3. GATES AND VALVES ^
Reqtiirements. For the control of water flow in hydro-
electric developments gates and valves are generally used. They
may be either of the sluice gate or gate valve type and the selection
of the type, as well as the number required, is governed by the
nature of the development. So, for example, in low-head plants,
only one set of sluice gates are, as a rule, needed, these being
installed in front of the turbine intakes, either in a gatehouse, as
in Fig. 89, or outside the power-house building at the dam struc-
ture, as in Fig. 70.
For high-head developments, however, two and sometimes
three sets of controlling devices are required, depending on the
pipe-line arrangement, and in order that the water may be projH
1 See also section on " Flashboards."
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GATES AND VALVES
145
erly shut oflf in case of emergency should, for example, one of the
valves become damaged or stick. In such plants sluice gates
are installed as headgates at the forebay or reservoir intake, while
gate valves are provided in the pipe line at the point where this
branches off to the different turbine units, and sometimes also
at a point close to the wheel casing in addition.
The gates should be of suflScient size to pass the required max-
Fia. 70. — Sectional Elevation of Power House, Turners Falls Power and
Electric Company, Showing Headgate Arrangement.
imum flow of water, and also of suflScient strength to withstand
the shocks and excessive pressures resulting from a quick closing
in case of emergency. This is a point which must be considered
in determining the minimum time in which the gates may be
closed. As mentioned under the chapter on Waterhammer and
Surge Tanks, the longer time allowed for closing the gates the
less will the excessive pressure caused by waterhammer be.
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WATER CONDUCTORS AND ACCESSORIES
Sluice Gates. These may be either of structural steel or cast
iron, the former generally being used for large intake openings.
With low-head developments these openings are now generally
divided in a number of vertical sections in order to insure a more
even distribution of the water to the speed ring of the turbine,
Fig. 71. — Rising-Stem Sluice Gate
with Floor Stand. (Ludlow Valve
Mfg. Co.)
Fig. 72.— Rising Stem Sluice
Gate. Side View of Gate
Shown in Fig. 71.
and this, of course, also very considerably reduces the size of the
gates, one set being provided for each section. Sometimes the
sections are also divided horizontally, as shown in Fig. 26, in
order to still further reduce the size of the gates. At the junction
of the upper and lower sections there is a reinforced concrete
beam which serves as a support and as a seal. The two gate
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GATES AND VALVES
147
sections are provided with separate guide slots so that they may
be manipulated independently. This type of gate is generally
lifted by means of chains.
The gates shown in Fig. 70 are the Broome type and are con-
structed of heavy steel plates run on a continuous chain of rollers
between the tracks on the gates and guides. A gantry crane,
Fig. 73. — Sectional Elevation of Power House of the Hydro-Electric Com-
pany of West Virginia, Showing Application of Tainter Gate.
electrically driven and running on the head wall, operates the
gates. This crane also carries a mechanical rack-raking device.
Gates which are raised or lowered by means of stems may be
either of the rising or non-rising stem type, the former being
preferable at intakes where there is no danger of the operating
stands being submerged, and where the rising stem may serve
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148
WATER CX)NDUCTORS AND ACCESSORIES
as an indicator of the gate position (see Figs. 71 and 72). For
gates which are installed in diversion dams for sluicing off excess
flood water in forebay ponds or reservoirs, the non-rising type is
preferable, as it permits be-
ing submerged without being
damaged by floating ice.
Tainter Gates. This type
of gate is occasionally used for
controlling the water passages
to the wheel chambers in
low-head developments, the
methods of application being
shown in Fig. 73. They are,
however, more used in connec-
tion with diversion dams.
Gate Valves. There are
niunerous different designs of
gate valves, the details of one
of the most improved designs
being illustrated in Fig. 74. It
is intended for high pressures
and consists of tlie stem, a
double disc and two bevel-
faced wedges, the wedges being
entirely independent of the
discs and working between
them.
By the action of the stem,
which works through a nut in
the upper wedge, the discs de-
scend parallel with their seats
until the lower wedge strikes
the stop in the bottom of the
case. The discs and upper
wedge, however, continue their
downward movement until the
face or bevel of the upper
wedge comes in contact with the face or bevel of the lower
wedge. The discs then being down opposite the valve opening,
the face of the upper wedge moves across the face of the lower
Fig. 74. — Ludlow Bronze Mounted
Doubl3 Gate Valve with Bolted
Stuffing Box.
A— Caae. B— Cover of Bonnet. C —
Stem or Spindle. D— Packing Plate or
Stuffing Box. J]— Stuffing Box Gland or
Follower. F— Stem Nut. GG— Gates.
H — Gate Rings. I — Case Rings. J — Top
Wedge. K— Bottom Wedge. L— Throat
Flange Bolts. M— Stuffing Box or Fol-
lower Bolts.
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GATES AND VALVES
149
wedge, bringing pressure to bear on the backs of both discs, from
central bearings, thus forcing them apart and squarely against
their seats.
In opening the valve, the first turn of the stem releases the
upper wedge from contact with the lower wedge, thereby instantly
releasing both discs from their seats before they commence to rise.
All gate valves and sluice gates should be fully bronze-mounted
to prevent corrosion. That is, the disc and seat rings should be
made of bronze, as well as the threaded portion of the stem, the
operating nut and the wedging apphances.
Where the water pressure is very great, by-pass valves may
be provided for equalizing the pressure on both sides of the valve
before it is opened.
Operatioii and ControL Sluice gates and gate valves may be
operated either by hand, water or electrically, the two latter
Fig. 75. — Gatehouse, Showing Gate-Lowering Mechanism. Mississippi
River Power Company.
methods being used extensively, resulting in a saving of labor,
while on the other hand acting as a protection in the case of
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150
WATER] CX)NDUCTORS AND ACCESSORIES]
trouble. This is evident by considering that some large valves
would require hours to close by hand. When sluice gates are
installed in gatehouses a traveling crane is often provided for
lifting them. Their dosing is then done through their own
weight, and brakes are installed
for regulating the same (Fig. 75).
Whatever method of operation
is chosen it should be simple and
positive in its action.
There are numerous hand-
operated lifting devices such as
rack-and-pinion with an operating
lever, windlass, floorstands with
threaded gate stems and operating
wheels, etc. Gear trains should
always be provided where there is
considerable pressure on the gate,
or, otherwise, it may be impos-
sible for the operator to start the
gates especially when Ihey have
been closed for some time.
Arrangements are, however, gen-
erally made for shifting the hand-
wheel directly to the stem after
the gate has been opened slightly,
in order that the opening may be
accomplished more rapidly. Roll-
ers and ball bearings are also
sometimes provided, either with
the discs or the Ufting devices so
as to reduce the friction.
Gate valves may also be
operated by hydraulic cyUnders.
The regulating valve consists of a flat valve which is operated
by a piston, this in turn being moved by releasing the pressure
on either side by means of small poppet valves which may be
operated by hand or electrically f)'om any convenient point. A
valve of the latter type is shown in Fig. 76, and the electrical con-
nections in Fig. 77.
A double-throw control switch and an alarm bell are mounted
Fig. 76. — Ludlow Hydraulic
Operated Cylinder Valve with
Electric Control.
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GATES AND VALVES
151
on a panel. The upper contact on the switch operates the valve,
and the lower is for the bell, which will ring only when the valve is
closed or open. This depends on how the connections are made,
and the operator can at all times ascertain what position the valve
is in. If the valve is connected so that the bell will ring when the
valve is closed, and the operator closes the bell circuit, and the
bell will not ring, he will readily understand the valve is open;
if he closes the valve circuit, or upper pole pf switch for a few
seconds, and again closes the lower or bell circuit and the bell
ValTtf CIrenIt
Fig. 77. — ConnectioDs for Electro-Hydraulic Valve Shown in Fig. 76.
rings, he will understand the valve is closed. The valve can be
operated by hand simply by lifting the small armature on the con-
trolling device.
Cylinder valves are, as a rule, more economical for smaller
Hizes, while for larger the electric motor operated valve (Fig. 78)
is to be recommended. Such valves are very reliable and can be
closed in a comparatively short time. Besides this, remote
control from the main control board in the power-house can readily
be provided.
The service of valve motors is exceedingly intermittent and
may vary from comparatively short intervals, such as once every
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WATER CONDUCTORS AND ACCESSORIES
hour, to weeks or even months. When the apparatus at the end
of long periods of idleness is called upon to operate it must per-
form its function without
fail, and must, therefore
be designed accordingly,
totally inclosed motors of
a moisture-proof design
being preferable. Metal-
line bearings are generally
used, as the motors may
be mounted in any posi-
tion from vertical to hori-
zontal. Due to the inter-
mittent natiu^ of the ser-
vice, efficiency or power
factor need not be con-
sidered, the main consid-
eration being reliable
operation.
The proper size of a
motor for driving a valve
will vary with the duty
and conditions under
which the valve operates.
A small valve may only
require a 1 -horse-power
motor, while very large
valves require up to 25-
H.P. motors. The size of
the valve is, however, not
the only factor determin-
ing the required motor
capacity, which also de-
pends to a very large ex-
tent on the pressure on
the valve and the time of
Fig. 78. — Heavy Pressure Motor-operated
Gate Valve Showing Motor Equipment
and Limit Switch.
openmg.
The torque requirements vary greatly during the operating
cycle. It is maximimi shortly after the time of imseating the
valve; that is, after the wedges have been released and the actual
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GATES AND VALVES
153
motion begins. It then drops somewhat until the valve has
opened about one-fourth, after which it takes comparatively
little power to complete the opening, as the pressure on the valve
is then comparatively small. When closing the valve, friction
only needs to be overcome in starting and there is no pressure on
BsmoM OoBtrol FMial
Op«i
limit Swlteh
Fig. 79. — A. C. One-station Remote Control Equipment.
the valve until it has begim to close. The torque is therefore
not very high imtil the valve is about three-fourths closed, after
which the pressure causes the torque to increase rapidly. At the
end of the closing cycle the torque does not, however, reach the
value it did during the period of starting.
Valve motors are, therefore, generally rated for maximum
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WATER CONDUCTORS AND ACCESSORIES
starting torque and either direct or alternating current motors
may be used. The former are mostly compound wound with a
sufficient shunt field to limit the speed at light load. With the
latter the squirrel-cage induction motor seems to be most widely
used for small and mediimi-size valvef?, principally on account of
its simplicity. It should be designed with a high-resistance
rotor to increase the starting torque, and it is generally found
B«mot« Control PmB«l
Clow-^
AraTl I
I — :qjivww«
Limit Switch
Fig. 80. — D. C. One-station Remote Control Equipment.
necessary to select a motor somewhat larger than what would be
the case with a compound-wound direct-current motor to perform
the same duty.
With certain valves it becomes necessary to overcome the
sticking due to wedging action when opening, and the drive is
therefore provided with a " lost motion " so as to give a hammer-
blow. For alternating current motors this is furthermore of value
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GATES AND VALVES
155
in that it permits the motor to speed up some and gain in torque
before the load comes on, the maximum torque, as a rule, occurring
slightly above zero speed.
Valve motors are generally thrown directly on the line, and
the control is accomplished by means of contactors for remote
control and large equipments. For hand control of smaller equip-
ments, ordinary knife switches are sufficient. Fuses give better
protection than automatic circuit breakers, in that they will
protect against a stalled motor but will not blow during start or
running.
Limit switches which will open the circuit when the gate has
reached its limit of travel should always be provided. Such
switches are geared to the valve stem and arranged to open the
contactors at a predetermined point of travel of the gate in either
direction. Provision is also made so that the open or closed valve
positions are indicated on the control board by means of two lamps.
When only one lamp bums it indicates open or closed valve posi-
tion, Es the case may be,
while both lamps burn in
any mid position.
Connection diagrams for
D.C. and A.C. remote-con-
trol equipments are shown in
Fig3. 79 and 80. These are
for single-station control, and
for multiple-station ^control
push buttons are substi-
tuted for the single-pole
double-throw pilot switch.
Pivot Valve. A type of
valve used in a number of
large plants for the purpose
of shutting off the turbine
from the penstock is the
pivot or " butterfly " type of
valve, illustrated in Fig. 81.
This type of valve is simple in construction and takes up very
little space. The operation is by means of a hydraulic cylinder,
having a trunk piston connected to the crank or lever shown. It
is reliable in service, but is not as tight against leakage as either
Fig. 81.— Pivot Valve. (Built by I.
Morris Company.)
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WATER CONDUCTORS AND ACCESSORIES
the Johnson valve or gate valve. In cases where leakage through
the valve can be carried off through an ample drain, the valve
can be used very satisfactorily.
The Johnson Hydraulic Valve. This valve consists essen-
tially of a circular body forming an enlargement of the pipe line
Open
Closed
Fig. 82. — Johnson Hydraulic Valve. (Wellman-Seaver-Morgan Company.)
or penstock, and having an internal cylindrical chamber contain-
ing a sliding plunger (Fig. 82). The closed end of the internal
chamber and the nose of the plunger are of conical form. They
are designed to guide the water smoothly as it enters and leaves
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GATES AND VALVES 157
the valve. The waterways throughout the valve offer no obstruc-
tion to the flow and consequently there is no appreciable loss of
head.
No external source of power is required for operation. When
the plimger is withdrawn into the internal or operating chamber,
the valve is open and presents an unobstructed passage for the
water. When the plunger protrudes from the operating chamber,
it seats against a ground ring in the neck of the valve body, form-
ing a water-tight joint. The standard control mechanism pro-
vides for only the open and closed positions of the plunger, but it
may be specially arranged to hold the plunger at intermediate
positions if desired.
The valve plimger is of the differential type, forming an annular
chamber A within the operating cylinder, in addition to the cen-
tral chamber B. By means of a suitable external control valve
and piping, either pipe-line pressure or atmospheric pressure may
be alternately applied to the chambers A and B. Admitting pipe-
Une pressure to A and exhausting it from B opens the valve;
reversing the operation closes it.
The external control valve may be operated by hand or
electricity and may, therefore, be located remotely from the
valve as from the switchboard, if desired.
Another application of this valve is for automatic pressure
relief. The valve plunger is held closed by air pressure so arranged
that it is automatically released, permitting the valve plunger to
open when the pipe-line pressure exceeds normal by some pre-
determined margin. The advantage of using air, rather than
water, lies in the rapidity with which air may be discharged, and
the consequent rapid opening of the relief valve.
Air Valves. In addition to sluice gates and gate valves pre-
viously described, air valves are often required in connection with
the pipe lines of hydro-electric developments. These may be of
two kinds: the automatic lever and float valve and the automatic
poppet valve.
The former is for use on pipe lines which follow the contour
of hilly country and where air may accumulate at nigh summits
and obstruct the flow of water. The valve is connected to the
outside of the pipe at its highest point or points, and when air
takes the place of water about the float in the valve chamber, the
float which is attached to a lever drops, thus opening a small valve,
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158 WATER CONDUCTORS AND ACCESSORIES
allowing the air to escape. As the water returns, it lifts the float
thereby closing the valve.
The poppet valve, on the other hand, is intended for use on
pipe lines to permit air to enter when water is being drawn off
and thus eliminates any danger of collapse from vacuum forming
in the pipe lines as, for example, when the head gates are closed.
Similarly, they may be provided to allow air to escape when the
pipes are being filled. The valve remains open until the water
reaches and lifts the copper float and closes the same, after which
it remains closed while the pressing is on..
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CHAPTER VI
STORAGE RESERVOIRS 1
Many watersheds have some natural storage features tending
to equalize the stream-flow as compared with the rainfall, while
with others surplus water in times of high flow can only be held
back for use in times of low flow by the construction of artificial
reservoirs.
Storage and Pondage. The impounding and acciunulation
of surplus water which may be utilized when needed is termed
either " storage " or " pondage." The former generally refers
to reservoirs located on a watershed at some distance from the
power-house, and where large quantities of water may be im-
pounded for use during the dry season. " Pondage," on the other
hand, refers to the storage for taking care of the daily fluctuation
in the load curve, otherwise canals, flumes and pipe lines will
have to carry the peak flow of water instead of the average. It is
often the case that the average demand for power during twelve
or fourteen hours of the day is twice as great as the demand for
the remaining ten or twelve hours. The small volume of power
required during a portion of the day permits an accumulation of
water at 'the power dam itself which can be used as a reserve force
to meet the higher demand during the other portions of the day.
Thus, a stream that during the twenty-four hours might develop
a continuous horse-power would, if relieved of half of the demand
for half of the day, be able, with small pondage, to supply con-
siderably more than the average during the remaining portion of
the day.
The importance of pondage should, however, not be exag-
gerated, as it can only be utilized at the expense of operating head,
but to counteract this it is possible to provide temporary flash-
boards by which the normal level may be raised several feet.
The storage is, however, of the greatest importance, as it wiU
usually greatly increase the earning capacity of any development.
^ See also section on ** Water Storage/'
159
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STORAGE RESERVOIRS
Limitations to Storage. There is, however, a limit to storage
and in no ease can sufficient impounding be maintained to give
to any stream the power representing anything like its maximum
flow. The excess run-oflf from any watershed varies greatly from
year to year, and it is generally considered to be the best prac-
tice to base the reservoir capacity on the run-ofif for the minimum
year, as impounding the water in years of heavy run-off for holding
over in storage to dry seasons is generally considered uneconomical,
among other things on account of the loss due to evaporation.
In general, there are two factors determining the practicable
amount of storage. The first consideration ia usually the topog-
raphy of the locality. In some locaUties a sufficiently high dam
may be built at a very reasonable cost, and it may provide storage
for an immense volume of water and thus greatly enhance the
minimum power of the stream. In other cases the conditions
may be entirely the reverse. A further practical consideration
is the value of the
land. Even with
favorable topographic
conditions the cost of
acquiring lands to be
flooded may be so
great as to make any
great amount of stor-
age impracticable.
Location of Reser-
voir. The relative
location of the pro-
posed reservoir site in
the drainage area
must, of course, also
be considered, and
likewise its location
with respect to the
point of distribution
so that proper outlets and conduits can be provided at a reason-
able cost.
Before accurate surveys are justified, it may become desirable
to approximately determine the quantity of water that a proposed
reservoir may hold. This is usually done by means of contour
Bw.
M f\
8«!.M
1
5i
f/x^ Sec.
-^ H V
Boalc oC Milei
Sec. 91
Fig. 83. — Ck)ntour Map of Reeervoir Site.
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STORAGE RESERVOIRS
161
maps, the topography being taken by means of transits and stadia,
and the contours plotted as in Fig. 83. The area is found by
planimeters and the volume by multiplying the vertical distance
between the contour levels with the mean area of the sections. A
certain dead space must be allowed at the bottom of the reservoir
as it is not advisable to draw off the water from the bottom level
on account of the silt and mud which accumulates there. The
foUowing table gives the capacity of the reservoir site outlined
in the above figure:
TABLE XXXV
RxBEBVora Capactft
Height of Water
above Bottom in Feet.
Area in Acres.
Capacity of Section
in Acre-feet.
Total Capacity
in Acre-feet.
10
10
0
0
20
36
230
230
30
74
550
780
35
110
460
1240
50
188
2235
3475
60
274
2310
5785
The imit measure of stored water is generally the " acre-foot,"
representing 43,560 cubic feet, and the curves in Figs. 84 and 85,
show the kilowatt-hours for different acre-feet storage on various
heads, and vice versa, the over-all hydro-electric efficiency being
assumed to be 65 per cent.
It has also been proposed to adopt the ''square-mile foot"
as a unit for expressing large quantities of stored water. This"
is equivalent to 27,878,400 cubic feet or, 640 acre-feet.
The building of storage reservoirs involves many engineering
problems, the most important being the dam construction, which
was treated in Chapter IV. Spillways must be provided for dis-
charging excess flood waters, and with earthen dams or masonry
dams of considerable height, outlets, in the form of tunnels or
otherwise, are generally provided some distance from the dam to
prevent any possibility of damage to the same. Provision must
also be made for outlets at the bottom of the reservoir, so that
excess accumulation of silt and mud may be sluiced away.
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162
STORAGE RESERVOIRS
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STORAGE RESERVOIRS
163
Intakes. The intake should be located sufficiently far back
from the dam in order that the water may be drawn out when
at its lowest level. It is also preferable to provide several intake
Iwld^r t& Bottom of Tq^wcr
[□(«!«
Fig. 86. — Concrete Intake Tower.
openings at different elevations, especially where the depth of
water is considerable. The upper openings should then be used
when the water level is highest and the others in order, as the water
is drawn out and the level lowered. In this manner the pressure
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164 STORAGE RESERVOIBS
and erosive effect is reduced, while, on the other hand, there is
less danger of a shut-down in case there were only one gate open-
ing at the bottom, which would be Uable to be clogged up by silt
and mud.
Such intakes are often built in the form of towers, a typical
design being shown in Fig. 86. There are four square intake
openings placed from 18 to 21 feet apart vertically and at angles
60^ to each other in the plan. The openings are provided with
screens and sUding steel gates which are controlled from the oper-
ating floor. There is also a secondary intake placed entirely inside
the tower, consisting of a standpipe 42 inches in diameter, built up
in four separate sections. Each section has a conical seat at the
upper and lower ends, and is seated on the one next below, the
bottom section seating on a heavy cast-iron elbow which connects
with the intake pipe. The water entering the intake openings
in the tower wall must, therefore, pass through the top of the
vertical standpipe and in this manner any silt or mud is pre-
vented from being carried along. As the water level goes down,
sections of the standpipe are removed. This is readily accom-
plished by means of a lifting gear, the pipe sections being closely
guided.
Seepage and Evaporation. Consideration must also be given
to seepage and extreme care should always be taken to insure
imperviousness of the reservoir bottom. It may thus be neces-
sary to strip the top soil until impervious strata are reached, while
fissures may have to be closed.
Ev^aporation must necessarily be taken into account when
determining the reservoir capacity. This loss can, however,
not be regulated, although a deeper and narrower reservoir will
have a less evaporation loss than a wider and shallower.
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CHAPTER VII
POWER-HOUSE DESIGN
1. BUILDING
General Design. The design of power-houses differs greatly,
depending on the conditions which are to be met. It is affected,
to a very great extent by natural conditions such as the location
with respect to the stream, the condition of the soil, etc. Low
and high-head developments require different types of turbines,
and these may furthermore be of a horizontal or vertical con-
iiiiiiiiiiiiiilll I
* i t t t
Fig. 87.— Power House, Mississippi River Power Company, Keokuk, Iowa.
struction, necessitating entirely different layouts. The number
and capacity of the generating units is obviously a determining
factor, and the location of the development is generally such that
a high-tension transmission is necessary so that provision must be
made for housing the transforming and high-tension switching
apparatus.
In designing the building, the arrangement of the apparatus
should natiu-ally be given first consideration, but this does not
mean that the architectural features sould be neglected. It is not
165
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166 POWER-HOUSE DESIGN
necessary that the building should be too ornamental. Sim-
plicity in design and harmony with the surroundings is very
desirable so as not to injure the scenic conditions, but, on the
other hand, attract the attention of visitors. Figs. 87 and 88 are
good examples of a pleasing architecture.
A hydro-electric px)wer-house building is generally divided
into two longitudinal bays, a front or main bay, containing the
turbines and generators, and a rear bay containing the trans-
Fig. 88. — Cohoe8 Hydro-Electric Power Development, Cohoes, N. Y.
formers, switching apparatus, etc. (see Fig. 89). The two bays
are separated either by a wall or by a row of supporting colunms,
and the rear bay is divided into two or more floors, and these in
turn into various rooms or compartments. When the space is
very limited, as on steep hill slopes, where the cost of excavation
becomes extra high, it is sometimes desirable to locate the switch-
and transformer-house some distance back from the generating
station and connect the two by a tunnel through which the cables
can be run.
Basements. In modem low-head developments, where ver-
tical turbines are used, the substructure not only serves as foun-
dation for the superstructure of the building, but is really the
hydraulic structure, in that the intakes, turbine casings and draft
tubes are molded directly in the concrete. In such plants one
or more basements or tunnels are necessary for providing access to
the turbines, and for housing the various oil-pressure pumps for
the governors and step bearings.
Where the floors must carry heavy loads, or when they are to
support the generator frames, step bearings, etc., they must be
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BUILDING
167
Fig. 89. — Sectional Elevation of Power House, Mississippi River Power Com-
pany, Keokuk, Iowa.
heavily reinforced with I-beams and supported with concrete
piers.
With horizontal turbines no basement is needed, although
tunnels are then, nevertheless, usually installed below the main
floor for cables, oil and water piping, etc. Ventilating ducts for
carrying fresh air from the outside to the different generators are
also essential, especially in low-head plants with slow-speed imits.
This subject is treated more fully under " Ventilation."
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168
POWER-HOUSE DESIGN
Foundation. The most important part of the building is the
foundation, and careful soundings must be made to ascertain the
underl3ring strata. If bedrock is found within moderate depth,
the foundation should be carried down to the same. For all soils
there is a certain safe bearing load, and if this is exceeded the
structure suppx)rted thereby is apt to settle. The safe loads
usually allowed in this country are given in the following Table
XXXVI.
TABLE XXXVI
Safe Bearinq Power of Soils ^
Bbabino Powbr in Tons pxr
Squarb Foot.
Minimum.
Maximum.
Rock, hardest kind »:
200
25
15
4
4
2
1
8
4
2
0.5
"Rnolc. AniiflJ tn Aflhlfir maflOTirv
30
Brick, eaual to ashlar masonrv
20
Brick of Door aualitv
7
Clav in thick beds alwavs drv
6
Clav in thick beds moderately dry
4
Clay, soft
2
Gravel and coarse sand
10
Sand, fine and comoact
6
Sand, clean and drv. . , , ,
4
Alluvial soils and uncertain sand
1
1 From " Treatise on Masonry ConBtniction," by Baker.
For the machinery foundations it is considered good practice
to use somewhat lower values. About one-half is a good working
basis for such work, thus allowing a maximum load of about 1000
pounds per square foot for ordinary alluvial soils. Clean, sharp
sand is considered to be a good bearing soil, and may only be
necessary to cover it with a concrete mat, which requires a mini-
mum of concrete. For soft or alluvial soils piling is almost always
required. The piles may be of wood, although in the last few
years much use has been made of concrete piles, both plain and
reinforced. Such piles are less apt to decay and their bearing
Note. A complete bibliography on the subject of " Bearing Value of
Soils " is contained in the Proceedings of the American Society of Civil Engi-
neers for August, 1917.
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BUILDING 169
power is higher dtie to their greater friction. They may also
be made of larger diameters than can be obtained with wood piles,
and a less number is therefore required to support a given load.
When designing foundations the first step is to ascertain the
total weight that will be sustained by the soil and then to pro-
vide a sufficient number of square feet of area of the base to bring
the pressure per square foot within the safe value. The weight
should include the machines, fittings, the weight of the founda-
tion itself, and, in the case of the turbines, the weight due to the
water thrust unless this is balanced. Separate foundation should
be provided for the different imits so as to isolate any failure as
far as possible.
Concrete is alwa3rs used for the foundations. They should
be solid for the machinery, while the building may be supported
on columns or arches so as to economize on the concrete. Where
there is danger of high water in the tailrace, the outside founda-
tion walls should necessarily be made water-tight so as to prevent
water from entering and flooding the basement. For such cases a
sump is, therefore, generally provided into which the seepage
may collect and from where it can readily be pumped out. A mix-
ture of one part cement, three parts sand and six parts gravel
or broken stone forms a concrete that is extensively used, and
which has given perfect satisfaction for machine foundations.
On small machines the foundation bolts and plates may be
placed in position before the concrete is put in. They should be
hung in place by a wooden template and the bolts surrounded by
stove pipe, conveyor pipe, or scrap-iron pipe, several inches larger
than the bolts themselves. This allows for mistakes in location
and variation in the machine parts, the holes being filled when the
base is grouted. With large machines, however, it is better to
have pockets in the concrete large enough for the foundation plates
to be dropped in. These holes can be fiUed in, grouting the
base, and serve the further purpose of making a good bond between
the foundation proper and the grout in and under the base.
Grout is preferable mixed half sharp clean sand and half cement.
It should be thin enough to flow readily and should be well pud-
dled into place. Before pouring, all dust and trash should be
cleaned off and the foundation thoroughly wet down. It is better
to use a fairly slow-setting cement on large castings. In some
cases cement for grouting has been set aside and aged a year
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170 POWER-HOUSE DESIGN
before using. Fresh or quickHsetting cement may heat enou^
while setting to cause expansion and distortion of large castings. A
record of the grout and room temperature should be taken as a check.
Floors. No combustible material of any kind should, if pos-
sible, be used in the construction of a px)wer-house. As the sub-
structure of the building is generally built of concrete it is but
natural that the floors should also be of concrete. A dark color is
preferable so as to render drops of oil inconspicuous. Tile or mosaic
floors are possibly the best floor finish for a generating room. It is
smooth, easy to keep clean and has a very handsome apperance
if made to conform with the general interior finish of the station.
Walls. The walls may be either of reinforced concrete con-
struction or of brick with a steel skeleton framework. Where
future extensions are contemplated a false wall is provided on one
end of the building. The interior should be kept as light as pos-
sible, and it is therefore advisable to apply a smooth siurface of
cement plaster and whitewash or paint the same. For more
important stations the walls may be faced with pressed brick and
up from the floor to about 10 feet with enameled brick. Where
the extra expense is warranted, the walls may be entirely lined
with enameled brick and a wainscoting of contrasting color,
preferably olive-green.
Roof. The roof of the building should alwajrs be supported
on the steel trusses, carried on the side of the walls or on the
steel columns. The slope should not be excessive, 2 inches per
foot being suflicient with gravel covering. This construction
requires less material, and is advantageous when the transmission
wires are to enter the station through roof entrance bushings,
or where the lightning arrester horns are to be installed on the roof.
The roof covering may simply consist of boards covered with
roofing paper, tar and gravel. Reinforced concrete is some-
times used in place of boards so as to make an absolutely fireproof
construction. Roofs covered with red tile are often used and
present a very pleasing appearance. Corrugated iron roofs are,
however, objectionable due to the liability of moisture condensing
on the inner surface and dripping into the station. They may
also cause the station to be extremely hot in the summer unless an
insulating lining is provided below the roof trusses to keep out the
heat. This, however, is objectionable and corrugated iron roofs
are therefore seldom used for power-houses. For tile or metal
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BUILDING 171
roofs it is necessary to provide steeper inclines than with gravel
roofs so that the water may run off rapidly. The height of the
trusses should be about one-third of the span. Monitors are
sometimes provided so as to give additional ventilating facilities.
Roof trusses with a raised chord, as in Fig. 101, are in many
instances of great advantage in that they provide an increased
headroom without unnecessarily raising the walls of the building.
This is of special importance in the high-tension part of the sta-
tion, where ample headroom must be provided for the busbars.
Windows. A good lighting is imperative, and large windows
are therefore essential. They should be symmetrically located
with regard to the generating units and their design should be
such as to harmonize with the building, arched windows being
very generally used. Skylights of glass tile placed in the roof
will also add considerably to the lighting. The window sashes
should preferably be metallic and the glass reinforced with wire
netting so as to prevent shattering when broken. Ribbed or non-
transparent glass is also desirable, because it keeps out the intense
rays of the sun. In order to provide for ventilation provision
should be made so that the windows can be readily opened, and
in large stations they are operated by electric motors controlled
from the main switchboard. Precautions should also be taken
so that rain, snow or dust will not blow in on the machinery or
apparatus. This is especially important on the switchboard side
where the wiring is exposed and it is, therefore, better practice
not to provide any means for opening the windows on that side.
For tropical climates all windows which are liable to be opened
should be equipped with mosquito screens.
Doors. The location of the doors is naturally governed by
local conditions. One of the openings should be of a sufficient
size to admit a railroad car and tracks should therefore also be
provided. Very often these doors are of the rolling type, this
design being most economical as regards space.
Traveling Crane. Provision should always be made for sup-
porting the track for a traveling crane, which should span the
generator room and run the full length of the station. The track
is generally supported on pilasters in the outside wall and on the
steel colmnns separating the generator and switch rooms. There
should be ample headroom allowed so that the various machine
parts can be readily removed when repairs arc to be made. This
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172 POWER-HOUSE DESIGN
is especially important with vertical units where the water-wheel
rotor is mounted on the same shaft as the generator field, and in
which case it should be possible to lift out the whole revolving
element by simply removing the top bracket and bearing of the
generator.
The type of crane depends largely on the size of the units,
weight of heaviest pieces and the number of units in the station.
In small stations a hand-operated crane may be ample, while very
large stations will require two electrically operated cranes. A few
stations have been equipped with a gantry type of crane just
long enough to straddle the generators and high enough for
the highest lift. This type deserves more careful consideration
than it has had heretofore. The span is shorter and consequently
lighter than an overhead crane. The building framework can be
designed simply for the roof load, with a material reduction in the
steel required.
The crane should be of sufficient capacity to lift the total
revolving element of vertical wheels and generators imless some
special arrangement of jacks under the generator rim, or on the
shaft, is provided. This support is necessary to reUeve the thrust
bearing for inspection or repairs. Jacks or supporting blocks
under the generator field rim are also of great assistance d^jring
the erection olF vertical units.
The question of armature repairs should be considered when
designing the crane equipment. A few coils can be replaced in a ver-
tical machine by removing two or more field poles. Extensive re-
pairs are best handled by lifting the entire armature above the field
rim and supporting it on substantial blocking. A temporary floor
is laid on the top of the field spider for a working platform. This
arrangement does not disturb the line up of the revolving parts
and usually makes a very material saving in time and expense.
Some special arrangenlent is usually necessary to provide
power for the electric cranes. The exact details depend largely
on local conditions and a careful analysis should be made. In
some cases a motor generator set may be purchased in advance
and later used as part of the permanent exciter equipment. In
others, an engine or turbine-driven generator set may be the best
solution. In any case, sufficient capacity for the heaviest lifts
must be provided. An under-powered equipment where the
heavy lifts have to be jumped a few inches at a time is decidedly
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BUILDING 173
unsatisfactory as well as dangerous. If ample driving power is
not available a flywheel will assist materially.
Slings, lifting devices, hooks, etc., should be designed with
ample safety factors and to allow safe, accurate and rapid assembly.
Wire slings should be oiled to prevent rusting and protected
from kinking or cutting on sharp comers by pads or their equiva-
lent. Angle pieces made from boiler plate are good, cheap and
durable. Any slings that show wear or weakening should, of
course, be replaced.
Ventilation.^ Particular attention must be given to the ven-
tilating problem in the design of the building; especially for large
installations where the heat to be carried away from the generators
is very great. The oversight of this important feature in stations,
otherwise well designed, has led to considerable trouble from over-
heating the machines; for if no provision is made for admitting
fresh air, the air in the machine pit and in the space around the
machine is used over and over again. Fresh cool air can be taken
to the generator pit through ventilating ducts especially built for
this ptu-pose below the floor, and from the pit the air is drawn up
through the machine by the fanning action of the rotor or forced
circulation may be provided by motor-operated fans, the heated
air escaping through openings in the roof. The size of the inlets
and outlets depends uix)n the losses to be dissipated, the allowable
difference in temperature between the inside and outside air and
the height of the building.
Mr. R. C. Muir in the " General Electric Review " gives the
following recommendations: " The maximum difference between
inside or room temperatmre and outdoor temperature should not
exceed 20** F. (11.1** C), dining hot weather, since the air entering
the machine is taken from the room and the air leaving the machine
is considerably warmer than the room temperature. The ven-
tilation scheme should be laid out for most severe or hot weather
conditions. It is very impx)rtant to make the difference in height
between inlet and outlet openings as great as the station will per-
mit, as is shown from Table XXXVII.
The amount of air required for the generating room can be
easily calculated, as follows:
One Kw.-hour will raise the temperatmre of 10,000 cubic feet
of air from 80** F. to 100** F., a rise of 20** F. (11.1** C).
' See also "Generator Ventilation."
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i74
JPOWERrHOUSE DESIGN
The total loeses in generating room equals (total Kv.A. gen-
erator capacity) — (total Kv.A. generator capacity X generator
eflBciency).
The total amount of air required for the generator room in
cubic feet per minute equals
10,000 X total loss per hoiu' in kw-hr.
60 •
The above method will give approximately twice as much
air as that required with the forced or positive ventilation schemes,
for the reason that when the ventilating scheme is such that a
definite amount of outside air will pass through the machine, a
temperature diflference of 30** F. to 40^ F. (16.7** C. to 22.7° C.)
between ingoing and outgoing air is not excessive.
TABLE XXXVII
QuANnrr of Air in Cubic Feet Discharged per MimrrB through a
Ventilating Duct of 1 Square Foot in Cross-sectional Abea.
Difference in Temperature op Air in Duct and OursroB— 20* F.
Height of Vent. Duct in Feet.
Cubic Feet per Minute,
10
153
20
217
30
265
40
306
to
342
60
375
niumination. This is mostly done by tungsten lamps, the
proper location and spacing, of com^e, being governed by the
general layout and arrangement of the apparatus. In the gene-
rator room 500-watt lamps are used very generally and are
mounted on the roof trusses and provided with intensity reflectors,
giving a very uniform and satisfactory illumination. In addition
the lamps are also mounted on brackets along the walls. For
other parts of the station the lamps vary in size from 25 to 500
watts.
The current for the lighting may be taken from the exciter
system, if not fluctuating too widely, or by means of step-down
transformers from the main biis. As a protective measure it is a
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ARRANGEMENT OF APPARATUS 175
good method to arrange about one-third of the lights, well dis-
tributed in the station, on a separate circuit, which, in case of
trouble, may be switched over to the exciter battery or other
reserve sotu-ce. In some stations this is accomplished auto-
matically.
For illuminating outdoor equipments flood-lighting has, of
late, been used with very great success.
Heating. The heating of the power-house building is ordina-
rily, to a very great extent, done by the heat radiated from the
machines, and provision is often made whereby during cold
weather the ventilating air may be used over and over again until
it reaches a certain temperature. In many stations separate
provision must be made for heating. In some this is done by
means of electrical heaters, while in others complete steam-heating
systems are installed. In connection with these a steam-cleaning
plant for waste, which necessarily is used in considerable quanti-
ties in large stations, can readily be provided.
Miscellaneous. Provision should, of course, also be made for
necessary repair shops, store rooms, offices, toilets, etc., and pro^
tective measures for accidents and fire must not be neglected. A
vacuum compressed-air system may be required for cleaning or
other purposes and a complete water-supply system to various
parts of the building is, of course, also necessary. Elevators and
ample stairway provision is essential so as to permit a ready access
to important paints, as, for example, between the generator room
and the switchboard gallery.
2. ARRANGEMENT OF APPARATUS
General Considerations. The arrangement of the apparatus
should be very carefully considered from the standpoint of sim-
plicity and reliability of operation. The purpose of the station
being to give reUable service consideration must also be given to
the causes of disturbances and means for minimizing their effects.
In anticipating these abnormal or so-called emergency conditions,
the failure of every piece of apparatus must be considered as a
possibility, and a definite plan worked out for limiting the mag-
nitude and area of such disturbances.
Turbines. With horizontal sets the turbines may be located,
together with the generators, in the generator room or in separate
wheel chambers built in the dam or partition towards the fore-
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176 POWER-HOUSE DESIGN
bay. The latter practice is only used for very low-head develop-
ments, where one of the power-house walls forms part of the
dam structure. With vertical units the turbines are always
located in a basement, the thrust bearing being suppx)rted on an
intermediate floor below the main floor, imless suspension bear-
ings are used, these being mounted on top of the upper generator
bearing bracket.
Govemors. The governors should be located on the generator
room floor close to the units which they are to control, and con-
nected to the operating cylinders on the turbines directly
below. The governor oil pumps with their pressure and storage
tanks should also be installed in the basement, and similarly
the oiling system for the turbo-generator units.
Generators. The turbo-generator units are located on the
main floor and are almost always arranged in a line along the long
axis of the station (Fig. 90). They should be spaced far enough
apart so that ample space for passage is provided between them.
Horizontal sets may be installed either at right angles (Fig. 91)
or parallel (Fig. 92) to the long axis, the latter method being
necessary for high heads where impulse wheels are used. The
arrangement of the rest of the equipment, such as the trans-
formers, may also be a determining factor in regard to which
direction the sets should be installed. If one transformer bank,
consisting of single-phase units, is to be installed for each gen-
erator, the space occupied by them may be of such a length that
it would be more economical to install the turbo-generator sets
parallel to the long axis, thus reducing the width of the building.
Exciters. The exciters are, as a rule, installed on the same
floor as the main generators and in the center of the station.
The advantage of such an arrangement is that the exciters will be
located close to the operating switchboard, and the amount of
copper required for the exciter leads is thus a minimum. The
system may readily be sectionaUzed, one exciter serving the
generators located in one-half of the station, and the other the
generators on the opposite side. This does not, of course, refer
to direct-connected exciters or to individual motor-driven exciters,
which are located near their respective generators.
Transfonners. Due to their weight, the step-up transformers
should preferably be located on the main floor. They are gen-
erally installed in isolated compartments in the rear bay, sep-
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ARRANGEMENT OF APPARATUS
177
Fia. 90. — Interior of Generating Station, Cedar Rapids Mfg. and Power
Company. Present Equipment, Ten 10,000 Kv.A. Generators. Ultimate
Eighteen Similar Units.
arated from the generating room by fireproof steel curtains.
These compartments should be suf5ciently large to allow a good
ventilation. A car track is provided on the generator room floor
in front of the transformer compartments whose floors are raised
so that the transformers can be run out on the car and moved to
some convenient place in the station where repairs can be readily
made. For large units it may be necessary to provide a hole in
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178
POWER-HOUSE DESIGN
Fig. 91. — Interior View of Generating Station, Connecticut Power Company,
Falls River Development.
the floor above the repair room so as to enable the transformer
core to be lifted out of the tank, or a pit may be provided into
which the transformer may be lowered so that suflieient head-
room is obtained for lifting out the core. Sometimes the repair
room is so situated that the main crane cannot be utilized for
dismantling the units. In such a case a chainfall supix)rted from
a heavy I-beam in the floor above may be provided. This, how-
ever, as a rule, only refers to smaller plants.
The oil tanks should be located in the basement, and par-
ticular care should be taken to avoid any fire risk. For this
reason it is advisable to install the tanks in separate enclosed
compartments and in certain cases these have been filled with
sand. Their location should also be such that in case of fire the
oil can readily be drained in the tailrace.
Current Limiting Reactors. As these are inserted either
between the low-tension bus sections or in the low-tension trans-
former leads, their location is in the low-tension switchroom, close
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ARRANGEMENT OF APPARATUS
179
Fig. 92. — Interior View, Big Creek Development, Pacific Light and Power
Company. 17,500 Kv.A. Generators.
to the apparatus which they are to protect. It is advisable to
enclose them in compartments, like the transformers, and pro-
vision should be made so that they can be securely anchored.
They should be installed at a distance of approximately half their
diameter from any iron or steel structure so as to prevent any
heating of this and consequently increased losses.
Switchboards. The different pieces of apparatus comprising
the switching equipment are distributed on the various floors
in the switch section of the station, each story being partitioned
to suit the various purposes. The operating room with the con-
trol switchboard is generally located on the second floor and in
such a position that the operator may have an unobstructed view
of the station and be able to readily communicate with the tur-
bine operators. A balcony, somewhat overhanging the generator
room in front of the switchboard, is often provided, or the operat-
ing room is built with a curved front wall extending out over
the generator room.
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180
POWER-HOUSE DESIGN
1 rmBtoilMlon LioM
No. 00 Copper Wire ^
Horn Osptv
Fia. 93. — Power-house Arrangement. Alabama Traction, Light and Power
Company. Lock No. 12 Development.
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ARRANGEMENT OF APr.^^^ATUS
181
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182
lO^ER-HOUSE DESIGN
Fig. 94a. — Floor Plan of Big Creek Power-house. Pacific Light and Power
Company. (For crossHsection see Fig. 94.)
Fig. 95. — Typical Hydro-Electric Power-house Arrangement. Cross-Section.
(For floor plan see Fig. 95a.)
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ARRANGEMENT OF APPARATUS
183
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184
POWER-HOUSE DESIGN
Fig. 96. — Sectional View of Hydro-Electric Power-house Arrangement with
Limited Space. (For floor plans see Fig. 96a.)
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ARRANGEMENT OF APPARATUS
185
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POWER-HOUSE DESIGN
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ARRANGEMENT OF APPARATUS
187
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188
POWER-HOUSE DESIGN
Fig. 98. — Sectional View of Power-house Arrangement. Mexican Northern
Power Company. (For floor plan see Fig. 98a.)
Fig. 99. — Sectional View of Power-house Arrangement. ^ Montana Power
Company, Rainbow Falls Development. (For floor plan see Fig. 99a.)
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ARRANGEMENT OF APPARATUS
189
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POWER-HOUSE DESIGN
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ARRANGEMENT OF APPARATUS
191
Fig. 101. — Power-house Arrangement, Georgia Railway and Power Com-
pany. Tallulah Falls, Georgia.
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192 POWER-HOUSE DESIGN
The switchboard containing the switches, etc., for the exciters
and other station auxiliaries, should be located on the main floor
at some convenient point, usually below the control-board gallery.
Oil Circuit Breakers. The low-tension oil circuit breakers are
generally of the enclosed type and, together with the low-tension
busbars, are located in compartments on the main floor back of
the transformer compartments. The switches themselves should
preferably be set in parallel rows and opposite the generator and
transformer bank which they control, so as to call for as short a
connection as possible and in order that these connections may be
of equal length. The high-tension oil switches and busbars, and
also as a rule the lightning arrester tanks, are installed on the
floor above.
Lightning Arresters. The aluminum arrester is now generally
used in all high-voltage stations. Both the arrester tanks and the
associated horn gaps may be located within the building, or the
horn gaps may be placed outside and the tanks inside, or both may
be placed outside, provided there is no danger of the electrolyte
freezing. Standard equipments of 27,000 volts and below are
usually designed as complete units to be installed inside the
station, whereas for those above 27,000 volts the horn gaps should
preferably be installed outside the station, although the tanks
may be inside. There is, however, a growing tendency to in-
stall the entire lightning arrester equipment outdoors for these
higher voltages.
The arrester should naturally be placed close to the line en-
trances, and the location should also be such that the path for the
discharge from the line conductors to the arresters and ground
will be as straight as possible. When installed out of doors, it
may be placed on the roof of the building or on a separate struc-
t\u« at the side of the building.
A number of modern station layouts illustrating some of the
nimierous manners in which the apparatus may be arranged are
shown in Figs. 93 and 101.
Outdoor Apparatus. With the introduction and successful
operation of the outdoor sub-station, this method of installing at
least part of the generating station apparatus outdoors should be
given careful consideration. A large installation of this kind is
that of the Utah Light and Power Company, where only the
generating and exciter units and the low-tension switching equip-
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TRANSPORTATION AND ERECTION
193
ment is located indoors, while the transformers, high-voltage
switches and lightning arresters are located outdoors.
A still more revolutionary power-house design has been sug-
gested by Mr. R. J. McClelland.^ As seen from Fig. 102, the
Fig. 102.— Perspective of 50,000 Kv.A. Outdoor-Type Generating Station.
plan proposes to put the generators and transformers, as well as
the high-tension equipment outdoors, while the exciters and the
more delicate control equipment are put under cover, where pro-
vision is also made for the repair shop.
8. TRANSPORTATION AND ERECTION
Transportation. The transportation of such large machines
as are generally involved in hydro-electric power stations requires
a careful consideration of the limitations imposed by the rail-
roads or carriers. It is furthermore evident that these points
must be considered at the time when the machines are selected
or designed.
The shipping limitations are the clearances (height and width)
and the weight. The former are governed by tunnels, bridges,
.} Electr. World, Sept. 25, 1916.
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194 POWER-HOUSE DESIGN
platforms, etc., and the latter by the carrying capacity of the
bridges as well as the cars. Both vary for different roads and
even divisions or sections of the same road, and in many instances
considerable advantages may be gained by detoming. For
example, it may be found that the extra expense of dividing cer-
tain parts of a machine in sections may be so high that a consider-
able saving may be made by detouring the shipment over a
route whose limitations are such that the parts can be built and
shipped as one piece, even if the extra distance were quite great.
Special cars may occasionally be obtained which will facilitate
the shipments of large capacity. These may be provided with
pits in which part of the machines may be recessed, thus decreasing
the over-all height, or they may be of extra large carrying capacity.
Unloading. The question of imloading and transporting
material and machine parts from the nearest point on the railroad
should have careful consideration early in the design work. The
dimensions of the largest and the weights of the heaviest pieces
should be obtained from all companies interested. Also, one
should know how these pieces will be boxed and shipped.
It is always preferable to deliver the machinery in the cars
under the station crane. Unfortunately this is often impossible
or impracticable on account of the expense involved. Local con-
ditions, however, usually determine the best arrangement for each
installation. In each case careful consideration should be given
to the job as a whole, and to all the material which must come in.
Steel cranes, water wheels, generators, transformers, switch-
board equipment, cable, piping, etc., must all be handled.
A carefully designed erection equipment, with the job as a
whole in mind, will effect material savings, as various contractors
will either pay for the use of this equipment or make correspond-
ing reductions in the total price.
In difficult country, or far from the railroads, it may be nec-
essary to arrange with the various manufactm^rs for shipment
partially, or totally, knocked down. The increased price should,
in such a case, be balanced against the transportation costs.
Car ferries, inclined railways with car (Fig. 103), skidwa3rs or
heavy trucking equipment, whatever is decided on, had best
remain under the direct supervision of the resident engineer or
general superintendent, who can determine the best schedule for
handling all of the material.
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TRANSPORTATION AND ERECTION
195
Fig. 103. — Inclined Railway with Special Car.
Apparatus Storage. In many cases material must be delivered
at certain times before it is needed, i.e., during the summer navi-
gation, before the rainy season, while the ground is frozen, etc.
The question of storage, therefore, needs careful consideration,
as there usually is insuflScient room in the power-house, espe-
cially before the building is completed.
The castings and rough machine parts may be stored in the
open. A derrick for unloading and reloading will answer on small
jobs. On large installations it may prove advantageous to install
one of the main cranes or a forebay crane on a temporary track
supported on timber framework over a skidway. Finished parts
must be protected from the weather, fittings and small parts from
sneak thieves.
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196 POWER-HOUSE DESIGN
Electrical apparatus must be stored in a dry place and kept
above the freezing-point. The best arrangement is an electric
heater which is large enough to keep the storage building above
freezing and arranged so that the temperature will alwajrs be
higher than that outside. Great care should be taken to prevent
fires. In the majority of cases a responsible watchman on duty
at all times is the best insurance against fire and thieves.
Schedule of Erection. A careful schedule of the erection
work should be made to insure rapid, efficient work and prevent
congestion. At least part of the building steel and the crane
should be erected before any of the heavy machine parts are
delivered. The delivery of water wheel parts should be arranged
for in the order required and with sufficient time allowance to
permit of the assembly work keeping step with the wheel pit
construction.
On large installations space and equipment must be provided
for the necessary assembly of the machine parts before they are
pl0,ced in their final position. Any convenient open space under
the crane, and centrally located in regard to the final location will
do for the wheel parts.
The generators must be protected from the weather and from
the dirt, smoke and cement dust usually present during the build-
ing construction. In the case of large generators it is often
necessary to assemble the punchings and wind the armatures on
the groimd. This is best handled in a temporary house, under a
crane. The roof can be made in sections, with eyebolts, to per-
mit easy removal with the crane and the handling of the armature
sections. This temporary building will protect the machines from
dirt, moisture and mechanical injury. The winders will also do
more and better work when protected from the noise, confusion
and dirt of the power-house imder construction.
In most cases the coils must be warmed before using. Where
this is necessary, convenient heating ovens should be made part
of this temporary house. These ovens should contain wooden
racks for holding the coils, and steam coils or electric heaters
under the racks for supplying the heat. In general the ovens
should range from 150° F. to 200° F. and should be large enough
to permit of coils being heated several hours. A little care in
arranging the ovens for the ready placing of cold and removing of
hot coils will affect materially the speed and costs of the winding
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TRANSPORTATION AND ERECTION 197
work. Some very large coils must be heated internally with
current. Direct current is best for this piu-pose. Usually one of
the exciter sets will be of the proper capacity; failing this it may
be necessary to secure an electrolytic generator of the proper
capacity and drive this by motor or engine. Current is also
needed for heating the coils in the split where the armatures are
shipped in sections.
Crane Service. This is usually the cause of considerable
friction between the various erectors and oftentimes one man will
tie up the crane unnecessarily simply to prevent some other gang
from using it, although this action is delaying the job as a whole.
The general superintendent, or resident engineer, should
allot the crane without fear of favor, considering the progress of
the work as a whole, or else allot it to the various gangs for stated
periods. In some cases the scheme of allowing the wheel erector
the crane mornings and the generator erector afternoons has
worked well. Both men can then plan their work ahead and avoid
delays.
Protective Features. All electrical apparatus and finely
finished parts of all machines must be protected from injiuy by
water, dirt and falling material during the erection and imtil the
power-house is roofed and glazed. In most cases a liberal supply
of tarpaulins will answer, although some cases warrant a tem-
porary shelter of lumber and roofing paper.
Some fire-fighting equipment should be installed before start-
ing the erection. Trash, excelsior, packing cases and skidding
should be cleaned out promptly, as the fire danger is great under
the best conditions. Competent watchmen should be in charge
whenever the erectors are not working, to guard against fire,
thieves and malicious mischief. This last is by no means a negli-
gible item, as every large installation sooner or later shows dam-
age, or attempted damage, of this character.
It is unsafe and almost foolhardy to start any machine while
the general construction is going on without a thorough inspection
just before turning over. There are numberless cases where these
inspections have brought to light bolts, tools, rocks and miscella-
neous metal that had no excuse for being anywhere near the
machine. These pieces are always in the air gap or at some
adjacent point where the motion of the magnetic field will draw
them into the air gap.
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198 POWER-HOUSE DESIGN
Cooperation. A conference of all interested parties should be
arranged before starting the erection, and the various steps of
the erection discussed and settled. This is especially important
in the wheel and generator erection as the successful operation
depends almost entirely on the careful line-up of these units.
Arrangements should be made at this meeting for checking up the
line-up of the various parts, as this is nearly always a loophole
for future discussion.
In case of trouble there is always the tendency to place the
blame on the other fellow's work. This can be absolutely avoided
by having ai] work checked by the wheel erector, the generator
erector and the resident engineer or his authorized representative
and all three signing a statement, in triplicate, each party keeping
his copy. This should read something as follows: " We agree
that unit No. is on the longitudinal center line within
mils. The cross center line within mils. On the proper
elevation within mils, and is level within mils."
Where a two-piece shaft is used insert a clause, " The water
wheel coupling is true within mils, the rim is true within
mils. The generator coupling face is true within mils, the
rim within mils." Where it is impossible to test the coup-
lings on the ground this test can be made at the factories and a
statement furnished. These statements should be called for in
placing the orders for the apparatus.
4. STARTING UP
General Precautions. Before starting the machines for the
first time they should be carefully inspx3cted and guarded to pre-
vent damage from tools or other foreign material being carelessly
or naaliciously left where they will cause damage. The machines
should be blown out with compressed air to remove dust and dirt.
The bearings should be flushed with kerosene or oil, and when
self-lubricated, filled with clean oil of- the grade reconmiended by
the machine manufacturers.
If the station is equipped with a central oiling system, all the
piping should be flushed with oil and the oil carefully filtered
before it is fed to the bearings. A temporary by-pass from the
feed pipe to the returns at the generator will be of great assistance
in cleaning and testing the oiling system. All piping should be
examined and tested for leaks.
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STARTING UP 199
The electrical connections should be carefully inspected by
men of known responsibility. Loose bolted contacts, oil switches
with no oil, or insufficient oil in the pots, dinner pails stored on
top of the oil pots, or in the bus compartment are common sources
of troubles.
After the machines are ready for operation the switchboard
instruments must be looked over and any necessary changes made
in the wiring. The synchronizing devices must be checked very
carefully. The majority of them are single phase and it often
happ>ens that mistakes in connections cause incorrect indication
on the meter. DifiFerent phases on the two machines may be con-
nected to the synchronism indicator or the phase rotation of the
two machines may be different. The phase rotation must be
checked either by potential transformers and lamps connected
across a machine switch on all three phases at once, or a small
induction motor may be run in turn on all the generators. When
a motor is available to check the phase rotation, the synchronism
indicator can be checked single phase with a potential transformer
and lamps.
Drying Out Exciters and generators will need more or less
drying out, depending on the amount of moisture they have
absorbed. It is assumed that they have been protected from rain
and leaking water from concrete forms. The only other way
moisture can get into the machines is by sweating or condensa-
tion, due to the machines being colder than the surrounding air.
This condition can be largely, if not altogether, avoided, by keeping
the p)Ower-house at an even temperature. Where heating the
whole building is impossible, and the humidity is high, the machines
may be enclosed in a temporary shelter with steam or electric
radiators. In winter weather the machines should be kept above
the freezing-point. In most cases it is, however, impossible to
prevent some condensation arid some drying is usually necessary.
The exciters should, of course, have the first attention. If
possible they should be started up and run for several dajrs with-
out'field. The windage will then assist materially in drying and a
plumber's torch or stove can be placed under the commutator.
Care should be used, however, to prevent overheating. The
temperature should not get higher than 60° C.
Where it is impossible to operate the exciter for any length
of time before starting, the preliminary drjdng can be accom-
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200 POWER-HOUSE DESIGN
pliflhed by hot air. This air can be forced through the exciter by
a blower, or boxing and barriers arranged to cause the hot air to
circulate through the machine by natural draft. This hot air
may be obtained from a steam radiator, a hot-air furnace, electric
heater or a bank of incandescent lamps. In any case the air
should not be higher than 80^ C. When a blower is used a cheese-
cloth screen over wire mesh is advisable on the blower intake to
reduce the amount of dust blown into the windings. The exciter
may then be brought slowly up to voltage as soon as the insulation
to ground tests satisfactorily.
The large A.C. generators should be brought slowly up to
speed, and a short-circuit heat run put on as soon as the bearings
are in satisfactory condition. This short-circuit current should
be the full load current only on maximum rated machines. Ma-
chines with an overload guarantee may be run at the overload
current. The short-circuit run should be continued until the
proper insulation resistance is reached. It is advisable, however,
to run twenty-four hours on short circuit, even when the insula-
tion tests satisfactorily.
After the short-circuit run, the machine should be brought up
to normal voltage and run for several hoiurs before going on the
load. This is to heat the iron thoroughly. On very large gen-
erators it is advisable to continue the drying for twenty-four hours
as follows: Two hours 10 per cent over voltage, then two hours
full load current on short circuit, the drying continuing by alter-
nating open and short circuit every two hours.
For transformer drjdng see section on " Transformers."
Insulation Resistance. Insulation resistance may be obtained
by the following method when a megger or bridge is not available:
Connect one side of a direct-current source of power to the
windings to be tested; connect the other side of the direct-current
circuit to a portable voltmeter and then read the voltage when the
free side of the meter is connected to the other side of the circuit
where it is attached to the windings. Call this reading V. Then
connect to the frame of the machine, being careful to get a good
contact; call this reading Fi. Then
where i2=the cold resistance of the insulation, and Ri^ihe resist-
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STARTING UP 201
anoe of the voltmeter itself, this value usually being given inside
the cover of the instrument.
Before using power from a commercial circuit for testing insu-
lation, testd should be made to determine if the supply circuit is
grounded. One side of the circuit must be free from grounds and
the ungrounded side should be used in series with a voltmeter in
taking resistance readings.
It is impossible to give any hard-and-fast rules regarding the
minirmiTn value of the insulation resistance that will cover all
classes and sizes of machines, and the results must be used with
judgment and common sense. The insulation resistance of a
machine indicates, as a fact, little more than the condition of the
insulation as regards the moisture; and the rate of change of the
resistance as the machine is being dried is, perhaps, the best indi-
cation as to when the drying has been carried far enough.
The following approximate rules have been developed to give
what may be termed a fair value of what the insulation resistance
should be. It must be understood, however, that they are to
be used merely as a guide:
For A.C. generators
p 3,000,000 X Rated volts
^" Rated Kw.
For exciters and D.C. generators
D 300,OOOXRated volts ,--^,,^
Rated current
The above formulae give the insulation resistance in ohms,
but as a rule it is given in megohms, which is equal to the ohms
as obtained above divided by one million.
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CHAPTER VIII
HYDRAULIC EQUIPMENT
1. TURBINES
Modern turbines inay be divided into two classes: Pressure,
reaction or Francis turbines. Pressureless, impulse or Pelton
turbines.
Reaction Turbines. This type is a combined potential and
kinetic energy wheel, or more properly speaking a turbine, since it
admits water all around the ^riphery of the runner and all parts
of the same perform useful work. The water enters the runner
at a speed which is lower than- the spouting velocity, and a pres-
sure head is left to be used for the acceleration of the flow of water
through the nmner.
The water may pass either radially inward or outward or it
may enter the runner radially toward the shaft but leave in an
axial direction, i.e., in a direction parallel with the shaft. In
this case the turbine is of the mixed-flow type, this being most
extensively used in this country.
The runner rotates partly from velocity action and partly
from reaction due to pressmre and consequent acceleration in
buckets. As the draft tube is closed, the nmner is full of water
and practically the total difference in head between head-water
and tail-water is useful.
The speed of a reaction turbine can be varied not only by vari-
ation of the runner diameter but also, and very effectively, by
varying the bucket angle and the angle between the entrance
speed and the peripheral speed. Combining both these means it
is possible to vary the speed of a pressure tiurbine for a given head
and capacity in the ratio 6:1.
Three different designs for reaction turbine runners are shown
in Figs. 104, 105, and 106. The first, Fig. 104, represents a low-
speed runner which would be used for relatively high heads and
relatively small quantities of water. The bucjcet angle j8 is less
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TURBINES
203
Fig. 104. — Low-speed Runner.
j=i
Fig. 105. — Medium-speed Runner.
Flo. 106.— High-speed Runner.
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204 HYDRAULIC EQmPMENT
than 90^ and the angle a of the water leaving the guides is also
small.
Fig. 105 represents a medium-speed runner, the angle P being
approximately 90^ and the angle a larger than in the previous
type.
Fig. 106 represents a high-speed runner for low heads and rel-
atively large quantities of water. It is seen that the angle fi is
larger than 90^ and angle a also considerably larger than before,
thus giving a very high peripheral velocity.
Comparing the above types it is also seen the width of the
buckets varies from a comparatively narrow to a wide size, while,
on the other hand, the shape changes from a forward to a back-
ward curved bucket as the speed increases.
Impulse Turbines. The impulse or tangential turbine is
generally known as the Pelton turbine. It is a kinetic energy
wheel, the water being discharged from one or more nozzles against
a number of buckets attached to the periphery of the runner,
and the momentum of the mass of water in its impulse upon the
runner buckets is, therefore, the main principle utilized in the
energy transformation. When the water leaves the buckets it is
moving at so slow an absolute velocity that practically its entire
energy has been imparted to the runner.
Since usually the number of nozzles is small as compared with
the number of buckets, the latter are in active use only during
piart of a revolution, and hence this type of prime mover is some-
times called a water wheel instead of a turbine. This distinction
seems, however, rather arbitrary, ancl can probably be traced to
an attempt to show that the impulse turbine is derived from an
undershot water wheel. It seems, therefore, better to consider
both types as turbines, since they both really involve the same
principles and action. As a matter of fact, the term water wheel
is loosely applied to all sorts of turbines.
The description of the tangential type of impulse turbine is
given on page 242.
The speed of an impulse turbine of a given diameter is variable
only within very small limits. The speed is practically deter-
mined by the head, and can be varied only by variation of the
runner diameter.
Selection of Turbines. In deciding upon the ntunber, capacity
and speed of the units in a water-power station, the combination
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TURBINES 205
of the tiirbine and the generator must necessarily be considered
together. Besides hydraulic conditions such as the head and its
variations^ storage facilities, etc., and the limitations of the
turbine design, a proper selection is governed by the load factor,
the natiu^ of the load, the reserve capacity, the reliability and
flexibiUty of the service, the cost and operating expenses, etc.
The units should be operated as near full load as possible and new
units should preferably be started as the load increases instead of
utilizing overload capacities. Where sudden overloads of con-
siderable magnitude come on the system for short periods it is,
of course, necessary to have turbine capacity sufficient to care for
them. Single units are never desirable except for multiple-plant
83rstems, in which case the necessary reserve can be obtained from
other stations. For single-plant systems the number of units
should preferably not be less than three or fom*, but above this
the number should be governed by the upper limit in design, con-
sidered both from a technical and economical standpoint. With
a small number of large units the first cost, the maintenance
charge and the necessary floor space is reduced, and the efficiency
is also usually better than for a larger number of smaller units.
The ultimate development may also influence the size, and it may
be found advisable to provide larger units for the initial develop-
ment than would otherwise have been chosen.
In water developments by far the larger majority of installa-
tions are subject to wide variations in the head. In many of
the low-head installations the back water may bring about a
change in head which is l)eyond the capacity of one wheel or
runner to accommodate, and in some cases additional runners
must be mounted on the same shaft and cut into service at times
of low head. In many of the large developments this change in
head is the limiting feature in design of the water wheel as related
to the generator capacity, for in all electrical work it is essential
that the speed of the generator be kept constant.
It is very generally known that the peripheral speed of a
water wheel bears a certain ratio to the spouting velocity of the
water under any given head, this ratio as a percentage varying
between 40 and 50 per cent for impulse turbines and between 60
and 80 per cent for reaction turbines. Hence the percentage
variation from, say, a mean of 60 per cent is only 33| above and
33| below for any given head. But the diameter, and conse-
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206 HYDRAULIC EQUIPMENT
quently the R.P.M. corresponding to the peripheral speed may
.vary widely according to type, make, and number of runners or
jets.
Specific Speed. Turbine runners of different makes are best
compared on the basis of their specific speeds, this being the
nmnber of revolutions per minute at the point of maximum
efficiency that a homologous or geometrically similar wheel would
give if it were to deUver 1 horse-power under unit head, usually
1 foot. With the same specific speeds the different designs vary
comparatively little, it being the aim of manufacturers to produce
a line of turbines covering all specific speeds with the highest effi-
ciencies possible at each specific speed, and turbines for use under
low heads should have as high a specific speed as possible with-
out sacrificing efficiency or other desirable characteristics. After
a certain design has been adopted for a certain specific speed, a
full series of such tiurbines can be laid out, all of identical design
with the original, each being an enlargement or reduction of
another.
If
Q = quantity of water;
A=head;
D = diameter of runner;
then for any ^.ven tmrbine:
Q varies as h^^^;
H.P varies as QXh or A'^*;
R.P.M. varies as h^^\
Hence, the horse-power delivered under 1 foot-head will be
fi^i = -TS7r*^d the speed will be R.P.M.i = — ^tt^ — '
If now the head is kept constant and it is assumed that all
dimensions of the runner are reduced proportionally, then the
dimensions will all remain in fixed ratio to the diameter, Z>, and
all areas of passages through the runner will vary in proportion to
D^; the velocities remaining constant on account of the constant
head.
Therefore, for tm-bines of homologous or geometrically similar
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TURBINES 207
design, but built in various sizes and operated under the same
head:
Q varies as D^;
H.P. varies as D^;
R.P.M. varies as yr.
Hence, the speeds -of a set of similar runners, operating under
the same head, will vary inversely as the square roots of their
horse-powers, and if one runner gives a speed of R.P.M. with a
power H.P., it follows that the speed of a 1 H.P. turbine will be
R.P.M.xVH.P. Thus, if the head be 1 foot, the speed of the
1 H.P. runner or its specific speed, iV„ will be
^, _R.P.M.^ /H.R.
^'- h'/2 ^\ h^/t '
or
Vhp
.V.=R.P.M.X-^.
If it is desired to obtain the specific speed according to the metric
system with English units (Ft. and H.P.) used in the formula, mul-
tiply the values obtained from the above formula by 4.45. In
transferring we have 1 foot equal to ^-^ meter and 1 English H.P.
equal to 0.986 metric H.P. Thus
A6/4xV0.986 /iV4
The value A*/* may readily be figured out as follows:
The diagram in Fig. 107 supplies a convenient graphic method
of deducing the specific speed of a runner from any given set of
conditions without the use of the formula.
In figuring the specific speed of a turbine with more than one
runner or nozzle, the H.P. used should, of course, be the output
from each runner or nozzle. Furthermore, as the above formula
applies to single-runner turbines, it follows that in the case of a
turbine of the same capacity having n runners of ||ie same spe-
cific speed, it is seen that the R.P.M. would be Vn times the
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208
HYDRAULIC EQUIPMENT
R.P.M. of the single-runner turbine. It is also readily seen that
for a given value of R.P.M. and A, the H.P. output is propor-
Bpeciflc Speed
'-, \\
^ SPECIFIC BPEtD CHWIT
Itirii lIiH Fi-lnt LBflhntrt " "■
lUcd-JlfLH H.P.H.*1T4b
Em ^^>^ xf^*!^
Fig. 107.— Specific Speed Chart.
(By Courtesy of Wellman-Seaver-Morgan Company).
tional to the square of the specific speed, and also that for a given
head and H.P. ti|e R.P.M. of a turbine is proportional to the spe-
cific speed.
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TURBINES
209
By comparison of the specific speeds it is possible to judge the
characteristics of water-wheel runners without considering their
actual speed; power or head. Other things being equal, a high
specific speed means a high actual speed, and a low specific speed,
a low actual speed in revolutions per minute. With low-hiead
developments the speed must be selected as high as is good en-
gineering practice in order to keep down the weight and conse-
quently the cost of the generators. With very high heads it is
mostly a question of keeping the speed reasonably low so as to
avoid the use of costly high-speed generators. The limit of high
speed for low-head developments is fixed by the progress of the art
of designing high-speed runners, and the limit of low speeds under
high heads is fixed by the risks involved in designing runners for
operation with very low coeflBicient of specific speed.
High speed imder low heads also means large discharge capacity
per unit diameter, resultuig in a large power capacity, while low
speeds under high heads mean a small discharge capacity per unit
diameter resulting in a small width of runner.
Reaction turbines have been built for specific speeds as low as 7,
but 12 is probably as low as should be used in normal practice.
Starting at this speed, the efficiency will increase as the specific
speed approaches more normal values, the efficiency reaching
the highest values between specific speeds of 25 and 75. Above 90
it drops again at a rapidly increasing rate, and above 100 specific
speed results are much more problematic, at least for the present,
but efficiencies over 90 per cent have been obtained with specific
speeds all the way from 25 to 90.
Pfau iQ his paper before the International Elngineering Con-
gress in San Francisco classifies tentatively Francis reaction tur-
bines as follows, the types being claimed to operate successfully
under the heads given.
TABLE XXXVni
Type.
Specific Speed.
Head. Feet.
A
Very low, 20-25
750
B
Low, 25-30
400
C
Medium low, 30-40
175
D
Medium high, 40-60
90
B
High, 60-80
40
P
Very high, 80-100
20
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210 HYDRAULIC EQUIPMENT
For impulse turbines of the Pelton type, specific speeds down
to very low values may be obtained with good results. The
highest efficiencies may perhaps be obtained with specific speeds
varying from 1 to 4, and will then be increasingly reduced as the
speed is increased up to about 6| or 7, which might be taken as the
extreme limit, the figures appl3dng to single-nozzle wheels. The
maximum obtainable efficiencies with an impulse wheel may be
taken as between 85 and 89 per cent, these being figures to the
center line of the nozzle. If two or more nozzles are used on the
same wheel, a reduction of several per cent will result, and of course
the power will be increased in proportion to the number of nozzles.
Where, therefore, the specific speed characteristics exceed the
above values, multi-runner turbines, more than one nozzle or
smaller units must be used.
There is no hard and fast rule for the choice of a reaction tur-
bine or an impulse turbine, the field of their respective usefulness
overlapping to a considerable degree. The thing which limits the
specific speed of reaction turbines under high heads is the risk of
corrosion of the buckets, while the reason for the non-use of
impulse turbines imder very low heads is the lack of economy
due to large dimensions and low speed required. The reaction
type of turbine is generally used for heads from 10 to 600 feet
and the impulse type between 300 and 3000 feet. The proper
system seems, therefore, to be very well fixed for low or high
heads, while for the intermediate range between about 300 and 600
feet, the proper system must be determined by referring to the
specific speed characteristics.
Assume, for example, an installation having a head of 1900
feet and where the generators would require turbines of 10,000
H.P. capacity running at 375 R.P.M. What type of wheel
should be installed?
_ v^io;^_
and, consequently, an impulse turbine should be selected.
On the other hand, with a 10,000 H.P. wheel to operate at
57.7 R.P.M. under a 32-foot head, we get
Ar.=57.7X^=76,
and a reaction turbine must be used.
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TURBINES 211
In selecting a type of wheel, the number of runners or nozzles,
their capacity and speed must be chosen with a view of obtaining
not only the highest eflSiciency, but also the most economical com-
bination of the prime mover and generator. For example, a
wheel is to be operated under a head of 400 feet and develop 1500
H.P. How many nozzles should it have and at what speed may it
operate? Assume that a specific speed of 4 will give a good efS-
ciency for the wheel, then the actual speed of the imit will be
R.P.M.=i><S=185.
Vl500
This speed, however, may be entirely too low for the generator,
and, by providing two nozzles, each supplying 750 H.P. the
speed would be increased to
R.P.M. = 186XV2 = 260.
and with four nozzles
R.P.M. = 186XV4 = 370.
Let us also see what the result would be if we tried to apply a
reaction turbine running at 720 R.P.M. The specific speed would
then be
JV.=720X^=16.
and, consequently, this type would undoubtedly be the most
advantageous to use for our case.
The efficiencies, especially at partial load, are related to the
specific speed, the curves of high specific speed runners being more
pointed than with the low specific speed type, thus allowing a
narrower margin for operation under the best conditions. This
is clearly shown in the curves in Fig. 108.
The maximum full-load capacity of a turbine is that point
beyond which the output decreases with an increase in gat« open-
ing. The margin between the point of maximum efficiency and of
maximimi capacity depends upon the specific speed of the runner,
and is smaller the higher the specific speed. This is illustrated
in Fig. 108, which shows that as the specific speed is increased the
point at which maximum efficiency occurs approaches nearer to
the power delivered at full gate opening. The specific speed may
thus be increased to such an extent that the point of maximum
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212
HYDRAULIC EQUIPMENT
efficiency and maximum output coincide. With low heads and
high specific speeds it is, therefore, desirable to operate wheels
near their point of maximum output, and to obtain the best re-
sults the generator should be designed with consideration to this
point.
Referring again to the curves in Fig. 108, it will be noted that
the full-load capacity occiuB at about 6 per cent above normal or
rated full load in all three cases. This is in accordance with the
general practice, the margin being allowed for governing. It is
also noted that for ciures B and C the efficiency is falling off very
rapidly at 6 per cent overload, and that should the gate be opened
still further the output would reduce instead of increase. If,
I"
A 80
-=
^
r
^
--
=:=:
r::
==
"^
^
?^
■
/
/
A- Specific Speed -25 Head-UO Ft.
B- " -80 •« - « "
C- " " -M ♦' - 90 "
/
/
/
V
0
//
/
J
7
L
5 10 16 20 tf
80 35 40 45 50 65 60 66 WTO 80 86
Hone Power in Per cent of Normal Load
90 96 100 106 U(
Fig. 108. — Performance Curves of Several Turbines for Various Heads and
Specific Speeds as Shown.
with low specific speed wheels, as represented by Curve A, the
gates were still further opened, the power would continue to
increase to some extent.
The point of maximum efficiency for wheels represented by
curve A occmB at about 90 per cent of normal full load, in the case
of B at 93.5 per cent, while, in the case of C, the maximum effi-
ciency occurs just at the point of normal or rated full load. Thus,
as stated before, the power at which the maximum efficiency occurs
approaches nearer to full load as the specific speed increases.
For wheels of low or moderate specific speed, as represented by
curve A, the efficiency remains very high over a very large range
in power, while for wheels of high specific speed, curve C, the
efficiency falls off rapidly as the power is reduced below the normal
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TURBINES 213
full load. For this reason it is desirable to run low-head wheels
under practically full load conditions. With high-head wheels
this is not so important, as the efficiency is still high at partial
loads. With wheels as represented by curve C, it is also neces-
sary to allow some margin above the normal full load for govern-
ing, as it IB desirable to operate the turbine at its point of max-
imum efficiency. With high-head wheels, curve A, such a margin
need not be allowed.
The curves plotted in Fig. 108 represent operating conditions
under constant head. This, however, is not always realized,
especiaUy in low-head plants where floods and dry seasons some-
times cause quite a variation in the head, and this has, as pre-
viously mentioned, quite a bearing on the selection of the water
wheel, and should, therefore, be given careful consideration.
If the speed of the unit could be allowed to vary at all times the
square root of the ratio of the heads, the shape of the performance
curve for any head other than normal would be the same as that
secured at normal head, but the output would vary as the J
power of the ratio of the heads. In the case of wheels driving
alternating-current generators a speed variation is not permissible
and the speed must be kept constant irrespective of any varia-
tion in head which may occur, and this will still further lower the
output due to the reduced efficiency when operating at the best
head and speed.
In Fig. 109 is plotted a set of curves illustrating the effect of
a varying head. A 10,000-H.P. tiu*bine is assumed to operate
normally under a 32-foot head, the speed to be constant for a
range of heads from 26 to 38 feet. As the head goes up to 38 feet
the shape of the curve approaches more closely curve B in Fig. 108,
while, when the head falls to 26 feet, the speed being constant, it
approaches more closely to curve C In other words, when oper-
ating under a 38-foot head, the speed is lower than the best speed
for the runner under that head, while, when operating under the
2&-foot head, the speed of the wheel is higher than the best speed.
Under 38-foot head the point of maximum efficiency is, further-
more, considerably below the normal full load at that head, while,
under 26-foot head, the power at which maximum efficiency occurs
is the actual full load, illustrating the points discussed above in
reference to the relation of the power at which maximum efficiency
occurs and the normal full-load power for various specific speeds.
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214
HYDRAULIC EQUIPMENT
Let us assume that a selection of a wheel is to be made for an
installation, and that performance curves are desired, showing the
expected efficiency for various loads and speeds. Curves A, B, and
C, in Fig. 108 may each represent a possible curve, dependent
upon the revolutions selected for the turbine in question, the rev-
olutions being directly proportional to the specific speeds, and
they will illustrate the manner in which the efficiencies at partial
gate openings will fall off in any one case, depending upon the
actual revolutions per minute selected for the design of the wheel.
Qrt
~
g
^
g
f
-
flO
%
n
%
S
1
"n
-«v
s
1"
Sj An
tf
^
d
%
i
i
1
1
1
%
^
P
«0
dS
a
Iff
IS
h
s
y
^
1
•3
•a
1
1
^
•j
^
W
^
n
1
1
1
n
iS
?:
^30
—
J
M
f
^20
^
10
jf
•
/]
5 10Ua0253035 40 45 60fi56065T0 7580869095 100 106 UO 115120 IS ISO IS
Hone Power In Per cent of Normal Full Load at Somial Head
Fig. 109. — 10,000 Horse-power Turbine-curves Showing Efficiency and Power
for Constant Speed and a Normal Head of 32 Feet for Various Heads
as Shown.
They will also give an idea as to the margin between the normal
full load and the power at which the points of maximum efficiency
will occur. In the selection of a speed for any installation, there-
fore, aside from the cost of the generators, the question of the
wheel efficiencies at partial gate openings has a considerable
bearing. Where a unit is likely to operate under a very wide
range in power, it would be advisable to select a wheel repre-
sented by curve A, giving a high efficiency for a considerable
range in power.
Actual Speed. For speeds used in a number of hydro-electric
developments and corresponding heads and capacities, see table
on page 316.
Characteristic Curves. For studying the action of a turbine
under different conditions of operation, the characteristic curves,
as shown in Figs. 110, 111, and 112, are extensively used, and
from these curves it can at a glance be seen at what speed the
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Fig. 110.
^.Efficiency Curves
of an
I^. Morris Ranner
1.0 i.i 1.2 1.3 1.4
.2 .S .4
Fig. 111.
.6 .1 .8 .9
^•H.Pi. Ouryes
of au
I.P. Morris Ranner
1.0 1.1 1.2 1.3 1.4
Fig. 112.
.6 .7 .8 .9 1.0 1.1 1.2 lot 1.4
Eqaal— Efficiency
ContoarCnrree
of an
LP. Morris Ronnex
215
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216 HYDRAULIC EQUIPMENT
turbine should be run for the best efficiency at any gate open-
ing.
To show how the curves are constructed a typical example is
given, based on actual tests given in Table XXXIX. The values of
the abscissse in the curves represent 0, the coefficient of peripheral
velocity, although sometimes values of HPi, are used for this
piupose. These two quantities are, however, directly propor-
tional, so that the change merely affects the abscissa scale of the
curves.
From the report, the values of head, revolutions per minute,
horse-power and efficiency are taken from the corresponding col-
umns for the various runs at each gate. From these are com-
puted the corresponding values of 4>, which is equal to
DXR.P.M.
0 =
Q0X^2gh'
in which D is the nominal diameter of the runner in feet, in the
case taken 25 inches or 2.0833 feet, and h is the head
in feet. The corresponding values of HPi or the horse-power
reduced to 1 foot head are also computed by dividing the
given horse-power by the three-halves power of the head,
thus
The result represents the power which the given runner would
develop if operated at the corresponding speed, that is, at the same
value of 4> under a head of 1 foot instead of the head used in the
test. The 0-efficiency and i^-HPi curves are now plotted for
each gate opening. Figs. 110 and 111.
In order to construct the curves of equal efficiency, Fig. 112,
the <t>-HPi diagram is selected and points having the same
efficiency on the ciures for different gate openings are joined in a
curve. In order to keep the diagrams clear the <t>-HPi curves
have been repeated in dotted lines on a separate diagram.
To illustrate the construction of one of the equal efficiency
contours for instance, take the line for 86 per cent efficiency.
Referring to the 0-efficiency diagram, a horizontal line repre-
senting the efficiency selected will intersect the curve for 2.5 gate
at 0=0.64, and will again intersect the same gate at 0=0.725.
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217
TABLE XXXIX
TE8TING FlUMB OF THE HOLTOKE WaTEB PoWEB Co., HoLTOEE, MaSS.
Report of tests of a 25-inch Right-hand I.P. Morris Company turbine wheel.
h
1
«a
II
5^
1^
© 1^
11
1^
11
1^
if
Z
O
&
W
Q
cr
(U
s
55
4.00
0.917
17.74
3
182.33
97.79
146.49
74.62
54
4.00
0.924
17.72
3
200.33
98.49
161.27
76.60
53
4.00
0.939
17.71
226.75
99.99
167.62
78.61
56
4.00
0.948
17.70
241.25
100.92
160.30
79.31
52
4.00
0.961
17.66
266.25
102.21
162.63
79.68
51
4.00
0.984
17.52
275.00
104.20
166.12
80.42
49
4.00
0.999
17.53
295.00
106.86
169.29
80.63
50
4.00
1.005
17.51
302.00
106.44
169.66
80.45
48
4.00
1.015
17.48
312.67
107.40
169.99
80.02
47
4.00
1.018
17.51
321.76
107.76
166.20
77.38
46
4.00
1.006
17.54
340.76
106.68
144.09
68.05
45
4.00
0.985
17.60
362.60
104.66
109.49
62.58
43
3.50
0.837
17.84
183.76
89.62
140.97
78.01
42
3.50
0.850
17.83
206.33
90.87
149.66
81.58
44
3.50
0.860
17.76
221.60
91.76
163.87
83.44
41
3.50
0.862
17.78
221.76
91.99
164.04
83.23
38
3.50
0.877
17.79
241.50
93.67
160.47
86.20
37
3.50
0.894
17.72
261.60
96.27
166.86
86.83
40
3.50
0.905
17.67
272.80
96.29
168.09
87.31
39
3.50
0.911
17.67
279.76
96.87
168.99
87.25
36
3.50
0.909
17.69
287.76
96.76
166.14
86.26
35
3.50
0.906
17.69
302.26
96.41
166.19
80.42
34
3.50
0.897
17.71
323.00
95.60
136.68
71.37
33
3.50
0.879
17.75
361.60
93.68
106.16
66.42
82
3.10
0.784
17.88
191.20
83.80
138.60
81.65
76
3.10
0.814
17.75
236.76
86.76
164.46
88.65
76
3.10
0.821
17.75
244.80
87.63
166.76
89.26
77
3.10
0.821
17.75
246.80
87.63
167.28
89.67
74
3.10
0.824
17.73
249.76
87.86
168.41
89.82
81
3.10
0.824
17.73
260.00
87.97
168.67
89.69
78
3.10
0.827
17.73
261.00
88.08
158.44
89.67
79
3.10
0.828
17.72
5
262.40
88.19
168.66
89.67
80
3.10
0.827
17.75
4
264.26
88.19
168.96
89.74
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HYDRAULIC EQUIPMENT
TABLE XXXIX— Continued
Tksting Flume of the Holtoke Water Power Co., Holtoke, Mass.
Report of tests of a 25-mch Right-hand I. P. Morris Company turbine wheel.
H
II
roportional Part of
the Full Discharge
of the Wheel in Per
Cent.
1^
5-!
g5i
si
uantity of Water
Discharged by the
Wheel. Cu.ft. per
Sec.
u
i
1^
z
^
P^
»
Q
tf
Ct
£
w
73
3 10
0.S24
17.74
4
266.75
87,86 !
156,30
88.62
72
:i.io
0,823
17.75
4
265,75
87,75
152.60
86 63
71
3.10
0.823
17.76
3
274.00 '
87.75
148,96
84 47
70
3.10
0.S20
17.77
4
187.53
87.53
140.87
80.04
60
3,10
0,820
17,77
4
309.50
87.53
130.87
74,36
6S
3 10
0,817
17.80 '
4
346.25
87.20
104.58
59 54
25
3,00
0.760
17.98
4
181.00
80.31
130.11
79,00
30
3.00
0.776
17.87
4
221.25
83,02
147 01
87,68
23
3.00
0.785
17.83
4
233,25
83.90
150.76
89.07
22
3.00
0.790
17,83
3
239.00
84.44
153.03
89,83
19
3.00
0,791
17,85
4
242.00
84,55
153.48
89.88
21
3,00
0,792
17.83
4
242.50
84.66
153,81
90.05
24
3.00
0.792
17,81
4
243,00
84,56
152 66
89.59
IS
3.00
0.790
17.85
4
249-50
84.44
150.71
88.37
17
3,00
0,788
17.86
4
257.25
84.23
147.63
86.73
16
3,00
0,784
17.86
10
265.10
83.90
144,12
85.00
15
3.00
0.786
17.84
3
293.67
84,01
133,06
78.45
14
3.tK)
0.787
17.84
4
323.25
84.12
117.16
68.99
13
3.rK)
0,780
17. 87
3
361.00
83.46
87.23
51 69
9
2-.50
0.047
18,12
4
169.75
69.69
114 85
SO 37
8
2-50
0.662
18.07
4
197.00
71.24
124.95
85.78
7
2.50
0.668
18.06
3
210,67
71,86
127.26
86.66
12
2.60
0,669
18.03
5
213,20
71.86
128.79
87.85
10
2.50
0,670
18.04
6
217.50
72.06
128.76
87.53
6
2.50
0.666
18.07
5
221.80
71.65
127,28
86,83
5
2.50
0.664
18.07
230,00
71.44
126.04
86.80
4
2.50
0.662
18.07
240,00
71,24
123 23
84.60
3
2.50
0,665
18.05
251,75
71.55
121.66
83.25
2
2.50
0.665
18.07
274.50
71.55
116.07
79.34
1
2.50
0.065
18,05
320,00
71.55
96.65
66.14
11
2.50
0.657
18.10
356.50
70.72
64.60
44,60
66
2.00
0.S3S
18.26
171,50
58.16
98.42
81.90
67
2.00
0,642
18.24
186.25
58,55
102,38
84.72
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TABLE XXXIX'-CwUinued
Testing Flume of the Holyoke Water Power Co., Holtoee, Mass.
Report of tests of a 25 Right-hand I. P. Morris Company turbine wheel.
^1
It
1
|5
Xrtional Part of
Full Discharge
of the Wheel in Per
Cent.
s
i
III
i
s
l^
uantity of Water
Discharged by the
Wheel. Cu.ft. per
Sec
II
4
2
O
^
»
p
OS
cr
Ah
H
65
2.00
0.542
18.25
188.75
58.64
102.62
84.74
64
2.00
0.537
18.28
196.75
58.16
101.02
83.98
63
2.00
0.535
18.29
205.40
57.87
99.26
82.88
62
2.00
0.535
18.29
216.50
57.87
98.09
81.90
61
2.00
0.534
18.40
226.00
57.78
95.56
79.87
60
2.00
0.532
18.31
238.40
57.59
93.61
78.45
59
2.00
0.535
18.31
255.75
57.97
92.69
77.18
58
2.00
0.538
18.32
284.75
58.26
86.00
71.21
57
2.00
0.533
18.33
5
334.40
57.78
60.60
50.57
32
1.25
0.332
18.53
3
142.00
36.18
55.76
73.60
31
1.25
0.332
18.65
3
158.33
36.26
57.39
74.99
30
1.25
0.326
18.66
3
185.00
35.69
55.88
74.15
29
1.25
0.323
18.65
3
215.00
35.29
51.95
69.76
28
1.25
0.318
18.65
3
247.33
34.80
44.82
61.03
27
1.25
0.315
18.65
3
276.33
34.39
33.38
46.00
26
1.25
0.310
18.65
3
302.33
33.83
18.26
25.58
89
4.00
0.915
17.65
4
423.00
97.33
88
3.50
0.842
17.80
4
426.50
89.86
87
3.10
0.751
17.95
3
418.67
80.52
86
3.00
0.720
18.02
4
415.75
77.31
85
2.50
0.604
18.21
4
401.25
65.23
84
2.00
0.482
18.39
4
381.50
32.28
83
1.25
0.305
18.70
4
323.50
33.35
Passing to the 4>-HPi diagram, points are located on the 2.5 gate
curve at the two values of 0 just found. These are two points on
the desired curve. Similar points of intersection of the 86 per
cent efficiency line with the 0-efficiency curves for other gates
are similarly located and the resulting points joined up.
The diagram obtained may be viewed as a contour map of a
moimd or hill, the heights of which in a direction perpendicular
to the paper may be imagined to represent efficiency. If the hill
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HYDRAULIC EQUIPMENT
is imagined to be cut by a plane perpendicular to the paper and
intersecting the paper in an ordinate at any given value of ^,
the resulting intersection would be a performance curve such as
one of those plotted in Fig. 109.
In Fig. 109, of course, the horse-power has been stepped up to
represent a large runner operating under a given head. The
performance curves can be conveniently plotted from the 4^
efficiency and 4^HPi curves by finding the corresponding values
of HPi and efficiency for certain required values of 4> which are
determined by the head and speed in a given installation.
Speed Regulation.^ The most generally used method for
governing the speed of reaction turbines is by means of wicket
gates or guide vanes which change the amount of water suppUed
by simply altering the water passage (see Fig. 113). The vanes
Fia. 113. — Typical Arrangement of Vertical Reaction Turbine, Showing
Relation of Wicket Guide Vanes to Casing and Runner.
rotate about pivots and are fastened to a shifting ring by link
motion, the ring being operated by pressure cylinders, actuated
by the governor. If the velocity of the water is checked too
suddenly dangerous pressures may be set up in the pipe lines and
the speed regulation may be affected. In order to avoid this,
^ See also sections on '' Governors " and " Waterhammer."
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relief valves are often provided, either of the pressure or the
synchronous by-pass type. The former is analagous to the
safety valve on a boiler and does not open until a certain pressure
has been obtained. The latter, however, is operated by the gov-
ernor at the same time as the turbine gates but in opposite direc-
tion, thus affording a by-pass so that there is no reduction in the
flow. To prevent waste of water these by-passes may be slowly
closed by some auxiliary device. It is obvious, however, that
such water-saving reUef valves are inoperative when the load is
thrown on, and, therefore, cannot then assist the speed governor
or prevent siu-ges in the pipe lines caused by the same. For pre-
venting these, siu-ge tanks or suflSicient flywheel effect of the tur-
bine imit must be relied upon.
For the speed regulation of impulse wheels there are three
methods in general use, viz. :
1. Hand-regulated needle nozzle with jet deflector.
2. Needle regulating and deflecting nozzle.
3. Auxiliary relief needle nozzle.
Either of the above involve the use of the characteristic needle
and nozzle tip, a sectional view of which is shown in Fig. 114, the
Fia. 114. — Sectional View of Pelton-Doble Needle Nozzle.
full lines illustrating the position of the needle when the nozzle
is closed and the dotted lines the needle position with jet dis-
charging.
The first sjrstem consists of a nozzle body in which is inserted
a concentric tapered needle as just described. By means of this
needle, which is manually controlled for this tjrpe of nozzle, the
jet area is adjusted intermittently to correspond to either the
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222 HYDRAULIC EQUIPMENT
stream-flow or the maximum anticipated load likely to be carried
within a certain time limit. The automatic speed regulation is
obtained by means of a governor which actuates a deflector,
which is placed in front of the nozzle tip and regulates the speed
by intercepting or deflecting the stream. It is, therefore, obvious
that this system of regulation thus does not permit of any economy
in the water consumption, unless the station attendant frequently
changes the needle adjustment by following closely the load
curve. It is, therefore, mainly intended for plants that are located
on streams where water storage is not feasible, or where other
power plants are located on the same stream, making it necessary
to allow the full flow of the stream to pass the plant; or on those
streams where irrigators' or riparian rights have a prime con-
trol, thus preventing the storage of water. The above holds also
for the second class of control, i.e., deflecting nozzles, as described
in the next paragraph and, of course, also, to a certain extent, to
water-wasting by-pass reUef valves for reaction turbines as pre-
viously described.
The needle-deflecting regulating nozzle, as shown in Fig. 115,
consists of an ordinary needle nozzle which is provided with a
ball-and-6ocket joint, permitting it to be raised or lowered so as
either to direct the full jet into the buckets of the wheel or to par-
tially or entirely direct the jet outside of the path of the buckets
of the wheel.
In both the stationary needle nozzle with the jet deflector and
the needle-regulating deflecting nozzle, the needle is usually oper-
ated by hand control, the needle being set to utilize to full advan-
tage the available supply of water. In plants where either of these
types of nozzles is installed and where there are forebay reservoirs,
economy in the use of water is secured by setting the needle at
different times during the day to cany the maximum load on the
plant, the needle being set to follow the general load curve of the
plant, while the momentary load changes and speed control are
taken care of by the governor either operating the jet deflector or
deflecting the nozzle.
In such plants, where large units are installed, the control of
the needle setting may be by means of an electric motor with
remote control from the switchboard, so that the power plant
operator can, from the switchboard, set the position of the needle
so as to carry any predetermined load that is desired, the needle
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setting being changed from time to time as the general condition
of the load changes. In such plants the overall consumption of
'water approximates, in a series of steps, the load curve on the
mover.
The deflecting nozzle may be equipped with an automatic
Fig. 116. — Combination Needle and Deflecting Nozzle. (Pelton Water
Wheel Company.)
regulating device so that the governor in rejecting the load on a
plant first operates the deflecting means and then brings about a
gradual resetting of the needle and nozzle opening.
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HYDRAULIC EQUIPMENT
The ideal type of nozzle, and the one that insures the most
sensitive speed regulation and highest economy of water consump-
tion is, however, the " axuiliary relief needle nozzle," Kg. 116.
I
I
I
This consists of a main needle nozzle and a synchronous by-pass
in the form of an axuiliary needle nozzle which discharges into the
tailrace. Both nozzles are operated by the power mechanism of
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the speed governor simultaneously, but in opposite directions.
The auxiliary nozzle opens when the power nozzle closes and vice
versa, the volumetric relationship between the two being adjusta-
ble, according to the conditions at the plant. This, in itself, would
prevent any pressure rise in the pipe conduit, but would not
afford any economy in water consumption. In order to save
water, it is necessary to keep the auxiliary relief nozzle closed
during a partial and slow motion of the main needle and also to
have it close at a safe rate of speed after it has been opened. This
Fia. 117. — 10,000 Horse-power Auxiliary Relief Type Nozzle. (Built by
Pelton Water Wheel Company.)
result is accomplished by a cataract cylinder or dashpot which is
inserted in the operating gear of the auxiliary rehef needle.
Fig. 117 illustrates a 10,000-H.P. auxiliary relief tjrpe nozzle
with direct-motion governor. Alongside the wooden scaffolding
is the governor oil-pumping system. To provide pressure oil to
operate the governor piston, this pumping set is operated by a
water wheel arranged with a control so that the wheel and pump
operate only when the level of oil falls below a predetermined
point.
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226 HYDRAULIC EQUIPMENT
Over-speed. Due to the action of the governor the nonnal
speed of the turbine is usually maintained constant under oper-
ating conditions. If the load changes, however, take place with-
out a corresponding regulation of the admitted quantity of water,
the speed will necessarily vary, increasing as the load decreases
and vice versa. If the load should suddenly drop ofiF with the
gates wide open and remain so for some reason or other, the speed
will rise considerably, sometimes resulting in disaster to the
direct-connected generators, and these should, therefore, always
be designed safely to withstand such runaway speeds of the
water wheels. These depend to a great extent on the hydraulic
development and the type of wheel used. For high-head plants,
where impulse wheels are used, the over-speed should preferably
be estimated at 100 per cent of the normal speed. For low heads
with reaction turbines, when the same are working at the most
eflicient speed, and the head is constant, the over-speed may be
from 60 to 80 per cent above the normal speed. Under low-head
conditions with a wide variation in the head and with wheels
designed for an intermediate speed to work imder these different
conditions, a runaway speed of up to 200 per cent may then be
reahzed under the maximum head. The above values are only
general, and it is most desirable that in all cases a detail analysis
is made, based on test data for the particular type of wheel which
is to be used, considering the extreme range of heads and the other
conditions under which the wheel is anticipated to operate.
To prevent dangerous over-speeds several types of overnspeed
devices are being used. One of these consists of a fly-ball mechan-
ism, independent of the turbine governor, driven from the shaft
of the unit which, in the event of excessive speeds, by means of
control valves admits water behind the piston in an auxiliary
cylinder on the governor. This causes it to move in such a man-
ner as to overcome the oil pressure in the control element of the
governor and shut down the unit.
Mechanical Designs. Reaction type: There is a very great
variety of turbine designs and while overlapping to a certain degree,
each has its particular field of apphcation. For example, the units
may be horizontal or vertical, the latter being now almost entirely
used for low and medium-head installations. As a fact, in about
90 per cent of the large installations built during the past two or
three years the turbines have been of the vertical-shaft type. The
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units may also have one or more runners, as previously explained,
and when a pair of runners are used the question arises whether
an outward discharge, requiring two draft tubes, or a center dis-
charge, requiring only one draft tube, is to be used.
Horizontal Turbines: The multi-runner horizontal turbine of
the open flume type is open to the objection that the gate mechan-
PiG. 118. — Horizontal Double-runner Open Flume Turbine with Cast-iron
Draft Chest and Steel Draft Tube. (S. Morgan-Smith Company.)
ism is submerged and cannot be efliciently lubricated, while the
entire machine is less accessible for inspection and repairs. The
only advantage which can be claimed for this unit is its higher
speed.
The most approved type of horizontal imit at present is either
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228 HYDRAULIC EQUIPMENT
the single or double discharge, both admitting of an exposed gate
mechanism. The double discharge has some advantages over the
single in that it is hydraulically balanced against end thrust. On
the other hand, if it has a central discharge, i.e., both runners dis-
charging into a conmion-draft tube (Fig. 118), the draft-tube con-
ditions are not so favorable, unless the runners are spaced well
apart.
Horizontal turbines for very low heads are necessarily set in
open flumes or wheel pits. For high heads, the volute or spiral
Fig. 119. — Single-runner Horizontal Turbine with Cast-iron Spiral Caae and
Single Discharge Tube. (Built by I. P. Morris Company.)
casing is the preferable type, the question of central, double or
single discharge depending on the conditions to be met (see Figa.
119, 120, and 121). For intermediate heads, the cylindrical plate
steel casing, Fig. 122, has been conmionly used in the past. It is
not as efficient, hydraulically, as the spiral casing, but is some-
times cheaper in first cost. In order to avoid prohibitive losses, it
is necessary to make the plate steel cylindrical casing much larger
than a volute casing, and the additional space and material would
tend to neutraUze or reverse the reduction in cost. If the pen-
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stock connection is at the top or the side, the gate mechanism may
be exposed, which is not the case if the penstock is connected at
the end. In the latter case, however, the hydraulic conditions
are better. In general, the plate steel cyUndrical type of casing is
more or less out of date. Fig. 122 shows a unit of the end intake
t)rpe which has given high efficiency in tests made on the com-
pleted installation.
Pig. 120. — ^Double-runner Horizontal Turbines with Cast-iron Spiral Case and
Double Discharge Tube. Hydraulic Power Company, Niagara Falls.
(Built by I. P. Morris Company.)
Vertical Turbines, Multi-runner vertical turbines are open to
the same objections as horizontal units in that the gate mechanism
is submerged and the machine more complicated. The best prac-
tice of to-day, therefore, adheres to the single vertical turbine.
The casing is of volute or spiral form and for low heads is usually
molded in the concrete foimdations of the power-house (Fig. 123).
For higher heads it is made of cast-iron, cast-steel or riveted-steel
plate, as conditions may require. Sometimes the metal casing is
imbedded in concrete under the floor which supports the generator
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HYDRAULIC EQUIPMENT
Fig. 121. — Double-Runner 22,500 Horse-power Horizontal Turbine with Cast-
iron Spiral Cases and One Common Discharge Tube. Long Lake Station
of the Washington Power Company. (Built by the I. P. Morris Com-
pany.)
Fig. 122. — Double-runner Horizontal Turbine. Cylindrical Case with End
Intake and Central Discharge. (1. P. Morris Company.)
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(Figs. 124 and 125). The thrust bearing is occasionally located
between the generator and the turbine, and supported by the
latter, but it is usually and preferably placed on top of the
generator, and supported by a spider mounted on the generator
Fig. 123. — Single-runner Vertical Turbine with Volute Casing and Draft
Tube Molded in the Concrete Substructure.
frame. The gate mechanism is of the exposed type, no parts
being in the water except the gates themselves, and all bearings
and pin connections are accessible for lubrication.
Runners: The nmners are mostly made in one piece (Fig. 126),
except for very large sizes where it becomes preferable to make
them in sections on account of shipping Uhiitations and so as to
assure sound castings. While bronze was used previously to a
very great extent so as to prevent corrosion, experience has proved
that this effect is primarily due to defective designs. For this
reason cast iron is now used to a much greater extent for runners
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HYDRAULIC EQUIPMENT
Fia. 124.— Vertical Turbine with Imbedded Circular Plate Steel Spiral Caaing.
(Allis-Chalmers Company.)
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Fig. 126# — Single-runner Vertical Turbine with Cast-iron Spiral Casing and
Steel-lined Concrete Draft Tube. (I. P. Morris Company.)
than formerly, especially for low and medium heads, while cast
steel is not considered a very desirable metal from considerations
of corrosion, on account of the unavoidable roughness of the sur-
face.
Damage to turbine nmners may be caused by both corrosion
and erosion, the two being of an entirely different nature. Mr.
H. B. Taylor thus explains their difference as follows: " Erosion is
entirely a mechanical action, while corrosion or pitting, is the
result of chemical action. The abrasive action of foreign sub-
stances in the water has the effect of first polishing the vane sur-
faces, and eventually cutting away the metal until the vanes
are worn entirely through. The eroded parts are, therefore,
smooth and can be readily distinguished from the pitted marks
which result from corrosion.
''It has been demonstrated that corrosion is primarily a ques-
tion of design and it has been clearly shown in practice where
sharp curves are resorted to, where contraction is not sufficient,
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234 HYDRAULIC EQUIPMENT
or where there are pockets formed in the surface of the vanes, pit-
ting or corrosion inevitably develops. It has also been demon-
strated that where air in large quantities is entrained in the water
carried to the turbine corrosion seems to take place very rapidly
if the design is not correct.
"A corroded vane surface has an appearance resembling a
sponge, the surface being extremely irregular and the pitted spots
Fig. 126. — Runner for Reaction Turbine. (Built by I. P. Morris Company.)
often opening holes entirely through the vane. Chemical analysis
of the corroded surfaces has brought out the fact that the metal
has been oxidized. In runners made of bronze or an alloy, mod-
ifications in the composition have been detected in the corroded
portions.
"The theory of corrosion as now generally accepted is that the
water in passing over any pocket or depressed surface, or in failing
to adhere to the surface of the vane, leaves spaces which are filled
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with eddies possessing high velocities and very low static pressure,
in which oxygen is liberated from the water. This oxygen is
beheved to be in the nascent state and rapidly attacks the sur-
face of the metal, forming an oxide doating, the greater part of
which is rapidly washed away by the water. When once the
depth of this pocket is increased by corrosion, it is natural that,
due to the greater area exposed, the pitting action should con-
tinue at an accelerated rate imtil the vane is entirely eaten
through."
Gate Mechanism: For controUing the flow of reaction tur-
bines there are two principal types of gates in use, the cylinder
gate and the wicket or swivel gate. The latter, Figs. 127 and 128,
Fig. 127. — T)rpical Arrangement of Gate Mechanism for a Small Vertical
Reaction Turbine.
offers decided advantages of the two. Wear and tear is greatly
reduced for small fractional loads due to better flow conditions,
resulting in higher eflSciencies than can be obtained with cyhnder
As previously stated, the exposed or so-called " outside "
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type of gate mechanism, is much superior to the older t3rpe8 in
which the moving parts are more or less submerged. The exposed
t3rpe, as apphed to spiral casing turbines for high heads, is the
ideal arrangement in that all bearings may be lubricated and the
gate-stem packings may be arranged to exclude water and grit.
The exposed mechanism has a further advantage in that it per-
mits a more direct connection between the operating ring, to which
the gate-stem levers are connected, and the regulating cylinders
Fig. 128. — ^Vertical Reaction Turbine, Showing the Gate-operating Mechanism
and Speed Ring. (Built by I. P. Morris Company.)
or " servo-motors " of the governor system. When the operating
ring is outside the wheel casing, it may frequently be directly
attached to the connecting rod of the regulating cylinder. Large
imits should have two regulating cylinders connected to the ring
at diametrically opposite points, so as to insure a balanced con-
dition.
The wicket gates, or movable guide vanes, are mostly made of
cast steel. They are subjected to rough usage on account of ice,
stones and rubbish in the water, and cast iron is too brittle for
such service. In very large units, the gate stems or fulcnims
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TUBBINES 237
should be detachable from the gates. The stem may then be
withdrawn from the gate and the latter removed without dis-
turbing the crown plate of the turbine. This is a great convenience
but, unfortunately, is feasible only in connection with large units,
and on smaller work the stems must either be cast or forged inte-
gral with the gates. The gate stems must, furthermore, be of
ample strength to resist the strain in case an obstruction is caught
between two gates and the full power of the governor is con-
centrated upon them. The links which connect the gate stem
levers to the operating ring should be the weakest element of the
gate mechanism, and should be designed to break before the
stress reaches the elastic limit of the material. of any of the
other parts.
Speed Rings. These were introduced in connection with the
large single-runner vertical turbine with volute casings molded
directly in the concrete. They consist of a series of curved vanes
outside of the turbine guide vanes, forming together with an
upper and lower crown (Figs. 113 and 128), a rigid frame to sup-
port the weight of the portions of the turbine and of the concrete
substructure of the power-house located above the casing, as well
as the generator and thrust bearing. The vanes are shaped to
suit the free passage of water entering the movable guide vanes,
and this arrangement is preferable in every way to round stay
bolts, the large, projected area and circular form of which causes
considerable hydrauUc losses. Besides this, there is a mechanical
advantage in the use of a rigid cast-iron connection between the
upper and lower speed-ring crowns.
Casings. The most efficient form of turbine casing in use at
present is that of volute or spiral shape, Fig. 119. This t3rpe has
been in common use under high heads for some years, and is now
being adopted with increasing frequency for low heads, partic-
ularly where the turbines are of large capacity. The materials
most conunonly used for medium and high heads are cast iron
and cast steel, the choice between them being influenced chiefly
by consideration of the stresses imposed. Large casings for high
heads are usually made of cast steel. Cast iron, although more
suitable for medium heads, may properly be used for high heads
if the casings are small and the material is worked at low stress to
provide an ample factor of safety against pressure surges which are
of more common occurrence in high-head than in low-head plants.
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As compared to plate steel, cast-iron casings have certain ad-
vantages, such as the lack of rigidity of the plate steel, its danger of
local weaknesses at the riveted joints, possibility of corrosion and
leakage developing undetected, especially corrosion on the outside
surface. Cast casings have, furthermore, the advantage that
they may be tested in the shops to a hydrostatic pressure well in
excess of that which they can ever be subjected to after installa-
Fig. 129.— Wooden Forms for Concrete Turbine Casings.
tion. On account of their strength and rigidity, they can also
serve as an excellent bed plate for the entire unit.
For low heads, and especially with large turbines, the casings
are usually molded in the concrete foundations of the power-house
by means of wooden forms (Fig. 129). If the casings are large
enough and the head high enough to produce serious stresses in
the concrete, they may be made of metal and imbedded in the
concrete. The principal controlling factor in this case is the
relative cost of such casings as compared with the cost of adequate
reinforcing steel for the concrete, which would be required if the
metal lining were omitted.
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Where the intake openings are large it has become general
practice to divide the openings by means of vertical piers in a
number of channels (Fig. 130). This insures a more uniform dis-
FiG. 130. — Sectional Plan of Cedar Rapids Wheel Chambers.
tribution of the water around the runner, while, on the other hand,
it strengthens the casing by subdividing the span. It also greatly
facilitates the appUcation of the gates, which otherwise would be
of a size hardly possible to manipulate.
Draft Tubes. A correct draft-tube design is absolutely es-
sential in order to obtain the maximum efficiency of a turbine
as a whole. It is an integral part of the design of the turbine and
should be furnished by the turbine builder. The fundamental
principles underlying their design and construction are that the
water shall leave the draft tube with as small velocity as possible
so that the maximimi amount of kinetic energy is abstracted from
the water. The velocity of the water in the tailrace must, fur-
thermore, be suflicient to prevent it from backing up and it is,
therefore, necessary that the water emerging from the draft tube
must have a velocity at least equal to that in the tailrace. In
order to accomplish this the draft tube should be constructed on a
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HYDRAULIC EQUIPMENT
long radius so as to change the direction of discharge from a ver-
tical to a horizontal plan. The section of the draft tube must also
be gradually increased from the discharge ring of the turbine
to the tailrace so as to gradually reduce the velocity of the water
from the turbine to the tailrace, and it is conmion practice to
gradually increase the section from the circular form at the tur-
bine to an oblong section at the end, the long axis being horizontal.
Good draft-tube design is fundamentally dependent upon the
proper elevation of the turbine above tail-water. The runner
Fig. 131.— Placing of Wooden Forms for Draft Tubes of Three 10,000 Horse-
power Turbines.
should be so located that the total draft head at the top of the
tube (i.e., the static elevation of the runner above tail-water added
to the velocity head at the throat of the runner) is well within the
theoretical limits of a vacuum; namely, approximately 34 feet,
depending on the barometer reading. If not, the water coliunn in
the draft tube will break, retimiing with a surge and causing water-
hammer. If, on the other hand, the vacuum in the draft tube is
near the breaking point, the continuity of the flow may be inter-
rupted at the discharge end of the water passages through the
runner, resulting in corrosion and pitting of the vanes.
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The residual velocity at the point where the discharge is
released to the atmosphere is an irreclaimable loss and should be
made as small as possible. The fact that this loss is not charge-
able to the turbine should always be taken into account in making
eflBciency tests.
It used to be conmion practice to make all draft tubes of steel
plate, but of late years they are usually like the wheel casings
molded in the concrete foundation of the power-house, except in
the case of small turbines (Figs. 131 and 132). It is not feasible
to build large draft tubes of plate, nor is it possible to obtain the
Fia. 132.— Lower End of a Molded Concrete Draft Tube.
smooth ciu^es and eflScient design characteristic of concrete
tubes.
Bearings, Most bearings of horizontal turbines are of the
ordinary babbitted generator type, except where submerged, in
which case lignum vitse bearings are used. Where water thrust is
to be taken care of thrust bearings must also be provided.
For vertical miits the thrust bearing is almost always located
above the generator on a cast-iron supporting truss, which at the
same time forms the generator head cover. The upper guide
bearing, which is located immediately below the thrust bearing, is
usually of the oil-lubricated babbitted type, while the lower one is a
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242 HYDRAULIC EQUIPMENT
water-lubricated lignum vitaB bearing, permitting it to be located
very close to the runner.
The lignum vitae is dovetailed into the bearing boxes in the
form of strips running parallel to the axis of the shaft and with the
end grain of the wood placed normally to the surface of the shaft.
Twenty or more of these strips, evenly spaced in a liberal length
and separated by spaces for circulation of cooling water, are so
proportioned as to present sufficient area to the shaft to insure
very satisfactory performance.
In the case of tiu-bines operated in clear water, the supply for
the bearing may be taken through a pipe directly from the wheel-
casing. A duplex strainer should be connected in the line to
remove any foreign substances which might otherwise reach the
bearing and damage it. In installations in which the water ca-
ries large quantities of foreign matter in suspension, a suitable
central filtering system should be provided.
For a description of the various types of thrust bearings, see
page 334.
Impulse Type, like the reaction type, impulse tiu-bines are
built in many different designs, the controlling factors differing so
materially in each installation that they not only affect the general
type or arrangement of the design, but also of details.
Horizontal and Vertical Wheels, Impulse tm-bines are almost
exclusively of the horizontal type. This not only represents the
most economical design, but it has many advantages of simplicity
of construction and arrangement of parts available for inspection,
lubrication, and cleaning. Vertical wheels have, however, been
built and operate satisfactorUy, and they may be used for com-
paratively low-head plants, where the water contains large quan-
tities of sand or grit. With this type up to six jets can be installed
in a single-wheel runner.
Runners. There are two general types of wheel-runners, the
double-lug bucket type and the chain or triple-lug bucket type.
In the former the wheel center consists of a single rim and the
buckets have two lugs which are machined to a press fit over the
rim of the wheel center and held in position by two bolts. In
the latter type, a double or U-shai:)ed wheel rim is required aiid
the buckets have three lugs, a forward center lug and two rear .
lugs. The forward center lug is a close fit between the two rims
forming the duplex wheel center, and the two rear lugs straddle
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the rims, the arrangement of the lugs being so designed that the
rear lugs of one bucket come directly in line with the forward lug
of the next following bucket. A single bolt, therefore, passes
through the rear lugs of one bucket, the rims and the central or
forward lug of the next following bucket, thus connecting up jaXl
of the buckets into a con-
tinuous chain. Fig. 133
shows such a type of wheel.
In the chain-type wheel
the base line of the buckets
or the distance between the
supporting bolts is very
much greater than it is with
double-lug buckets. This
type of construction is,
therefore, particularly suit-
able for all installations
where the ratio between the
diameter of the jet and the
pitch diameter of the wheel
is small, that is, where a
large diameter of jet is
applied to a comparatively
small diameter of wheel.
This is always the case
where a very large power output is required, with a turning speed
comparatively high, as proportional to the head of water, thus
calling for large buckets on a comparatively small wheel. It is also
especially suitable for extreme cases of large horse-power and high
heads, making the wheel runner of the most stable construction.
The buckets are ellipsoidal, which causes the water jet to
impinge without shock or disturbanbe, and it is discharged along
natural lines over the entire bucket surface. The central portion
of the front entering wedge or lip of the bucket is cut away in the
form of a semicircular notch, and this opening allows the solid
circular water jet to discharge upon the central dividing wedge
of the bucket without being split in a horizontal plane, with the
result that all eddy currents are avoided and the full force of the
jet is expended for useful work, resulting in the maximum bucket
eflSciency.
Fig. 133.— Tangential Water Wheel
Equipped with Ellipsoidal Inter-
locking Chain Type Buckets. (Built
by Pelton Water Wheel Company.)
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244 HYDRAULIC EQUIPMENT
Arrangement of Runners. The two principal runner arrange-
ments are the single-overhung and the double-overhung. In
addition there is also the self-contained type. The first-named is
mounted on an overhung extension to the generator shaft (Figs.
116 and 134), no extra outboard bearings being provided, and the
second type comprises simply two single-overhung wheels, one
being mounted on a shaft extension at each end of the generator.
This is the ideal construction for large units and is extensively
used. With the double-overhung type it is possible to make a
Fig. 134. — Single Overhung Impulse Turbine, Governor Regulated by Jet
Deflector. (Built by Pelton Water Wheel Company.)
prime mover of double the power output, maintaining the same
speed of rotation with the same conditions of water pressure.
For very large units, two wheels on each side of the generator may
be used, making foiu- wheels per unit. This usually requires four
bearings, the generator rotor being mounted between the two main
bearings, with an outboard bearing at each end, two wheels being
located between one main bearing and one outboard bearing. The
self-contained type has its own shaft, bearing, base and housing,
one or more runners being mounted on the same shaft and in the
same housing. It is mainly used for small capacity units.
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Referring again to Fig. 116, a water connection for throwing a
fine spray of water through the hollow shaft will be noted on the
outer end of the right bearing. Within the housing of a tangential
wheel there is a very definite vacuum due to the action of the
revolving wheel as a centrifugal blower and the action of the jet
of water acting as an injector. Therefore discharging a fine spray
of water into the open end of the shaft, this is drawn through and
is most effective in cooling.
The illustration (Fig. 116), also shows what is termed a " tail-
race ventilator." This is a labyrinth passage from the bottom of
Fig. 136. — Impulse Turbine with Two Nozzles per Wheel. Arranged with
Auxiliary Relief.
the generator pit to the water-wheel pit, tne vacuum existing in
the water-wheel pit bringing about a very definite circulation of
air which it draws out of the bottom of the generator pit.
The three principal types of nozzles used with impulse tur-
bines were described under " Speed Regulation,'' page 221.
While one jet per wheel is used in most cases, there may be installa-
tions where the head of water available is low, as compared with
the quantity of water and where it is desired to maintain a com-
paratively high speed of rotation. Under such conditions two
jets of water may be applied to each wheel from the same nozzle
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246 HYDRAULIC [EQXnPMENT
body, the jets being approximately 90° apart. Such an arrange-
ment is shown in Fig. 135, this sketch representing a unit with
four wheels and eight jets, developing 10,500 H.P. under an
effective head of 380 feet at 200 R.P.M.
Housings, The general tjrpe and construction of wheel
housings or casings for impulse turbines is illustrated in Fig. 134,
the best practice being to provide a separate housing for each
wheel to prevent interference from discharged water. The lower
part is usually made of iron castings and the upper housing or
cover of steel plate riveted into a cast-iron frame. This type of
housing for large imits is claimed to be preferable to a housing
made entirely of cast iron, as it is Ughter to handle and elimi-
nates any danger of breakage where the shaft of the nmner passes
through the sides of the housing, and water leakage is prevented
by means of a centrifugal disc and water guard, which device in-
sures a frictionless packing. For small units, on the other hand,
the self-contained cast-iron housing is, as previously stated, to be
preferred.
2. GOVERNORS'
Before the advent of the automatic voltage regulator, close
speed regulation by water-wheel governors was of much greater
importance than now. for anv deoarture from normal had an
immediate effect on the voltage. With the automatic regulator
in operation, reasonable changes in speed have no appreciable
effect on the voltage, but they do, of course, affect the frequency.
A sUght variation in frequency, is to be expected, for like all gov-
ernors for prime movers, the water-wheel governor requires a
certain change in speed to ensure good governing.
Factors Affecting Speed Regulation. While primarily the
regulation for speed originates with the governor, it also involves
the consideration of the pipe-line conditions and those devices
required for Umiting the pressure rise therein, and besides the
effective flywheel effect of the rotating elements of the generator
and water wheel.
Variations in the velocity of the water in the pipe line will
always occur, and every retardation in velocity of the moving
water column will bring about an increase in the pressure, in-
versely in proportion to the time occupied for a given change. It
1 See also '' Pipe Lines/' " Water Hammer and Surge Tanks."
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GOVERNOBS 247
is thus evident that the quicker the governor movement, the greater
the pressure rise will be, while, if the governor movement is made
slower, the speed increase will be greater, and a proper balance
between the two is, therefore, the correct time for adjusting the
governor closing stroke. Few conditions will, however, warrant
a stroke quicker than 1} seconds.
In addition, the flywheel effect must be considered the greater
the inertia of the rotating masses and the higher their rotation,
the smaller the speed variation will be. A sufficient rotating mass
to supply stored energy (WIP) must, therefore, also be intro-
duced to keep the speed within permissible limits.
To secure a constant speed with a water wheel operated under
a variable load, the energy produced by the water wheel must be
varied proportionally to the load, and the method of achieving this
in practice, except for tangential impulse wheels with deflecting
nozzles, consists essentially of varying the size of the gate or valve
openings through which the water to the wheels is admitted (see
" Speed Regulation," page 220).
The regulation of hydro-electric imits, as stated, requires a
certain departure from normal speed before the governor can act.
Since the immediate effect of the gate motion is opposite to that
intended, the speed will depart still further from the normal, which,
in turn, tends to cause the governor to move the gate too far, with
the result that the speed will not only return to normal as soon as
the inertia of the water and the rotating parts is overcome, but
may rush far beyond normal in the opposite direction.
A given gate opening will produce a certain velocity of the
water in the penstock and the energy of the moving water will be
equal to the weight of the water in the penstock multiplied by the
square of the velocity and dividing this product by 64.4. For
example, with a penstock 300 feet long and 6 feet in diameter, the
weight of the water would be 530,000 pounds, and assuming a
velocity of 5 feet per second, corresponding to the head and full
gate opening, the total kinetic energy of the water would be
^^^=206,752 foot-pounds.
If the gates are now instantly closed to about one-quarter
gate opening so that the velocity would be reduced to 1.6 feet per
second, the corresponding kinetic energy would only be 18,517
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248 HYDRAULIC EQUIPMENT
foot-pounds. The loss of energy is, therefore equal to 205,752—
18,517 foot-pounds, and this amount will be transferred to the
water issuing. from the gate apertures, which, therefore, wiU have
its velocity increased until the 187,235 foot-pounds of energy has
been absorbed. The kinetic energy of the water column will,
therefore, be transferred to the water wheel at the very moment
when it is desired to reduce the energy produced by the wheel.
In the same manner, if the load be thrown on and the gate again
instantly opened full, the same amount of energy which the water
column gave out on being retarded in the previous case will be
absorbed by the water column in accelerating its velocity to 5
feet per second. The energy delivered to the wheel will, therefore,
be reduced, causing its speed to drop off, just when the opposite
is required, and this action cannot be overcomie by rapid move-
ment of the gate, but, on the contrary, is intensified by more
rapid gate movement. It is, therefore, obvious that after the
governor has been set in motion by a change of speed, some means,
other than the return of the speed, must be provided to stop it
when it has moved the gates the amount required by the change
of load which was the cause of the change in speed that originally
set the governor in motion. The means provided for this pur-
pose is a dashpot, known as the '^ compensating " mechanism,
and is an essential feature of all quick-acting water-wheel govern-
ors. Compensation may thus be considered the act of stopping
and waiting for the result of the gate movement.
It is a comparatively easy matter to calculate the speed-
regulation in cases where the inertia of the moving water column
is a negUgible quantity, such as with open flumes and short draft-
tubes. For such conditions, the following formula apphes:
d = 81,000,000 yff^yjpj
where d = percentage temporary change in speed for load
thrown off;
H.P.= maximum horse-power capacity of the turbine;
r=time in seconds occupied by the governor in moving
the turbine gates through their range;
W IP = weight of rotating parts multiplied by square of
radius of gyration of generator;
iV= normal speed of rotating parts in R.P.M.
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GOVERNORS 249
For installations with long penstocks the regulation becomes
much more serious and is difficult to calculate acciu-ately due to
the many variable factors involved, such as the length of the pipe
line, the effective head and velocity of flow, time of governor
action, flywheel effect and effect of standpipes, etc.
The final speed after a load change will be that due to the
initial kinetic energy of the rotating parts and the excess or
deficiency above or below the load requirements during the time
of gate adjustment. This excess or deficient energy is due to the
excess or deficiency in the quantity of water during the change in
addition to that of the energy required to accelerate or retard the
water colimrn in the penstock.
The effect of a standpipe must also be considered in absorbing
the excess power. When such a structure of sufficient size is
installed close to the wheels, the conditions will approach those of
an open flume, while, if located some distance from the plant,
they become similar to those of a closed penstock of a Jength equal
to the distance from the draft-tube to the standpipe.
Action of Governor. The obvious tendency of a governor, as
explained above, is to permit the speed to oscillate above and below
normal. A successful governor must, therefore, anticipate the
effect of any gate movement, and in order to overcome the effect
of the pressure change in the penstock the governor must move
the gate sUghtly beyond the final position, in order to restore the
speed to normal; the final motion of the gate being a slow move-
ment back to the final position. This last slow movement is con-
troUed by the compensation device as explained. The percentage
variation in speed which will occur before the governor begins to
move the gate, or the limits within which the governor is inopera-
tive, shoidd be a minimum. This is generally realized with
hydraulic governors where it varies from practically nothing to
0.75 per cent.
Tlie speed with which the governor moves the gate is a most
essential element of a good governor. No general rule can be
given of the rate at which the governors should open or close the
gates. It can be more rapid the shorter the penstock and the
lower the velocity of the water. The effect of both rapid opening
and closing of the gates should be investigated in every projected
plant, in order to guard against drawing down the pressure at
critical points in the penstock below that of the atmosphere, and
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250 HYDRAULIC EQUIPMENT
thereby causing danger of collapse, or permitting increases of
pressure beyond the strength of the penstock.
The duration of the momentary variation between the first
departure of the speed from normal and its complete restoration to
steady speed should also be a minimum. It is governed by the
energy contained in the water column as well as the flywheel
effect. By increasing the flywheel capacity the speed variation
can be reduced, and thus a plant with a moderate length of pen-
stock and a small flywheel capacity will give a large momentary
variation over a short interval of time, while the same plant with
a larger flywheel capacity will give a comparatively small varia-
tion over a longer time interval. The latter is, however, more
favorable from an operating standpoint.
The speed regulation of a number of 10,000-H.P. recently
installed reaction turbines, operating under a 96-foot head, at
185 R.P.M., is given in the foUowing. It is based on a total fly-
wheel effect {WR^) of 1,700,000, a pipe Une diameter of 11 feet,
and a pipe length of 190 feet.
Load change, per cent 10 25 50 100
Speed change, per cent 0.9 2.1 3.5 16
These governors were furthermore guaranteed to restore the
speed of^the units to within 0.5 per cent of normal from any change
in load, and will begin to act before the speed has changed more
than 0.5 per cent from normal.
An imnecessarily close regulation should not be required when
considering such extreme conditions as full load thrown suddenly
on or off a unit, conditions which sddom occur in a plant, and
when they do occur it is usually due to a short circuit or a dropping
of load under circumstances in which regulation ceases to be a
consideration.
Pipe-line Pressure Caused by Governor Action. In order to
arrive at the maxtmimi pressing developed in the pipe lines by the
governor action, the following formula may be used with sufficient
^^^y^ ^_0.027XLXt;
where P=maximirai pressure change in pounds p)er square inch;
L = length of water column in feet;
t; = velocity in feet per second;
r=time in which water column is stopped in seconds.
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GOVERNORS 251
Relief valves at the turbine case are sometimes employed to
obviate the difficulties of long feed pipes, but it is evident that
they can be of use only upon the load going off. They can be of
no use upon the load going on, for they cannot supply to the
moving water column kinetic energy which it has lost and which
it must regain before it can flow at the higher velocity required
by an increase of load. Standpipes are better; in fact, they are
often imperative. If of improper design, or of insufficient capacity,
they frequently add to the difficulty of obtaining regulation. If
of proper design, they simply result in shortening the closed water
column; that is, they bring the tin-bine nearer to being set under
open-water conditions which are the most favorable conditions.
Unfortunately, the conformation of the country is often such that
a standpipe is unfeasible, and reliance must be placed on reUef
valves to prevent dangerous water pressures being developed and
upon flywheels to Uberate or absorb kinetic energy as the closed
water colunm absorbs or liberates it.
Energy Output of Governor. In order to be of ample capacity
to control the gates promptly and still have a margin for speed
regulation of the wheels, it is necessary that the governor should be
capable of developing an effort in excess of the maximimi effort
required to merely operate the gates themselves. Practical expe-
rience seems to indicate that this margin should be about 100 per
cent of the maximum effort required to move the gates.
Governors are nominally rated in foot-pounds at a given pres-
sure, the rated effort being equal to the nominal rating divided by
the length of the stroke, expressed in feet. It has, however, been
suggested to rate a governor by its maximimi torque produced or
also by its energy produced per second. This latter term would be
an indication of both the power suppUed for and the rate of the
gate motion to be produced by the governor.
Arrangement and Operation. The movement of turbine gates
requires a relatively large amount of energy and indirect-acting
governors are therefore almost exclusively used, employing either
mechanical energy as with the so-called mechanical governor or a
compressed fluid as with the hydraulic governor.
Mechanical governors obtain their energy mechanically by
belt drive from the prime mover and transmit it by friction coup-
lings, etc., to the gate shaft. They are not very sensitive but
exposed to considerable wear, for which reason they are only
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252 HYDRAULIC EQUIPMENT
used for very small units. In fact, they are being rapidly dis-
carded.
A hydraulic pressure governor system can be divided in two
distinct parts — ^the pumping outfit and the governor imit proper.
The pumping outfit in its simplest form consists of a power
pimip, a pressure tank, a receiving tank and suitable connecting
pipes, valves, gauges, etc. The fluid which is used to operate
the power cylinder of the governor is obtained from the pressing
tank, which normally should be about half filled and of sufficient
capacity to provide for a series of governor strokes, even though
the pump be temporarily inoperative. The receiving tank receives
the fluid after it has performed its work in the governor, the func-
tion of the pump being to draw the fluid from the receiving tank
and force it into the pressure tank together with a sufficient amount
of air to obtain a pressure of from 100 to 200 pounds per square
inch. This compressed air is the immediate source of energy for
operating the governor, and although the pump accumulates or
renews this energy at a comparatively slow rate, it is available
for use in the governor as rapidly as the requirements of regulation
demand. It is this principle which makes possible the rapid
movement of the gates, which is essential to close speed regu-
lation.
Two general sjrstems of pressure supply are in successful use,
one utilizing oil and the other water. Water is advantageous in
the case of large plants. High-epeed, multi-stage centrifugal
pumps of relatively small size may be used, while for oil, plunger
or gear pumps are required. The cost of oil necessary for the
pressure sjrstem of a large plant is also an important item, but, on
the other hand, the wear on valves and valve sleeves, etc., is un-
questionably less with oil than with water. Each of these two
systems has its advantages and disadvantages which, should be
carefully considered in each installation.
Water treated with a soluble oil may also be used as a gov-
ernor fluid. A small percentage of soluble oil will supply the
required lubricating qualities, and will prevent rusting or cor-
rosion. The use of this fluid, handled by centrifugal pimips, is
probably the best practice in the case of large stations.
Many large plants are now equipped with central pressure
systems. The pumps are sometimes motor-driven with auto-
matic pressure control. Sometimes the motors are allowed to
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GOVERNORS 253
run continuously and the pumps are equipped with unloading
valves. Each unit has its own accumulator or pressure tank
situated close to the goveror to eliminate the effect of inertia in
the supply pipe, and unless the discharge piping is of hberal size,
each unit should have a local simip tank from which the oil or
water returns by gravity to the central reservoir supplying the
pumps. This latter method complicates the piping, and it is
better to use a large return pipe and only one sump tank. Both
oil and water systems are now generally of the open type; that is,
they are arranged to discharge under atmospheric pressure. The
closed or vacuum system, at one time conmaonly used, has been
discarded, even with individual pumping systems, because of the
tendency to break down the oil.
The principal elements of the governing unit proper are:
One or two power cylinders or servo-motors, suitable mechanism
for transmitting the movement of the power piston to the gate
shaft, a main or relay valve, a pilot or regulating valve, a safety
stop, a centrifugal speed governor and a compensating device.
In addition they are also usually arranged so as to permit of hand
control as well.as remote control and when required a load limiting
device may be provided.
The admission of the fluid from the pressure tank to the power
cylinder and back to the receiver tank is regulated by the main or
relay valve. This must, in most cases, be of such a large size as
to make it impossible to control directly from the centrifugal speed
elements, and for this reason an intermediate pilot or regulating
valve is provided. This is connected to the centrifugal mechanism
and r^ulates the admission of the pressure fluid to the main
relay valve, and this, in turn, to either end of the piston in the
power cylinder, which transmits its motive power to the gates or
nozzle mechanism of the turbine when a speed variation occurs.
The movement of the relay valve is always such as to return the
pilot valve to its neutral position after a load variation has oc-
curred, resulting in a movement of the governor piston.
The rapid growth in size of units has brought about a corre-
sponding change not only in the size of governors, but also in the
arrangement. Standard governors were formerly self-contained;
that is, the control and power elements were combined in the gov-
ernor itself. It was necessary only to connect the centrifugal
element to the turbine shaft and the power element to the tur-
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254 HYDRAULIC EQUIPMENT
bine gate mechanism, and the installation was complete excepting
the pumping system. While this arrangement is still in use with
small units, it is no longer used for large imits. In the latter case
the centrifugal control mechanism and regulating valves are now
combined and localized in an '' actuator " placed in any con-
venient position near the imit, and the power element or servo*
motor is incorporated in the design of the turbine. By separating
these elements, each of them may be located in the most advan-
tageous position with respect to the individual function it has to
perform. For example, in the case of vertical units, the actuators
may be placed on the generator floor and the servo-motors in the
wheel pit, directly connected to the gate mechanism.
Methods of ControL Governors up to about 60,000 foot-
pounds capacity are often equipped with mechanical hand con-
trol independent of the servo-motor. This is, however, scarcely
feasible with larger governors on accoimt of the time that would be
required to develop so much power by hand. They are, there-
fore, equipped with hand control of the operating pressure only.
This control is independent of the centrifugal speed element,
and is of great value for adjusting the load on thjB unit and for
synchronizing purposes. In addition to local hand control all
governors are now as a rule also equipped with manual remote
control. The mechanism is equipped with a small reversible
motor electrically connected with a double-throw control switch on
the switchboard, and enables the operator to control the load and
speed from the switchboard.
Numerous plants can be found where the units must first be
paralleled by hand and the governor " cut in " after the generators
are tied into the power sjrstem. The reason may be found in the
lack of harmony of flywheel effect, the velocity of the water and
the length of the pipe line. If one of the three could be properly
altered, the trouble could possibly be eliminated.
Sometimes it is required to carry a fixed load irrespective of
the load or speed variation of the system and such fixed loads may
be less than that developed at full gate opening. This reqiiire-
ment necessitates the use of a load-limiting device, which prevents
the distributor of the regulating valve from attaining a position
beyond the amount desired. A load-limiting device also allows of
an adjustment according to the head or quantity of water available
at various times, and it should preferably be remote control.
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GOVERNORS
255
Typical Designs. A description of the many governors on
the market and their operation can be readily obtained from the
numerous trade catalogs and will not be gone into here. Fig. 136
Fio. 136. — Pelton Oil Pressure Governor of Moderate Capacity with Self-
contained Rotary Pumping Set Located within Governor Base. (Built
by Pelton Water Wheel Company.)
shows a Pelton oil pressure governor with self-contained pumping
set. Fig. 137 illustrates a Lombard governor of very modem
design, which is built in sizes from 3000 to 30,000 foot-pounds.
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HYDRAULIC EQUIPMENT
It is very homologous in design and is intended for direct con-
nection to either horizontal or vertical wicket-gate turbines. The
illustration shows the governor arranged for connection to a
horizontal gate shaft, and when it is to be connected to a vertical
shaft it is provided with a Lnshaped sub-base which constitutes a
steady and supporting bearing for the upper end of the gate shaft.
Fig. 137.— Lombard Type T Governor.
This governor is also provided with a hydraulic hand control
which may be instantly thrown in and out of action. A hand
pump, mounted on the governor frame, is also provided for moving
the turbine gates when, for any reason, the pressure is let down in
the pressing tank.
Fig. 138 is the type of actuator governor furnished by the
Lombard Governor Company for the Mississippi River Power
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GOVERNORS
257
Company, the servo-motors or power cylinders developing 250,000
foot-pounds being located on the floor below. The distinguishing
feature of this design is that all adjustable parts are enclosed
within the cast-iron frame, thus preventing their being tampered
with by unauthorized persons. The back consists of plate-glass
doors through which all working parts may be readily inspected.
The face of the actuator carries the various dials which indicate
Fig. 138. — Lombard Governor Actuator. Mississippi River
Power Company.
speed of turbines, gate opening of turbine gates, pressure on the
accumulator system, and back pressure, if any. There are also
provided hand wheels controlling the main throttle of the gov-
ernor system, throttle for the relay valve system and a hydraulic
hand control. The central hand wheel controls an adjustable
gate-setting device by means of which the maximum amount
of turbine gate opening may be regulated at the will of the
operator.
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HYDRAULIC EQUIPMENT
Fig. 139. — Large Capacity Hydraulic Governor.
Company.)
(Built by I. P. Morris
Fig. 139 illustrates a double floating-lever type hydraulic
governor adapted to large turbines as built by the I. P. Morris
Company.
3. PRESSURE REGULATORS OR RELIEF VALVES
Pressure regulation is a problem which must be considered in
connection with the speed regulation of a plant. As previously
stated, if the pipe lines are long, either suflScient flywheel effect
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PRESSURE REGULATORS OR RELIEF VALVES 259
must be provided to permit a slower governor action or a surge
tank must be used. If such a surge tank cannot be located close
to the power-house, relief valves must £dso be provided, and some
conditions may require all the devices.
Relief valves are of two principal types, the synchronous by-
pass governor operated, and the direct-pressure operated. Their
design is essentially the same, except for the control mechanism.
The first becomes immediately operative with the closing gate
motion and this action continues imtil the gates stop moving.
The water rejected by the turbine as the gates close is discharged
through the regulator. Thus the penstock velocity instead of
being suddenly checked, resulting in waterhanuner, remains
practically unchanged. The device is made water-saving by the
use of a dashpot, which permits of a relative motion of the con-
nection between the turbine gate mechanism and the by-pass
valve. The adjustment of the dashpot is made such that the
by-pass, after having been opened due to a sudden closing of the
turbine gates, is closed within a period which is suflSciently long
to prevent a dangerous pressure rise in the pipe line. If the load
goes ofif gradually and the gates are closed at a rate slower than
that produced by the dashpot, the pressure regulator remains
inactive. If the gates are again opened before the dashpot has
closed the pressing regulator, then it should close synchronously
with the gate motion, otherwise an e?cess quantity of water
is discharged, causing a drop of pressure in the pipe line.
The second class of relief valves, or the direct-pressure operated
type, do not act imtil the pressure in the pipe hne or turbine
casing has risen above normal and are, therefore, a more direct
means of protecting pipe Unes against dangerous pressure rises,
such as caused by the clogging up of the gates, etc. Governor-
operated pressiu-e regulators are, however, made which permit of
an automatic action independent of the gate motion to take care
of such emergencies.
In order to obtain ideal results, the maximum capacity of
the regulator should be equal to the full-load discharge of the
turbine less the discharge required to run at synchronous speed
without load. Ordinarily some sacrifice is made to reduce the
size of the regulators. They are seldom installed in excess of
75 per cent of the maximiun turbine discharge, and in many cases
not more than 40 per cent or 50 per cent is provided. In such
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HYDRAULIC EQUIPMENT
FiQ. 140. — Governor-operated Relief Valve. (Wellman-SeaveivMoiigan
Company.)
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PRESSURE REGULATORS OR RELIEF VALVES
261
cases, of course, some pressure rise occurs in the penstock. The
size of regulator depends largely upon the water velocity in the
penstock and upon the length of penstock between the turbine and
the forebay or between
the turbine and the surge
tank, if one is used. It is
usually attached directly
to the turbine casing and
discharges into the tail-
race, and the discharge
should not be connected
to the draft tube.
Fig. 140 illustrates a
governor-operated pres-
sing regulator used with
reaction turbines. It is
mechanically connected to
the gate mechanism of the
turbine but the power re-
quired to operate it is sup-
plied by the pressing in
the penstock. No load is
imposed upon the gov-
ernor nor any pressure
drawn from the governor
system. The connection
to the turbine gate
mechanism simply oper-
ates the pilot valve of the
regulator which controls
its action.
Fig. 141 shows another
type of governor-operated
relief valve, in which the
valve is interconnected
with the turbine gates
through a self-contained
oil-pressiure system, the operation of the relief valve being pro-
duced directly by the motion of the turbine gate. Above the
elbow forming the body of the reUef valve casing will be noticed
Fig. 141. Governor-operated Relief Valve.
(I. P. Morris Company.)
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262 HYDRAULIC EQUIPMENT
a large cylinder containing a balancing piston, the purpose of
which is to equalize the load on the valve, allowing, however,
a small residual force tending to close the relief valve. Above
the balancing cylinder is a smaller cylinder containing a piston
for operating the valve. The two pipe connections shown at the
ends of this small cylinder are joined by pipes to the two ends
of a jack cylinder moimted on the tailrod on one of the operating
cylinders of the turbine. The jack cylinder and the operating
cylinder of the reUef valve displace equal volimies when their
respective pistons move through the full stroke. The relief valve
is thus forced to move by an incompressible fluid coliunn, and the
operation is similar to that which would be obtained by a direct
mechanical connection between the turbine gates and the relief
valve.
The slow-closing feature of the valve operation is obtained by
by-pass connections joining the two ends of the operating cylinder.
A needle valve permits the rate of closing to be adjusted. The
method of operating this reUef valve has several advantages.
One of these is the positive action obtained, the effect of which is
to prevent the turbine gates moving at a rapid rate, if for any
reason the reUef valve should fail to move owing to any accidental
cause, such as lodging of obstructions in the reUef valve. Thus, if
the reUef valve is imable to open, the turbine gates will be auto-
matically prevented from closing, except at a slow rate which will
not endanger the penstock.
For relief valves used with impulse wheels see section on " Tur-
bines," page 221.
4. WATER-FLOW METERS
One of the most convenient means of measuring the amount of
water taken by a hydrauUc station and for ascertaining the
efiiciency of the turbines is the Venturi meter.
Venturi Meter. It consists of a meter tube, which is inserted
in the pipe line similar to a section of pipe, and of a register which
is piped to the tube and which can be located at any convenient
place in the station, as shown in Fig. 142.
The interior contour of the meter tube is shown in Fig. 143,
and the accuracy of the meter greatly depends upon its proper
design. As the water flows from A toward the throat B, its
velocity rapidly increases and the pressure at B becomes materi-
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WATER-FLOW METERS
263
ally less than the pressure at A, This difference in pressure
between A and B can be accurately measured, and bears an exact
ratio at all times to the rate of xflow through the throat B. After
passing the throat, the velocity begins to decrease with an accom-
panying rise in pressure, and when C is reached the pressure tem-
porarily lost at B has been almost entirely regained. Therefore, a
properly proportioned tube not only provides a basis for accurate
FiQ. 142.— Method of Installing Venturi Meter.
Fig. 143. — Principle of Venturi Meter Tube.
measurement of the flow, but it will deliver practically the same
amount of water as a straight pipe of equal length and diameter.
Conmiercial tubes are made in two or more sections, as seen
from Fig. 142, and near the inlet and at the throat are annular
chambers communicating with the interior of the pipe by numer-
ous ventholes. The throat portion is lined with bronze accurately
bored to a definite diameter and contour.
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HYDRAUUC EQUIPMENT
Connections to the registering instrument are made by two
small pipes, one at the inlet pressm-e chamber and the other at the
throat pressure chamber. No water flows through these pipes as
they simply transmit the two pressures, the difference in which
controls the readings of the instrument.
Registers. There are different kinds of registers, the most
complete being illustrated by Fig. 144. At the back there are
two vertical wells connected at the bot-
tom. One well is subjected to the
inlet and the other to the throat
pressing of the Venturi Meter Tube,
these pressures being transmitted by
the two small pipes as previously
mentioned. In one well is a heavy-
metal float resting upon the mercury,
a part of which flows from this well
to the other well in direct proportion
to the changes in flow through the
Venturi Meter Tube. This is accom-
plished by having the receiving well
of a variable cross-section. Conse-
quently, the large float descends in
direct proportion to the change in rate
of flow and its motion is transferred
to the main shaft of the instrument
by means of a rigid float rod and suit-
able gearing. The movement of the
shaft is in turn transferred by means
of rack-and-spur gearing to the long
main lever of the instrument which
carries the chart pen and the integrat-
ing coimter.
The recorder dial contains a large
circular chart giving an unbroken
autographic record of the rate of flow through the meter tube.
The coimter dial shows the total amoimt of water (gallons,
cubic feet, etc.) which has passed through the tube.
The indicator shows the exact rate of flow in gallons per day
or other imits at the moment of observation.
Where the expense of installing a complete registering outfit
Fig. 144. — Venturi Meter
Register.
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WATER-FLOW METERS
265
\ !■!
!l
is prohibitive, or for testing the accuracy of register instru-
ments, the manometer may be advantageously used, and it may
be connected with the same pipes
that serve to connect the tube ^ „ ^
with the registering apparatus.
Manometer. The Venturi
Meter Manometer as illustrated
in Fig. 145, consists essentially of
a U-tube using the same principle
as a barometer. The large mer-
cury well is connected to the up-
stream of the Venturi Meter Tube
and the throat of the Venturi
Meter Tube is connected to the
small vertical glass tube, thus the
downward motion of the mercury
surface in the mercury well is
very slight in comparison with
the upward motion of the mer-
cury surface in the small glass
tube. The slight motion of the
large surface is properly corrected
in the fixed scales of the instru-
ment. The rate of flow corre-
sponding to the difference in height
of the mercury surfaces is read on
the graduated scale. This instru-
ment is absolutely accm^te, con-
taining no moving parts whatever
except the mercury iself .
5. WATER-STAGE REGISTERS
Automatic water-stage regis-
ters are divided into two classes —
those making a printed record,
and those making a graphic record.
In the first type a printed record of the gauge height and time
is made, while in the second type the record is traced by a pen or
pencil on the surface of a paper sheet, both moving in harmony
with time and height.
Fia. 145. — Barometric Venturi
Manometer.
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i
Fig. 146. — Automatic Stage Register Making Printed Record. (Manufactured
by W. & L. E. Gurlcy, Troy, N. Y.)
266
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WATERrSTAGE REGISTERS
267
The first tjrpe of register is designed to give printed records of
the rise and fall of water continuously for a long period of time,
and is especially adapted for stations where it is impracticable or
impossible, by reason of inaccessibility, for the observer to visit
the station for long intervals of time and where the record to be
Fig. 147. — Tape Reel for Use with Water Stage Printing Register.
of service should be continuous. The records are given at inter-
vals of fifteen or thirty minutes.
Fig. 146 shows an automatic water-stage register making a
printed record, and Fig. 147 shows a tape reel for handling and
examining the records. . A graphic recording register is shown in
Fig. 148.
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268
HYDRAUUC EQUIPMENT
In installing an automatic register (Fig 149) it is necessary
to provide a well for the float, connected with the river by an
intake pipe, a house to shelter the register, and staff or hook
i
Fig. 148. — Automatic Graphic Recording Water Stage Register. (Manufao
factured by W. & L. E, Ourley, Troy, N. Y.)
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WATER-STAGE REGISTERS
269
gauges with bench marks for checking the record and maintaining
the datum. The well and the house should be located far enough
back from the river to be out of danger from floating ice or
drift and to provide sufficient protection for the well and pipes
to prevent freezing. A permanent ladder should extend to the
bottom of the well, so that the float and intake can be readily
Fig. 149. — Method of Installing Automatic Water Stage Register.
inspected. If the register is to be maintained for a long period
the well should be lined with concrete, otherwise a heavy plank
lining may be used. The intake pipe should be placed well
below the lowest stage of the river and provided with a screen
for keeping out silt and foreign material. It should also be pro-
vided with check gate as it enters the well, so that the flow can
be reduced if necessary to eliminate wave action.
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CHAPTER IX
ELECTRICAL EQUIPMENT
1. GENERAL CONSIDERATIONS
Before entering into a detailed study of the apparatus com-
prising the electrical equipment, there are two broad problems
which require a more careful consideration and must first be
decided on, inasmuch as they have an important bearing on the
entire equipment. These problems deal with the voltage and the
frequency.
Voltage. There are three voltages between which a distinc-
tion must be made in a hydro-electric power system; viz., the
generator voltage, the transmission voltage and the distribution
voltage.
Generator VoUage. When additions to an existing plant or
system are made, the voltage of the new generators is generally
determined by that of the old machines, or by some other con-
dition of the installation. In new installations, however, the gen-
erator voltage can be determined only after considering a number
of factors. For example, a compromise must, as a rule, be found
between the increased cost of a high-voltage machine and its
control equipment as compared with the reduced cost of the bus-
bars and connections caused by the smaller amoimt of copper
required. Whether generators are to be wound for a high voltage
for direct transmission, or for low voltage and step-up transformers,
is to a certain extent also decided by the relative cost of the two
methods. If economically feasible the latter method with step-up
transformers is, however, the most reliable and to be recommended.
In other instances the nature of a local load may be such that,
by installing high-voltage generators, power for this load may be
directly transmitted at the generator voltage; while at the same
time step-up transformers may be provided for raising the pres-
sure of the current which is to be transmitted for greater dis-
tances. The standard generator voltages are given imder " Syn-
chronous Generators."
270
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GENERAL CONSIDERATIONS 271
Transmission Voltage. The transmission voltage should be
chosen to insure the most economical ensemble. Many factors
affect the problem variously, and their nature makes a mathe-
matical expression difficult and, as a rule, unsatisfactory. The
distance of the transmission is naturally the factor which governs
the choice of the voltage to the greatest extent. The crossHsection
area and, consequently, the weight to the transmission conduc-
tors, varies inversely as the square of the voltage for a given load.
The cost of the conductors is, therefore, reduced 75 per cent every
time the voltage is doubled, and it would, consequently seem
proper to use the highest voltage possible in any given case.
Though with increasing voltage, the cost of the conductors de-
creases, the cost of other apparatus and appliances increases.
This involves transformers, switching equipment, lightning
arresters and line structure and insulators, while, of course, the
necessary safety requirements become stricter with higher
voltages.
With very high voltages and long lines the capacity current of
the lines becomes considerable, especially in sixty-cycle systems,
and may reach values higher than the full-load ciurent. Its
greatest objection is that it loads the generators with current which
represents no power, and where small units are used it may often
render it impossible to throw one machine on the line alone.
Much more serious, however, is the impairment of the voltage
regulation incident to very long lines, i.e., the voltage variation
between no load and full load, especially for inductive loads. By
providing S3mchronous condensers, it is, however, possible to
compensate for the wattless currents and improve the regulation.
Another factor which has a limited bearing on high potentials
for transmission purposes is corona, as experience has shown that
if the voltage on a given line is raised beyond a certain point the
air at the surface of the conductors breaks down as an insulating
medium and becomes luminous. The most serious objection to
corona comes from the losses, which increase at a high rate as the
voltage is raised above this luminous or so-called visual critical
point. This critical voltage increases with the size of the con-
ductors and their spacing, and by properly choosing these values
the losses may be materially reduced or entirely eliminated. For
high altitudes corona starts at lower voltages and this should be
given careful consideration (see section on " Station Wiring.'*
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ELECTRICAL EQUIPMENT
The factors determining the proper transmission voltage are,
as a rule, of an economical nature, and, while no fixed formula
for determining the voltage can be given, in general it may be
said that the most economical voltage is the one for which the
annual cost of the energy loss added to the annual cost for depre-
ciation and interest on the first cost, becomes a minimum. In
determining the value of the energy loss, a mean value for a
number of years should evidently be taken, and the value should
160,000
123,000
.100,000
I 76,000
60,000
86,000
/
^
"^
/
/
i
/
/
/
0 6
B K
Transmiss
» 1,
ion Distanc
50 a
;e in Milea
w a
n
FiQ. 150. — Approximate Voltages for Power Transmission of
Various Lengths.
be based on the cost for which the power can be produced. The
interest and depreciation as well as operating charges should only
be applied to such items that will vary with changes in the volt-
age, such as the line conductors and tower line, the generating
and substation buildings, transformers, switching equipment and
Hghtning arresters.
An approximate average scale of voltages for transmission
lines up to 250 miles in length is given in Fig. 150.
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GENERAL CONSIDERATIONS 273
Disiribviion. Voltage The selection of the proper distributing
voltage is also an important matter. Where large territories
have to be served from high voltage transmission circuits, the
general practice seems to indicate that the most economical volt-
ages for such systems are in the neighborhood of from 22,000 to
33,000 volts. A second or even third transformation is, therefore,
necessary before the power can be used for motors or lighting.
The distribution of alternating current for general commercial
purposes is accomplished almost universally by 2300 volt mains,
suppl3dng step-down tran^ormers located near groups of con-
sumers, whose premises are served by secondary mains at 115 to
230 volts. Single-phase circuits are quite generally used for
lighting service, while power service is, as a rule, given from two-
phase or three-phase mains. The former S3rstem is used chiefly
where this method of distribution was established in the early
period of the development, and where it is too extensive to warrant
a change to the three-phase system, which is standard for all new
installations where a polyphase supply is wanted for power service.
For small- and medium-sized cities a three-wire, " delta "-
connected, 2300-volt system is very generally used for power dis-
tribution, while for larger cities there is a steady trend toward the
four-wire, " Y '^-connected system operating at 2300-4000 volts.
There are numerous advantages with this system where feeders
are extended more than two miles from the point of supply, and
where adjacent towns within a radius of five miles may be served
without step-up transformers or substations. It is possible to
regulate the phases separately, and there is not so much of a
necessity for maintaining a carefully balanced load. Even for
secondary distribution the four-wire, three-phase system, oper-
ating at approximately 115-200 volts, is being generally used.
With this system lighting and motor service may be given for all
ordinary retail purposes from the same circuit, the principal dis-
advantages being that there are three phases to be kept balanced.
Frequency. The subject of frequency for commercial power
and lighting systems, far from being settled, is discussed again with
every new installation. Frequency affects the operating charac-
teristics of circuits and apparatus, and also their cost.
The frequencies most commonly employed in this country
are 25 and 60. In general it may be said that, where lighting
load is predominating, 60 cycles should preferably be selected;
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274
ELECTRICAL EQUIPMENT
while, if the load mainly consists of power, 25 cycles is often prefer-
able, especially if the load consists of a large number of syn-
chronous converters. With a large induction motor load it may,
on the other hand, be more advantageous to use 60 cycles on
account of the greater number of speeds, which are possible with
this frequency.
In the following discussion the influence of frequency will be
treated in connection with frequency changers, generators, trans-
formers, transmission lines, induction motors, synchronous con-
verters, railroad work and illumination.
Frequency Changes. Frequency changers are primarily used
for efifecting a change in frequency. They are either utilized for
obtaining a frequency high enough for lighting purposes from a
low-frequency system, or, as a means of interchanging power
between systems operating at different frequencies.
The change from 25 to 60 cycles or vice versa requires a set
running at 300 R.P.M., which is a serious limitation because this
speed is much too low for the economical design of frequency
changers of small or moderate size. If an exact ratio is not abso-
lutely necessary, as when power is taken from an existing system
for lighting and industrial purposes, and the frequency changer
is not intended for tying two generating systems together, the
available range of speed is greatly increased as shown in the fol-
lowing table.
TABLE XL
Frequency-Changer Combinations
Fbbquknct.
Polka.
Speed.
Generator
Frequency.
Motor.
Generator.
Motor.
Generator.
25
62.5
4
10
750
4.17 per cent high
25
62.5
8
20
375
4.17 percent high
25
60
10
24
300
Exact
25
58.3
6
14
500
2.78 per cent low
25
56.3
8
18
375
6. 18 per cent low
60
26.7
18
8
400
6.8 per cent high
60
25.7
14
6
514
2.8 per cent high
60
25
24
10
300
Exact
60
24
20
8
360
4 per cent low
60
24
10
4
720
4 per cent low
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GENERAL CONSIDERATIONS 275
While synchronous motors are abnost invariably used with
frequency changers, induction motors may be used if proper
arrangements are provided for adjusting the slip so as to insure
a satisfactory parallel operation. This adjustment, of course,
means the introduction of a permanent resistance and a corre-
sponding loss, and is, therefore, undesirable unless other advan-
tages of greater importance can be obtained. Where only one
set is required speed adjustment is not necessary, and the motor
may be designed with a sUp which will just be sufficient to bring
the generator frequency to the right value.
Generalors. 'The frequency of sjmchronous generators in
alternations per minute is equal to the number of poles times the
revolutions per minute, and the periodicity or cycles per second
is shown by the following equation:
^ , Number of poles X rev. per min.
Cycles ^ ^ .
Due to the fact that there is a natural relation between the
windings of electrical apparatus which varies inversely as the
square of the frequency, the higher the frequency the greater is,
in general, the peripheral velocity at the same revolutions per
minute. Increase in peripheral velocity means a larger diameter
with a smaller length and a better natiu'al ventilation. The
higher periodicity in definite pole machines is also preferable
in that the load of the rim of the spider is better distributed and
smaller in amoimt at the point of attachment of poles.
The induced e.m.f. is directly proportional to the frequency
and, due to the lower core loss with lower frequencies, the effi-
ciency is naturally better at 25 than at 60 cycles. The cost is
also increased by the frequency there being a natural tendency
for 25-cycle apparatus to be heavier than 60-cycle. As a general
rule, the labor item is higher on the higher frequency machines,
and the material item higher with the lower frequencies.
Parallel operation is more satisfactory at low frequencies, so
far as the variation in angular velocity is concerned. Due to
other factors, the conditions for parallel operation depend more
upon the relations between natural and impressed frequencies,
rather than upon the absolute value of either.
Traruformera, The frequency has a very important bearing
both on the design and operation of transformers. With trans-
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276 ELECTRICAL EQUIPMENT
fonners and other electric apparatus using two windings and an
iron core, the ratio of turns, other factors remaining the same, will
be approximately inversely as the square root of the frequency.
The lower the frequency the larger the flux, and the larger the
number of turns for the same voltage. Therefore, transformers
increase in cost and weight as the frequency decreases.
The regulation of 25-cycle transformers is not quite as good as
for 60-cycle on account of the increased drop, due to the great
number of turns and their increased mean length, and the efli-
ciency is also somewhat less.
Operating 25-cycle transformers on a 60-cycle circuit decreases
the flux density and the core loss. Operating a 60-cycle trans-
former on a 25-cycle circuit increases the density and core loss, and,
in general, gives a prohibitive exciting current. Frequency also
enters into the mechanical forces to which a transformer may be
subjected, as the reactance increases with the frequency, and,
while the mechanical force varies directly as the square of the
current, a 25-cycle transformer operating on a 60-cycle circuit
would be subject to about one-half the mechanical strains on short-
circuit. The limit of reactance in a transformer is from 8 to 10
per cent at 60 cycles and somewhat higher at 25 cycles.
Transmission Lines. Transmission lines are designed from
considerations of regulation and efficiency and, as explained more
fully imder " Voltage," the regulation is better as the frequency is
lower, and so for commercial work 25 cycles is preferable to 60
cycles, considering the line alone. The capacity current plays,
as stated, also an important part with small units and high volt-
ages, rendering it often impossible to throw one machine on the
line alone. Both the reactance and the capacity current of the
line are proportionate to the frequency as shown by the following
equations:
Reactance = 2irfL ;
Capacity current = 2ir/CJ?;
The resistance of wires and cables canying alternating cur-
rents is also affected by the frequency, in that the current is not
distributed uniformly over the cross-section of the conductors, the
current density being higher near the periphery. This is known as
" skin effect ** and results in an increased resistance. The eflfect
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GENERAL CONSIDERATIONS 277
is, however, negligible for low frequencies and small conductors,
but increases rapidly for higher frequencies and large conductors.
With magnetic material it is much higher than with non-magnetic,
and its effect should be considered where iron conductors are used
and for heavy copper work.
Induction Motors. The speeds of 25-cycle induction motors
for general application are practically limited to 750, 500 and 375
R.P.M., while the corresponding speeds for 60-cycle motors would
be 1200, 900, 720, 600, 514, 450, and 400 revolutions. Twenty-
five-cycle motors could, of course, be woimd for two poles, giving a
speed of 1500 revolutions, but this is rarely done except in the
very small sizes. The objection is that since the flux per pole is
twice as large as in the four-pole type, the section of iron back of
the slots must be twice as great, for the same rotor diameter.
Moreover, the end connections become very long and the machine
difficult to wind and consequently the cost is very materially
increased.
The efficiency depends upon a number of features. The lower
frequency will, of course, tend to make the iron loss less, but on the
other hand, the copper loss will be considerably greater on accoimt
of the longer end connections, and, as a rule, the efficiency is foimd
to be somewhat lower for low- than for high-frequency motors.
The power factor of an induction motor is expressed by the
ratio tt — 1 • x- It is affected by the reactance and the mag-
Kv.A. mput
netizing current. At constant line voltage the latter remains
practically constant, while the former varies with the current.
The shape of the power factor curve, that is, the power factor at
fractional loads and overloads, therefore, depends upon the rela-
tive values of the magnetizing ciurent and the reactance.
R
Power factor = cos 0 = •=.
A motor with a relatively large magnetizing current and a low
reactance will, in general, have a low-power factor at fractional
loads and a rapidly increasing power factor at higher loads, while
a motor with a relatively low magnetizing cmrent and a high reac-
tance will have a high-power factor at fractional loads and only a
slightly greater power factor at overloads.
The 25-cycle motor has an inherently lower reactance and
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278 ELECTRICAL EQUIPMENT
requires less magnetizing current, for which reason its power
factor is considerably higher than for high-frequency motors.
The starting torque and the maximum torque depend inversely
on a function of the reactance, and are, therefore, higher for low
frequencies.
The starting torque of an induction motor is equal to:
the starting current is equal to
E
Z'
the running torque is equal to
, E^sri
the maximum torque is equal to
k ^ .
[{2{r+VW+X^)]'
where k = constant ;
J? = applied voltage;
« = slip;
r=stator resistance per phase;
fi == rotor resistance per phase;
X= total reactance;
Z = total impedence ;
Comparing the weights based on motors of the same capacity
and speed, it is found that, on the average, 25-cycle motors will
weigh about 15 per cent more than 60-cycle motors. For the
smaller sizes there is very httle difference in the cost, but as the
sizes increase there is a marked difference in favor of the 60-cycle
motors.
Synchronous Converters. Ji synchronous converter being in
effect a combination in one machine of a synchronous motor and a
direct-current generator, the important factors in which the fre-
quency is concerned have to do almost entirely with the contin-
uous-current side. The continuous-current generator, as a rule,
nms at frequencies much below 25 cycles, and at the frequencies
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GENERAL CX)NSIDERATIONS 279
of synchronous converters, especially for 60 cycles and above,
the problems of commutation and commutator construction be-
come of importance. The pole pitch on the commutator, arma-
ture or field, is the space passed through in one alternation, and
it is thus seen that there is a natural tendency for higher per-
ipheral speeds at the higher frequencies, and it is the limitation
of peripheral speed which fixes the limits of design.
With direct-current machines this occurs with turbine-driven
generators and in the commutators, which are necessarily mechan-
ical in construction, consisting, as they must, of a certain amoimt
of insulation. Direct-current generators are, therefore, more
limited in speeds than alternating-ciurent, and the same holds
true when they are combined as in rotary converters.
Improvements in design have made the 60-cycle synchronous
converter entirely satisfactory for the conditions under which
such machines operate. In eflBiciency 26-cycle converters are
slightly higher than the 60-cycle.
Railroad Work. Twenty-five cycles has been recognized as
the standard frequency for railway systems in this country.
Until not long ago all systems were of the altemating-current-
direct-current type, alternating current being generated and
transmitted to the various substations, where it was changed to
direct current by means of sjmchronous converters. The choice
of this frequency was, therefore, chiefly caused uy the less satis-
factory operation of the earlier types of 60-cycle converters.
Even with the successful operation of the present 60-cycle
converters, there is no reason for changing the standard 25-cycle
frequency. While 60 cycles would be preferable as far as the
generators and transformers are concerned, this is ofiFset, however,
by the advantages of the 25-cycle transmission system and the
lower cost of synchronous converters for larger capacities. Where^
the supply is 60 cycles, synchronous motor-generator sets are very
often used for the conversion.
With the introduction of the alternating-current railway motor,
60 cycles is obviously entirely eliminated, due to the excessive
impedence drop and " skin effect " caused by the alternating;
ciurent flowing in the rails. The 25-cycle system, on the other
hand, is fully satisfactory for this service, and, although the 16-'
cycle sjrstem has been advocated, its advantages over the 25-cycle
system have not been proved to be of suflicient weight to neces-
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280 ELECTRICAL EQUIPMENT
sitate a change in the present standard frequency. In Europe,
however, a few single-phase systems are using this frequency.
Illumination, Where alternating cmrent is used for lighting,
the 60-cycle frequency is generally used. No arc lamp has as
yet been developed that will operate with entire satisfaction on
frequencies of less than 40 cycles, and incandescent lamps cannot
be used to advantage on frequencies of less than 30 cycles.
Low-voltage incandescent lamps show no flicker; but the effect
of fatiguing the eye is noticeable at 25 cycles, especially in high-
voltage lamps.
In systems where lighting predominates a 60-cycle frequency
should, therefore, be selected, while, if most of the energy is to be
used for power purposes the condition may be such that 25 cycles
would prove to be preferable, in which case frequency-changers
can be provided for changing the current required for lighting
purposes to 60 cycles.
2. SYNCHRONOUS GENERATORS
Alternating-current generators may be classified into two
general classes according to their general characteristics: S3rn-
chronous generators and Induction generators. The former type
is used almost entirely while the latter is used only occasionaUy
for special cases as explained under the section of Induction
Generators.
The generator forms one of the most important parts of the
equipment in a hydro-electric development and a thorough knowl-
edge of its characteristics and design is of the utmost importance.
The subject will, therefore, be treated somewhat more in detail
than would at first seem desirable.
General Description. Most alternating-current generators
are of the revolving field type. The armature, which is then
stationary, consists of a laminated iron core supported by a cast-
iron frame, the inside periphery of the core being slotted to carry
the armature winding. Inside the stator revolves the rotor or
revolving field system, and as S3mchronous generators are not
self-exciting, the field excitation is obtained from some external
direct-current soiu'ce.
Induced E.M.F. The e.m.f's. and currents are alternating,
i.e., have one-half wave or alternation, first positive and then
negative, for each pole passed by a given armature conductor.
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SYNCHRONOUS GENERATORS 281
A cycle is a complete wave of two alternations and the frequency
is equal to the product of the number of pairs of poles and the
speed of the machine in revolutions per second; it is, therefore,
strictly proportional to the speed of the machine.
The wave shape of the e.m.f.\ depends on the distribution of
the magnetic flux at the armature surface, and the total e.m.f.
is the sum of the e.m.f . waves in the different armature conductors,
added in the proper phase relation. The instantaneous values of
the e.m.f. and current are constantly changing from maximum
positive to maximum negative and the specified or effective value
is equal to the square root of the average value of the square of
the instantaneous values. For a true sine wave shape it is equal to
the maximum value divided by V2.
The phase relation differs symmetrically for pol3rphase sys-
tems. In the two-phase system the terminal voltages of the two
circuits differ in phase by 90 electrical degrees, Fig. 151, and in the
Fig. 151. — ^Two-phaae Alternating Current.
three-phase system, the terminal voltages of the three circuits
differ in phase by 120 electrical degrees, Fig. 152. The terminal
voltage of two-phase generators is equal to the e.m.f. of the arma-
ture circuits and the line current equal to the current in these cir-
cuits. For three-phase machines, however, the armature winding
can be connected either Y or A, which will be discussed more fully
later. If the winding is Y-connected, then the terminal voltage
is equal to Vs times the e.m.f. per armature circuit and the line
current equal to the armature current. If the winding is A-con-
nected, then the terminal voltage is equal to the e.m.f. per circuit
and the line current equal to Vs times the current in the armature
circuit. In general, when speaking of current and voltage in
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282 ELECTRICAL EQUIPMENT
in a three-phase system, under current the Y-current or current
per line and under voltage the A-voItage or voltage between lines
Fig. 152. — ^Three-phase Alternating Current.
wires is understood. This subject is covered more fully in the
section on " Armature Connections."
The e.m.f. induced in the armature circuit is determined by
the following formula:
in which A?/ = wave form factor;
fc,=slot factor;
ii0= winding pitch factor;
/= frequency in cycles per second;
n=s number of armature conductors connected in series
per phase (twice the number of turns per
phase);
0=flux per pole in maxwells.
The form factor of an e.m.f. wave is defined as the ratio
5- ^ and for a sine wave this value is equal to 1.11.
average voltage
The armature winding is generally distributed, that is, the
armature conductors are placed in more than one slot per pole per
phase. The principal advantages of such a distribution is the
closer approximation toward a sinusoidal wave form, while, on the
other hand, the total radiating surface of the coils is increased.
With a distributed winding the e.m.f. will, however, be some-
what reduced because the voltage induced in the conductors in
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SYNCHRONOUS GENERATORS
283
the different slots are somewhat out of phase with one another,
and for this reason the slot factor h, for which the values are
given in Table XLI, must be introduced in the formula. With
two-layer windings the value of k, should correspond to the num-
ber of slots per layer per pole per phase and not to the total num-
ber of slots per pole per phase.
TABLE XLI
Values of Slot Factor k.
Slots per Pole
per Phase.
Two-phase.
Three-phase.
1
2
3
4
5
6
1.000
0.924
0.911
0.907
0.904
0.903
1.000
0.966
0.960
0.958
0.957
0.956
The windings may be arranged for full or fractional pitch. In
the former case the coil spans a distance exactly equal to pole
pitch while in the latter case it
spans a lesser distance. Frac-
tional pitch windings are very
generally used, the advan-
tages being a better wave and
shorter end connections of the
windings, resulting in a sav-
ing of annature copper be-
sides making the machine
shorter. This is especially
the case for machines with a
small number of poles. It is
evident that the e.m.f's. in-
duced on both sides of the
same coil are not exactly in
phase with each other in a fractional pitch winding, so that a
larger flux will be required than with a full-pitch winding. This
is allowed for in the voltage formula by introducing a winding
IM
^
=^
■^
^Aon
^/^
^
•g
/
5oJio
/
f
/
/
60 70 80 90
Per cent Wlodlnc Pitch
100
FlQ. 153.-
-Valuea of Winding-pitch
Factor.
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284 ELECTRICAL EQUIPMENT
pitch factor, K, its values for different per cent pitch being given
in Fig. 153. They are simply based on the formula:
ia0»Bin
ln(Xx(K.-),
where x is the per cent pitch.
For single-phase generators the annature is generally wound
similar to a three-phase machine, one-phase being left normally
idle. With this arrangement the slot factors ks are the same as
given for three-phase windings. If the winding is furthermore
distributed as with purely single-phase generators, when it covers
considerably more than two-thirds of the annature surface, the
values of these slot factors should be reduced.
The flux 0, obtained from the previous formula is that which is
necessary in the armature for inducing the required e.m.f., i.e.,
the useful flux. Due to the leakage between the poles it is, how-
ever, necessary to provide a greater flux in the field poles and the
yoke to compensate for this leakage, and this must be considered
when calculating the ampere turns of the field winding. This
increased flux is obtained by multiplying the useful flux by a leak-
age coefficient. The average values for this factor at no load,
depending on the diameter per pole, may be obtained from Table
XLII.
TABLE XLII
Pole Leakaqb CosFncnBMTB
Diameter per pole, inches: 2 3 4 5 6 7 8
Leakage coefficients: 1.4 1.35 1.3 1.26 1.22 1.18 1.16
Effect of Power Factor on Operation. Assuming all conditions
except the load constant, the terminal voltage of an alternating-
current generator will fall as the load increases. This is due to
the resistance of the armature conductors and the synchronous
reactance, the latter combining the effects of the annature reac-
tion and the armature reactance or self-induction. For a con-
stant terminal voltage with increased load, the armature resistance
and self-induction require an increase in voltage while the demag-
netizing effect requires only an increase in the magnetic flux to
make up for the reduction in flux caused by the armatm^ current.
The latter does not require any increase in the generated voltage
since the action is conflned to the magnetic flux.
The drop in voltage, due to the armature resistance, requires
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SYNCHRONOUS GENERATORS
285
Fio. 154. — ^Armature Reaction.
Current in Phase.
no explanation beyond the statement that the voltage drop is iii
phase with the current flowing.
The armature reaction, which represents the resultant e.m.f.
of the armatiu^ currents, de-
pends on the current and the
number of effective turns in
series per pole per phase. It
noiay have a magnetizing or
demagnetizing effect, or it may
shift the field flux from one
side of the pole to the other,
or its effect may be a com-
bination of the two. The
energy component of the cur-
rent will only cause a shifting
or distorting effect, while the
wattless component will cause
a demagnetizing or magnetiz-
ing effect, depending on
whether the current is lag-
ging or leading. These effects
are illustrated in Figs. 154 to
156.
Rg. 154 represents two
conductors of an armature
coil. These are midway under
a north and south pole, re-
spectively, and the e.m.f. in-
duced in the coil is obviously
a maximum for this position.
The current in the coil will
also have the maximum value
as it is in phase with the e.m.f.
and the flux produced by the
same will have a crofis-magnetizing effect not directly opposing
the field ampere-tiuns, but simply causing a distortion of the field
flux. The current in the armature, however, always lags behind
the induced e.m.f. by reason of the inductance, and even with
unity power factor in the external circuit, the armature reaction is
demagnetizing to a certain extent.
Fig. 155. — ^Armature Reaction.
Current Lagging.
Fio. 156. Armature Reaction.
Current Leading.
• Annatare OoDdactoc
0 In-pbase GompoDeni
of Armatore Carrent
0 WatttoM CompoDent
of Armature OaxrcBit
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286 ELECTRICAL EQUIPMENT
In the position shown in Fig. 155 the e.m.f. generated in the
coil has a value somewhere between zero and maximum, zero cor-
responding to a coil position midway between the field poles.
The armature current, which, in this case, is lagging somewhere
between 0^ and 90^, can be considered as made up of two com-
ponents, an in-phase component having a cross-magnetizing
effect, and a 90^ lagging component having a demagnetizing
effect. At zero power factor the wattless armature current,
lagging 90^, has a maximum value, and consequently the greatest
demagnetizing effect.
In Fig. 156 the current is leading and its effect is just opposite
to that when the current was lagging. It is thus seen that, in a
generator, the field is weakened by a lagging current and strength-
ened by a leading current.
The armature reaction in polyphase generators is materially
different from that in single-phase machines. In the former its
total effect combines that of the several phases and hajs a constant
value provided the load is balanced. If unbalanced it will be of a
more or less pulsating nature of double frequency, as is always the
case in single-phase generators.
The armature self-induction is caused by the leakage flux
which is set up by the armature current and which does not inter-
link with the field flux. Since the armature current is alternating,
the local or leakage flux, which does not become linked with the
main field, will be continually altering in magnitude and direction,
so that there is set up a self-induced e.m.f. proportional to the
leakage flux of each phase and lagging 90^ behind the current.
The armature leakage is usually local, and thus a distributed
winding with many slots will have a smaller leakage inductance,
since the flux generated by each imit of current will be linked with
a smaller number of ampere turns.
The exact value of the self-induction of an armature winding is
somewhat difficult to determine, its magnitude depending upon
the reluctance of the paths taken by the leakage flux. There are,
however, several methods in use which give results which agree
very closely with those afterwards obtained experimentally.
If L is the self-induction, expressed in henrys, and / the fre-
quency, the inductive reactance is equal to 2vfL, It is of the same
nature as resistance and is expressed in reactance ohms. The
counter e.m.f. caused by it is lagging 90^ behind the current, and
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SYNCHRONOUS GENERATORS
287
the e.m.f. which it consumes and which has to be impressed, must
thus be leading 90^ ahead of the current. This is illustrated in
Fig. 157.— E.m.f. and M.M.F. Diagram. Non-inductive Load.]
Fig. 158. — E.M.F. and M.M.F. Diagram. Lagging Inductive Load.]
0
Fig. 159.— E.M.F. and M.M.F. Diagram. Leading Inductive Load.
the diagram, Fig. 157, where the vector XI denotes the e.m.f.
consumed by the reactance X.
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288 ELECTRICAL EQUIPMENT
The vector Et represents the terminal e.m.f. and / the current
which in this case is in phase with the terminal e.m.f., the load
being non-inductive. The e.m.f. consumed by the resistance is
equ^ to RI, in phase with /, and Eg is the e.m.f. which must be
induced to obtain a terminal e.m.f. Et and overcome the effects
of the resistance and reactance, thus causing a current to flow.
The flux required to produce Eg is 90^ ahead of this e.m.f ., the
magneto-motive force or ampere-turns to produce the same being
represented by Fg. Due to the demagnetizing effect of the arma-
ture current, t.6., the armature reaction, the vector Fg is the
resultant of the m.m.f . of the armature current Fa, and the total
impressed m.m.f. or field excitation Fe. The m.m.f. Fa is in
phase with the current, and after having determined the value of
Fg and Fa, the necessary field excitation F« is obtained by com-
pleting the parallelogram.
The effect of a lagging inductive load is shown in Fig. 158 and
of a leading inductive load in Fig. 159. For the same terminal
voltage Et, it is seen that, as compared with a non-inductive load,
a much higher field excitation is required with a lagging inductive
load, and a lower field excitation with a leading inductive load.
The field excitation required to produce the terminal voltage Eg
at open-circuit would be obviously less than the field excitation
with non-inductive load.
Field Excitation. The excitation or filed ampere-turns
required to produce the magnetic flux which is necessary in order
to induce a desired e.m.f. depends on the character of the mag-
netic circuit, i.e. J on its dimensions and on the material of which it
is made up. The values are readily obtained by reference to
standard saturation curves, similar to the ones shown in Fig. 160,
these curves, of com-se, depending upon the quaUties of the iron
or steel which is used. The total magneto-motive force per mag-
netic circuit is equal to the siun of the m.m.f's. necessary for
establishing the required flux in the separate parts of the circuit
which are in series; viz., the pole pieces, the field spider, the air
gaps, the teeth and the armature core.
The relation of the e.m.f. produced by an alternator at no-load,
i.e., open circuit, to the field current when the alternator is driven
at constant speed is represented by the no-load saturation curve.
Such a curve is shown by curve A, Fig. 161, and it is seen that this
curve is almost a straight Une for small exciting currents. At low
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SYNCHRONOUS GENERATORS
289
excitation, the reluctance of the air gap is very high and that of
the iron very low, and, therefore, the former may be considered
as constituting the entire reluctance of the magnetic circuit.
Since the reluctance of air is constant regardless of the flux density,
at small excitations the flux will be proportional to the mag-
neto-motive force, and, therefore, the open circuit voltage is pro-
portional to the field current, hence the curve is straight. As
the field becomes stronger, however, the proportion of the air-gap
reluctance to the entire reluctance decreases because the per-
meability of iron decreases with increased flux density, and,
therefore, the e.m.f . increases less rapidly with increased excitation.
ISO
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Fig. 160. — Saturation Curves.
It was pointed out in the previous section that when a current
is flowing in the armature circuit, i.e., under load, the field ampere-
turns required to maintain normal terminal voltage, exceed the
no-load ampere-turns required for normal voltage, due to the
resistance and the synchronous reactance of the armature circuit.
A number of more or less accurate methods have been proposed
for calculation of the above components, and thus determining the
required field excitation at full load. IQiowing the resistance
and the leakage reactance or self-induction of the armature, the
voltage drop caused by these is added vectorically to the terminal
voltage, this giving the voltage which must be induced (see Figs.
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290
ELECTRICAL EQUIPMENT
SIM
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Fig. 161. — Alternator Characteristics.
157 to 159). Knowing from the no-load saturation curve the
required net excitation at this voltage, and correcting it for the
effect of the armature re-
action, the necessary total
field ampere-turns are ob-
tained. The result of such
calculations for different loads
and power factors are repre-
sented by the load-character-
istic curves. Such a full-load
characteristic of an alternator
is shown by curve J?, Rg. 161.
In order to get the best
combination for automatic
voltage r^ulation an alter-
nator should preferably have
a range in excitation from
no-load to maximum load, with approximately 80 per cent
power factor, of the ratio of not more than one to two. With
125 volts excitation, the voltage should, therefore, not be allowed
to exceed 125 volts at maximum load, 80 per cent power factor,
and the corresponding no-load excitation should be about 70
volts. Should the excitation voltage be 250, the same ratio should
hold true.
The excitation required varies considerably for different
machines, depending upon the size, the number of poles, the speed
and the regulation. For alternators of different capacities, but
otherwise similar, the relative excitation naturally decreases as
the size of the alternator increases. High-speed machines gen-
erally require less excitation than slow speed, due to the smaUer
number of poles. With a large number of poles, however, the air
gap is usually smaller, and this will somewhat offset the higher
excitation for slow-speed machines. In general, it may be said
that small machines with many poles require a proportionally
large excitation and large machines with few poles a small exci-
tation. The curves given in Fig. 162 give the approximate exci-
tation required by water-wheel driven synchronous generators.
The values given are per Kv.A. per R.P.M. of the generator capa-
city, and is based on a maximum continuous rating at 80 per cent
power factor.
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SYNCHRONOUS GENERATORS
291
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Fig. 162. — ^Approximate Excitation of Water Wheel-driven Polyphase Syn-
chronous Generators. Per Kv.A. per R.P.M. Based on Maximum
Rating at 80 per cent Power Factor.
Regulation. The regulation of an alternating-current gener-
ator is the rise in voltage when a specified load at specified power
factor is reduced to zero; the speed and field excitation remaining
constant. It is expressed in per cent of normal rated-load voltage,
and unless otherwise specified understood to refer to a non-induc-
tive load.
A close inherent regulation was formerly considered one of
the essential requirements of a good generator, but fortunately
this idea is now entirely changed. A low percentage regulation
may be obtained in two ways; first , by designing the generator
with a field magnetically strong as compared with the armature,
so that the self-induction and demagnetizing effect of the armature
is comparatively small, resulting in a small increase in field current
required to maintain normal voltage with increase in load; and,
second, by saturating the magnetic circuit, particularly in the
field, where high densities do not increase the losses or temperature
rise.- Both of these methods are, however, detrimental to the
present-day operating practice. A decrease in the synchronous
reactance, would proportionally increase the short-circuit currents
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292 ELECTRICAL EQUIPMENT
of the machine and dangerously increase the severe mechanical
strains produced by the same on the apparatus, as these increase
with the square of the current. A highly satiu*ated machinei
on the other hand, is detrimental to the use of automatic voltage
regulators. With these regulators a close inherent r^ulation
machine is not necessary as a good regulation of the system can,
nevertheless, be maintained. The regulator automatically in-
creases the field excitation as the load increases and thus main-
tains a constant terminal voltage. If desired, it can also be
adjusted so as to increase the voltage with the load and comr
pensate for the line drop.
Modem water-wheel-driven alternators have a regulation at
unity power factor of aroimd 20 to 25 per cent. This is con-
sidered entirely satisfactory as the voltage regulation is best taken
care of by automatic voltage regulators.
Short-circuit Current. In speaking about the short-circuit
current of an alternator, distinction must be made between the
instantaneous short-circuit current and the sustained or permanent
short-circuit current.
The sustained short-circuit current of an alternator is limited
by the armatiu^ resistance and reactance, as well as its reaction
on the field. It is equal to
z:
where E is the generated e.m.f . corresponding to the field excita-
tion, and Z, the "synchronous impedance," representing the
combined effect of the above three factors. This formula, there-
fore, gives the value of the sustained short-circuit current, while its
instantaneous value wUl be very much higher. This is due to the
fact that in the first instant, when the generator is short-circuited,
the current is limited only by the resistance and self-induction of
the armatiu^ circuit, while a time lag of sometimes a few seconds
takes place before the armature reaction becomes effective. The
armature resistance and reactance are thus the only two quan-
tities that limit the instantaneous short-circuiting current. This
limiting effect is, however, not constant, but decreased slightly
with high short-circuiting currents due to their saturation of the
magnetic field.
Fig. 163 represents an oscillogram of a typical three-phase
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SYNCHRONOUS GENERATORS 293
short circuit, the generator being short circuited at the terminals
of the armature winding. Comparing the currents for phases
A and C, it is noticed that the latter gives an approximately sym-
metrical relation of the current crests with respect to the zero-
axis, while in the former case the wave is displaced so that the
maximnm peak of the initial current is nearly double that of phase
A, the actual ratio for the average machine being about 1.8. In
calculating the instantaneous short-circuit current which may occur
under the worst conditions, an unsymmetrical current wave should,
■W/WVWWwwwvwv//'sri
/vWWWWWWWM^^vv^
Cnmniin
^CmreDtia
^ FImmO
Fia. 163. — Oscillogram of Three-phase Alternator Short Circuit.
therefore, be considered as well as the fact that the short circuit
may occur when the generator is excited for full load, which would
mean a still further increase of say 10 per cent in the flux and in
the short-circuit current. Thus, for a generator, with 20 per cent
reactance, the maximum peak would be -^r^r- or five times the normal
ZU
mean effective current times V2 times 2.
The sustained short-circuit current is, as previously stated,
limited by the synchronous impedance, or less exactly, the syn-
chronous reactance, of the generator, and, neglecting saturation,
it is directly proportional to the field exciting current. Although
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ELECTRICAL EQUIPMENT
synchronous reactance is a fictitious quantity, expressing as it
does in a single quantity both the armature reaction and the
armature self-induction or reactance, it, nevertheless, represents
the equivalent of a true reactance and may be expressed in ohms
and taken just as any other reactance in determining the sus-
tained short-circuit current. It can also be combined in the
ordinary way with any external reactance.
The per cent synchronous reactance is determined from the
Amperes Field
Fig. 163a. — Saturation and Synchronous Impedance Curves.
saturation and synchronous impedance curves, Fig. 163a, as
follows:
In order to produce the normal current In a field current F«
is required, which would cause an open-circuit voltage e. A field
current Fb would produce on open circuit a normal voltage E if
there were no saturation. Hence, e is consumed in the syn-
chronous reactance with normal current flowing, and the per
cent synchronous reactance is
x.«|xioo=^xioo.
This, combined with the per cent reactance and resistance of the
external circuit, will give the sustained short-circuit current Ie,
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SYNCHRONOUS GENERATORS 295
corresponding to the field current Fg, and it is then only necessary
to increase Is in the ratio of the actual field current on the alter-
nator at the time of short circuit to Fb That is, the sustained
short-circuit current at load excitation Fi is
PB
If a voltage regulator is used, the generator field current corre-
sponding to the maximum voltage across the collector rings must
be taken as Fi.
For water-wheel-driven alternators the sustained short-circuit
current based on full-load excitation is generally from two to three
times the normal full-load current.
When a short circuit takes place the current becomes lagging
and its effect will be to demagnetize the field poles. Assume, for
example, a generator with short-circuit current ratio of ten times
the normal full-load current. Then tan 0 = 10 and 0=84.5^
Thus cos 0 or the power factor under short circuit is equal to 0.09.
However, it requires an appreciable time to reduce the magnetic
flux to its low short-circuit value, since it is surrounded by the
field coils, which act as a short-circuited secondary opposing a
rapid change in the field flux, that is, in the moment when the
short circuit starts it begins to demagnetize the field, and the
magnetic field flux, therefore, begins to decrease. In decreasing,
however, it generates an e.m.f. in the field coils, which opposes
the change of field flux, that is, increases the field current so as to
momentarily maintain the full field flux against the armature
reaction. The field flux, however, gradually decreases, and
also the field current which increased considerably the first
moment. This is clearly illustrated in the oscillograms shown in
Pig. 163.
Armature Connections. Synchronous generators may, as
previously mentioned, be connected either single-phase, two-phase
or three-phase. Single-phase machines are rarely used, and when
two-phase machines are required it is, as a rule, in connection
with some existing system. Three-phase machines, on the other
hand, are used almost exclusively, due to the many advantages
of this system over the other two.
A three-phase cmrent may be obtained from an ordinary
closed coil winding by making connections to point on the winding
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ELECTRICAL EQUIPMENT
spaced 120^ apart as in Fig. 164. Such a method is, however,
rarely used because the e.m.f.'8 of the sections, which are com-
bined with each other to form one-phase of the three-phase cir-
cuit, are out of phase with each other, and the resultant e.m.f.
Fig. 164.
Fio. 165.
Fig. 166.
Fig. 168.
Fig. 167.
and, consequently, the capacity of the machine is reduced, simply
because the most effective use of the windings is not obtained.
The highest output is, however, obtained with the delta and star
connections where groups of similar phase relations are connected
in series or paraUel as in Figs. 165 to 168. Of these, however, the
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SYNCHRONOUS GENERATOBS 297
star connection is preferred, the main advantages of this con-
nection being:
1. It is possible to bring out a lead from the neutral point,
which is useful for various purposes.
2. The cost is less than with delta connection, requiring
approximately only 58 per cent of the turns.
3. It is not possible for circulating ciurents of triple frequency
to flow in the windings.
If E represents the effective e.m.f. of each group and / the lim-
iting current which can be carried by the same, the corresponding
three-phase capacities of the various arrangements will be
Rg. 164: 3XV3£X/=6.196£/;
Rg. 166: 3X2EXl=6EI;
Fig. 166: 3X2IXE=6EI;
Fig. 167: 2V3EXIXV3^6EI;
Rg. 168: V3^X2/XV3=6£/.
For two-phase connections the capacities are the same for the
different combinations shown in Rgs. 169 to 172. If Ei repre-
sents the e.m.f. of each group and / the permissible current it
equals 4EiL
The armature winding of single-phase generators can be
arranged either for purely single-phase duty or on the basis of the
same winding being used both for polyphase and single-phase
flervice, the latter method being the one mostly used. When
intended for three- and single-phase service any one of the con-
nections shown in Rgs. 173 to 175 can be used, although the star
connection in Rg. 175 is by far the most common..
The single-phase e.m.f's. will be the same as three-phase with
the exception of the arrangement shown in Rg. 174, where the
single-phase connection is obtained from diametrically opposite
points on the closed-coU winding.
The comparative capacities of the machines when used for
smgle-phase and three-phase service should obviously be based
on the losses and heating in the individual armature coils or group
of coils and not on the total armature losses. The reason for this
is that the armature loss is not equally divided among the differ-
ent groups of coils and the heating therein will consequently be
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298
ELECTRICAL EQUIPMENT
^ E-
FiQ. 169.
Fig. 170.
Fig. 171.
Fig. 172.
Fig. 173.
Fig. 175.
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SYNCHRONOUS GENERATORS 299
higher in groups carrying the highest current. When a poly-
phase machine, therefore, is loaded single-phase its capacity is lim-
ited by the current which any individual coil can carry, and this
current is obviously the same whether polyphase or single-phase.
With the connection, as shown in Fig. 173, the three-phase
rating is the same as in Fig. 164; viz., 3xV§-BX/, or equal to
5.19&EL The corresponding single-phase rating is V3EX1.5I
or equal to 2.598 E; the two groups of the winding carrying the
limiting current / while the other four groups carry a ciurent equal
to -, the total current thus being 1.5/. The single-phase capacity
with this connection is, therefore, equal to 50 per cent of the cor-
responding three-phase rating.
The diametrical connection shown in Fig. 174 gives a much
higher rating than the previous one. The relative capacities,
however, depend on whether the six terminals are utilized in
connection with transformers for obtaining three-phase power.
As each half of the winding can carry the limiting ciurent /, the
total current is equal to 2/, and the single phase rating 4EI, the
single-phase e.m.f . being 2E. The corresponding six-phase rating
is equal to &EI, and the single-phase rating is, therefore, 66.7
per cent of this rating. For straight three-phase connection,
however, the three-phase rating becomes 5.196-B/ and in this case
the single-phase capacity is 77 per cent of the three-phase.
With star connection shown in Fig. 175, two of the phases
carry all of the current while the third phase is idle and could be
omitted, although it is generally added, being a reserve in case
of accident to either of the other phases. With the star arrange-
ment, as shown, two-thirds of the winding is almost in phase with
the single-phase terminal e.m.f., being 86.6 per cent effective, and
this arrangement is, therefore, about 15 per cent more effective
than the delta connection shown in Fig. 173.
The three-phase rating is SEXixVs or equal to 5.196S/,
while the single-phase rating is equal to 3EI; thus 57.7 per cent
of the three-phase rating. This is by far the most common method
of connecting armature windings for single-phase service.
The general practice in building single-phase generators is to
use a Y-wound stator and give it a rating from 65 per cent to 70
per cent of the three-phase rating. This is possible, since one-
third of the armatiu'e slots will either be vacant or filled with
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300
ELECTRICAL EQUIPMENT
Fig. 176.
coils in which no current is flowing, and so serve to cany away the
heat from the two-thirds of the stator in which
there is current.
With two-phase alternators, single-phase
current may be taken off from two of the termi-
nals, and assmning the same limiting current /
per coil and a coil e.m.f. Eu we get the single-
phase capacity for Fig. 169, V2Ei X2/, or equal
to 2,828^i/ which is 70.7 per cent of the cor-
responding two-phase rating 4JEiI.
For the arrangements shown in diagrams
Figs. 170 to 172, the single-phase rating will be
equal to 2JE^i/, while for Figs. 176 and 177 it
will equal 2.828EiL
A comparison of the two-phase and three-phase capacities
both with respect to each other and
to the single-phase ratings obtained
is readily made. As Ei is equal to
V2XEy the two-phase ratings 4-Bi/,
when put in terms of three-phase,
will be 4Xy/2XEXl or equal to
5.656^7. When comparing this with
the ratings obtained from the various
arrangements given on page 297, it is
seen that the three-phase closed-coil
arrangement gives a less output than
for two-phase, while the other three-
phase arrangements give an increased
rating.
The best single-phase rating ob-
tained from a three-phase winding
occurred with the closed-coil arrange-
ment, Fig. 174 and was equal to 4EL
For a two-phase winding, on the other
hand, the best single-phase rating was
shown to be equal to 2.828-Bi/. As Ei is equal to V2E, this
equals 2.828xV2XBX/, or 4EI; thus the same as with closed-
coil winding, shown in Fig. 174.
The above capacities have, as previously stated, only refer-
ence to machines which can be adapted to both polyphase and
Fig. 177.
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SYNCHRONOUS GENERATORS 301
single-phase service. For machines designed for purely single-
phase duty, the ratings can, however, be somewhat higher. This
is due to the fact that the armature winding can be more efficiently
spaced and proportioned, in which case the limit in output as a
rule is determined by the temperature rise in the field.
Wave Shape. The e.m.f. in a conductor is proportional to the
rate of cutting the lines of force, and has, therefore, a wave form
of the same shape as the curve of flux distribution. Due to the
non-uniform flux distribution in definite pole machines, caused
by the slots, the shapes of the pole-pieces, the armature reaction,
etc., the wave will never have a perfect sine shape. It may, how-
ever, be considered as the resultant of a number of sine waves
consisting of a fimdamental and harmonics. The third and fifth
harmonics are generally predominating in three-phase machines,
while even harmonics are seldom
found in the e.m.f. wave of an
alternator. This is due to the j/^ \\ /^ PMiuTetnd
fact that the resultant of a fimda-
mental and an even harmonic
gives an unsymmetrical ciurve, as
shown in Fig. 178, where the re- ., ^^ -. * • i ri- * * j
-, ^ .1 - Pig. 178. — Unsymmetncal Distorted
sultant curve is made up of a E.M.F. Wave,
fundamental and a second har-
monic. If, therefore, the e.m.f. wave is sjrmmetrical, it may be
assumed that no even harmonics are present.
With fractional pitch-windings certain harmonics are elim-
inated, depending on the pitch. For example, if the pitch of the
coQ can be shortened by - of the pole pitch, then the nth harmonic
n
and its multiples wiU be eliminated.
The analyzation of a wave involves a considerable amoimt of
work, but, in general, it is possible to tell at a glance which har-
monics are predominating. With a positive third harmonic, that
is, if counting from the zero point of the complex wave the har-
monic wave rises, the complex wave will be flat-topped. If, how-
ever, the harmonic is negative, that is, if after crossing the base
line, it rises in opposition to the complex wave, its effect will be to
produce a distorted wave of the peaked type. A fifth harmonic,
however, if positive will give rise to a peaked saw-toothed wave,
and if negative to a flat-topped wave.
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302
ELECTRICAL EQUIPMENT
Complex alternating current waves as mentioned above can
be represented by their equivalent sine wave, having the same
efifect as the complex wave. They have the same effective value,
that is, the same square root of mean square of the instantaneous
values of the complex wave. Thus, considering all complex
alternating currents as represented by equivalent sine waves, all
investigations become applicable to any alternating current cir-
cuit irrespective of the wave shape. Terms such as reactance,
impedance, etc., are based on the assumption of a sine wave or
equivalent sine wave.
The objections to higher harmonics are, among other things,
their effect in increasing the maximum value of the e.m.f. and
JUnnoaie
N«gAt]««Kk
Fig. 179.— Symmetrical Distorted E.M.F. Waves.
the correspondingly increased insulation strain, as shown by the
peaked waves in Fig. 179. In certain cases the triple frequency
voltage estabhshed by the generator is of sufficient value to cause
heavy triple frequency currents to circulate. A considerable
distortion of wave shape might also affect the performance of
induction or synchronous motors. Here, if the distortion of the
voltage wave acting at the motor terminals is considerable, the
rotating field produced will be more or less of a pulsating charac-
ter. Induction motors might operate uneconomically with a pos-
sibility of dead points in the starting torque, or with a considerable
coimter torque during running. Synchronous motors or con-
verters may hunt, or even fall out of step. Or if the wave shape
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SYNCHRONOUS GENERATORS 303
of the induced counter electro-motive force greatly differs from the
pressure wave acting at the terminals of a synchronous motor or
converter, excessive heating might result, thus lowering the
efficiency of the system. These results are, of course, to be
expected only if the distortion is considerable, and for this reason
it has become a general practice to limit the maximum permissible
deviation of the complex wave from a true sine wave to 10 per
cent. This deviation is to be determined by superimposing upon
the actual wave, as measured by an oscillograph, the equivalent
sine wave of equal length, in such a manner as to give the least
difference, and then dividing the maximum difference between
corresponding ordinates by the maximum value of the equivalent
sine wave.
For three-phase machines the three circuits are, as previously
stated, connected either in star or delta. The line voltages of
the three phases are 120^ apart and their simi must, at any instant,
be zero. Since the third harmonics are in phase with each other,
they would not add up to zero and, therefore, cannot exist, and for
the same reason a third harmonic of the line ciurent cannot be
present. In a balanced system, third harmonics can exist only
in the voltage from line to neutral or Y-voltage, and in the current
from line to line or delta ciurent, as will be explained in the fol-
lowing.
Fig. 180 represents a delta-connected three-phase generator
with a predominating third harmonic e.m.f. in each phase. As
the three triple harmonics are in phase, the machine is really
running imder short circuit, as far as the triple harmonic is con-
cerned. This triple-frequency current is internal in the windings,
and the e.m.f.'s which causes it to flow are short-circuited in the
closed delta, and will, therefore, not appear in the terminal e.m.f.'s.
The circulating current may be of great magnitude, entailing large
PR losses in the windings with corresponding loss of efficiency.
If the generator is Y-connected, as in Fig. 181, the terminal
e.m.f. between A and B is the resultant of the two e.m.f. vectors
OA and OB, thus OA—OB, the negative sign of the latter on
accoimt of its direction. The triple harmonics are the same as
in the previous case, but by adding the e.m.f. waves in a and b,
corresponding to OA and OB, we get the resultant c. OB, that is
6, must, of course, be reversed and the triple harmonics will cancel
and no triple harmonic can, therefore, exist in the terminal e.m.f..
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ELECTRICAL EQUIPMENT
but the fundamental e.m.f . wave is, of coursei larger than in each
of the phases.
If the neutral is grounded the potential difference from line to
groimd may not be the line voltage divided by VS; but, super-
imposed on this voltage, there may be the triple-frequency e.m.f.
A B
Fig. 180.
Fig. 181.
and the maximum value of the wave may be greatly increased,
thus increasing the insulation strain.
In a balanced three-phase system, third harmonics can,
therefore, only exist in the voltage from line to neutral or Y-voltage;
in the current from line to line, or generator delta current; and
in the line current only if the generator neutrals are groimded or a
return circuit provided.
Grounding of Generator Neutral. With two generators oper-
ating in parallel, a difference of potential will exist between their
neutrals equal to the vector difference between their phase e.m.f s.
With the neutrals interconnected a local current would flow, lim-
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SYNCHRONOUS GENERATORS
305
ited by the generator impedance at triple frequency; while, if
the triple-frequency e.m.f.'s in the two generators were equal and
exactly in phase, there could be no neutral potential or current.
Owing, however, to the difference in the angular velocity of the
machines, different wave forms, different excitation, etc., this
condition never exists; and a triple-frequency current, therefore,
always flows between the neutrals, if interconnected. This cur-
JNo.1 |No.8 |No.8 |No.4
V ^K i^x >\.
[ \ ^ i {
iReflistanoe
Fio. 182. — System of Grounding Generator Neutrals.
|No.1 |No.8 ::No.8 ;|no.4
.,.4^ -»4v -^"x >^
Fio. 183. — System of Grounding Generator Neutrals,
can be grounded at one time.)
(Only one neutral
rent may be of considerable magnitude with low reactance ma^
chines, and, if excessive, precautions must be taken for preventing
it. This can be done by grounding only one generator at a time,
if the generators are to be groimded, leaving the neutrals of the
other machines isolated. Arrangements must then also neces-
sarily be made so that any one of the generator neutrals can be
grounded, as shown in Figs. 182 and 183.
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306 ELECTRICAL EQUIPMENT
Whether the generator neutral should be grounded or not
depends on the operating conditions. If an uninterrupted
service is the most essential consideration, the system should not
be grounded, while if it is more desirable to limit the voltage
strains, imposed by grounds, it may be advisable to ground the
neutral, thus limiting the stress to the Y-voltage. Groimding may
also be advisable where selective action is desired on a number
of outgoing feeders, especially imderground, so that individual-
feeders may be disconnected even in the case of grounds.
The use of a resistance in the grounded neutral of a system
offers the advantages of limiting the current which flows through a
ground on one phase, and thereby eliminates the danger of mechan-
ical destruction due to the excessive ciurents at the dead short-
circuit, which would occur with a ground on one phase of a S3rstein
with the neutral grounded without resistance. Such a groimding
resistance, however, abandons the advantage of the dead grounded
system that the voltage between Unes and ground can never exceed
the Y voltage. It is, therefore, not permissible where the appa-
ratus cannot safely stand the delta voltage of the line. This is
the case with low-voltage generators feeding a Une or cable through
step-up auto-transformers. With dead-grounded generator neu-
tral the voltage between generator and ground is fixed, but with
resistance in the neutral ground, a dead ground on the high-
potential phase puts nearly delta voltage of the high-potential
circuit on the low-potential generator, and thereby seriously
endangers it, if the step-up ratio of the auto-transformer is 1 :2.
If it is higher there is every likelihood that the generator will be
destroyed. The same is the case when connecting together trans-
mission systems of diflferent voltages through auto-transformers.
In any case, if auto-transformers are not considered safe, trans-
formers must be used.
A grounding resistance should have a value high enough to
limit the neutral current, but still low enough to insure that, if a
ground occurs in one phase, it will permit a sufficiently large cur-
rent to flow in the neutral to open the protective circuit-breakers.
Non-inductive resistances are preferable to reactances, since they
eliminate the danger of high-frequency oscillations beween lines
and ground through the generator reactance in the path of the third
harmonic, by damping the oscillation in resistance. The ground-
ing of the neutral through a reactance may, therefore, be
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SYNCHRONOUS GENERATORS 307
very dangerous, owing to the poesibilities of a resonance voltage
rise.
If three auto-transformers, Y-connected with the neutral
grounded as the only ground, are used to step up the generator
voltage, abnormal potentials to ground may result, due to the
presence of high harmonics. The distortion does not appear in
the voltage between the lines because the distortion between one
line and the neutral is canceled by that of the other two lines.
The voltage distortion may be eliminated by providing a path
for the triple-frequency exciting current which is required for the
magnetization of the transformer. This is done by connecting
the transformer neutral to the generator neutral.
Rating. Synchronous generators should be rated by the
electrical output, and this should be expressed in kilo-volt-
amperes (Kv.A.) and not in kilowatts (Kw.) \mless the power
factor of the load is also given. Preferably both should be given,
80 as to avoid any misunderstanding whether Kv.A. or Kw. is
meant, for example 2000 Kv.A. (1600 Kw.-.8 P.F.).
Most water-wheel-driven generators are now given a maximiun
continuous rating, without any overload provision, except that
they must be able to carry momentary loads of 150 per cent of
the amperes corresponding to the continuous rating, keeping the
rheostat set for load excitation.
The rated full-load current is that ciurent which, with rated
voltage, gives the rated kilowatts or rated kilo-volt-am'peres.
In machines in which the rated voltage differs from the no-load
voltage, the rated current should refer to the former. The rated
output may be determined as follows:
If B=full load terminal voltage and 7= rated current, then
EI
for a single-phase generator Kv.A. =t7w^q-
For a two-phase generator the total output is equal to the out-
put of the two single-phase circuits, and if 7, in this case, is the
rated current per circuit, the output for a two-phase generator is
TT A 2B7
^^•^=iooo-
For a three-phase generator there are three circuits to be con-
sidered, whether the machine is star or delta connected. If £ is
the terminal voltage and 7 the Une current, then for a three-phase
, rr A 3EI V3EI
generator ^^'^'-^3X1000^1660'
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308 ELECTRICAL EQUIPMENT
The rating of a generator is usually determined by its permis-
sible temperature rise caused by the current. This rise neces-
sarily increases with increasing load and also with decreasing
power-factor. Thus, for a given Kv.A. output, the total heat
losses are larger for low than for high power factors, the differ-
ence being due to the heat generated by the increased field cur-
rent which is required to overcome the armature reaction and
maintain the given current and terminal voltage.
Alternating-current generators are generally designed to oper-
ate a normal load and 80 per cent power factor without ex-
ceeding a specified temperature rise; and should such a machine
have to be operated with a load having a lower power factor, its
rating will be reduced when based on the same temperatine guar-
antee. The true operating power factor should, therefore, be
carefully considered in selecting the capacity of the generating
units. The power factor depends not only on the t3rpe of appa-
ratus comprising the load, but also on the load factor at which
they are operated.
To obtain the total Kv.A. capacity of a system, the sum of
the wattless components of the different loads should be calcu-
lated, the efficiency, power factor and load factor being duly
considered. The total capacity is then equal in Ev.A. to
V(Total Kw. energy)2+ (Total Kv.A. wattless)^,
and the combined power factor of the load
Total Kw. energy
Total Kv.A. •
It is obvious that a generator must not be permitted to be
operated under such conditions that it will attain such excessive
temperatm^ which will cause the insulation employed in their
construction to deteriorate, and the A.I.E.E. Standardization
Rules contains the following table, giving the highest tempera-
tures and temperatiu^ rises to which various classes of in«iilfif.ing
materials may be subjected. While it was recognized that the
manufacturers could successfully employ class B insulation at
150^ C. and even higher, it was not felt that sufficient data was
available to recommend this and the institute adopted 125^ C.
as a conservative limit for this class of insulation, any increase
above this figure being considered a special guarantee. The ambient
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SYNCHRONOUS GENERATORS
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temperature of reference, that is, the cooling air surrounding
the machine is given as 40^ C, and by deducting this ambient
temperature from the maximum permissible temperature given
above, the permissible temperature rise is obtained. As it is
usually impossible to determine the maximum temperature
(hottest spot) attained in insulated windings, a correction factor
must be applied to the observable temperature, so as to approx-
imate the difference between the actual maximum temperature
and the observable temperatiu^ by the method used. This
correction, or margin of security, is provided to cover the errors
due to fallibility in the location of the measuring devices, as well
as inherent inaccuracies in measurement and methods.
TABLE XLIII
Permibsibub Temferatcrbs and Temperature Rises for iNauLATiNG
Matekialb
1
2
CUn.
Description of Material.
Maximum
Temperature
to which the
material may
be subjected.
Maximum
Temperature
Rise.
A.
Cotton, silk, paper and similar mate-
rials, when so treated or impreg-
nated as to increase the thermal
limit, or when permanently im-
mersed in oil; also enameled wire*.
105^ C.
66** C.
B.
Mica, asbestos and other materials
capable of resisting high tempera-
tw^, in which any Class A material
or binder is used for structural pur-
poses only, and may be destroyed
without impairing the insulating or
mechanical qualities of the insulation.
126«C.
86*»C.
C.
Fireproof and refractory materials,
such as pure mica, porcelain,
quartz, etc
No limits ftHAnifiAd
* For cotton, silk, paper and similar materials, when neither impregnated nor
immersed in oil, the highest temperatures and temperature rises shall be 10*> C. below
the UmlU fixed for Class A.
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ELECTRICAL EQUIPMENT
There are three different methods provided for determining
the temperature of different parts of a machine. These will be
briefly described in the following and the respective permissible
temperature rises given, based on class A insulation.
I. Thermometer Method. This consists in appl3ring a thermom-
eter to the hottest accessible part of the completed machine.
With this method a correction of 15° C. must be made,
that is, the permissible observable temperature rise as
read by the thermometer cannot exceed 60° C.
An exception to this rule is the case, when thermometers are
appUed directly to the surfaces of bare windings, as the field coils.
Then only a 5° C. correction has to be made, so that the permis-
sible observable temperature rise is limited to 60° C.
II. Resistance Method, This consists in the measurement of the
temperature of windings by their increase in resistance, cor-
rected to the instant of shut-down when necessary. In the
application of this method, careful thermometer measure-
ments should also be made, whenever practicable, in order
to increase the probabiUty of revealing the highest observ-
ble temperature. Whichever measurement yields the
higher temperature that temperature shall be taken as
the *' highest observable " temperature and a hottest-
spot correction of 10° C. added thereto. The permissible
temperature rise with this method is, therefore, 65° C.
TABLE XLIV
Temperature Coefficiemtb of Copper Resistance
Temperature of the Winding,
in <> C. at which the Initial
Resistance is Measured.
Increase in resistance of
Copper per «> C. per Ohm of
Initial Resistance.
0
0.00427
5
0.00418
10
0.00409
15
0.00401
20
0.00393
25
0.00385
30
0.00378
35
0.00371
40
0.00364
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SYNCHRONOUS GENERATORS
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The temperature coefficient of copper may be deducted from
1
the formula
-. Thus, at an initial temperature
(234.5+0*
i=40° C, the temperature coefficient of increase in re-
sistance per degree centigrade rise, is =0.00364.
Table XLIV deduced from the formula, is given for con-
venience of reference.
III. Efkbedded Temperature — Detector Method. This method con-
sists in the use of thermo-couples or resistance tempera-
ture detectors, located as nearly as possible at the esti-
mated hottest spot. When this method is used, it shall.
Double-layer Winding. Single-layer Winding.
Fig. 184. — Methods of Locating Temperature Detectors.
when required, be checked by Method II; the hottest spot
shall then be taken to be the highest value by either
method, the required correction factors being applied in
each case. Temperature detectors should be placed in at
least two sets of location, as shown in Fig. 184.
The corrections to be added to the ** observable " tempera-
ture when Method III is used, are as follows: In the case
of two-layer windings, with detectors between coil sides,
and between coil side and core, add 5** C. to the highest
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312 ELECTRICAL EQUIPMENT
reading. In single-layer windings, with detectors be-
tween coil side and core and between coil side and wedge,
add to the highest reading lO"" C. plus l"" C. per 1000 volts
above 5000 volts of terminal pressure.
Thus, for a three-phase machine with an 11,000-volt single-
layer winding, the correction to be added to the maximum " ob-
servable " temperature in estimating the " hottestnspot " tem-
perature, is 16° C, and the permissible temperature rise is,
therefore, 49** C. For double-layer windings the permissible
rise is 60° C. and for single-layer windings for 5000 volts or less
55° C.
Increased altitude has the effect of increasing the temperature
rise of some types of machinery. In the absence of information
in regard to the height above sea level at which the machine is
intended to work in ordinary service, this height is assumed not to
exceed 1000 meters (3300 feet). For machinery operating at an
altitude of 1000 meters or less, a test at any altitude less than
1000 meters is satisfactory, and no correction shaU be applied to
the observed temperature. Machines intended for operation
at higher altitudes shall be regarded as special, and when a ma-
chine is intended for service at altitudes above 1000 mecers (3300
feet) the permissible temperature rise at sea level shall be reduced
by 1 per cent for each 100 meters (330 feet) by which the altitude
exceeds 1000 meters.
Efficiency. The efficiency of a generator is the ratio of the
kilowatt output to the kilowatt input at the rated Kv.A. and
power factor. The difference between these two quantities is
equal to the losses. The method commonly and most readily
used for obtaining the efficiency is to determine these losses and
then compute the efficiency by dividing the power output by the
sum of the power output plus the losses.
The guaranteed efficiency should always refer to the energy
load and it is most important that the power factor of the load is
also given. In certain cases the guaranteed efficiency is based on a
Kv.A. output, but the inconsistency of such a method is apparent,
as the following example will illustrate:
Assume a generator rated 100 Kv.A. (100 Kw. 1.0 P.F.) or
100 Kv.A. (80 Kw. .8 P.F.), and that the losses at unity and 80
per cent power factors are 10 and 11 Kw. respectively, the effi-
ciency is then:
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SYNCHRONOUS GENERATORS 313
Based on 100 Kw. 1.0 P.F.
100
Eflf.^^QQ Q«91 per cent.
Based on 80 Ew. .8 P.F.
80
Eff. = g^q:^=88 per cent.
Based on 100 Kv.A. .8 P.F.
^'" 100+11 "^ per cent.
From the last two values it is seen that for 80 per cent power
factor if based on the Kv.A., a 2 per cent greater efficiency guar-
antee can be made, although this value has no meaning, as it is
based on apparent power.
It is, of course, equally important that all the losses are included
and that they are figured on the same basis, in order that a fair
comparison may be made of the efficiencies guaranteed by differ-
ent manufacturers.
The A.I.E.E. Standardization rules require that for syn-
chronous generators the following losses are included in deter-
mining the efficiency: (1) core losses, (2) PR loss in all windings
based upon rated Kv.A. and power factor, (3) stray load losses,
(4) friction of bearings and windage, (5) rheostat losses corre-
sponding to rated Kv.A. and power factor.
Bearing Friction and Windage may be determined as follows:
Drive the machine from an independent motor, the output of
which shaD be suitably determined. The machine under test
shall not be excited. This output represents the bearing friction
and windage of the machine imder test.
Core Loss. Follow the above test with an additional reading
taken with the machine separately excited so as to produce at
the terminals a voltage corresponding to the calculated internal
voltage for the load under .consideration. The difference between
the output obtained by this test and that obtained by the
previous one shall be taken as the core loss, neglecting the brush
friction. The internal voltage shall be determined by correcting
the terminal voltage for the resistance drop only.
PBLoss may be calculated directly from the resistance meas-
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314 ELECTRICAL EQUIPMENT
urement, the current being based on the rated Kv.A. and power
factor. The resistance of the windings should be taken at 75® C,
or the values corrected for this temperature. It is important that
this is followed.
Stray Load Losses. These include iron losses, and eddy-
current losses in the copper, due to fluxes varying with load and
also to saturation.
Stray load losses are determined by operating the machine on
short circuit and at rated-load current. This, after deducting
the windage and friction and PR loss, gives the stray load loss
for polyphase generators. For single-phase generators they are
much larger.
Field-Rheostat Losses shall be included in the generator losses
where there is a field rheostat in series with the field magnets of
the generator, even wheYi the machine is separately excited.
In making eflSciency tests after installation in the power
station, it may occasionally be possible to drive the unit by its
exciter when the same is direct connected; but for large units
and when the direct-connected exciters are not provided the
retardation or deceleration testing method is resorted to. This
test is based on the principle that every moving body possesses
a certain definite amount of energy, due to its motion. It is
described in detail in an article by Mr. R. Treat in the General
Electric Review for June, 1916.
A convenient and most satisfactory method of detennining
the efficiency of a generator after installation may be employed
where there are two or more units in the power house available
for the use of the test, or where the unit under test may be varied
in conjunction with some other imit of sufficient size located
elsewhere in the system but which may be segregated for the
purpose. The method for determining the core losses and the
friction windage losses consists in operating the generator as
a synchronous motor and measurmg the input by watt-
meters.
When the retardation method of testing is used, it is to be
recommended, if possible, to check such tests by means of the
input method.
A new method of artificially loading generators for tests in
hydro-electric power stations is described in an article in the
General Electric Review for April, 1917.
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SYNCHRONOUS GENERATORS
315
#
96
97
It-T-i
iod-1 iO-P«
P.—
—
_F«
ITm
L<L0.8P,,
p.
&9b
^
^
.^
■""■
=£S
1^
y
y^
^
7f>^
Cd 94
h
/
-y
91
90
0 1
3 4 5 6 7 8 9 10 11 12 18 U 15 16 17 18
Generator Capacity la Thousand Kv.A.
Fig. 185. — Approximate Efficiencies of Polyphase Water-wheel-driven
Alternators.
The curves in Fig. 185 represent approximate efficiencies of
polyphase water-driven alternators, the ratings being maximum
continuous.
Speed. The speed of water-wheel-driven generators is deter-
mined by the frequency of the system and by the hydraulic con-
dition, that is the speed of the wheel, which, in tiun, is governed
by the size of the unit and the head.
With a fixed frequency the number of poles must be increased
in inverse proportion to a reduction in the speed. To accommo-
date this increased number of poles the diameter must necessarily
be larger and with this follows also an increased amount of material
and labor. The cost of slow-speed machines must, therefore,
necessarfly be much higher than for machines of higher speeds.
Table XLV shows what has actually been the practice in re-
gard to the speed of hydro-electric units. This table covers a
number of years' manufacture of wheels and generators, and can
hardly be said to represent latest practice, and future speeds may
be considerably higher than these, particularly in the smaller units
on the higher heads. It is seen that the speeds range from as low
as 55 R.P.M. to as high as 600 R.P.M., these figures, of course
referring to direct-connected units.
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ELECTRICAL EQUIPMENT
TABLE
Actual Speeds op Water-
H«iUl
In
Kv-A
. Capacity oi
CSNERATO&.
200
300
400
500
600
700
800
000
1000
1250
1500
1750
2000
2500
3000
3500
4000
4500
5000
5500
9000
15
100
180
20
ICKl
171
m
■I2b
225
120
25
120
112
133
80
35
180
157
97
225
164
180
40
225
45
164
116
164
50
55
00
65
,
257
225
225
70
....
150
75
iio
200
180
85
100
375
514
300
225
300
225
125
....
150
340
175
400
200
J57
400
375
375
...
225
250
164
800
450
200
514
350
400
ibn
:i00
300
450
500
400
600
375
450
600
m
360
514
700
300
800
300
900
250
1000
400
1100
1200
600
450
1800
1400
1500
600
420
1600
1700
1800
1900
2000
600
Voltage. Standard generator voltages for all frequencies
are 240, 480, 600, 2300, 4000, 6600, with the correspondiDg
motor voltages 220, 440, 550, 2200, 6000. There is no motor
voltage corresponding to 4000 volts, since this is only used
on three-phase, four-wire lighting distributing systems. In addi-
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SYNCHRONOUS GENERATORS
317
XLV
WHEEL-DRIVEN GENERATORS.
KTA. CAPAcrrr or Ginbrator.
Head
ID
Feet.
6500
7000
7500
8000
8500
9000
ftSOO
10000
IIGOO
12000
125O0
13000
UOD(
mm
16(KK)
1
iriMX)
15
20
25
57.7
55.4
30
35
40
45
M
94
116
50
56
60
100
65
70
75
144
85
100
250
125
250
180
250
225
150
187
250
175
187
500
420
200
428
225
360
250
300
375
350
400
400
500
400
514
600
450
400
500
600
700
800
200
315
900
300
1000
1100
300
1200
300
360
1300
1400
400
1500
1600
300
1700
1800
375
1900
2000
1
tion, 11,000 volt is also standard for 60 cycles, and 13,200 volt
for 25 cycles.
When a generator is wound for 240 volts it does not necessarily
follow that it may be reconnected for 480 volts; and, vice versa, a
480-volt machine cannot always be reconnected to 240 volts by
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318 ELECTRICAL EQUIPMENT
changing the number of circuits. The above is particularly true
of generators with large diameters and a great number of poles.
Small machines with few poles can, as a rule, be reconnected or
rewoimd for any voltage up to and including 2300. It is a com-
mon but erroneous idea that machines wound for 2300 volts,
delta connected, can be simply reconnected to 4000 volts Y.
While this is all right so far as mere voltage is concerned, the slot
in the armature may not be large enough to accommodate the
extra insulation required for the higher voltage. In large machines
the above change may sometimes be made without much diffi-
culty, but small machines require as a rule, new coils and fre-
quently new punchings.
Parallel Operation. In order that an alternating-current gen-
erator shall be able to carry a load, a current must flow corre-
sponding to this load. The e.m.f. required to generate this cur-
rent is the resultant of the terminal and the induced e.m.f.'s of
the generator, the displacement between these e.m.f.'s being due
to the impulse of the prime mover. In the same manner when
two or more generators are operating in parallel the division in
load between the different units is entirely dependent on the
turning efforts of the prime movers, and a change in the field
excitation, as with direct-current generators, will have no eflFect
whatsoever.
For a satisfactory parallel operation it is important that the
e.m.f.'s of the generators are the same and that they are operated
in perfect synchronism, as if this is not the case cross currents
will flow between the units. These cross currents may be either
wattless or they may represent a transfer of energy, depending on
whether they are caused by a difference in the e.m.f. or a speed
variation of the machines.
When two alternators are operating in parallel at the same
speed, their e.m.f.'s are naturally in opposition as shown in Fig. 186.
Let OA be the e.m.f. of generator No. 1 and OB the e.m.f. of
generator No. 2, the difference in their values being caused by a
stronger excitation of the latter machine. The resultant e.m.f.
OC will be in phase with OB, and, being impressed on the syn-
chronous impedance of the two generator armatures in series, it
will produce a cross current, lagging nearly 90^ behind the e.m.f.
of generator No. 2 and leading nearly 90"* in advance of the e.m.f.
of generator No. 1. This is practically true, as the impedance
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SYNCHRONOUS GENERATORS
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can be considered to consist almost entirely of the reactance of the
circuit. The cross current will, therefore, have a magnetizing
effect on generator No. 1 and a demagnetizing effect on generator
No. 2, and consequently keep the voltages the same. The cross
current is wattless, consimiing no power except that corresponding
to the PR loss in the circuit. It is thus evident from the above
that a change in the field excitation can hs^-ve no effect on the load
of the machine.
If the excitation of the two machines is the same, but the gov-
ernor adjustments differ, a cross current will also be produced as
shown in Fig. 187. OA represents the induced e.m.f. of generator
No. 1, leading 6 degrees in advance of the bus-bar voltage, while
OB represents the induced e.m.f. of generator No. 2, lagging $
degrees behind the bus-bar voltage. The resultant OC will cause
A-^
Qm.*»
-►B
0 C
FiQ. 186.
Fig. 187.
a cross current to flow and as the resistance of the circuit is small
compared to the reactance, it will lag nearly 90° behind OC, and
practically be in phase with the e.m.f. of generator No. 1, and in
opposition to the e,m.f. of generator No. 2. It will thus consume
p)0'^er of the leading machine No. 1, that is, retard it, and supply
power to the lagging machine No. 2, that is, accelerate it, and thus
pull the two machines together. It is evident from the diagram
that it is the reactive component ID of the cross current that pro-
duces the synchronizing power, and that the power component
OD has no effect in this respect. A certain amount of reactance is
therefore necessary for a satisfactory synchronous operation, and
the larger the reactance is, compared to the resistance, the larger
is the synchronizing component of the cross current. Increasing
the reactance would, therefore, increase the synchronizing force,
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320 ELECTRICAL EQUIPMENT
but there is a limit hereto also, as with a very high reactance the
total cross current would be reduced, and thus also the syn-
chronizing current.
The synchronizing force is a function of the short-circuit cur-
rent ratio of the generator and may be defined as the torque per
d^ree displacement.
The torque in foot-pounds corresponding to a given Kw.
energy load is:
Kw.X33,000 ^Kw.X7040
R.P.M.xarX.746 R.P.M. '
The synchronizing torque is then equal to
^_Kw.X7040
where 6 is the angle of displacement.
Assume a generator rated 475-72-1250 Kw. 1.0 P.F.-IOO-
2300 V. having a synchronous impedance limiting the short-cir-
cuit cmrent to three times normal. The current flowing can, with
sufficient accuracy, be assumed to be proportional to the sine of
the displacement between the terminal or bus-bar e.m.f. and the
induced generator e.m.f. At short circuit, this displacement
would be approximately 90**, thus the short-circuit current would
correspond to sin 90"* = 1. As this current has been assumed to
be three times full-load current, the latter would correspond to a
displacement of 0^^ the sine of which would be equal to J.
Sine 6=i and ^ = 19.5 degrees.
The synchronizing torque of this generator with a certain dis-
placement, for example, 10 degrees, would be:
rn 1250X7040 .-^-. ^ ,
^'^ 100X19.5 ^^^^^ foot-pounds.
The cross current of the above generator with a certain dis-
placement, for example, 10°, would be:
Sin. 10*^=0.17.
Full-load cmrent =315 amp.
0 17
Cross current =^r^X 315 = 160 amperes.
Strictly speaking, this is not a cross current but the transfer
of current to the generator in question from the others, which are
reUeved of a corresponding amoimt.
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SYNCHRONOUS GENERATORS 321
Where troubles from excess cross ciirrents are found, it can
usually be found due to a too close regulating machine, having a
too high short-circuit ratio in combination with insufficient fly-
wheel capacity.
In considering the function of flywheel effect, a sharp distinc-
tion should be made between momentary speed changes or speed
fluctuations and slow changes or adjustments due to the speed-
load characteristic of the water wheel and governor, or what is
properly called speed regulation. All prime movers that operate
together to supply, power to a common load must operate at a
lower speed when loaded than when unloaded, in order that the
several prime movers will properly divide the load. It is also well
to differentiate between the fimction of flywheel effect in water-
wheel-driven generators and in reciprocating engine-driven gen-
erators. In the former the single purpose is to restrain speed
changes during the necessarily long period of adjustment of input
to output. In the latter the most important function is to pre-
vent the excessive changes in angular velocity during a single
revolution that would, otherwise, be caused by the varying torque
delivered by the engine cylinders. WhUe with engine-driven imits
flywheel effect is important from the standpoint of steady parallel
operation, this is not the case with water-wheel installations.
With the latter the flywheel effect influences the speed only with
sudden changes in load, and during the short time interval during
which the hydraulic conditions are changing to meet the new-load
conditions.
The division of the load was entirely dependent on the angular
displacement between the bus-bar and induced generator e.m.f.'s
caused by the turning movements of the prime movers. It is,
therefore, evident that the speed regulation of the prime movers
must be the same, i.e., they must drop in speed from no load to
full load by the same percentage and in the same manner. If this
is not the case, the alternator connected to the prime mover of
closer speed regulation will take more than its share of the load
under heavy loads and less under light loads, and a too close speed
regulation is, therefore, not desirable for parallel operation of
alternators. To illustrate this further: Assume prime movers of
different speed regulation as shown in Fig. 188. When operating
in parallel it has previously been proven that, if an irregular speed
exists, a transfer of energy will take place between the alternators,
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ELECTRICAL EQUIPMENT
tending to retard the machine of the higher speed and accelerate
the machine of the slower speed, thus tending to hold the machines
in S3mchronism at a speed corresponding to the load. The
division of the load between the imits depends then only on the
action of the governors, and it is seen from the cmires that at a
load Cf the machines will divide the load equally. For other loads,
the ratio will be different, for example, at a certain lighter load
the ratio may be ~, while for a certain heavier load it may be -^\
The division of load between two alternators depends, there-
fore, as stated, primarily upon the speed-load characteristics of
the prime movers, the governors of which must be adjusted for
Fig. 188.
a definite drop in speed from no load to full load. With flat speed
characteristics the division of the load will be of an unstable
nature. By adjusting the field 4he form of the energy deUvered
by the generator can be changed but not the amount. What
really occurs with a change in field adjustment of any piece of
synchronous apparatus operating in parallel with another, is a
change of the power factor of that machine.
The above refers also to different stations operating in parallel
on the same system, and the division of load and wattless current
between the stations must, therefore, be handled differently. On
a network supplying power over a large territory, the power factor
will often be low and there will be considerable wattless current
to be taken care of.
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SVNCHRONOUS generators 323
A successful parallel operation of several stations on a system
is, as a rule, not difficult, inasmuch as the line characteristics, i.e.,
resistance and reactance, are generally such that they little inter-
fere with the synchronizing force of the generators. This force is,
as stated, greatest when the machines are over-excited, and the
only case where a machine would drop out of step would be on
extensive S3rstems where large lagging cmrents are required for
voltage regulation. These currents naturally greatly reduce the
S3mchronizing force in that they weaken the field, but there is
generally no danger of a shut-down imless a very heavy load should
suddenly come on.
Many different methods are used for dividing and regulating
the load on a large system. In some cases one or more generators
in a large station or one or more stations in a large system will do
the governing, taking care of the load, the other generators or
stations being then operated with constant gate opening and con-
stant load. Plants having large pondage are usually selected to
take care of the load fluctuations while those with little or no
storage should preferably be operated so as to take the full flow of
the stream. In many systems such stations are equipped with
induction generators which require very Uttle attention, possibly
only once a day. They may be started up in the morning or kept
running all the time, and as they are dependent on the other
synchronous apparatus on the system for their excitation, their
speed and frequency is determined by them. As there are no
governing devices, means must be provided for disconnecting the
units from the system as well as shutting the gates, should the load
be dropped for some reason or other, thus preventing overspeed.
When steam-turbine stations are used as auxiliaries these carry,
as a rule, little load ordinarily, but on the contrary, often a full
load of wattless current, and besides they are always ready in
case of emergency to pick up the load.
In this connection it may be well to point out a fallacy that
often exists with large customers, in that they specify that their
lines shall be independent of the rest of the system and that their
load be suppUed by separate generators. Such requirements are,
of coiu'se, based on an assumption that a better service can be
obtained in this way, as his lines or generators are not affected by
the fluctuation on the rest of the system. This is, however, in
most instances not the case, as changes in his load will affect the
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speed on his generators and the regulation of his lines much more
than if the fluctuations were divided among a greater number of
generators and lines. So, for example, in a large system, what
would be 50 per cent load thrown on or oflf one generator if it were
feeding a separate customer would, perhaps be only 5 or 10 per cent
load on the entire system and neither speed nor voltage would be
materially affected. In general, it may, therefore, be said that
in many cases it is preferable to operate everything in parallel
and to have the governors on as many machines as feasible. This
naturally reduces the work of the governors, as a change in load
then only requires each governor to work through a small range,
allowing a more sensitive adjustment and less speed deviation
than would be the case if the system were divided up into sections
with different generators supplying individual loads.
Mechanical Design. Revolving Field Type. Alternating cur-
rent generators are almost always of the revolving field type, this
construction being preferable as compared with the revolving
armature t3rpe. Besides relieving the high potential armature
winding from strains imposed by a centrifugal force, it gives an
increased space for the winding, which is of greatest importance.
Only two collector rings are required for handling the field cur-
rent, the energy and voltage of which is relatively small com-
pared to that which would have to be handled in the case of a
revolving armature generator of the same capacity.
Method of Drive. With regard to the method of drive water-
wheel-driven generators are almost always of the direct connected
type, only the very smallest sizes being belt or rope driven.
Horizontal or Vertical. Water-wheel-driven generators may
be either of the horizontal or vertical type, the latter being now
very extensively used in low-head developments where it becomes
desirable to place the generators above the highest flood level.
This arrangement requires less excavation, and obviates the neces-
sity for special construction to protect from flood water, which
would be necessary with horizontal units. In order to obtain
commercial speeds for direct connection to horizontal generators
it has been necessary for extreme low-head developments to put
a nimaber of runners on the same shaft. Recent improvements in
the design of single nmner turbines for low heads resulting in
increased speeds, as well as the comparatively low cost of vertical
generators operating at from one-third to one-half the speed of
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horizontal generators, have made the construction of vertical
units for extreme low heads lAuch simpler than horizontal units.
The draft-tube excavation required is, of course, much less and
involves less expense. For high-head developments with impulse
wheels, horizontal imits are of com-se preferable.
Stator Frame, The main function of the stationary armature
frame is to support the punchings and it should, therefore, be of a
rigid construction so as to prevent any sag of the punchings due
their weight and an unbalanced magnetic pull. It is usually of a
box type construction, and for smaller sizes they are, as a rule,
made in one piece, while for larger units they are split so as to
facilitate an easy handling and shipping. A number of openings
are provided for ventilation, a subject which is treated more in
detail in the latter part of this section.
The core consists of sheet-iron laminations carefully annealed
and treated so as to minimize both hysteresis and eddy-current
losses. The punchings are stacked together so that the lamina-
tions overlap each other. They are held rigidly in place by heavy
steel clamping fingers, air circulation being provided for by air
ducts formed by spacing blocks inserted at frequent intervals
between the laminations. The outer circumference is dove-
tailed for fastening to the frame, while the slots for the windings
are punched at the inner circumference, the slots generally being
of the open type so as to permit the use of form-wound coils, which
can easily be removed and replaced in case of damage. With the
open slot construction means must be provided to guard against
the generation of eddy currents, due to the unequal flux distribu-
tion. This is done by subdividing the individual conductors
either by using several wires in parallel or, in the case of con-
ductors of large cross-section, by using pressed cable; the eddy
durents are thus reduced to a negligible quantity.
Armature Winding. The armatiu-e winding is generally of the
lap or barrel-wound type. Fig. 189, and the chain winding has
b^n practically abandoned as it requires coils of different shapes,
especially with the widely distributed windings which are used in
modem machines.
The coils should be taped and treated with an impregnating
compound, the number of layers and dippings being determined
by the operating voltage. The materials used should be very
carefully selected to avoid deterioration or diminution of the dielec-
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326 ELECTRICAL EQUIPMENT
trie strength, this being especiaJIy important for high potentials.
After being tested the coils are inserted in the armature slots in an
armor of horn fiber or mica,
. , .__ , ^^ J retaining wedges of wood
^^^^^to 1^ ^c dovetailed into the sides
f id^HB^ p^^ of the slots near the top. Ac-
i /S^^^S^ 1^9 cording to the A.I.E.E. rules
the insulation should be such
that the winding will with-
stand a test voltage for one
minute continuously of twice
the normal voltage plus 1000
volts. The frequency of the
testing circuit shall not be less
than the rated frequency of
the generator.
J lie ' » * t AWV^^^ff Where heavy windings pro-
P / » »' / *fflviK3^B ^^^^ beyond the laminations,
"jt^-'I^ ^uWS^V _ g^ additional support is pro-
FiG. 189.— Lap or Barrel-type vided by means of an insu-
Armature Winding. lated metal ring or brackets
to which the outer ends of
the coils are fastened, thereby protecting them from mechanical
displacement or distortion due to magnetic disturbances caused
by violent fluctuations or short circuits. This bracing of the
armature winding is particularly necessary with single-phase
generators where the severe mechanical strains are imposed on
the armature windings by the pulsating flux.
Flexible terminal leads provided with suitable connection joints
should be brought through the frame near the bottom. With
three-phase machines it is in many cases necessary to bring out the
neutral lead, as the machine may have to be operated on the four-,
wire principle or it may be desired to ground the neutral.
! Field Spider, The rotating field generally consists of pole
pieces mounted on a cast-iron or steel ring connected to the hub
by means of arms of ample crossngection. For smaller and
medium-size machines the field centers may, however, consist of
built-up punchings to which the pole pieces are dovetailed. Where
shipping conditions permit, the field spider and the rim may be
cast in one piece, otherwise it must be split into sections. When
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SYNCHRONOUS GENERATORS 327
split, this can be done either lengthwise or crosswise to the shaft.
The former method is used when the diameter of the rotor is very
large and the latter method when the length is large (see Fig. 190).
Tte sections should be securely held together by heavy bolts and
link keys, and when the field is split crosswise to the shaft one set
of arms should preferably be provided for each section so as to
insure a rigid construction.
Field Poles. The pole pieces are built up of laminated sheet
steel punchings, spreading at the pole face so as to secure not only
a wide polar arc for the proper distribution for the magnetic flux,
but also for holding the field coils in place. These pimchings are
either riveted or bolted together and reinforced by two stiff end
plates. For machines of moderate speed the poles are simply
bolted to the rim, while for machines of higher speeds they are
solidly mounted on the spider by means of dovetail slots in the
rim (see Fig. 190). These dovetailed grooves should be made
somewhat larger than the corresponding part of the punchings
and a tight fit is obtained by means of steel wedges, which are
guarded from falling out by two bolted end rings. For high-speed
water-wheel-driven generators which must be designed for a nm-
away speed of twice normal, it often becomes necessary to pro-
vide additional precautions against the increased centrifugal
stresses at such occasions. SoUd steel rings as shown in Fig. 191,
are then often provided at each end of the rotor, these rings being
securely bolted both to the rim and each pole piece. On some
very high-speed machines, a design as shown in Fig. 192, is often
used. The field centers are here constructed of rolled steel plates
and the pole pieces are securely dovetailed thereto, thus making
a very substantial construction.
The revolving parts of water-wheel-driven generators should
be designed so as to keep the stresses due to centrifugal force,
well within the elastic limit of all the material at the run-away
speed of the water wheel. This speed varies with different
types of wheels and different conditions of installation; but the
general practice is to design the rotors with a 100 per cent over-
speed in view.
Flywheel Effect. This problem should be considered when the
design of the rotor is decided on, as well as when a comparison
between different proposed generators is made. This is really a
hydraulic problem, and where additional flywheel effect is required
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I
f
I
I
I
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o
8
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Fig. 191.— Revolving Field of 3000-Kv.A., 600-R.P.M., Horizontal Alternator.
I
Fio. 192.— Rotor of 10,000-Kv.A. High-speed Water-wheel-driven Generator.
Field Center Made up of Rolled Steel Plates, into which the Pole Pieces
are Dovetailed.
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it should, properly speaking, be put into the runner of the wheel
or an external flywheel provided. It is, however, invariably
found that such an arrangement is objectionable and nearly alwa3rs
more costly than to design the generator rotor for the desired fly-
wheel effect, which means additional material in the rotor rim or
by increasing the diameter of the same. A good value of the WR^
for water-wheel-driven generators has been given as 10,000,000
per Kw. maximum rating, divided by the square of the speed ex-
pressed in revolutions per minute; thus
TI7D2 xr / N 10,000,000
WIP perKw. (max.) = ^^^ p j^ .g.
Field Winding. Two methods are used for winding* the field
coils; viz., the wire wound and the strip wound. For small
machines, where even for moderate exciting voltages it is neces-
sary to have many turns of small section, the cotton-covered wire-
wound coil is usually selected. The necessary insulation may be
placed on the assembled pole piece and the winding wound directly
thereon. Heavy metal and fiber collars are provided at the ends
and serve to clamp the conductors together and prevent move-
ment due to mechanical stresses.
The wire-wound field coil, however, has its limitations both
mechanically and electrically. As the centrifugal force of the
field coil increases, the vertical component of the force will reach
a critical value where the crushing stress on the cotton insulation
around the individual wires becomes excessive, while at the same
time the horizontal component tends to tear the wires from the
pole. From the electrical standpoint the hmitation is that of
heating. It is evident that the heat generated in the inner layers
of the winding can reach the outside surface of the winding only
by passing through the insulation of each succeeding layer. This,
of course, results in a very considerable difference in temperature
between the inner and outer layers and in order to operate the
former at safe temperatures it is necessary to adapt compara-
tively low-current densities in the copper; this, in turn, resulting
in a heavy winding and consequently high centrifugal forces.
In order to obviate these difficulties, inherent to the wire-
woimd field, it is customary to construct the winding of copper
strip wound on edge, as shown in Fig. 190. The method of insu-
lating this type of winding is similar to that described for wire-
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wound coils with the exception that the insulation between turns
consists of vamisli, paper, asbestos, etc. It is evident that this
type of coU will not only stand much greater vertical forces, but
also, on account of the high moment of inertia of this flat strip, it
is better able to resist the horizontal component of the centrifugal
force. In extreme cases it is necessary, however, even with strip
winding to place brackets between the field coils to overcome this
tendency toward lateral distortions of the coil, as shown in Fig.
192. Means should also be provided to thoroughly fasten the
connections between the coils, and prevent them from working
loose, due to the strains imposed by the centrifugal force.
The bare outside edge of the copper strip is exposed to the
direct fanning action of the rotor, and since the temperature drop
in the copper itself is negligible, that is, for the widths of strip
ordinarily used, the heating of the coils is due almost entirely to
surface drop. As a result, a much higher current density can be
used than would be permissible with the wire-wound field.
The exciter current is conveyed to the revolving field through
two collectorrings mounted on the shaft of the machine.
According to the A.I.E.E. rules field windings for A.C. gen-
erators must withstand a one-minute test voltage of a value ten
times that of the exciter voltage; but in no case less than 1500
volts nor more than 3500 volts.
Shaft, Shafts are, as a rule, furnished with water-wheel-
driven generators and provided for couplings to be connected
to the water-wheel shaft. Occasionally one single piece shaft is
used for mounting both the water-wheel runner and the generator
field.
Provision is often made for moving the frame along the shaft
for convenience in repairing the windings. With the construction
shown in Fig. 193, this, of course, means an extra long and con-
sequently larger and more expensive shaft, and in many cases the
advantages are hardly worth the extra cost. With the base con-
struction shown in Fig. 194 a movement of the armature frame is
obtained without the additional expense of a heavier shaft and
sometimes also larger bearings.
Bearings. The bearings of horizontal units are ordinarily of
the self-aligning pedestal type arranged for oil ring lubrication.
In large bearings, particularly for highnspeed service, it often
becomes necessary to provide artificial water cooling for carrying
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ELECTRICAL EQUIPMENT
Fig. 193. — Horizontal Generator Showing Arrangement for Moving Frame
in Case of Repair, and Method of Mounting Direct-connected Ebcciter.
Fig. 194. — ^Large Horizontal Generator, Showing Method of Moving Fnune
in Case of Repair.
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oflf the heat generated. Thin, coil-shaped copper pipe is embedded
in the lower bearing half just below the surface of the babbitt and
oooling water is forced through the coil. If the water wheel is
of the overhung type, the size of the bearing nearest the wheel must
be of suflScient size to take care of the extra weight. Whether the
water thrust is balanced or not must also be considered.
With vertical units the present practice is to support the
Fig. 1»5.— Typical
of Modem Vertical Generator with Direct-con-
nected Exciter.
revolving element of the entire imit from a thrust bearing moimted
on top of the generator frame. Two guide bearings are usually
provided with the generators, one in the upper bracket directly
below the thrust bearing, and the other one supported in a bracket
below the revolving field (Fig. 195). Generally, one guide bearing
is provided in connection with the water wheel. This is usually
a babbitted bearing, although sometimes the lining is of Ugnum
vits. In case of very low-speed machines, where it is possible to
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ELECTRICAL EQUIPMENT
use an exceptionally short shaft, it is sometimes possible to omit
the bearing immediately below the revolving field, but, in gen-
eral, it seems preferable to have a bearing at this point. The
thrust bearing must sustain not only the weight of the revolving
element but also the unbalanced water-thrust, and the top
bracket must, therefore, be of adequate strength and is usually
heavily reinforced, as shown in Fig. 205.
There are two general classes of thrust bearings; those which
depend upon a film of oil between two plates, and those which have
hardened rollers between two hardened surfaces. The first class
may be subdivided into (a) those which are supplied with oil
under pressure and (6) those which revolve in a bath of oil imder
atmospheric pressure. There are also combinations of the two
classes. In either case the bottom plate is stationary and some-
times mounted on a spherical self-aUgning washer, while the top
one rotates with the shaft.
Oil-pressure Bearings. In this type of bearing, oil imder high
pressure is pumped into an annular chamber between a revolving
and a stationary disc (see Fig. 196), and the pressure required to
Fig. 196. — Assembly of an Oil-pressure Bearing.
separate the plates is, of course, dependent on the superincumbent
weight and the area of the bearing plates. This type of bearing
is not extensively used with water-wheel-driven units, as when
taken in connection with the necessary pumps and auxiliaries it is
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usually more expensive than the other types. A drop in the
pressure of the oil supply or a momentary failure of the same
would cause serious damage to the bearing.
^
Fig. 197. — Kingsbury Thrust Bearing.
Contact-plate Bearings. To this class, which is the mopt gen-
erally used, belong the Kingsbury and the Spring-thrust bearings.
The former consists of a stationary and a revolving plate sub-
mersed in a bath of oil under atmospheric pressure. The lower
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ELECTRICAL EQUIPMENT
stationary plate is divided into a number of babbitted s^ments
spaced sufficiently apart to permit a free circulation of oil (see
Fig. 197). Each segment or shoe has a single pivot support located
toward one end of the shoe, slightly beyond the center of gravity
in the direction of rotation. This arrangement causes the space
Fig. 198. — Spring-supported Thrust Bearing, Showing Rubbing Surface of
Rotating Ring; Stationary Ring with Sawcut is Raised to Show Arrange-
ment of Springs.
between the shoe and the thrust block on the shaft to open slightly
at the other end of the shoe, where the oil is drawn in by the
rotation of the thrust block. The film of oil on the face of the
shoe thus assumes the form of a very fine wedge constantly urged
forward by the rotation of the thrust block. This bearing may be
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operated with surface pressures of 400 to 500 pounds per square
inch. A considerable excess of area must be provided, however,
to take care of the starting and stopping conditions which are
much more severe than the running conditions.
The spring-thrust bearing (Figs. 198 and 199), automatically
adjusts itself to imequal loading due to inaccuracies in workman-
ship or in alignment. This is of the utmost importance as, while a
bearing may be properly adjusted when installed, a distinctive
feature of the spring-supported bearing is that it will automatically
adjust ^tself while in operation if there is a loss of aUgnment due to a
settling of foundation or to other causes.
As seen from the illustrations, the thrust collar is keyed to the
yEvtAlidntf ma^
Fig. 199. — Spring Thrust Bearing.
shaft and transmits the weight of the revolving parts to the
rotating ring of the bearing. This ring has a smooth rubbing
surface and is so designed that a rapid circulation of oil is main-
tained. The upper surface of the stationary ring is the stationary
rubbing surface of the bearing. The ring rests on springs held in
position by means of center pins, while dowel pins are provided to
keep the stationary ring from revolving.
The rubbing surfaces are in a bath of oil, the quantity of oil
circulated from an outside source depending on the losses and the
cooling conditions. Water cooling coils may be installed in the
bearing housing which will reduce the amount of oil, and for
smaller bearings, at low speed, no circulation of oil from a source
outside the bearing housing is required.
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ELECTRICAL EQUIPMENT
A combined guide bearing and spring-thmst bearing has also
been de\reloped for carrying moderate weights. These bearings
are very economical in the space required and usually do not
require oil circulation from a source outside the bearing housing.
Roller Bearings. This bearing consists also of a revolving and
a stationary plate, which, in this case, however, are separated by
r r
Fig. 200. — Assembly of a Roller Suspension Bearing.
hardened steel rollers, held in a brass retainer and arranged radially
to the shaft (see Fig. 200). The oil enters at the inner periphery
of the brass cage and discharges between the rolls into the sur-
rounding chamber.
Combination Bearings. Roller bearings for large units are
constructed in some cases to incorporate the oil pressing feature
also. The latter is combined with the rollers in such a manner
that the weight may be lifted off the rollers for ordinary oj)eration
and carried by them only in the event that the pressure should
accidentally fail. Or it may be carried ordinarily on the rollers,
the pressure being held in reserve in case of trouble w^ith the
rollers.
A platform with ladders leading to it should be installed on the
top of the machines so as to facilitate the inspection of the bear-
ings. Bridges are often provided from such platforms to a gallery
running along one wall of the power-house.
Lubrication. The advent of the adoption of thrust bearings
has presented a new engineering problem, that is, the proper
design of an oil-circulating and oil-filtering system so that these
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SYNCHRONOUS GENERATOBS 339
bearings will at all times be supplied with continuous streams of
cool, clean oil.
The lubrication of pressure bearings requires a positive dis-
placement type of pump such as a triplex pump, preferably directly
geared or chain-driven from the turbine shaft. As a continuous
supply is absolutely essential two pumps are sometimes installed
for each unit, one being motor driven. A central oil supply may
also be used in starting up or in case of emergency. The inter-
connection of the thrust bearing and the governor oil-supply sys-
tem by the use of one set of pumps is not to be reconunended.
For the lubrication of thrust bearings, requiring no pressure,
a central oiling and filtering system of the gravity type, as shown
in Fig. 201, is generally employed. Clean oil is stored in over-
head reservoirs, then is distributed to the thrust and guide bear-
ings on each unit by means of a suitable system of piping. After
passing through the thrust and guide bearings the used oil flows
by gravity to filters located in the basement, where it passes
through the filtering medium and over cooling coils, and the puri-
fied oil is then returned by automatically controlled pumps to the
overhead reservoirs ready for re-use.
The oil piping should be laid out carefully to permit of readily
draining and cleaning the pipes, and air pockets should be avoided.
Return drain should be amply large and properly pitched to rapidly
and thoroughly remove used oil. It is better to err on the safe
side and have the returns a size or two too large rather than too
small with consequent flooding of machines and wastage of oil.
AU feed pipes should be of brass or reamed steel pipes. All joints
should be carefully reamed and the piping blown out with steam
or compressed air as they are installed. Arrangement for a tem-
porary connection from the feed pipes to the return drains at the
machines is advisable. This allows of thoroughly flushing out all
dirt by kerosene or oil before any oil is fed to the bearings. The
piping should be equipped with valves and unions to permit
readily disconnecting a machine for repair work.
All bearings should be equipped with sight feeds or some sim-
ilar arrangement to show when the oil is feeding profusely. This
should preferably be in the return as this indicates that oil is
actuaUy going through the bearings. Also the oil temperature for
each bearing can be measured when necessary. There are many
indicators on the market for this purpose. One of the best schemes
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ELECTRICAL EQUIPMENT
is a fitting with a spring cover on one side that permits the operator
to actually put his fingers in the return oil. Inspection is quickly
made, the oil stream is clearly seen, or may be tested by the
fingers when the hght is poor, and there is no chance of a dirty
sight glass giving fake indications.
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ELECTRICAL EQUIPMENT
The details of a filter commonly used are shown in Fig. 202,
and the detail of the filter miits in Fig. 203. It is the devel-
opment of this type of filter miit which has made possible the
continuous filtration of the enormous quantities of oil required in
modem hydro-electric plants. As will be noted from Fig. 202,
this design permits of installing a very large amount of filtering
Fig. 203. — ^Peterson Filtering Unit, Showing Method of Placing
Bag Over Frame.
surface in a comparatively small space, and inasmuch as the cloth
on individual units is free from folds or plaits every square inch
of it is eflfective in filtering the oil. Each unit consists of gal-
vanized wire screens held in a metal frame. The cloth is in the
form of a bag which is brought up over the top of the filter unit and
retained in place by a cover which is held down by two thumb
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nuts. The oil passes from the outside to the inside of the filter
units, then out through nozzles which project through the wall of
the filtering compartment to the clean oil compartment. The
nozzles on each unit fit into spring-actuated valves so that any
individual imit can be withdrawn and cleaned without interfering
with the continuous operation of the filter. When the filter unit
is withdrawn this valve closes and prevents imfiltered oil from
flowing into the clean oil compartment.
In order to afford the operators complete control over the
operation of the oiling system and also to provide necessary plant
Fio. 204. — Oil Piping Arrangement, Showing Indicators.
records it is customary to arrange the oil piping at the individual
units as shown in Fig. 204. Such equipments include sight-
flow indicators, oil meters and recording as well as indicating
thermometers.
Instead of installing a central system, as described above, it is
occasionally found desirable to provide each generator with its
own individual oiling and filtering system. A plant equipped in
this manner is shown in Fig. 205. The filter is of the same general
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ELECTRICAL EQUIPMENT
design as described above and sets alongside of each generator.
Dirty oil from the bearings flows by gravity into the filter, while
the clean oil is pumped direct to the bearings by means of a rotary
pump, belt or chain driven from the governor shaft. The dis-
charge of this pump is provided with a reUef valve with by-pass
leading back into the clean oil compartment of the filter. The
piping at these units is arranged practically the same as shown
in Fig. 204, that is, the inlet and outlet lines are provided with
thermometers, sight flow indicators, etc.
Fig. 205 shows the installation at the plant of Colimibia Mills,
Inc., Minetto, N. Y. This plant contains six 2000 H.P, imits
Fig. 205. — Individual Oiling and Filtering Systems for each Generating Unit.
Peterson System.
and in order to insure continuous operation an auxiliary filter,
with necessary pumps, oil storage tanks, etc., is located at the end
of the generator room, with clean oil and dirty oil manifolds con-
necting with the individual filters on each machine. If, for any
reason, it is desired to cut out one of the individual oiling systems
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SYNCHRONOUS GENERATORS 346
this auxiliary system at the end of the room can immediately be
thrown on to any one of the generators.
While there are many modifications of the systems described
above, they will serve to indicate the general types of oiling and
filtering systems now in vogue. The design of these oiling sys-
tems is a highly specialized branch of engineering because in laying
them out and determining the pipe sizes it is necessary to take into
consideration the kind of oil to be used, and especially its viscosity,
the flow of oil being dependent upon the viscosity of the oil, which,
in turn, varies with the temperature of the plant. These factors
all have to be considered in la3ring out the piping, calculating the
quantity of filtering surface and designing the pumps.
Ventilation. With large generating units the question of
ventilation becomes of great importance; and modern machines
are, therefore, being designed to control the path and utilize the
cooling effect of the moving air to the greatest extent. Such a
machine is shown in Fig. 194. The frame is provided with ven-
tilating holes only above the base line, no outlets being provided
toward the pit. The end-shields are so designed that they enclose
the end of the rotor; and all of the air for ventilating the machines
is forced by means of fans on the rotor into the end shields where
it is put imder pressure, thus ventilating the end windings. The
air which passes through the core and windings below the base is
forced out of the large openings in the feet of the armature frame.
This will prevent the collection of heated air in the pit, which may
again be returned to the field, and so used over and over, and
become more and more heated. In certain instances no fans
need be provided, the field poles themselves providing the required
fan action. Another very noticeable feature of this construction
is the quiet running of the machines.
For machines requiring a large amount of cooling air it is
becoming general practice to provide ducts whereby fresh air may
be taken directly from the outside to the generator pit. With
moderate and high-speed machines, which have a suflBcient fan-
ning action in themselves, it is only necessary to provide hoods
for enclosing the ends of the machine over the pit, as shown in
Fig. 206. The air is then drawn directly from the outside and
enters both ends of the generator and is forced through the stator
and out in the station. The bottom of the frame has no holes so
as to prevent the heated air from re-entering the pit.
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ELECTRICAL EQUIPMENT
This method of ventUation is also readily adopted with vertical
units. The fresh air is drawn from the pit and forced through
holes in the spider between the pole pieces through the ducts in
the stator arid then out in the station through the opening in the
top. In case it is objectionable to let the heated air out in the
station, as in the summer time, it may instead be piped to the out-
side. The top of the generator may be covered with a sheets
steel hood to which a duct leading to the outside may be attached.
Fig. 206. — Horizontal Water-wheel-driven Generator, Showing Hoods Pro-
vided for Ventilation.
During the winter months it is, of course, advisable to discharge
the heated air into the station in order to heat the same.
With the advent of very slow-speed machines and low periph-
eral velocities where fans attached to the rotor cannot be effec-
tively used, it may become necessary to resort to forced ventila-
tion by providing motor-driven fans, as shown in Fig. 207. The
ventilating system should preferably be sectionaUzed, each section
being provided with* at least two fans — one for spare. Where
three fans are provided, the combined capacity of two must be
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SYNCHRONOUS GENERATORS
347
able to provide the required amount of air for the section in
question, the third being kept in reserve. Each fan inlet should
be equipped with a damper for controlling the air admission and
an automatic shut-off damper on the discharge so that when one
fan is shut down no leakage will occur through the fan from the
air chamber. The amount of air to each generator is regulated
by dampers in the ducts leading from the air chamber to the wheel
pits, and these dampers may be regulated from the generator floor.
The entrances to the wheel pits should be provided with air-tight
doorSy and the pressure in the wheel pits should be kept approxi-
Air Chamber for Units 1 to 8 Air llirht Door,
Vw Set H
Fan Set «f 2 Fan Set '^S
PLAN VIEW
ew.,-!a«^....rv..^.^^ £le4aTiON
SECTION A-A
Fig. 207. — Plan and Sectional Elevation of Ventilating System for Large
Horizontal Slownspeed Generators.
mately one inch of water, or just enough to insure a positive air
passage through the generator.
The air ducts should be as straight as possible, and the per-
missible air velocity may vary from as low as 300 or 400 feet per
minute for small or very slow-speed machines to as much as 1000
or 1500 feet for higher speed machines.
An approximate figure for the amount of air required is from
125 to 150 cubic feet per minute per kilowatt loss. Should,
however, the air in passing through the machine rise in tempera-
ture more than 15^ to 20^ C, it indicates that the air does not
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348 ELECTRICAL EQUIPMENT
effectively conduct away the heat and the supply should then be
increased.
For a further consideration, of the ventilation of the generator
room, see page 173.
Brakes. In large, modem water-power installations the units
are very often provided with brakes, in order to stop them quickly.
Foreign material may obstruct the gates, preventing their closure;
so that, imless a brake is provided, it may not be possible to stop
the wheel without closing the emergency gates. The brakes are
generally appUed to the generator rotor, the wooden face bearing
directly on the field rim, and the required pressure being obtained
by means of the oil pressure which is used for operating the gov-
ernors, or air pressure from the compressed air system.
A band brake is also sometimes used, consisting of a flanged
pulley mounted on the main shaft and rotating in a steel brake
band into which are bolted blocks of maple. The band may be
tightened around the pulley by a worm gear operated by a hand
wheel on the main generator floor above.
8. mDUCTION GENERATORS
Output and Excitation. The induction generator is simply
an induction motor driven above its synchronous speed. It
requires a wattless exciting current for its operations and can,
therefore, not be operated as a self-contained unit, but alwajrs in
connection with synchronous machines, generators or motors.
These machines will then furnish the necessary excitation, and
also entirely govern the voltage and frequency of the induction
generator.
The output depends on its speed above synchronism, and, with
the speed of the induction generator constant, it can only be
increased by decreasing the speed and thus the frequency of the
synchronous machinery. There can be no permanent short-cir-
cuit current flowing inasmuch as the exciting current disappears
when a short circuit takes place, and the momentary current rush
is also very small.
Comparative Capacity of Induction and Sjmchronous Gen-
erators. Inasmuch as the induction generator cannot furnish
any wattless exciting current for the inductive load on the system
or for its own excitation, it follows that this must be furnished
entirely by the synchronous machines, thus increasing their
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INDUCTION GENERATORS 349
capacity. For example, assume a system with a load of 8000 Ew.
0.80 P.F., and that it is desired to install an induction generator
having a capacity of 5000 Kw. 0.80 power factor. What would
the required capacity of the synchronous generators then be?
The wattless components of the load and the induction gen-
erator which the synchronous generators must supply will be 6000
Kv.A. and 2660 Kv.A., respectively, and, as in addition they must
furnish the remaining energy of 3000 Kw. their capacity would
have to be '
Kv.A. « V30002+86602 = 9150,
thus almost twice that of the induction generator. A somewhat
larger generator could, therefore, carry the entire load without
any induction generator.
For a higher power factor, however, the condition would be
different. If the power factor, for example, were 0.95 instead of
0.80 the total wattless Kv.A. to be suppUed would only be 2600+
2650 » 5250 and the capacity of the synchronous generators
Kv. A. = V30002+52502 = 6045.
For low-power factors it is, therefore, not very advantageous to
use induction generators.
Operation. When putting an induction generator into opera-
tion it is only necessary to bring it up to speed and close the switch.
Synchronizing is not needed inasmuch as the machine cannot
generate any e.m.f . until excited from the Une, and when so excited
it will, of course be in phase.
The first current rush is only exciting current because the load
cannot be {Hcked up until the field is established. If the current
rush should be undesirably large it can readily be reduced by
inserting reactances when the machine is thrown on the circuit.
These coils can then be cut out as soon as a steady condition is
reached.
When driven by governor-controlled water wheels, the speed
of the induction generator will drop slightly with the load, and
in order to divide the load properly it will be necessary for the
speed of the synchronous generators to drop still more. The
best method of operating induction generators is, therefore, to
drive them with wheels without governor control. In this manner
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350 ELECTRICAL EQUIPMENT
their output will be kept constant and the load fluctuations will
be taken care of by the synchronous generators.
Places of Utilization. The foremost use of induction generators
is, therefore, to be expected in stations where no storage is pro-
vided and where the entire output must be utilized or wasted.
Such stations will need very little attendance, due to their sim-
plicity; probably only once or twice a day. Means must, how-
ever, be provided for disconnecting the unit from the system and
shutting the gates should the power for some reason or other go
ofif the line. This would, of course, mean that the generator would
be unloaded and the unit reach an overspeed which must be
automatically guarded against.
General Construction. The construction of an induction gen-
erator is identical to that of an induction motor with a low-
resistance squirrel-cage secondary winding. The machine requires
a very small air gap and carefid consideration must be given to
the ventilation.
4. EXCITERS
One of the problems in connection with large generating sta-
tions which has been given comparatively Uttle attention until
lately, is that of excitation. It is, however, of the greatest im-
portance, as upon it depends, to a large extent, the successful
operation of the plant. The capacity of the exciter imits, the
proper division of the required exciter capacity into several
units, the method of drive, whether by separate prime-movers,
by individual motors, or whether direct connected to the main
generating units, the arrangements and connections of the dif-
ferent imits, the proper system of automatic voltage regula-
tion, etc., are all factors which demand a careful consideration
when designing a power plant.
Separate Excitation. With very rare exceptions all synchron-
ous machines are separately excited, the excitation being obtained
from some direct-current supply source. Generally, separate
direct-ciurent generators are provided for this purpose, and when
so utilized are termed " exciters."
A separately excited generator has no inherent tendency
toward regulation, this being either eflfected by a rheostat in the
field circuit or by means of diflferent systems of automatic voltage
regulation, as treated more fully in the next section.
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EXCITERS 351
Capacity and Rating. The exciters should have a capacity
suflScient to excite ail of the synchronous apparatus in the station
when these machines are operating at their maximum load and
at the true operating power-factor. It is not enough to provide
for the excitation when operating at unity power-factor, because
the excitation which is required at lower power-factors is con-
siderably higher than at unity power-factor. It is considered
good practice to make the combined capacity of all the exciters
equal to the excitation required for all the generators, when these
are operating at their maximum load and stated power-factor
(usually 80 per cent), plus a 20 per cent addition for possible
variations in the required excitation.
Auxiliary station apparatus should not be operated from the
exciter system, since troubles are always Ukely to occur in these
circuits that may damage the exciters at times when such damage
would cause considerable inconvenience in the operation of the
station. In many stations, station auxiUaries are now entirely
operated by alternating current, and the direct current for the
control circuits can be easily taken care of by the use of a small
motor-generator set combined with a storage battery. No com-
plications are then introduced by voltage fluctuations caused
by automatic voltage regulators. Reserve capacity in case of
breakdowns should, of course, be provided, the amount depend-
ing on the number of units.
Exciters are now given a maximum continuous Kw. rating
based on a temperature rise not exceeding 50** C, as measured
by thermometer, above an ambient room temperature of
40° C.
Voltage. The pressure most commonly used for excitation
is 125 volts. For A.C. machines of very large capacity requiring
a large excitation, it will, however, usually be found more econom-
ical to use a 250-volt excitation. This higher voltage will permit
the use of smaller exciter and field switches, while leads of reduced
size from the exciters to the bus-bars and from the bus-bars to
the generator field may be used, and the cross-section of the bus-
bars cut in two; all this being of importance in reducing the cost,
especially in large installations. A considerable saving can also
generally be accomplished in the exciter itself. Machines for
125 volts require a commutator twice as large as those for 250
volts; and with water-wheel-driven units, where they must be
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352 ELECTRICAL EQUIPMENT
designed to safely withstand double speed, the construction often-
times involves considerable difficulties and expense.
Characteristics. When exciters are to be operated in connec-
tion with automatic voltage regulators, as is almost always the
case, it is most important that they are designed with this point
in view. The densities, especially in the fields, should be fairly
low, as with high density the time element required to vary the
voltage from one point to another would be so long as to materially
afifect the regulation. The operating range should, therefore, be
below the bend of the saturation curve.
The exciter should preferably have a time element so that it
will be responsive to changes in the field excitation to the extent
that, by inserting an external resistance equal to about three times
the resistance of the field, the voltage will fall from 125 to 25 volts
in from six to eight seconds. An ideal exciter designed along
these lines should also give at full field 165 volts and the increase
in the field current from 125 volts to 150 volts should not be over
60 per cent.
For alternators operating at maximum inductive load 125 volts
is generally required for the excitation, and in order to get a satis-
factory regulation when an automatic regulator is used, the
exciter must be designed so as to be able to give 165 volts momen-
tarily. It is also necessary that the increase in the exciter field
cmrent should be small, so that the exciter will respond quickly
to the short-circuiting of the rheostat, and thus insure the desired
alternator excitation. Should the excitation voltage be any other
value than 125, viz., 250 volts, the above values would be pro-
portionally changed.
Shunt vs. Compound Wound. While an exciter can be either
compound wound or shunt wound, the former is considered prefer-
able for parallel operation with automatic voltage regulation.
Non-regulating exciters should be more or less highly saturated
in order to insure a stable parallel operation. If such exciters
were to be used with automatic regulation, they would be rather
slow to correspond to the changes in field excitation. If a shunt-
wound exciter is designed for a low saturation so as to make it a
good regulating exciter, the tendency might be an unstable oper-
ation when running in parallel without a regulator. Shunt-wound
exciters are, however, generally provided with commutating poles
to overcome the above difficulties.
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EXCITERS 353
The series field excitation of regulating exciters should not
exceed 30 per cent of the total excitation, and the resistance
of the rheostat should be about three times that of the resistance
of the exciter shunt field when hot.
For regulating exciters, which are not to be operated in parallel,
the shunt-wound type is entirely satisfactory, provided it has been
designed with this point in view, that is, for low saturation.
Speed. The speed of an exciter depends on the method of its
drive and on its capacity. Extremely slow or high speeds mean
excessive cost with the addition of mechanical difficulties for
high speed. This is especially important in hydro-electric in-
stallations, where the exciters are turbine driven, in which case
they must be designed to withstand the increased stresses due to a
double-speed. This fact should not be neglected when making a
decision on the speed of a water-wheel-driven exciter.
Method of Drive. While the exciters can be either belt-driven
or direct-connected to the machines driving them, the latter prac-
tice is almost exclusively used except in the very smallest plants.
The direct connection may be either to the main generators, to
separate water wheels or to motors, usually of the induction type.
Sometimes, although rarely, an exciter may be foimd that is
connected both to a motor and a turbine, the latter running idle
when the motor is carrying the load, and vice versa.
Mechanical Design. The mechanical design of exciters does
not dififer from other direct-current generators. They may be
either of the horizontal or vertical type, the latter construction
being used for units direct connected to vertical main generators
or directly to vertical water wheels. When intended for direct
connection to horizontal water wheels they are almost invariably
of the pedestal bearing type, the shaft being provided with the
necessary coupling. Care should be taken in designing the bear-
ings to see that the water thrust, if any, is provided for. The
same construction is also generally used for large motor-driven
sets. Fig. 208, the two units being mounted on a conmion base.
Occasionally only two bearings are used and a conmion shaft.
For horizontal imits direct-connected to the main units, shaft
and bearings are generally omitted, the exciter armature being
mounted on an extension to the generator shaft and the frame
supported on an extension to the generator subbase, as shown in
Pig. 209.
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354
ELECTRICAL EQUIPMENT
Vertical direct-driven exciters, Fig. 210, are ordinarily pro-
vided with one or two guide bearings and a short shaft with
Fig. 208. — Induction Motor-drivan Exciters.
Fig. 209.— 3000-K.W. Frequency Changer Set, Showing Mounting of Direct-
connected Exciter.
coupling. The rotating element is supported by means of a
thrust bearing located on the upper bearing bracket. It should
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EXCITERS 355
be of suflScient size to take care not only of the weight of the
exciter armature, but also of the revolving element and water
thrust of the turbine.
In the case of a vertical generator the direct-connected exciter
Fig. 210. — ^Vertical Water-wheel-driven Exciter, Showing Thrust
Bearing at Top.
is usually carried by the thrust-bearing bracket, as shown in
Fig. 211.
Arrangement and Connections.^ The question always arises
whether direct-connected exciters should be provided for each
unit or whether a central supply source, consisting of as few units
as possible is preferable. Either arrangement has its advantages
and disadvantages. The great advantage in a water-wheel-driven
exciter arrangement lies in the fact that it is independent of the
A.C. system with its load and speed fluctuations. Two units are
then usually provided, either of which has a capacity to take care
of the entire excitation of the plant, thus providing a 100 per cent
* See also Voltage Regulation.
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356
ELECTRICAL EQUIPMENT
Fig. 211. — Vertical Generator with Direct-connected Exciter.
reserve capacity. Occasionally three units are installed, two of
which, combined, can take care of the entire excitation, the third
unit being the reserve. This method may be the most desirable,
on account of the possibiUty of debris or ice clogging up the small
exciter turbines and shutting them down. Under such condi-
tions it would naturally be more advantageous to keep a motor-
driven set in reserve for such an emergency. From an economical
point of view, however, it is evident that two motor-driven units
with a spare water-driven unit would cost less. An objection to
motor-driven sets which is occasionally raised is that they are
liable to drop out of step when a short circuit occurs on the system.
This is, however, not the case with well-designed sets under
momentary short circuits, and where it has occurred, it has been
prevented by equipping the sets with flywheels. This, of course,
increases the expense of the sets and is, as a rule, not justified.
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EXCITERS
357
Exciters direct connected to each of the main units are, as a
rule, used in plants having a small number of units. They are, of
course, afifected by the speed fluctuations of the main imits, and
at runaway speeds they may cause over-voltages amounting to
two or three times the normal voltage, thus greatly endangering
the apparatus on the system. Such over-voltages must, there-
fore, be guarded against either by providing means for artificially
loading the system, should the outside load drop, or, preferably,
by providing high-voltage cut-out relays, which will automatically
insert resistance in the exciter field circuits and thus prevent an
excess voltage rise.
Where two or three units are used, each exciter should have a
capacity suflSicient to excite two generators, while with four or
iiQ. 212. — SyiStem of Exciter Connections.
more units it will undoubtedly be more advantageous to make the
capacity of each exciter correspond to the excitation require-
ments of one generator and provide a motor-driven exciter for
spare. This may then have the same capacity as one of the direct-
connected exciters or, for larger stations, it may have twice the
capacity or two sets may be installed.
The economical question should, of course, also be consid-
ered in deciding between the two systems. Direct-connected
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358
ELECTRICAL EQUIPMENT
exciters will, as a rule, be of a rather slow speed and thus more
expensive per Kw. than water-wheel-driven units, the difference,
however, diminishing as the head and number of units increase.
On the other hand, water-wheel-driven exciters involve the cost
of the hydraulic equipments, and besides the additional expense
of the building caused by the space occupied by these units. The
eflSiciency is, however, mostly in favor of direct-connected units.
The general practice is to provide one or two sets of common
bus-bars to which all the exciters are connected in parallel and
ifftli IF1I¥BTT
' T r r r T r »-- r
I * X X ill Rheoautl
SUtion
Liffhtins
f
Fig. 213. — System of Exciter Connections.
from which the fields of the different generators are excited, a
rheostat being inserted in each field circuit.
In the arrangement shown in Fig. 212 there are three exciters,
two of which are water-wheel-driven, the reserve being motor-
driven. Only one set of exciter bus-bars is shown, although
frequently an auxiliary set i§ also installed. The equaUzer con-
nection and the exciter shunt fields are left out so as to simplify
the diagram. Means are provided for sectionaUzing the bus, as
shown. Power for the induction motor is taken from the main
bus, and any number of motors can be started by one compen-
sator if a common nmning and starting bus is provided.
Fig. 213 represents a comparatively large system with not less
than six direct-connected exciters operating in parallel. There
are two sets of bus-bars, one for excitation and the other for
emergency or auxiliary service, and switches are provided so that
the exciters can be connected to either set as desired. One exciter
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EXCITERS
359
can, if necessary, be connected to the auxiliary bus while the others
are operating on the field-bus. As previously stated, however, it
is not considered good practice to use the excitation system for
the auxiUary service. To provide spare capacity for the system
shown, a motor-driven exciter can be installed, feeding the iaux-
iliary bus and the field switches made double-throw instead.
In very large plants the general tendency is to so arrange the
system that each generating unit shall form a complete plant in
itself, capable of independent operation, although normally the
units are operated in parallel. Each generator is, therefore,
^ lL llllltll'
Ci^&l^&i^
6 mm
- _ witliJJinat
6-
Fig. 214. — System of Exciter Connections.
provided with its individual exciter, which may be. either direct
connected, as previously described, or also motor driven with
power from a separate s6urce. Which system is the most eco-
nomical and advantageous depends entirely on the conditions.
There are two large systems in operation which use the latter
scheme, differing only somewhat with respect to the power supply,
which, however, is entirely independent in either case.
One of these arrangements ^ is illustrated by the representative
diagram in Fig. 214. The exciters, which have a capacity cor-
responding to that required by their respective generators, are
not operated in parallel, but have their terminals connected
directly to the generator fields through the collector rings. The
regulation is accomplished by adjusting the exciter fields (see
Voltage Regulation), thus eliminating large field rheostats in the
* Mississippi River Power Co.
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360
ELECTRICAL EQUIPMENT
main field circuits^ as well as their losses. The exciter sets (Fig.
215), receive their driving power normally from an entirely inde-
pendent som-ce, consisting of two auxiliary water-wheel-driven
low-voltage alternators with their own individual direct-connected
exciters (Fig. 216). These alternators feed into a set of bus-bars,
to which the exciter motors are normally connected. Provision
is also made, however, so that the exciter sets can be fed from
the main bus. One step-down transformer is provided for each
Fig. 216. — ^Exciter Set for Generating Unit in MissiBsippi River Power Com-
pany's Plant at Keokuk.
bus section and supply power to an auxiliary exciter bus which is
sectionalized in the same number of groups as the main bus.
Connection can also be established (not shown in diagram), in
case of emergency, with a storage battery which ordinarily is
used for the operation of the oil switches.
Besides supplying power for the exciter sets, the auxiliary
alternators also supply power for the station service and lighting,
although provision is made so that it can also be taken from the
main bus.
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EXCITERS
361
In the other installation ^ mentioned the supply system for
the exciter sets consists of two low-voltage generators arranged
for combination drive, one end being connected to a water wheel
and the other to an induction motor which obtains its driving
power through step-down transformers from the main busses.
The water wheel is used for normal operation. In either system,
each auxiliary alternator is capable of carrying the entire exciter
load of the station.
FiQ. 216. — ^Auxiliary Generators with Direct-connected Exciters.
Supply for Motor-driven Exciters shown in Fig. 215.
Power
It is advisable to keep a spare exciter set on hand to replace
any one that may break down, inasmuch as each exciter has only
sufficient capacity to excite one generator only. The process of
changing requires but a very short time.
Exciter Batteries. The use of storage batteries as a reserve
source for field excitation has of late been increasing considerably.
The method of connecting and operating such batteries varies
somewhat with the arrangement adopted for furnishing the
* Ontario Power Company.
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362
ELECTRICAL EQUIPMENT
normal supply of exciting current, and the method employed for
controlling the field excitation. Where the exciting ciurent for
all of the machines is taken from a common exciter bus, the bat-
tery would ordinarily be floated directly across this bus, provided
its voltage is substantially constant. If the exciter bus voltage
Yoltmster OouwctiaH
Ft. Na 1 ChMg* "A"
Pt.NaS " "r
Pt.NaSTotalBattnr
Pt.NowlBu
Fig. 217. — Diagram of Connections for Exciter Battery for Emergenc^^ Service,
Normally off Line.
is varied from time to time by manual control, the battery can
still be kept constantly connected to the bus, but the number of
cells in circuit must be adjusted by means of an end cell switch
whenever the exciter bus voltage is changed.
If the exciter bus voltage is constantly varied automatically,
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VOLTAGE REGULATION 363
as by T.A.-regiilator control, the battery cannot be connected
directly across the bus. In such a case two difiFerent methods of
handling the battery have been used. The first consists in pro-
viding a constant potential exciter bus to which the battery is
normally connected, and introducing between this bus and the
conmion excitation circuit a booster whose voltage is automatically
controlled by the T.A. regulator. This gfystem is described in
detail in the section on " Voltage Regulation/' page 369.
The second method consists in connecting the two outer ter-
minals of the battery to the corresponding sides of the exciter bus
and opening the battery circuit in the middle, with an automatic
switch at this point for connecting the battery in one series in case
of failure of the normal source of exciting current. The two halves
of the battery are provided with a trickling charge to keep the cells
in a healthy and fully charged condition, by connecting through
high resistance to the opposite side of the bus, as shown in diar
gram. Fig. 217.
Where there is no common excitation circuit, but each alter-
nator is provided with its own independent exciter, a different
arrangement is adopted. In such a case an emergency exciter
bus is used to which the battery is normally connected and to
which a spare exciter may be connected when required. Should
the som'ce of excitation for any one of the alternators fail, its field
circuit is automatically connected to the emergency exciter bus
and the spare exciter may then be started up, if it is not already
in service, to relieve the battery as soon as this can conveniently
be done.
5. VOLTAGE REGULATION
Hand Regulation. The simplest system of regulation is by
means of hand-operated rheostats connected in the field circuits of
each generator. The pressmre of the exciter bus is then generally
kept constant at the rated exciter voltage and all the regulation
is done by manipulating the generator rheostats. In order to
regulate the exciter voltage it is, of course, also necessary to pro-
vide rheostats in the exciter fields.
T.A. Regulator. Of the various schemes proposed for auto-
matic voltage regulation, the T.A. regulator is now most widely
used. With this system the desired voltage is maintained by
rapidly opening and closing a shunt circuit across the exciter field
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364
ELECTRICAL EQUIPMENT
rheostat. The rheostat is first turned in until the exciter voltage
is greatly reduced and the regulator circuit is then closed. This
short-circuits the rheostat through contacts in the regulator and
the voltage of the exciter and generator immediately rises. At a
predetermined point the regulator contacts are automaticaUy
opened and the field current of the exciter must again pass through
the rheostat. The resulting reduction in voltage is arrested at
once by the closing of the regulator contacts which continue to
vibrate in this manner and keep the generator voltage within the
desired limits.
Method of Operation. An elementary diagram of the type
T.A. regulator connections with an alternating-current generator
and exciter is shown in Fig. 218. The regulator has a directr
D.OL Oaatrol
Fig. 218.— Elementary Connections of Type T.A. Automatic Voltage
Regulator.
current control magnet, an alternating-current control magnet,
and a relay. The direct-current control magnet is connected to
the exciter bus-bars. This magnet has a fixed stop-core in the
bottom and a movable core in the top which is attached to a piv-
oted lever having at the opposite end a flexible contact puDed
downward by four spiral springs. For clearness, however, only
one spring is shown in the diagram. Opposite the direct-current
control magnet is the alternating-current which has a potential
winding connected by means of a potential transformer to the alter-
nating-current generator or bus-bars. There is an adjustable com-
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VOLTAGE REGULATION
365
peDsating winding on the alternating-current magnet connected
through a current transformer to the principal lighting feeder. The
object of this winding is to raise the
voltage of the alternating-current
bus-bare as the load increases. The
alternating current control magnet
has a movable core and a lever and
contacts similar to those of the direct-
current control magnet, and the two
combined produce what is known
as the " floating main contacts."
The number of relays vary ac-
cording to the number and size of
the exciters, and while the funda-
mental principle of operation of all
the forms of T.A. regulators is the
same, certain modifications are
necessary. The relay consists of a
U-shaped magnet core having a
differential winding and a pivoted
armature controlling the contacts
which open and close the shunt cir-
cuit across the exciter field rheostat.
One of the differential windings of
the relay is permanently connected
across the exciter bus-bars and tends
to keep the contacts open; the other
winding is connected to the exciter
bus-bars through the floating main
contacts and when the latter are
closed neutralizes the effect of the
first winding and allows the relay
contacts to short-circuit the exciter
field rheostat. Condensers are con-
nected across the relay contacts to
prevent severe arcing and possible
injury.
The regulator may be mounted on the switchboard or on pedes-
tals, as in Fig. 219, this particular form having twenty relays,
divided into two groups.
Fig. 219.— Type T.A. Automatic
Voltage Regulator Mounted
on Pedestal.
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S66 fiLECtRlCAL EQUIPMENT
Cyde of Operation. The circuit shunting the exciter field
rheostat through the relay contacts is opened by means of a single-
pole switch at the bottom of the regulator panel and the rheostat
turned in until the alternating-current voltage is reduced 65 per
cent below normal. This weakens both of the control magnets
and the floating main contacts are closed. This closes the relay
circuit and demagnetizes the relay magnet, releasing the relay
armature, and the spring closes the relay contacts. The single-
pole switch is then closed and as the exciter field rheostat is short-
circuited the exciter voltage will at once rise and bring up the
voltage of the alternator. This will strengthen the alternating-
current and directrcurrent control magnets and at the voltage for
which the counterweight has been previously adjusted the main
contacts will open. The relay magnet will then attract its
armature and by opening the shimt circuit at the relay contacts
will throw the full resistance into the exciter field circuit tending
to lower the exciter and alternator voltage. The main contacts
will then be again closed, the exciter field rheostat short-circuited
through the relay contacts and the cycle repeated. This operation
is continued at a high rate of vibration, due to the sensitiveness of
the control magnets, and maintainB not a constant, but a steady
exciter voltage*
Regvlatar Arrangements. The most generally used r^ulator
arrangement consists of one common regulator for several exciters
operating in parallel. Such a regulator should have sufficient
capacity to take care of all the exciters, whether it is necessary to
operate them all at one time or not. EquaUzing rheostats must
also be provided with such an arrangement in order that each
exciter shall carry its share of the load. The full field voltage of
one exciter may, for example, be considerably higher than another
and it may build up quicker when its rheostat is short-circuited
by the automatic regulator. Assuming that the field rheostats of
the two exciters are set so that, with the regulator contacts open,
the voltages are equal, the more sluggish exciter will tend to main-
tain its voltage at a lower point than the more active one. The
contacts, of course, open and close at the same speed on both.
The more active exciter would, therefore, tend to take more than
its share of the load. To cause proper division, the resistance in
the field circuit of the more active naachine should be increased.
When an exciter requires more than one relay, the resistance of its
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VOLTAGE REGULATION 367
field rheostats is divided between the relays and a change in posi-
tion of the movable arm would unbalance the load on the different
contacts. An external resistance is, therefore, provided called
the equalizing rheostat and inserted in the field circuit of the more
active exciter (usually the higher speed), as shown in the dia-
gram. EquaUzing rheostats are required for all but one of
several exciters in parallel. Compoimd wound exciters in par-
allel are also provided with equaUzer connections in the same way
as other D.C. generators.
It is also possible to operate a conunon regulator in connection
with two or more exciters when these are not operated in parallel
on the exciter bus, although such an arrangement is not recom-
mended as the best operating conditions. With certain modifi-
cations, the connections are just the same as if the exciters were
in parallel. If the exciters to be thus operated have similar char-
acteristics, very satisfactory regulation will probably be obtained
over the whole saturation range, but if the exciters have different
characteristics, it may happen that if satisfactory parallel opera-
tion of the alternators is obtained at one point of the saturation
curve of the exciters, successful operation will probably not be
obtained at a different point. Under various load conditions it
will, therefore, be necessary for the operator to either adjust the
generator field rheostats or the equahzing rheostats, which should
be provided as with the previous arrangement.
A third arrangement is that of individual regulator operation.
In large central stations, where there are installed a large number
of A.C. generators and exciters, and it is desired to operate the
generators in parallel but not on the exciters, each exciter being
arranged to excite its own individual generator fsee Fig. 214, page
350), it is possible to operate a voltage regulator on each combina-
tion of generator and exciter. The generator, exciter and regu-
lator then form an operating unit in itself, and can be operated
without affecting the operation of the other units. This is accom-
plished by simply placing a current transformer in the opposite
phase from that to which the potential transformer for each regu-
lator is connected (Fig. 220).
At unity power-factor the phase angle between the current and
the potential transformer acting on the regulator magnet core is
90® and the current winding of the regulator has no effect upon
the voltage of the regulator. However, should the voltage of
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368
ELECTRICAL EQUIPMENT
one alternator tend to increase above that of any of the others,
a circulating current would flow between this alternator and
the ones having the lower voltage. This exchange current, of
course, Would be out of phase with the voltage and, therefore,
would swing the current in the current coil of the A.C. magnet
in phase with that of potential current of this magnet. This
would cause the regulator on this unit to reduce the generator
voltage, which would, of course, eliminate the possibility of any
cross currents between the different alternators operating upon
the bus-bars. Of coiu*se, if the voltage on one machine tended to
EseilerFMd
FiQ. 220. — Individual T.A. Regulator Operation with Exciters not in ParaUel.
Main Generators Operating in Parallel.
drop, the regulator would operate in the opposite direction, causing
the voltage on this generator to rise, which would aldo eliminate
the above-mentioned cross currents.
Very complete instruction for the connection and operation of
the diflferent forms of T.A. regulators can be obtained from the
manufacturer.
Line Drop Compensation. Compensation for line drop may
also be obtained with these regulators. For ordinary installations
the compensating winding on the alternating current control
magnet is connected to a current transformer in the main feeder.
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VOLTAGE REGULATION
A dial switch is provided by which the strength of the alternating-
current control magnet may be varied and the regulator made to
compensate for any desired line drop up to 15 per cent, according
to the line requirements.
This arrangement is very satisfactory for general use but where
the power-factor of the load has a wide range of variation, as in
IblnContMU
Fig. 221. — ConnectioDB for Line Drop Ck)mpeDsator.
transmission lines, better results can be obtained with a special
line drop compensator, adapted to the regulator. This compen-
sator (see diagram Fig. 221), has two dial switches which are con-
nected to a number of taps of a resistance and a reactance coil, so
that the value of these can be adjusted to compensate accurately
for line losses with loads of varjring power-factor.
KR System of Regulation. This system is particularly
adapted to plants where it is necessary to maintain a constant
exciter voltage as in cases where it is desirable to operate motors
and other auxiliary station apparatus from the exciter bus. This
system also permits of the use of a storage battery in multiple
with the main exciters.
By teferring to Fig. 222 it will be noted that there is a third
bus employed and a D.C. booster connected between this bus and
one of the exciter busses. The main generator fields then are
connected across the outside bus, the voltage of which is deter-
mined by the voltage of the booster. This booster is usually
excited from a separate exciter whose field is connected from the
neutral of the above-mentioned battery and the neutral of a set
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370
ELECTRICAL EQUIPMENT
of resistances marked 72-1, ft-2, and fi-3, respectively. These
resistances in series are connected in parallel with the storage
battery and the main exciter. The booster exciter field connec-
tion is made between resistance R-1 and R-2, while resistance R-3
is short-circuited by means of the regulator relay contacts. These
resistances are so proportioned that R-l is considerably greater
than R-2 J and that R-2 plus R-S is greater than R-l. It will
be readily seen that when R-3 is short-circuited by the regulator
contacts the direction of excitation upon the booster exciter field
L4J ^t\
KirHtrr -
EsilU«T
Swkteh ''A"
FflOHT VIEW KoB TntluotlYO
Fig. 222. — Type T.A. Voltage Regulator in Connection with KR System of
Regulation.
will be in one direction; and when this resistance jR-3 is inserted
in circuit by means of the relay contacts being open, the direc-
tion of excitation through the exciter field will be in the opposite
direction.
The design of the above resistance is also such that there will be
full excitation upon the booster exciter in each instance, making it
possible to obtain the full boosting and bucking condition upon the
main D.C. booster. Assuming that the voltage of the main
exciters is 250 and that the D.C. booster is capable of giving 50
volts in each direction it will at once be noted that the voltage
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VOLTAGE REGULATION
371
obtainable across the main generator fields will be from 200 (the
difference between 250 and 60) to 300 volts (the sum of 250 and 50
volts).
High-voltage, High-current Relays. A cut-out relay has been
devised to be used in connection with T.A. regulators for guarding
against short circuits and voltage rises in transmission systems. If
a voltage regulator is Used and a short circuit should occur some-
where on the system, — ^for example, in the transmission lines, — the
action of the regulator would naturally be to deUver the maximum
excitation to the fields of the exciters and generators, so as to keep
up the voltage of the system. This, in turn, necessitates that the
Fig. 223. — Connections of High-voltage, High-current Cut-out Relay with
Type T.A. Voltage Regulator and Two Exciters in Parallel.
governors of the prime movers be wide open, and if the short cir-
cuit should be suddenly relieved, the voltage often rises to very
high values, owing to the time element involved in closing the
governors and in demagnetizing the fields. The connections for a
high-voltage, high-current relay operating in connection with two
exciters and one T.A. regulator are shown in Fig. 223. The relay
is provided with a current coil and a potential coil, and will
automatically insert resistance in the exciter field and thus reduce
the exciter voltage in case of excessive loads or voltages on the
main system.
Synchronous Condenser Regulation. The question of regula-
tion of large high-voltage systems involves a number of diflScul-
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372 ELECTRICAL EQUIPMENT
ties not encountered in low-voltage work. In the latter case the
energy loss is generally the limiting factor and the regulation can
often be improved by installing larger conductors, which at the
same time will reduce the line loss. With high-voltage systems
the gain of doing so is very slight and other means must be resorted
to for keeping the regulation within commercial limits. The
effect of the inductance and capacity of the line causes the voltage
to vary within very wide limits from full to no load. At no load
the large capacity current causes a rise of voltage from the gener-
ating station to the receiving end, while at full load the lagging
inductive current taken by the load, in general, more than offsets
the effect of the capacity current and causes a drop of voltage
from the generating station to the receiving end. It is evident
then that by installing a synchronous condenser at the receiving
end and by taking advantages of the characteristics of this ma-
chine, the receiving voltage can be kept constant at a determined
value or approximately so, by adjusting the synchronous con-
denser field causing the condenser to draw a lagging current from
the line at no load and a leading current at full; thus, by varying
the power-factor.
The automatic regulation of the condenser field current is
readily accomplished by means of a T.A. regulator. In this
instance the regulator does not, therefore, hold a constant power-
factor, but, by varjdng the same, holds a constant A.C. voltage
provided there is the proper capacity in the synchronous con-
denser upon which it is operating. The regulator endeavors to
hold just as much leading current upon the condenser as there is
lagging current upon the main transmission line; or else it will
endeavor to maintain the proper lagging current to counteract
for any leading current that exists upon the transmission system.
The connections and adjustment for the regulator are the same
as when being used upon an A.C. generator with the exception
that greater care should be exercised in the adjustment.
In a system of this kind, if the synchronous condenser has not
ample capacity, there is danger of burning out the fields, due to
the fact that the regulator is trying to maintain constant A.C.
voltage upon the system. It is verj' important, therefore, that
the highest safe voltage at which to operate the condenser fields
be determined, and the regulator adjusted for this limiting value,
which may be about 135 volts for a 125-volt excitation.
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TRANSFORMERS 373
The regulator then cannot hold a higher voltage than 135,
and should the voltage reach this value and tend to go higher, the
regulator would maintain a constant exciter voltage of this value
of 136; but the A.C. voltage would necessarily drop due to the
fact that it would be requiring a higher exciter voltage than
this value in order to maintain the A.C. voltage for which the reg-
ulator might be adjusted. The above value of 135 is selected only
as a matter of convenience and the regulator may be set for
whatever value it is safe to operate the condenser fields. If
they could be operated to as high as 145 volts the regulator should
be adjusted at 145 instead of 135.
For a fmlher study of the subject of " Sjrnchronous Condenser
Regulation," the reader is referred to an article by F. W. Peek, Jr.,
in the General Electric Review for Jime, 1913.
6. TRANSFORMERS'
Fundamental Principles. A constant potential transformer
consists essentially of an iron core upon which are wound two
wiadings, a primary and a secondary. When one \rinding is
connected to an alternating-current supply of power, an alternating
magnetic flux is excited in the iron core and an alternating voltage
is induced in the secondary winding, as its turns are surrounded by
the same flux as the primary. If the now secondary winding
is closed through a resistance or other load a current will flow
therein.
In an " ideal " transformer, power would be transmitted
from primary to secondary without any loss. In actual practice,
however, this is not quite possible on account of the losses which
take place in the iron core and the windings. Similarly, in an
ideal transformer, the ratio of primary to secondary voltage
would be equal to the ratio of the number of turns in the respective
windings. In a real transformer there is, however, also a voltage
drop caused by the resistance and leakage reactance of the wind-
ings. This reactance is due to the leakage flux which links with
the turns or part of the turns of one winding only.
The action of a transformer can best be understood by means
of a vector diagram (Fig. 224). Consider first the open-circuit
' Part of this section is taken from an article on " Transformer Connec-
tions '' in the General Electric Review by one of the authors and Mr. L. F.
Blume.
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374
ELECTRICAL EQUIPMENT
condition, i.e., no current flowing in the secondary winding. The
primary e.m.f. OB, causes an exciting current OMi to flow, this
current consisting of two components MMi, and OM. The com-
ponent MM I is in phase with the e.m.f. and supplies the iron core
loss due to hysteresis and eddy currents, while OM, which is in
quadrature with the e.m.f., represents the magnetizing current
and is thus in phase with the flux. The
secondary e.m.f. OB2 is exactly opposite
^c the primary in phase and its value is
equal to that of the primary times the in-
verse ratio of the turns of the two wind-
ings.
Suppose now that the transformer is
loaded, in which case a secondary current
OA2 will flow, proportional to the load.
If the load was non-inductive this current
would be in phase with the secondary
terminal e.m.f. OD2, thus lagging behind
the induced e.m.f. (^82^ due to the leak-
age reactance. In this particular case how-
ever, the load is inductive and the current
OA2 lags f behind the terminal e.m.f. 0D2^
degrees, the corresponding power factor of
the load being cos 0. The secondary ter-
minal e.m.f. OD2 is less than the induced
e.m.f. OB2 on account of the resistance
drop B2C2 and the reactance drop C2D2.
These values are the product of the secondary current times the
resistance and the reactance, respectively, of the secondary wind-
ing, the former being in phase with the current and the latter in
quadrature.
When the secondary current flows it disturbs the equilibrium
by tending to demagnetize the core, and the primary current
increase until, in addition to 'the exciting current OAf 1, a current
flows, the magnetizing effect of which just balances the magnet-
izing effect of the secondary current. This additional current
is represented by MiAi and it is just equal and opposite to the
secondary current OA2 times the inverse ratio of the number of
turns in the windings.
The total primary current 0-4 1 is, therefore, seen to be corn*
Fig. 224. — Theoretical
Transformer Diagram.
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TRANSFORMERS 375
posed of the exciting current OMi, which is practically constant
for all loads and the load current MiAi. The impressed primary
e.m.f. ODi is a Uttle greater than the primary counter e.m.f.
OBi on account of the resistance drop BiCi and the reactance
drop CiDi, the values being the product of the primary current
OAi times the resistance and leakage reactance^ respectively, of
the primary winding. The former is in phase with the current,
the latter in quadrature.
Induced e.mi. The relation between the coimter e.m.f. of
a transformer and the various factors, such as flux density, number
of turns, frequency, etc., are determined by the following formula:
£=4.44X/XnX«X10-8;
in which J? = mean effective e.m.f.;
/= frequency in cylces per second;
n= total number of turns of the primary winding;
^= total magnetic flux in maxwells.
This equation is based on the assumption that the e.m.f. is a
true sine wave.
Ratio. The A. I. E. E. Standardization Rules state that
"The voltage ratio of a transformer is the ratio of the r.m.s.
primary terminal voltage to the r.m.s. secondary terminal voltage
under specified conditions of load." It also defines " the ratio of
a transformer, unless otherwise specified, as the ratio of the
number in turns in the high-voltage winding to that in the low-
voltage winding, i.e., the turn-ratio."
The two ratios are equal when one of the windings is open
and the transformer does not carry any load. When loaded, the
resistance and inductance of the windings cause a drop in the
voltage, thus modifying the ratio of transformation sUghtly.
The ratio of a transformer refers, of course, to the turns
which are connected in series, high-voltage as well as low-voltage.
In many instances it is desirable for the sake of interchangeability
and standardization to split up the windings in groups of sections
which may be connected either in series, parallel, or series-parallel.
This is almost always the case with distributing transformers,
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ELECTRICAL EQUIPMENT
where the low-voltage winding may be connected for 115-230
volts. This makes possible the following connections:
HIOH-VOLTAOB.
LOW-VOI.TAQB.
Rfttio.
Connection.
Voltage.
2300
2300
ParaUel
Series
115
230
20:1
10:1
For transformers of very high voltages it is often requested
that the high-voltage winding be designed for series-parallel con-
nection. So, for example, by designing a transformer with a high-
voltage of say 110,000-66,000 volts, it is possible to operate the
system at the lower voltage mitil the load has increased to a point
necessitating a change-over to the higher transmission voltage.
Magnetizing Current. The effect of the magnetizing current
in transformers sometimes leads to the question of considering its
proper limitations. It was previously shown that this current is
wattless with the exception of a small PR loss and has Uttle influ-
ence on the values of the total current in the transformer when it
is operating at full load, but as the load decreases the effect be-
comes more prominent until at no load it is most noticeable,
and the power-factor naturally very low. This is an important
point where a large number of small transformers are operating
on a system, and for such cases it has become quite conmion to
limit the magnetizing current to a value not exceeding about 10
per cent of the full-load current, a value which cannot be consid-
ered detrimental to the system.
There is also another limitation which is given consideration in
connection with large transformer units. Such transformers are
nowadays built of high-grade steel, which has a core loss per
pound much less than formerly, and this has in many instances
made it advisable to increase the core densities. If, however,
these are increased much above the bend of the saturation curve
an unstable operation is Uable to follow, and for such conditions,
the limitation of the magnetizing current is governed by the per-
missible core density, usually around 90.000 lines per square inch.
With over-voltages causing a saturation of the core the mag-
netizing current increases very rapidly, but with the above limi-
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TRANSFORMERS 377
tation, based on normal voltage, an over-voltage of around 10 per
cent, which is to be expected, should not cause an excessive mag-
netising current.
With regard to efficiency and regulation the effect of the mag-
netizing current is insignificant.
Reactance. The percentage of the total flux that links with
the primary but does not link with the secondary winding, plus
that which links with the secondary but not the primary, is the
per cent reactance of a transformer. Thus, if 96 per cent of the
primary flux cuts both primary and secondary, the transformer is
said to have a 5 per cent inherent reactance.
The factors affected by the reactance of a transformer are its
regulation, parallel operation, mechanical stresses and eddy-
current losses. A low-reactance transformer has naturally a
better regulation than one of high reactance, especially for highly
inductive loads, and in order to obtain a good voltage regulation
it waa formerly the custom to design transformers with a reac-
tance as low as 1} to 2 per cent. Such a low reactance is, however,
often detrimental to the safe operation of a transformer from the
mechanical point of view. If a short circuit sho\ild occur at the
secondary terminals of a transformer, and the power supply at
the primary is sufficient to maintain the primary terminal voltage^
as may be the case in very large generating systems, the primary
and secondary currents of the transformer are limited by the
impedance only, and with the exception of very low reactance
transformers it is essentially the reactance which determines the
total impedance and thus the short-circuit current.
As the primary and secondary currents are opposite in phase,
they repel each other, the force being approximately propor-
tional to the square of the current. It therefore follows that the
repulsion, which is small at full load, may reach enormous values
under short-circuit conditions if the transformer reactance is low.
For example, in a transformer having a 2 per cent reactance the
short-circuit current will be 50 times normal and the mechanical
stresses will increase as the square of this or 2500 times, amount-
ing to many hundred tons. This clearly illustrates the necessity
of a very rigid construction and also the advisability of reducing
the short circuit to a safe value. This may be done by increasing
the transformer reactance, and modem practice tends toward the
use of considerably higher internal reactances than was formerly
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378 ELECTRICAL EQUIPMENT
used. In general it may be said that it is usually difficult to go
above an 8 to 10 per cent reactance in a 60-cycle moderate size
transformer (1000 to 2000 Kv. A.), without undue eddy-current
losses, and that the allowable maximum would be considerably
less than this in low voltage designs. For 26-cycle transformers,
a higher reactance may be obtained, since the eddy-current losses
are, of course, less at a given density.
Regulation. The regulation of a constant-potential trans-
former is defined by the A.I.E.E. rules as the difference between
the no-load and rated-load values of the secondary terminal
voltage at specified power-factor (with constant primary impressed
terminal voltage), expressed in per cent of the rated-load secondary
voltage, the primary voltage being adjusted to such a value that
the transformer delivers rated output at rated secondary voltage.
All parts of the transformer affecting the regulation should be
maintained at constant temperature between the two loads, and
where the influence of temperature is of consequence, a reference
temperature of 75^ C. shall be considered as standard. If a
change of temperature occurs during the test, the result shall be
corrected to the above reference temperature.
For non-inductive load the regulation varies approximately
from less than 1 per cent for large sizes to around 3 per cent for
smaller units. For inductive load it is naturally higher. It can
be determined by loading the transformer and measuring the
change in voltage with change in load at specified power-
factor.
The A.I.E.E. recommends the foDowing method for comput-
ing the regulation for any specified load and power-factor from
the measured impedance watts and impedance volts.
Let P= impedance watts, as measured from short-circuit test
and corrected to 75° C;
Eg = impedance volts ;
7X= reactance drop in volts;
Z= rated primary current;
£= rated primary voltage;
gr=per cent drop in phase with current;
(y,=per cent drop in quadrature with current.
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TRANSFORMERS 379
IX-
■=^/-.•-Q^■
Then:
1. For unity power-factor, we have approximately:
Per cent regulation = gr+^.
2. For inductive loads, where the power-factor (cos if>) equals
m and the reactive factor (sin ^) equals n. Per cent regulation
^mqr+nqx-\ 200 '
Core and Shell Tjrpe« Transformers are of two fundamental
designs, namely: The shell and the core type, and occasionally a
combination of these two is also used (Fig. 225). In the shell type
the iron circuit surrounds the transformer coils, while in the core
type the copper windings surround the iron core. While the sheD-
type transformers have been most extensively used in the past,
core-type transformers are now built for the largest sizes, and are
rapidly superseding the former type. With the core type design,
the arrangements of cores and the circular coils present a con-
struction which offers a maximum resistance to the mechanical
distorting forces. This mechanical strength, combined with the
inherent reactance of this type of transformer, produces a unit
which is exceptionally able to withstand severe service. On the
other hand, the circular coils can readily be insulated for the very
highest voltages in use.
Method of Cooling. Transformers may be divided into four
classes, depending upon the method of cooling, viz., natural draft,
air blast, oil immersed self-cooled and oil immersed water-cooled.
Natural-draft transformers have the core and coils exposed directly
to the air, and depend entirely upon the natural circulation of
the air for their cooling. They are built only for very low voltages
and stnall sizes. Air-blast transformers depend upon a forced cir-
culation of air over the surface of the core and coils to carry away
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380
ELECTRICAL EQUIPMENT
the heat. They may be built for large capacities, but the voltage
rarely exceeds 30,000 because of the difficulty. of insulating them
properly.
Oil immersed self-cooled or water-cooled transfonners are gen-
erally used with hydro-electric power developments, the latter in
Single-Phase
Three-Phase
Vertical
J
1
1
^
^
1
1 1
1
=
View
n
1
=
n
1
1 1
1
=
OopeTJT»
Shell Trpe
Combimitioo
Core i Shell
Type
Fig. 225. — Different Types of Transformer Core Construction.
the generating station, while either type may be used with the sub-
stations, depending upon the availability of cooling water. Both
types are built for the largest capacities and the highest voltages.
Self-cooled oil immersed transformers have the core and cofls
immersed in a tank of oil, the tank usually being corrugated so as
to increase the surface available for dissipating the heat generated
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TRANSFORMERS 381
in the core a^d coils. Sometimes external tubes or radiators,
through which the oil circulates, are used for the same purp)08e.
Water-cooled oil immersed transformers depend upon the circu-
lation of water through a coil placed in the top of the tank to carry
away the heat from the oil, about J gallon being required per
minute per Kw. loss, the temperature of the incoming water being
15° C.
For conditions where long and definite periods of light and
heavy load occur, as in small winter and large sunmier service,
a combination self-cooling and water-cooUng design has been
provided. Such transformers are placed in the regular sheet-
steel tanks of the self-cooled design, excepting that they have
smaller surfaces and are in addition provided with water-cooling
coils to take care of the super-load. They can readily be designed
to carry 50 per cent of the maximum load without water circula-
tion and not exceed the rated temperature rise. The increase in
the cost over the water-cooled design is slight and will often be
found a good investment when cooling water has any appreciable
value.
Special precautions must naturally be taken to protect trans-
formers of the outdoor type both from the extreme heat and from
the cold in the winter. The former can readily be obtained
by providing sunshades, and in certain instances very good results
have been obtained by simply painting the tanks white. It is
more difficult, however, to provide for the cold winter temperatures,
especially with water-cooled transformers. With the trans-
formers in service there seems to be no danger of freezing, and if
such should be the case some sort of heating grids could readily
be provided in the bottom of the tanks. The main difficulty lies
in the formation of moisture which takes place when the temper-
ature of the transformer is allowed to faU below that of the sur-
rounding air; this appUes also to indoor transformers. Pre-
cautions must, therefore, be taken that this does not happen, and
may be accomplished by either reducing the water rate at times of
cold weather, or by using the cooling water over and over again.
An oil with special low freezing-point may be used in transformers
in rare locations experiencing extreme low temperatures.
Single and Polyphase Transformers. Transformers are made
either as single or polyphase units, the latter being generally of the
three-phase type. The single-phase design is by far the most
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382 ELECTRICAL EQUIPMENT
flexible, as by different connections an}'- combination can be
obtained. Economical considerations are, however, often the
determining factor in deciding on what type to use.
Three-phase designs may be connected either in delta or Y,
and the units may be either of the sheD or the core type con-
struction. In delta-connected shell-type transformers, should one
phase be damaged, it is possible to operate the remaining two
phases in open-delta at 58 per cent of the combined capacity, by
simply disconnecting the damaged unit of the three single-phase
transformers, or in the case of three-phase shell-type units by dis-
connecting and short-circuiting the damaged phase, both high-
and low-voltage. This will reduce the flux passing through the part
of the core surrounded by these windings and limit the current in
the damaged winding to a fraction of the normal full-load current.
Y-connected shell-type transformers of both the single- and
three-phase t3rpes cannot be operated with one phase damaged,
except where the neutral is grounded, in which case they may be
operated at 58 per cent of their total capacity by short-circuiting
both the high- and low-voltage windings of the damaged phase.
Such a scheme is, nevertheless, not very satisfactory for motor
operations on account of the unbalancing of the phases and the
reduced voltage. Lights can, however, be operated successfully
by connecting them between the live single-phase wires and the
neutral.
In the case of three-phase core-type transformers, even though
the windings are delta-connected, it is impossible to operate when
one phase becomes short-circuited. This is due to the fact that
the three phases are magnetically interlinked in such a manner that
any one phase is a return path for the fluxes in the other two
phases. This means that when one phase is short-circuited the
short circuit is transmitted magnetically to the other two phases
in such a manner that when the two phases are excited large
short-circuit currents flow, the short-circuit phase acting as sec-
ondary and the remaining phases as primary. In the three-phase
shell-type transformer this does not occur, because the fluxes in
the three phases are independent of each other, and, therefore,
the flux in one phase can be reduced to zero without affecting the
other. However, if the damaged winding can be open-circuited
or removed from the core, the transformer will operate satisfactory
connected open-delta.
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TRANSFORMERS 383
Rating. A transformer should be rated by its tdlovolt-ampere
(Kv.A.) output. It is simply eqiial to the product of the voltage
and current, and is, therefore, the same whether the different coils
are connected in series or parallel. If the load is of imity power-
factor, the kilowatt output is the same as the kilovolt-ampere
output, but if the power-factor is less, the kilowatt output will be
correspondingly less. For example, a 100 Kv.A. transformer will
have a full-load rating of 100 Kw. at 100 per cent power-factor,
90 Kw. at 90 per cent power-factor, etc.
The A. I. £. £. Standardization Rules identify self- and water-
cooled oil immersed transformers as to Kv.A. rating by their
maximimi continuous capacity at 55^ rise. With an ambient
room temperature of 40** C. air for the former and 26** C. incoming
water for the latter, the observable temperatures would be 95°
and 80° C. respectively. The rules further specify that the tem-
perature of the windings of transformers is always to be ascer-
tained by Method II, i.e., the resistance method. (See page 310,
" Rating of Generators ")• This method allows for -a correction
factor of 10° C, so that for self-cooled transformers the hottest-
spot temperature is limited to 106° C. and for water-cooled to
90° C. The oil shall in no case have a temperature, observable
by thermometer, in excess of 90° C.
For air-blast transformers the rules specify that a correction
sludl be applied to the observed temperature rise of the windings,
and it is to be noted that air-blast transformers constitute the
only instance wherein it is required that a correction shall be ap-
plied to take into account the precise ambient temperature at
time of the test. This is due to the difference in resistance, when
the temperature of the ingoing cooling air differs from that of the
standard reference. This correction shall be the ratio of the
inferred absolute ambient temperature of reference to the inferred
absolute temperature of the ingoing cooling air, i.e., the ratio
274 5
— -— ^ — r ; where t is the ingoing cooling-air temperature.
Thus, a cooling-air temperature of 30° C. would correspond
to an inferred absolute temperature of 264.6° on the scale of copper
resistivity, and the correction to 40° C. (274.6° inferred absolute
274 6
temperature) would be =1.04, making the correction factor
^04.0
1.04; so that an observed temperature rise of say 60° C. at the
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384 ELECTRICAL EQUIPMENT
testing ambient temperature of 30** C. would be corrected to
60X1.04=62° C, this being the temperature rise which would
have occurred had the test been made with the standard ingoing
cooling-air temperature of 40** C.
Efficiency. The efficiency of a transformer is the ratio of the
kilowatts output measured at the secondary terminals to the kilo-
watts input measured at the primary terminals. The difference
between these two values equals the losses, which consist of the no-
load losses, the PR losses and the stray-load losses. The no-load
losses consist of the hysteresis and eddy-current or core loss in
the laminations, the PR loss due to the exciting ciurent and the
dielectric hysteresis loss in the insulation. The PR losses should
include the copper loss in all the windings, primary as well as
secondary, and the stray-load losses consist of the eddy-current
loss in the windings and core, due to fluxes varying with the load.
They should also include the stray loss in other parts of the trans-
former. In determining these losses care shall be taken that they
are corrected to a reference temperature of 76** C.
The efficiency is generally given at miity power-factor, but
can readily be figured out for any power-factor as the losses are
independent of the same a& long as the Kv.A. is not changed.
For example, assimie a 1000 Kv.A. transformer having a total loss
of 14 Kw. or 1.4 per cent based on 1000 Kw. at unity power-factor.
Based on 800 Kw. 80 per cent power-factor the loss would be
1.76 per cent. In the former case the efficiency at full-load would
be 98.62 and the latter 98.28, which illustrates the importance of
basing the efficiency identically.
The efficiency depends upon the voltage and the sLee of the
unit and varies from about 97 to as high as 99 per cent for trans-
formers generally used in hydro-electric work. For 26 cycles the
losses are somewhat higher and the efficiency somewhat lower on
account of the larger amount of material required for this fre-
quency as compared to 60 cycles.
Sometimes the all-day efficiency of a transformer is required
for comparison, and this may readily be figured from the following
simple formula:
A]l-D»7 BffloiflDoy- „ . „ _ -..
KV.A. HOiiM per Day Output _____
KvJL. Hn. per Dbv Output + 24 X No-load Lom+No. of 9n.x/>i2+Stny-load Liaa
Voltage. In regard to the use of the terms high-voltage,
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TRANSFORMERS 385
low-voltage, primary and secondary, the A.I.E.E. standardiza-
tion rules read as follows:
" The terms high-voUage and hw-voUage are used to distinguish
the winding having the greater from that having the lesser number
of turns. The terms 'primary and secondary serve to distinguish
the windings in regard to energy flow, the primary being that which
receives the energy from the supply circuit, and the secondary
that which receives the energy by induction from the primary."
The terms primary and secondary are, however, often confused,
and in order to avoid any misunderstanding it is preferable to
use the terms high-voltage and low-voltage instead of primary
and secondary.
In every S3rmmetrical three-phase circuit there are two voltages
which should be clearly distinguished:
(1) The voltage between lines, called the " delta-voltage "
and (2) the voltage from line to neutral, called the " Y-voltage."
Under balanced conditions
Y-voltage= delta-voltage divided by V3, and
Delta-voltage =Y-voltage times Vs.
Transformers designed to be suitable for use in either delta or
Y-connection have, as a rule, on the name plates the line voltages
which apply for both connections. The line voltage resulting
from Y-connection is followed by the letter " Y " — ^for example,
10 000
if the transformer voltage is given Jfkn v> *^ signifies that
both voltages are line voltages but the latter is the voltage result-
ing when the transformer is connected in Y. The sjonbol ** Y "
is used as an abbreviation to indicate that sufficient insulation has
been provided so that the. transformer may be connected in Y for
the line voltage with which the letter is used, but this S3rmbol
should not be confused with " Y-rvoltage." The expressions
" delta-voltage " and '* Y-voltage " are often loosely used for
"voltage when connected in delta " and " voltage when cgn-
nected in Y " and misunderstandings are often caused thereby.
If, however, the facts are kept clearly m mind that a " Y " in the
voltage rating of a transformer stands for " Y-connection " and
that " Y-voltage " is only a part of the line voltage, there should
be no cause for misunderstanding.
The transformer voltage depends, of course, on the nature of
the system. The primary voltage of the step-up transformers is,
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386
ELECTRICAL EQUIPMENT
for example, governed by the generator voltage and may be any-
thing up to 13,200 volts. The secondary of the step-up trans-
formers and the primary of the step-down transformers is deter-
mined by the most economical transmission voltage, which may
be as high as 150,000 volts. The secondary of the step-down
transformers is finally governed by the potential of the distrib-
uting system. Where this is extensive its voltage may be com-
paratively high, may be 33,000 or even higher, while, for smaller
systems it may only be 2300 volts and even lower. The voltages
generally used for power transformers are as follows:
Low-Voltage.
High-Voltage.
2,300
6.600
11,000
13,200
16,500
22,000
33,000
44,000
66,000
88,000
110,000
150,000
The test voltage which shall be applied to determine the
dielectric strength of the insulation is specified by the A.I.E.E.
rules as twice the normal voltage of the circuit to which the
transformer is connected plus 1000 volts. The test shall be made
at the temperature assumed under normal operation, and the
frequency of the test circuit shall not be less than the rated fre-
quency of the apparatus tested. The duration of the application
of the voltage shall be one minute, and it shall be successively
applied between each electric circuit and all other electric cir-
cuits and metal parts grounded. Inter-connected pol3rphase
windings are considered as one circuit and all windings except
that under test shall be connected to ground. Transformers
which may be used in Y-connection on three-phase circuits shall
have the test based on the delta or line voltage.
The following exceptions to the above rule are given:
(1) Alternating current apparatus connected to permanently
grounded single-phase systems, for use on permanently grounded
circuits of more than 300 volts, shall be tested with 2.73 times the
voltage of the circuit to ground plus 1000 volts. This does not,
however, refer to three-phase apparatus with grounded neutral.
(2) Distributing transformers for primary pressures from
660 to 6000 volts, the secondaries of which are directly connected
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TRANSFORMERS 387
to consumer's circuits, shall be tested with 10,000 volts from
primary to core and secondary combined. The secondary winding
shall be tested with twice normal voltage plus 1000 volts.
Under certain- conditions it is permissible to test transformers
by inducing the required voltage in their windings, in place of
using a separate testing transformer. By '^ required voltage " is
meant a voltage such that the line end of the windings shall receive
a test to ground equal to that required by the above general rules.
Transformers with *' graded " insulation shall be so marked,
and shall be tested by inducing the required test voltage in the
transformer and connecting the successive line leads to ground.
The term " graded " is used to indicate the emplo3rment of less
insulation towards the end of the windings where the insulation
stresses are low, i.e., towards the groimd, and more insulation at
the high-potential ends. Such transformers usually have the wind-
ing groimded within the tank and all transformers so connected
shall be tested by induced voltage.
Until the adoption of the sphere gap as a method of voltage
measurement, transformers were generally tested by the use of
the needle gap. This resulted in more or less inconsistent tests,
due mainly to the effect of the variation in humidity and also to
some extent due to temperature, barometric pressure and corona.
Accordingly, when needle gaps were used for voltage measure-
ments, the actually appUed voltage depended upon the particular
season of the year and the atmospheric conditions at that time,
and this naturally resulted in that in many instances the trans-
former tested did not receive the required voltage. With the
adoption of the sphere gap the variation in the applied voltage is
eliminated and by insisting upon this method of measurement it is
safe to assume that the full potential is actually applied. This is,
of course, of great importance with very high voltage transformers.
Taps. It is customary to provide the high-voltage transformer
windings with taps for four 2J per cent steps below the normal
operating voltage so as to compensate for voltage drop in the line.
Fig. 226 illustrates this point, the diagram representing a single-
phase system for the sake of simplicity.
For the step-up transformers in the generating station it is
obvious that taps are not required, but they are sometimes pro-
vided for the sake of imiformity with the step-down transformers.
Thus, with a 10 per cent voltage drop in the line, the conductors
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388 ELECTRICAL EQUIPMENT
can be connected to the 10 per cent tap, thereby compensating
for the line drop. As this tap is used when the load is greatest
it follows that, theoretically, the taps should be of full capacity;
i.e., the current carrying capacity of the high-voltage winding
should correspond to the lower voltage value. Often, however,
reduced capacity taps are specified, and reUance is placed on the
ability of the transformer to carry the increased current safely.
o
WTap
t^ittiVf
Fig. 226.
On account of the low-voltage winding the capacity of the trans-
former is, however, based on the full rated voltage.
Sometimes large power transformers have their high-voltage
windings so arranged that the two halves can be connected either
in parallel or series. The former connection corresponds to
only half the voltage of the latter and is for use during the first
period of operation of a system when the load is light and when the
lower operating voltage is sufficient. When the load has increased
so as to necessitate a higher voltage, the two windings are con-
nected in series, thereby doubling the transmission voltage.
Transformers are sometimes arranged for supplying simul-
taneously two loads, one at full voltage and the other at half
voltage. The question then often arises as to how much each
side may be loaded without causing overheating of the trans-
formers. This can readily be ascertained from the curves in Fig.
227. For example, with a full voltage load of 75 per cent it is pos-
sible to load the half voltage circuit for 40 per cent current, which
is equal to 20 per cent the capacity.
Where taps are not essential for the satisfactory operation of a
system, they should be avoided as much as posable, especially in
very high-voltage transformers, and standard practice does not
contemplate any taps for voltages below 6600, nor above 66,000.
It is evident that taps are difficult to insulate and bring out to the
connection board and that they, therefore, introduce additional
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TRANSFORMERS
389
weaknesses in the design of a transformer and thus decrease the
reliability of operation.
Induction motors, synchronous motors and synchronous con-
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100
verters started from the A.C. side require frequently transformers
with taps for reducing the potential at starting in order to prevent
a heavy rush of current.
Fig. 228 shows the arrangement of taps for starting three-phase
converters, leads 1, 2, and 3 being the operating terminals, and
leads 1, 4, and 5 those for starting at half voltage. Lead 6 is
merely for the purpose of making the three transformers dupli-
cates. With some converters it has been found advantageous
to insert resistance in the starting connections so as to still further
lower the applied voltage.
Large converters are usually connected six-phase diametrical,
and when started from the alternating current side, it has been
customary to provide taps on the transformers for one-third and
two-thirds voltage, as shown in Fig. 229. Leads 1 to 6, inclusive,
are the operating terminals; leads 1, 3, 5, 7, 8, and 9 are for the
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390
ELECTRICAL EQUIPMENT
first step, and leads 1, 3, 5, 10, 11, and 12 for the second st^p.
Leads 2, 4, and 6 are for the final or full-voltage step. Leads
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1, 3, and 5 are connected directly to the converter and the starting
is done by two triple-pole, double-throw switches, as shown.
Recent improvements in the design of synchronous converters
have, however, made possible the elimination of the second start-
ing tap, and it is now general practice to use only one partial
starting voltage, requiring one three-pole, double-throw switch
for six-phase converters.
Number and Size of Units. The number and size of the trans-
former units and whether they should be single- or three-phase
depends entirely on the nature of the development and on the con-
ditions to be met. With moderate voltage developments it has
in the past been the general practice to install one transformer
bank for each generator and of equal capacity to the same, even if
the size was not the most economical. With a large number of
units it was then natiu'ally more advantageous to install three-
phase transformers, while in plants consisting of one or two gen-
erating units, where the cost of a spare three-phase unit was not
warranted, it was foxmd preferable to install single-phase units.
With present modern high-voltage systems where it is unde-
sirable to paiallel the outgoing transmission lines on the high-
tension side of the transformers or to carry out any high tension
switching, which may cause siu'ges, it has become a general
practice to install the transformers in groups, each having a
capacity corresponding to one line; the transformer group and
the line thus being considered as a unit. Transmission lines
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TRANSFORMERS
391
may have a capacity up to 30,000 or 40,000 kilowatts, depending
on the voltage, and inasmuch as it is now possible to build single-
phase transformers for one-third this capacity, the arrangement
is entirely feasible; otherwise it would be possible to install
two banks in parallel for each Une.
Connections. Among the great variety of transformer ma-
nipulations in power and general distribution work, either for
straight voltage transformation or for phase transformation, the
following are the most generally used:
Voltage transformation:
Single-phase;
Two-phase;
Three-phase, delta-delta;
Three-phase, delta- Y, and vice versa;
Three-phase, Y-Y;
Three-phase, open-delta;
Three-phase, T.
Phase transformation:
Two- or three-phase to single-phase;
Two-phase to six-phase;
Three-phase to six-phase.
Voltage Transformation. Single-phase. The windings may be
divided into sections and variously connected to meet different
requirements. So, for example, are most standard distributing
transformers made with two low-voltage coils.
Fig. 230 represents the straight connection of two trans-
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FiQ. 231.
formers to 1000-volt mains, the transformer consisting simply of
single high- and low-voltage windings.
Figs. 231 to 233 represent different connections of transformers
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392
ELECTRICAL EQUIPMENT
which are provided with two coils. So, for example, in Fig. 231
the two low-voltage coils are connected in parallel to supply 100
volts.
In many instances it is deemed advisable to operate a three-
wire circuit from the low-voltage side of transformers, and thereby
reduce the cost of copper for the feeders. Such a connection is
represented in Fig. 232, where the low-voltage coils are con-
nected in series and their junction connected to the neutral wire.
This method of connection is used very extensively and is known
as the Edison Three-wire System. When used for combined
power and lighting load, the motors are usually connected to the
two outside wires, and the lights between the outside and neutral.
The neutral wire generally carries less current than the out-
side wires, except in the case where the entire load is on one side.
The neutral wire should, for this reason, be of sufficient cross-
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Fig. 233.
section to safely carry a current which will blow out the main fuses
in case of short circuit on one side of the system.
Fig. 233 shows the three-wire distribution where a grounded
neutral wire is employed, this system also being widely used for
general distribution, lighting, small motors, etc.
The four terminals of the low-voltage coils are,as a rule, brought
outside the case in such proximity that they can readily be con-
nected in any desired manner by joining adjacent terminals.
Connection blocks are seldom used for the low-voltage winding of
distributing transformers, because of the large current-carrying
capacity required.
The voltage stress on the windings naturally depends on the
voltage of the mains to which they are connected, and also on
abnormal operating conditions such as accidental grounds, light-
ning surges, etc. For the arrangement shown in Fig. 231 it is
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TRANSFORMERS 393
obvious that under normal conditions the maximum voltage stress
between the high-voltage leads is 1000 volts, and to ground 500
volts. If a ground should occur at one of the high-voltage con-
nections to the mains, the stress will be 1000 volts.
In the case of the low-voltage winding, if the two coils are con-
nected in series and non-grounded, the stress to ground imder
normal conditions is 100 volts, which is also the maximum stress if
the junction point or neutral is grounded. If not, and with one
lead grounded, the stress becomes 200 volts. The stress between
the two windings is equal to the high-voltage plus or minus the
low-voltage, depending on the arrangement and connections of the
coils.
In order to avoid the danger of excessive voltages being im-
pressed on the low-voltage circuits, caused by crosses between
the high-voltage and low-voltage lines or windings, grounding of
the low-voltage circuit is now generally advocated for all voltages
up to 250 volts. No point of the circuit can then, except under
unusual conditions, rise above its normal potential, and such
grounding, therefore, prevents accidents to persons and damage
by fire to property. If the low-voltage side, on the other hand,
is not groimded, and the transformer breaks down, the high-
voltage may be impressed on the low-voltage circuit, and a per-
son touching any bare part of the low-voltage circuit is Uable
to receive the full shock of the high voltage, if he were grounded
by contact with, for example, a gas fixture, etc. Furthermore,
if the low-voltage side is not grounded and there is a ground on
the high-voltage circuit, the high-voltage impressed on the fittings
of the low-voltage circuit might cause a fire.
For a two-wire 110-volt circuit it is common practice to con-
nect the ground to one side, while with a three-wire Edison cir-
cuit the neutral wire is grounded, limiting the potential from either
outside wire to groimd to 110 volts. On a 220-volt single-phase
power circuit the middle or neutral point of the transformer wind-
ing should be groimded.
To prevent any increase of the potential stress between ground
and either low-voltage wire, the ground should be well made so
that it cannot readily be broken. It should not be fused and
should consist of a conductor which, without overheating, can
carry a current sufiicient to blow the main fuses.
Two-phase. This system practically consists of two separate
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394
ELECTRICAL EQUIPMENT
single-phase circuits, the two e.m.f/s and currents being 90 elec-
trical degrees or one-fourth of a cycle out of phase with each other
(Rg. 234).
Two single-phase transformers are mostly used for two-phase
systems, and the most common connection is that shown in
fig. 235. The high-voltage windings of the two transformers are
connected respectively to the two phases of the supply mains.
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It is sometimes also desirable to operate a three-wire two-phase
distribution, as shown in Fig. 236. In this case the voltage across
the outside wires is \/2 or 1.41 times the voltage of each individual
transformer. This is clearly xmderstood by a reference to the
FiQ. 236.
vector diagram in Fig. 237, and is due to the 90° phase difference
between the two e.m.f .'s, so that instead of adding them numer-
ically they must be added vectorially. The current in the neutral
wire is also 1.41 times the current in either of the outside wires,
provided the load is balanced.
Transformers in two-phase work are sometimes intercon-
nected, as shown in Fig. 238, where a common return is used od
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TRANSFORMERS
395
both high- and lo\^-voltage sides. Very few systems are, however,
operated on this plan.
By connecting together the middle points of the low-voltage
windings, as shown in Fig. 239, two 100-volt main circuits ac
and be are obtained. Also four 70-volt (50X V2) side circuits ab,
bcy cd, and da.
This method of connection is used when the neutral is to be
brought out in connection with Edison three-wire service of rotary
converters. If the converter is started from transformer with
Fig. 238.
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one-third and two-third voltage taps, provision must be made for
opening the neutral connection when starting, so as to avoid short-
circuit.
Another two-phase arrangement is shown in Fig. 240, and is
commonly called the five-wire system. It is accomplished simply
by connecting the low-voltage windings at the middle and bring-
ing out an extra wire from these points.
With the connections shown in Fig. 235 the maximum insula-
tion stress in case of a permanent groimd is 1000 volts on either
phase of the high-voltage side, but a simultaneous grounding of
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396
ELECTRICAL EQUIPMENT
lines 1 and 4, 1 and 3, 2 and 3, or 2 and 4 or their connection,
causes insulation stresses y/2 times this value or 1414 volts. On
the low-voltage winding the corresponding stress would be 141
volts.
With the two low-voltage windings connected for a three-wire
distribution, as in Fig. 236, the maximum stress when one of the
outside wires becomes grounded is 141 volts, while, if the junc-
tion or neutral point is grounded it is limited to 100 volts.
Some systems are supplied with two-phase generators in which
the neutral points of each winding are connected together. In
this case simultaneous grounding or connection of any two lines
Fig. 240.
from the generator cause a short-circuit on one-half the generator
winding.
For grounding two-phase systems several methods are em-
ployed. With a four-wire distribution the mid-point of each
transformer winding should be independently grounded unless
the motor windings served are interconnected so as to prevent it.
In that event the neutral of one transformer only should be
grounded. With the three-wire system the neutral point should
be grounded and the same appUes to the systems shown in Figs.
239 and 240.
Three-^hdse. The following are the most common methods
in which transformers may be connected for a three-phase system:
Delta-Delta.
Delta- Y, or vice versa.
Y-Y.
Open-delta.
T-connection.
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TRANSFORMERS
397
DeltordeUa. With the delta-delta system the leads of three
single-phase transformers are connected to the mains as shown
in Fig. 241. The e.m.f.'s and currents differ in phase 120
electrical degrees, and the line voltage is equal to the individual
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transformer voltages. This voltage is commonly denoted the
" delta-voltage " to distinguish it from the " star or Y-voltage ^
in the star-connected combination. Similarly the line current
must be distinguished from the cinrent flowing in the closed delta
winding.
The voltage and current relations are easily explained by
referring to the vector diagram in Fig.
242.
If we denote: S= delta-voltage, or volt-
age between phases;
€= Y-voltage, or voltage
between phases and
neutral;
/=Y-ciUTent or line cur-
rent;
then:
and
Fig. 242.
i=delta-ciuTent or current in delta winding;
E
E=eV3ore^—=y
V3
J=2V3ort=— =.
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398 ELECTRICAL EQUIPMENT
When speaking of the voltage and current or line voltage and
line current of a three-phase S3rstem, without further qualifica-
tions, the delta-voltage and the Y-current are understood.
Delta-connected transformers must be wound for the full-line
voltage but for only 58 per cent line current. The windings must,
therefore, have a greater number of turns than for star connec-
tion, while they can be of a smaller size.
The maximum insulation stress in case a permanent ground
occurs does not exceed the normal voltage stress, pro\dded the
ground is at the transformer terminals. When, however, the
ground occurs on the transmission line at some distance from the
transformer terminal the reactance drop due to the charging current
adds to this stress. On this account with long distance high-volt^
age transmission lines operating on the deltardelta system, a dead
ground of one wire may cause the potential of the other two wires
to rise above ground considerably above normal potential, thereby
increasing the insulation stress. This increased stress may exist
both at the generating and receiving ends of the transmission line.
With a delta-connected 220-volt distributing system the ground
connection should be made to the mid-point of the winding of one
transformer. This gives 110 volts to ground from the phase wires
next to the groimd connection and about 200 volts from the other
phase to ground.
Where 2200-220 volt transformers are connected delta-delta
for three-phase power service, one of the imits is occasionally made
larger than the other two, and a tap from the middle point of the
low-voltage winding brought out so that a o^Tpvolt single-phase
three-wire service may be obtained for lighting purposes.
If one transformer or one phase of the three-phase transformers
is disabled, the other two may then be used in open-delta.
The capacity of a group of delta-connected transformers is
equal to VsxEXl Kv.A., where E represents the transformer or
line voltage and / the line current. The current in the trans-
former windings is equal to — =.
V3
DeUorY, Delta-Y connection or vice versa, as shown in Fig-
243, is used to a great extent, and it is especially convenient and
economical in distributing systems, in that a fourth wire may be
led from the neutral point of the low-voltage windings.
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TRANSFORMERS
399
The current and voltage relations in the delta side are the same
as in the deltar-delta connection. On the Y-connected side, how-
ever, one end of each winding is connected to a common neutral
point and the other three ends to the lines. With this connection
the number of turns in a transformer winding is 58 per cent of
that required for delta-connected transformers, but the cross-
section of the conductors must be correspondingly greater for the
same output. For high voltages the currents are, however, gen-
erally so small that, in may cases, the size of wire in the high-
voltage winding must be governed by mechanical considerations,
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Fig. 243.
and the size of wire may have to be the same for either system.
The delta connection is, therefore, sometimes somewhat more
expensive.
If the neutral point of the Y-connected system is ungrounded,
the transformer insulation must be capable of standing the stress
of the full line voltage, since a ground on any line will throw full
voltage on parts of the transformers. With grounded Y the
stress is, of course, limited to the Y-voltage. This is, however,
only true for step-up transformers at the generating end of trans-
mission line, and also only when the neutral is sohdly grounded.
When the neutral is grounded through a resistance the insulation
in transformer may be subjected to full voltage stress, and under
any conditions the step-down transformers may be subjected
to full voltage stress.
For distributing service the transformers have, as previously
stated, often their low-voltage windings Y-connected and the
neutral brought out, forming a four-wire system, as shown in Fig.
244. The single-phase service is then obtained by tapping between
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400
ELECTRICAL EQUIPMENT
any line and the neutral, while for three-phase work the line wires
are tapped directly, the voltage between these beingVs times the
single-phase. This system results in a copper saving of 56 per
cent, assuming that the four wires are of the same cross-section.
If the main three-phase hne potential is fixed, this method
offers no saving; on the contrary, it requires 33 per cent more
copper. In any case, however, the use of the four-wire system
gives increased flexibility, and the neutral wire carries all un-
balanced currents.
This system is mostly used for a combination of motor and
a b
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Fig. 244.
lighting loads. The lighting service is operated from a 2300-volt
phase voltage and the power service from the 4000-volt line voltage.
Transformers are sometimes designed so as to be suitable
for either delta-delta or delta-Y connection, in order to permit the
user to increase the capacity of a transmission line by raising
the line voltage, which can be accomplished by changing the con-
nection from delta to Y on the high voltage side. Such trans-
formers are necessarily more expensive than they would be if
designed for straight delta-delta, and used at the lower voltage
only, because they must be insulated to withstand the higher line
voltage.
The rating of a group of delta- Y-connected transformers is
the same as for the straight delta-delta connection.
Where power is transmitted with delta-Y step-up and Y-delta
step-down transformers, service may be maintained with one
step-down transformer cut-out, the connections being made as
shown in Fig. 245.
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TRANSFORMERS
401
A' B' C represents the Y-connected high-voltage winding of
the step-up transformers and a b c the high-voltage winding of
the step-down transformers, of which the phase od is out of ser-
vice. A three-phase open-delta connection a' 6' c' is thus obtained
on the low-voltage side.
The capacity is reduced to 57 per cent of the original value, and
Fig. 245.
care must be taken not to connect a' c' in the position a' c", since
this will not give a three-phase relation. The neutral connection
on the high-voltage side should preferably be made through a
wire, but can be made by solidly grounding the neutral of both
transformers. The system will, however, be electrostatically
and electro-magnetically unbalanced, and the usual disturbances
characteristic of such a condition will be observed, the severity
depending oh the circuit characteristics.
S3mchronous converters are frequently installed in connection
with Edison systems, where three-wire direct-current is required.
Fia.246.
The three-wire feature is readily obtained by connecting the neu-
tral wire directly to the neutral point of the low-voltage winding
of the step-down transformers. Care should, in such a case, be
taken in using only such connections, that the transformer will
act as an auto-transformer, that is, that the direct current in
each transformer divides into two branches of equal m.m.f.
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402 ELECTRICAL EQUIPMENT
If this is not done, the direct current will produce a uniKiirectional
magnetism in the transformer, which, superimposed on the mag-
netic cycle, would tend to raise the magnetic induction beyond
satiu^ation, and thus cause excessive exciting current and heating
except where the unbalanced ciurent is comparatively small.
Such a connection is shown in Fig. 246 which represents a delta-Y-
connected step-down transformer with the neutral brought out.
It is evident that in this case each transformer low-voltage winding
receives one-third of the neutral current, and if this current is not
small, as compared with the exciting current of the transformer,
it will cause an increase in the magnetic density.
A sjnstem with a distributed Y or " zig-zag " connected low-
voltage winding, as shown in Fig. 247, has, however, been devised,
and will eliminate the flux distortion due to the imbalanced
direct current in the neutral. Two separate interconnected wind-
ings are used for each leg of the Y. The unbalanced neutral cur-
rent flowing in this system may be compared in action to the
effect of a magnetizing current in a transformer. The effect of
the main transformer currents in the high- and low-voltage wind-
ings is balanced with regard to the flux in the transformer core,
which depends upon the magnetizing current. When a direct-
current is passed through the transformer, unless the fluxes
produced by the same neutralize one another, its effect on the
transformer iron varies as the magnetizing current. For example,
assume a transformer having a normal ^mpere capacity of 100 and,
approximately, six amperes magnetizing current, and assume
that three such transformers are used with Y-connected low-
voltage windings for operating a synchronous converter connected
to a^three-wire Edison system. Allowing 25 per cent unbalancing,
the current will divide equally among the three legs giving 8.33
amperes per leg, which is more than the normal magnetizing cur-
rent. The loss due to this current is, however, inappreciable,
but the increased core losses may be considerable. If a dis-
tributed winding is used the direct current flows in the opposite
direction around the two halves of each core, thus entirely neu-
traUzing the flux distortion.
Whether the straight Y or the interconnected Y connection is
to be used is merely a question of balancing the increased core loss
of the straight Y connection against the increased copper loss and
the greater cost of the interconnected Y system. The straight Y
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TRANSFORMERS
403
connection is much simpler, and it would be quite permissible to
use it for transformers of small capacities where the direct current
circulating in the neutral is less than 30 per cent (10 per cent per
transformer) of the rated transformer ciurent.
When three-phase core-type transformers are used, it is not
necessary to resort to the zig-zag connection, as in such trans-
formers the direct current flows along the core from end to end in
the same direction on all three legs, and since the direct mag-
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FiQ. 247.
netism must find its return path through the air and the case
outside of the core, its effects are practically negligible.
On account of the 30° displacement between the voltage from
line to neutral and that across each half of the transformer legs
of the zig-zag connected windings, the low-voltage side operates
only at 86.6 per cent of the normal capacity, which it would have
if operated straight Y.
Y-Y. This connection is not ordinarily to be recommended
for a bank of three single-phase transformers or a three-phase
Bhell-t3rpe unit. This is due to the fact that the triple frequency
component of the exciting current necessary for normal magnet-
ization cannot flow, which results in a third harmonic and its
odd multiples appearing in the e.m.f. from line to neutral, and
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404 ELECTRICAL EQUIPMENT
thus causes an excessive stress on the windings. No triple fre-
quency * harmonic appears, however, in the line voltage, which
remains normal, because the third harmonics across the three
transformers are in phase with each other.
The triple frequency component does not exceed 75 per cent
of the fundamental and with densities commonly used has an
average value of 50 per cent of the fundamental. An exception
to this, however, is the case when the transformers are operated
with grounded neutral and connected to a transmission line pos-
sessing electrostatic capacity. In such a case the induced triple
harmonics may be intensified to values as high as two or three
times normal.
To obviate the above increase in voltage, it is necessary to
make neutral connections in such a maimer that the triple har-
monic exciting currents necessary for sine wave excitation can
flow, thereby eliminating the triple harmonic voltage. This is
accompUshed first, when the transformer neutral is grounded,
and a Y-delta bank of transformers with grounded neutral of
sufficient Kv.A. capacity is coimected to the line, second, when
the primary neutral is connected to the neutral of the generator,
this case only being possible for step-up transformers. It should
be noted that by grounding the high voltage neutrals of both step-
up and step-down transformers the danger from triple voltage
intensification is not eliminated.
It should be kept in mind, however, that when such ground
connections are relied upon for eliminating triple third harmonic
voltages, such voltages are restored by disconnecting any ground
connection, and also that the third harmonic groimd currents are
Uable to subject parallel telephone or telegraph systems to serious
interference.
The above does not refer to three-phase core-type transformers,
which, owing to their construction, are not subject to these addi-
tional strains.
No stable neutral can be maintained on a bank of transformers
with both high- and low-voltage windings Y-coimected when un-
grounded, since it may shift to any position.
Open-delta. When single-phase or three-phase shell-type trans-
formers are used, it is possible to maintain operation if one phase
is damaged. Such a combination is shown in Fig. 248, and is
termed the open-delta or V connection. In three-phase core type
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TRANSFORMERS
405
designs it is possible to operate open-delta when the damaged
winding is open-circuited. With V-connected three-phase shell-
type transformers the damaged phase should be short-circuited
to prevent stray fluxes from the other phase from inducing volt-
ages in the damaged windings.
With the V connection the current in each transformer is 30®
out of phase with the transformer voltage, so that each trans-
former under non-inductive load operates at only 86.6 per cent
power-factor. Based on a three-phase load, the cutting out of
one transformer would therefore reduce the current-carrying
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capacity not to two-thirds of 100 per cent, which equals 66.6 per
cent, but to two-thirds of 86.6 per cent which equals 58 per cent.
Assiuning that each transformer shall have a capacity of
OPT
-^=1.5^7, it must be capable of carrying 1.73E/ kilovolt-
amperes, because the transformer voltage is equal to the line
voltage E, and the transformer cmrent equal to the line current
1.737. Therefore, the single-phase rating of each transformer
1 73
must be -:p=-= 1.155 or 15i per cent greater than one-half the
group rating.
Sometimes it is desired to parallel a number of transformers
in such a way that certain of the transformers will form a delta
group while the others may be connected in open-delta or V.
Such a combination may be caused by the desire to increase the
capacity by adding spare transformers of insuflScient number to
form a group of complete deltas or through the failure of one or
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406
ELEOTRICAIi EQUIPMENT
more units originally installed. It is not, however, generally
realized that such an arrangement will, in general, prove either
uneconomical as to capacity, if all the units are kept to rated
currents, or disastrous to the imits on the legs having the smaller
numbers, if it be attempted to work all units at overloads guar-
anteed for single-phase operation. Not only is this from the addi-
tional 16i per cent capacity required on imits for open-delta
service, but a fmlher increase in current takes place in the V-con-
nected transformers due to change in phase relation, and for this
reason when delta and V groups are operated in parallel the result-
ant capacity is not the sum of the individual delta and V ratings.
More than one V group cannot be used advantageously with a
TABLE
XLVI
Number of
TraDsformen
Connectioo
Three-phase CapacltF
of Oroap Id per cent
orSiDgle-phawRattng
A
100
A
aej}
A^
A
88JB
100
A
A
80
A
A
aao
A
A
82
A
A
A
100
A
A
A
»1
A
A
A
T»
A
A
A
88
delta group of transformers nor with two or more paralleled delta
groups. Three delta-connected transformers when added to
another delta group will give more capacity than if four trans-
formers, connected in two V groups, were added to the same delta
group. This is because the four transformers, which would form
two V groups, can be rearranged to form a delta group (one trans-
former remaining idle), and the delta group will have the capacity
of three transformers while the two V groups will add the capacity
of only two transformers. The addition of two transformers,
connected in V, in parallel with a delta group adds the capacity
of only one transformer to the capacity of the total group.
Although two V-connected groups should never be used in parallel
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TRANSFORMERS
407
with a delta group, they may be paralleled with one another and
in this case will give a greater capacity than three units con-
nected in delta. The capacity of the two V groups would be
0.866 times four or 3.46 as against three, the corresponding
rating of three transformers connected in delta.
Table XL VI gives the transformer capacities available with
various combinations of open and closed delta groups.
T-T, lAs with the open-delta arrangement, the T-T con-
nection requires only two single-phase transformers,. Ptgr'249,
representing the diagram of conneetionr. , A is called the main
transformer and is provided with a 50 per cent voltage tap to
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which the teaser transformer jfi^ is connected. This transformer
may be designed for only 86.6 per cent of the line or main trans-
former voltage, but generally it is made identical with the main
transformer and operated at reduced flux density. It should be
noted that although the teaser operates at 86.6 per cent of line
voltage it is unnecessary to provide an 86.6 per cent tap as is
often supposed. On this account it is possible to operate two
identical transformers connected T-T as well as open delta, when
one transformer of a delta-delta bank bums out, the only require-
ment for the T-T connection being a 50 per cent tap. Although
interlacing is not required between halves of the main winding
nevertheless each half of the primary winding must be properly
wound with respect to the corresponding half of the secondary
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408 ELECTRICAL EQUIPMENT
winding. The three-phase capacity of the T connection as is
shown ixi the table is the same as for the open-delta connection,
that is, 86.6 per cent of single-phase capacity, but on account of
the fact that the teaser operates at a lower flux density, the ef-
ficiency of the T connection is somewhat greater than In the open-
delta or V connection.
Two ordinary transformers may also be used with T connect
tion provided a 50 per cent tap is available. It is also more
economical, to operate with T connection than with V connection,
when one transformer has burned out.
The T connection, as shown in ^ig. 250, ciui also be used for
three-phase synchronous converters, and the neutral point can
readily be brought out for Edison three-wire service. The neutral
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is then brought out from a point at one-third the height of the
teaser winding and the m.m.f. of the direct current i will balance,
as shown in the diagram.
For T connection with ungrounded neutral the voltage stress
is the same as for the delta system, and with grounded neutral
the voltage stress between line and ground is limited to 58 per
cent of normal.' *
Assuming again that as with the open-delta connection the
two transformers shall be capable of supplying a load equal to
-— = 1.5EJ, the Kv.A. rating of the main transformer must,
therefore, be equal to 1.73EI, while the Kv.A. of the teaser trans-
former only is equal to 1.73/X0.866£=1.5B/. The two trans-
formers are, however, designed to carry the same currents and are
generally made identical, so that the single-phase ratings of either
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TRANSFORMERS 409
1 73
transformer must also here be -f^ = 1.155 or 15.5 per cent greater
1.0
than one-half the group rating.
Phase Transformation. Of the connections for transforming
one pol3rphase system into another with a different number of
phases, the following are the most commonly used:
Two- or three-phase to single-phase.
Two-phase to six-phase. -
Three-phase to two-phase.
Three-phase to six-phase.
Two- or Threerphase to Single-phase.^ It is practicaUy impos-
sible to transform from polyphase to single-phase by means of
static transformation with balanced conditions. Various schemes
have been proposed and investigated, but none of the combina-
tions give better results than can be obtained by simply using a
transformer across on phase.
The reason for this is explained by Dr. Steinmetz (A.I.E.E.
1892) to be as follows:
'^Single-phase power changes from a maximum to zero and back
to maximum every half cycle, while polyphase power is delivered
at a constant rate. Therefore, any system capable of transform-
ing from balanced polyphase current to single-phase current must
be capable of storing energy during the interval of time when the
power delivered to the single-phase side is less than the power
received from the three-phase side. The transformer is incapable
of fulfilling this requirement."
Nevertheless, it is desirable to know the best method of
taking single-phase power frpm a three-phase system and often
ingenious although compUcated connections are proposed with the
idea of more uniformly distributing a single-phase load. Most
of these schemes do not present a single feature that is superior
to the placing of the single-phase load directly across two wires.
When there is one feature which is apparently superior, there are
generally imdesirable features which more than offset it. The
four schemes shown in Figs. 251 to 254 are ones conmionly sug-
gested and Table XL VII gives the characteristics of these con-
nections and shows that they are inferior to straight single-phase
* Three papers on Single-phase Power Service from Polyphase Sjrstems
appeared in A.I.E.E. Proceedings for October, 1916.
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410
ELECTRICAL EQUIPMENT
transformation. All values except for power are given with
reference to straight single-phase as unity. The total value of
power delivered is the same in all cases. By straight single-phase
is meant connecting one transformer between two wires of a three-
phase system. The only condition under which there seems to
be an advantage is in schemes 1 and 3 where it will be noticed
A. 1.155 1
B. 2.31 I
C. 1.155 1
Power Factor ». 806.
Fig. 251.
A, 2 I
B, 0
C, 21
Power Factor « . 666
Fig. 252.
Br
WE-
5 -N^
A, 1.155 1
B, 2.31 I
C, 1.155 1
3^, .635
Power Factor "1^, 1.
Av. .778.
Fig. 253.
■^ A
.707E-H I
-,7OTE ^ I
-^
A, 2.23 I 3^. .707.
B, .1631 Power factor = 1^. .707.
C, .599 I Av. .707.
Fig. 254.
that a delta-connected generator has a maximum current of 0.577
as against 0.667 for the straight single-phase. To offset this, both
schemes 1 and 3 require two transformers possessing greater total
capacity and also imposed upon the line a greater maximum
current.
Two-phase to Six-phase. The double-T connection, as shown
in Fig. 255, is generally used in cases where a six-phase synchronous
converter is to be operated from a two-phase supply system, and
where the two-phase voltage requires some transformation in
order to obtain the correct alternating-current voltage for the
converter. The cost of double-T-connect«d transformers and a
, standard six-phase rotary converter will occasionally be less than
that of two-phase transformers and a special two-phase converter.
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TRANSFORMERS
TABLE XLVII
411
Capacity.
Power-
QBNERATORfl.
Scheme No.
No.
Trans.
Trans.
Each.
Cap.
Total.
factor for
Non-induc-
ttve Load.
Y- con-
nected.
Delta con-
nected.
Cur-
rent.
Watu
Cur-
rent.
Watts
1
2
0.577
1.55
0.866
0.577
1.155
0.577
i
i
i
0.570
0
0.577
i
0
i
2
3
0.500
1.500
0.666
1.0
0
1.0
i
0
i
1
}
i
i
i
i
3
2P
/ 1.000
I 0.577
P 0.635
0.577
i
0.577
i
1.577t
S 1.000
1.155
i
0
0
/ SI. 000
I 0
Av. 0.810
0.577
i
0.577
i
( 0.707
4
2P
0.557*
I 0.150*
1.821*t
P 0.707
1.115
0.622
rO.644
0.622
S 0.707
0.815
0.333
0.172
10.471
0.045
0.333
S
/ 0.707
I 0.707
Av. 0.707
0.300
0.045
Straight
Single-phase
1
1.00
1.00
1.00
1.0
0
1.0
i
0
J
1
i
i
i
i
* Onebalf of main has capacity of 0.557; other half 0.150; total capacity computed
on basis that both halves are alike and of lanr® capacity.
t On basis of primary capacities when there is a difference between primary and
secondary.
T connection, however, requires specially designed transformers,
and the complication of starting taps and switches is a disad-
vantage.
The syBtem requires two transformers of the same impedance,
each equipped with two low-voltage windings, connected in such
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412
ELECTRICAL EQUIPMENT
a way that they are displaced 180"* from each other, thus producing
the six-phase relation.
The voltages are the same as for the T-connected three-phase
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Fig. 255.
system, and each transformer must be 15 per cent greater than
half of the power required for the rotary.
The neutral can also be brought out on the six-phase side,
although this furthermore increases the complication of the con-
nection.
Three^hcLse to Two-phase. A number of schemes for three-
phase to two-phase transformation, and vice versa, have been
devised, but the most commonly used method is the T con-
nection for either balanced or unbalanced service.
'Balanced T or Scott Connection. This connection is-Aown in
Kg. 25ft and requires two transformers which on the three-phase
side are connected in T, the number of effective turns in the teaser
winding being 86.6 per cent of the number of turns in the main
winding. On the two-phase side both mains and teaser windings
are identical and, as shown in the figure, are electrically inde-
pendent, when supplying a two-phase, four-wire system. Gen-
erally, the main and teaser transformers are made identical for
the sake of interchangeability, in which case the three-phase
winding is provided with both a 50 per cent and an 86.6 per cent
tap, as shown by the dotted lines in Fig. 256, so that when used as a
main the 50 per cent tap is used and when used as a teaser the
86.6 per cent tap is used, the 13.4 per cent winding bemg left idle
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TRANSFORMERS
413
Each of the two halves of the three-phase winding should further-
more be distributed over the entire winding length of the core in
order to prevent flux distortion and poor regulation. The T
connection requires 6.7 per cent more copper than single-phase
transformers delivering the same power on account of the idle
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Fig. 256.
copper in the teaser and also on account of the fact that wattless
currents flow in the three-phase side of the main winding.
The neutral of the three-phase side, which is one-third the
height of the teaser winding, can be brought out for four-wire
operation although the transformer construction is somewhat
complicated thereby. When operating without the neutral point
grounded on the three-phase side, the maximum insulation
strain, if a permanent ground occurs, is equal to the line volt-
age vi?
Unbalanced T. This connection may sometimes be of use in
emergency conditions where a transformer with an 86.6 per cent
tap is not available and a teaser transformer of the same voltage
as the main transformer must be used.
In this connection two transformers of exactly the same
capacity and voltage are used. The phases, however, are no
longer strictly 120° apart, and it is assumed that the same con-
nection is used at each end of the line. As it is not a true three-
phase system, any attempt to operate in multiple with a three-
phase S3rstem or three-phase apparatus will cause serious unbal-
anced currents.
The unbalanced T connection occurs when voltage is applied
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414
ELECTRICAL EQUIPMENT
from the two-phase side. When balanced three-phase voltages
are applied the voltages on the two-phase side will be unequal.
The connections and voltage relation of this system are shown
in Fig. 257. With equal currents in the two-phase system, the
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Fig. 257.
currents in the three transmission wires will be the same as in the
coils, namely: a =112 amperes, 6 = 112 and d=100, with the
voltages as indicated in the diagram.
An unbalancing of the two-phase distributing network afifects
the currents in the three transmission wires, in that an increase of
the load on phase D further increases the unbalancing, while, if
phase E be loaded in the neighborhood of 15 per cent in excess of
phase £>, the transmission line currents become practically bal-
anced.
With no neutral the maximum insulation stress under all con-
ditions arising from a permanent ground would be 1.12 times F.
Symmetrical or Woodbridge Connection, In the previous two
T-connected methods, the two-phase windings are electrically
distinct. There are, however, a number of schemes in which the
windings on the two-phase side are electrically interconnected
in one way or another.
Such a system of connections is shown in Fig. 258. It con-
sists of three windings, one for each phase. Two of the phases
are identical, each consisting of two coils, wound for 0.577 times
the two-phase line voltage and ha\dng a current capacity of 0.577
times the two-phase line current. The third phase consists of
three coils, one being wound for 0.577 times the line voltage and
the other two being identical and wound for 0.212 times the line
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TRANSFORMERS
415
voltage. The respective current capacities are 0.421, 1, and 1
times the line current.
One advantage of this system is the fact that voltages and
currents do not exceed those which would occur in single-phase
operation, giving an internal power-factor of the system of 100
per cent, whereas in the T connections the average power-factor
is only 96.4 per cent. The three-phase side may be connected
either delta or Y. This connection, requiring less copper and
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Fig. 258.
being sUghtly more efScient than the T connection, is recom-
mended in place of the T connection for three-phase units, pro-
vided no taps are required on the two-phase side. If single-phase
imits are desired, the use of this connection becomes doubtful
owing to the multiplicity of leads and coils on the two-phase side.
The connection is very seldom used, principally on account of
the electrical interconnections of the phases on the two-phase
side. This prevents it from being used on a three-wire system,
while, on the other hand, a cross between the two phases results in
a short-circuit.
Three-phase to Three-phase — Two-phase. It is possible by means
of transformer connection to derive from a three-phase primary
circuit a four-wire secondary circuit, three wires of which rep-
resent a three-phase system and the four wires making a two-phase
system. Prom such a system independent three-phase or two-
phase loads may be taken simultaneously. This may be accom-
plished by three single-phase transformers provided with special
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416
ELECTRICAL EQUIPMENT
windings or by one three-phase transformer, as shown in Fig. 259.
Primary winding may be connected either Y or delta and is in
no wise different from an ordinary three-phase winding. The
secondary, however, is provided with 15^ per cent coils in two of
the phases and 15^ per cent taps in the other phase in such a
manner which are interconnected, as shown in Fig. 259.
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Fig. 259.
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Fig. 260.
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This may also be accomplished by means of two transformers
T connected as shown in Fig. 260.
The choice between the two methods given above of obtain-
ing three-phase and two-phase on four wires depends for the most
part upon whether the three-phase or the two-phase load predom-
inates. Where the three-phase load is predominant, it is evident
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TRANSFORMERS
417
that a connection given in Fig. 260 is superior, but where the
two-phase load predominates, the T connection is preferable.
Three-phase to Six-phase. In transforming from three- to six-
phase, there are four different connectionSi which may be used,
namely:
Diametrical.
Double-delta.
Double-Y.
Double-T.
Diametrical. The diametrical connection, as represented in
Fig. 261, is the most commonly used of any three-phase to six-
phase transformations, and there is very little reason for using
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Fig. 261.
any other connection for the operation of six-phase converters.
It requires only one low-voltage coil on each transformer which
are connected to diametrically opposite points on the armature
windings. It furthermore gives the simplest arrangement of
switches, transformer taps and connections for starting six-phase
converters from the alternating current side, while on the other
hand it is possible to operate a six-phase converter at reduced
capacity with one transformer out of service, leaving. the other
two connected across their respective diameters.
With diametrically connected low-voltage windings, the high-
voltage windings should preferably be connected in delta so as
to avoid the triple frequency harmonics of the e.m.f., as described
under Y-Y connection on page 403. With regulating pole con-
verters, however, the high-voltage windings must be connected Y
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418
ELECTRICAL EQUIPMENT
on account of the fact that the third harmonic voltage is made
use of to obtain the direct-current voltage regulation and in such
a case the windings must be insulated for double line voltage to
groimd and 3.46 times normal Y-voltage across windings, due to
the presence of the third harmonic e.m.f 's. The middle points of
the diametrical windings can readily be connected together and
brought out for three-wire Edison service, the unbalanced three-
wire direct current having no distorting effect. Arrangements
should then be made for opening the neutral connections during
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Fig. 262.
starting to avoid short circuit. When used with regulating pole
converters the neutral must be isolated.
The current in each coil on the low-voltage side is equal to
y output of transformer in watts . .i_ i j - i i j
/= — V, , ,. 7-^ — i — r- assmnmg the load is balanced
3 X diametrical voltage
and that the power-factor is unity.
With six-phase diametrical connection with common neutral,
one-half the output can be taken from the low-voltage side for
operating three-phase without change of diametrical voltage.
If full three-phase output should be desired, the coils can be con-
nected in delta in which case the diametrical voltage is increased
14 per cent. Hie full three-phase output at 1.73 times the dia-
metrical voltage may be obtained by connecting the coils in Y,
in which case the neutral should be grounded and if the high
windings are Y-connected the system is subject to the dangers
of the third harmonic e.m.f's. as previously explained. It must
also be ascertained if the insulation of the windings can withstand
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TRANSFORMERS
419
the increased voltage safely. If the secondary windings are made
up of two distinct sections, which is not, however, standard prac-
tice, the connections may be made as in Fig. 262. The latter
connection is, however, somewhat compUcated and when three-
phase operation with full output is desired and without change of
voltage, the double-delta connection is generally preferable.
Dovble-deUa. For the double-delta connection two inde-
pendent low-voltage coils are required for each transformer, as
shown in Fig. 263. The second set are all reversed, and then con-
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Fig. 263.
nected in a similar manner to the first set, so that the two deltas
are displaced 180°.
The high-voltage windings should preferably be connected
delta, as it permits the system to be ox)erated with only two
transformers, in case one should be damaged.
The current in each coil for double-delta is equal to J=
output in watts , . ^ . , „ , r . p,«
-T-r r. ;; — :; and the ciurent m each line equals 7X1.73.
delta voltage X 2 X 3
Full output, three-phase may also be obtained by connecting
as shown in Fig. 262.
Double-delta connection cannot be used with Edison three-
wire service, as it has no neutral, and in such cases separate auto
transformers would be required.
Dovble-Y. Like the double-delta, this system requires two
sets of low-voltage coils, displaced 180®, as shown in Fig. 264.
The high-voltage windings may be either delta- or Y-connected
even with regulating pole converters, but in this case the two low-
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420
ELECTRICAL EQUIPMENT
voltage neutrals must not be connected together. Where the
high-voltage windings are Y-connected the danger of Y-Y oper-
ation should be considered, and the neutral should be grounded.
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Fig. 264.
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Fig. 265.
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The current in each leg is equal to 7= and
YvoltageX 1.73X2
the line current has the same value.
Double-T, Fig. 265 represents the double-T connection for
transforming from three-phase to six-phase. The low-voltage
connections are similar to the two-phase — six-phase system shown
in Fig. 255, and the high-voltage windings are connected in T.
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TRANSFORMERS
421
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Pigs. 262 to 265 are the connections of single-phase trans-
formers used for six-phase operation, and they do not apply to
three-phase units.
Parallel Operation. In order that two or more transformers
or groups of transformers shall operate successfully in parallel it
is necessary that they are connected so that their polarity is the
same, that their voltages and voltage ratios are identical, and that
their impedances in ohms are inversely proportional to the ratings.
The polarity expresses the phase relation between the high and
low voltages as measured at the terminals. When the trans-
formers are of the same manufacture, they usually have the same
polarity, while if of different makes some may have the high- and
low-voltage windings in phase and others 180° apart.
Effect of Polarity on Parallel Operation It i^ easy to deter-
mine the right polarity of two single-phase transformers which are
to operate in parallel. Kg. 266 represents such a case in which
all connections are made except fci.
If now the voltage between fci and di
is zero it indicates that the two trans-
formers have the same polarity, while
if the polarities were opposite the
voltage from fci to di would be the
sum of the two transformers, and the
joining of the two leads would cause
a short-circuit. When testing for
polarity the two terminals should,
therefore, be joined through a fuse or automatic switch. If the
fuse does not blow, the connection may be made permanent,
while, if the fuse blows the two leads of one transformer must be
reversed.
With three-phase transformer banks operating in parallel it is
also necessary that the phase relation of the voltages in the two
banks is the same, both as to direction and position. It is, there-
fore, not possible to parallel a group of transformers which is
connected in delta on both high- and low-voltage sides with a
group connected in delta on the high-voltage side and Y on the
low-voltage side or vice versa. On the other hand, it is possible
to parallel a delta-delta connection with a Y-Y connection, and
also a delta-Y connection with a Y-delta connection.
Three-phase transformer banks divide themselves into three
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Fig. 266.
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422
ELECTRICAL EQUIPMENT
groups, depending upon the angular displacement between high-
voltage and low-voltage windings. These groups are given in
Fig. 267, which shows that the delta-delta connection and the Y-Y
connection are similar, both capable of being connected so as to
Groap
Angular
Dtoidaceinent
OroupU
Angular
Displacement
180"
A BX Y A BX Y
C Y X C Y X
AV XY
A B Z A B Z
C Z 0 Z
A^^ X>
A B X A B X
Fig. 267.
Group HI
Angular
give an angular displacement of zero degrees between high voltage
and low voltage, or an angular displacement of 180 d^rees between
high and low voltages. Group 3 consists of the delta-Y or Y-delta
bank, in which the angular displacement is 30^.
Three-phase transformer banks will not operate in parallel
unless the angular displacements between high and low voltages
are equal. The operative parallel connections are as follows:
TABLE XLVIII
Operative Parallel Connections
LOW-VOLTAQK SIDE
HIQH-VOLTAGB BIDE
A
B
A
B
1
Delta
Delta
Delta
Delta
2
Y
Y
Y
Y
3
Delta
Y
Delta
Y
4
Y
Delta
Y
Delta
5
Delta
Delta
Y
Y
6
Delta
Y
Y
Delta
7
Y
Y
Delta
Delta
8
Y
Delta
Delta
Y
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TRANSFORMERS
423
There are four other combinations possible for these two
banks of transformers, but these combinations will not operate
in parallel. These are as follows:
TABLE XLIX
Inoperative Parallel Connbctionb
LOW-VOLTAOB BIDE
HXQH-yOLTAOB SIDB
A
B
A
B
1
Delta
Delta
Delta
Y
2
Delta
Delta
Y
Delta
3
Y
Y
Delta
Y
4
Y
Y
Y
Delta
For example, consider case No. 2 — ^low-voltage sides in delta
and high-voltage sides in Y and delta respectively. Then as-
suming the low-voltage sides already paralleled and high-voltage
sides open, the phase diagrams are as follows where 4, B, C, a,
6, c represent one bank
A
A
/r^
\
\Q
Fig. 267a.
Low-voltage Side.
Fig. 267b.
High-voltage Side.
and X, y, Z, x, y, z the
second bank. (See Fig.
267a).
Then if b t^nd y be
joined on the low-voltage
side, serious displacement
voltages occur between a
and X and c and z (see
Fig. 267b), and if these terminals are connected, these displace-
ment voltages will cause heavy short-circuit currents and destroy
the transformers.
The reversal of two leads of either the high-and-low voltage
windings will reverse the polarity, this being identical with re-
versing one winding. Reversing the Une leads of a delta- or T-
connected combination will, however, not reverse the polarity,
since the transformer leads themselves must be changed in order
to make the change in polarity.
With delta-delta connection, the reversal of one or two
high-voltage windings will immediately produce a short-circuit
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424 ELECTRICAL EQUIPMENT
when the low-voltage delta is closed and the maximum voltage
difference will be double line voltage.
For delta- Y connection, such a reversal w'll not produce a
short circuit when the Y is closed, but the voltages and phase
relations will be unequal. The maximum potential difference
will equal the line voltage.
A reversal of one or two high-voltage windings with a Y-
delta connection will immediately produce a short circuit when
the delta is closed, and the maximum potential difference will
be double line voltage.
With Y-Y connection the result of reversing a high-voltage
coil will be the same as for the delta-Y connection.
Effect of Ratio on Parallel Operation. For successful paraDel
operation, correct ratios between the high- and low-voltage wind-
ings of the different banks is, as previously mentioned, also essen-
tial, otherwise a cross-current will be established, even if the ratios
are only slightly different. This current is then due to the dif-
ference of the two voltages divided by the simi of the impedances
of the two transformers, and its effect is to balance the voltages of
the two transformers with a resultant equilibrium of the two
transformers.
To determine this current, assume that ei and zi are the volt-
age and impedance in low-voltage terms of one transformer and
€2 and Z2 are corresponding terms of the second transformer, con-
nected in parallel with the other. The circulating current would
then be
1 =
Zi + Z2
where 21 and Z2 are expressed in ohms. Or expressed in percentage
of normal current by the following formula:
^ , • Per cent voltage difference,, -^^
Per cent / = 5 ^^ ^. j X 100.
bum of per cent unpedance
For example, suppose that the voltage ratios of two trans-
formers are such as to cause a voltage difference of 2 per cent. If
each transformer furthermore has a 2 per cent impedance, the
circulating current is equal to
2
Per cent / = ^rro ^ ^^ ~ ^ ^^ ^^^*'
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TRANSFORMERS 425
which means that a current equal to 50 per cent of normal circulates
between the transformers in both high- and low-voltage windings.
It adds to the load current in the transformer having the higher
induced voltage and subtracts in the other, causing the former to
carry the greater load.
The imp)edance Zi can be found for the first transformer by
impressing a voltage on the low-voltage winding with the high-
voltage winding short-circuited. The current is then read, and if
E
I is the current and E the voltage, then zi =-y. In the same man-
ner Z2 is determined.
With three-phase delta-delta-connected transformers different
voltage ratios will cause unbalanced voltages and set up a circu-
lating current within the delta in both the high- and low-voltage
windings. Unbalanced voltages outside the delta can, however,
not produce any circulating currents within the delta, and un-
balanced voltages applied to a delta-connected transformer bank
cannot be equahzed on the low-voltage side by the introduction
of additional voltage in the delta.
As with single-phase transformers the value of the circulating
cmrent is obtained by dividing the voltage difference by the total
impedance of the transformer bank. For example, if three trans-
formers having impedances of 4 per cent are connected delta-
delta, and one has a ratio 1 per cent greater than the other two, the
resulting circulating ciurent will be
Per cent /=^—^x 100=8.33 per cent.
When the load is taken from such a bank, the load currents and
circulating currents are superimposed, and the transformer having
the highest secondary voltage will carry the greatest load, as
before.
With delta-Y-connected transformers a slight difference in the
ratios has a very small effect compared with a delta-delta-con-
nected bank. This is due to the shifting of the neutral point,
causing an equaUzation of the voltages.
Effect of Impedance on Parallel Operation. In addition to
identical polarities and voltage ratios a successful parallel opera-
tion of transformers requires that their impedances are in inverse
proportion to the load which they are to carry, so that the voltage
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426 ELECTRICAL EQUIPMENT
drop from no load to full load is the same in all the units, both id
magnitude and phase.
The impedance of a transformer is generally expressed as the
voltage drop at normal load in percentage of normal voltage. It is
the resultant of two components; the resistance drop, which
depends only on the ohmic resistance of the windings and is in
phase with the current, and the reactance drop, which depends
on the magnetic leakage between the high- and low-tension wind-
ings and is 90® out of phase with the current.
Thus per cent ZZ=V (per cent IR)^+ (per cent /X)^,
where ZZ= total impedance drop;
7/2= resistance drop of high- and low-voltage windings;
/Xss reactance drop of high- and low-voltage windings.
The value of per cent IZ is easily obtained by short-circuiting
one winding and measuring the e.m.f. which must be applied at
the terminals of the other winding to force full-load currents
through the winding at normal frequency. The impedance may,
therefore, be measured directly.
The resistance e.m.f. is equal to the high-voltage ciurent mul-
tiplied by the equivalent resistance of the transformer, which may
be obtained by measuring the resistance of both the high- and low-
voltage windings, and, adding to the resistance of the high-voltage
windings that of the low-voltage multipUed by the square of the
ratio of transformation.
The reactance e.m.f. may be calculated from the known values
for the impedance cm.f . and resistance e.m.f. Thus
IX=V(/Z)2-(/i2)2.
In the majority of power transformers, the total resistance
drop is small compared to the reactance drop, in which case the
p)er cent impedance drop (per cent IZ) can be taken as approx-
imately equal to the per cent reactance drop (per cent IX). In
many lighting transformers, however, where the reactance is
made as small as possible, this cannot be done without introducing
considerable error.
The following formulae may be used for finding the division of
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TRANSFORMERS 427
load between any number of transformer banks operating in par-
allel on single-phase circuits.
/ Kv.A. \
J Vper cent ZZ/i ,
^^""Z Kv.A. \ / Kv.A. \ ^^^
\p)er cent IZ) \ \per cent IZ/2+] ...
/ Kv.A. \
J \per cent/Z/2 j
^^•"/ Kv.A \ / Kv.A. \ ^^"^
\percent/Z/i \per cent /Z/2+; . . .
where /i = load current in transformer bank No. 1;
72= load current in transformer bank No. 2;
ZL=line current for any given load;
' 'rr) == capacity rating of bank No. 1, divided by its
per cent IZ/ ^ *- -^ °
per cent impedance;
' ^ ' ) = capacity rating of bank No. 2, divided by its
per cent/Z/2
per cent imp)edance.
The above formulae are, however, only correct when the relative
ratio between the resistance and reactance of all the transformers
are equal. If not, the sum of the individual load currents will be
greater than the current in the line, due to a phase difference
between the gurrents in the different transformers. The error
introduced by the inequalities in the values of this ratio is gen-
erally so small that it can be safely neglected.
For delta-delta connected transformers the effect of different
impedances is also an unequal division of load among the three
transformers. The curves of Fig. 268 show the relation of current
in the three legs of the delta, assuming two legs always to be alike
in percentage impedance and capacity. The absciss* represent
ratio of impedances of like legs to the odd leg.
Z3 Z3
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428 ELECTRICAL EQUIPMENT
Where Zi, Z2, and Z3, are the impedances of the different legs.
oer cent IZ
But since Z is proportional to ^—^^ — r — we can write
(per cent ZZ\ /per cent IZ\
Kv.A. /i^V Kv.A. /a
(per cent IZ\ /per cent IZ\
Kv.A. /3 \ Kv.A. /a
If Zl= line current for any given balanced load, and Zi, Z2, and h
are the leg currents, with the same load, the ordinates of the cur\^e
represent the ratio of leg current to Une current fi = ir and 7-,
respectively.
If, for example, we have three transformers connected in delta-
delta, with capacities and impedances as follows:
Kv.A.i = 100, per cent ZZi = 2;
Kv.A.2 = 100, per cent ZZ2 = 2;
Kv.A.3= 50, per cent ZZ3 = 2.3;
Line voltage = 1000;
we find that
and
also
^»=:J?=0.68;
It, iL
^=0.40.
It.
If /i = 100 amp., the normal current for that transformer,
^'^=0:68=^^^*'"P-
Z3 would then be equal to 147X0.40 = 59 amp. or 18 per cent
overload on leg 3.
Again, if we assume that Z3 = 50 so as not to overload leg 3,
then Zl = 125 and Zi = 85 and legs, 1 and 2 are, therefore, carrj'ing
only 85 per cent of their rated capacity. This means that without
any overload on any of the three transformers, the system can
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TRANSFORMERS
429
cany only 125 amp. line current or 87 per cent of the rated capacity
of the three transformers.
At the point where r=0, we have the current in legs 1 and 2
equal to the line current, giving the condition of open delta. By
1.0
1
—
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r
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—
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—
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2
Q
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ft
4
0)
T— Batio of Impedances
Fia. 268.
decreasing the capacity of leg 3 to zero, which is the same as
increasing its impedance to infinity, we have but two legs on which
to carry the three-phase load.
With delta- Y-connected transformer banks a small difference
in the per cent impedance has, as for the voltage ratios, a negligible
effect. For example, if two transformers having impedances of
6 per cent are connected in delta- Y with another transformer
ha\dng an impedance of 3 per cent, the potential of the neutral
point will be shifted at full load by an amount approximately equal
to one-third of (6%-3%) or 1 per cent of the normal voltage of the
transformer.
Mechanical Design. For self-cooled power transformers of
moderate capacity the tanks are generally made of corrugated
sheet steel (Fig. 269), the bottom of the top edges of which are
permanently cast into the base and the top rim simultaneously
with the pouring of the castings, thus forming a perfectly cast-
welded joint. For larger sizes tubular tanks are usually supplied.
These are of the plain steel-plate construction with a* number of
wrought-iron tubes, so arranged with connections at top and bot-
tom as to allow a natural circulation of the oil between the tank
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ELECTRICAL EQUIPMENT
and the tubes (Fig. 270). All the jointB are welded and oil-tight.
For the very largest sizes, where the tank with attached radiator
tubes becomes too large for transportation, a design shown in
Fig. 269.— Self-cooled Transformer with Corrugated Tank. Outdoor Type.
Fig. 271 has been used. It consists of separate radiator sections
of welded, fluted steel, which may be detached dining trans-
portation.
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431
For water-cooled transformers the tanks are mostly of a heavy
steel-plate construction with all joints welded (Fig. 272). Some-
times a corrugated design is also used to increase the radiating
surface.
It is advisable to have the transformer covers tight-fitting to
Fig. 270. — Combination Self-cooled, Water-cooled Transformer.
prevent entrance of moisture. This is effectively accomplished
by placing a gasket between the tank and the cover. In order,
however, to maintain atmospheric pressure in the air space above
the oil, " breathers '' are, as a rule, used. This equalizes the
pressure within and without the tank and prevents the precipi-
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ELECTRICAL EQUIPMENT
tation of moisture from the enclosed air, which would take place,
due to imequal pressure and the resulting condensation, if adequate
faciUties for breathing were not arranged. The chloride-filled
breather is generally considered the best type, its location being
shown in Fig. 276.
The tanks may also be completely filled with oil and provided
Fig. 271.— 8000-Kv.A., 44,000-6600-Volt Radiator Type, Outdoor Trans-
former.
with expansion tanks, thus giving the extreme protection against
moisture or the collection of explosive gases.
Most tanks are suitable for indoor or outdoor service if proper
cover and bushing equipment is provided.
In order to facilitate moving it may sometimes be advisable to
equip the transformers with wheels or trucks. If wheels alone are
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433
Fig. 272. — 4000-Kv.A.-55,000-Volt Single-phase Water-cooled Transformer
desired, they are usually mounted on axles attached to the base of
the tank. Trucks, on the other hand, consist of a structural steel
frame with wheels fitted into the same.
When reasonably pure water can be obtained, no trouble is
experienced with cooling coils in water-cooled transformers, but
if the water is imusually impure the cooling system is liable to
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434 ELECTRICAL EQUIPMENT
give trouble due to the pipe coils being clogged up or destroyed in
three ways:
1st. Corrosion due to air in the water.
2d. Corrosion due to acids or alkali in the water.
. 3d. Deposit of solid matter from the water.
The special grade of iron used in the manufacture of cooling
coils offers much greater resistance to corrosion than ordinary
steel does. On this account, it is only under exceptionally severe
conditions that it is economical to take the extra precaution of
using copper coils; brass being considered inferior to copper.
Iron coils will not be noticeably corroded by the air ordinarily
held in suspension in the water. If the cooling water is taken from
a supply of shallow or rapidly moving water, such water is likely to
contain an abnormal amount of air which will rapidly attack the
inner surface of the cooling coil. When it is suspected that the
water contains acid or alkali it should be analyzed and the results
referred to the experts for advice. A one-gallon sample is neces-
sary for a proper analysis.
When there is an excessive quantity of alkali or earth salts in
solution, the heating of the water will cause a deposit of this salt
previously in solution. Such an action will, of course, take place
regardless of the material of the cooling coil and can be best
guarded against by operating wdth a rapid flow of water with its
resulting low temperature and flushing action. When the water
has much suspended solid matter, that is, if it is muddy, it should
be filtered, or in less severe cases protection could be obtained by a
rapid flow of water. The deposit of such solids in the water will
become more rapid as the surface is roughened by deposit or cor-
rosion, due to the increased resistance in the path of the outer
portion of the column of water.
Wrought-iron cooling pipe is ordinarily made of extra heavy
lap-welded inch or inch and one-half pipe, withstanding a test
pressure of 1000 pounds per square inch. Copper coils, on the
other hand, are mostly designed to withstand a test pressure of
250 pounds per square inch and are, therefore, not as desirable as
iron coils from a mechanical standpoint.
The coils, which may be constructed in single or multiple
layers, are placed inside the upper part of the tank and are usually
bolted to the same By means of a three-way valve at the inlet
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TRANSFORMERS
435
(Fig. 273) the water may be admitted to, shut-off from, or drained
from the coil, the draining being by gravity.
Water-flow indicators are desirable in order to enable the
attendants to quickly observe that the water is flowing inasjnuch
Fig. 273. — Typical Transformer Installation Showing Water Piping Con-
nections and Three-way Valve.
as most water-cooled transfonners would overheat in a short time
if the water supply were shut off. There are two kinds of flow
indicators in general use. The sight-flow indicator and the check-
valve indicator. The former is of the open type and consists of a
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ELECTRICAL EQUIPMENT
funnel-shaped bowl into which the water flows and from which it
drains into the waste. The latter is constructed on the check-
valve principle. It is provided with a valve rod working through
Fig. 274. — Water-cooled Shell-type Transformer Removed from Tank.
a water-tight bushing and acting to close an electric circuit which,
in turn, may light a lamp or operate a relay-depending on the
condition of the water flow. When this is stopped or reduced
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TRANSFORMERS
437
below a certain point, the circuit is broken by the action of a
springy and the lamp goes out. It may also be obtained with an
indicator for use on open-circuit signal systems, in which case the
signal circuit is closed when the water flow is interrupted.
With the shell-type construction the core iron is assembled
Fig. 275,— Core for 4000 Kv.A. Core-type Transformer.
around the coils (Fig. 274), and follows the coil assembly instead
of preceding it as in core-type construction. The cores for the
latter are two-legged for single-phase (Fig. 275) and thr^e-legged
for three-phase units. They are built up from sheet laminations
of high-grade non-aging siUcon steel, clamped at top and bottom
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ELECTRICAL EQUIPMENT
between angle irons, and are insulated from the windings by oil
duets and cylindrical insulating tubes.
Fig. 276. — 5000-Kv.A. Circular Disc-coil, Core-type, Three-phase Trans-
former, Facing Low-voltage Side.
The windings of shell-type transformers consist of rectan-
gular shaped coils, while, for the core-type design these have a
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TRANSFORMERS 439
circular shape which has many advantages over the former, in
that they can be more easily insulated and supported to with-
stand the mechanical stresses due to short-circuits.
With shell-type windings the coils are assembled into several
primary and secondary groups so mixed as to obtain the proper
compromise between voltage regulation and a desirable reactance,
the spacings being furthermore dependent on the required dielec-
tric and the oil flow necessary for cooling.
With the core-type diBsign, the following three diflferent wind-
ing arrangements are in use:
1. Interleaved disc coils, for low and moderate voltages.
2. Concentric cylinder coils, for intermediate voltages.
3. Concentric disc cylinder coils, for high voltages.
With the interleaved construction the coils are assembled
horizontally over an insulating cylinder around the core, the
primary and secondary coils being interleaved in synmietrical
groups with insulating oil ducts and barriers between them
(see Figs. 276 and 277). They are usually wound with rectangular
conductor, one turn per layer. The whole structure is securely
braced at each end by plates rigidly engaging with the steel channel
core clamps. There are usually four or more groups in the wind-
ings, depending upon the capacity, voltage and the required react-
ance.
The concentric cyUnder type involves a construction in which
all the coils are in the form of cylinders assembled concentrically
around the core legs, insulated from each other and from the core
by insulating cylinders (Fig. 278). The low-voltage coils are
placed nearest the core and may be wound with rectangular strip
on edge or flat depending upon the number of turns and the size of
conductor required. The high-voltage coils may be single- or
double-cylinder edge-wound coils or, if the size of conductor is
small, the winding may be broken up into a number of small sec-
tions and wound with round wire in layers.
The concentric disc cylinder type is a combination of the
above, the high-voltage coils being of the disc form and wound
the same as the coils for the interleaved disc type, while the low
voltage coils are cylindrical the same as in the concentric cylinder
type (Fig. 279). The high-voltage coil is placed outside and the
low voltage inside, next to the core, cylindrical insulations being
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1 IP
1 IP
( IS
Fig. 277. — Interleaved Disc CJoil Windings for Ck)re-type Transformers.
p
( 1
r__j
"1^
P
( 1
t —1
J 1
^
Fig. 278. — Concentric Cylinder Coil Fig. 279. — Concentric Disc-cylinder
Windings for Core-type Trans- Coil Windings for Core-type
formers. Transformers.
440
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TRANSFORMEBS 441
placed beween the core and the low-voltage coil, and between the
high- and low-voltage coils the same as used for the other types.
This construction is necessary for transformers of the higher
voltages, requiring a greater number of turns and an increased
amount of turn insulation. Therefore, it can be seen that, at a
given capacity a point will be reached where it will be impossible
to use cylindrical edge-wound coils because the conductor will
become too thin to wind on edge, while, on the other hand, the
losses may limit the use of such a construction before the mechanical
considerations. As the edge-woimd conductor becomes thin on
account of increased turns and insulation, the width, which is the
thickness of the cylinder, must be increased sufficiently to give
the proper current carrying capacity. This width is perpen-
dicular to the leakage flux and eddy ciurent losses are accordingly
set up in the conductors. It is quite possible to reach a point
where an increase in the width of the conductor will give an
increased total loss in the copper on account of the eddy current
losses increasing faster than the PR loss decreases, due to a layer
conductor. The disc coils effectively overcome these difficulties^
first, because the width of the coils is sufficient to accommodate
the required turns, and second, because the width of the rect*
angular conductor is parallel to the leakage flux and, therefore,
does not increase the eddy current loss.
After the coils are wound they are clamped to dimensions and
thoroughly baked and vacuum treated to insure the complete
elimination of moisture. Nimierous treatments in insulating
compounds are then applied, sealing up all interstices and cement-
ing each coil into a soUd structure. The coils are then subjected
to further baking, after which the clamps ai'e removed and the
proper number of tapings applied, followed by the final series
of treatments and bakings, after which the coils are ready for
assembly.
The taps are always placed in the coils located in the central
portions of the winding where the potential strains are at a mini-
mum. To faciUtate the bringing up of several leads from the t^ps,
a new arrangement is being used in modem transformers. It
consists of multi-conductor leads, two or more insulated cables
being boimd together and heavily wrapped with varaished cambric,
forming a stiff solid structure that is easUy supported and well
insulated from groimd (Fig. 276). Each element of the group
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442 ELECTRICAL EQUIPMENT
terminates in a threaded stud mounted in a circular fiber disc with
arrangement for interconnection by short links. To prevent the
possibility of short-circuiting sections of the winding, all threaded
studs, between which short circuits could be made, have the same
thread and dimensions, while the studs to be connected differ in
size. The connecting link is also fitted with couplings which differ
in size from one another so that unlike studs on the circular disc
may be coupled; this arrangement rendering harmful connections
impossible.
When the above-described multi-conductor arrangement does
not prove practical on account of very high voltages or too many
taps, a terminal connection board, generally made of oil-treated
maple, can be used, to which all leads are brought, separately
bushed and provided with suitable terminals for interconnections.
This board is normally submerged in the oil.
The main leads in self and water-cooled power transformers
arc brought out through insulating bushings in the cover. Usually
only two high-tension terminals are brought out for single-phase
units, while for three-phase units three or four bushings may be
provided, depending on whether the neutral is to be brought out.
The same also applies to the low-tension leads.
The design of the leads for moderate voltages involves no
difficulties. For indoor transformers they usually consist of a
metal rod heavily insulated with several wrappings of black var-
nished cambric, fiber collars being added for the high-voltage
ranges to increase the creeping surface (Fig. 272). For outdoor
service these leads are covered with a petticoated porcelain
bushing. The conductor may also consist of a flexible cable
pa&sing up through a tube making connection between the line
and the transformer winding. The lead proper (flexible cable)
may, therefore, be disconnected from the line at the top of the
bushing and slid down through it, in ca*je it is desirable to remove
the cover from the tank without disturbing the cone.
For higher voltages, above 70,000, the bushing design involves
greater difficulties, it being necessary to carefully equalize the
potential and keep the gradient at or below the amount which is
safe for the weakest point. The latest type of compound-filled
bushings with one-piece porcelain shells is undoubtedly the most
satisfactory design brought out to date (Fig. 280). They consist
of a single top and a single bottom porcelain with a central section
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TRANSFORMERS
443
of metal grounded to the cover. The central metal section
extends below the oil level of the transformer to prevent corona.
This type is also provided with a flexible cable passing through a
metal tube extending the length of the bushing and supported at
top and bottom, connection being made at
the top through a water-tight cap. The
central metal tube is surrounded by con-
centric insulating cyUnders dividing the oil
space. The joints between the top and
bottom porcelains and metal sections are
gasketed and clamped, so that they are
absolutely oil-tight. The upper porcelain is
surmoimted by a heavy glass expansion
chamber which is also used as a gauge in
filling.
OiL Transformers should contain suffi-
cient oil to completely immerse the core,
windings and cooling coil, and a gauge
should be attached to the tank in a con-
spicuous place to indicate the oil level,
while a valve should be provided at the
bottom for drawing oflF the oil.
Transformer oils should have good in-
sulating properties, a high flash and low
viscosity, so that the heat may be readily
conducted from the coils and core to the
radiating surfaces. The flash and burning
points are second in importance only to
viscosity, and, in fact, vary together; that
is to say, an oil having a high burning-point
compared with another oil will probably be
high in viscosity. It is this property of oil
to resist ignition until it is first heated to a
temperature, known as its fire or burning-
point, which enhances its value as an insulating and cooling
medium. At a temperature somewhat below the fire or burning-
point the oil gives off vapors which, as they come from the surface
of the oil, may be ignited in Utile flashes or puffs of flame. This is
known as the flash-point. The oil will not support combustion,
however, until these flashes are sustained iminterruptedly, or, in
Fig . 280.— 155,000-Volt
Compound Filled
Flange-clamped Por-
celain Bushing.
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444 ELECTRICAL EQUIPMENT
other words, until the buming-pomt is readied. It is, therefore^
obvious that high flash and burning-points are desirable in in-
sulating oils in order that the fire risk attendant on their use
may be reduced to a minimum.
Of extreme importance is also the percentage of deposit, which
may be thrown down from an oil in service. Most organic sub-
stances, when exposed to even moderate temperatures, are sub-
ject to slow chajsges, which, in case of oils, are probably due to
chemical change, such as oxidation of some of the constituents,
and when this deposit is excessive efficient cooling is very much
restricted. Somewhat similar to this deposit, some oils produce a
jelly-like substance, which forms after continuous operation, and
in general, the higher the temperature the more rapid these changes
take place. A very sUght trace of the deposit is in no degree
harmful and will ordinarily only be found under the most severe
conditions following a long period of service.
Transformer oils must also be watched for presence of injurioas
impurities such as acids, alkalis and free sulphur. An access of
acid particularly would result in deterioration of insulation and
other materials of which the transformer is constructed. Free
sulphur, even in extremely minute quantities, is seriously detri-
mental to the windings, the chemical action on exposed copper
causing the conductors themselves to be gradually eaten through.
These characteristics are, however, very carefully watched by the
transformer manufacturers, so that the oils furnished are ordinaril}'
free from such injurious impurities.
The characteristics of oils in general use vary somewhat,
depending on the type of transformer as well as on the practice
of the transformer manufacturer. One of the largest of these sup-
plies oil of the following characteristics for its water-cooled trans-
formers:
Flash-point 130** C.
Burning-point 145** C.
Freezing-point — 15** C.
Viscosity at 40** C 40 sec.
This kind of oil is also supplied with oil-cooled transformers
and combination self- and water-cooled transformers where the
guaranteed normal load temperature rise is less that 50^ C
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TRANSFORMERS 445
Where the rise is 50^ C. and higher, oil with the following char-
acteristics is used:
Flash-point 160**C.
Burning-point 175° C.
Freezing-point — 10° C.
Viscosity at 40° C 60 sec.
Transformers which may be operated mider severe weather
conditions, such as outdoor types, may also be supplied with an
oil having a freezing-point of —30° C.
The necessary puncture strength of oils is: 40,000 volts punc-
ture with J-inch discs spaced 0.2 inch apart; or, 22,000 volts
puncture with 1-inch discs spaced 0.1 inch apart.
In order to ascertain the temperature at which a transformer
is operating, it is advisable to equip them with thermometers and
these should be located in such a place that they can easily be
read. Different thermometers are in use, some being of the
ordinary mercury type, this being mostly suppUed with self-cooled
transformers and may be equipped with electrical contacts for
connecting to an alarm circuit.
A thermometer which is very extensively used in connection
with water-cooled transformers is illustrated in Fig. 281. It
depends for its operation upon the expansion of mercury in a
sensitive steel tube. The bulb is connected to the indicating
instrument by a small capillary steel tube, this tube being con-
nected to a spring to which the indicating pointer is attached
through a rack and pinion. The capillary tube is of such length
that the bulb may be placed in the oil at the hottest part of the
transformer. Variations of temperature at the bulb cause cor-
responding contraction or expansion of the Hquid confined in
this bulb, and this is transmitted to the capillary tube connecting
to the indicating mechanism. The instrument can readily be
equipped with contact points for connection to an alarm circuit.
Drying Transformers. Transformers shipped assembled, but
not filled with oil, should be very thoroughly and intelligently
inspected before deciding that the drying may be omitted. In
every case a thorough inspection is necessary, and if there is any
evidence of mildew or moisture, a drjdng-out run is necessary.
Recent improvements in design and method of shipping make it
practicable where conditions demand it, to ship transformers with
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446 ELECTRICAL EQUIPMENT
such precautionary measures that drying in most cases will be un-
necessary. Large transformers with properly constructed tanks,
provided with chloride breathers may be shipped with or without
oil. Small high-voltage transformers may be shipped filled with
oil using chloride breathers where necessary. With such ship-
ments careful examination, if shipped without oil, and oil tests if
shipped oil filled, are of utmost importance. The oil samples
should be taken both from top and bottom after the tank has
Fia. 281. — Thermometer with Electrical Connections for Uae on
Water-cooled Transformers.
stood for twenty-four hours, the required puncture strength of the
oil to be as previously given.
Where transformers are shipped without the oil in the tanks
it is almost invariably necessary to dry them out first. This may
be accomplished in several ways, of which the " external " and
the " internal '^ heat methods are mostly used.
The " external ^' method requires the circulation of heated air
through the transformer in its tanks. Dry air is forced at a tem-
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TRANSFORMERS
447
perature of 85° C. into coils and insulation at the bottom of the
transformer, allowing same to escape at the top. The quantity of
air should be such that the temperature of escaping air is approxi-
mately the same as the ingoing temperature. Various pipes and
.deflectors may have to be used to properly distribute the air,
and precautions should be taken to prevent oil from running
from the transformer into the heater as it may cause a serious
fire. The quantity of air to give good results with different size
tanks is as follows:
Diameter in In. or Equiva-
lent Area of Tank.
Cu.ft. Air per Min.
54 to 72 inclusive
78 to 96 inclusive
102 to 120 inclusive
126 to 144 inclusive
150 to 168 inclusive
600
900
1200
1500
1800
An outfit which is especially adapted for furnishing hot air for
transformer drying is shown in Fig. 282. It consists of an electric
air heater blower and air strainer. The air heater requires 20 to
25 Kv.A. at 110 or 220 volts to operate it, and the blower about
Fig. 282. — Hot-air Drying Outfit for Transformers.
2 H.P. to drive it at normal output. The air strainer when in
operation should be wrapped with cheesecloth to prevent the dust
from entering the blower and being blown into the transformer.
This cloth should be changed from time to time as the dirt accu-
mulates on it.
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448 ELECTRICAL EQUIPMENT
In cases where it is impractical to apply the hot-air method for
drying, the " internal " or short-circuit method may be used.
The transformer should then preferably be taken out of the tank
or, otherwise, the manhole cover should be removed and the valve
in the base opened to give as great a circulation of air as possible
under the conditions.
This method requires one winding to be short-circuited and a
voltage appUed to the other so that sufficient current will flow in
the windings to raise the temperature to approximately 70** C.
The amount of current necessary to effect this temperature ranges
between one-fifth and one-third of the full-load current, depend-
ing upon the room temperature and the design of the transforaier.
The impedance volts necessary to give the specified range in cur-
rent varies from 0.4 to 1.5 per cent of the rated voltage of the
winding to which the impedance voltage is appUed.
The temperatm^ of the winding can be determined by the
increase in resistance, which is calculated as follows:
Let ftc = resistance at room temperature, or cold resistance;
fc=room or coil temperature for cold resistance;
Rh = hot resistance ;
iji = temperature of windings hot;
then
, RH{2SS+tc)-238Rc
^'"^ Re '
and rise
= tH-tc.
A simple method for determining the temperature of the wind-
ing is to assume that for each per cent increase in resistance the
temperature rise is approximately 2|° C.
The duration of the drying run depends upon the voltage and
size of the transformer and also upon its condition as to moisture
at the time it is dried. For transformers under 20,000 volts the
drying should be continued not less than twenty-four hours;
20,000 to 30,000 volts, 48 hours; between 30,000 and 40,000 volts.,
seventy-two hours. Higher voltages may require longer. It is
obvious that some consideration must be given to the capacity of
the transformer. Transformers of less than 100 Kv.A. may only
require twenty-four hours. For transformers between 200 Kv.A.
and 500 Kv.A. the process may be limited to thirty-six hours;
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TRANSFORMERS 449
between 500 Kv.A. and 1000 Kv.A., to forty-eight hours; be-
tween 1000 Kv.A. and 2000 Kv.A. to sixty hours; for all larger
capacities the process should be carried on for at least seventy-two
hours. In case there is no evidence that the transformer is unduly
moist, discretion may be used in slightly decreasing the limits
given for the voltage. A transformer of 20,000 to 30,000 volts,
for instance, having a capacity of 200 Kv.A. or less, may be dried
in only twenty-four hours. The limits given for the capacities,
however, should be rigidly adhered to, and in no case should the
process be carried on for less than twenty-four hours.
While the insulation resistance of a transformer cannot be
relied upon as a siu-e indication of its condition at any one time, the
general trend of megger readings as a drying nm proceeds is a
fairly accurate indication of the progress of drying. The drying
process should be continued imtil the curve becomes approxi-
mately flat at an elevation considerably above the low point of
the curve. Variation in temperatures causes wide variation in
resistance, the values varying inversely. If the megger shows a
short circuit, that is, an insulation resistance too low to be read,
it is very likely due to an excessive amount of moisture. Low
readings also sometimes indicate the presence of moist spots in the
insulation. Widely different megger readings may be obtained
on different transformers, but average readings should be approx-
imately alike for transformers of the same capacity and design.
Shell-type transformers have, in general, a lower insulation resist-
ance than core-type.
Oil Diying. Oil, whether shipped in sealed barrels or in
special tank cars direct from the manufacturer, may require
drying at its destination before it is suitable for use in high- volt-
age transformers. All oil should be tested before using, but, if
it is absolutely necessary to use a part of oil from barrels before
tests can be made, the barrels should be allowed to settle for sev-
eral hours and then the oil pumped from the top to within 4 inches
of the bottom; i.e., do not use the oil which settles in the bottom
until it can be tested and dried if necessary. Oil drums should be
stored lying on their sides.
The best method for dr3ring and filtering oil consists of forcing
it under pressure through several layers of blotting paper, which
removes all moisture and solid matter held in suspension in the oil.
A filter press, such as shown in Fig. 283, has been developed for
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ELECTRICAL EQUIPMENT
this purpose, and by this method from 360 to 1200 gallons of oil,
according to the size of the press, can be treated in an hour.
The essential portions of the filter consist of a series of alternate
flat cast-iron plates and frames, the blotting paper being placed
between them, and the whole clamped tightly by means of a
large screw and lever at one end. Both plates and frames have
large cored holes in the lower comers, serving as inlet and outlet
for the oil. The surface of the plates, except for a one-half inch
rim round the edge, is grooved or corrugated both vertically and
Fig. 283.— Method of Using Oil Dryer and Filter to Dry OQ in a
Transformer as Installed.
horizontally on both sides, forming the checkered or so-called
" pyramid " surface which supports the paper and forms channels
communicating with the outlet at the corners. This form of
surface is more eflScient than a single set of corrugations or the
use of perforated metal. The oil enters at the lower left-hand
corner of the filter, passes through a series of cored holes in the
plates and frames and punched holes in the blotting paper and
enters and fills in parallel the chambers formed by the frames and
plates. It then passes through the blotting paper, along the
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TRANSFORMERS 451
grooves of the pyramid surface, to the lower right-hand comer
of the plate, and then through a series of small holes drilled from
the surface of each plate to a cored passageway, similar to the
inlet. A rotary gear or multi-stage centrifugal pump is used for
forcing the oil through the filters.
One of the greatest advantages of this outfit is that the treat-
ment can be carried on while the transformer is in operation, and
without the use of separate tanks for the oil, as seen in the illus-
tration.
Oil Testing. The sample bottles or cans should be thoroughly
cleaned and dried before using, and it is generally satisfactory
to rinse very thoroughly with clean, dry oil and allow the recep-
tacle to drain for a few minutes. The test samples should be taken
only after the oil has settled for some time, varying from eight
hours for a barrel to several days for a large transformer. Cold
oil is much slower in settling and may hardly settle at all. Oil
samples from barrels should be taken about J inch from the bot-
tom of the dnrni and a brass or glass " thief " can be conveniently
used for this purpose. The same method should be used for
cleaning this as is used for container.
A compact oil-testing set by means of which the dielectric
strength of oil can easily be determined is illustrated in Fig. 284.
It consists of a testing transformer with an induction regulator
for voltage control and an oil-spark gap, all of which are assembled
as a unit. Before using, the spark gap should be cleaned by simply
rinsing with clean, dry oil. Its terminals, which are 1.0 inch in
diameter, should be adjusted 0.1 inch apart by means of a gauge.
The spark receptacle should be nearly filled with the oil and
allowed to stand for a moment to give bubbles time to escape,
especially if the oil is cold. The rate of increase of voltage should
be as fast as can be accurately read on the voltmeter, the total
time of application of voltage, from zero to breakdown valve,
usually being about five seconds The average voltage of five
tests is generally taken as the dielectric strength of the oil.
When drawing samples of oil from the bottom of transformers,
or large tank, several quarts should be drawn off before taking
sample in order to eliminate dirt or water which may have accumu-
lated in the valve, connecting pipes, etc. The best way to clean
and dry oil drums is to rinse them very thoroughly with five or
ten gallons of gasolene, benzine, or dry transformer oil. The
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452
ELECTRICAL EQUIPMENT
rinsing operation should be repeated several times, using fresh
liquid each time and draining the drums very thoroughly after
each rinsing.
Operation. Artificially cooled transformers should not be run
continuously, even at no load, without the cooling medium.
Fig. 284.-^0,000-Volt OU-testing Set.
Therefore, it is essential to maintain a proper circulation of the
cooling system.
K the water circulation of water-cooled transformers is for any
reason stopped, the load should be immediately reduced as much
as possible, and a close watch kept on the temperature. Reduce
the load if for any other reason the oil at the top, near the center
of the tank, approaches 80° C. This temperature should be rec-
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TRANSFORMERS 463
ognized as an absolute limit and must not be exceeded It should
be held only during an emergency period of short duration.
The ingoing cooling water should never have a maximum tem-
perature of over 25° C.
Nearly all cooUng water will in time cause scale or sediment to
form in the cooling coils. The time required to clog up a coil
depends on the nature and amount of foreign matter in the water.
The clogging materially decreases the eflSciency of the coil and is.
indicated by a high oil temperature and a decreased flow of water,
load conditions and water pressure remaining the same.
The most frequent cause of clogging of iron cooling coils is a
large quantity of air in the water, resulting in the formation of a
scaly oxide.
Scale and sediment can be removed from cooling coils without
removing the coils from the tank. Both inlet and outlet pipes
should be disconnected from the water system and temporarily
piped to a point a number of feet away from the transformer,
where the coil can be filled and emptied safely. Especial care
must be taken to prevent any acid, dirt or water from getting
into the transformer.
Blow or siphon all the water from the cooling coil and then fill
it with a solution of hydrochloric acid, specific gravity 1.10.
(Equal parts of concentrated hydrochloric acid and commercially
pure water will give this specific gravity.) After the solution has
stood in the coils about an hour, flush out thoroughly with clean
water. If all the scale is not removed the first time, repeat until
the coil is clean, using a new solution each time. The number of
times it is necessary to repeat the process will depend on the con-
dition of the coil, though ordinarily one or two fillings will be suf-
ficient.
The chemical action which takes place is very noticeable
and often forces acid, sediment, etc., from both ends of the coils;
therefore, it is well to leave both ends open to prevent abnormal
pressure.
When water-cooled transformers have operated for some time,
especially if the operating temperature? are high, the oil may
leave a deposit on the outside surface of the cooling coils. Any
deposit decreases the eflSciency of the coils and should be re-
moved. This condition of the coils is indicated by higher oil
temperature, water flow and load conditions remaining the same
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454 ELECTRICAL EQUIPMENT
The coil should be examined whenever indications point to the
formation of a deposit.
When water-cooled transformers are idle and exf)osed to cold,
the water must be drained or blown out of the cooling coils. In
addition to draining or blowing out the water, the cooling coil
should be dried by forcing heated air through it. If not con-
venient to force heated air through the coil, enough alcohol
should be poured into the coil to fill the two bottom turns of each
section.
During the first month of service of transformers having a
potential of 40,000 volts or over, samples of oil should be drawn
each week from the bottom of the tank and tested. Samples from
aU transformers should be drawn and tested once every six months.
If at any time the oil should puncture below the safe voltage
the filter press may be used for treating it without taking the
transformer out of service. Oil should be drawn from valve in the
base, passed through the filter press and returned to the trans-
former through the cover, discharging into the tank diagonally
opposite the valve in the base and so directing the discharge that
it is not directly over the coils and insulation. Circulate until
the oil tests satisfactorily.
The oil level in transformers should be kept up to the mark on
the oil gauge. On oil-cooled transformers with external cooling
pipes, the oil must be above the top pipes in the tanks or the oil
will not circulate and transformer will overheat.
When chloride breathers are provided, only anhydrous chlor-
ide of calcium in half-inch lumps or larger should be used. The
frequency with which new chloride may be added will depend on
the changes in temperature and the humidity of the atmosphere.
Oil-cooled transformers, occasionally, are operated under con-
ditions of poor ventilation, overload, or over-voltage. Any of
these conditions, or a combination of them may raise the tem-
perature of the oil abnormally high, causing the oil to throw down a
deposit which forms on the transformer surfaces. Should the
deposit on any surface, except the base, reach an average thick-
ness of about J inch, the oil should be renewed as soon as possible.
Before putting new oil into the tank the sediment should be
removed from aU surfaces and the windings cleaned by forcing
dry, clean Transil oil through all ducts and against all surfaces
until all deposit is removed.
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TRANSFORMERS 455
Temperatures should be read daily (or more often), and if an
oil temperature of 80° or over for the self-cooled is indicated, or 65°
or over for the water-cooled, the transformer must be cut out of
service at once and the cause of the excessive heating looked into.
These or higher temperatures of oil may indicate that the interior
temperature of the windings were exceeding the safe hottest spot
value, this being limited to 105° C. for self-cooled and 90° C. for
water-cooled transformers as previously stated.
Regardless of oil temperatinre as indicated by thermometers,
transformers should not be operated at overloads not stipulated
by the specifications. When operatmg water-cooled transformers
at an overload the amount of water should be increased in propor-
tion to the load. On account of the increased amount of water
during overload, the temperature of the oil will not rise as fast as
the temperature of the windings and any of the causes leading
to excessive heating will have more pronounced effect under these
conditions. Therefore, transformers during overload should be
watched with especial care to see that the oil temperatures are
kept well below the temperature limits specified.
Compartments in which oil-insulated self-cooled transformers
are installed should be thoroughly ventilated. Openings for cool
air should be provided at various points near the floor, and outlets
should be in or near the roof, which should not be closer than 6 to
10 feet from the top of the transformer. The room temperature
in which transformers are installed should not exceed the tem-
perature of the air entering the room by more than 5°, and pre-
smnably, the entering air will come from the outside, or, at least,
from a source not much warmer than the outside air.
There is practically no danger of condensation of moisture in
transformers which have no chloride breathers if the oil at all
time IB kept 10° or more above the room temperature. It is also
desirable, especially in moist climates, to keep the oil in idle
transformers (not equipped with breathers), slightly warm in
order to eUmiinate the chance of the oil becoming moist. This
may be accomplished by appl3ring voltage alone for a few hours
each day Water-cooled transformers should be watched to see,
that the oil temperature does not drop below the limits specified;
and if it does, the amount of water must be decreased until the
oil attains a temperature of at least 10° above the surround-
ing air.
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ELECTRICAL EQUIPMENT
Oil-supply System. Many different schemes are used in
laying out the oil-supply system. The piping should, however,
always be arranged so that the transformers may be readily and
quickly drained for inspection and in case of emergencies. This
draining also refers to the piping itself. Storage tanks should be
provided for both filtered and unfiltered oil, and these are gener-
ally located in the basement. Sometimes they are installed in
compartments and occasionally the tanks are further imbedded in
sand as an additional fire protection.
A flexible oil-piping system for a transformer installation is
shown in the diagram (Fig. 285). This system will allow the oil
To Sewer
I I
To oil Swltcb Tanks*
Z *Note;- Iq very lar^e InstaUatloiM
^ where oil switctaes are not
7 located near tniDsforinera, a
^ delivery header for oil
^ switches Is rocommeoded
2
&
DralD and Storage
Taoks below Floor
Level of Traas-
formers
±
Oil Filter and Pamp
=^ Located on Floor Level of Tanks
Storoffe Tank for
OU Switches
Fia. 285. — Diagram Showing Method of Arranging Transformer Oil Piping.
to be circulated from any transformer to either tank; from one
tank to the other, either directly or through the filter press; and
finally, from either tank to the transformers, either directly or
through the filter press. A connection to the sewer or tailrace
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TRANSFORMERS 457
should also be provided for draining ofif the oil in case of emer-
gency. The movement of the oil may be accomplished either by
applying compressed air to the tanks or by means of the motor-
driven pump of the filter press or other separate pumps.
Occasionally an intermediate oil tank is provided and installed
on the main floor or gallery at an elevation that the oil can be
drawn into any of the transformers by gravity. The oil is then
pumped from the storage tanks in the basement after being fil-
tered. A motor-driven air compressor and vacuimi pump may
also be required, being operated as a vacuxmi pump for exhausting
the air from the transformer cases so that the oil may be drawn
into the same, or as a compressor for pumping in air in the inter-
mediate storage tank to assist gravity in emptying the same.
Cooling Water System. The design of the cooling water
system depends on the nature of the development, i.e., whether
low-head or high-head, and also on whether a suflScient continuous
water supply can be obtained. This is not the case in many sub-
stations and imder such conditions it becomes necessary to pro-
vide cooUng ponds and reservoirs. The water from the pond is
pumped to the transformers and after passing through the coohng
coils it is returned to the pond, where it is cooled. This may be
eflfected either by a spray or by providing a basin of such dimen-
sions that a suflScient cooling is obtained by a radiation of the heat
from the water to the air. The latter method is much superior
to the former in which air is liable to be carried along with the
water, causing a rapid oxidation of the iron cooling coils.
For the generating station transformers it is customary to
take the cooUng water from the forebay or from the penstocks.
In the former case it may be necessary to provide pumps for con-
vejring the same through the cooling coils. For high-head develop-
ments where the pressure may be too high for the cooling coils,
a reducing valve must be installed, but this is, as a rule, not neces-
sary in low-head plants or with iron cooling coils which can with-
stand a much higher pressure than copper coils.
The water should be taken from at least two separate intakes,
and it is needless to say that it must be free from silt and sus-
pended particles. For this reason strainers should be. provided
before it enters the distributing headers, and these strainers should
be so arranged that they can be readily removed and cleaned.
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458 ELECTRICAL EQUIPMENT
7. CURRENT-LXMITING REACTORS
Purpose of Reactors. Modern generating and transmission
systems have reached such magnitudes as to make it necessary to
very carefully analyze the abnormal conditions, which may take
place during short circuits on the system, with a view of pro-
viding such means as may be required for protection not only of
the apparatus involved, but also the service as a whole. This is
the function of a reactor by means of which the flow of current on a
short circuit may be limited to a safe value. It accomplishes this
purpose by reason of the voltage drop or back pressure which it
exerts in the circuit.
By means of the proper installation of reactors the whole
station, or even several stations, may be operated in multiple while
at the same time the several sections may be protected from each
other and each section from the individual circuits which it feeds.
Troubles may be localized or isolated practically where they orig-
inate without communicating their disturbing effects.
When a short-circuit occurs on a system the voltage will drop,
depending on the magnitude of the short circuit and the inherent
characteristics of the generators, i.e., their impedance. A severe
short-circuit, such as may occur when there are no reactors, will
cause the voltage to drop to a low value in a few cycles, whereas
on a less severe short-circuit, the time taken for the voltage to
drop to the same low value will be longer. Synchronous apparatus
will stand a complete loss of power for a few cycles only, but will
stand a 'reduction of voltage for a longer period. It is important
then that the value of short-circuit be small and that it be cleared
in the shortest possible time. Introducing reactors will limit the
maximum value of the current, and with the latest type of relays,
the time required for selective switch action is very short, so that
a trouble can be locaUzed and cleared before the apparatus on the
rest of the system is affected.
The protective and localizing functions of a reactor are, how-
ever, quite distinct. The former, since all the evil effects of heavy
current — excessive mechanical stresses, heating, etc., are pro-
portional to the square of the current, is measured in terms involv-
ing the square of the total reactance, while the latter is measured
in terms of the first power of the reactance involved.
The chief purpose of a reactor is, therefore, to limit the flow of
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CURRENT-LIMITING REACTORS 459
current into a short circuit with a view to protect the apparatus
from overheating as well as failure from destructive mechanical
forces; also protecting the system as a whole against shut-down
by maintaining the voltage on part of the system while the short
circuit is being cleared.
Rating. Reactors are generally spoken of as introducing a
certain per cent reactance in a circuit. This is the ratio of the
voltage drop across the reactor (when the rated current of the cir-
cuit at rated frequency is flowing through the reactor), to the
voltage between line and neutral on three-phase circuits, or the
voltage between the lines on single-phase circuits. The reactance
is, therefore, expressed as being single-phase in either case.
The kilovolt-ampere (Kv.A.) rating of the reactor is the product
of the voltage drop across the reactor and the rated current. For
generator, transformer and feeder reactors the rated current is
usually taken as equal to the current-carrying capacity of the
apparatus, while, for bus sectionalizing reactances, it is determined
by the power which must be transferred over the reactor. This is
very often chosen so as to correspond to the capacity of one of the
generators.
Current-limiting reactors should furthermore be designed for
the maximum load current they will have to carry. Being self-
cooled and having neither iron nor oil to provide thermal storage
they reach their maximmn temperature very quickly. Therefore,
in cases where the apparatus or circuits must carry overloads for
two hours or more, this overload current should be considered the
rated current of the reactor, and the capacity should be selected
on this basis. Under this assumption, a temperature rise of 86** C.
represents common practice, the rise being based on an ambient
room temperatm^ of 40® C.
As reactors, as a rule, do not have an iron core to become
magnetically saturated, the reactive drop will be proportional to
the current. That is, if a circuit having a 5 per cent reactor were
to be short-circuited at the reactor terminal on the load side and
having full sustained voltage on the supply side, the sustained
current would be limited to 100-^5 or twenty times normal. It
should be remembered that transformers and generators in cir-
cuit with the reactor also have definite values of reactance which,
when expressed in terms of the current of the circuit (per cent
reactive drop with normal current flowing) may be added directly
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460 ELECTRICAL EQUIPMENT
to the reactance of the reactor to determine the total apparatus
reactance of the circuit. This total reactance, plus the reactance
of the line up to the point of short-circuit divided into 100, gives
the approximate short-circuit current (the result being expressed
in number of times normal).
Care must be exercised in calculating the possible short-circuit
current of a system that the various per cent reactances are on the
same basis, i.e., on the same current value. For example, if the
reactance for a 6000 Kv.A., three-phase transformer is given as
6 per cent but a value is required which corresponds to one of the
generators, having a capacity of, say, 4000 Kv.A., three-phase,
4000
the corresponding value would then be ^7^7^X6=4 per cent.
Similarly, it must also be remembered that reactance values
given for single-phase transformers really refer to a bank of three
such transformers. For example, the reactance of a 6000 Kv.A.,
single-phase transformer is given as 3 per cent. This, then, usually
refers to the full-load current from a bank of three such units, i.e.,
18,000 Kv.A., so that if the reactance were to be converted to the
basis of a 6000 Kv.A. generator, its corresponding value would be
— -— X3 = 1 per cent. A careful consideration of the above is of
the greatest importance when reactance values for generators,
transformers and transmission lines of dififerent capacities are to
be combined.
For the designation of the rating of a current limiting reactor
the following method is generaUy used:
" Type Frequency Kv.A Volts Drop
Amperes Reactor to give per cent reactive drop
in Kv.A volt phase circuit."
The type s3mabols generally used are CLS, CLQ and CLT.
The meaning of the symbols is as follows:
C.L. — Current-limiting reactor.
8. — Single-phase (may apply to any one reactor of a
group of two or three for use in two- or three-
phase circuits).
Q. — ^Two phase (two single-phase reactors mounted
together).
T. — ^Three-phase (three single-phase reactors mounted
together).
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CURRENT-LIMITING REACTORS 461
ft
Far Example: A 6 per cent reactor in a 60-cycle, 6600-volt,
100-amp., single-phase circuit, means that the reactor will have a
drop of 5 per cent, or 330 volts, when the rated current is flowing.
The rating of the reactor will be as follows:
C.L.S.— 60 (cycles), 33 (Kv.A.), 330 (volt drop), 100 (amperes)
reactor — to give 5 per cent reactive drop in a 660
Kv.A., 6600 volt single-phase circuit.
In the case of three-phase circuits the percentage drop is
always based on the voltage between hne and neutral.
For Example: A 6 per cent reactor in a three-phase 60-cycle,
660Q-volt, 100-amp. circuit means that each reactor (of the three)
6600
will have a drop of — 7^X0.05 = 191 volts when normal current is
V3
flowing.
The rating will then be as follows:
C.L.S.—60 (cycles), 19.1 (Kv.A.), 191 (volts drop), 100
(amperes) reactor — ^to give 5 per cent reactive
drop in 1145 Kv.A., 6600-volt three-phase circuit.
Rating as Affected by Frequency. A reactor designed for a
given frequency may be used in a circuit of different frequency, in
which case the per cent reactance is approximately equal to the
ratio of the frequency for which it is to be used to the frequency
for which it is designed times the per cent reactance for which
it is designed.
For Example: A 3J per cent 25-cycle reactor may be used in a
40-cycle circuit, in which case the per cent reactance is approxi-
40
mately 7rrX3i = 5.6 per cent.
25
Rating as Affected by Voltage. A standard reactor can be
used for lower voltage circuits than those for which it is designed,
in which case the per cent reactance is increased in the ratio of the
voltage for which it is designed to that for which it is to be used.
For Example: On an 11,000-volt three-phase circuit requiring
the introduction of about 3| per cent reactance, it will be possible
to use a 13,200 volt 3^ per cent reactor. The reactance will be
^.^13,200 .^ ,
Rating as Affected by Current. A standard reactor may be
used for lower currents than that for which it is designed, in
which case the per cent reactance decreases with the ratio of the
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462
ELECTRICAL EQUIPMENT
current for which it is to be used to the current for which it is
designed.
For Example: A 3J-per cent 350-amp. reactor may be used in a
^ 300
300-amp. circuit where it will insert 3^ X^t^t, = 3 per cent reactance.
350
From the foregoing it is seen that a 3J per cent, 25-cycle,
13,200- volt, 360-amp. reactor will introdifce in a 40-cycle, 11,000-
40
volt, 300-amp. circuit a reactance of approximately 3JX—
^13.200^300 __.
Effect of Reactance on Power-factor. Increasing the reac-
tance in the system results but in a slightly lower power-factor,
the curve in Fig. 286 showing the variation of power-factor with
per cent reactance. It is to be noted that if the power-factor of
the circuit were 90 per cent, corresponding to a reactance of 44 per
cent, then the introduction of a 3J per cent reactor would increase
iUU
E^
■^
"
90
^
^
'Sfc,,
V,
\^
80
X
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£fi0
\
X
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\
s
\
§40
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\
^80
\
20
\
I
10
I
1
t\
1
10 :» 30 40 50 00 70 80 90 100
Per Cent Reactance of Circuit
Fig. 286.
the reactance of 47§ per cent and the power-factor would be low-
ered to 88 per cent. The introduction of a slightly larger reactor,
say 4.2 per cent, would decrease the power-factor to practically
the same amount. On the other hand, if the power-factor of the
circuit were 70 per cent, the introduction of a 3^ per cent reactor
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CURRENT-LIMITING REACTORS
463
would reduce the power-factor to about 66 per cent and a 4.2 per
cent reactor to 65.5 per cent.
Effect of Reactance on Regulation. As in the case of the power-
factor, an increase in the reactance results in a slightly poorer
regulation, the effect being more marked if the operating power-
factor is much below unity. The curves in Fig. 287 show the vari-
ation in regulation with per cent reactance, and it will be noted
Mi
Corv. A-P.F.-IOOJ
" B-P.F.- 9I;
- C-P.F.- Ml
• D-P.F.- W
I Before Inaertiiw RMctoace
( «« M U
( M U .<
IT X .i n
J
I
/
J
/
J
J
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q
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/
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y
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/
^
9
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r
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i
f
/
/'
/
/
B
/
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f
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/
f
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r
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2 8 4 5 6 7 8
Per Cent Reactance of Circuit
Fig. 287.
10
that with a 90 per cent power-factor the introduction of a 3J per
cent reactor will increase the regulation 1.6 per cent and a 4.2
per cent reactor 1.9 per cent. With a power-factor of 70 per cent
the increase in the regulation would be respectively 2.5 and 3.0
per cent. However, the amount by which the voltage of the
system is lowered is not seriously large and can readily be com-
pensated for by increasing the voltage of the generators.
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464
ELECTRICAL EQUIPMENT
The above discussion shows that a reactance somewhat above
that required for current Umiting protection does not materially
affect the regulation or the power-factor, and in many cases it
may, therefore, be advantageous to use a somewhat higher reac-
tance than that which would be required, and thereby gain the
advantage of reduction in cost which can be obtained by using
standard ratings.
Losses. The losses in reactors are not a serious matter but
should, of course, be taken into consideration in laying out the
system. They are due to the PR and eddy-current losses in the
conductors and possibly average 5 per cent of the rating of the
reactor. In some cases, however, the losses may be somewhat
higher and in others considerably less.
Assume, for example, a 4 per cent feeder reactor on a 3000-Kv.A.
feeder, the three coils would have a combined capacity of 120
Kv.A. or 40 Kv.A. per coil. The
losses at 5 per cent would equal
about 2000 watts per coil or 6 kilo-
watts on the 3000 Kv.A. feeder;
that is to say, one-fifth of one per
cent at the maximum load of the
feeder which may last only for a
comparatively short period during
the day. Since the losses are
nearly all copper losses which go
•down as the square of the current,
at one-half load, the losses would
only be one-fourth of the above.
Bus reactors, on the other
hand, carry normally very Uttle, if any, current and the losses
under normal operations are, therefore, negUgible.
Inductance. The inductance of ciurent limiting reactors
may be calculated with sufficient accuracy by the following fo^
mula by Prof. Morgan Brooks:
Fig. 288.— Reactance CoU.
L =
(27rriV)2
6+1.5/+r
Xf'Xf"X 10-^ henrys,
m which (see Fig. 288),
r = mean radius of coil in centimeters;
6 = axial length of coil in centimeters;
f = thickness of winding in centimeters.
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CURRENT-LIMITING REACTORS
465
Both b and t include the thickness of insulation or, if the turns are
air insulated, are equal to the pitch of the winding times the num-
ber of turns. If there is only one turn, the values are equal to the
diameter of the wire.
iV = total number of turns in coil;
F' and F" are correction factors depending on the coil shape;
F' =
10&+13<+2r
106+10.7<+L4r'
F"=0.61og,o(l00+fg').
The reactance, X, is equal to 2ir/L ohms.
Location. Reactors may be located in the system in such a
way that they will not only reduce the mechanical strains due to
short circuit, but will also practically localize its eflfect to the cir-
cuit or section where it occurs. They may thus be placed in the
generator leads, between the bus-sections, in the low-tension trans-
former leads or in outgoing low-tension feeders. Which one of the
above locations or combinations thereof is preferable depends upon
a number of conditions, each location having its advantages and
disadvantages.
Generator Reactors. With reactors in the generator leads
(Fig. 289) the current flowing in the armature winding of the
generator is limited, and this
m^
M^
method, therefore, gives protec-
tion to the generator itself. It
necessarily also limits the cur-
rent that can flow into any
short-circuit beyond the react-
ors, inasmuch as the amount of
current which can flow is limited
to what the generators can sup-
ply. An objection to generator
reactors is the fact that a short-circuit on or near the busbars
will cause a voltage drop on all the lines or feeders connected
thereto. If the short is severe, the voltage may drop to zero
and this, of course, will cause all the synchronous apparatus con-
nected to the system to drop out of step. It is, therefore, evi-
FiG. 289.— Generator Reactors.
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466 ELECTRICAL EQUIPMENT
dent that reactors in the generator leads offer no protection to
troubles of this nature.
In hydro-electric power systems with slow- or medium-speed
multi-polar generators, the inherent reactance of these is, as a rule,
sufficiently high and the construction such that the machines can
safely withstand momentary short-circuits, and generator reactors
are very seldom used in hydro-electric plants. If such reactors
are used, they should be placed in the line leads as close to the
generator as possible and not in the neutral.
Bus Reactors, These are very extensively used in hydro-
electric stations and permit of an unlimited extension of the sys-
tem. The bus-bars are divided
[ into sections by reactors (Fig.
A 1a aAa 290), and trouble may thereby
-^000^
6 6 6 0
be confined to the particular sec-
tion on which the short-circuit
takes place, while under noraial
operation a free exchange of cur-
rent may take place, thereby
retaining the advantage of par-
FiQ. 290.— Bus Reactor. allel operation. A shorlHiircuit
then can seriously involve one
bus-bar section only, and the destructive power of a short-circuit
is limited to the generating capacity of that one section plus the
limited power which can flow from the two adjoining sections.
The voltage of the section upon which the short-circuit takes
place falls to zero and the reactors connecting the two adjacent
sections each thus consume the total voltage during the transfer of
the short-circuit current. Strictly speaking, the transfer does not,
however, take place by a drop of voltage between the sections,
but by a phase displacement between the voltages of the bus-bar
sections, as explained later.
Bus reactors aflford, of course, no protection to the generators
connected to the section on which the trouble occurs, but they
give added protection to the generators on the other sections.
Transformer and Feeder Reactors. With modem high-voltage
transmission systems where the transformers are connected on the
unit principle so as to form a part of the transmission line, reactors
in the low-tension transformer leads (Fig. 291) may be of consid-
erable value for protecting against short-circuits in the lines,
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CURRENT-LIMITING REACTORS
467
where they, of course, mostly take place. Modem transformers
are, however, generally built with a comparatively high inherent
reactance, so that they can safely withstand short-circuits, and
reactors are, therefore, very seldom installed in this manner.
Reactors in low-tension feeders (Fig. 292) are, however, very
common and have many advantages. The probability of a
short-circuit in a feeder is far greater than in any other part of
the system, and the short-circuit current through a feeder switch
may be considerable, since the current from all the generators will
pass through the same and possibly also the current from other
m^
OOOOOOOO
Fig. 291. — ^Transfonner Reactors.
Fig. 292.— Feeder Reactors.
synchronous machines on the system. By means of feeder
reactors, however, such troubles may be still more limited than if
bus reactors were provided, and it is merely a question of cost
whether such reactors can be afforded.
Feeder reactors, of course, only give protection for those short-
circuits which occur on the feeders beyond the point where they
are installed, and do not give protection to short-circuits which
occur on the busbars or in the generators, transformers or their
connections.
Stdt System. This scheme (Fig. 293) was proposed by tne
late Mr. H. G. Stott, of the Interborough Rapid Transit Company
of New York, and is now being quite extensively used in connec-
tion with large steam turbine-driven central stations. The
feeders are grouped and fed from diflferent bus sections which are
individually energized by generators deUvering current through 5
per cent reactors. The bus sections are normally operated sep-
arately but may be instantly connected by tie switches. To per-
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468
ELECTRICAL EQUIPMENT
mit this emergency connection, each generator in operation is
permanently connected to a common S3aichronizmg bus through
2 per cent reactors which keep the generators in step and also
serve the purpose of bus-tie reactors. When this scheme is em-
ployed with a bus divided into several sections the voltage regular
tion is much better when there is current exchange than when
Feeders
~^-
^-
>5 Per cent
oS Per cenl
I Generator I— < i ( Generator j__4 1 ( Generator ] ,
> 2 Per cent
>a Per cent
^yoclironlxidff Bob
Fig. 203. — Stott System of Reactor Arrangement.
ordinary bus-tie reactors are used. This is obvious from the fact
that to get the same protection as here obtained, 5 per cent bus-
tie reactors would have to be used and the energy exchanged
between two non-adjacent sections would suffer a large voltage
drop. If it is not considered necessary to protect the generators
themselves against current surges, the 5 per cent reactors may be
omitted.
Number of Reactors. The following is considered the best
practice for locating reactors in various circuits:
(a) For single-phase circuits a single reactor in one side of the
line.
(6) For tw(Hphase, four-wire circuits two reactors, one in one
side of the line of each phase.
(c) For two-phase, three-wire circuits one reactor in each of the
outside lines (as distinguished from the neutral or conunon wire).
(d) For three-phase circuits one reactor in each line.
Size of Reactor. The selection of proper reactors for a system
requires, first of all, a complete investigation of the possible sboit
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CURRENT-LIMITING REACTORS 469
circuit currents which are liable to be set up due to faults in the
various parts of the system. When a short-circuit occurs, the
maximum short-circuit current is hmited by the total eflfective
impedance at that instant in the generators, transformers, and
transmission lines to the fault in question. This value is, how-
ever, not constant, but decreases rapidly until a value limited by
the synchronous impedance of the generators is reached (see
" Synchronous Generators," page 292). A sharp distinction must,
therefore, be made between an instantaneous and a sustained
short-circuit, the former being dependent upon the instantaneous
effective impedance of the system and the latter on the sustained
effective impedance. Except for long transmission and distribution
lines, the resistance is, as a rule, of such small value compared to the
reactance, that for all practical purposes it may be neglected and
the calculations based on reactance only instead of impedance.
As previously stated, a severe short-circuit may result in a
mechanical destruction of the apparatus or an overheating of the
same. The former is, of course, chiefly due to the instantaneous
current rush, while the sustained short-circuit current ordinarily
determines the thermal effect.
The instantaneous short-circuit current is readily calculated,
being equal to the normal current multiplied by 100 and divided
by the total reactance to the fault, expressed in per cent. For
modem water-wheel-driven generators the inherent reactance
varies from 15 to 25 per cent and for transformers from 6 to 10
per cent. As expressed in per cent it may be obtained from the
formula:
_ZXKv.A,
^ 10X£2 •
where p= reactance in per cent;
X= single-phase reactance in ohms;
E= voltage between phases in kilovolts.
The reactance in ohms per mile of one wire of a sjrmmetrical
three-phase circuit is
Z=2ir/L=27r/r^.74 logio|+.0805)l0-3l,
in which a = spacing between centers of conductors in inches;
r= radius of conductors in inches.
In considering the amount of current that will feed into a short
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470 ELECTRICAL EQUIPMENT
circuit, the 83aichronous apparatus connected to the system in the
form of load must, of course, also be taken into account, as on a
short-circuit there is a tendency for them to feed back into the
system, due to the inertia of their rotating elements. It is, of
course, also evident that strictly " spare " equipments need not
be included in the calculations.
In dealing with the effects of short-circuits we must consider
the damages which they may cause to generators, transfonners,
circuit breakers, cables or bus-bars and against which protection
must be provided in the form of reactors for limiting the excessive
currents to values which may be safely withstood by the apparatus.
Generators and transformers are, as previously stated, now
designed with such mechanical rigidity that they can safely with-
stand the mechanical forces arising from dead short-circuits across
their own terminals.
As far as oil circuit breakers are concerned, the problem is
much more difficult and their rupturing capacity is, as a rule, the
limiting feature in determining the value of the permissible short-
circuit current. The power which has to be broken on a short
circuit depends naturally on how quickly the circuit breaker opens
and also on the rate at which the short-circuit current dies down.
Due to inertia, it is, of course, impossible for a breaker to open
instantaneously and consequently no breaker is ever called on to
open the momentary short-circuit current that occurs during the
first few cycles, but it has to be strong enough mechanically to
resist the magnetic stresses set up dining such a short-circuit.
Large capacity breakers equipped with " instantaneous " acting
relays can be made to open in about one-quarter of a second and
if the short-circuit occurs close to the generating station the
power which has to be broken averages approximately 60 per
cent of the maximum instantaneous value. If the trouble should
occur at a considerable distance from the power-house, the rate
at which the short-circuit current dies down would be much
slower, so that the power which would have to be broken might
be nearly equal to the instantaneous value, but due to the addi-
tional reactance of the Une this value will, as a rule, be less than
the above, which, therefore, should be used in governing the cur-
rent which must be broken under the worst conditions. For non-
automatic switches or switches equipped with definite time limit
relays with a setting over 0.8 second, the rupturing capacity
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CURRENT-LIMITING REACTORS 471
corresponds to the sustained short-K^ircuit current, while, for
switches with inverse time action, the condition approximating
''instantaneous/' as above, must be assmned. The maximum
instantaneous value means the root-mean-square value 'of a S3an-
metrical wave. Similarly for the rupturing capacity of oil circuit
breakers, as tests have shown that the wave becomes practically
symmetrical in the minimum time in which a breaker can open.
There is a great variety of oil-circuit breakers in the market
with rupturing capacities of several hundred thousand Kv.A.
As a rule, switches with the higher rating will be required near
the generating station, while under some conditions smaller
switches may be used, for instance, in substations, where the
added reactance of transfonners and lines serve to reduce the
value of the short-circuit current.
The mechanical forces acting between the conductors of a
three-phase cable may be obtained from the following formula.
It is assumed that all three conductors are equally spaced and
simultaneously short-circuited, the r.m.s. current being equal in
each phase. Then the force, Fo, tending to repel any conductor in
a direction at right angles to a plane passing through the other
two is:
-, 4.67XPX10-7
/Tp- pounds per foot,*
where J = r.m.s. value of sine wave =
V2 '
a = Distance between conductors in inches.
Thus, in a paper insulated, lead-covered cable, the force is exerted
on the over-all wrapping around all three conductors and also on
the lead sheath, and the tensile strength of the paper and lead
must be sufficient to withstand the stress thus placed upon them.
On bus-bars this force tends to throw the bars away from the
center of the equilateral triangle of which each bus is assimied to
form one apex, and produces a tension or compression on the bus-
bar clamps, depending on the location of the insulators. The
bus-bars, due to their spacing being inherently greater than the
conductors of a cable, are subject to a much lower disruptive
force per unit length, but, on the other hand, since they are sup-
1 Gross, A.IJS.E., Jan., 1915.
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472 ELECTRICAL EQUIPMENT
ported at only frequent intervals rather than continuously, as is a
cable, the force on any support may become excessive.
The above refers to a three-phase short circuit. If, however,
the short is between two of the conductors instead of between
all three, the force will only be 86.6 per cent of the three-phase
value, based on the same current.
If the bus-bars are installed in the same plane, the force acting
on the outside bars is only 86.6 per cent of what it would be if the
bars were spaced at the vertices of an equilateral triangle.
The heating of cables may, on the other hand, be the limiting
feature as far as the permissible short-circuit current is concerned,
since it is quite possible for the temperature of the conductor to
rise to such a point as to endanger the insulation of the cable even
in the short time that it takes an oil switch to open, especially if it
is non-automatic or provided with a definite time-limit relay.
The calculations involved in determining the temperature rise are
intricate and the reader is referred to a paper by I. W. Gross in
A.I.E.E. Proceedings for January, 1915.
In calculating the short-circuit current let us, as an example,
first assume a system consisting of four 10,000 Kv.A. generators,
with 10 per cent inherent reactance, operating in parallel on a
bus. With a short circuit in one of the step-up transformers,
what would be the required instantaneous rupturing capacity of
the low-tension transformer circuit breaker?
Since the four generators are connected in i)arallel, the com-
bined reactance will be equal to -j-=2.5 per cent and the total
10000
short-circuit current, expressed in Kv.A., equal to ^ _ XIOQ
2.5
=400,000 Kv.A. The bus-bars must then be designed to with-
stand the mechanical stresses due to twice this current on account
of the possible unsymmetrical nature of the cmrent wave, while
the rupturing capacity of the switch would have to be about 60
per cent of the above, or 240,000 Kv.A.
As far as the generators themselves are concerned, it has pre-
viously been stated that those of modern design are now being
designed to safely withstand short-circuits. The generator
switches under the worst condition, i.e., with a short in one
of the generators, would be called upon to break the combined
current of only three generators, and as these switches as a rule
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CURRENT-LIMITING REACTORS 473
are made non-automatic, it would only be the sustained value of
the current, thus probably about two and one-half times the
normal rating or 75.000 Kv.A. With an automatic voltage
regulator holding up the excitation, this value would, however,
be greatly increased.
If the inherent reactance had been less than the above, or the
capacity of the generators greater, it might have been necessary
to install external reactors in the generator leads to limit the
short-circuit current which the switch would have to rupture, as
shown in Fig:^289. This is, however, never done in hydro-
electric stations, and if such a condition should arise the bus is
generally sectionalized by means of reactors as shown in Kg. 290
and as explained in the following.
As previously stated, the purpose of installing bus-bar reactors
is to limit the amoimt of current that can flow into a fault in one
section of the bus-bars, and so confine the disturbance to that part
of the system on which the fault occurs. Bus reactors should
have a reactance sufficiently high so that in case of a short-circuit
on one bus section the voltage of the adjoining sections is not
seriously disturbed by the current flowing from them over the
reactors into the short-circuit. On the other hand, it is highly
desirable to operate all the generators of the station in parallel,
and this necessitates a reactor of a low enough reactance to permit
the interchange current between the bus sections to take carp of
the required distribution of the load along the bus.
The amoimt of reactance to be installed involves a careful
study of the layout of the system. Probably a value allowing a
transfer of power equal to the capacity of one generator (one-half
from each adjacent section), may be considered sufficient. If
then each generator had a short-circuit current of eight times
normal full-load cmrent, the value of the reactors would have to be
25 per cent, based on the full-load current of one generator, and
the current carrying capacity would have to correspond to one-
half of the full-load cmrent of one generator, this being the full
load on the reactor. The displacement between the sections on
the above assmnptions would be approximately 7^*^, a value at
which the generators of the sections could safely be maintained in
parallel. As a fact, this could be done safely at twice this angle
and they would probably not fall out of step until the displace-
ment was three or four times this value.
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474 ELECTRICAL EQUIPMENT
The number of sections into which a bus should be divided
depends largely upon the individual sytem, and the conditions
under which it is expected to operate. In the above example,
with four generators on the section, the total power which an oil
switch may be required to rupture would be equivalent to the
short-circuit current of five generators or forty times the full load
of one generator. If the generators were rated, say, 20,000 Kv.A.,
and the switch equipped with instantaneous relays, the switch
would have to rupture 40 X 20,000 X. 6 =480,000 Kv.A.
When dealing with the subject of bus reactors, it may be of
interest to consider their action a little more fully, and, in order to
obtain some idea of the angular relations of the currents and
voltages the following case will be considered.
Assmne an arrangement as illustrated in Fig. 294. The equip-
ment consists of four 20,000 Kv.A. generators, having a short-
circuit ratio of eight times normal full-load current. The bus is
divided in two sections by means of a reactor which will peraiit a
power transfer equivalent to one-half the capacity of one generator,
as shown. The power-factor of the load is 0.8 and it is assumed
that the generators are to carry equal loads and that the voltages
of the two bus sections A and B are kept the same.
It is at once apparent that the generators on section A must
supply 10,000 Kv.A. through the reactor to section B, and in
order to limit the amount to this value, a 25 per cent reactor is
required, this figure being based on the rating of one generator.
Based on the actual transfer energy (one-half the capacity of one
generator), it would be 12i per cent; thus, a total of 1250 KvA.,
three-phase, or 416 Kv.A. per single reactor.
The diagram illustrating the current and voltage relations may
be constructed as follows: Draw OA and OB, representing the
equal voltages of the two sections, in such a manner that AB,
which represents the voltage across the reactor, is 12J per cent of
OA. Since this voltage differs in phase from the current prac-
tically 90*^ (neglecting the reactor losses), it follows that the
angular position of the circulating current is midway between the
voltages OA and OB. OC represents the current on section A
lagging approximately 37*^ (cos <t> = .8) behind its voltage Oi,
while OD represents the current on section B, this, in turn, lagging
37*" behind the voltage OB. OC and OD should be drawn to scale
BO that theix lengths represent the actual proportions between the
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CURRENT-LIMITING REACTORS
475
loads; i.e., OC should correspond to 30,000 and OD to 50,000
Kv.A. CE and DF now represent the current flowing through
80,000 EtA.
Four 80.000 KvA, Generators
B I A
FkG. 2^. — Arrangement of Bus Reactor and Diagram Showing
Current and Voltage Relations.
the reactor, the phase position of these corresponding to the middle
line between OA and OB, The current of the generators on sec-
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476 ELECTRICAL EQUIPMENT
tion A is represented by the vector OE and that of the generatws
on section B by OF. It will, therefore, be noted that the current
through the reactor increases the load on generator A and de-
creases that on B. Similarly, the power-factor of the load on A
has been increased and that on B decreased. The projection OF
on OB equals the projection OE on OA showing that the energy
deUvered by the generators on each section is equal.
The size of feeder reactors depends on the size of the feeders,
the relation of their capacity to that of the generators and the
capacity of the feeder circuit breakers, i.e., their safe rupturing
capacity. In general, the reactor required for an overhead cir-
cuit will be lees than for an underground cable, because the former
usually has a higher reactance.
As an example, assume a 100,000 Kv.A. station, the inherent
reactance of the generators being such as to limit the short-
circuit current to six times full-load current. In case of a short
circuit on one of the feeders close to the bus-bars, not less than
600,000 Kv.A. would pass into the fault, and if the capacity of
the feeders were 3000 Kv.A., this would be equal to two hundred
times the normal capacity of the feeders and the reactance of the
generators would, therefore, only be equivalent to one-half per
cent reactance in the feeders.
If now a 3 per cent reactor is placed in each feeder the total
reactance will be equal to 3.5 per cent and the worst possible short
3000
circuit conditions would be equivalent to -^-r- X 100 =86,000
3.5
Kv.A., or 28.6 times the normal capacity. The voltage of the
bus instead of dropping to zero, would only be reduced to 28.6X3
or to approximately 86 per cent of its normal value.
Besides the above, the problem must also be dealt with from
the economical point of view. For example, the cost of the
different types and sizes of reactors must be compared, the space
occupied thereby must be considered as well as the eflFect which
the introduction of reactors may have in permitting less expensive
switches and apparatus to be used.
The magnitude and intricate connections of modem transmis-
sion systems makes the determination of the probable short-circuit
current at the various points a very tedious work, and, in order to
facilitate the calculations it is always desirable and almost neces-
sary to graphically represent the system in a diagram with the
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CURRENT-LIMITING REACTORS
477
reactances given for the different apparatus and circuits. Those
values should preferably be expressed in per cent, based on some
nominal capacity such as the capacity of the principal generating .
unit as previously explained. The procedure of calculation is
best explained by an example:
Assume a network, as shown in Fig. 295. The various por-
tions of the circuit have the per cent reactance indicated, all based
8ab.Sta.
z.ost
8ub.8W
Fig. 295. — Typical Connection of a Simple Transmission System.
on 10,000 Kv.A. Stations No. 1 and 2 are generating stations,
each containing a number of generators with a combined reac-
tance, as shown. For a three-phase short circuit at A, the short
circuit Kv.A. is found as follows:
6.2+3 = 9.2
3.3+1.52=4.82
1
1
1
=3.16
9.2 ' 4.82
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478 ELECTRICAL EQUIPMENT
3.16+3.54 s 6.7 total reactance of circuit from Station
No. 1 to short-circuit.
1.43+0.75=2.18
1
1 . 1
=0.685
2.18 ' 1
0.686+1.6=2.285
1
1
= 1.215
2.285 ' 2.6
1.215+0.765=1.98
1.98+7.4+2.5=11.88 total reactance of circuit from Sta-
tion No. 2 to short-circuit.
1
4.29 combined reactance £rom Station
6.7 ' 11.88
No. 1 and 2 to short-circuit.
100
f^X10,000=23.3XlO,000=233,000 Kv.A. afshort-dr-
4.A9 .,
CUlt.
The proportion of this furnished by Station No. 1 and Station
No. 2 may be found as follows:
^ : = .0842
11.88
Station No. 1:
1400
m^X233,000= 149,000 Kv.A.
Station No. 2:
^^X233,000=84.000 Kv.A.
In like manner the proportion of this Kv.A. that flows over
each individual portion of the circuit may be readily determined
In certain cases a system may consist of such a complex net-
work of lines so as to make the calculations exceedingly difficult
and the results consequently more or less uncertain. To aid in
the solution of problems of this nature, an electrical device has
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CURRENT-LIMITING REACTORS 479
been designed by which the results can be obtained directly and
with sufficient accuracy for most practical purposes.
It consists of a table under which are mounted a number of
rheostats of the disk type having the operating handles pro-
jecting through the top of the table as shown in Fig. 296. To
each handle is fastened a pointer which revolves over a graduated
dial on top of the table, the graduations being in per cent reac-
tance (actually resistance). The terminals of each of the rheo-
stats are brought out to metal blocks, also fastened to the top of
the table. These blocks contain holes in which may be inserted
Fig. 296. — Device for Calculating Short-circuit Currents.
taper plugs connected together by flexible leads so that the rheo-
stats can be interconnected in any desired manner. The resistance
of the rheostats is taken as representing reactance in an actual
system, and a rheostat may thus be set for any value of equivalent
reactance and plugged into the network if desired. Direct-
current at 125 volts is used for operating the table, the negative
side being connected to ground and when it is desired to place a
short-circuit on any part of the system, that point is simply con-
nected to the ground in such a manner as to establish a short-
circuit through the rheostats representing the generators and the,
rheostats representing the interconnected network of lines. The
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ELECTRICAL EQUIPMENT
current in any part of the sytsem can be read by means of an
ammeter.
For a more complete description of this calculating tabkthe
reader is referred to the " General Electric Review " for October,
1916.
Fig. 297 shows a complicated network in which a number of
generators feed a conunon bus at points separated by bus-bar
AX Kv-
-»m.wo Kv^
— nmr^
O
%!f
lOi
1 901,000
Kv-a.
ll9S,000
-v28,000 Kv^
— Tnnnr^—
O
19M
101,000
Kv-iu
-».7.000 Kv-A.
-/yyyip
116,000
Kv-a.
:iL«
-►5S,000 Kr-m,
-nnnp
Of
o
145,000
Kr-m.
SM,000
Kr-m,
3.1tf
1»T.M
7.1*
-»1S,000 Kr-fc
— ^I'lTV"
0'
18,000
Kv-ft.
SMf
Fig. 297. — Short-circuit Current Calculations.
reactors. The percentages of reactance given are based on 45,000
Kv.A. The short-circuit occurs at the point A. The solution of
this problem is rather involved, and it has been accomplished in
this case by means of the calculating table described, with the
results indicated on the figure.
Single-phase Short-circuit Currents. Heretofore, we have
dealt with three-phase or balanced currents. Of late years the
tendency has been more and more toward the operation of systems
with transformers connected in Y and neutral groimded on the
high-voltage side. When a ground occurs on the Une a three-
phase short circuit does not result but rather a single-phase short-
circuit. A brief outline of the method used in handling such
problems is given in the following, and for a more detailed study of
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CUREENT-LIMITING REACTORS
481
the subject the reader is referred to an article in the '' General
Electric Review " of June, 1917, by W.W. Lewis, entitled " Short-
Circuit Currents on Grounded Neutral Systems."
Referring to Fig. 298: Let G represent a generator, T\ a trans-
former with high voltage winding connected in Y and neutral
Fia. 298. — Single-phase Short Circuits.
grounded; T2 a transformer stepping down the voltage for the
load L. The ohmic reactance of the generator is represented by
xi; of the step-down transformer by X2] of the grounded trans-
former by z'y of the portions of line from transformer to the point
A by T/i and 2/2, and of the total length of line by y, E is the normal
hi^-tenaion voltage. All reactances, etc., are expressed in terms
of their high-voltage equivalents.
Assume a ground at A, Then currents will flow as indicated
by the arrows. The value of the current is expressed by the fol-
lowing equation:
t =
.577g
xi+z+yi
or expressed in per cent reactance based on the normal three-
phase line current I
100/
t =
per cent Izi+per cent ly i+per cent Iz'
Now consider the arrangement of Fig. 299, i.e., ungrounded
transformer Ti at the generating end and transformer T2 with
groimded neutral at the load end. The short-circuit current will
flow, as indicated by the arrows. The delta winding of trans-
former T2 serves to cause equal in-phase currents to flow in each
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ELECTRICAL EQUIPMENT
leg of the Y. The voltage drop in each part of the circuit is in
phase with the voltage of the short-circuited leg a-i, and the
^^ — y
Fig. 299. — Single-phase Short-circuit Currents
total voltage drop is equal to cr-d or 0.866B. The following equa-
tions may be written from the figure:
.8665 = i{xi+X2+y+2yi) +e,
2(e-iz)=i(y2+z);
from which we find
.866S
t =
(x.+..)+|+^^+|'
or expressed in per cent reactance based on normal three-phase
line current I
._ 100/
' i{%ixi+7oix2)+%iy+7oiyi+7oi^
Based on these fundamental equations it is possible to sdve
problems in cases involving a number of generating stations, a
network of lines, etc. As the number of generating stations
increases, however, the equations increase in complexity and the
solution becomes quite laborious. The labor is lessened some-
what by representing the network by an equivalent circuit with
the component parts expressed in per cent reactance and solving
either by the sUde rule or by the calculating table.
An example will illustrate this. In Fig. 300 let d and Gs
represent generators, Ti and T2 transformers with isolated neutrals
and Ts a transformer with grounded neutral. The percentages
of reactance based on 10,000 Kv.A. 100,000 volts and three-phase
are indicated.
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CURRENT-LIMITING REACTTORS
483
For a ground on one line at the point A, giving a single-phase
short-circuit, currents flow, as shown by the arrows. An equiva-
Fia. 300. — Calculation of Single-phase Short-circuit CuirentB.
-IM -3.M
FiQ. 301. — ^Elquivalent Short-circuit Corresponding to Fig. 300.
lent circuit for Fig. 300 may be drawn as shown in Fig. 301.
This circuit may be solved as follows:
10+3.33+4-1-4=21.33
12+4+10+10=36
1 1 1
1 . 1 .0469+. 0278 .0747
= 13.4
21.33 ' 36
3+2+3+7=15
13.4+15=28.4
100
ti+t2=^X/=3.52X67.7=203
0469
n = ^Q;^X203 = .628X203 = 127.5 amps.
0278
t2=^^X203=.372X203=75.5 amps.
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484 EILECTRICAL EQUIPMENT
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CURRENT-LIMITING REACTORS 485
Mechanical. Design. Current-limiting reactors must be de-
signed so as not to saturate at short-circuit when the full-circuit
voltage comes across the reactance, and for that reason they are,
as a rule, built without an iron core. There is, however, no the-
oretical objection to the use of iron and if, for example, a reactor
for say 25 per cent were required, it would be feasible and pos-
sibly even economical to provide an iron core, which, in such a
case, would have to have a normal magnetic density of one-
fourth the saturation. For 3 to 10 per cent reactors, however, an
excessive amount of iron would be required to prevent saturation
at short-circuits, thus making an iron core highly tmeconomical.
The latest construction of reactors is shown in Kg. 302. It is
known as the " cast-in " type because of the fact that the winding
is cast and directly supported in the concrete structure.
The conductor, which may consist of one or several cables in
multiple, is wound radially in conical layers, an ample factor of
safety being preserved between each and every turn. The adja-
cent layers are inclined in opposite directions with ample spaciogs
between the layers, the spacing varying with the voltage of the
circuit and the munbers of layers required. Ample spacing is
essential during short-circuit conditions since there is almost
always arcing at the point of short-circuit which may set up high-
frequency disturbances. Any two layers thus converge toward the
point where the interconnecting cross-over is made and where the
maximum voltage between the layers is consequently equal to
<that between turns.
The windings are held rigidly in their position by the vertical
coil supports which are cast around the turns after these have
been woimd in a form. The concrete is thereafter cured under
high steam pressinre which gives it a mechanical strength obtained
in no other way.
8. SWITCHING EQUIPMENT
The engineering problems in connection with the operation
of high-voltage hydro-electric transmission systems are very
largely those which have to do with preventing interruptions to
the service and which isolate and localize electrical disturbances
before they can become of a general nature. This resolves itself
not only into the general design of the apparatus but also to a
careful study of the best possible arrangement of the different
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486 ELECTRICAL . EQUIPMENT
circuits and the method of switching. Reliability and contin-
uity of service are the main considerations, but besides this the
protection of the apparatus from injury should not be lost sight of.
The switching equipment is the key to the entire system, and
the first requisite to decide on is the system of connections, the
diagram of which should be worked out with the greatest care,
taking into consideration the various equipments and the normal,
as well as possible abnormal, operating conditions of the entire
system. The design of the control boards and the selection and
arrangement of the oil circuit breakers, bus-bars, etc., depends
greatly on the system of connections; in fact, the design of the
entire power-station.
In taking up the various problems dealing with the design of a
switching equipment, space will only pennit the fundamental
principles to be dealt with, and only some of the more important
apparatus can be briefly described. It would be of Uttle value to
go into the minute details of the engineering features connected
with a switching equipment because the art changes so rapidly,
and new and improved lines of apparatus are brought on the
market so rapidly, that they change for ahnost every new impor-
tant installation.
System of Connections and Relay Protection. In laying out
the S3rstem of connections and the protective switching and
relaying equipment for a high-tension transmission sjrstem, there
are a number of general principles which must be kept clearly in
mind. Chief among these is continuity of service which is now of
prime importance and this has been brought about mainly by
the steadily increasing demand for a much higher standard of
service than formerly. This, in turn, involves a flexibiUty in the
arrangement of the connections so as to reduce to the absolute
minimum the amount of apparatus which will be automatically
disconnected in case of trouble, and also to provide for sectional-
izing any apparatus for inspection and repairs. Besides this, the
protection of the apparatus from injury should be given careful
study. These considerations are, however, very closely con-
nected and must naturally be treated together. In this connec-
tion it should be noted that the function of an automatic selective
switching is not any longer correlated to the idea of protecting
the apparatus against ordinary overloads, but that the relays are
intended to operate only on breakdowns, although their setting
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SWITCfflNG EQUIPMENT 487
is usually given in per cent overload of the rated capacity of the
circuit.
The particular system of connections to be used depends
obviously on the conditions to be met, and each system must
be studied and an individual solution applied. There are, how-
ever, many points of similarity, and the solution in one case will
serve as a partial guide, at least in others. In any event, the
system as a whole should be carefully considered in deciding on
the connections, and the conclusions should not be based on the
condition in a generating station or a substation alone. The
characteristics of the customer's load conditions must be care-
fully investigated and futiu*e probable loads and additions pre-
determined as far as possible.
It is especially essential to provide an uninterrupted service
for large and important customers, as the success of the project
depends in most cases entirely on the ability to maintain a satis-
factory service for these, but, on the other hand, the smaUer cus-
tomers must also, of course, be considered and given the best
service possible. For this reason the power to important cus-
tomers is often supplied from two sources, such as from two sub-
stations or by means of double-line circuits, etc. Two such
sources of supply are, of course, the ideal arrangement, in which
case one of them would be automatically cut out in case of trouble
while the other would be kept in operation and continue to carry
the load. This, however, is not always possible for every cus-
tomer.
In a general way the service of a large power system with its
transmission and distributing lines can be likened to a combined
express and local train service of a transportation company. The
transmission lines feeding the different substations on the system
correspond to the express trains and must be absolutely free from
interruption, for which reason such lines should be so arranged
that any substation is fed by two independent circuits. The
local train service would, on the other hand, correspond to the
distributing liDes, and any interruptions which might be per-
mitted to occur, should be confined to these local circuits. Of
course, if the service demands, even these circuits can be installed
in duplicate.
In a power transmission system the chief source of trouble is
always the transmission line and it can mostly be traced back to
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488 ELECTRICAL EQUIPMENT
the insulators. This subject of insulator design has been studied
very carefully during the past few years and great improvements
have been made, but they have as yet an apparent deterioration
causing breakdowns from time to time. Together with atmos-
pheric disturbances in districts frequented by Ughtning storms, it
makes the transmission line a vulnerable part of the system and
the largest percentage of troubles is caused, thereby. Apparatus
troubles are furthermore often traced directly to line troubles as a
secondary cause from arcing groimds, surges, etc.
The secret of success in relay protection is speed. That is,
the faulty sections should be cut out so rapidly as to prevent the
synchronous apparatus connected to the system from falling out
of step and stopping. The time limit for this differs, however,
depending on the stability of the apparatus and where the short-
circuit occurs. The closer ^o the machines, the shorter the time
before they drop out.
The longer an arcing ground hangs on, the more damage
it will do in breaking insulators and melting off the transmission
wires. The arc is very small to begin with, but increases rapidly
in size and should therefore be quickly cleared so as to cause as
Uttle damage as possible.
Interruptions can, in many cases, be traced to the customer's
own fault. For example the motor breakers may be set at such
low-tripping value, that if the power of the system should mo-
mentarily drop off and come on again, the heavy current rush
would trip the breaker and disconnect the machine. To provide
against such interruptions the breaker need, of course, only be
set for a sufficiently high value. Similarly, with motor breakers
provided with low-voltage releases, which would cause the motor
to be cut off from the system on any momentary voltage drop unless
provided with a time-limit device. Such relays should therefore
be avoided as far as possible if strict continuity of service is
essential.
The time in which a fault might be cleared depends naturally
on how quickly the switches may disconnect the faulty section.
This in turn depends on the rapidity of the switch action, and on
the characteristics of the relay which is used for closing the trip-
ping circuit of the oil circuit breaker.
Due to the inertia of the moving parts it is, of course, impos-
sible for a breaker to open instantaneously, and it requires approx-
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SWITCHING EQUIPMENT 489
imately one-quarter second for a large breaker to open after the
tripping coils have been energized. The time interval between the
moment at which a short-circuit takes place and the moment at
which the tripping circuit of the breaker is closed may be varied
at will by selecting relays of different time settings.
By means of such overload relays in connection with reverse
power, balanced, differential and pilot wire relays, the character-
istics and uses of which are described in the section on " Relays,"
it is possible to obtain a selective automatic switch action, which
will only disconnect the faulty section of the system without
interrupting the remainder thereof. The types of relays and their
arrangement to accomplish such a result depend entirely on the
system of connection and the conditions to be met.
The generators should preferably be paralleled on a low-
tension bus and this should be arranged so that it can be inspected
and cleaned from time to time without shutting down the sta-
tion. With smaller stations a single bus may be sufficient and
by sectionalizing the same the operation may be so arranged that
one section can be cleaned when the units belonging thereto are
cut out during Ught load. As a rule, however, important stations
should be provided with double generator buses (Fig. 303) and
the generators connected thereto either by means of double oil
circuit breakers or by means of one common oil circuit breaker and
two sets of disconnecting switches, one for each bus. Double
oil circuit breakers are preferable as they permit the transfer to
be done entirely from the main switchboard and thus insures a
speedier operation. This also applies to the transfer on the high-
tension side, and in this case it is even more important, due to
the greater difficulty of manipulating the large high-tension dis-
connecting switches. Double oil circuit breakers further permit
of inspection and repair of one breaker, while the other is in service.
The low-tension buses should, furthermore, be sectionalized
if the capacity of the station is large, so as to limit the short-cir-
cuit current to a value which can safely be ruptured by the oil-
circuit breakers, as fully described in the section on " Curren1>-
limitmg Reactors."
The transformers should preferably be grouped so as to
forai units with the lines and with such an arrangement the
double low-tension bus is preferable in order to obtain the most
flexible method of transfer.
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490
ELECTRICAL EQUIPMENT
Stations may, however, be found in which the transformers
are grouped with the generators, as in generating station C (Fig.
T
'Snb^titiOD
FiQ. 303.— Tjrpical System of Connections.
305). In such a case a parelleling bus may be omitted and simply
a low-tension transfer bus provided.
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SWITCHING EQUIPMENT
491
'SubYI
T. T .^snbin:
8«b ymt^y^ 4?j'a'"' IT
.' > ■ I
I '. ! I.
d Q
f 4 f *
^Sabn
PJ tZ^ ? 't'
B ?:?
^
«»^
f>f^f^ .g^
Oeneratioff
SteUpQ
Fig. 304. — ^Typical System of Connections.
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492 ELECTRICAL EQUIPMENT
The reason for grouping the traneformers with the lines is to
avoid switching on the higl:\-tension side of the transformers.
Paralleling of the high-tension side should also be avoided and this
appUes especially to delta-connected transformers where the surges
set up by arcing grounds on one line may be transmitted to the
other line. With transformers having the high-tension windings
Y-connected and the neutral grotmded, paralleling on the high-
tension side may not be so serious and may in certain cases be
advisable for the sake of flexibility.
Means should, however, always be provided for transfer
on the high-tension side, and this may be done in various ways
as indicated in Figs. 303 and 304, in the former case simply by a
tie between the two lines and in the latter by a transfer bus.
Such means for transfer should also be arranged at intervals
along the transmission lines, perferably at substations (Fig. 305),
or places where branch lines are tapped to the main line.
It is customary to make the generator circuit breakers non-
automatic, but for very large and important imits it may be
desirable to protect them against internal short circuits, which is
readily accomplished by means of differential relays as described
under " Rela3rs."
The switch and relay protection of the transmission lines, tie
lines, etc., is very compUcated and no general rules can be given
except to state that the protective features should be of such a
selective nature that when trouble occurs, the section involved
should be inmiediately disconnected without the dropping of
imnecessary load or power. The protective devices to accomplish
this depend entirely on the conditions involved and are best
explained by considering a few typical examples.
Example I: This refers to a system as illustrated by the
disgram in Fig. 303 and consists of one generating station feeding
a single substation over two parallel transmission lines.
All the high-tension Une circuit breakers are non-automatic
and are only intended for sectionalizing purposes, as are the high-
tension tie breakers, which should be open under normal operation
so that the system would only be operated in paraUd on the low-
tension side of the step-up as well as the step-down transformers.
The low-tension transformer circuit breakers in the generating
and substation respectively should be of the automatic tjrpe, the
former being provided v^th time-limit relays and the latter with
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SWITCHING EQUIPMENT
493
OeDeratlDff- Station jL
Fig. 306. — Typical System of Connections.
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494 ELECTRICAL EQUIPMENT
reverse power relays in connection with overload relays which,
in a system of this kind, can be set for practically instantaneous
action.
The time settings of the relays should, in general, be so arranged
that the substation circuit breaker trips out first and then the
breaker in the generating station, thus disconnecting only the
faulty line. The load is then shifted over to the other line which
remains in service and may overload the transformers of this hne.
This will not cause any danger, as transformers can readily cany
up to 100 per cent overload for a few minutes until the operator
has had time to open the high-tension circuit breakers of the faulty
line and close the tie circuit breakers and the low-tension trans-
former breakers, thus again paralleling the transformers. The
overload relays on the generating station breakers should, there-
fore, be set sufficiently high so that they can carry the entire load
without tripping.
The outgoing substation feeder circuit breakers should be
equipped with inverse time-limit relays set proportionaDy lower
than the overload relays in the generating station. In a system
of this kind the time element may be very short, which is an
important item, as previously mentioned. The substation line
relays can, therefore, be set for instantaneous action on reversal
and, in such a case, the generating station overload relays need
only be set for a second at the most. The feeder relays may also
be set for nearly instantaneous action in order to have them trip
before the overload line relays in the generating station.
Example II: This refers to a somewhat more complicated
system, as illustrated in the diagram. Fig. 304. It consists of
one large generating station still feeding one main substation from
which several distribution systems are supplied.
The main substation in this case is fed over three parallel
transmission Unes and as far as the relay protection for these is
concerned, it may be done in the same manner as explained in
Example I, but interconnected reverse power relajrs may also be
used in either case.
The first consideration in relaying a system of this kind is to
keep the power on the main substation bus, no matter what hap-
pens, and in protecting the various circuits beyond, the sub-
station bus may be treated just as if it were the generating sta-
tion bus.
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SWITCHING EQUIPMENT 495
Substations II and III are fed in tandem, the fonner by three
parallel transmission lines and the latter by only two, and the
relaying of these lines should be identical with the main trans-
mission lines with the exception, of course, that the time settings
have to be proportionally lower. This clearly demonstrates the
point of graded time settings, and it is evident that the circuit
breakers furthest away from the generating station should have the
lowest setting and the succeeding relays in each section, counting
towards the generating station, should each have an ^increase in
the time element of about half a second. This may put an
excessive time on the breaker nearest the generating station and,
in that case, by the use of inverse time limit relays without def-
inite minimum time setting, taking advantage of both the time
and current difference, it may be possible to considerably shorten
the time on all the relays. This usually involves a careful calcu-
lation of the actual short-circuit values to determine the required
settings. In certain cases where the time setting of the relays
nearest the generating station has become rather high, it has been
the practice to also install an instantaneous overload relay in
parallel with the time limit relay on the circuit breaker nearest the
generating station and to set this relay very high, the idea being
that, in case of a severe short-circuit, it should disconnect the cir-
cuit inamediately. The use of such an arrangement is, however,
questionable as it often happens that the instantaneous relay
acts when it should not, thus crippling the entire service of all the
sections in the series.
Substations IV to VIII are connected on the ring system prin-
ciple and the relaying can be done in several ways. One way
would be to provide reverse power and overload relays on the
incoming line circuit breakers in each substation and inverse time
limit relays on the outgoing line circuit breakers, this being, of
course, on the assumption that the power is being fed into station
VI over both lines. Circuit breakers a, c and e would then be pro-
vided with overload relays only and /, d and h with reverse power
relays in combination with overload relays. The settings of the
overload relays would be in the following order: a, c, 6, /, d and 6;
a having the highest setting and 6 the lowest.
Example III: This illustrates a system consisting of three
generating stations feeding a number of substations, the con-
nections, as illustrated on the diagram Fig. 305, being on the
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496 ELECTRICAL EQUIPMENT
ring principle. In a case of this nature the current is liable to be
fed in either direction at any time, and the protection would best
be accomplished by equipping all the circuit breakers where
parallel connection is made by balanced or interconnected reverse
power relays. Where transformers are involved this would be on
the low-tension side of these, the interconnection being between
similar phases of the two parallel lines.
Where balanced current conditions may be assured, the
relays may be set for instantaneous action, otherwise it might be
necessary to impose a slight time delay. In case one line should
become disabled it will then immediately be disconnected and
arrangements can be made whereby the circuit breakers of the
other line would be automatically provided with time-limit fea-
tures by the opening of the circuit breakers of the disabled line.
Oil Circuit Breakers. Oil circuit breakers are nearly always
used for rupturing alternating-current circuits, due to the fact
that they do not cause any abnormal disturbances in the circuit,
and because they confine the destructive effects of the arc to
a small volume. One of the distinctive features of the oil circuit
breaker is that the current is interrupted when the current which
is maintaining the arc passes through zero, at which point the
electro-magnetic energy is minimum. It remains so until the
voltage between the contacts rises to a sufficient value to punc-
ture the oil insulation. When this takes place the flow of cur-
rent is reestablished and flows for another half cyde and so on
imtil sufficient insulation is interposed between the contacts to
resist the maximum voltage. This feature is taken advantage of,
and modern oil circuit breakers are designed with a view of utiliz-
ing the pressinre developed by the arc to introduce a large amount
of oil between the contacts.
Owing to the great range and the amount of current, voltage
and power to be handled by oil circuit breakers for such cir-
cuits, various types have been designed to suit different conditions.
For moderate amoimts of power, where the size and cost of the
breaker is to be kept to a minimum, it is often possible to locate
all of the poles of the breaker in one oil tank. For slightly larger
amounts of power, each pole is placed in a separate oil tank, but
all poles are mounted on the same frame; for still greater amounts
of power, at moderate voltages, each pole is in a separate tank,
and each tank is in a separate masonry compartment, while for
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SWITCHING EQUIPMENT 497
very high voltage work, each pole is in a separate steel tank of
such substantial construction as to be proof against any explosion
due to the effect of short circuit.
The circuit-breaker rating should be based on the maximum
current which it is to carry continuously without overheating, and
a breaker. should therefore be selected which has a capacity at
least equal to the maximum rating or the one or two-hour overload
rating of the circuit. At the normal rated- load, current-carrying
parts should not heat more than 30° C, above an ambient tem-
perature of 40** C, providing the connections to the breaker do
Act heat to a greater extent. The rise on tripping solenoids and
accessory parts shall not exceed 50° C. The dielectric test should
be 2\ times rated voltage plus 2000.
In selecting the proper type of breaker to use for a certain
case, it is not enough that the breaker has a sufficient current-
carrying capacity or that it is capable to withstand the operating
voltage. The amount of energy or kilovolt-amperes which the
switch may be called upon to rupture under abnormal conditions,
such as a short-circuit, is a very important matter and deserves
the most careful attention.
Based on its rupturing capacity, the rating of an oil circuit
breaker is necessarily more or less empirical, and is generally
determined by exhaustive short-circuit tests. It depends prin-
cipally on the amount of oil over the break at the starting of the
arc, the amount of space above the oil for gas expansion, the shape
and strength of the oil tank and its fastenings and on the length
and rapidity of the contact movement.
There are many different ways of rating oil circuit breakers,
but it appears that the most logical way would be to base the rup-
turing capacity on the maximum " instantaneous " kilovolt-
amperes which the switch would be capable of rupturing. By
" instantaneous '' is here meant the elimination of time-limit
relays in tripping. The problem of choosing an oil circuit breaker
for a given location would then resolve itself in determining the
kilovolt-amperes that can be delivered on short-circuit through the
breaker. This value depends naturally on how quickly the oil
circuit breaker opens and also on the rate at which the short-
circuit current dies down. Due to inertia, it is, of course, impos-
sible for a breaker to open instantaneously, and consequently no
breaker is ever called on to open the momentary short-circuit
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498 ELECTRICAL EQUIPMENT
current that occurs during the few first cycles, but it has to be
strong mechanically to resist the magnetic stresses set up during
such a short-circuit. Large-capacity breakers equipped with
" instantaneous " acting relays can be made to open in about
one-quarter second, and the power which has to be broken under
such conditions averages under the worst conditions approxi-
mately 60 per cent of the maximum instantaneous value. For
non-automatic switches or switches equipped with definite time-
limit relays with a setting over 0.8 second, the rupturing capacity
corresponds to the sustained short-circuit current, while for
switches with inverse time action the condition approximating
"instantaneous," as above, must be assiuned. When speaking
of the maximiun instantaneous value, the root-mean-square value
is meant.
There is a great variety of oil circuit breakers in the market
with rupturing capacities of several hundred thousand Kv.A.
As a rule, switches with the higher rating will be required near the
generating station, while under some conditions, the added react-
ance of transformers and lines serve to reduce the value of the
short-circuit current. (See also section on " Current-limiting
Reactors.")
Unfortimately there is some difference in rating oil circuit
breakers, and it is very important, in any oil circuit breaker nego-
tiation, that the actual meaning of the guarantee is fully under-
stood. So, for example, the term "rupturing capacity" has
been given two meanings; one, as indicating the rated Kv.A.
capacity in generators which may be short-circuited and under
such conditions opened by the breaker in question; the other, as
indicating the actual current which the breaker opens at the time
of short-circuit, this capacity generally being expressed in Kv.A.
equivalent to the actual current opened at the normal circuit volt-
age. Furthermore, the term " ultimate breaking capacity " has
been used to indicate either of the above conditions, and it can be
seen inmiediately to what confusion this difference in the meaning
of the guaranteed rating can lead. The importance of a clear
understanding of just what is meant cannot be over-emphasized.
Fig. 306 represents a type of circuit breaker which is intended
for use in small and moderate-capacity stations for voltages up
to 22,000. It can be mounted on the pipe frame supporting the
switchboard panels, on framework remote from the panel, or in
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SWITCHING EQUIPMENT
499
cells, depending on the ampere capacity or the voltage. It may
be operated by hand from the switchboard by means of operating
rods through a system of bell
cranks, or electrically by
means of a solenoid con-
trolled from the main switch
board.
The stationary contacts
consist of copper fingers
flared at the tips, one ex-
tending so as to act as an
arcing tip. The movable
contact blades are wedge-
shaped, confining the arc of
the blade, protecting the
actual contact surfaces from
the damaging effect of the
arc.
The oil vessel is of heavy
sheet metal hned with treat-
ed laminated wood. Multi-
pole switches of smaller
capacity have all poles in one tank with treated wooden barriers
between each pole, while for larger capacities one tank is pro-
vided for each pole.
In the more important large capacity stations where it is of the
utmost importance to prevent trouble in any one circuit or phase
being conmiunicated to other pants of a station or system, the oil
circuit breakers are located in separate compartments, and in some
cases barriers isolate each phase, and even each oil tank is separated
if additional safety factors are desired.
The oil circuit breaker with the highest rupturing capacity
which has so far been put into service is of the general type shown
in Fig. 307 and its ultimate development with maximum isolation
in Fig. 308.
These switches are generally known as type H, and are made
for carrying very high currents (up to 4000 amperes), and are most
generally used for the ordinary generator voltages up to 13,200,
although they can be obtained for voltages up to 70,000.
Each pole is made up in part, of two separate seamless steel
Fig. 306. — Small and Moderate-capac-
ity Oil Circuit Breaker. Remote
Controlled and Mounted on Pipe
Frame Work.
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500
ELECTRICAL EQUIPMENT
vessels, in each of which the circuit is broken under oil. There
are thus two breaks per pole, the general construction of the oil
vessel being apparent from Fig. 309. Each contact consists of a
Fig. 307. — High-capacity Motor-operated Oil Circuit Breaker with Two
Tanks for Each Phase, and Phases Isolated from Each Other.
metal rod which bears against the inner surface of four longi-
tudinal segments of a cylinder secured in position by helical
springs. This arrangement insures a heavy and imiform contact
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SWITCHING EQUIPMENT
501
pressure, and automatically compensates for any wear of the
surface of either the stationary contact segments or the contact rod.
When the arc is ruptured, whatever burning results takes place
on the bell mouth of the stationary contact segments or on the
Lik.
Fig. 308.— High-capacity Oil Circuit Breaker with Tanks Arranged in Tandem
and Separated by Barriers.
rounded end of the movable contact rods, and in no case causes
damage to the working contact smfaces. The contacts are self-
aligning and easily renewable.
For higher-current capacities, however, additional primary
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502
ELECTRICAL EQUIPMENT
contacts are provided. These carry the greater part of the
current flowing through the switch and obviate the necessity of
having large currents to pass within the oil vessel. These nuiin
contacts are outside the oil ves-
sel but inside the fireproof com-
partments of the ceU, and so
placed as to secure the maxi-
mum radiation. In opening the
breaker they break contact be-
fore the contact rod, which opens
the circuit and ruptures the con-
sequent arc under oil. The main
contacts are of the laminated
brush type or of the ordinary
wedge-shaped finger type.
To prevent throwing oil, a
baffle is used in each oil vessel.
By the baffle, the movement im-
parted to the oil by the expan-
sion of the gases formed by the
arc when the circuit is opened
imder load is checked and di-
verted in such a manner as to
allow the gases to separate from
the oil and escape through the
vent in the cover of the oil ves-
sel, while the oil itself is forced
back into the region of the break-
ing arc under pressure, thus
shortening the time of breaking
the arc, confining the disturbance
or explosive effect on short cir-
cuit and practically eliminate
flashes due to hot gases and the
oil from the oil vessels. The
movement of the oil away from
and towards the center of the oil
vessel on the breaking of the cir-
cuit and also the movement of
the gases, are indicated in Fig. 309. The oil loses its velocity
Fi«. 3n9.— Oil Vessel for High-
capacity Oil Circuit Breaker
Showing Oil Baffle Arrangement
and Contacts.
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SWITCHING EQUIPMENT 503
before the cover of the oil vessel is reached and, therefore, its
tendency to be thrown out is reduced.
For each vessel there are two insulating bushings. The upper
one is clamped to the oil vessel cover and serves as guide to the
movable contact rod and also insulates the rod from the oil vessel.
The bottom bushing is fastened to the base supporting the oil
vessel by means of a metal clamp which holds it in proper align-
ment. Generally these switches are bottom connected but can
be obtained for combination bottom and back connection.
The operating mechanism is located above the cell structure
and connected to the contacts by operating rods of specially
treated wood. Direct-current motor drive is reconmiended for
use whenever possible, and when no other suitable source of direct
current is available, a storage battery with motor generator for
charging may be installed. (See ** Oil Circuit Breaker Bat-
teries.") Alternating-current motors can be furnished if for any
reason direct-current operation is not practicable. It should be
borne in mind, however, that with alternating-current motor
operation, a constant source of alternating current should be
available unless it is agreeable to close by hand some oil circuit
breaker, which would provide the necessary operating current.
This type of breaker is, of course, always controlled by the
control switch on the main switchboard. It may be non-auto-
matic or automatic, the latter feature being obtained by circuit-
closing relays, with the relay contacts connected in multiple with
the contacts of the opening button of the control switch. When
the relsLys operate, they close a direct-current auxiliary circuit
through the tripping magnet of the oil circuit breaker and it
immediately opens.
Fig. 310 illustrates Si, line of tank-type oil circuit breakers which
is used for stations of moderate and large capacity for voltages
from 35,000 to 110,000. Indoor and outdoor breakers are prac-
tically similar. The only difference consists of the addition to the
indoor breaker of a few parts to enable it to be serviceable both
from a mechanical and an electrical standpoint under all weather
conditions.
A noteworthy advance in these breakers consists of mounting
them on framework and in the handling of the tanks by a tank-
lifting device. Such a construction, however, is limited to
switches below 110,000 volts. The Ufter consists of a detachable
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ELECTRICAL EQUIPMENT
frame equipped with shaft, handle worm gear and winding and
unwinding drums. The advantage of this equipment is that it
allows a tank to be removed or placed in position without diffi-
FiG. 310. Typical 35,000- volt Oil Circuit Breaker of the Tank-type Cto-
struction Mounted on Framework.
culty. The device is readily detachable and can be moved by one
man from one breaker to another. These breakers are always
top-connected and self-contained. They are made for either
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SWITCHING EQUIPMENT 605
automatic or non-automatic operation, and may be closed by hand
or solenoids.
The automatic breakers are tripped under overload by series
trip coils or secondary relays, the latter method being almost
entirely used in modern installations. The secondary tripping
mechajiism consists of a system of toggles and latches so con-
structed that only a slight pressure is needed to open the breaker.
The tripping coils may be energized from standard current trans-
formers, from bushing-type current transformers or from a source
of constant potential, the current adjustment being accom-
plished by varying the position of the plunger in the trip coil and
the inverse time relay by a dashpot. (See also " Relays.")
The operating mechanism is secured to the cast-iron cover of
the heavy welded sheet-steel tank. There are two fixed contacts
. in each switch element between which one phase of the circuit is
made and broken by a horizontal contact blade. Each contact
blade is connected to the operating mechanism by a specially
treated, hard wooden rod which passes through the cover of the
switch in an insulating bushing. The stationary contacts con-
sist of widely flared fingers and long arcing tips which also act as a
guide to the entering blade. The movable contacts are wedge-
shaped, which confines the arc to the top edge of the blade and
the flared portion of the finger tips. The contacts are always
smooth and bright due to the sliding effect which they are sub-
jected to on opening and closing, and the arrangement of the
burning tips.
The design of the bushings depends entirely on the voltage for
which the switch is intended. For the 35,000-volt size, they are
made in one piece of wet porcelain and extend from the terminal
to the contacts below the oil. For higher voltages each bushing
consists of two porcelain sections, an upper and a lower, joined
together by heavy supporting iron flanges, which also serve as a
means of attaching to the breaker or for housing the bushing trans-
formers, where such are required. For moderate voltages the
contact rod which passes through the bushing is simply insulated
by an insulating material and the bushing filled with an insulating
compound of high dielectric strength. For higher voltages, 70,000
and above, the bushings generally contain a number of cylinders
of insulating material concentric with the conducting tube, the
whole being filled with compound. These cylinders in connection
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ELECTRICAL EQUIPMENT
Fia. 311.— 135,000- volt Oil Circuit Breaker. Front Unit Supported on Frame-
work to Show Interior Construction.
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SWITCHING EQUIPMENT 507
with equalizing shields serve to evenly distribute the potential
gradient of the bushing.
For each pole there is a separate oil tank provided with gas
vents and oil gauges. Drain-cocks may also be obtained if desired
and are to be recommended for all large floor-mounted switches.
Pig. 311 shows a large-capacity tank-type oil circuit breaker for
indoor services at 135,000 volts. It is almost identical to the
switches previously described, the main points of construction
being apparent from the illustration. At the upper end of each
bushing is a combined expansion chamber and gauge glass which
affords opportunity to view at all times the insulating compound
with which the bushings are filled. The terminal on the upper
end of a bushing is of such shape that it can be used for attaching
a crane hook to lift the bushing out of or replace it in the breaker.
High-grade mineral oil should be used for all oil circuit breakers.
It should have a high flash and ignition point as well as high
resistance to carbonization.
Relays. Relays may be defined as protective devices used in
connection with circuit breakers to disconnect any part or section
of a system on which a fault occurs but leave the rest of the system
in operation without being further affected by the faulty section.
In general, a relay consists of, first, a coil or system of coils con-
nected either directly in series or in parallel with the circuit con-
trolled or to secondaries of current or potential transformers, the
current and potential coils then being wound for a low value,
usually five amperes for the current coil and 110 volts for the
potential coil, although other values might be used if desired.
In the former case it is termed a primary or series relay and in the
latter a secondary relay. Second, a relay consists of a movable
part such as a plunger or a revolving disk, etc., whose travel is
controlled by the relay coils, and third of a contact device which
is actuated by the movable part and which controls the operating
circuit, such, for instance, as the trip coil of the circuit breaker
to which it is connected. Although smaller circuit breakers
may be opened by the relay core striking the tripping latch
directly, larger breakers are usually provided with separate
tripping coils, the cores of which, when completing their travel
strike the latch and release the switch.
The impedance of a relay coil is relatively small compared to
that of an oil circuit breaker trip coU, and if a nimiber of instru-
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ELECTRICAL EQUIPMENT
ments and meters are connected to a current transformer their
accuracies are naturally affected by the total load imposed on the
transformer secondary, decreasing rapidly as the load rises above
a certain point. Some oil circuit breaker trip coils have a high
impedance, and meter combinations requiring considerable accu-
racy consequently should not be used in series with them. By inter-
posing a relay, which cuts out the trip coils except at the moment
of trouble, the total load can be very materially reduced. The
relay therefore simply serves to control the tripping circuit and
may be either circuit-closing or circuit-opening. In the former
case (Fig. 312), the relay contacts are normally open and the trip
coils dead, but at the moment of operation contact is made, thus
Oil
Switch
Mi
<> ? 9
O
TVfpOon
r
I
'"W" Ground
tioiiir
Terminal
i Board
G«ncnitOr
Hi
6
I
[i
Fig. 312. — Connections of Circuit-
closing Relay.
Fig. 313. — Connections of Circuit-
opening Relay.
completing the circuit and energizing the trip coil, which in turn
causes the switch to be released. In the latter case (Fig. 313)
the relay contacts are normally closed and the trip coils de-ener-
gized, because the current will then take the path of least resist-
ance through the contact blocks and not through the comparatively
high impedance path through the trip coil winding. When a shortr
circuit occurs on the main circuit, the contacts open, and force the
current through the trip coils, which then operate and open the
switch. As noted from the diagrams, circuit-closing relays require
a separate source of power, preferably direct current, for operat-
ing the trip coil, while for the open-circuit type the tripping cur-
rent is obtained from the secondary of the current transfcrmer.
Circuit-closing relays, are, however, almost exclusively employed
in connection with the circuit breakers used on large power systems
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SWITCHING EQUIPMENT
509
and circuit opening relays only in those cases where direct current
is not available. On account of the heavy secondary currents
which are liable to flow on severe short-circuits and due to the
comparatively high impedance of the trip coil, which may tend
to hold up the voltage, a considerable arc is liable to be set up when
the contacts are opened, and there is therefore a limit above which
it is not safe to use circuit-opening relays. As a rule they should
not be used when the short-circuit current exceeds ten times the
normal rating of the current transformer.
There are a large number of different types of relays, but only
a few of those in ordinary use on power transmission systems will
be considered. Neither will any detailed description of their con-
struction be given as changes and improvements are made so fre-
quently that this would soon be obsolete. It will therefore be
the aim in the following to merely deal with their fundamental
principles and characteristics.
Overload Relays. These may be instantaneous, definite time
limit and inverse time limit. With instantaneous relays, the
0«*isr
Bkffik
Fig. 314. — Instantaneous Overload Plunger- type Relay.
contact device will operate immediately and close the tripping
circuit of the breaker when the abnormal conditions which the
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ELECTRICAL EQUIPMENT
relay is to take care of make their appearance and start the moving
part of the relay. With definite time-limit relays there is, as the
name implies, a definite time delay imposed between these two
moments, independent of the magnitude of the disturbance, and
the time hmit therefore becomes practicaQy constant for any
given setting. With inverse time-Umit relays the time delay is
inversely proportional to the magnitude of the disturbance, so
that with a heavy short-circuit it
will be practically instantaneous
for any time setting, while on a
Ught overload the time may be
several seconds, depending on the
setting.
For instantaneous overload
relays the plunger tj'pe (Fig. 314)
is considered the best. It simply
consists of a core or plunger
which is movable within a sole-
noid. When a suflScient amount
of current is passed through the
winding the core is pulled up and
causes the cone-shape9 disc at
the top to bridge the gap between
the contacts. The position of
the plunger with respect to the
coil is adjustable, the lower its
position the more current is re-
quired to pull it into dosing
Fig. 315.-Double.poleBeUow8 Type P^^^^^^^ ^^^ ^^ adjusting its
Inverse Time Limit Overload position it may be set to take any
Relay. predetermined strength of cur-
rent within the range of the coil.
Inverse time-limit relays may be either of the bellows tynpe
or the induction type. The former (Fig. 315) is similar to the
instantaneous type to which a compressible leather bellows has
been interposed between the moving part and the contact device.
When the relay is not operating, the bellows is fully extended and
the moving core presses against the same and tends to force the
air through an aperture. The air must be driven out of the bel-
lowes and the bellows compressed completely before contact can be
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SWITCHING EQUIPMENT
511
made. The rapidity with which the air escapes, that is, the time
intervening between the start of the moving part and the com-
pletion of contact, is a function of the power behind the com-
pression moving part, which in turn depends on the magnitude
of the electrical force actuating the relay coil. The size of the hole
through which the air escapes can be varied so that different time
elements may be obtained for disturbing forces of the same mag-
nitude, and different time curves for the same range of disturb^
ance.
In the induction type overload relay (Fig. 316), the actuating
forces are due to the interaction of induced currents in a moving
metal element with the induc-
ing magnetic field. A lami-
nated iron core is surrounded
by one or more windings, and
in the air gap of the core is
pivoted the moving element,
usually a Ught aluminum
disc. When current is passed
through the main windings,
eddy currents are induced in
the disc which tends to rotate
and close the contacts after a
predetermined angle of motion.
The retarding force is pro-
duced by having the same disc
pass between the poles of
permanent magnets, in which
case the eddy currents induced by these will retard the motion.
The relays are designed for use in the secondary circuit
of current transformers, and the normal rating, or continuous
current-carrying capacity, is 5 amperes. Taps are provided in
the relay winding, and by inserting a metal plug in a current
tap plate, settings 4, 5, 6, 8 and 10 amperes may be obtained,
these figiu*es representing the lowest current values required to
close the relay contacts. Any tap setting, multiphed by the
ratio of the current transformers, gives the corresponding primary
or line current.
A time-current index plate is provided as a guide for deter-
mining the settings of the relay, and the current values are
Fig.
316. — Induction Type Overload
Time Limit Relay.
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ELECTRICAL EQUIPMENT
indicated by the figures 1.5, 2, 3, 5, etc., in the " Times current
tap setting " column. These figures can be translated into
amperes by multiplying them by the current tap setting which
is to be used. Time settings are made by a lever which changes
the length of travel of the disc, the time scale being at the bottom
of the index plate. Therefore, with the time lever set over a
definite graduation mark, the values given in the correspond-
ingly marked column are the approximate time delays, in seconds,
which will be obtained at the current values opposite in the
0 1 i 3 4 5 6 7 8 0 10 20 80 40
Current, in Multiples of Current Tap Setting
Fig. 317. — Induction Type Time Limit Relay Characteristics.
" times current tap setting " columns. In general, the time
delay values should be chosen at a current value approximating
the short-circuit current of the line, and the proper setting of
the time lever for a given time delay may be determined by
referring to the table on the time current index plate. First
determine which factor in the "times current tap setting"
coluLmn represents the current at which this time delay is
desired. The position of the time lever can then be found by
an inspection of the row of time delay values opposite this
factor.
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SWITCHING EQUIPMENT
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Fig. 317 shows a number of time-current characteristic curves
of this relay and the constantly decreasing time as the current
increases should be noted. The curves consist of an inverse time
portion up to approximately 20 times the minimum current, set-
ting, blended into a definite time portion instead of converging.
The above type of relay may also be used where a definite
time action is required. Otherwise a bellows type relay may
be used in which the moving part starts immediately when the
tripping value is reached and compresses a spring, and this in turn
actuates the diaphragm and the contact device, the time required
by the spring for this operation being entirely independent of the
magnitude of the disturbance, but dependent only on the stored-
up energy of the spring and the setting of the air-escape hole. To
ii
[^
rVft
u
Tbree-Phase
Inductive Load In
Power StatioD
Three-Phase
Ungrounded
Tbree-Pbaae
Grounded Neutral
Fig. 318. — Circuit-closing Overload Relay Connections Showing Use of
Single-, Two- or Three-pole Units.
obviate inaccuracies due to slow closing it is advisable to combine
this relay with an instantaneous one. No mechanical action would
then be exerted on the spring until the disturbance had risen to a
value sufficiently large to operate the instaneous relay and to
throw the definite time limit relay into circuit. Where direct
current is available, the coil of the instantaneous relay should be
connected to the main A.C. circuit and the definite time limit
relay, having a D.C. potential coil, connected to the contact device
of the instantaneous relay, and tripping in turn the circuit-dis-
connecting device. Where no direct current is available, a cir-
cuit-opening instantaneous relay in combination with a definite
time limit relay with A.C. coil is required, so that the definite time-
limit relay is not connected in until the disturbance has reached
a value sufficiently high to operate the instantaneous relay.
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514 ELECTRICAL EQUIPMENT
Bellows-type relays axe very rugged and are extensively used
for ordinary service, while the induction relay is desirable where
extreme accuracy is required such as to insure selective switch ac-
tions on compUcated networks.
Overload relays are usually made single-pole, but one, two or
three relays may be combined as the conditions may demand,
the usual practice being shown by the connection diagrams in
Fig. 318. Single-pole relays may be used on single-phase and
balanced three-phase circuits; double-pole relays on ungrounded
three-phase circuits and two-phase circuits which are not inter-
connected; triple-pole relays on three-phase grounded neutral
and interconnected two-phase circuits.
Reverse Power Relays. These operate on a reversal of the
energy in the circuit to which they are connected. They may
be either of the dynamometer type or the induction type.
The dynamometer type (Fig. 319) consists of a potential coil
pivoted in the center of a current coil in such a manner as to
obtain dynamometer action, the two coils being mounted in a
magnet frame. The pivot which supports the potential coil also
supports the movable contact, and when the flow of power is in
normal direction or at no load, the contact lever is held against
a stop by a spring. Upon reversal of power the potential coil
tends to turn and throws the contact lever against a station-
ary contact, completing the tripping circuit of the oil circuit
breaker.
The dynamometer type of relay is generally built in single-
pole imits which may be combined in the same manner as overload
relays, for the protection of polyphase circuits, as previously
described. Figs 320 and 321 show the connections for a relay
of this type as used on three-phase nongrounded and grounded
circuits. Three potential transformers are shown for the latter
case, but two may be used if the volt-ampere load permits.
Reverse power relays are in themselves always instantaneous
and for time action they must be combined with overload relays
with such features. An overload relay is always recommended
for the induction type reverse power relay, even for instantaneous
isLction due to its sensitiveness. This overload relay, although not
necessary, is nevertheless also recommended with the dynamom-
eter type. When used in connection with overload relays the con-
tacts of both relays are connected in series so that both must
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SWITCHING EQUIPMENT
515
operate before the breaker will be tripped. Any t3rpe of overload
relay can be used, although the plimger type is recommended when
instantaneous action is desired. Otherwise the induction t3rpe
may equally well be used.
The induction type reverse power relay is based on the prin-
PiG. 319. — Single-pole Dynamometer-type Reveree-power Relay.
ciple of the wattmeter, in which a disc or rotating element is actu-
ated by both current and voltage windings. The torque generated
is proportional to the instantaneous products of the ciurent and
voltage, i.e., the watts.
The relay shown in Fig. 322 is the polyphase type and the
arrangement of the driving elements on a common shaft has sev-
eral advantages. There are three separate driving elements, each
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ELECTRICAL EQUIPMENT
TemlBftl
Fig. 320. — Connections for Dynamometer-type Reverse-power Relay.
Three-phase Ungrounded Circuit.
+ -
Fig. 321. — Connections for Dynamomet>er-type Reverse-power Relay.
Three-phase Circuit with Grounded Neutral.
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517
having a current coil and a potential coil used for both quarter-
SLnd three-phase circuits. The third element is required for delta
or ungrounded Y circuits in order that each phase may be properlj'
represented in every short-circuit. If two elements were used
many single-phase troubles
would involve only one of these
elements and the benefit of poly-
phase action would be lost.
Although only one element may
be involved in case of a groimd
on a grounded Y circuit, the
voltage triangle will not have
become so badly distorted as
when a single-phase line to line
short exists. For delta or un-
groimded Y circuits two cur-
rent and two potential trans-
formers are sufficient. The
third ciu'rent coil carries the re-
sultant current of the two cur-
rent transformers and the third
potential coil is connected across
the open delta of the two poten-
tial transformers. These elements all operate through one shaft
to control one set of contacts. In this three-element relay, two
discs are used, the upper one of which is driven by one element
and the lower by two elements, one in front and one in back.
The polyphase construction makes the action of the relay more
reliable than could be obtained by means of three single-phase
relays because of the fact that any incorrect tendency on the part
of one phase is balanced by a similar but opposite incorrect ten-
dency on some other phase. The incorrect tendencies being
balanced out, the true net power direction will not be over-
powered.
The polyphase relay should not be used on systems having the
neutral grounded, except after proper investigation, imless two
or more parallel lines are involved and the relays are inter-
connected in a balanced group. In such case the power currents
are balanced out and the fault current controls the operation of the
relay.
Fig. 322. — Polyphase Induction-type
Reverse-power Relay. Cover and
Register Removed.
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ELECTRICAL EQUIPMENT
Figs. 323 and 324 give the connections for this type of relay
both for ungrounded and grounded three-phase circuits. Three
potential transformers to be used in the latter case if thevoltr
ampere load is too great for only two.
Interconnected Reverse Power Relays. For two or more parallel
Fig. 323. — ^Connections for Poljrphase Induction-type Reverse-power Relay
for Ungrounded Three-phase Circuits.
tie lines, over which energy may normally be fed in either direction,
reverse power relays with interconnected current coils may be
used at each end of the tie Unes. The interconnection of the cur-
rent coils is such that the influence of each circuit on its relay will
be completely overcome by the other circuit so long as conditions
are normal. If a short should occur in one line, the unbalanced
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SWITCHING EQUIPMENT
519
condition will result in the isolation of that line without affecting
any other.
In the diagram (Fig. 325), the solid arrows indicate the rela-
tive directions and intensities of the energies in the various parts
of such parallel lines when in normal operation and with power
Fig. 324. — Connections for Polyphase Induction-type Reverse-power Relay
for Grounded Three-phase Circuiis.
being fed from Station A to Station B. Should power be reversed
and fed from B to A, then all solid arrows would be inverted. In
either case it will be noted that the current coils of all relays oppose
each other. There will be no tendency to operate under these
conditions no matter how much current may be carried by the tie
line.
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ELECTRICAL EQXnPMENT
Consider^ for example, that one of the two lines is shorted at
S, near Station A. The dotted arrows then indicate the changes
that take place. Power flows out from Station B over both lines.
The weaker influence of line No. 1 tends to prevent any action
of these relays but it may be sufficiently overpowered by the heav-
ier current in line No. 2, in which case the relay 26 wiD operate.
TieUae'l
Diiccfioa of OBfTcat
10 Operate Bahy
StaUon^B"
Fig. 325.— iSimplified Connection Diagram of Interconnected Reverse-power
Relays.
At the same time any force exerted in the relay 16 will simply
oppose the closing of its contacts. The same is true of relay la.
Consequently neither oil switch of line No. 1 will be disturbed.
The effect in relay 2a, however, is very different. Here the
currents are both in the proper direction to operate the relay.
This relay, therefore, trips its oil switch inunediately, and, return-
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SWITCHING EQUIPMENT
521
ing to relay 2b, it will be seen that the opening of oil switch 2a
will have resulted in the reversal of the current in line No. 1. If
the relay 26 has not operated previously, it cannot fail to do so
now. Had the short-circuit occurred at some othei- point, the
energy intensities and directions, and, consequently, the order of
the operations, would have been somewhat changed from those
outlined above, but, in any event, the final outcome would have
been the isolation of the injured line
without afiFecting its companion.
It may be observed that with line
No. 2 cut off, the counteracting in-
fluence in the relays of line No. 1 is
removed. Under these conditions a
short-circuit outside of the tie line
might result in the opening of the one
remaining circuit. This difficulty
may be overcome by the use of auxili-
ary switches connected so as to render
the second line nonautomatic follow-
ing the opening of the oil switch in
the faulty line, or better still, to
automatically insert instead, time
Umit overload relays.
Balanced Relays. These are in-
tended for protecting parallel cir-
cuits against faults which would
materially unbalance the currents in
these parallel lines. In the case of
parallel outgoing lines, when a short-
circuit occurs on one line, the current
in that line will become greater than
in the others, and by reason of this difference the circuit breaker
of that line will be opened. So long as no fault exists on any
line, no relay will tend to trip, therefore, no amount of balanced
overload on the lines would open any circuit breaker. Balanced
rela3rs operate on current alone, and should be used on the
power end of the circuits only.
Splitrconductor Relays, This system consists in splitting each
conductor into two parts and using a relay which operates when-
ever the current in the two halves becomes unbalanced. The
■Tripping
' Battery
Fig. 325a. — Split-conductor
Method of Relay Protection.
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ELECTRICAI. EQUIPMENT
diagram (Fig. 325a), illustrates the connections for one conduc-
tor. It involves a standard overload relay but a special current
transformer. This has three windings; two primary to which the
two halves of the split conductor are connected, and one secondary
connected to the relay which controls the circuit breaker trip coil.
Under normal operation the current divides equally between the
two parallel paths and in each transformer the magnetizing efifect
of the two primary coils are equal and opposite. The transformer,
therefore, oflFers no impedance to the current flow and the sec-
ondary windings and relays are unaffected. If a fault develops
in one of the two parallel conductors, however, it is evident that
the balance between the two primary transformer windings will
be upset, thus producing a magnetizing effect on the secondai^'
windings, exciting the relays and tripping the circuit breakers.
Differential Relays. These are intended for the protection of
generators, transformers, etc., from internal short circuits and
A.C. Oonantor
Tkmnaforman
Oircuit BrMtker
Olrcalt Breaker
ft • utrcau on^m&t
Fig. 326.— Differential Relay Con- Fig. 327.— Diflferential Relay Con-
nection for Generator Protection. nection for Transformer Protection.
operate always instantaneously. They are of the ordinary plunger
type and may be provided with one or two coils, one generally being
used for generator protection and two for protecting transformers,
as shown in Figs. 326 and 327.
When one current coil is used, the secondaries of the current
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SWITCHING EQUIPMENT 623
transformers are connected in series in the circuit containing the
relay coil and, in such a manner, that, imder normal conditions, the
current would simply circulate in the secondary circuit and not
enter the relay coil due to its higher impedance. If, however,
trouble should occur in the generator, there would be a reversal of
current through the ciurent transformer nearest the oil circuit
breaker, and the two secondary currents would naturally oppose
each other, in which case both would take the path through the
relay coil. This would, therefore, receive the resultant of both
currents and trip out the oil circuit breaker and disconnect the
faulty generator imit from the system.
If it should so happen that the two current transformer prima-
ries differ from that of the power transformer, which may easily
occur when tap connections are changed, the secondary ciurents
in the two current transformers would not be equal. This would
mean that there would be a resultant current or flux in the relay
which would be equivalent to that difference, and satisfactory
operation would be affected to some extent. It is, therefore,
important that, with normal load on the power transformer, the
unbalanced current, that is, the difference between the secondary
currents in the current transformers connected to the two sides
of the power transformer should be zero. Otherwise two coils
should be used, as shown in Fig. 327. These are wound on the
same core, the coils being connected separately to current trans-
formers in the primaries and secondaries of the power trans-
former. Normally the coils oppose each other, with resultant
zero flux in the relay core. When a winding of the power trans-
former is short-circuited, the other Unes in parallel feed back into
the short, reversing the direction of one coil so that the flux in
the core becomes cumulative and the relay operates. "When
used in connection with generators the neutral point must be
opened for the insertion of cmrent transformers, as shown.
Pilot Wire Relays. For a single tie line, over which energy
may normally be fed in either direction, reverse power relays at
each end of the circuit connected by means of pilot wires, will open
both ends of such a line whenever trouble exists on that line, and
under no other conditions. Energy may flow in either direction
so long as the energy in the two ends of the line shall flow in the
same direction. These relays are equipped with double-throw
contacts, the construction of the relays being such that so long as
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ELECTRICAL EQUIPMENT
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SWITCHING EQUIPMENT 525
energy flows in the same direction in the two ends of the line, all
the contacts of the relays connected to the tie line will take a
uniform position. If the direction of energy should change
over the entire line, both contacts would simultaneously reverse,
bringing them once more to a uniform position. Under these
circumstances, the circuit of the low-voltage trip (see Fig. 328),
will be imbroken and the tripping circuit will consequently be
kept open. A slight time delay is provided for the overload
relays simply to insure sufficient delay to allow all relay contacts
to swing to their proper position on the occurrence of a normal
reversal of energy in the tie line. If, however, trouble should
occur between the stations, power would be fed into the line from
each end, and, as a consequence, the relay contacts on one end of
the line will remain at one side while the relay contacts at the
other end of the circuit will be thrown to the opposite side. This
will result in opening the circuit of the time-limit, low-voltage
rdays, and the falling of the low-voltage relay plungers will close
the oil switch tripping circuits at each end of the line and isolate
the circuit.
High-iensicn Series Relays. These are, in general, of the same
principle as the ordinary plunger type relay. They are chiefly
used with high-tension oil circuit breakers for overload protection
where current transformers are not installed or warranted, and
may be either of the instantaneous or inverse time-limit type.
The coil is connected directly in series with the Une and moimted
on a post-type insulator, the size of which depends on the voltage.
The plunger of the relay is by means of a long wooden rod con-
nected to a circuit-closing switch which can be mounted on any
vertical flat surface below the location of the relay coil.
Over-^oUage Relays. These may be either instantaneous or
time limit and are similar in construction to overload plunger-
type relays, differing only in that potential windings are sub-
stituted for the current coils. They may be used to protect gen-
erators, transformers or other power apparatus against damage due
to abnormal voltages. For this purpose the relay should be con-
nected so as either to open up the field circuit of the alternators
or introduce into each field circuit a sufficient resistance to insure a
reasonably low potential on the system.
The conditions most frequently responsible for a dangerous
rise in potential is the loss of load on a power-station while the
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526 ELECTRICAL EQUIPMENT
generators are operating under considerable excitation. The
abnormal voltage is, therefore, usually accomplished by a de-
creased current. To guard against the possibility of opening the
Nl/
Potcntl«l iff ^ |«wltch which BhoHfl
WfoJSer ^ h*" flew -^
—ir
/ BoDTCt ^[ToopeaiiureoaoC
rto opening coll of I ^ ^^ fl«id'«witeh or of
->jficM-fwilchorof Potential ?[^ \ f>|«^
Pot.
Relaj
ntial
uormer
Poteni
Tranut
: $IteU7
<Lo^
r>\ •witch which ahorta
Current
Tranftformer
Fig. 329. — Simplified Diagram of Over-vcltage Relay Connections.
field circuit under any condition, other than the loss of load, a
circuit opening overload relay or circuit closing underload relay
may be connected to the line with its contacts in series with those
oif the over-voltage relay. Fig. 329 shows the connections.
Low-voltage Relays. These are of the circuit-opening plunger-
type provided with a potential winding regularly wound for use
on the 110-volt secondaries of potential transformers.
In operation, so long as the potential is about normal, the
plunger is held up, causing the contacts to remain open. When the
potential falls below one-half normal, the plunger is released and
the circuit closed. In some cases the plunger must be pushed up
by hand, after potential has been apphed. Usually, however,
coils are used which will automatically raise the plunger when
normal voltage is restored.
Underload Relays, These are made with circuit-closing con-
tacts for instantaneous operation and are similar to low-voltage
relays with the difference that current coils are substituted instead
of potential coils.
Trip-free Relay. This is a safety device intended for use with
electrically controlled circuit breakers, in that it prevents them
from being held closed on overloads. To accomplish this, the trip-
free relay is simply added to the standard control wiring. After
the breaker comes out on overload it cannot be thrown in again
until the closing contacts of the control switch have been allowed
to retm-n to the open position. The diagram in Fig. 330 illustrates
the connections.
Signal Relays. These are used for indicating to the attendant
the automatic opening of circuit breakers. When these are closed
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SWITCHING EQUIPMENT
527
Operating Bme» '
FomII
Aaziliaryl
Switch ?
JHB
CloslBjT > Switch f ?
Coll S J- ^
Oontrol
Relay
rollL
"^Slf
I
to nearect opcratiaff
pMitive BtM depending
on whether Relay is
moanted near the
Gircnii Breaker or on
the Panel
=SD'"^Trlp Free
A Cloeed when Oil Switch is Closed.
B Cloeed when Oil Switch is Open.
Fig. 330. — Connections for Trip-free Relay.
Jo Cloelnff
Contact
a?
Relay
► « , . __ To Corrent
Transfermer
in Main Line
Red Lamp
.^Controlling Switch
^
To Opening
Contpct
Oreen Lamp
lii VoU Operating
To Clodng
Contact
[tUelay
Pose _^
n
. To Cnrrent
Tranafermer
in Main Line
Red Lamp
^ Controlling Switch
^
Green Lamp
To Opening
Contact
Bell
Battery
L
rC
Relay Bos ^
Fig. 331. — Connections for Bell-alarm Relay.
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ELECTRICAL EQUIPMENT
by hand and opened either by hand or by some automatic tripping
arrangement, a circuit-closing auxiliary switch for closing the alarm
circuit is so moimted on the operating mechanism that when the
circuit breaker is opened by the hand-closing mechanism, the aux-
iliary switch does not operate. But if the tripping is affected by
the automatic mechanism, the auxiliary switch will close and
throw in circuit the alarm device.
On electrically operated circuit breakers no arrangement of a
mechanically operated auxiliary switch, which will allow it to
distinguish between nonautomatic
and automatic opening, can be con-
ventionally made. Consequently, to
inform the operator of automatic
opening, there is used generally a
bell alarm relay with its operating
coil connected in the power supply of
the circuit-breaker tripping coils,
(Kg. 331). The operation of the
relay is not affected by the control
switch circuits, and is energized only
when current passes through the
tripping circuit contacts of one or
more of the protective relays.
Whenever a circuit breaker is
automatically tripped, the relay coil
is energized for an instant through
the circuit of the overload trip. As
it may be necessary to ring an alarm
bell for some time to attract the
operator's attention to the fact that
a device has been opened automatic-
ally, the relay plunger is notched so
that it remains up in the closed posi-
tion until pulled down by hand,
which shuts off the alarm bell by
opening the bell-alarm circuit.
Control Relays. These are used in connection with the con-
trol switches for electrically operated oil circuit breakers, etc.
Since these control switches, as a rule, are not constructed to open
a current of sufficient capacity to operate the closing coil of the
^Pio. 332. — Solenoid Control
Relay.
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SWITCHING EQUIPMENT 529
solenoid, for example, it is necessary to use a control relay with its
operating coil connected across the closing contacts of the con-
trol switch and the relay contacts in series with the solenoid closing
coil. This relay is illustrated in Fig. 332 and the connections in
Fig. 351.
Switchboards. The switchboard of the modern large power
station is, strictly speaking, not a switchboard in the original sense
of the word. While for small stations the entire instrument and
switch equipment may be mounted directly on the board, for
large stations the oil circuit breakers and bus-bars are always
mounted at some distance from the same, the location being deter-
mined by convenience of wiring and safety. In such a case the
switchboard is rather a control board and contains only the con-
trol switches, instruments and the various other auxiliary devices
such as indicating lamps, plugs and receptacles for measuring
the voltage and for synchronizing, etc.
The design of a switchboard involves a careful consideration
of the apparatus to be controlled, the system of connections,
arrangement of cables and other wiring, and on the general design
of the station. The various apparatus on the board should be
arranged so as to faciUtate the operation, and for this reason the
board is always divided up in panels corresponding to the machin-
ery or circuits which are to be controlled. The exciter and the
regulator panels are generally located at one end, then the generator
panels, station panel, transformer and outgoing line panels in order
mentioned. This arrangement may, of course, be different so as
to more closely correspond to the arrangement of the apparatus.
Blank panels should preferably be provided for future machinery
from the beginning. The expense of such panels is very httle and
it facilitates the addition of instrument equipments for future
units considerably. In such a case it will only be necessary
to remove the blank panels, have the necessary instruments and
wiring moimted thereon, then replace them on the framework
and make the necessary remaining connections, thus causing the
least disturbance to the rest of the equipment.
Pipe framework is now almost universally used for support-
ing the panels on account of neatness and simphcity . The material
of the panels may be slate or marble. Where live parts are
mounted indirectly thereon, slate should not be used if the voltage
is higher than 1200, and marble is limited to about 3300. Natural
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530
ELECTRICAL EQUIPMENT
black slate is best suited for switchboard work, as it is not easily
marred or stained and can readily be matched when making
extensions.
The small wiring on the back of the panels should be done
neatly and regularly to facilitate tracing of connections, and it
should be arranged in a manner best suited for connection to the
control wires coming to the board.
The back and ends of the board may be closed by a wire and
Fig. 333. — ^Arrangement of 2300-volt Switchboard with Switches Mounted
on the Pipe Work Supporting the Panda.
grille-work screen to prevent tampering with the apparatus
back of the panels, while, on the other hand, they greatly enhance
the appearance of the installation. Switchboards provided with
these screens comply with the most stringent rulings of safety
first regulations since the screens afford complete protection
against accidental contact with live parts by operators and
others.
Switchboards may be classified according to the style of con-
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SWITCHING EQUIPMENT
531
struction or according to the manner in which the oil circuit
breakers are mounted and controlled. Based on design we
have:
1. Vertical panel boards.
2. Benchboards.
And, according to method of control:
1. Self-contained boards.
2. Mechanically remote-control boards.
3. Electrically (remote-control boards.
Shovld b« sunk in floor nlxght \
ly if Oil Switch Can i« to be "
rtmoved with Switch open
I!
FiQ. 334.-rArrangBment of 2300-volt Switchboard with Mechanically Remote-
control Switches Mounted on Open Pipe Work.
The self-contained switchboard is always of the vertical type,
Fig. 333, and has all the apparatus, including the oil circuit
breakers mounted near the panels.
The mechanically remote-control board is also of the vertical
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ELECTRICAL EQUIPMENT
panel type Fig. 334, but the oil switches and bus-bars are
mounted on a pipe or other structure somewhat to the rear of
the panels, the switches being operated by handles, located on
the front of the panels, through the medium of mechanical con-
necting rods.
The electrically remote-control switchboard may be either of
the vertical panel tjrpe or of the bench-board type, depending on
Fig. 335. — ^IVpical Vertical-type Switchboard with Hand-operated Ofl Cir-
cuit Breakers. Front View.
the conditions to be met. The oil circuit breakers and the bus-
bars are installed in the most convenient place in the station, oft^n
at a considerable distance from the board The breakers are
then operated by means of solenoids or motors, which in turn are
controlled from the switchboard.
The proper type of switchboard to be selected depends on the
apparatus involved, particularly the oil circuit breakers and the
bus-bars, and these in turn on the power to be handled, the voltage,
operating features, spacfe available, etc.
With stations of large capacity and high transmission poten-
tials, requiring a heavy switching equipment, manual control is
practically impossible, partly from mechanical reasons and partly
on account of the increased space factor required by the breakers,
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SWITCHING EQUIPMENT
533
buses, etc., and recourse was had to the methods of remote con-
trcd.
Commencing with the manually operated remote-controlled
switches equipped with rods and bell cranks, good practice finally
recognized the desirabiUty of employing solenoid or motor-
operated breakers controlled from a central point. This arrange-
FiG. 336.— Rear View of Switchboard Shown in Fig. 335.
ment permitted the location of the control board without reference
to the location of the breakers or the apparatus which they con-
trol. Absolute isolation of the high-tension equipment may thus
be secured, thereby largely eUminating the personal hazard and
danger of accidental contact and making possible the use of the
Qunimum amount of high-tension busses inside the station.
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ELECTRICAL EQUIPMENT
It is difficult to give any accurate recommendation as to where
the dividing line should be between the different arrangements.
In general, it may, however, be said that those shown in Figs. 333
and 334 can be used for voltages up to 6600 and station capacities
not exceeding 5000 kilowatts. For higher capacities and voltages
it is advisable to mount the oil circuit breakers in compartments.
In fact, most high capacity switches for moderate voltages are
Fig. 337. — Typical Vertical Type Switchboard with Electrically Operated
Remote-control Oil Circuit Breakers.
made for cell mounting, but above 22,000 volts they are, as a
rule, of the open design.
Figs. 335 and 336 show the front and rear views of a typical
switchboard of the vertical panel type with hand-operated oil
circuit breakers mounted at the rear of the panels. Fig. 337
shows a similar board for electrically remote control circuit
breakers.
It is often found in a large and complex installation that if all
the instruments and apparatus were located on a vertical switch-
board, its dimensions would be too great for convenient opera-
tion, and many appliances such as control switches, sjTichronizing
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SWITCHING EQUIPMENT 635
and potential receptacles could not aU be accommodated in a
position most convenient for the operator. To overcome these
diflSiculties the benchboard has been introduced. In this manner
the useful surface has been increased by an amount almost equal
to the top of the bench, the latter oflFering an excellent position for
control apparatus, bringing it within distinct view and convenient
reach of the operator.
Another advantage is also incidentally obtained by reason of
the greater distances between the instnunents and the operator,
which enables him to observe a greater nimiber of instruments
from any point while manipulating the control apparatus. A
further advantage may be taken of this condition by increasing
the height of the instnunent section, if desirable, in order to
allow room for more instruments, which may be read without
difficulty.
Figs. 338 to 341 show different types of bench boards in use
and the relative locations of the different pieces of apparatus.
Which type should be used depends entirely upon the apparatus
involved and on the local conditions. It is thus often foimd that
a bench board of a certain design will give the best result for con-
trolling the machines, while a vertical panel board will be more
feasible for feeder circuits. When separating the boards the
nmnber of operators required should always be considered.
. Pedestal control boards are occasionally used, but there seems
to be no real advantage in splitting up the equipment to such an
extent. Figs. 342 and 343 illustrate two typical bench board
designs, and Fig. 344 shows the control room of the Mississippi
River Power Company at Keokuk. The operation in this sta-
tion is completely controlled by a chief dispatcher, who is in tele-
phonic commimication with all parts of the system. A special
desk is provided for him, on which is moimted the telephone
switchboard, while, in front of this desk a miniature arcnshaped
switchboard is installed which contains a set of mimic bus-bars
showing by means of small indicating lights the open or closed
position of all the breakers in the station. It also contains
graphic voltmeters and ammeters for recording the voltage on
each bus section and the current in each of the outgoing lines.
The main control switchboard is divided into sections corre-
sponding to the bus sections, with an additional section for the
auxiliary equipment. The arrangement of these boards is at
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ELECTRICAL EQUIPMENT
Met«r«
Pok and Sjmehr. Receptaeles^
Oontrol SwitcbM &, L&m^
Mimic BiMM.
nd.Rhe<Mtat
Control
ReUj*
Removftbla
OriUPnnola
Fig. 338. — A Simple Type of Combination Control Board and Instrument
Board Showing the Locations Best Suited for the Various Pieces of
Apparatus.
T^|ti>ffti]k»r«
En^biu %\gna\%
CtoDtrol HwEtrhpi iV Lamm,
Fid RU*Hi*!4*
Conlrol
laiifumirali
luiaf*
fiirtMa^ ttd
laiM-RiqalliS
Fig. 339. — An Enlargement on the Arrangement Shown in Fig. 338, which
Meets the Demand of Greater Working Surface by the Addition of
Rear Panels.
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SWITCHING EQUIPMENT
537
Pot. and Synch. Receptacles
Oontrol Switdies 6l Lamp
Mimic Buses
na. Rheostat
Control
Instnimonts
Meters and
Graphic Instruments
Relays
Testing Links
and Switches
for Relays and
Instruments
Fig. 340. — Control Board with Independent Instrument Board. This arrange-
ment offers more useful surface than does that of Fig. 338.
ments
r
View of
/
Removahia
Grill Panels
Pot. and Syneh« Receptacles^
Oontrol Switches & Lamgi ^
Mimic Buses
Fid. Rheostat
Oontrol
Relays
Gallery Rail
O
Removable C
GriU Panels
Gallery
FiQ. 341. — A Gallery Type of Bench-board which Permits the Operator View-
ing the Machines through the Board.
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538
ELECTRICAL EQUIPMENT
the present time in the form of an L, although ultimately it will be
in the form of a U with the dispatcher board in the center.
Diffused illumination in the control room is provided by means
of a skyUght, which forms the entire ceiling. In order to prevent
glare on the instruments it also became necessary to provide amber-
colored glass in the windows. At night a diffused illumination is
accomplished by tungsten lamps, which are mounted back of the
skylight panes.
Instrument Equipment. The instrument and meter equip-
ment for any particular installation should be chosen with the idea
Fig. 342. — Typical Benchboard of the Continuous Type.
of getting something which is satisfactory from an engineering
standpoint, at the same time keeping in mind its cost in proportion
to that of the total installation, and also considering the class of
attendants who will operate the board. It is not good economy
to invest in an elaborate set of instruments when the man who
operates the plant does not understand their use. In the large
installations, where more intelligent help is employed, the efficiency
of the plant can be greatly improved by the use of instruments
which are understood, but which would be more than useless in
the hands of the unskilled attendant.
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SWITCHING EQUIPMENT
539
Obviously it is difiScult to establish exact dividing lines which
will cover all conditions. The tables given in the following give
the instrument equipment recommended for use on the circuits
eniunerated. Special operating conditions and requirements will
Fig. 343.--Typical Benchboard of the Gallery Type.
often demand different measuring apparatus than that given, but
the table will, in all cases, serve as a guide in choosing a suitable
equipment.
Instruments of each different function are valuable under
certain conditions or to aid in accomplishing certain results. To
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540
ELECTRICAL EQUIPMENT
assist in the choice of these and to explain the advantage gained
by using each particular instrument the information in the follow-
ing paragraphs will be found useful.
For Direct-ctirrent Installations. Direct-current Ammeters.
(1) On machines of all kinds heating is the factor which deter-
mines the load which can be carried safely assuming the voltage
normal. Ammeters give an indication of the heating of circuits
FlQ. 844. — Mississippi River Power Company. Chief Operator's Room
Showing Control Boards and Switchboards.
in which they are connected and consequently are indispensable
for machine circuits.
(2) They show the division of load between machines.
(3) On feeder circuits they indicate which feeders are over-
loading the machines, and also furnish a means for indicating
the gradual growth or decline in the demands made upon the gen-
erating apparatus by any particular feeder, thus giving a warning
that the capacity of the apparatus must be changed, or the
feeder load rearranged.
Direct-current Voltmeters. (1) They show that machines
are being operated at a voltage not too high to damage their
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SWITCHING EQUIPMENT 541
insulation, or to damage apparatus for which the machines fur-
nish power.
(2) They are required when paralleling machines, which must
be of the correct polarity and at very nearly the same voltage
in order to enable throwing them together with the least disturb*
ance.
(3) They can be used as ground-detecting devices by making
proper connections to the system.
Curve-Drawing Instruments, (1) They give a permanent
record of the running conditions of the circuits in which they are
connected without the loss of time and possible chance of error
which occur when such records are computed from the readings
of indicating instruments. Showing, as they do, the distribution
of the load for every hour of the day throughout the year, they
place in the hands of the management very valuable information
which forms the basis for future extensions or improvements of
service and load distribution.
For Altematmg-current Installations. AUemating<urrenl
Ammeters. (1) They give an indication of the heating of the
armature of the machine. This is a thing which the indicating
wattmeters will not do because of the fact that it measiu-es only
the energy component while the ammeter measures the reactive
as well as the energy component of the current, both of which
produce heating.
(2) In case machines in multiple are running at the same power-
factor anmieters show the division of load.
(3) On feeder circuits, ammeters indicate which feeders are
overloading the machine.
(4) On overhead-transmission lines the use of three anameters,
one in each phase gives an indication of trouble on the lines, such
as grotmding.
AUemating-currerU Voltmeters. (1) They show that machines
are being operated at a voltage not too high to damage the in-
sulation, or to damage apparatus for which the machines furnish
power.
(2) They are valuable when paralleling machines which must
be at very nearly the same voltage in order to enable throwing
them together with the least disturbance to the system.
(3) They can be used as ground-detecting devices by making
proper connections to the system.
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542 ELECTRICAL EQUIPMENT
(4) The compensated type or ordinary type with line drop
compensator is useful to indicate at the power station the voltage
at any predetermined point of a feeder.
Direct-current Field Ammeters, (1) They give an indication
of the heating in the fields of machines.
(2) They assist in locating trouble in a machine. For in-
stance, in case the alternating current voltmeter on a generator,
which is supposedly operating normally, shows that there is no
voltage generated, a glance at the field ammeter may show no
reading, in which case it is evident immediately that the field
circuit is broken or the exciter system in trouble.
(3) They give an indication of cross currents in generators.
For instance, consider a generator panel containing nmin alter-
nating-current ammeter, power-factor indicator, voltmeter, and
field ammeter. If the machine is up to speed, the amount of
field current in excess of normal which is required at a given power-
factor to hold normal voltage, shows proportionately the amount
of cross current.
(4) They are of great value in the fields of synchronous
motors, because for any given load and power-factor the armature
current is a minimum for a certain value of the field current for
which the field can be adjusted with the aid of the field ammeter.
Indicating Wattmeters, (1) They show the actual power in a
circuit no matter what the power-factor since they measure the
energy but not the reactive component. This makes them valu-
able in the circuits of alternating-current machines operated in
multiple since they show the division of load between machines,
something which ammeters alone do not indicate, except when
machines are operated at exactly the same power-factor and
voltage.
(2) In the absence of curve-drawing instnmients, they fur-
nish a means for obtaining the load curve of a station.
(3) They indicate reversal of power in a circuit which an
ammeter will not do.
Power-factor Indicators, (1) It is a well-understood fact that
it is most economical to operate power plants at as high a power-
factor, as possible in order to get maximum output from the
machines. The power-factor indicator is very useful in telling
directly what this power-factor is. Proper wiring arrangements
can be made to use only one instrument per board, plugging it to
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SWITCHING EQUIPMENT 643
different circuits. In this way the circuits of poor power-factor
can be discovered and steps taken to improve conditions if con-
sidered desirable. Where synchronous condensers are used for
power-factor correction, the power-factor indicator connected to
the bus or circuit to be corrected, becomes particularly valuable.
(2) Generators in multiple will operate at maximum output
when they are all running at the same power-factor, reducmg
cross currents to a minimum. The power-factor indicator affords
the easiest means of making this adjustment, since it shows the
power-factor of each machine at a glance without the necessity
of computing this from the readings of other instruments.
(3) The reading of a power-factor indicator in connection
with that of an ammeter and voltmeter makes it possible to readily
figure the kilowatt output of a machine without the use of an
indicating wattmeter.
Reactive VoUrampere Indicators. (1) They measure the idle
or reactive portion of the power and are the only instruments
which do so directly.
(2) In connection with the reading of an indicating wattmeter
the readings of the reactive volt-ampere indicator give an easy
means for figuring the power-factor.
(3) They are considered in some cases more valuable than
power-factor indicators since they given an actual quantitative
reading in kilovolt-amperes while the power-factor indicator gives
a reading in per cent only. This fact can readily be seen from an
inspection of the following simple formula:
T> r X True watts
Power-factor =-
Apparent watts'
(Where the apparent watts is the vector sum of the true watts
and the reactive watts.) The reading of a power-factor indicator
gives no actual indication of magnitude of the idle current which
cause heating. For instance, at light load a power-factor of 0.7
or 0.8 would be no cause for alarm, while at full load or overload
it might mean serious heating due to idle currents. This is espe-
cially true on synchronous converters, where on account of the
rectifying action of such machines, the cross-section of copper is
made smaller than in a generator of the same capacity.
Frequency Indicators. (1) Machines operate most econom-
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544 ELECTRICAL EQUIPMENT
ically at the frequency for which they are designed, which makes
the use of the frequency indicators evident.
(2) They are valuable when synchronizing machines, since
they can be connected on the incoming machine and indicate its
speed, showing whether it is too high or too low. However,
where a s3nQchronism indicator is installed they are not required
for this piu-pose, since this instrument shows whether the speed of
the incoming machine is high or low.
Synchronism Indicator, (1) The synchronism indicator affords
the quickest and safest means for paralleling machines, since it
shows when the machines are in step and in phase, indicating by
the position of the needle the difference in the phase relations
between the machines, and telling whether the incoming machine
is running too fast or too slow. It is superior to synchronizing
with lamps, because the latter give no indication of the relative
speed of the incoming machine. The lamps will indicate when the
machines are of the same frequency, but the phase relations can
be judged only by the brilliancy of the light.
When synchronizing with lamps dark, the phase relation of the
machines will be shown by the brilliancy of the light to a point
where the machines are approximately 45*^ out of phase, below
which point there will not be sufficient voltage across the lamp to
make it glow. Again, in case there is an inopportune failure of
the lamp, the operator might be misled iad throw the machines
together when out of phase with possible disastrous results.
When synchronizing with lamps bright, it is difficult to deter-
mine, after watching the lamps for some time, at just what instant
they are burning at full briUiancy, and, therefore, at just what
instant the machines are in synchronism.
Synchronizing on high-tension lines, while often desirable,
has been out of the question because of the excessive cost and
space required for installing the necessary potential transformers
for a secondary synchronism indicator. A glow synchronism
indicator is now available for this purpose on circuits of 13,200
volts and above. The new indicator depends for its operation
upon the principle of electrostatic discharge in a vacuum.
The instnunent case resembles the ordinary round pattern
switchboard instrument. Inside the case are receptacles for hold-
ing the special glowers which project through holes in the cover.
Connections from the line to the device are made through con-
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SWITCHING EQUIPMENT 546
densers, which consist of siispension insulators having an insula^
tion equal to that used on the line. Normally the glowers have
the appearance of ordinkry spherical frosted incandescent lamp
bulbs. When, however, there is a proper difference of potential
across their terminals they will glow with a reddish hue. When
the lines are not in synchronism, the glowers will light up in
succession, showing the relative direction of rotation and indi-
cating whether the incoming machine is running fast or slow.
When i^mchronism is reached there will be no rotating effect, and
one glower will be dark while the other two will glow at about
half brilliancy.
Electrostaiic Ground Detectors. (1) They give a constant
indication of the condition of the system with respect to grounds
which, if not detected immediately, often result in very serious
burnouts or voltage disturbances.
(2) They are superior to any system of ground detecting which
necessitates the plugging of potential transformers and lamps or
voltmeters to different phases of a polyphase system; first, because
the polyphase electrostatic ground detector shows, at a glance,
whether there is a ground on any phase, while with the other
scheme it is necessary to plug the primary side of the transformer
to the different phases before the test is completed; and, second,
because the electrostatic ground detector is supplied with a scale
for reading the severity of the ground while with lamps only an
approximate indication is obtained ordinarily, and for high
resistance grounds no indication whatever, since the ordinary 125-
volt carbon lamp will not glow at much less than 25 volts across
its terminals.
Temperature Indicators. (1) It is of great value to know the
temperatitfe of certain parts of generator and transformer wind-
ings that are inaccessible for thermometer measiu*ements. An
instnunent known as the temperature indicator has been pro-
duced to determine these temperatures. Copper coils of known
resistance are placed in the parts whose temperature it is desired
to know. The changes in resistance are shown on the scale of
the indicator, which is marked in degrees Centigrade correspond-
ing to the change in resistance. The instrument itself is a differ-
ential voltmeter with three terminals. The connections are such
that one of the moving coil windings is in series with a resistance
coil which has a zero temperatm-e coefficient and a resistance equal
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546 ELECTRICAL EQUIPMENT
to that of the copper temperature coil, and the other winding is in
series with the copper temperature coil. When the temperature
of the copper coil rises, the current in that branch of the circuit
decreases and causes a corresponding deflection toward a higher
temperature on the scale of the instrument. The reverse is the
case when the temperature falls.
Curve-drawing Instruments. (1) They give a permanent
record of the running conditions of the circuits in which they are
connected without the loss of time and possible chance of error
which occiu" when such records are computed from the readings
of indicating instruments. Showing, as they do, the distribution
of the load for every hour of the day throughout the year, they
place in the hands of the management very valuable information
which forms the basis for future extensions or improvements of
service and load distribution.
The following tables give the instrument equipment usuaBy
employed for use on the circuits enumerated. In giving these,
each circuit is considered a complete unit in itself. A combina-
tion of two imits does not mean that all instruments listed for each
separately will be used on the combination. For instance, where
a generator and transformer are permanently connected together
and operated as a unit, there is no necessity' for using an ammeter
in the transformer circuit, since it would simply dupUcate the
reading of the generator ammeter. Other similar cases are numer'
ous, such as combined generator and feeder circuit, combined
transformer and feeder circuit, etc. Special operating conditions
and requirements will often demand different measuring apparatus
than that given, but the tables will at least serve as a guide in
choosing a suitable equipment in all cases. The small letters
in the tables refer to the notes following the tables.
Ctirrent and Potential Transformers. When the voltage or
current of the circuit to which the instruments are to be con-
nected exceeds a certain limit above which primary instruments
are not built, potential and current transformers are employed,
the instnunent coils being operated from the secondaries of these
transformers. As a matter of safety to the operator, secondary
instnunents are recommended for all circuits in excess of 650
volts.
Since the normal rating of the secondary of current transform-
ers is 5 amperes, secondary current coils are ordinarily wound
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SWITCHING EQUIPMENT
547
TABLE L
Direct Curreki!
Name and Number op Instruments Used.
Circuit Measured.
^«^BAK^%A*V A:WA\0Vm9%AM V*X* •
Ammeter.
Voltmeter. *
Two-wire generator
1
1 per switchboard plugged to
each generator
Two-wire exciter gen-
1
(d)
erator
Brush arc generator
1 (Plugged to read
each machine cir-
cuit)
None required
Two-wire feeder
1(a)
None required ordinarily
Railway feeder
1
Plug to station voltmeter to
read troUey voltage
Two-wire battery t
1 (Zero center)
1 plugged to read battery and
bus voltage
Two-wire synchron-
1
1 per switchboard plugged to
ous converter
each machine
Two-wire motor
Ub)
None required
Three-wire generator
2 (One in positive and
1 per switchboard plugged to
one in negative
read voltage between outside
lead)
wires of each machine
Three-wire feeder
2 (One in positive and
one in negative
lead)
None required ordinarily
Three-wire synchron-
2 (One in positive and
1 per switchboard plugged to
ous converter
one in negative
read voltage between outside
lead)
wires of each machine
Three-wire balancer
1 (Zero center) (con-
1 plugged to each machine of
nected in neutral)
the balancer set
(a) On multiple-circuit feeder panels controlling feeders of small capacity, am-
meters are usually omitted.
' (b) On small motors, ammeters are usually not furnished.
(d) Where there are only two exciters operating in parallel, one voltmeter is used
on each exciter equipment. Where there are three or more exciters, two voltmeters
are employed and mounted together on a swinging bracket at the end of the board,
usually on the same bracket containing the alternating current voltmeters and syn-
chronism indicator. One is connected to the bus and the other is arranged to be
plugged to any machine to read voltage at any time. In many instances exciters are
direct connected or belted to the alternating-current machines, the fields of which they
excite, and are not operated in parallel, no separate panels being furnished to control
them. In such cases no measuring instruments are furnished, the field ammeter of
the alternating current machine taking the place of the exciter ammeter, while
there is ordinarily no use of the voltmeter.
* Where the different types of circuits given in the first column occur in the same
board, only one voltmeter need be supplied, providing the scale is suitable for the volt-
age of all circuits to be measured.
t Due to the large number of methods of connecting batteries, no definite instru-
ment equipment can be listed to apply to all cases. The above represents a simple
equipment for measuring charging and discharge current and voltages as indicated.
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548
ELECTRICAL EQUIPMENT
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660 ELECTRICAL EQUIPMENT
for this capacity. When, with a certain capacity of current
transformer determined by the load of the circuit, the scale of the
instriunent would be too large to allow a good reading at light loads,
4-ampere windings may be used, the scale then being about 80
per cent of that corresponding to that used with the 6-ampere
winding. Secondary potential coils for all instruments except
voltmeters are ordinarily wound for 110 volts, the voltage of the
secondary side of standard potential transformers.
Instruments may be operated from the same cmrent trans-
formers which are used with the oil circuit-breaker trip coils or
relays, providing the volt-ampere load is such that the accuracy
of the instrument and transformer combination comes within
certain set limits. Wattmeters, however, should not be connected
to the same cm-rent transformers which are used with differential
or reverse power relays or with compensated voltmeters (indi-
cating or contact-making) or Une-drop compensators.
The same potential transformers can be used for operating
instruments and potential coils of relays, low-voltage release or
other apparatus as long as the rated secondary volt-ampere load of
the transformer is not exceeded. This load and its power-factor
must be clearly distinguished from the load and power-factor of
the main circuit which are measured by the measuring outfit
of which the instrument transformer is a part.
The term " equivalent secondary connected load " is used in
connection with a circuit to denote the volt-ampere load carried
by the secondary of an instriunent transformer when this load
differs from the result of combining the volt-amperes of the separate
devices in series or in multiple because the secondary is inter-
connected with other instrument transformer secondaries. The
power-factor of the equivalent secondary load of a current trans-
former imder these conditions is also affected by the intercon-
nection.
The volt-ampere of the various secondarj^ devices, such as
indicating instruments, meters, relays, etc., varies considerably
and should be obtained from the manufacturer.
The secondaries and cases or frames of current transformers
should be grounded whenever possible. The switchboard wiring
should be carefully considered to see if this can be done without
interfering with the proper operation of the instruments connected
to the transformers. The grounding of the cases serves the double
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SWITCHING EQUIPMENT 651
purpose of protecting the switchboard attendant SLnd freeing the
instruments from the effects of electrostatic charges which might
otherwise collect on the cases and cause errors.
The primary of current transformers should never be left in the
line with the secondary open-circuited, as this will set up a heavy
flux through the core, over-saturating the iron and causing it to
greatly overheat. If for any reason, therefore, it becomes neces-
sary to remove the meter or any current-carrying device from the
secondary circuit of a current transformer, the secondary should
be short-circuited by a wire or some other means. - .
Potential transformers are used to insulate the meters from the
high potential circuit as well as to do away with a large amount
of resistance in series with the meters which would be necessary
if the meters were connected directly to the high-potential cir-
cuits. Except in special cases, they are generally prptected by
fuses inserted in the primary leads.
The connections for the multitude of instruments, meters,
relays, etc., with their citfrent and potential transformers which
are used in the modem power station are very intricate. While
for individual equipments such connections may be standardized,
the combinations used in a large station are generally such as to
make the connections more or less special in order to give the best
results. Individual diagrams are as a rule contained in the
bulletins issued by the various manufacturers, and the making
up of the main wiring diagram for any important installation
should be left to the manufacturer supplying the switchboard.
A typical diagram of connections for an individual exciter, an
A.C. generator and an outgoing feeder is shown in Fig. 345 as an
example.
Key to Symbols
A. = Ammeter.
B.A.S. = Bell-alarm switch.
C.T. = Current transformer.
F. =Fuse.
F.A. = Field anmieter.
F.S. = Field switch.
G.C.S. = Governor-control switch.
K.S. = Knife switch.
L.S. = Limit switch (included with governor motor).
O.S. = Oil switch.
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562 ELECTRICAL EQUIPMENT
P.I.W. *=Pol3rphafie indicating wattmeter.
P.R.W.= Polyphase watthour meter.
P.R.
= Potential receptacle.
P.P.
= Potential plug.
P.T.
== Potential transformer.
Rheo.
« Rheostat.
S.
«Shmit.
S.R.
= Synchronizing receptacle.
S.P.
s Synchronizing plugs.
T.B.
-Terminal board for secondary leads from current and
potential transformers.
T.C.
=Trip coil on oil switch.
V.
« Voltmeter.
Bzdter and Field ControL For the electrical control of
exciter circuits it is usual to omit fuses or other overload devices in
order to prevent any interruption in the supply of field current to
the alternating-current generators, thereby insimng continuous
operation, which, in most stations, is an essential feature and
is of more importance than protection of the exciters from dam-
age. Also as an insm-ance against injury to the alternating-
current generator field windings. When trouble occurs in the
exciting sjrstem and ope is the overload devices on all the exciters
connected, the generator field circuits are broken at points where
no discharge resistances are interposed and the generator field
windings are consequently liable to pimcture by the high-induced
voltage to which they are subjected. If overload protection is
insisted upon, it is recommended that the overload devices,
fuses or circuit breakers, be based on double the normal capacity
of the exciter so as to open only in case of very serious trouble.
For large plants having a number of exciters in parallel and
where the expense involved is of secondary consideration, it is
customary to provide reverse-current circuit breakers without
any overload attachment. The reverse-current device serves to
disconnect a defective exciter while the remaining exciters con-
tinue in service.
Circuits for motors driving exciters are usually considered as
feeder circuits and overload protection is accordingly recom-
mended for the motor. A time-limit device is preferable for this
overload feature, and, if an instantaneous device is used, it should
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SWITCHING EQUIPMENT
553
be set very high. When operating conditions make it necessary,
the overload feature can be very readily disconnected. With
motor-driven exciters operating in parallel, it is also advisable to
equip the exciter circuits with reverse-current circuit breakers, so
as to prevent any set which might be disconnected from the bus
on the motor side to continue to operate by its exciter running as a
motor and taking power from the exciter bus. The D.C. breaker
could, of course, also be provided with a shunt trip arrangement
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554 ELECTKICAL EQUIPMENT
■whereby the opening of the A.C oil circuit breaker would in turn
trip the D.C. breaker.
For small and medium size installations the field switches are
usually of the ordinary knife switch type mounted directly on the
main switchboard. For large installations it is, however, com-
mon practice to .employ solenoid-operated carbon-break circuit
^•[breakers. These are often mounted on panels near their respective
exciters so as to reduce the length of connections to a minimum,
and controlled from the main board.
Occasionally a separate direct-current switchboard is provided
and located at some convenient place near the exciters. On this
board is then mounted all the exciter and field switches as well as
other low-voltage switches and circuit breakers for the various
station circuits.
Field switches for disconnecting the individual fields of the
A.C. generators should always be provided. These switches are
known as " field discharge switches " because their design is such
that when they are opened a discharge resistance is automatically
inserted in series with the field circuit. If this should be suddenly
broken, an excessively high potential may be induced in the field
winding which might puncture its insulation. By inserting a
resistance in the circuit, the e.m.f. induced in the field coils by the
dying magnetic flux produces a current through this resistance;
thus, the energy stored up in the magnetic field, when the cur-
rent was compelled to increase against the induced counter e.m.f.,
is now discharged in this resistance where it appears as heat.
The construction of the switch is such that in opening the same
the resistance circuit is closed before the field is disconnected
from the exciter or field bus, while, in closing the switch the
tesistance circuit is opened before the field is connected to the
. exciter. By this means all destructive arcing is also avoided,
JFor the field can never be broken without shunting it through
•the discharge resistance. Certain types of switches are, on the
• other hand, provided with a stop so that they cannot be com-
pletely opened until this has been withdrawn, thus giving the
induced field energy time to be dissipated through the discharge
• dip to' the discharge resistance before the circuit is broken.
' - Field switches may be either hand operated or solenoid oper-
ated, similar to the exciter switches. In the former case they may
be identical to ordinary knife switches, to which discharge clips
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SWITCHING EQUIPMENT . 555
have been added, and mounted on the front of the panel. It is
becoming very general practice, however, to mount the hve part
back of the switchboard and operate it by a handle from the front
of the board. This type of field switch is regarded as a " safety .
first " device of great importance and is to be recommended in all
cases. The switchboard attendant cannot come in contact with
the live parts or arc when operating, and instruments and other
adjacent equipment are safe from damage by burning which
occasionally happens with the front-of-board type.
With benchboard equipments and with large capacity vertical
switchboards where remote control is desirable, solenoid-operated
field switches are often employed. While controlled from the
main board, they may be located at the most convenient pointy
for example, near the generators or on the exciter board. They
are similar in construction to the non-automatic, self-contained,
solenoid-operated, air circuit breaker with the addition of a dis-
charge switch (Fig. 346).
Solenoid-operated field switches for A.C. generators and for
synchronous motors started, as is usual with motors of 250-volt
excitation, with the field short-circuited, should be double-pole
with common closing and common opening coil. No provision
is made for automatically interrupting the discharge circuit
after the switch opens, although the discharge blade can be ope-
rated by hand. Where economy is of importance, it is sometimes
customary with A.C. generators to provide one single pole solenoid-
operated field switch for one pole and ordinary knife switch for
the other, the former being remote-controlled from the main board
while the latter is hand-operated.
With sjmchronous motors Started from the A.C. side with
field open as is usual with motors of 125-volt excitation, solenoid-
operated field switches are made ordinarily of two single-pole
elements with independent opening and independent closing
coils. Both poles close simultaneously and connect the discharge
resistance across the field; but one pole precedes the other a short
time in opening. When the other pole opens, the discharge cir-
cuit is interrupted.
Occasionally the field switch has been used to cut the voltiage^
ofiF a machine in case of trouble and this is becoming more and>
more a general practice. The switch is then equipped with a shunt -
trip and an overload relay is installed in the main circuit, in wjiich-
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ELECTRICAL EQUIPMENT
case an overload in the latter will cause the field switch to trip,
thus killing the voltage of the generator.
The operating mechanism of field rheostats depends on their
size which in tium governs their location. The smallest
Fia. 346.— ^lenoid-operated Field Switch.
up to about 25 amperes, can usually be moimted directly back
of the board, and it is only necessary to extend the shaft of the
rheostat and connect it directly to the handwheel on the front d
the panel. Concentric handwheel mechanisms are also very
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SWITCmNG EQUIPMENT
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common, one of the wheels being for the exciter field rheostat
and the other for the main generator field rheostat. Such arrange*
ments permit of quite a saving in the space required.
For larger sizes it becomes necessary to mount the rheostats
remote from the switchboard, in the basement or otherwise.
The operating mechanism may then consist of a sprocket-wheel
chain drive, operated by a handwheel on the front of the board,
or it may be electrical, either in the form of ratchets or motors
controlled from the main board.
A typical arrangement of a
sprocket-wheel chain drive is
shown in Fig. 347, but it is, of
course, evident that the rheostat
proper can be located in many
different positions than what is
shown. This class of control is
generally limited to rheostat
capacities of up to about 350
amperes.
In many installations it is,
however, not possible to locate
the rheostat so that the dial
switch can be operated by means
of chain drive from a hand-
wheel on the panel. For such
conditions the rheostat can be
equipped with an electrically
operated ratchet switch (Fig.
348), which can readily be con-
trolled from the main board, and
the rheostat proper can be located in any part of the station.
The capacity is limited to the same as the chain-operated type,
i.e., about 350 amperes, and the operation is as follows:
The switch arm is carried around by pawls which engage
the knurled rim of a wheel to which the switch arm is rigidly
fastened. These pawls are controlled by a core actuated in com-
mon by the solenoids AA. When the solenoids are de-energiaed
the pawls are disengaged and in their normal position rest equi-
distsint from the solenoids. To cut resistance into the field, it
is necessary to close to the left the single-pole switch B. This
Fig. 347.— Sprocket-wheel Chain
Drive for Field Rheostats.
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ELECTRICAL EQUIPMENT
energizes the left-hand solenbidi engages the leflrhand paT'I and
movea the dial switch in a clockwise direction. When the solenoid
core has reached its extreme point of travel, the winding of the
solenoid' is automatically open-circuited by the small switch C,
and the pawl is immediately pulled to its neutral position by a
Spritig, automatically closing the circuit of the solenoid switch by
tjhe small switch C« The same cycle of operation is then repeated
until the switch B is opened. If it be desired to cut resistance
out of the field circuit the single-pole switch Bis closed to the right
when the same cycle of operation is performed and the dial switch
Looking at Face of Switch
Fio. 348. — Connections of Solenoid-operated Ratchet-driven Field Rheostat
Switch.
ijaoves in a (Soimter-clockwise instead of a clockwise direction.
Each end of the switch dial is provided with a limit switch, D,
which is automatically operated by the switch arm to open the
circuit of the solenoid when the resistance is entirely cut in or
out. The purpose of the limit switch, D, is simply to protect the
apparatus in case the controlling circuit is left closed when the
difij swdtch has reached its extreme point of travel in either
direction.
For circuits above 300 to 350 amperes the motor-operated type
of rheostat (Fig. 349) is the most practical, as the heavy contact
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SWITCHING EQUIPMENT
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on the dial switch is not easily overcome with the solenoid or hand-
wheel control. The motor is of the series type with a field wind-
ing enabling the dial switch to be operated in either direction
by the control switch on the main board. As with the ratchet-
driven type, each end of the switch dial is provided with a limit
?f * 3¥^
Fig. 349. — Electrically Operated Motor-driven Rheostat
switch which is automatically operated by the switch arm to open
the motor circuit.
Voltmeter and Synchronizing Receptacles. These are devices
which provide a ready means for connecting a voltmeter to any
machine or any phase of the same and thus reduce the number
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ELECTRICAL EQUIPMENT
of instruments required. Also, for making the necessary connec-
tions at the time of synchronizing. The contact elements are of
brass and come through the panel to the front, but are counter-
sunk in a hard rubber escutcheon plate, which makes accidental
contact very unUkely. The plugs have brass contacts supported
by a hard rubber shield, which
also serves as a protection to
the hand.
As will be noted from the
diagram of connections (Fig.
345), eight-point voltmeter
receptacles are provided for
the A.C. generator so that
the voltage across all the three
phases can be read in turn
when the plug is inserted.
With the synchronizing
scheme, as shown in Fig. 345,
the synchronizing is actually
done between the machines.
For this reason two plugs are
required, one of which is in-
serted in the receptacles of one
of the machines which is run-
ning and the other in the re-
ceptacles of the machine
which is to be started and
sjrnchronized.
Ammeter Transfer Recep-
tacles. These are for reading
the current in any of three
phases on one ammeter by
changing the connections from
the front of the panel. Each unit of a group consists of a brass
plug switch receptacle with fiber insulation, with contacts back
of the panel and with a molded bushing on the front. For read-
ing the current, the transfer plug is inserted in rotation in each
of the three receptacles of a group. Between such readings the
plug can be left inserted in one receptacle, thus giving a continu-
ous indication on that phase.
Fig. 350. — Automatic Throw-over
Switch.
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SWITCHING EQUIPMENT 561
Throw-over Switches. A sudden failure of the source of
power for the Ughting system in the power station is a more or
less frequent and troublesome occurrence. To take care of such
an emergency and facilitate the re-estabUshment of normal con-
ditions where apparatus may have been shut down due to the fail-
lu-e of power, a switch for automatically throwing the lights to an
auxiliary or reserve source becomes very handy. The switch
shown in Fig. 350 accomplishes this result. The device consists
of a special double-throw switch held closed by a latch on one
throw against a pair of springs.
To close the hghting circuit with the normal source of power in
operation, the switch is thrown in the lower set of contacts and
latched in the closed position by hand. When a failure of the
source occurs, a low-voltage release is caused to drop its armature,
tripping the latch free from the crossbar above it. The springs
on the hinge cUps of the switch then quickly force the switch into
the upper set of contacts, which are connected to %he reserve
source of power. At the same time an auxiliary switch at the
top is thrown into contact, causing a bell or other indicator to
operate to attract the station attendant's notice. After the
resumption of normal conditions, the switch must be thrown by
hand into the lower contacts and latched.
Calibrating Terminals. A quick and convenient method of
making connections for caUbrating instrmnents, etc., is very
desirable, and this has led to a very general use of providing
calibrating terminals on all important switchboards. These may
be mounted either on the front or back of the panels, the choice
being governed by the conditions. For example, where it is
difficult to carry on such tests on the back of a board, the ter-
minals may readily be mounted on the front, while if there is
plenty of room in the rear, it may be advantageous to locate the
caUbrating terminals there in order to utilize the space on the
front otherwise.
The terminals for the ciu-rent transformer connections should
be such, that the testing instrument can be connected in the cir-
cuit without breaking the continuity of the circuit, as explained
under " Current Transformers."
Control Switches. Remote electrically operated oil or air
circuit breakers are controlled by small double-throw control
switches, usually mounted on the main switchboard. How-
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ELECTRICAL EQUIPMENT
Olodng _ ^
OpermtiogBoaes
-mA Auxiliarj
,^-Yy^ Switch
Red L*inp
Cl<M!Dff_
Contact
Openiiiff_
ConlAct
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- lue onlj on
269 V. or 0UO V,
ever, since the energizing current of the operating mechanism may
be considerable, such as for motor-operated breakers or for the
closing coil of solenoid oper-
ated breakers, it is not custom-
ary to rely on the control
switch for breaking this cur-
rent, and an intermediate con-
trol relay (Fig. 332) is pro-
vided for this purpose. The
operating coil of this control
relay is then connected across
the closing contacts of the
control switch and the relay
contacts in series with the
motor circuit or the solenoid
closing coil (Mg. 351).
Control switches should
always be designed so that
all connections may be made
on the back of the panel, and
80 as to render it impossible to operate by accidentally leaning
against the switch. This is accomplished in the " pull-button "
type, which has the contacts on the back of the panel, with pull
.Control
Switch
Green Lamp
Opemting Bn—
Fig. 351. — Connection for Control
Switch for Direct-current Solenoid-
control Circuits.
Fig. 352.— Pull-button Control Switch.
rods brought through the panel to the handles on the front (Fig.
352). The switch returns to the open position by reason of a
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SWITCHING EQUIPMENT 563
spring and both throws (closing and opening), are interlocked. It
is provided with a mechanical device to indicate which throw was
last closed and, in addition, with red and green bulPs-eye lamps to
indicate the actual position of the circuit breaker. The necessary
auxiliary switches for these lamps are provided with the breaker.
Mimic Buses. It is sometimes customary to place on the
switchboard copper connections, known as mimic buses, rep-
resenting the main connections of the station. These are often
desirable as they keep before the operator the whole arrange-
ment of the circuits, enabling him to see at a glance what is the
proper switch to open or close. On the other hand, their use may
sometimes cause either a crowded or uns3anmetrical arrange-
ment.
Figs. 337, 342, or 344, illustrate the use of such mimic buses.
Bus and Switch Structures. As previously stated, bus-bars or
electrically operated oil circuit breakers are not necessarily placed
near the controlling switchboard, but should be placed with con-
venience to connections and safety from fire and in handling.
Isolating barriers or compartments are recommended for
voltages up to 15,000 where the capacity is above, say, 5000 Kw.
in order to prevent any destructive effects of short-circuits from
spreading and involving the entire bus structure.
Furthermore, the compartments act as a guard against anyone
touching the exposed parts of the buses and breakers and gives a
certain amount of fimsh and completeness to the station. The
cost of the cell structure is not of great consideration and is only a
small percentage of the total cost of the station.
For higher voltages the currents naturally become corre-
spondingly less, minimizing the destructive effects of short-circuits,
and, on the other hand, the spacings required are greater so that
open work generally becomes preferable.
Various materials have been used for bus and oil circuit
breaker compartments, namely, brick, concrete, soapstone and
slate, and sometimes a combination of brick with one of the other
materials. Brick compartments are the cheapest and if properly
made give the best appearance. The use of common brick is,
however, not recommended because most of the walls are four
inches thick and the sizes of the brick vary so, while, on the other
hand, the bonds are so large that a neat job cannot generally be
obtained. Inasmuch as the cost of laying the brick is about 75
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664 ELECTRICAL EQUIPMENT
per cent of the total cost| very little is added by substituting a
face brick. With this type of construction the compartment
shelves are generally made of concrete or soapstone, from 2 to 3
inches thick, depending on the size of the compartment.
Concrete, although more costly, has gained in favor over
brick work, and therefore the majority of bus and switch compart-
ments nowadays are built of concrete, especially for the laiiger sta^
tions. In some cases complete forms are made, usually of wood,
and the whole compartment poured, giving a very substantial
construction. It is more often the case, however, that concrete
slabs are used, set in cement.
The general dimensions of bus and switch compartments are
determined by the minimum distance allowable between conductors
and ground (see table LII, page 627), the brick or concrete being
considered as ground. The switching apparatus also governs to
a great extent the dimensions of the compartment, although even
here it is generally a matter of ground distance in the apparatus.
For mechanical reasons and accessibility the distances are gen-
erally increased somewhat; this also to guard against joints,
clamps or bolts acting as spillways at times of abnormal voltage
rises on the system. Low-voltage compartments, where relatively
heavy copper is used, should have proportionally more liberal dis-
tances than those for equal capacities but of higher voltages, with
connections of smaller size.
Removable doors are recommended for all openings of compart-
ments to prevent accidental contact with live parts, and in the
case of oil circuit breakers, to prevent the scattering of oil should
it be forced out of the oil vessels. Compartment doors should
be made of light, fireproof material and swimg from the top to
allow free movement in case of explosion in the compartment.
Asbestos lumber with a light wood frame has proved to be the most
satisfactory construction for compartment doors. Compartment
doors should be considered as ground, that is, in respect to all live
parts.
The arrangement of switch and bus structures varies consider-
ably, depending not only on the S3rstem of connections, but also
on the different designs of the circuit breakers. It is therefore
impossible to give any definite recommendations that wiD meet
all conditions. In addition to the illustrations shown in the sec-
tion on " Arrangement of Apparatus," page 175, Pigs. 363 to 357
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SWITCHING EQUIPMENT 565
are given, which show some typical arrangements which are self-
explanatory.
In la3ring out the structure attention should also be given to
the current and potential transformers. The latter with their
fuses require considerable space for higher voltages and have to be
installed in certain positions. This refers especially to oil-cooled
transformers and expulsion fuses, so that if in the preliminary
design these points are not taken into consideration considerable
diflSculty may be encountered in finding suitable accommodation
for them. When current and potential transformers are installed
in separate compartments, holes should be left in the partition
walls to accommodate conduits for the secondaries between
phases, and in case of potential transformers porcelain bushings
should be provided for the primaries.
For voltages above 15,000 the circmt breakers are, as a rule,
of the top-connected tank construction and compartments are
entirely omitted, especially for the higher voltages. The conduct-
ors must necessarily be spaced farther apart and at a consider*
able distance from the floor, so as to be out of reach. Different
arrangements are used for nearly every new station, as seen from
the illustrations. Figs. 93 to 101.
The busbars are an important part of the installation, carrying-
the whole energy of the plant in a confined space. The material
is usually copper and the conductors may be either cylindrical
rods or tubes or rectangular bars. The former are generally
used for the high-tension ouses and connections, but the latter are
essential for lower voltages where large currents are to be carried,
necessitating a larger cross-section. In such cases the bus is
laminated, i.e., it consists of a number of bars arranged side by
side with ventilating ducts between. This insures a large radiat-
ing surface, while at the same time this construction permits a
tapering of the bus so as to utilize the material to the best advan-
tage. Additional bars may also readily be added in case the
capacity needs to be increased in the future.
The buses as well as the connections to the oil circuit breakers,
etc., should be so proportioned as not to attain an excessive tem-
perature rise under the maximum current which they are intended
to carry. For direct-current work the features affecting the tem-
perature rise are the size of the bar, the number of laminations,
spacing of laminations, spacing between poles, whether the bars
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566
ELECTRICAL EQUIPMENT
axe run flat or on edge, and whether open or enclosed in compart-
ments. For alternating-current work the heating in addition
depends on the skin-effect and the
inherent reactance of individual
laminations and phases.
The permissible heating will de-
pend on the fact whether these bus-
bars are simple uninterrupted car-
riers of electricity from one end to
another, or whether connections
are taken off the bus at certain
Fig. 353.
Fig. 354.
Typical Low-tension High-capacity Switch and Bus Structures.
points to circuit breakers, etc. In the latter case the heating of
the bus-bars or of the whole combination from bus to circuit
breaker must be kept at a low enough figure so that the total
temperature rise is below the temperature rise permitted for the
breaker, which generally is 30° C. The connection bars should,
therefore, in such cases be so proportioned as not to develop a
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Fia. 355.
Fig. 356. Fia. 357.
Typical Low-tension High-capacity Switch and Bus Structures.
567
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ELECTRICAL EQUIPMENT
temperature rise in excess of this value and the bus-bars not in
excess of 35° C. above the ambient temperature.
The curves in Fig. 358, which have been derived from a large
number of actual tests, show how the current density in amperes
per square inch, based on a 30° C. rise, will vary in accordance with
the number and width of lamination. The bars are I inch thick
and run on edge, and the spacing between the laminations is also
i inch and between the centers of the phases 8 inches.
The great variations in the density for the dififerent conditions
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Fig. 358. — Permissible Amperes per Square Inch in Copper Connections.
Installed in Open Air on Edge.
i" Spacing between Laminations.
Laminations i" thick.
8" Spacing between phases
30*^ C. Temperature Rim.
is apparent from the curves. An increase in the spacing between
laminations from J inch to J inch will naturally increase the ven-
tilation, and thereby the permissible cm'rent which can be carried
at 30° C. rise, at least on direct-current. For several lamina-
tions, run flat, that is, with their width parallel to the floor, the
heating will be at least 25 per cent greater than when the bars
are run on edge. Furthermore, consideration must be given to
the fact that the ventilation of buses in compartments is not as
good as in the open, and for this reason it will generally be advis-
able to limit the temperature rise for such conditions to a figure
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SWITCHING EQUIPMENT
56d
iBaraperpluae
i
i Bars per phase
somewhat below the permissible temperature rise of buses in the
open.
Skin-effect can best be taken care of by arranging the bus-bars
so as to simulate a cylinder or tube, and this is done by running
the laminations as much as possible in pairs, as shown in Fig. 350.
The distance between the pairs should_ then
be as great as the space of the bus-bar com-
partments will permit.
With the bars run flat in the compart-
ments, the connections can, as a rule, be
made easier, but, as previously stated, the
ventilation becomes poorer than if run on
edge. On the other hand, installing them
on edge gives a more substantial construc-
tion in that it increases their strength and
abiUty to withstand short-circuit stresses.
With alternating current bus-bars run
flat, the reactance of the laminations in
the outside phases varies quite consider-
ably, this effect being more noticeable the
less the distance between phase centers.
The effect of this difference of the inductive
reactance in the bars, due to the different
distance between the middle phase and the
individual laminations, will cause the lami-
nation nearest the middle pha^ to develop
the least reactance, and the lamination
farthest away from the middle phase to develop the highest
reactance. Therefore, the lamination nearest the middle phase
will carry the highest ciu-rent and the bar farthest away from the
middle phase the lowest current. If the bus-bars are placed on
edge this difference of inductive reactance in the laminations
disappears, and the only effects to be looked out for on A.C.
bus-bars is then the matter of ventilation and skin-effect.
Both the buses and the connections should be securely sup-
ported and the insulators should be bolted or clamped to the wall
or slab and not cemented, since this construction causes consider-
able inconvenience when it becomes necessary to exchange an
insulator. Several different lines of bus-bar supports are now on
the market, two typical types being illustrated in Figs. 360 and
Q Bars per phase
Fig. 359.— Method of
Paiiing Bus-bars to
Reduce Skin Effect.
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ELECTRICAL EQUIPMENT
Fig. 360.— Bus Insulator;
Bus Laid Flat.
Fig. 361. — Bus Insulator;
Bus on Edge.
361. The former is for
mounting the buses on edge
and the latter on the side or
flat.
In stations of large capac-
ity precautions should be
taken in supporting the
buses in the compartments,
due to the great stresses
which are exerted imder
short-circuit conditions. This
subject is dealt with in
detail in the section on
"Current-limiting Reactors,"
page 458. Fig. 362 shows
the design for a support to
be used under such condi-
tions. It consists of two
porcelain insulators, fitted
loosely into the horizontal
compartment barriers, as
shown. Two alloy clamps of
similar design, held apart by
four brass pillars fitting
loosely into holes in the
clamps, form the support for
the bars. The top damp
has a threaded stud extend-
ing into a hollow in the top
insulator. By tightening the
nut on this stud against the
top insulator, the whole sup-
port is held firmly in place.
By loosening this nut to the
limit of its travel against the
top clamp, it is possible to
lift the top clamp for the re-
ception of new laminations
of bus or to remove the top
insulator, there being just
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SWITCHING EQUIPMENT
571
enough play to permit it to clear the top stud. Subsequently
the remaining parts of the support can be easily removed for
repair or inspection. The individual laminations of the bus are
separated by fillers, and the
number of laminations can be
varied at will by using pillars
of the proper length.
The bus supports should
be located near openings in
the compartments so as to be
accessible for cleaning and
inspection (Fig. 363). This
also refers to all the clamped
joints between the buses and
the connections.
For very high voltages the
buses generally consist of
round copper rods or tubing,
the sizes given in Table LVI,
page 638, being quite com-
mon. These buses are gener-
ally supported from the roof
trusses by suspension insula-
tors and the connections on
post-type insulators mounted
on the walls (Fig. 364).
For long buses, provision
must also be made for expan-
sion and contraction due to
temperature changes. The
diagram in Fig. 365 gives the
linear expansion of copper
buses, the values being based
on an installation tempera-
ture of 25° C. = 75° F. The actual expansion over any tem-
peratiu^ range on the chart is the algebraic sum of the expansion
values shown for the temperature limiting range. The chart
has been corrected for variations in the coeflScient, and the actual
temperatiu'es should, therefore, be used.
The problem of bringing a high-tension wire out of a building
Fig. 362. — Bus-bar Support for Large
Capadties in Compartments.
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572 ELECTRICAL EQUIPMENT
is similar to bringing one out of a transformer. It is usually
best to bring the high-tension conductors out through the roof,
although in some cases a wall outlet may be advantageous. No
fixed rule can be made in this respect since the method depends on
the particular layout, arrangement of buses, disconnecting switches,
and lightning arresters. For pressures of 100,000 and higher, the
Fig. 363. — Low-tension Bus Compartments.
weight of the outlet bushings and their great size as well as the
required ground clearance from steel must be taken into consid-
eration when designing the roof. Figs. 366 and 367 show two
typical designs of line entrances.
Owing to the cost of providing suitable buildings for trans-
formers and switching equipments operating at very high poten-
tials, the question of placing this apparatus outdoors is one that is
receiving a great deal of attention. Numerous transformer and
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SWITCHING EQUIPMENT
573
switching stations of this kind are in successful operation, and,
while the practice has only been in connection with a few generat-
ing stations, the results obtained from these installations have
clearly demonstrated the practicabihty of such a design. Notable
among such systems is that of the Utah Light & Power Company.
The high-tension buses and connections together with the dis-
connecting switches, choke coils, lightning-arrester horn gaps, etc.,
are generally mounted on steel structures or trusses supported on
towers, the layout being governed by the equipment and the
method of control which has been adopted. The line wires
should be securely anchored before entering the station structure
Fig. 364. — ^Tjrpical High-voltage Bus and Switch Structure.
and no unnecessary strains should be permitted in the wires inside
the structure. Consideration should be given to deflections
resulting from different pulls on the connections and also to un-
equal settlement of supporting towers, which may readily cause
excessive stresses and insulator breakages, resulting in service
interruptions. The spacing of all the conductors, as well as that
of apparatus should be liberal but not large.
The oil circuit breakers and transformers are generally located
on the ground, the oil circuit breakers being placed below the dis-
connecting switches. It is often desirable to provide some sort
of housing or roofing for partially protecting the oil circuit break-
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674
ELECTRICAL EQUIPMENT
ers, and where low-tension switching equipments and attendance
are required a small building must necessarily be installed. Such
a building can then contain also a repair shop, storage-battery
equipment for operating the oil switches, etc. The transformers
should be placed on concrete foundations of a sufficient height to
be clear of water, and the stations should further be well paved
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Temperature Degrees
Fig. 365. — Linear Expansion of Copper Bus-bans.^
and drained around the apparatus. Transfer tracks with a
truck will also be found very convenient when moving the appa-
ratus. Cement walks should be laid on that portion of the ground
where the operator is most apt to pass in his inspection trips and
work about the place. The oil piping to the transformers and
» By courtesy of General Devices and Fittingis Company.
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• SWITCHING EQUIPMENT
575
Fig. 366.--Typical Wall Entrance for Moderate Voltage.
Fig. 367.— Typical Roof Entrance for High Voltage.
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ELECTRICAL EQUIPMENT
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SWITCHING EQUIPMENT
577
switches, and the water piping, if water-cooled transformers are
provided, should be so arranged that connections can be made or
broken for any unit without disturbing the operation of the other.
Figs. 368 to 370 illustrate typical outdoor arrangements,
and Fig. 371 shows how the low-tension leads can be brought from
the building through tunnels to the outdoor structure. The
leads shown in the illustration come from the low-tension terminals
of a transformer located above.
Disconnecting Switches. In all high-tension circuits it is
customary to install knife-type disconnecting switches for iso-
lating oil circuit breakers, feeders, etc., and for making various
Fig. 369.— 66,000-volt Outdoor Substation. ;
'i
connections that do not have to be opened under load. For'
voltages of 2500 or less, these disconnecting switches are mounted [
directly on a base of marble or similar material, while for higher
voltages post insulators of various kinds mounted on pipe work
or steel bases are used to support the switch jaws. Up to 33,000
volts, these disconnecting switches are made for either front
connection or rear connection or both. For higher voltages they
are invariably made for front connection only, and in order to
insure rigidity and prevent oscillations where the blade becomes
very long, as for switches of the higher voltages, the blades may
be of a truss design (Fig. 372).
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ELECTRICAL EQUIPMENT
Disconnecting switches are usually operated by means of an
insulating rod or switch hook which is made of selected material
especially treated for the purpose and capable of safely with-
standing the operating voltage. For medium voltages, holes are
provided in the ends of the switch blades for the insertion of the
hook, but for higher voltages where the length of the handle may
Fig. 370.— 110,000-volt Outdoor Transformer and Switching Station.
be up to 15 feet or more, it becomes difficult to insert the hook
and this is provided on the switch blade instead, as will be noted
from the illustration. Sometimes means are provided for ground-
ing the handle when in use.
When disconnecting switches are so mounted that the blade
forms the portion of a loop, the switch may be thrown open by
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SWITCHING EQUIPMENT 579
the magnetic repulsion suddenly set up by a large rush of current
consequent upon a heavy overload or short-circuit. This with
very few, if any exceptions, results in damage to the switch,
caused by its opening under heavy load. To obviate such possible
results, disconnecting switches should be provided with safety
locks which hold the switch blade in a closed position until opened
by the operator. The catch is closed automatically when the
Fig. 371. — Showing Method of Bringing Low-tension Leads from Outdoor
Transformers to Building through a Tunnel.
switch is closed, and it may be of a design so as to serve in addition
as a guide for the blade in closing.
The ordinary high-voltage knife-blade disconnecting switch,
operated by a hook on the end of a long rod, necessitates an amount
of space of the operator directly below the switch and perpendicu-
lar to its base, depending both upon the length of the blade and of
the rod used to open and close it.
Where the space is restricted this design may therefore not
be the best suitable and a switch as shown in Fig. 373 has been
developed for such conditions. It is operated from directly below
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ELECTRICAL EQUIPMENT
by a disconnecting switch hook. There is not needed the room
which would otherwiae have been necessary for the operator to
use the switch hook at the considerable an^le required.
FiQ. 372.— 110,000-volt Disconnecting Switch with Safety Catoh and Opening
Device.
The insulators, insulator caps, and terminals are standard.
The blade is a copper rod with a cast eye fastened on one end and
a readily renewable solid brass contact tip on the other. The sta-
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SWITCHING EQUIPMENT
581
tionary contacts are the same as those used on H-type oil circuit
breakers.
When' the switch is opened a flange near the tip of the blade
prevents the blade from dropping below the upper part of the lower
stationary contact. A wide
flare on the lower end of
the upper contact leads the
blade into place when the
switch is being closed.
After the blade is closed
a slight turn to the right or
left by the operating rod
locks the blade in position
and prevents it from open-
ing except when desired.
Sometimes the discon-
necting switches are wired
up to indicating lamps
mounted on the control
switchboard. These lamps
are then inserted in the
miniature bus-connections
and will show to the oper-
ator whether the switches
are in the open or closed
position.
The switch shown in
Fig. 374 is for use on
heavy outdoor service. All
the three poles are operated
simultaneously by a lever
Fig.
373. — Special Disconnecting Switch
for Restricted Quarters.
or handle which can be located at any height from the ground
and locked in either open or closed position. It is of the single-
break type, equipped with a horn-type arc deflector on the sta-
tionary contact. The shape and location of the horn in conjunc-
tion with the upward movement of the switch blade definitely
confines the arc on rupturing the exciting current of a line to the
horn and blade and quickly ruptures the arc without short-cir-
cuiting the Une or involving adjacent apparatus. In operating
the disconnecting switch the blades move in a vertical plane
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582
ELECTRICAL EQUIPMENT
describing an arc 90° to go to the full open position. When the
switch opens an arc, the arc is drawn upward on the arc deflector
and the end of the switch blade.
Fry^7¥
L,
Fig. 374. — 110,000- volt, Three-pole, Single-throw, Disconnecting switcL
The construction of the switch blade is such that any snow
or ice that has collected on stationary contact or contact parts of
the switch are readily removed either on opening or closing the
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SWITCHING EQUIPMENT 583
switch. The operating mechanism can be thoroughly grounded
to prevent any danger to the operator.
A suspension-type switch for mounting directly in a trans-
mission Une at the point of support of a tower is shown in Fig. 375.
The blades are suspended underneath a string of strain insulators
^
Fig. 375.— 90,000-volt Outdoor Disconnecting Switch with Strain Insulators.
and open downward. The end of the switch with its T-shaped
casting is supported from the suspension insulators, and the L-
shaped casting on the opposite end is connected directly to the
span and is dependent on this to support it in an approximately
horizontal position. The blade guide serves also as a safety
catch to hold the blade closed.
Signal Systems. In large power stations it becomes essential
to provide some means of communication between the switch-
board operator and the machine attendants, and different systems
of illuminated dials, bells or whistles are used. It is important
that this apparatus should be located in a position most convenient
to the operators, so as to save time and avoid possible errors at
critical moments. Direct visual signals between these persons
are practically impossible, without a moving or turning by the
switchboard operator from his position before the instnunent
and control apparatus. This should not be expected of him, as it
would mean relocating himself with reference to the switchboard
equipment for every signal received or sent.
In stations of moderate size it may be sufficient to install one
conmion large illuminated sign which is visible from any place in
the station. It contains the unit numbers and the most important
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5S4
ELECTRICAL EQUIPMENT
signals such as " start," " stop," " stand-by," etc., and is con-
controlled from the switchboard, a whistle being used for calling
the operator's attention to the signals. Sometimes provision
is also made for answering or returning the signals to the switch-
board.
Possibly the most satisfactory and most generally used signal
system is the individual push-button equipment, shown in Fig.
376. It consists of an individual stand for each machine unit with
the signals mounted thereon, as shown. Similar signal equip-
FiG. 376. — Individual Push-button Signal Equipment with Stand for One
Machine.
ments are also provided on the respective machine panels on the
benchboard, the two corresponding equipments being connected
together electrically. The signals consist of colored glass win-
dows with white letters illuminated by small lamps behind. Oppo-
site each signal is a three-way push-button switch, and a gong is
installed near each machine and also at the switchboard. Pushing
a button, for example, at the switchboard rings the gong at the
machine to which the signal is sent simultaneously illuminating
the particular signal which was sent at both places. The gong
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SWITCHING EQUIPMENT
585
keeps on ringing and the signal remains illuminated until the
machine operator acknowledges the signal by pressing the cor-
responding button on his equipment. The connection diagram
for a small equipment of this type is shown in Fig. 377.
It is, of course, not necessary to install the signals near the
machines on pedestals. They are often located on the nearby
wall where they can easily be seen, and occasionally various
colored lamps are installed at the side of the respective signals so
that they can be read more quickly and distinctly from a distance.
One company, for example, uses a blue light beside the " stand-
L-.-
kl kl 1^1
R«layaad
• ' * * ' aa}cl|Gong> — * * ' i
ki ki kl:
<^
Swil
ja
itab««
mpaj
MAchlne Stand
Fig. 377. — Connection Diagram of Two Signal Equipments with Three Signals
by " signal, a red for the " fast," a green for the " slow " and
white for all the others.
What the signals should read depends, of course, to some
extent on the local operating conditions. The following are,
however, very conmion: "Stand-by," "start," "fast," "slow,"
" stop," and " O.K." These are used in the power-house of the
Pennsylvania Water and Power Company, their meaning being as
follows:
" Standi ": Stand near governor and await fmiiher orders.
Correct any apparent governor trouble. Trouble impending.
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586 ELECTRICAL EQUIPMENT
The " Stand-by " signal is to be used during the cutting out of
units, tests, Ughtning storm, or other expected troubles.
'' Start ": Start unit at once on hand control.
*' Start Fast ": (Combination signal). Start unit as quickly
as possible.
<< Faa ": If unit is not on the bus, increase speed. If unit is
on the bus, increase gate opening gradually. If the signal is
flickered, increase rapidly.
" Stop ": Shut down unit at once.
" O.K. ": Unit on bus. Engage governor-control motor gear.
Conditions normal. Further attention not needed. Cancels
" Start " or " Fast " signal. The " O.K." signal is also used when
unit has come to rest and field has been taken off.
The whistle used in this power station is electrically controlled
from the switchboard and is operated by compressed air at 300
pounds pressure. It is located at one end of the power-house and
is loud enough to be heard over the noise of the machinery in all
parts of the building, and can be heard outside the building for
quite a distance. It is used principally for calling persons con-
nected with the operation, the code being as follows:
Attention to signals —
Assistant operator
Machine man — —
lightning storm on
" On hearing this signal a special arc extinguisher observer will
report to operator."
Hydraulic floorman
Hold frequency
This is an emergency signal to be used in case the station is
swamped or running away. " If the station is swamped, force all
machines to fuU gate opening; if running away, close all hand-
control machines until frequency returns to n(»inal. If governor
system has failed, governor machines must be changed over to
hand-control and regulated imtil frequency returns to normal.
Pumpman must make every effort to hold pressure on governor
and handrcontrol systems, starting pumps and taking any other
necessary steps. Extra men, unless otherwise detailed, to report
to floorman on governor floor."
Emergency stand by
*' Serious general emergency existing or impending. All
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SWITCHING EQUIPMENT
587
attendants stand by. Extra men report to floorman or operator,
unless otherwise detailed. Chief and assistant chief operators
proceed to benchboard, maintenance men report to chief operator."
There is another emergency whistle located on the roof of the
building, for the purpose of calling assistance during operating
emergencies and for calling the
operating heads and company
physician in case they could not
be located by telephone. This
whistle can be heard a distance
of five or six miles.
A novel signal system is used
by the Mississippi River 'Power
Company in its station at Keo-
kuk. In general it consists of
transmitting and receiving dials
with the signal words plainly
marked thereon. A pointer on
the receiving dial is electrically
connected to follow the position
of a handle on the transmitting
dial. Fig. 378 illustrates a ped-
estal containing a transmitter
(lower dial) and a receiver
(upper dial). One pedestal is
located in front of each genera-
tor in the generator room (Fig.
3), and a similar equipment,
although without the pedestal,
is located on each generator
panel in the control room.
A diagram of connection of
the apparatus, which is known
as position indicators, is given in
Fig. 379. Each complete equip*
ment consists, as said, of two machines, a transmitter and a re-
ceiver, connected as shown and resembUng in design small induc-
tion motors. The stators are provided with an ordinary closed
winding, three equidistant points being permanently connected
t<^ether. The rotors are bipolar, connected in multiple and ener-
Fia. 378. — Signal Equiptnent at
Mississippi River Power Com-
pany. Generator Room Ped-
estal.
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ELECTRICAL EQUIPMENT
Fig. 379. — Diagram of Connections of
Position Indicator.
gized from a 25-cycle, 125 volt, sincle-phase source; the stator
being energized by inductions from the rotors.
The movement of the transmitter rotor, which is mechanically
operated by a handle, induces voltage in the stator winding.
This voltage is transmitted by the three-phase tie to the stator
^ of the receiver and dupU-
^v^^cs^^^ Z cj^tes in it the same polar-
ity and voltage conditions
developed in the transmit-
ter stator, but in the reverse
direction. The rotor of the
receiver is energized in the
ekme direction as that of
the transmitter, and conse-
quently reacted upon by
tiie polarized stator until
their magnetic axes coincide
and the rotors of the transmitter and receiver are in the same
relative position. With the rotors thus, no current flows between
the stators. Any difference in the position of the transmitter
and receiver rotors causes a flow of current and resultant torque
which moves the receiver rotor and dial pointer to the same rela-
tive position as that of the transmitter. On both the pedestals
and benchboard, at each side of the transmitter handle, are located
double push-button switches which are employed for operating
signal lamps, whistles and bells.
The method of signaling is as follows: When the switchboard
operator desires to send a signal he turns the handle of the trans-
mitter until its dial indicates the signal he wishes to send. This
signal will be indicated on the dial of the receiver in the generator
room. He then pushes the button on the right of the handle.
This Ughts a lamp on the generator (Fig. 3) and blovjs a whistle
in the generator room to attract the attention of the man in chai^ge
of the particular machine. As soon as the attendant has read
the signal on his receiver, he will turn the handle of the transmitter
on the pedestal to the same signal. He will then push the button
at the right of the handle, which will extinguish the lamp and
cut out the whistle. Next he will push the button at the left of
the handle, which operation will light a lamp in the switchboard
room and also ring a signal bell indicating to the switchboard
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SWITCHING EQUIPMENT 589
man that the generator attendant has received the signal and also
just what signal he received. The switchboard operator, after
having seen this returned signal, will push the button at the left
of the transmitter handle, which will extinguish the lamp and cut
out the signal bell. This completes the cycle of sending and
receiving a signal.
The system is identical to that used on the Panama Canal to
indicate the position of the lock machinery.
The signal i^tem in any important station is alwa3rs sup»
plemented by a multiplenstation interconmiunicating telephone
system. This is used when special orders or instructions are to be
given.
Multi-recorder. The multi-recorder is a device for recording
on a strip of paper the exact time of the occurrence of any elec-
trical phenomena and is appUcable in central stations for record-
ing switching operations, line surges and other disturbances
beyond the control of the operator. In case of accidents such a
record is of particular value because it enables the engineer to know
where and when the trouble started and how the switching was
done.
The recorder consists essentially of a number of stamps operated
by a clockwork and printing the time, within fraction of seconds,
of the event to which they are relayed. A description of this device
is given by Prof. E. E. F. Creighton in the A.I.E.E Transactions,
1912, page 825.
Oil Circuit Breaker Batteries. The operation of remote-con-
trol oil circuit breakers, field switches, field rheostats, signal lights,
etc., necessitate an absolutely reliable source of energy which
should be entirely independent of the regular distribution circuits
and held in reserve exclusively for this purpose.
It is therefore usual to ftistall a motor-generator set consisting
of an induction motor driven by power from the A.C. circuit,
direct connected to a direct-cxurent generator. In order, however,
to insure continuity of service in case of an interruption in the
supply of current from this machine, whether due to failure of
the power supply on the A.C. circuit or to some derangement
in the machine itself, it is standard practice to install a storage
battery, which is normally kept floating across the terminals of
the direct-ciurent machine. This motor generator is kept run-
ning continuously except for such brief periods of time when it may
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590 ELECTRICAL EQUIPMENT
be necessary to shut it down for inspection or repairs, and under
normal conditions it carries the steady load due to the signal lamps,
and supplies a small amount of charging current to the batteiy
in order to keep it fully charged at all times and ready for ser\'ice.
This direct-current machine is of the shunt-woimd type having
a decidedly drooping characteristic, so that when a heavy demand
occurs, due to the opening or closing of oil switches, ^tc, the load
is divided between the machine and the battery, and the machine
itself is thus protected against excessive momentary overload.
The normal voltage of the control circuit is approximately
125 volts, but the D.C. generator is designed for the maximum
charging voltage of the battery, which may rise to about 2.80
volts per cell. The ampere capacity of the generator should be
equal to the normal charging rate of the battery plus the current
required for the signal lamps.
It will be noted from the above that imder ordinary conditions
of operation the battery does very Uttle work, and the maximum
demand upon it occurs only when it is necessary to open or dose
a number of switches simultaneously at a time when the motor
generator set is inoperative.
The ampere capacity of the battery is determined by ascer-
taining the maximum possible demand due to the simultaneous
operation of as many of the remote-control devices as are Uable
to be operated at once, and, selecting a battery of sufficient size
to supply this current for the period of time necessary without
dropping in voltage below a certain permissible minimum. The
number of cells is usually fixed at 60, and for this number a
floating voltage of about 127 volts is suitable.
Standard remote-control apparatus is usually designed to
operate over a comparatively wide range of voltage variation,
owing to the fact that such apparatus* is in some cases operated
from an exciter circuit whose voltage is varied by automatic
regulators. In order to provide ample margin of safety, a mini-
miun voltage of 90 is usually fixed for the battery when carrying
its maximum load. This is equivalent to 1.5 volts per cell. A
properly designed storage battery equipped with low-resistance
intercell connections and provided with conductors of ample
capacity for connecting to the switchboard may be discharged at
five times the one-hour rate (twenty times the eight-hour rate)
for a period of one minute without dropping below the limiting
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SWITCHING EQUIPMENT 591
voltage of 1.5 per cell above mentioned. Oil switch batteries are
frequently, therefore, designed to work at five times the one-hour
rate when the maximum possible load is to be carried with the
motor generator set shut down. In order to determine the
maximum possible load, it is usual to figure that not more than
two remote-control switches will be closed at one time, and not
more than one-half of the total number of automatic switches
will be tripped simultaneously. When more than twenty oil
switches are installed, it is considered safe to figure on not more
than one-third of the total number of automatic switches being
tripped at the same time. The duration of any single switching
operation is but a fraction of a minute, and a battery subjected
to intermittent discharges at high rates recuperates rapidly during
the intervals of rest, so that a battery figured, as above, will easily
handle as many successive operations as are Uable to be required.
The current required for the operation of oil circuit breakers, etc.,
varies with the size and make, and should be obtained from the
respective manufacturers.
In some cases an emergency station lighting circuit may be
arranged for connection to the oil switch battery in case of com-
plete interruption of other sources of Ught. To provide for this,
a battery of greater ampere-hour capacity may be required than
that determined by the oil switch service alone.
In order to permit giving the battery a charge to maximum
voltage by raising the voltage of the generator without subjecting
the signal lamps and remote-control apparatus to this high voltage
a tap is taken from the battery to the switchboard by means of
which a group of 10 cells may be cut out. At the beginning of
charge the entire 60 cells are connected to the dynamo, whose
voltage is raised suflSciently to dehver the charging current,
while 50 cells are connected across the control circuit. The cur-
rent required for the signal lamps under these conditions passes
through the end cell group in addition to the charging current of
the main battery, and the charging of the end cells is, therefore,
completed before that of the main battery. The end cell group
is then cut out and the charging of the remaining 50 cells is com-
pleted. The maximum voltage of these 50 cells at the end of
charge will be nearly 140 volts. The signal lamps are designed
to stand this voltage for a short time, and the standard remote
control apparatus will operate satisfactorily at this voltage.
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ELECTRICAL EQUIPMENT
In Fig. 380 is shown the diagram of connections for this scheme.
The negative bus is divided into two sections and two single-pole,
double-thi-ow knife switches, A and B, are provided, one connected
to each section of the negative bus. When A is thrown down the
60 cells of battery are connected across the generator terminals,
12B Volt Opsnttiac Bu>^
Motor-Generfttor Bet
Nonnal (Floatioff) :
CharsrcfiOGelb:
CharveM Cells;
Motoc Q«D«nitor Set a
Fig. 380. — Diagram of Connection for Floating Oil Circuit-breaker Battery.
and when B is thrown down the two sections of bus are connected
together and current is furnished to the control circuit by the
dynamo with the battery floating in parallel. This is the normal
position of these switches.
At the beginning of the charge, switch B is thrown up con-
necting the control circuit across 50 cells, and the voltage of the
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OVER-VOLTAGE PROTECTION 593
dynamo which is still connected across 60 cells, is raised until the
desired charging current is obtained. When the 'end cell group is
fully charged, as indicated by free gassing and maximum specific
gravity, switch A is thrown up, cutting out the end cell group
and the charging of the main battery is completed.
An overload circuit breaker is provided in the positive lead
from the generator. In some cases a reverse-current trip has been
provided for this circuit breaker; but this is usually omitted,
owing to the fact that a momentary variation of frequency on the
83rstem might lower the speed of the motor generator set and reverse
the ciurrent, thus tripping the circuit breaker unnecessarily. A
momentary reversal of current through the generator would
usually be quite harmless.
In the battery leads. fuses are inserted rather than circuit
breakers, as it is not desired to have the battery circuit open
except under extreme conditions, such as short-circuit in the con-
trol S3rstem.
When the battery is kept continually floating at practically
constant voltage across the D.C. operating bus, and another
source of current, such as a motor generator set, is provided to
supply the steady load of signal lamps, etc., so that the battery
work is limited to occasional momentary discharges when the oil
switches are operated or to such sustained discharges as may be
called for in case the normal source of current should fail — in other
words, where the conditions call for strictly emergency stand-by
service from the battery — the Exide or similar type of battery in
glass jars is recommended, this being the* same type that is now
generally used for stand-by service in the large central station
lighting systems. Where a method of operation is adopted in
which the battery is discharged continuously on the bus until
nearly exhausted and then recharged, thus involving repeated
cycles of charge and discharge, the Manchester type of plate or
similar is recommended, the Exide plate being only reconmiended
for use on floating batteries at approximately constant voltage
and discharging only under temporary emergency conditions.
9. OVER-VOLTAGE PROTECTION
Classification of Over-voltages. High-voltage disturbances
may be divided into two broad classes. First, that covering
actual high voltages in which the excess voltage exists between the
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594 ELECTRICAL EQUIPMENT
phase conductors or between the phase conductors and ground.
Second, that covering locaUzed high voltages in which the excessive
potential difference exists between two points along the same con-
ductor. In these cases the " conductor " is supposed to include
the line wires as well as the generator and transformer windings.
To the first class belong those distiu*bances which are caused
by overspeeds, poor regulation and resonance, while the nature
of disturbances caused by switching, arcing -grounds, and Ught-
ning may be such that they may belong to either class. Where
the impulses or traveling waves set up are of comparatively low
frequency and consequently of sloping wave front, the disturbance
can, however, genertdly be classed with the former, and when of
high frequency and steep wave front with the latter.
Excessive over-voltages are very apt to occur when water-
wheel-driven generators run away, especially if they are provided
with direct-connected exciters. Actual experience has thus
demonstrated that under such conditions the generator and trans-
mission voltages may reach three times their normal value, which
of course subjects the apparatus to unreasonable strains. To
provide against this, automatic brake equipments are provided
or else high voltage cut-out relays which automatically insert
resistances in the exciter fields if the voltage exceeds a certain pre-
determined value.
In the design of modern long-distance transmission lines it
is generally the regulation, or the variation in voltage which occurs
when the load is thrown on or off, that is the governing factor
rather than the energy loss. Not only may the voltage drop
under load be quite large, especially when the load has a low power-
factor, but with the high-transmission voltages now in use the
capacity effect of the lines becomes very high, which in turn ma^^
result in a considerable voltage rise at the substation at light
loads. This is now one of the chief arguments against isolated
delta connection for long-distance high-tension lines. It was
formerly claimed that such a system could be temporarily
operated with one line grounded. Recent experiences on laiige
systems, however, indicate that this is not feasible, as in the
event of a ground the charging cm-rent, which is a function of
the voltage from wire to neutral, will be increased because the
natural is shifted from the center of the delta to one comer.
This increase will be about 73 per cent and will of course in
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OVER-VOLTAGE PROTECTION 695
turn cause an additional voltage rise at no load, which is not
pennissible.
The voltage rise caused by the charging current in a long line
may cause a breakdown of the air nearest the line conductor and
cause corona which may seriously increase the transmission losses.
They may also unduly strain other insulations on the system and
afifect the operation of the Ughtning arresters, the normal voltage
range of which should be kept within reasonable limits for satis-
factory operation. On the other hand it is well known how the
operation of motors is affected by voltage variations and that
the life of lamps is seriously reduced if the voltage is too high,
not to speak of the unpleasantness of a variation in the intensity
of the illumination, which of course accompanies a fluctuation in
the voltage.
From the above it is imperative that the regulation of a modem
system be kept within certain permissible limits, and with high-
voltage systems this is most readily accomplished by installing
synchronous condensers with automatic voltage regulators in the
substation. As previously stated, the large-capacity currents
of long-distance Unes cause a rise of voltage from the generator to
receiver at Ught load, while at full load the lagging current taken
by the load will cause a drop of voltage from generator to receiver.
It is, therefore, evident that the voltage may be kept constant or
within certain limits, at the receiving end, if a synchronous con-
denser is installed there, and its field adjusted so as to make it
take a lagging current at no load and a leading current at full load;
in the first case to oflfset the effect of the line capacity and in the
second to offset the surplus lagging load current.
Resonance must also be guarded against, as it can give rise
to large currents which may open the circuit protecting devices
and interrupt the service, or the potential may be raised to a value
at which the installation of the system is broken down. In an
electric circuit the inductive reactance and the capacity reactance
oppose each other. If of equal value they neutraUze each other,
in which case the resistance of the circuit limits the value of the
current. This may, therefore, reach very high values and when
passing through the inductance and capacity the voltage at these
would in turn be very high.
To illustrate this further; assume a circuit having a resistance
of say 60 ohms and a capacity reactance of 1000 ohms, then thQ
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596 ELECTRICAL EQUIPMENT
total impedance would be equal to \/5^+ToO(^ = 1000 ohms
approximately. With 100,000 volts impressed on this circuit
100 000
the current flow would be ' =100. If now in addition
lUUU
the circuit contains an inductive reactance of 1000 ohms, it is
evident that this entirely neutralizes the capacity reactance and
that the current is only limited by the 50-ohm resistance, thus
in this case equal to — ^ — =2000 amperes. With this current
oU
flowing the voltage across either the inductance or capacity be-
comes equal to 2000X1000=2,000,000 volts, which of course
would be far beyond destruction. Of course, this extreme con-
dition does not apply to an ordinary transmission line where the re-
sistance, inductance and capacitance is distributed, but destruc-
tive voltages may be set up where inductance and capacitance
is concentrated.
Fortimately, the characteristics of transmission systems are
such that their inductive reactance is not large enough to neu-
tralize the capacity reactance at the fundamental generator
frequency. Since, however, the inductive reactance increases
and the capacity reactance decreases proportionally to frequency,
the two reactances come nearer together for high frequencies,
such as for the high harmonics of the generator wave. These
may, therefore, be the cause of resonance rise of voltage between
the line capacity and circuit inductance. With modem alterna-
tors, however, the higher harmonics are generally so small that
there is not much danger from resonance.
Abnormal voltages can also be caused by traveling waves
which are set up when the equiUbrium of an electric circuit is
disturbed. Such disturbances may originate in the circuit itself
as by switching or they may be due to external causes, such as
atmospheric lightning phenomena.
When an electric circuit is connected to a generator or other
source of energy, a wave of voltage and current shoots out along
the line with a very high velocity and charges the same. If the
maximum value of the voltage is e and the maximum value of Uie
current i, the wave possesses per unit length an electrostatic
energy of -^ watt seconds and an electro-magnetic energy of —
watt seconds, C being the capacity in farads and L the inductance
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OVER-VOLTAGE PROTECTION
697
in henrys per unit length (cm.), of the circuit. These two quan-
tities are equal or -— = — - and the relation between the voltage
and ciurent at a certain point of the traveling wave is, therefore.
'=\&'
\§^
is termed the '' natural impedance " of the circuit, and is of
great value in the study of transient phenomena.
If the line is open-circuited at the farthey end, it is obvious
that when the wave reaches this point it cannot flow any fmiiher,
-M-
■^«
Fio. 381. — Reflection of a Travel-
ing Wave at the Open-circuited
End of a Line.
Fig. 382.— Reflection of a Travel-
ing Wave at the Short-circuited
End of a Line.
but is reflected, the voltage and current of the reflected wave
being of the same values as in the original waves because the
energy remains constant. The total current of the incoming and
reflected wave must, however, be zero on account of the open-
circuited line, and the whole energy is, therefore, stored at this
point in the electrostatic field. The reflected current wave must
therefore be reversed and its value equal — t, while the value of the
voltage wave at the end of the Une where the original and reflected
waves overlap is, therefore, equal to 26, as shown in Fig. 381.
When the end of the line. is short-circuited, however, the con-
ditions are entirely reversed. In that case the voltage at this
point must be zero, and all the energy is stored in the electro-
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ELECTRICAL EQUIPMENT
magnetic field, the value of the total current at the end of the line
being equal to 2i, Fig. 382.
The wave travels twice forth and back over the entire length
vyz^/VyvyyvwM g:- of the line, after which the
'&^M
mm^mm;^mm^Mmm
t-O
conditions return to the
same state as at the begin-
ning, Fig. 383. It will, how-
ever, continue to oscillate
forth and back until
damped out by the resist-
ance and leakage of the
line, after which it assumes
a stationary condition with
a charge corresponding to
the voltage of the generator.
The wave length, or
rather the distance which
the wave front travels in
completing the above cycle,
is obviously equal to four
times the length of the line,
and the frequency of the
oscillation is
V _ 1
where I is the length of the
hne, and v or — ==: the
Vie
velocity at which electric
energy travels through a
circuit whose inductance
Fia. 383.-One Complete Oscillation of a f^^^ capacity p^ unit
Traveling Wave Set Up when Switching length are L and C. This
velocity for overhead hnes
is equal to the velocity of
light, or 188,000 miles per second. The waves in the above illus-
trations are shown of a rectangular form which could only be
the case if the generators had no resistance or inductance. Ordi-
narily, however, they are of a more or less sloping character.
mmmmmm^-
±^
\^^^^^:^^^^^::mm^^^^-^^
^^>S^^^:>^:>:<Sc^^^^
in an Open-circuited Line.
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OVER-VOLTAGE PROTECTION 599
In the above it was assumed that the end of the line was either
open- or short-circuited. If a non-inductive resistance, R, is
connected across the end of a line, the voltage of the reflected
wave, and thus the total voltage at this point, necessarily depends
on the value of this resistance. When fi= oo it naturdly resem-
bles an open-circuit in which case the maximum voltage is equal
to double the normal value, while if R—0, or negligible, thus
resembling a short-circuit, the voltage is zero. With R=^-^
4
there is no reflected wave at all. If R >y]p there is a partial
reflection with reversal of current, while, if R<-v/pj there is a
partial reflection with reversal of voltage. With an inductive
receiving circuit, this acts in the first instant as a resistance of
infinite value, and voltage reaches double value, while a con-
denser under similar conditions would act as a short-circuit, and
the voltage would be zero.
From the preceding it follows that when a dead high-tension
transmission line is to be energized the best practice to follow
would be to switch the Une onto the dead transformers first by
means of the high-tension switch and then energize the com-
bination of line and transformers by closing the low-tension
switch to the generating source, this sequence of closing the
switches will obviate the high-tension surges and, consequently,
minimize the danger of insulation breakdown.
It is also of greatest importance to consider the changes which
take place at a transition point between two circuits of different
characteristics, when a traveling wave passes from one to the
other, such as, for example, where an undergroimd circuit joins an
overhead, or where a transmission line is connected to a trans-
former.
Assume that a traveUng wave with the voltage e and the cur-
rent i approaches from a circuit having a natural impedance
^"4.
"S.-
and enters a second circuit with a natural impedance of
j^ . Part of the wave will then be reflected and part
transmitted. It is also evident that at the transition point the
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600 ELECTRICAL EQUIPMENT
potential will be the sum of the incoming and reflected waves,
while the current will be represented by the difference of the two
waves since they travel in opposite direction. If we thus denote
the voltage and current of the reflected wave by 62 and 12 and of
the transmitted wave by ei and ti, we get the following relation
at the transition point.
€+62 = €1;
but
€
e2
The amplitude of the transmitted voltage wave is, therefore,
and of the reflected voltage wave
Similarly we get for the current
2Z2
and
''^z^W
. Z2 — Z1.
''-z:+z^'
If, therefore, Z2 has a higher value than Zi, it foDows that the
voltage of the traveling wave is transmitted to the second circuit
at an increased amplitude and vice versa. A traveling wave
originating in an underground cable will, therefore, enter an over-
head circuit with an increase in voltage, while a wave originaUng
in an overhead circuit will pass into a cable system with a lower
voltage.
These relations between the reflected and transmitted waves to
the incoming wave are, however, only applicable to cases where
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OVER..VOLTAGE PROTECTION
601
rAAAAAAAA^— I
z,
z.
the wave in passing the transition point continues its travel in the
form of a wave; that is, in case we have distributed inductance
and capacity on both sides of the transition point. If, on the
other hand, resistance, inductance and capacity are concentrated
at the transition point, the conditions become entirely dififerent,
and it has been suggested that such a scheme should be used for
protecting transformers and machinery against the traveling
waves entering from the line. The use of inductance and capacity
has been advocated for some time, and both have the properties
of changing the wave front of the transmitted wave so that it
begins with zero and rises gradually to its full value. The reflected
wave, however, will have a rectangular or steep wave front, sim-
ilar to the incoming wave.
The energy of the incoming wave is naturally also split up in
two parts, corresponding to the transmitted and reflected waves,
but there is no reduction in the
total energy. This has led to the
suggestion by Gino Campos to
use a resistance shunted across
an inductance (see Fig. 384). In
addition to considerably smooth-
ing out the wave front of the
transmitted wave, if causes some
of the electro-magnetic energy to
be dissipated. The inductance
forces a wave with steep front
to pass through the resistance,
in voltage and gives the transmitted wave a lower value than the
incoming, while on the other hand part of the energy of the wave
r is dissipated into heat. The
working current, however, passes
through the inductance with a
negligible drop. This combina-
tion is connected in series with
the line, as shown.
Another combination consist-
ing of a resistance in series with a
condenser or capacitance, but connected between the line wires
or between the line wires and ground is shown in Fig. 385. Both
of these devices or combinations are particularly effective as
L
Fig. 384. — Protective Device, Con-
sisting of an Inductance Shunted
by a Resistance'. This combina-
tion is for Series Ck)nnection in a
Circuit.
This, in turn, results in a drop
■AWvAA-
FiG. 385. — Protective Device, Con-
sisting of a Capacitance in Series
with a Resistance. This combi-
nation is used in shunt with a
circuit.
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602
ELECTRICAL EQUIPMENT
protective devices as they
dissipate the energy of high-
frequency waves. They are,
therefore, generally termed
" high-frequency absorbers/'
Fig. 386 shows how the
reflection and transmission of
a traveling wave takes place
in a particular case with in-
ductance and resistance con-
centrated at the transition
point. The ampUtude of the
waves as well as their wave
fronts are, of course, dep)en-
dent on the natural impe-
dancesof the circuits on either
side of the transition point,
as well as on the value of the
inductance and resistance
concentrated at this point.
The calculations
are, however, of a
rather intricate
nature and be-
yond the scope of
this book. It is
seen, however,
that with a pro-
tective device of
this kind, both
the trsmsmitted
and reflected
waves have steep
fronts although of
less height than
the original wave.
This has led to
Fig. 386.— The Reflection and Transmission of a the suggestion of
Traveling Wave with Concentrated Inductance and adding a con-
Resistance at the Transmission Point. denser to Campos'
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OVER-VOLTAGE PROTECTION 603
combination, in which case the voltage at the front of both the
reflected and transmitted waves would be zero. Both these
devices are patented.
The above has dealt with the excess voltages which could
occur when a line is connected to a source of energy. Dangerous
voltages are, however, also liable to be set up when a loaded or
short-circuited line is suddenly broken. In this case the voltage
rise depends on the value of the interrupted current, and the rapid-
ity with which the circuit is broken, and again on the natural
impedance of the circuit.
It was previously shown that the energy of a circuit was stored
in both the magnetic and dielectric fields, corresponding to the
current and voltage values. At a certain instant, therefore, the
two stored quantities are equal, while if the current is zero all the
energy must, of course, be stored in the dielectric field and vice
versa. We thus had:
2 2 '
and the relation between voltage and current
^=W-
For transmission work the ratio
-^ = 138 log — ohms,
C T
and this value generally falls between 400 and 200 ohms. For
transformers, however, it is considerably higher, being around
3000, while an tmderground cable has a much lower natiural im-
pedance than an overhead circuit.
For example, if in a circuit having a natural impedance of
400 ohms, a current with a maximum value of 200 amperes is
suddenly broken, the surge pressure cannot exceed 200X400=
80,000 volts, because this is the maximum value of the voltage
wave which is necessary for storing in the dielectric field the whole
amount of energy which was previously stored in the electro-
magnetic field.
Traveling waves similar to the above are also set up by atmos-
pheric lightning phenomena. The gradual accumulation of static
charge on a line from the neighboring atmosphere increases its
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604 ELECTRICAL EQUIPMENT
potential with respect to the earth, which may ultimately become
so great as to puncture the insulators. Suppose now that there
is a Ughtning discharge between cloud and cloud or between
cloud and ground. This is followed immediately by a redistri-
bution of the electrostatic field, and a general equalization of
potential occurs. The static charge so set free moves along the
line as an impulse or traveling wave. Such waves may have a
potential many times greater than that caused by switching, and
they may have a very steep wave front and thus produce high
potential differences between points along the conductor, such as
across individual transformer coils or group of coils.
Several forms of protective devices of more or less value have
been devised to guard against abnormal voltage conditions. Of
these the aluminum-cell electrolytic Ughtning arrester possesses
ideal characteristics against such high-voltage disturbances,
where the excess voltage occurs between the phase conductors or
between the phase conductors and ground. The films of the
arrester introduce a barrier to the normal potential of the system,
but allow the energy of an abnormal disturbance to discharge
readily. The arrester is generally used in connection with choke
coils, the function of which is to retard and reflect the incoming
waves sufficiently to allow the arrester to better perform its duty.
Overhead ground wires are also very generally used to protect
transmission lines against excessive static charges, the cost of
high-voltage lightning arresters making their installation along
the line impractical.
The nature of high-frequency disturbances is a comparatively
recent discovery, and the means and methods for preventing
them and protecting against them is still being studied and inves-
tigated. The greater damage caused by such high-frequency
disturbances has occurred in high-voltage transformers, as would
naturally be expected. The best protection against them, there-
fore, is to insulate heavily the individual coil groups, while
inductances and energy-absorbing devices may, as stated, have to
be relied upon for further protection.
Lightning Arresters. Aluminum-cell electrolytic lightning
arresters are nowadays used almost entirely for Ughtning pro-
tection of high-voltage transmission systems. This type of
arrester has an enormous discharge capacity, and its general
characteristics are well known. The arrester, however, is not a
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OVER-VOLTAGE PROTECTION 605
universal protector against all kinds of interruptions. For
example, while it meets the usual, and most of the tmusual, needs
in protection against disruptive potentials from lightning, an
arrester located in the station cannot, and is not expected to, pro-
tect an insulator out on the line from a lightning flash. Neither
is it designed to protect against surges of comparatively low
potential.
The design is based on the characteristics of a oeU consisting
of two aluminum plates, on which has been formed a film of hydrox-
ide of aluminum, immersed in a suitable electrolyte. This film is
formed on the aluminum plates by a series of chemical and electro-
chemical treatments at the factory. Up to a certain critical
voltage this hydroxide film has the property of insulating, or
rather opposing, the flow of ciurent and is, therefore, closely
analogous to a counter electro-motive force. Up to this critical
voltage only a small leakage and charging current can flow, but,
during any rise above this voltage the current flow through the
cell is limited only by the actual resistance of the electrolyte,
which is very low.
The action is comparable to that of the well-known safety
valve of a steam boiler by which the steam is confined until the
pressure rises to a given value, at which point the valve opens and
releases the excess pressure. This action of the aliuninum cell is
also closely analogous to that of a storage battery on direct-cur-
rent. Up to about two volts per cell, the storage battery, when
charged, opposes an equal counter electro-motive force, shutting
off the flow of current; but for voltages above this value the cur-
rent is limited only by the internal resistance of the cell. This
characteristic makes the aluminum' cell ideal as a means of dis-
charging abnormal potentials or surges in electric circuits. It
practically prevents the flow of current at operating voltages,
but instantly short-circuits such abnormal portion of a potential
wave, or surge, as would be dangerous to the insulation of the
system.
A volt-ampere characteristic curve of the aluminum ceD on
alternating-current is shown in Fig. 387, and it should be noted
that the critical alternating-current voltage is between 336 and
360 volts. This curve gives the discharge rate only up to 5 am-
peres in order to better illustrate the normal and critical voltage
points. Above this value the discharge rate depends almost
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606
ELECTRICAL EQUIPMENT
entirely upon the internal resistance of the electrolyte, for exam-
ple, at double the nonnal operating voltage, or 600 volts per cell,
the current discharge is about 600 amperes for a brief time.
When a cell is connected permanently to the circuit, two con-
ditions of voltage are involved, which may be distinguished as the
temporary critical voltage and the permanent critical voltage.
For example, if each cell has 300 volts appUed to it constantly,
and the voltage is suddenly raised to, say, 326 volts, there will be
a considerable rush of current until the film thickness has been in-
creased to withstand the extra 26 volts; this usually requiring
*00| 1 1 1 1 r T 1 1 1
;::;:e;e;I::"4:-!-t
, . , , 1
..... .^_^=t^
= T="
— r ^^ ^ • -
/
Hz : "" ,_^
r
^ 1
r t *" n~
1
sW 3-- * -
x^ iT"ii"
+ T '^
,
& IE ~
«ifln X-- -H
£ 13 -1- -
1 1_
J
1
80 7 ■
~r
/ —1
I~
-- - :: ::^
Amperes
Fig. 387. — ^Volt-ampere Characteristic Curve of an Aluminum Cell on Alter-
nating Current.
several seconds. In this case 325 volts is the temporary critical
value of the cell. Similar action will occur at any potential up to
about the permanent critical voltage, or the voltage at which the
film cannot fmi^her thicken and therefore allows a free flow of
current. If the voltage is agam reduced to 300, the excess thick-
ness of the film will be gradually dissolved, and if it varies period-
ically between two values, each of which is less than the perma-
nent critical value, the temporary critical voltage will be higher.
This feature is of great importance as it provides a means of dis-
charging abnormal surges the instant the pressing rises above the
impressed value.
The number of cells for a circuit is so chosen that the maxi-
miun voltage per cell will be approximately 300 volts, or always
less than the permanent critical voltage.
Besides the valve action already described there is another
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OVER-VOLTAGE PROTECTION 607
characteristic of the cell of great importance. The thin insulating
film of aluminum hydroxide between the conducting aluminum
and the conducting electrolyte acts as a dielectric, and the cell,
therefore, is an electrostatic condenser. Due to this capacity,
however, aluminum arresters cannot be connected permanently
to the circuits and horn gaps are, therefore, inserted in series with
the connections.
Another characteristic of the aluminum ceU is the dissolution
of a part of the film when the plates stand in the electrol3rte and
the cell is disconnected from the circuit. The film is composed of
two parts; one part is hard and insoluble, and apparently acts as
a skeleton to hold the more soluble part. The action of the cell
seems to indicate that the soluble part of the film is composed of
gases in a liquid form. When a cell which has stood for some time
disconnected is reconnected to the circuit, there is a momentary
rush of current which re-forms the part of the film which has dis-
solved. This current rush will have increasing values as the inter-
vals of rest of the cell are made greater. If the cell has stood dis-
connected from the circuit for some time, especially in a warm
cUmate, there is a possibility that the initial current rush will be
sufllcient to open the circuit breakers or oil switches. This cur-
rent rush also raised the temperature of the cell, and if this tem-
perature rise is great it is objectionable. When the cells do not
stand for more than a day, however, the film dissolution and initial
current rush are negligible. Suitable means, as later described,
are provided with the arresters for throwing them directly on the
line and charging them by a very simple operation, and thus the
film may be always kept in good condition.
The aluminum Ughtning arresters for alternating-current cir-
cuits from 1000 to 155,000 volts consist essentially of inverted
aluminum cones arranged in stacks and insulated from one another
(Kg. 388). An electrolyte partially fills the space between adjacent
cones, so forming aluminum cells connected in series. The stacks
of cones with the electrolyte between them are then inmiersed in
a tank of oil. The electrolyte being heavier than the oil remains
between the aluminum cones. Between the stack of cones and
the steel tank, tubes of insulating material are placed. These
improve the circulation of the oil and increase the insulation
between the live parts. The oil improves the insulation between
cones, prevents evaporation of the solution and, due to its heat-
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608
KLECTRICAL EQUIPMENT
To Sphere - Horn OafJ
Cast dr^ffC9r*!^wr,
£ ^ft^i^ ^hm^Se^ts
ff^ufaty
Fig. 388.— Section through Tank of 130,000-volt Aluminum-cell Lightning
Arrester.
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OVERrVOLTAGE PROTECTION 609
absorbing capacity, enables the arresters to discharge continuously
for long periods, a very valuable feature of these arresters. The
tanks are of steel with welded seams.
The location and arrangement of aluminum lightning arrester
installation depend greatly upon the station layout. In general
the arrester should be installed as near as possible to the apparatus
or station to be protected. The ideal arrangement would be to
have the tanks and horn gaps installed as a complete imit just
inside the station. For lower voltage equipments this is feasible,
as the arcing at the gaps is not severe even in abnormal cases.
Above 27,000 volts, this practice is usually questionable and it is
reconmiended that the horn gaps be installed outside the building,
with leads tapping the line near its entrance to the station, the
object, of course, being to isolate any arc from the station appara-
tus. The tanks, cones and transfer device may be installed inside
of the station in a suitable compartment. This requires the use
of an extra set of either wall or roof entrance bushings in addition
to those used for the hne entrance leads.
Wherever horn gaps are mounted inside the building sufficient
clearance should be allowed over them. The exact distance to
be allowed depends upon the voltage and the nature of the material
or apparatus under which the horns are installed. If there are
cables, wires, buses, or any material which would be damaged
by fire, considerable distance should be allowed. On the other
hand, if there are only concrete and iron beams of the floor or
roof a much smaller clearance is permissible. Normally there is
no appreciable arc at the gaps, but in abnormal cases where the
film has been allowed to get out of order, the arc might be of
considerable size. Where there are no buses or inflammable
apparatus, the following are the minimum clearances from the
tops of horns to be allowed:
Feet.
Up to 16,100 volts 3
16,100 to 37,900 volts 4
37,900 to 75,000 volts 6
Above 75,000 volts, the horn gaps should never be placed
indoors.
The horn gaps for arresters for 27,000 volts and above are
supported on a pipe framework which is so designed as to permit
mounting op either wooden or steel towers, or, if desirable, on the
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610
ELECTRICAL EQUIPMENT
roof of the station or on suitable brackets on the outside wall of the
station. They should be so located that the pipe and lever, by
which they are operated, can be brought down in a place convenient
for the operator and if possible where he can observe the arcing
at the horns during discharge.
With lightning arrester equipments for higher voltages there
is, however, a growing tendency to install the entire equipment
outdoors (Fig. 389). Any objection to installing arrester tanks
out of doors comes, of coiu*se, from the increased liabiUty of freez-
ing the electrolyte in cold weather and the abnormal film dis-
FiQ. 389. — Outdoor Iiightning Arrester Installation.
solution when exposed to the sun on hot da3rs. This, therefore,
has a bearing on the electrol3rte which should be used. These
are two kinds, both of which freeze at about 20° F. One will,
however, better withstand severe winter temperatures and the
other excessive sununer temperatures. Should, therefore, for
example, the operating temperature during summer exceed 100° F.,
with freezing temperature in winter, it would be preferable to
use the electrolyte for the warm weather and provide means
to prevent freezing during the winter months. The electroljie
may not be injured by freezing, but when frozen the internal
resistance of the arrester is considerably increased and hence
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OVER-VOLTAGE PROTECTION
611
its discharge rate is materially lowered. Where warm climatic
conditions prevail the arrester should be in as cool a place as pos-
sible and protected from the direct rays of the sim (Fig. 390).
A high initial temperature will reduce the available heat storage
capacity of an arrester and its abiUty to care for long continuous
discharges. A high operating temperature also increases the rate
of dissolution of the films which would necessitate more frequent
charging. In some cases it may be found advisable to charge
two or more times a day. When operating imder conditions of
high temperature any failure to periodically charge the arrester
Fio. 390. — Oatdoor Ughtning Arrester Installation Showing Protecting Shield
against Sun.
increases the liabiUty of damage from a heavy charging cur-
rent.
Only arresters of the outdoor type, with special bushings and
covers, should be installed out of doors. Care must be taken to
see that the bushings and covers are correctly assembled to be
water-tight. The arresters may be mounted either on a platform
between poles or on a platform near the ground and surrounded
by a fence. The position of the arresters should preferably be
such that their operation can be observed by the station attendant.
While installing arresters out of doors care must be taken not to
let the wooden and fiber parts of the cone stack become wet in
case of rain and to keep dust from the cones and electrol3rte.
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612 ' ELECTRICAL EQUIPMENT
The wiring connections of lightning arresters are important.
The discharge circuit should contain minimum impedance and
hence must furnish the shortest and most direct path from Une
to groimd. The most severe disturbances which an arrester is
called upon to handle are of high frequencies, and it is therefore
imperative to eliminate all necessary inductance. The features
favorable for low inductance are short length of conductor, large
radius bends and large surface of conductor. Copper tubing is
strongly recommended for wiring high-voltage arresters. It has
the advantage over either copper strip or solid conductors in that
it is easily supported, requires fewer insulators, and is therefore
cheaper to install.
In all lightning arrester installations, good, permanent, low-
resistance grounds are essential for the satisfactory operation of
the arresters. Poor grounds cause loss in protection with an
ultimate loss in apparatus. It has been customary to ground a
lightning arrester by means of a large metal plate buried in a bed
of charcoal at a depth of 6 or 8 feet in the earth. A more satis-
factory method of making a ground is to drive a mmiber of 1-inch
iron pipes 6 or 8 feet into the earth about the station, connecting
all these pipes together by means of a copper wire, or, preferably,
by a thin copper strip. A quantity of salt should be placed
around each pipe under the surface of the earth and the ground
thoroughly moistened with water. It is advisable to connect
these earth pipes to the iron framework of the station, and also
to any water mains, metal flumes, or trolley rails that are avail-
able. For the usual size station the following recommendation is
made: place three earth pipes equally spaced near each outside
wall, making twelve altogether, and place three extra pipes
spaced about 6 feet apart at a point nearest the arrester.
Where plates are placed in streams of running water, they
should be buried in the mud along the bank in preference to laying
them in the stream. Streams with rocky bottoms are to be
avoided. Whenever plates are placed at any distance from the
arrester it is necessary also to drive a pipe in the earth directly
beneath the arrester, thus making the ground connections as short
as possible. Earth plates at a distance cannot be depended upon.
Long ground wires in a station can not be depended upon imless a
lead is carried to the multiple earth pipes described above. As it
is advisable to occasionally examine the underground connections
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OVER-VOLTAGE PROTECTION 613
to see that they are in proper condition, it is well to keep on file
exact plans of the location of ground plates, ground wires and
pipes, with a brief description, so that the data may be readily
referred to. From time to time the resistance of these ground
connections should be measured to determine their condition.
This is very easily done when pipe grounds are installed, as the
resistance of one pipe can be accurately determined when three or
more pipes are used. For example: If there are three pipes,
namely, Z, 7, and Z, and the resistance of X+Y=20 ohms, as
measured by a voltmeter, the resistance of X+Z = 15 ohms, and
the resistance of Y+Z = 20 ohms, then, by solving the equations:
X+Y=20;
X+Z=15
Y—Z= 5 subtracting;
y-z= 5
Y+Z = 20
2F =25 adding
y=12iohms
Z = 20-12^ = 7iohms
-X: = 15-7i = 7iohms.
The resistance of a single pipe ground in good condition has an
average value of about 15 ohms. A more approximate method
of keeping accotmt of the condition of the earth connections is to
divide the earth pipes into two groups and connect each group to
the 110-volt Ughting circuit with an ammeter in series. If there is
a flow of about 20 amperes the conditions are satisfactory pro-
vided the earth pipes are properly distributed around the station.
Aluminum cell arresters for non-grounded as well as grounded
circuits above 7250 volts consist of four units, each containing a
single or a double stack of cells depending on the voltage. Three
of the units have one terminal connected to the circuit, the other
being connected together; the fourth unit is inserted between this
multiple connection and ground. This gives the same protection
between line and line as between line and groimd. A transfer
device is provided for interchanging the ground unit with one of
the line imits during the charging operation so that the films of all
the cells will be formed to the same value.
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614 ELECTRICAL EQUIPMENT
It was previously stated that it is necessary to charge the cells
from time to time to prevent the dissolution and consequent rush
of dynamic current which would otherwise occur when the arrester
discharges. The charging operation consists simply in simul-
taneously closing the three horn gaps and holding them closed for a
period of five seconds, the full line potential thus applied across
the line cells causing a small charging current to flow and reform
the films to their normal condition. Thereafter, with the horn
gaps open in their normal position, the position of the transfer
device is reversed and the horn gaps again closed for five seconds
and returned to normal position. The complete charging opera-
tion takes but a few seconds and should be performed daily (ff
even oftener should conditions so demand.
Most arresters are now provided with charging resistances so
as to minimize the oscillations set up by the chaining and their
harmful effects on nearby telephone lines, at the same time also
greatly increasing the life of the cones and the electrol3rtes. An
auxiliary horn gap, fitted with a charging contact, and in series
with the resistance is installed above and in parallel with the main
gap (see Fig. 391). At the time of charging the contact bridge
the auxiliary gap and charges the cells through the resistance,
the cmrent flow being limited to a modei-ate value.
The charging current taken by an aluminum cell arrester is
the best means of indicating its condition, and the value may
readily be ascertained by a device known as a charging-current
indicator. An arrester in good condition has a charging current
of approximately 0.26 ampere on 25-cycle circuits, 0.30 ampere on
40-cycle, and 0.40 ampere on 60-cycle circuits. Should these
values be doubled, the arrester must be charged more frequently
and the current carefully measured until it comes down to normal.
It is only when this additional charging fails to reduce the charging
current that an inspection of the ceDs is necessary. The essential
parts of the charging-ciurent indicator are an ammeter mounted
on a specially constructed switch stick and a set of jacks. These
jacks are so connected in the arrester circuit that when the amme-
ter switch stick is inserted in them and the horn gaps shortrcir-
cuited, the charging current flows through the meter.
Most modem arresters have their horn gaps provided with
spheres which greatly decrease the dielectric spark lag, espedaDy
for voltages with steep wave fronts. The arrangement shown
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OVER-VOLTAGE PROTECTION
616
Fig. 391. — Lightning Arrester Sphere and Horn Gaps with Charging
Resistance
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ELECTRICAL EQUIPMENT
in Fig. 391 provides three gaps which may be so set as to provide
three paths for the discharge. All low-frequency discharges
would form corona and ionize the gap between the horns, passing
across the same and to ground through the resistance and the
cells while a high-frequency discharge would pass through the
upper of the two sphere gaps and similarly to ground. The
lower sphere gap has a wider setting than the upper sphere gap,
but if the quantity of the discharge is too great to be dissipated
through the upper paths, the dischai^ automatically shunts to
#-
Fig. 392.— 90,000- volt (^hoke Coil for Station Service.
the main gap, where it is not impeded by the resistances, and goes
directly through the cells to ground. The resistance is of low
value and consequently all but the heaviest discharges are taken
care of by the auxiliary paths.
A knowledge of all discharges is of immense value to operating
engineers in studjdng conditions of abnormal voltage on trans-
mission and cable systems. For this purpose a discharge recorder
has been developed, which will register the time and nature of dis-
charges through an arrester. This recorder consists of four spark
gaps so arranged that the discharges between lines or between
lines and ground pass through the gaps. The spark gaps are
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OVER-VOLTAGE PROTECTION 617
assembled with a clock-operated drum in such a maimer that a
continuous record is obtained, showing all discharges by means of
punctures in a moving roll of paper. This paper passes through
the gaps at a rate of about 1 inch per horn*, which gives an accurate
record of the time and duration of each discharge. Besides being
valuable in recording discharges due to abnormal voltages on a
system, the discharge recorder is of value in indicating and
recording the daily charging of the Ughtning arresters. With such
a recorder it can be told whether the arresters are or are not
being properly charged by the station operator; and besides the
puncture gives some indication of the condition of the arrester.
Except in underground cable systems, choke coils should
always be installed in the circuit between the Ughtning arrester
and the apparatus to be protected, thus holding back incoming
Fig. 393. — Strain-type Suspension Choke Coil for Station or Outdoor Service.
impulse from the latter until the lightning arrester discharges to
earth.
Choke coils are built either according to a stationary or sus-
pension design. Of the former, the hour-glass type (Fig. 392)
is the most satisfactory, in that it avoids the necessity of supports
between the turns, so that high-frequency disturbances in ground
are prevented from passing across the turns. The air insulation
between the turns is also preferable, so that in case of impulses
with extremely steep wave fronts, causing arcing between turns,
they will re-insulate themselves.
Suspension choke coils (Fig. 393) can usually be incorporated
with the other high-tension wiring, thus saving a number of ex-
pensive insulators, for ,which reason they in many instances
may prove preferable.
Fig. 394 shows a thunderstorm map for the years 1604-1913,
as prepared by the U. S. Weather Bureau.
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ELECTRICAL EQUIPMENT
Arcing Ground Suppressor. Arcing ground suppressors as
well as short-circuit suppressors, described in the next section,
are used for protecting Une insulators against arcs and the con-
sequent vicious surges accompanying such accidental arcs, which
generally follow after Ughtning discharges.
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619
The arcing ground suppressor, as described in the following,
is intended to be used with non-grounded systems. It is abo
Fig. 395. — Elementary Diagram of Arcing Ground Suppressor.
limited to steel tower lines, as on a wood-pole line the resistance
of the pole is liable to prevent suflScient current flowing to ground
to reduce the potential sufficiently to operate the relay.
The arcing ground suppressor, as generally built, consists
of three single-pole, independent, motor-operated oil switches,
electrically and mechanically
interlocked, to prevent more
than one operating at the
same time. Each switch is
connected to ground on one
side and to the line on the
other. The suppressor is con-
trolled by a phase-selecting
relay, which remains inactive
while the system is balanced,
but when unbalanced, due to a
ground on one phase, it oper-
ates the corresponding phase
of the suppressor, which, in
turn, grounds the same phase
of the line, thus shunting the
current and extinguishing the
arc. The switch is then auto-
matically opened and will remain so provided that the ground was
only temporary, such as an insulator spilling over. If the ground
Fig. 396.— Phase-selecting Relay for
Arcing Ground Suppressor.
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620 ELECTRICAL EQUIPMENT
is of a pennanent nature; such as caused by the puncture of an
insulator, the switch will immediately close a second time and be
locked in the closed position until opened by hand after the ground
has been removed. Should, however, the switch stay open for a
fraction of a second after the first stroke, the "second stroke
device " would become inoperative, as it will only come into action
when the switch starts to close the second time immediately after
the first time. To prevent the possible operation of the suppres-
sor in cases of short-circuits, an overload relay may be provided
which opens the control circuit of the suppressor.
Fig. 395 shows an elementary diagram of an arcing ground
suppressor and Fig. 396 the phase selecting relay for the same.
Short-circuit Suppressor. This device operates on the same
principle as the arcing ground suppressor, but it is intended for use
on grounded systems where any arc to ground would form a short-
circuit. The suppressor is connected between each line wire and
ground, and consists of a fuse in series with a gap which is instantly
closed when a short-circuit, caused by an arc-over or ground,
occurs. The arc is thus shunted until the fuse blows which gives
sufficient time to allow the arc to extinguish itself. For a single-
phase short-circuit two of the fuses will blow and for a three-phase
short-circuit all three fuses. If the trouble does not clear itself
or if there is a dead ground, of course, the main oil circuit breaker
will finally disconnect the entire circuit as usual.
Protection of Telephone Lines. Telephone lines paralleling
high-tension power transmission Unes are subjected to influences
which may under certain conditions interfere with the proper
transmission of speech. This interfering influence is in all cases
due to the static induction from the high-tension transmission
line. Under normal operating conditions, that is, with fairly well-
balanced three-phase circuits, this influence will be sUght, but with
abnormal operating conditions on the transmission line the effect
created on a telephone line may increase to such an extent as to
become destructive. In addition to these influences the tele-
phone Une is subjected to disturbances occasioned by lightning
discharges, which, however, are very similar in character to the
effects created by abnormal conditions on the transmission line,
that is, during the time of switching with unbalanced phases or
arcing grounds, etc.
Under normal operating conditions the effect of the static
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OVER-VOLTAGE PROTECTION 621
induction upon the two wires of the telephone line is practically
the same, with the result that the two wires wiU assume a certain
potential with regard to earth. With a well insulated and properly
transposed metallic line, the potentials of each wire against ground
will be nearly alike, and hence there will be no difference of poten-
tial between the two wires themselves. In telephone work,
however, even the smallest difference of potential between the
wires will create a flow of current through the telephone receiver.
This current, being alternating, produces a noise in the receiver
which may be loud enough to make talking impossible. The
higher the voltage of a transmission line and the closer the tele-
phone line is located to the same, the more prominent will be the
noise in the telephone, with slightly unbalanced telephone lines.
As this disturbing current is due to a difference of potential, it is
obvious that the noise in the receiver is in a measure independent
of the absolute value of the voltage on each Une to ground, and
that it cannot be eUminated unless the voltage on both wires be
made exactly alike. This condition, which is termed '^ bal-
anced," is realized by properly insulating and transposing the
telephone lines. The larger the number of transpositions per
mile, the more will the potential on the wires be equalized and the
better the insulation of the Unes, the less will there be a chance for
a leak to ground, causing a drop of potential on that particular
wire, with a subsequent result of unbalancing the line and ren-
dering it noisy.
From the above, it will be seen that as far as the noise on the
line is concerned it can be kept down within any limits, provided
the telephone line is properly transposed and substantially insu-
lated. On the other hand, it will be seen that the existing poten-
tial between telephone lines and ground, by reaching high values
may not necessarily impair the transmission of speech, but will
seriously strain the insulation of the instruments and make the
use of the same by the operators dangerous.
- Various schemes and devices have been developed for the pro-
tection of telephone lines with more or less satisfactory results.
The proper protective equipment to be used depends entirely on
the arrangement of the lines and the abnormal conditions against
which it is requirecl to protect.
For lightning disturbances only, the standard vacumn gap
gives the best and most reliable discharge path for these poten-
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622 ELECTRICAL EQUIPMENT
tials to ground. On the other hand, where there are induced
potentials in the telephone line either between lines or from lines
to ground, that is either due to electro-magnetic or electrostatic
induction, a multi-gap arrester, using knurled cylinders for the
electrodes, is used between lines and ground. This is to avoid
continual grounding of the telephone lines through the low break-
down path of the vacuum arrester due to the induced potential to
ground which may be of quite high value. The vacuum gap is
put across the telephone lines where the induced potentials can
be controlled by careful transposition. Here the vacuum arrester
holds the voltage across the telephone apparatus to a value below
its breakdown.
Where there is any possibility of induction troubles and this
may occm* up to one-quarter or one-half mile away from the
power circuit under abnormal conditions, the telephone line insu-
lating transformer is of prime importance. This provides an
insulation barrier of 25,000 volts test between the telephone
instruments and the lines. On the line side of these transformers,
which should be used at every telephone station, are installed
the combined multi-gap and vacuum-gap unit which hold the
voltages to ground and between lines to moderate values. In
series with this in the telephone lines are fused switches for cut-
ting of! the apparatus in case of heavy continued dischai^ges
through the gaps, caused by induced potentials or crosses. They
can also be operated as straight switches to cut off the station in
any emergency.
As a fiu-ther protection in case of induced potentials particu-
larly for potentials to earth, the drainage coil or bleeding coil can
be used. These should be few in niunber, usually two, as too
many will seriously affect the operation of the telephone circuits.
These coils give a high impedance path across the telephone line
thus shunting the high-frequency talking currents, but provide at
the same time a low impedance path for the flow of equal currents
from both lines to groimd at the center of the coil. These coils,
where used, should be protected by cut-outs to guard against
burn-out from heavy currents under abnormal conditions on the
power line.
With the addition of possible crosses with the power line the
only additional feature to the above scheme is the double-pole
horn gap which serves as an auxiliary protection to the telephone
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OVER-VOLTAGE PROTECTION 623
line insulation until the phone or power lines burn oflF. Where
there is a cross but no paralleling, it is only necessary to use the
fused switch on either side of the cross to isolate this section in
case of a break.
Prom the standpoint of protection, telephone circuits can be
classified as follows;
Class 1. Telephone circuits which do not cross or parallel
power lines.
Class 2. Telephone circuits which cross but do not parallel
power lines.
Class 3. Telephone circuits which parallel power lines but
are not on the same towers or poles and do not cross power Knes.
Class 4. Telephone circuits which are on the towers or poles
with the power lines.
This classification covers every possible case, from a telephone
line far removed from the power circuit to one mounted on the
transmission towers themselves. Classes 3 and 4 are the most
conunon. The sources of trouble vary from lightning only in
Class 1, to lightning, crosses, and induction in Class 4.
The reconmiendations for the protection of the telephone
circuit according to the classification of the circuit into which it
falls are as follows:
Class 1. Telephone circuits which do not parallel or cross
power lines.
Disturbances: Lightning.
Recommendations: Vacuum-tube lightning arresters from
each Une to groimd at all telephone stations.
Class 2. Telephone circuits which cross but do not parallel
power lines.
Disturbances: These circuits are subject to Ughtning dis-
turbances and to contact with high-voltage power lines
through broken wires, etc. • They are not subject, to any
extent, to electro-magnetic or electrostatic induction.
Recommendations :
1. Combined double-pole fused switch and vacuum-tube
Ughtning arrester in series with the main telephone
line on both sides of crossing at nearest telephone
stations.
2. Combined vacuum-tube and air-gap lightning arresters
at all other stations.
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624 ELECTRICAL EQUIPMENT
C^ass 3. Telephone circuits which parallel power lines, but
are not on the same towers or poles and do not cross power lines.
Disturbances: These circuits are subject to lightning disturb-
ances, and electro-magnetic and electrostatic induction.
They are not subject to contact with the power lines.
Recommendations :
1. Insulating transformers at all telephone stations.
2. C!ombined double-pole fused switch and vacuum-tube
Ughtning arrester at all telephone stations on the line
side of the insulating transformer.
3. Drainage coils, preferably one at each end of line.
A diagram of connections for the apparatus used on
this class of telephone circuits is shown in Fig. 397. The
with ExpuUlon Pum* *i»«i«"u«i vf
To
Tslephond
ApjMiratus
.Vacoum ■
Gap Adjustable
n
Tal«phona Una Inaalaliajr Transfocmar
Fig. 397. — Diagram of Connections for Protective Apparatus Recommended
for Telephone Lines, Classes 3 and 4.
double-pole horn gap shown on the diagram is not used
on this class of circuit, but on circuits coming under
Class 4.
Class 4. Telephone circuits which are carried on the towers
or poles with the power lines.
Distm-bances: These circuits are subject to lightning dis-
turbances, electrostatic and electro-magnetic induction,
and to crosses with the power lines.
Recommendations :
1. Insulating transformers at all telephone stations.
2. Combined double-pole fused switch and vacuum-tube
lightning arrester at all telephone stations on the
line side of the insulating transformer.
3. Double-pole horn gap across line at each station on
hne side of all other apparatus for the protection of
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STATION WIRING 625
insulators on telephone circuit in case of crosses with
power lines after series fuses are blown.
4. Drainage coils installed with fuses at each end of
line; possibly an additional coil at the middle if
the voltage to ground is not held to a safe value
by two coils.
10. STATION WnUNG
Experience has shown that in a great number of instances
the shut-down of power plants has been caused by a defective
installation of the station wiring. The design and construction
of the cabling and wiring siystem of a station is, however, of equal
importance to the rest of the equipment.
It is obvious that the main electrical conductors should be of
such a character and so installed as to minimize as far as possible
any trouble from short-circuits or grounds, and particularly to
confine such distiu-bances, in event of its occurrence, to the cir-
cuit affected. It is Ukewise apparent that such buses or circuits
on which a short would mean a complete station interruption
should be stUl better insulated and protected.
The general practice of not providing automatic protection
on the excitation system makes it essential to properly install
all the exciter field circuits and to provide sufficient insulation to
care for the high inductive voltage inherent to field circuits. The
safety of the instrument and control system wiring should f mlher-
more not be neglected, because in the event of trouble the main
circuits may become involved through the accidental operation
of an oil switch or the failure of a switch to open on an outside
short-circuit. Every cable and wire should, therefore, have a
definite place provided for it in advance, just as much as any
other piece of machinery, and wires carrjdng currents of different
voltages should, as far as possible, be kept apart from each other.
Insulation. The principal materials used for cable insulation
are: rubber compound, saturated paper, and varnished cambric.
Rubber insulation is commonly used on low-voltage cables of
small size— «ay up to 600 volts and No. 0000 B. & S. For larger
sizes and higher voltages, either paper or varnished cambric in-
sulation may be used. The latter is very much less hydroscopic
than paper insulation. In fact, while not offered as being water-
proof in itself without a lead sheath, it is nevertheless sufficiently
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626 ELECTRICAL EQUIPMENT
moisture resisting to be largely used in braided form in relatively
dry places. In lead-covered form, there is little likelihood of an
appreciable amount of moisture being absorbed at the ends of the
cable while open for the purpose of jointing or terminating. This
type of cable is likewise mechanically stronger and less likely to
have the insulation injured during installation.
Of two cables — ^the one insulated with paper and the other
insulated with varnished cloth — each properly proportioned to
stand the working pressure and the same factory tests, if each
is installed by the same installation gang and under the same con-
ditions, that insulated with varnished cloth will have the greater
factor of safety after installations for the reason just mentioned,
that it is less Ukely to be injured by bending and less likely to
absorb moisture while the ends are open. It, therefore, does not
require so much skill ir. handling and jointing. Varnished cloth
insulation Ukewise has the characteristic of being better able
safely to withstand, temporarily, higher voltage surges without
injury than either rubber or paper insulation.
When cables are run exposed the insulation should be pro-
tected by a good fireproof covering of asbestos so that in case of a
short-circuit the trouble will not be communicated to adjacent cu*-
cuits. When run in conduit or ducts this type of covering absorbs
moisture and the weatherproof covering should be substituted;
as a fact, a lead covering is usually required for damp places.
All lead-covered cables should be provided with endbells for
preventing moisture from entering the cable at the ends. These
endbells and terminals may be designed for either horizontal
or inverted positions and for convenient connections to the
machine terminals or busbars.
Open Wiring. If the number of cables in close proximity
does not make the run too congested or hazardous, it may be per-
missible to use wires or cables insulated for full potentiaJ, rigidly
supported on insulators also good for full-working potential.
This arrangement gives double protection, since either the insu-
lation or the insulators afford sufficient protection in case one
should fail. On the other hand, the runs, being exposed, are under
constant observation. Where the eonductor does not exceed No.
0000 B. & S. size, it should be solid and not stranded, the former,
of course, being more rigid. Where the amount of current to be
carried is large copper bars are used. This is usually the case for
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bus-bars. They are seldom insulated because the addition of insu-
lation on a group of bars greatly reduces their carrying capacity
by stopping the air circulation between the laminations.
Where the voltage exceeds 13,200 bare conductors consisting
of solid wire, copper tubing or iron pipe are generally employed.
The use of tubing or pipe makes it possible to reduce the niunber
of expensive insulators for supporting it. To insulate such high-
voltage conductors is expensive and quite unnecessary because
when properly installed they are widdy spaced and kept well
away from the floor.
Table LII gives dimensions for the spacing of rigid conductors.
These values are based on striking distances between points, and
are for guidance in determining proper distances between con-
ductors and for general construction work.
TABLE LII
Spacing of Rigid Conductobs
DlMBNniONB
IN Inches.
Outdoors.
iLdoors.
To Ground.
Between Live
Pa*ts.
To Ground.
Between Live
Parts.
2,000 to 3,500
3i
4
3
3J
3,501 to 7,500
6J
6
4i
5i
7,501 to 15,000
9
10
7
9
15,001 to 25,000
14
151
lOJ
14
25,001 to 37,000
19J
22
14i
19i
37,001 to 60,000
254
29
19
25J
50,001 to 73,000
36
41
27
36
73,001 to 95,000
47
53
34J
47
95,001 to 115,000
56
64
41
56
115,001 to 135,000
66
75
48
66
135,001 to 155,000
75
86
55
75
155,001 to 175,000
85
97
62
85
175,001 to 195,000
94
108
69
94
Correction for Altitude
Sea level to 1000 feet — Use table.
1000 to 3000 feet — Add 10 per cent to spacing in table.
3001 to 5000 feet — Add 20 per cent to spacing in table.
5001 to 7000 feet — Add 30 per cent to spacing in table.
7001 to 9000 feet — ^Add 40 per cent to spacing in table.
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628 ELECTRICAL EQUIPMENT
Cable should be supported every foiu* feet in vertical runs and
every three feet in horizontal runs, while for tubing the distance
between the insulators may be increased to about 10 feet. When
dealing with large conductors carrying heavy currents, care
should be taken, as explained under the section of " Current Lim-
iting Reactors," to rigidly support them so that they will not be
torn from their supports when severe short-circuits occur.
Cables in Ducts or Conduits. It is not always convenient
or desirable to run all of the conductors exposed for several reasons.
There may be no suitable place to support such cables. The
congestion may be so great that it would be hazardous in other
respects. They may be subject to mechanical injury. They
may be in a bad location from a " safety first " standpoint. If
therefore, for any of the above reasons it is undesirable to run
conductors exposed, then they may be run in conduit or ducts and
ma> be provided with a protecting weatherproof braid or lead
sheath as the occasion demands. It should be borne in mind that
if the lead sheath is omitted the conduit or ducts should be thor-
oughly drained to some pit so that water cannot remain in them.
Iron conduit should not be employed on alternating currents
unless all conductors of the circuit are in the same conduit. The
general practice is to use iron conduit up to about two inches in
diameter, above which fiber conduit is generally used.
This type of conduit is formed in cylindrical shape from fiber
or wood pulp under pressure. The pulp is thoroughly saturated
with a bituminous compound so as to kill any vegetable matter or
bacteria which would tend to promote decay.
It has been found that the majority of all initial cable troubles
are directly traceable to some injury to the lead casing when being
drawn into the duct, due to the roughness of the walls, and the
cement which has seeped throu^ the joint and formed cutting
edges after hardening. Cable troubles are also due to stray cur-
rents leaking through the joints, as a result of improper installa-
tion and the impossibility of securing proper alignment. These
objections, however, are eliminated by the use of fiber conduit,
due to the smooth interior and water-tight joints. UnUke joining
tile conduit, the connection made with fiber conduit is ideal,
affording perfect alignment, without the use of mandrels or dowel-
pins, and not having to use cement, mortar or burlap at the joints.
It is also true that fiber conduit is impervious to moisture, gases,
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STATION WIRING 629
acids, or other corrosive elements; thus, water, gas and stray cur-
rents cannot reach the cable protected by this material. It is a
good non-conductor, doing away entirely with the trouble with
stray currents, and it is also an absolute prevention against
electrolysis, which destroys many cables, gas and water pipes
during each year.
Control and instrument wiring and field and exciter circuits
are invariably run in iron conduit; first, because they are so
numerous and their directions varied, and second, because of
their small size they require protection against mechanical injury.
The cheapest and least conspicuous place of installment is in the
concrete floors.
The practice of choosing a conduit having an inside diameter
at least 30 per cent greater than the outside diameter of the cable
will give good results, and Table LIII also gives the size of con-
duit recommended for different sizes of conductors. All con-
ductors of cables for duct service should be stranded to facilitate
installation.
In laying out a conduit job, first ciscertain the size and nimiber
of wires required, then take the sizes of conduit from Table LIII.
One-half inch is usually used for branch conduits and is the small-
est size permitted by the National Electric Code. In running
several conduits together, a pull-box will be found more economical
than elbows for making turns, as one pull-box will take the place
of several elbows. Do not pull wires through conduits with a
block and tackle, as it will not only injure the insulation, but
wedge the wires in such shape that they cannot be removed readily
if desired. Be careful to ream out the end when conduit is cut,
as the bur may otherwise cut through the insulation. Conduits
should be securely fastened to walls and ceiling by use of pipe
straps or hooks. Plug all exposed ends of conduit in new buildings
to prevent plaster and dirt from falling into it.
Single vs. Multiple Conductors. Low-voltage cables for
direct-current service, such as exciter and field leads, are as a rule
of the single-conductor type. This, however, does not refer to
control and instrument wiring for which multi-conductors with as
many as a dozen conductors are used. These are as a rule of
different-colored braids so as to facilitate identification during
installation.
Whether single- or multiple-conductor cables should be used for
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ELECTRICAL EQUIPMENT
TABLE LIII
Conduit Sizes for Different Size Wires
Am-
Size or Pipe.
Am-
Sizi
E OF Pipe.
No.
Circular
peres,
Circular
peres.
B. &S.
Mils.
Rub-
1-
2-
3-
Mils.
Rub-
1-
2-
3-
ber.
Wlre.
Wlre.
Wlre.
ber.
Wire.
Wire.
Wire.
18
1,020
3
1
600,000
390
2
2
31
16
2,583
6
1
660,000
420
2
31
14
4,107
12
J
600,000
460
2
31
12
6,630
17
i
660,000
476
2
31
10
10,380
24
1
700,000
500
2
31
8
16,610
33
1
760,000
626
2
31
6
26,260
46
li
800,000
660
2
31
5
33,100
64
*
11
860,000
675
2i
4
4
41,740
66
li
900,000
600
21
4
4}
3
62,630
76
U
960,000
626
2i
4
41
2
66,370
90
2
1,000,000
660
2i
4
4i
1
83,690
107
2
1,100,000
690
2i
4
5
0
106,600
127
2
2
1,200,000
730
2J
4
5
2.0
133,100
160
2
2
1,300,000
770
2i
41
5
3.0
167,800
177
2
2J
1,400,000
810
3
41
6
4.0
211,600
210
2
2i
1,600,000
860
3
5
6
200,000
200
2
2i
1,600,000
890
3
5
6
260,000
236
2i
2i
1,700,000
930
3
6
6
300,000
270
2i
3
1,800,000
970
3
6
7
360,000
300
2i
3
1,900,000
1010
3
6
7
400,000
330
1§
3
3
2,000,000
1060
3
6
7
450,000
380
2
3
3i
the alternating main conductors depends on the size, length of
run and whether they are lead covered or not. When lead cov-
ering on cables is required, multiple-conductor cables are always
preferable, since the eddy currents in the lead sheaths of the single-
conductor cables increase the energy loss. In fact, single-con-
ductor, lead-covered cables should not be used in large sizes on
alternating-current circuits without careful consideration.
With high-voltage, single-conductor, lead-covered cables, static
discharges may take place through the insulation to the lead,
which rapidly injures the insulation and a breakdown soon fol-
lows. If the cable is not lead-covered a static discharge may take
place to the duct, this also having a tendency to break down the
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STATION WIRING 631
insulation in time. In multiple-conductor cables this action does
not occur, the static activity being neutralized.
Single-conductor cables are made in sizes up to 2,000,000 CM.
and three-conductor cables up to 500,000 CM.
General Practice. The following is a general sunamaiy of
prevailing practice covering the kind of conductors and the manner
in which they are installed in a station.
Bare Grounded Conductors, Bars, tubing, cable, wire: Used
for all kinds of ground connections or ground return circuits.
Bare Conductors on Insulators, Bars, tubing, wire: Generally
employed for circuits above 13,200 volts.
Insulated Conductors on Insulators, Wire, cable, rods; Used
for all circuits up to 13,200 volts when not housed in compartments
or conduits.
Insulated Conductors in Iron Conduit, Cable: Employed
for voltages up to 1200 volts generally for small-capacity circuits
where size of conduit does not exceed 2 inches.
Insulated Conductors in Clay or Fiber Ducts. Cable: May be
used for large capacity circuits for voltages up to 13,000 provided
ducts are maintained free from moisture.
Leaded Conductors in Ducts or Conduits. Cable: Used for
voltages up to 13,200 when ducts or conduits are subject to mois-
ture.
For convenience of reference, station wiring may also be classi-
fied as follows:
1. Exciter and field wiring.
2. A.C generator and low-tension transformer wiring.
3. Control and instrument wiring.
4. High-tension wiring.
Exciter and Field Wiring. These leads consist, as a rule,
of single-conductor rubber-covered cables with a double weather-
proof braid (or tap)e and braid), although for sizes larger than No.
0000 B. 4& S. the insulation may be varnished cambric. Because
of the inductive discharge in field circuits, causing an excessive rise
in potential when opening the circuit, it is important that a liberal
margin of safety is allowed in the insulation. For damp locations
lead-covered cables may be required. These leads are mostly
installed in iron conduits.
Generator and Transformer Wiring. For this wiring varnished
cambric insulation is, as previously stated, preferable, the thick-
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632 ELECTRICAL EQUIPMENT
ness of the insulation varying with the generator voltage. Fcnr
absolutely dry locations a good weatherproof braid may well
serve as a mechanical protection against abrasion, but the ducts
should nevertheless be provided with drains so that the cables will
under no circumstances lay in water which may be accumulated
from condensation. For damp localities, lead-covered cables
should always be used, and to be on the safe side the use of such
cables is always to be recommended. Endbells are always re-
quired for such cables.
.Exposed main wiring is generally considered out of date, but,
if used, the cables should be well supported and guarded and per-
fectly covered with a fireproof covering to prevent a fire from
spreading from one circuit to another. The installation of the
cables in ducts or conducts is much to be preferred.
Fiber ducts should be used for all alternating-current cables,
although iron conduit is permissible if all conductors of one cir-
cuit are run in the same conduit. With single-conductor, lead-
covered cables, and preferably also for multi-conductor, fiber
conduits should be used.
Whether single- or three-conductor cables are to be used de-
pends on the size, the length of run and the loss in the lead sheatL
Single-conductor cables are, as stated before, made in much larger
sizes than three-conductor and have, of coimie, a greater radiating
capacity, but on the other hand, especially for long runs, it is found
that three-conductor cables will be more economical, especially
for lead-covered cables. This is evident when one considers that
three lead sheaths, each, however, somewhat smaller, will be
required as compared to one. On the other hand, the eddy-cur-
rent losses in the lead sheath for a single-conductor cable is not
negligible, while with a multi-conductor cable they are entirely
neutralized. Lead sheaths are as a rule groimded at one end to
get rid of accumulation of static electricity and a ground of the
lead sheath at the other end of the cable can very easily occur
without being noticed, resulting with single-conductor cables io
circulating currents in the lead sheath. These cmrents are only
hmited by the resistance of the lead and the losses caused thereby
may be quite considerable. Of course, where the size is such that
two or more conductors per phase are required it is posBible to
" nest " the conductors so as to neutralize the inductive effects.
In selecting cables for generator leads, a larger factor of safety
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STATION WIRING 633
should be allowed than for ordinary cable practice. Since such
leads are not usually protected by any automatic circuit breakers,
it is good practice to select a cable for this purpose with an insu-
lation thickness 50 per cent greater than the normal working
voltage of the generator.
Control and Instrument Wiring. Under this class would be
grouped the control circuits for oil switches, rheostat and governor
motors, etc., secondaries of current and potential transformers
and all other similar conductors. These conductors are always
of a very flexible rubber-covered weatherproof multi-conductor
type, installed in iron conduit. Occasionally where the location
is very damp a lead covering may be desirable. With this cable
it is possible to pull it through a conduit some 100 feet in length
with four standard conduit bends in the run.
The best practice is to lay the conduits in the floor and let
them terminate as near the switchboard sill as convenient. Fre-
quently the ends of the conduits are bent to point upwards and
cut to extend just a short distance above the finished floor. This
often necessitates a number of visible crossings of the leads where
the conduits cannot be run to the desired point. To obtain a
neater construction, a pull-box with cover can be provided in the
floor along the back of the board, and the conduits arranged so as
to terminate in the walls of the box. Provision is then made for
bringing the leads from this box to the desired point at the bottom
of the board, the necessaiy splices and crossings being made in the
box.
High-tension Wiring. For circuits above 13,200 volts, bare
conductors are generally used because of the increased cost of
ordinary insulation for such high voltages, and because such con-
ductors are necessarily spaced far apart and generally located at a
considerable distance from the floor. They are, therefore, rigidly
mounted on insulators and carefully guarded.
Size of Cables. (Current-canying Capacity.) For the com-
paratively short nms encountered in power stations the size of
the conductors is generally governed by the permissible current-
carrying capacity and this, in turn, is determined within practical
limits by the maximum temperature which the insulation sur-
rounding it will withstand. First, the temperature must not be
high enough to cause too rapid a rate of deterioration of the insu-
lation. This temperature is, roughly, 86° C. for saturated paper,
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634 ELECTRICAL EQUIPMENT
75° C. for cambric, and 60° C. for rubber. Second, the tem-
perature must not be high enough to decrease the puncturing
resistance of the insulation below safe limits. This temperature
varies with the normal working e.m.f. of the circuit. Based on
these two considerations, it is reconunended that the maximum
operating temperatures of the conductors of insulated cables be
limited to the values given below:
Heating and Temperature of Cables {Standardization Ruks of
the A J.E,E,) . The maximum safe-limiting temperature in degrees
C. at the surface of the conductor. in a cable shall be:
For impregnated paper insulation (85--B);
For varnished cambric insulation (75--B);
For rubber compound insulation (60-0.25-B);
where E represents the eflfective operating e.m.f. in kilovolts
between conductors.
Thus, at a working pressure of 6.6 Kv., the mRYiTnnm safe-
limiting temperature at the surface of the conductor or conduc-
tors in a cable would be:
For impregnated paper insulation 78.4° C.
For varnished cambric insulation 68.4° C.
For rubber compound insulation 58.35° C.
The actual maximmn safe continuous-current load for any
given cable is determined primarily by the temperature of the
siUTOimding medium and the rate of radiation. This current
value is greater with direct than with alternating-currents, and
decreases with increasing frequency, being less for a frequency of
60 cycles than for 25 cycles. This difference in carrying capacity
for direct- and alternating-current is of sUght practical importance
for conductors less than 500,000 cir. mils in area, at commercial
frequencies, i.e., 25 and 60 cycles.
Furthermore, owing to the fact that alternating-current flowing
in large cables has greater density on the surface of the conductor
than in the center, so-called skin eflfect, an ordinary cable will not
carry as many amperes alternating-current with the same tem-
perature rise as it will direct-current. To overcome this, it has
in the past been conunon practice on single-conductor cables,
700,000 cir. mils and larger for 60 cycles and 1,000,000 cir. mils and
larger for 25 cycles, to make up the cable in annular form, using a
non-conducting core (usually fiber), and stranding the copper
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STATION WIRING 635
wires around this. The annular form thus increases the canying
capacity by utiUzing more of the. copper and there is a further
increase in the capacity due to the larger radiating surface. In
view of this fact that the rope core cable has a greater carrying
capacity due to its increased radiating surface it could advan-
tageously be adopted for all cables, direct-current or alternating-
current, for sizes 700,000 cir. mils and above.
It is apparent from the above that the carrying capacity of a
cable depends on so many factors that no table can be given which
applies to all conditions, and considerable care should be exer-
cised in selecting the size if it is necessary to economize. Tables
LIV and LV will, however, serve as a guide for determining the
safe current-carrying capacity imder three assumed conditions,
X, Y, and Z. Condition X is such as to require the maximum-size
cable while condition Z is the most favorable requiring the mini-
mum size.
The use of these tables is best illustrated by a couple of exam-
ples:
Assume that it is desired to find the safe size of a single-con-
ductor, varnished cambric, insulated cable, installed in duct, the
operating voltage being 6600 volts and the continuous current to
be carried 1000 amperes.
Referring to the first column in Table LIV we must use the
next higher current values or 1075, and it is seen that the cable may
have a size from 1,250,000 CM. to 2,000,000 CM., depending on
the operating condition. Then going to Table LV we find in the
eighth line from the top (corresponding to our case) that two con-
ditions, Y and X, are given, the former being limited to a 1,000,000
CM. cable and the latter to a 2,000,000 CM. By comparing the
results from the two tables it is apparent at once that the Z con-
dition is out of the question entirely and furthermore that the Y
condition, corresponding to 1,500,000 CM., also gives too small a
value as this condition was Umited to a 1,000,000 CM. cable.
The size must, therefore, correspond to condition X or 2,000,000
CM.
As another example, assume that a 750-volt varnished cambric,
insulated cable in conduit is to carry 175 amperes. What size is
required?
Referring again to Table LIV we have three different sizes to
choose from, 4/0, 2/0 and 1/0. From Table LV, sixth line from
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636
ELECTRICAL EQUIPMENT
TABLE UV
Cxtrbent-Carbtinq Capacitt of Cables
(Continuous Rated Apparatus)
Maximum Ampere
Capacity
Condition Z.
Condition Y,
Condition X.
Permissible.
'
25
#10
*9
%%
35
»S
«8
«6
50
#6
#6
«4
70
#6
#4
%2
110
#4
«2
1/0
130
#2
1/0
2/0
175
1/0
2/0
4/0
225
2/0
4/0
300,000
290
4/0
300,000
400,000
360
300,000
400,000
500,000
450
400,000
500,000
600,000
550
500,000
600,000
760,000
675
600,000
750,000
1,000,000
775
750,000
1,000,000
1,250,000
900
1,000,000
1,250,000
1,600,000
1075
1,250,000
1,500.000
2,000,000
Cables in Multiple
1300
2- 750000
2- 750000
2-1OO0000
1500
2- 750000 ,,
2-1000000
2-1250000
1750
2-1000000
2-1250000
2-1500000
2100
2-1250000
2-1500000
2-2000000
2600
3-1000000
3-1250000
3-1500000
3100
3-1250000
3-1500000
3-2000000
4200
4-1250000
4-1500000
4-2000000
5200
5-1250000
5-1500000
5-2000000
6200
6-1250000
fr-1500000
6-2000000
the top, we see that this case also involves all three operating
conditioiis and that the limit of the Z condition is a 4/0 cable, so
that it will be safe to use a 1/0 cable for our case.
Suppose, on the other hand, that the current to be carried had
been 675 amperes. This would have come within the limit of the
Y condition and the required size of the cable would be 750,000
CM
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TABLE LV
Classification of Conditions X, F, and Z
To
To
To
To 4/0
500.000
1.000.000
2.000.000
IncluBive.
CM.
CM.
CM.
Inclusive.
Inclusive.
Inclusive.
SiKGLB Conductor:
In free air:
Up to
750 V.
z
Z
Z
Z
V.C. and paper
3,500 V.
z
Y
Y
Y
7,500 V.
Y
Y
Y
Y
15,000 V.
Y
Y
Y
Y
Rubber
. 750 V.
Y
Y
Y
Y
In ducts:
760 V.
Z
Y
Y
X
V.C. and paper
3,600 V.
7,500 V.
Y
Y
Y
Y
Y
Y
X
X
15,000 V.
Y
Y
Y
X
Rubber
. 750 V.
Y
Y
X
X
Three Conductor:
In free air:
760 V.
Y
Y
V.C. or paper..
3,500 V.
7,500 V.
Y
Y
Y
Y
15,000 V.
Y
Y
Rubber
.. 750 V.
X
X
Inducts:
'p
750 V.
Y
X
V.C. or paper..
3,500 V.
7,600 V.
Y
Y
X
X
15,000 V.
Y
X
Rubber
. 750 V.
Y
X
Single-conductor lead-covered cables above 600,000 CM.,
25 cycles and 3/0,60 cycles, should only be used after special con-
sideration is given to the leadnsheath current, and multiplied
single-conductor cables on 60-cycle circuits shall be suitably
arranged to eliminate initial induction and thus balance the
reactance and apportion the current carried in each conductor.
For secondary instrument current wiring, where the watts
loss in the secondary leads must be kept within certain limits,
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638
ELECTRICAL EQUIPMENT
so as to deduct as little as possible from the permissible instru-
ment load on the transformer, it is the recommended practice to
make runs up to 75 feet of 19/25 multi-conductor cable, corre-
sponding in conductivity to a No. 12 B. & S. wire. For runs of
from 75 to 150 feet, 19/22 cable, corresponding in conductivity
to No. 10 B. & S. wire, should be used for mechanical reasons
as well as for increased conductivity. For potential and control
wiring, 19/25 cable may be used in practically all instances. The
above distances refer to llOrVolt circuits and for 220 volts they
can, of course, be doubled. In general, the size of control leads
must also be determined from the standpoint of voltage drop, the
TABLE LVI
Size and Ampere Capacity of Copper Tubing
Maximum Con-
tinuous Ampere
Capacity.
Outside
Diameter,
Inchea-
Inside
Diameter,
Indies.
150
300
500
i
a
.776
1.084
p)ermissible drop depending on the minimum voltage required for
the apparatus in question. This is generally stipulated by the
manufacturers.
Instrument transformer secondaries should be permanently
grounded. Where secondaries cannot be grounded at any point,
as for instance in the case of instruments and meters which have
secondary current and primary potential coila, the secondary
wiring must be insulated and installed to safely withstand primary
potential. One common ground bus, not less than No. 4 B. & S.,
should be run across the back of the switchboard, to which appa-
ratus mounted on the LJ^ritchboard intended for grounding should
be connected. The switchboard pipe framework, except when
insulated, should be connected to this ground bus, one connec-
tion being made for every three pipe joints in series.
Steel work supporting high-potential switching equipment
should be carefully grounded at several points so as to prevent
the possibility of high voltage occurring between sections of the
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STATION WIRING 639
steel work. No ground connection for this service should be of
less than No. 6 B. & S. flexible cable.
For open high-tension wiring utilizing bare conductors, the
size depends on the current to be carried as well as the heat-
radiating conditions. For very large alternating currents, such as
in low-tension bus-bars of large size, the skin-effect may be appre-
ciable, requiring a low current density. As a rule, this may vary
anywhere from as low as 300 to 400 amperes per square inch to
1500 amperes per square inch, depending on the conditions. This
is dealt with more fully under the section on "Bus-bars," page 565.
For very high-voltage work using copper tubing the sizes given
in Table LVI are quite common.
Corona Limit of Voltage. Attention must also be given to
the possibility of tjie formation of corona when the size of high-
tension conductors is determined. Table LVII gives the highest
safe three-phase voltage for any given size of wire. The values
are based on sea level but may be corrected for other altitudes
by the correction factors given in table LVIIL
Economical Considerations. In determining the size of a
conductor the economical side of the problem should not be lost
sight of, although it may not be of such great importance for the
station wiring as for the distribution or transmission system.
The most economical area is that for which the annual outlay
equals the annual cost of the energy loss, and according to this rule,
the cheaper the power, the less should be the capital outlay for
the ccMiductors, thus allowing a smaller size to be used and a corre-
spondingly increased loss. In general the cost of ducts, insulators
and supports may be considered as not affected by the variation
in size, but that the outlay is only affected by the comparative
cost of the cable itself.
Voltage Drop. In a continuous-current circuit, the drop at
the terminals of a circuit with resistance R and traversed by
a current / ampere, is /X/2 volts. Likewise in an alternating-
current circuit the drop in voltage of a circuit with an impe-
dance Z, traversed by a current of / effective amperes, is/ XZ
volts.
The voltage drop in alternating current circuits, therefore,
depends on both the resistance and reactance, but with wires close
together, as in conduit work, the reactance will generally be small.
The drop should be calculated for the given power-factor, load.
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640 ELECTRICAL EQUIPMENT
and corresponding current, and the following approximate fonnula
may be used.
Voltd drop per wire=/i2 cos <I>+IX sin ^,
where / = current per wire in amperes;
JB= resistance in ohms per wire;
X= reactance in ohms per wire;
Cos <^= power-factor of load.
Volts drop of two-phase circuit = 2 X (volts drop per wire).
Volts drop of three-phase circuit = 1.73 X (volts drop per
wire).
Resistance as well^ as reactance values for single-conductor
cables are given in Table LIX. The values afe for 2000 feet of
wire, i.e., for each wire of a circuit of that length, and apply equally
well to bare or lead-covered cables as the insulation or lead cov-
ering has practically no effect on the self-induction.
Table LX gives reactance and impedance values for one mile
three-conductor cables. Unlike the reactance values given in
Table LIX, which were single-phase, these values are three-phase,
i.e., by multiplying them by the current the drop in the full-line
voltage (not voltage to neutral) is obtained directly. In calculat-
ing the values a 2 per cent allowance for spiral of strands and a
2 per cent allowance for spiral of conductors has been made. All
the results are based on a cable one mile long but can, of course, be
obtained for any shorter distance by reducing the figures given in
direct proportion. Similarly, the values correspond to a fre-
quency of 60 cycles. For any other frequency, the values given
must be multiplied by that frequency and the result divided by 60.
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TABLE LVII
Corona Limit of Voltaqb
Kiloyolt8 between Lines Three-phase Cables
SEA LEVEL
size B. A 8.
Diameter in
Inches.
Spacing Fkbt.
or Cm.
8
10
12
14
16
20
0
00
000
0000
250,000
300,000
350,000
400,000
450,000
600,000
800,000
0.374
0.420
0.470
0.530
0.590
0.620
0.679
0.728
0.770
0.818
1.034
95
104
114
125
138
98
108
118
130
144
151
161
171
178
188
102
111
121
135
149
156
166
176
184
194
234
104
114
124
138
152
161
170
180
190
199
241
106
117
127
141
156
165
175
185
194
205
244
109
121
132
146
161
171
180
192
200
210
256
To find the voltafce at any altitude multiply the voltaf^e found above by the a
corresponding to the altitude, as given in Table LVIII.
For oingle-plufle or two-phase find the three-phase volts above and multiply by
1.10.
TA3LE LVm
Altitude Correction Factor S
Altitude. Feet.
a
Altitude. Feet.
i
0
1.00
5,000
0.82
500
0.98
6,000
0.79
1000
0.96
7,000
0.77
1600
0.94
8,000
0.74
2000
0.92
9,000
0.71
2500
0.91
10,000
0.68
3000
0.89
12,000
0.63
4000
0.86
14,000
0.58
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ELECTRICAL EQUIPMENT
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TABLE LX
Approximate Reactance and Impedance of Three Conductor Cables
PER Mile
60 Cycles
Thickness of Insulation.
Size.
2/32 by 2/32 In.
3/32 by 3/32 In.
4/32 by 4/32 In.
A
B
A
B
A
B
6
4
2
1
1/0
2/0
3/0
4/0
250,000
300,000
350,000
400,000
450,000
500,000
0.307
0.288
0.272
0.264
0.260
0.253
0.247
0.243
0.239
0.236
0.233
0.231
0.229
0.228
3.843
2.423
1.546
1.232
0.988
0.798
0.648
0.519
0.470
0.410
0.370
0.342
0.320
0.304
0.345
0.323
0.302
0.292
0.282
0.276
0.268
0.263
0.257
0.252
0.248
0.246
0.243
0.241
3.845
2.427
1.552
1.238
0.993
0.806
0.656
0.544
0.478
0.421
0.380
0.352
0.330
0.314
0 .^79 • ?
0 351
0 :.<2s
0.:ii5
' 0.304
0.297
0.287
0.279
0.273
0.267
0.262
0.259
0.256
0.254
h n/r
ja f . o-K>
* 2 4..'.
1 oo7
1 2V1
1.000
0.815
0.665
0.553
0.488
0.430
0.390
0.361
0.340
0.325
Thickness op Insulation.
Size.
6/32 by 5/32 In.
13/64 by 13/64
8/32 by 8/32 In.
A
B
A
B
A
B
6
4
2
1
1/0
2/0
3/0
4/0
250,000
300,000
350,000
400,000
450,000
500,000
0.407
0.376
0.351
0.337
0.325
0.315
0.304
0.295
0.288
0.281
0.276
0.272
0.268
0.266
3.852
2.435
1.562
1.250
1.006
0.822
0.673
0.561
0.496
0.438
0.396
0.371
0.349
0.334
0.443
0.410
0.381
0.365
0.352
0.340
0.328
0.317
0.310
0.301
0.296
0.291
0.287
0.283
3.855
2.440
1.570
1.258
1.013
0.830
0.685
0.572
0.510
0.452
0.413
0.384
0.364
0.348
0.473
0.439
0.407
0.390
0.375
0.360
0.350
0.338
0.330
0.320
0.313
0.308
0.301
0.298
3.860
2.446
1.576
1.265
1.023
0.840
0.695
0.585
0.522
0.465
0.426
0.398
0.375
0.360
A — The three-phase reactance of a cable 1 mile long.
B — The three-phase impedance of a cable 1 mile long.
Note. — Of the two figures given for the insulation — for example 6/32 by 5/32 —
one is the insulation thickness around each conductor and the other the thickness of
the insulation belt around the three conductors. The former only is of importance
as far as the reactance value is concerned as it determines the distance between the
conductors.
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CHAPTER X
ECONOMICAL ASPECTS
PRELIMINARY CONSIDERATIONS
Like every other commercial imdertaking, the promotion of
a hyro-electric development involves a very careful preliminary
investigation, as upon this will largely be based the success of
obtaining financial support for the enterprise. Such investiga-
tions should be considered from the engineering as well as the
commercial side, and the man to whom this responsible task is
entrusted should have a sound and conservative judgment in
analyzing such propositions.
This appUes to small developments as weU as large ones, and
possibly more so to the former because an error which would be of
minor importance in a large plant may involve serious financial
consequences in a small one.
No two streams offer quite the same problem of power devel-
opment, and a multitude of conditions must, therefore, in every
case be investigated. These involve a complete and most effi-
cient study of the watershed, rainfall and hydrographic data for
determining the available stream-flow and the storage possibilities.
Estimates of the probable market for the power and the planning
of the development as to type and size, so that the total annual
cost, including fixed charges, to deliver the necessary power, will
not exceed the amoimt the available customers can afford to pay,
the rates generally being governed by the cost of competing
power generated from fuel.
The location of the development should be such that it will
insure the most economical results. Usually this is when the
maximum head is utiUzed, but considerations must also be given
to the land which may be overflowed by so increasing the head.
A study of the watershed may, furthermore, show that several
developments of a smaller size will give better economy than one
large plant, and that in this manner the entire system may be
served in such a way that the power from the new developments
644
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COMPILATION OF WATER POWER REPORTS 645
will form a more economical addition to that which may ahready
be supplied by other plants; in other words, that the load factor
will be such as to improve the load factor of the other plants and
of the system in general.
As a rule, it does seldom pay to develop a stream for the max-
imum stream-flow, and the question always arises as to how much
above the minimum stream-flow the plant should be built out for.
This also involves the problem of providing for water storage, if
such is feasible, or for auxiliary steam power.
The cost estimates should be made with the greatest care to
leave undone no amount of work or experiment which will serve
to make certain the ground upon which the estimates are made.
After having estimated liberally for all known requirements, it is
well to provide additionally a substantial sum of money and so
arrange the finances that, if, contrary to expectations, the esti-
mates should be exceeded, sufficient funds remain in the treasury
for completing the development, as nothing is so discouraging,
and in many cases so disastrous, as a reorganization of the under-
taking at its very beginning.
Every feature of the proposition should, of course, be investi-
gated from the legal point of view. This involves the real estate
flowage rights, rights of way, rights of occupying public high-
ways, etc. Such matters must be carefully attended to from the
beginning.
A very complete general guide for the compilation of wat^
power reports and field data has been prepared by Mr. J. T. John-
ston, Hydraulic Engineer of the Water Power Department of
the Dominion 6f Canada, and is contained in its 1914 Annual
Report. This guide is of such completeness and usefulness that
it is reprinted in the following in full.
GENERAL GUIDE FOR THE COMPILATION OF WATER POWER
REPORTS AND THE SECURING OF FIELD DATA^
The increasing number of inspections and field investigations
on the part of the field engineers of the Dominion Water Power
Branch, has rendered desirable the preparation of a uniform guide
upon which may be based the various reports forwarded to head
* From the 1914 Annual Report, Dominion Water Power Branch Depart-
ment of Interior, Canada.
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646 ECONOMICAL ASPECTS
ofiBce, in order that, so far as possible, their form may be stand-
ardized.
It is also considered that a guide of this description can be
used to advantage by the engineer when making his field investi-
gations into the projects under examination. A careful study in
the field outlined herein, will, as a rule, prevent the overlooking
of important data which should be secured on the ground.
The guide is, therefore, submitted for a dual purpose; first,
for use as a framework for the standardization of the test of power
reports submitted by field engineers, and second, for use by
engineers while in the field as a general memorandum of the
various features calling for attention and field study.
Field investigations vary in character, the majority dealing
with the following conditions: (1) Applications for water-power
privil^es, such applications being unaccompanied by detailed
data as to the site of Ptream. (2) Applications for water-power
privileges accompanied by fairly well-developed plans, setting out
the general scheme of development. (3) First-hand investiga-
tion of entirely new sites or series of sites, for the purpose of study-
ing power, storage and conservation features.
In preparing the following instructions, the above has been
kept in view, and the outline hereunder is intended to serve as a
general guide, only such portions being utilized as are directly
applicable to the class of report under preparation. It is not
intended that these instructionts should limit a repnirt solely to the
ground covered herein ; much must be left to the discretion of the
engineer in charge of the investigations. The points briefly dealt
with represent, however, the general important features which
require investigation and discussion, in order that the ground may
be completely covered.
Summary op Principal Divisions
A brief summary of the sections and subheadings follows:
Further details of the ground to be covered under each section
are given later.
I. Sources of data used in report.
(1) Why investigated and scope of investigation.
(2) Personal examination — route followed and time con-
sumed.
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COMPILATION OF WATER POWER REPORTS 647
(3) Run-oflf records from departmental stream measure-
ment offices.
(4) Maps.
(5) Existing reports.
(6) Miscellaneous.
II. Summary of report.
III. General introductory.
Description, including location as to province, river,
cities, township, range and section.
IV. Water Supply.
(1) General description of drainage area.
(2) Actual records if available, showing maximum, min-
imum, and mean discharge for each month, also
absolute minimum for year. Measurements on
ground if foregoing are not available.
(3) Rainfall, temperature, evaporation.
(4) Storage, already developed and effect of same.
(5) Storage possibilities —
(a) Location of reservoir site or sites.
(6) Height of dam and class of dam suitable,
(c) Capacity of reservoirs and extent of adjacent
drainage basin.
(6) Prior water rights above and below power site —
water supply, irrigation or power.
(7) Ice conditions, during winter months and in spring
flood (frazil, anchor and floating ice),
(a) Under present conditions on river.
(6) After construction of plant.
(c) Without storage.
(d) With storage.
V. Description of existing Pcmer Development on the River.
VI. Detailed Work at Site irwestigated.
(1) Scope of the inspection at the site.
(2) Accessibility of site and transportation problems.
(3) Detailed information and plans of site —
(a) Contour plan of site.
(6) Cross section,
(c) Profiles.
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648 ECONOMICAL ASPECTS
(4) Foundation conditions.
(5) Flooding and pondage.
(6) Existing interests.
VII. Possible Power Developed.
(1) Horse-power at wheel shaft without storage —
(a) At minimum flow.
(6) For the nine high months.
(2) Horse-power at wheel shaft with storage. Dis-
cuss utilization of local pondage at site for peak
VIII. Estimates.
Cost of power developed — capital and annual.
Cost of storage — capital and annual.
IX. Market for Power.
(1) Present.
(2) Future.
(3) Length of transmission lines, etc.
X. Suggestions and Recommendations.
XI. Appendices, r^,
(1) Plans pertinent to the actual sites investigated.
(2) Photographs.
(3) Run-off records.
(4) Gauge records.
(5) Reports.
(6) Maps and plans of existing power plants and struc-
tures, etc.
Details as to the Foregoing Sections
I, Sources of Data used in Report
This section should set out the basis and authority on which the
investigation was instituted, outline the scope of the same, and the
organization by means of which the field data were obtained.
It is also intended to summarize the sources of information
upon which the subject matter of the report is founded, and to
set out in full the degree of thoroughness with which the inves-
tigation has been carried on.
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COMPILATION OF WATER POWER REPORTS 649
II. Summary of Report
All the essential features of the report should be brought to-
gether here, in a brief statement forming a concise smnmary of
the whole, tabulation of results being made where possible.
III. General Introductory
This section should cover the general features of the situation
being investigated. This involves a general description of the
river and its characteristics, and of the basin as a whole, touching
on drainage area, somrce, direction, drop, falls, rapids, banks,
river bed, tributaries, lakes, muskegs, swamps, forest, cultivation
along banks, settlements, glaciers, general topographical and
geological features, etc., and giving the definite location of the
site under study.
IV. Water Supply
(1) General Description of Drainage Area. — Under general
description of the drainage area those features should be deaH'
with which are of direct importance to the question of the water
supply, such as probabiUty of sudden floods, influence of the sea-
sons, etc.
(2) Run-off Records. — If the site inspected is situated on one
of the rivers covered by any of the systematic stream measurement
work carried on by the department, the existing records should
be utiUzed as a basis upon which the run-off may be <iiscussed.
A smnmary of the essential features of the discharge co>»Ting
high, low and mean flow, etc., should be inserted, while tlie reitorda
in their complete form should be attached as appendices in Section
XI of the report. Where no records have been taken on the river,
estimates or measurements of the flow at the time of the inspection
should be made, either by meter or by whatever method of stream
measin-ement is most applicable or convenient. From this, in
conjunction with high-water marks in evidence and from the tes-
timony of local inhabitants as to extreme low- and high-water
conditions, and from a study of the run-off conditions of streams
in the vicinity, as careful an estimate as is possible should be made
of the extreme low- and high-water conditions on the river, also
of the average low and high flows which may be exp)ected. With
these data, the months and seasons in which the above conditions
are usually in evidence, must be given.
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650 ECONOMICAL ASPECTS
(3) Rainfally Temperature and Evaporation. — The maximuin,
minimum and mean annual rainfall as recorded at the nearest
stations maintained by the Meteorological Service should be
discussed, being utilized in estimating the run-off if stream-flow
records are not to hand. Temperatiu^ and evaporation records, if
available, should also be fully considered.
(4) Storage Already Developed. — If storage is already in opera-
tion in the river basin above the site, a full discussion of the same
is required under the heads of location; owners and operators;
date of installation; area and volmne of reservoir and of tributary
drainage basin; description and condition of dam and structures;
effect on natmral run-off conditions, actual experience since being
placed in operation covering date, time of filling and emptying
reservoir; gauge records if available (to be attached in full in
appendix); method of control; photographs, comments, etc., etc.
Copies of plans of structures are to be secmred if possible.
(5) Storage Possibilities. — ^The question of storage possibilities
and locations on the upper waters should be covered as thoroughly
as the conditions of the inspection, and the detailed instructions
issued therewith, may be required. If a visit is made to any lakes
m the upper basins, the general elevation of the banks of the same
relative to the water service should be recorded, with notes as to
what flooding would result if the lakes were raised to various
definite limits. When the reservoir is in a surveyed district the
approximate land flooded should be given in sections and quarter
A I • i'. outlets all the conditions affecting the construction of a
dam, and tlie type of structmre advisable, are required. This will
include foundation conditions; height and character of banks; a
section across the river at the point selected for the dam carried
sufficiently far up the banks to cover all possible limits to which it
may be advisable to hold the lake surface.
A profile should be secured of the water surface from the lake
outlet to the dam site. Should there be a possibility of securing
storage by means of dredging or otherwise clearing the outlet, a
profile should be obtained of the water surface, and, if possible,
of the river bed from the lake to a sufficient distance below the
dam site; any other field information necessary to determine what
is involved in the construction of a dam and in the operation of a
storage reservoir is also required.
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COMPILATION OF WATER POWER REPORTS 651
When circumstances render it inadvisable to visit the upper
waters of the basin for the purpose of personal inspection, a review
of the storage situation, as far as it can be gathered from existing
maps and from local information, should be included.
The surface area and capacity of all storage reservoirs consid-
eredy t(^ether with the area of the drainage basins adjacent to the
same and their sufficiency to fill the reservoirs, should be fully
covered; the beneficial effect of such storage on the flow of the
river should be discussed.
(6) Prior Water Rights. — Any existing or projected schemes of
municipal water supply, irrigation or water power, which have
diverted or may in the future permanently divert a portion of
that river flow, thus reducing the water available at the site,
should be investigated and reported on.
(7) Ice Conditions, — The general conditions in winter along the
river as a whole, covering time of freeze up, conditions in mid-
winter, and time and manner of break up in the spring, should be
secured from whatever local sources may be available, or, if pos-
sible, from personal observation. The question of anchor and
frazil ice under present conditions should be considered carefully,
also that of ice jams in the spring, both above and below the site.
The possible formation of ice jams below the site and the conse-
quent effect on the tail-water and floor elevation of the power-
house, should be particularly noted.
The frazil and anchor-ice conditions, to be anticipated at the
site after the construction of the plant, should be discussed. In
this connection a careful study covering the winter conditions and
troubles experienced in the operation of any existing plants on the
river, together with methods of remedying the same, is advisable.
The probable effects on ice conditions of the development of
storage for the purpose of increasing the wint^ flow, should also
be covered.
V. Description of Existing Power Plants
Existing power developments along the river should be dealt
with under the following general heads: Ownership of plant and
when constructed; description of layout and structures (dam,
intake, penstocks, timnels, canal, forebay, power-house, founda-
tions, transmission, substations, etc.), and present conditions of
the same; head at different seasons; installation (electrical and
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652 ECONOMICAL ASPECTS
hydraulic machinery in detail) ; auxiliary power, power-ioad and
power-factor, daily load curves if possible, use of power, market
for power, present and future; special features, etc., comments
and photographs. Plans of plant to be secured if possible and
attached to appendix.
VI. Detailed Work at Site Investigated
(1) Scope of the Inspection at the Site, — If a definite and well-
defined project be investigated, the engineer making the inspec-
tion should study the general scheme carefully in the light of his
personal inspection of the ground, and should record his opinion
as to the engineering and economic feasibihty of the same, pointing
out whatever weaknesses may be apparent, and recommending
whatever changes in design, layout or scheme of development he
may consider advisable.
When no definite scheme of development has been proposed,
the inspecting engineer is expected to outline the most feasible
scheme which his study on the ground may suggest, setting out the
head available and method of securing the same. He should also
gather all information and field data which may be essential to its
proper consideration and to getting out the estimates. A layout
of his scheme, together with all pertinent data, should be plotted
on the contour plan of the site.
Arrangements should be made on the ground for the installa-
tion and continued reading of gauges at all points where the record
of the same is advisable.
Numerous photographs illustrating the site are required.
(2) Accessibility of Site. — Secure all data with reference to
accessibihty of the site. This includes the distance to the nearest
railway line; the ease or difficulty of building a spur line to the site
should the size of the development warrant it; the condition of
any roads in the vicinity and their suitability for heavy transport;
the length of new road that may be required; the use which can
be made of water transportation as a means of access. In brief,
the best means of connecting the site with existing lines of trafSc,
should be covered.
(3) Detailed Information and Plans at Site. — (a) Contour Plan,
— Enough rough instrument work must be done to permit of plot-
ting a fairly accurate contoiu" plan of the whole vicinity covered by
the proposed layout. These contours should extend above the
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COMPILATION OF WATER POWER REPORTS 653
highest elevation to which there is any possibility of raising the
head-waters of the proposed plant. Sufficient notes should be
taken to plot on the said plan, with the elevations, any rock out-
crops which may be in evidence. Should the rock outcrop along
both banks of the river, the continuous line of demarcation be-
tween the rock and the overlying material should be plotted, vnlh
the devaliana, along both shore lines. The plan should also indi-
cate all other classes of material, such as clay, gravel, sand, loam,
etc., which may be in evidence together with notes as to whether
the site is wooded, cleared or cultivated, etc.
Water levels (together with date of taking, and river-flow, if
possible) should be recorded and plotted on this plan at all im-
portant points, such as the brink and foot of falls and rapids,
marking the limits of the still water above and below. All eddies
and back waters should be marked and the elevation and date
recorded. The general line of the brink and foot of any falls
which will be involved in a proposed scheme of development should
be secured and tied in to the plan. The high- and low-water levels
to be expected in the tail-water of the projected power station
are of particular importance. Maximum high-water marks along
the shore should be carefully noted.
All natural features of which advantage might be taken in
la3dng out a power-plant should be fully shown on the plans and
discussed in the report.
(6) Cross-section, — ^A cross-section of the river bed and both
banks along the line of the proposed dam, and sections of any
alternative sites which may present themselves to the engineer on
the ground, should be secured and plotted. Sections when plotted
should indicate the character of the ground surface and river bed
and of foundation conditions, either in evidence or assumed,
throughout.
(c) Profiles. — A profile of the river surface from the upstream
limit of the new pond created by the plant is desirable, but is not
essential should the circumstances of the inspection render the
securing of the same inadvisable. In all cases, however, a profile
of the river surface and, if possible, of the river bed, from a point
up stream from the dam, to below the tail-race of the px)wer-plant
is required. A profile section through the dam, intake, head-
race (or pipeline, as the case may be), power-plant, and tail-race,
showing such governing elevations as, head-water, crest of dam,
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654 ECONOMICAL ASPECTS
floor of generator room, tail-water, etc., should also be obtamed
in the best manner which circumstances may dictate.
Profiles of any pipe or canal lines are also required.
(4) Foundation Conditions. — Full note should be made of the
natiu-al conditions of the ground and river bed at the proposed
dam and power-house site. If there is rock in sight a full state-
ment of its character, weathering qualities, etc., is required. If
no rock is in evidence as careful an investigation of the existing
conditions as circumstances permit is required.
(5) Flooding and Pondage, — The direct flooding which will be
caused by the construction of the proposed or any feasible plant
at the site should be determined approximately either by inspec-
tion or if necessary by rough instrument work. If the land has
been surveyed the flooded portion can be listed by sections and
quarter sections.
The utiUzation of this local pondage in connection with peak
loads at the project plant should receive general consideration.
(6) Existing Interests, — All existing interests, such as bridges,
trails, roads, railways, buildings, etc., that may be affected by the
construction of the plant and by the consequent flooding, should
be fully reported on. The question of the logging and fishing
interests on the river should be discussed in considerable detail.
VII. Possibk Power Developed
The question of power possible of development should be dis-
cussed from the standpoints of, first, no storage available, and
second, storage available. Under the first head the power avail-
able at minimum flow and the power which might be developed
during the eight or nine months not included in the extreme low-
water season should be covered.
Under both headings the beneficial utilization of the local
pondage for peak loads and the consequent increased power out-
put should be dealt with.
VIII. Estimates
Approximate estimates of the capital and annual operating
costs of the proposed scheme of development and the basis on
which these are made should accompany the report, together with
similar estimates of the cost of any proposed storage reservoirs.
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COMPILATION OF WATER POWER REPORTS 655
IX. Market for Power
This will involve as thorough an investigation as the circum-
stances warrant of the present and future power market in the
surrounding municipalities and district. Possibilities for the local
use of power at the site and in the immediate vicinity are also to
be covered. With the question of power market, the question
of distance of transmission necessary to reach the same requires
careful consideration.
X. Suggestions and Recommendations
Suggestions, comments or recommendations with reference to
the foregoing and the writer's opinion as to the questions at issue
should be set out in full. The location of suitable metering sta-
tions for the continuous record of the river-flow at vital points
should be covered in these recommendations. The question of
sources of power other than water, in the vicinity and their pos-
sible more economic development is, at times, most important.
All recommendations should be set out definitely and concisely.
XI. Appendices
(1) Plans. — (a) A general plan (a section of pubHshed map is
desirable) showing the location of the power and storage sites
with reference to centers of population. (6) A general plan (a
section of pubhshed map) showing the whole drainage basin above
t!ie power site, together with storage reservoirs, (c) Contour
plans of the sites of power plants and' storage dams, (d) Cross-
sections along dam sites, (e) Profiles of reach of river affected and
of pipe and canal fines. (/) Any other plans warranted by the
nature of the investigation.
All plans, sections, and profiles, etc., should be suitably num-
bered, and should be referred to in the text by these numbers
whenever necessary. A complete list of the above plans, giving
numbers and description, should be included in the table of
contents of the report.
(2) Photographs, — A set of all the views taken to illustrate tlie
different features of the report should be mounted and included.
Where these views deal with power-plant and storage-dam layouts,
they should be accompanied by a sketch plan showing the point
from which each is taken and the direction the camera faced. The
fihns should be numbered, dated and titled, in order that all prints
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656 ECONOMICAL ASPECTS
may be immediately recognized. A complete list of the photo-
graphs, giving numbers, date and subject should be included in
the table of contents of the report.
(3) Run of Records, — All tabulated records and plotted curves
which may have been seemed.
(4) Gauge Records. — Copies of all gauge records which are of
interest in connection with the power or storage features of the
report.
(5) Reports. — Copies of any existing reports which may have
been made with reference to power development on the river.
(6) Maps. — ^Any maps which may usefully illustrate the report,
and any plans which may have been obtained covering existing
power-plants, storage works, bridges, etc., etc.
Investigation and Inspection of a Series of Sites
Frequently the investigation of a river involves the considera-
tion and detailed inspection of a series of power sites. In such
cases, the report covering the work should follow the foregoing
guide, with the following sUght changes.
It will be noted in the foregoing, that Sections I to V can be
applied as they stand, to the compilation of a report on a series
of sites. Sections VI to VIII are directly applicable to each indi-
vidual site; Section IX is applicable to individual sites or to
groups as conditions may warrant, and Sections X and XI are
applicable as they stand to the ending up of the report. In pre-
paring a report on a series of sites, the only alteration advised
in the foregoing guide is that under Section VI, each site is treated
as a unit and completely covered according to the outline in Sec-
tions VI to IX. The new Sections VII and VIII will correspond
to X and XI in the foregoing synopsis.
Following is the outhne for a report covering a series of inves-
tigated sites, with the necessary alterations:
I. Sources of Data Used in Report.
(1) Why investigated and scope of investigation.
(2) Personal examination, route followed and time con-
sumed.
(3) Run-ofif records from departmental stream measure-
ment offices.
(4) Maps.
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COMPILATION OF WATER POWER REPORTS 667
(5) Existing reports.
(6) Miscellaneous.
II. Summary of Report,
Concise statement of results of investigations covering all
essential features of the report. Tabulation of results as to power
and storage.
III. Generallntrodudory.
Description, including location as to province, river, cities,
township, range and section.
IV. Water Supply.
(1) General description of drainage area.
(2) Actual record if available showing maximum, min-
imum and mean discharge for each month, also
absolute minimum for year. Measurements on
ground if foregoing are not available.
(3) Rainfall, temperature, evaporation.
(4) Storage already developed and effect of same.
(5) Storage possibilities.
(a) Location of reservoir sjte or sites.
(b) Height of dam and class of dam suitable.
(c) Capacity of reservoirs and extent of adjacent
drainage basin.
(6) Prior water rights above and below power site;
water supply, irrigation or power.
(7) Ice conditions during winter months and in spring
flood (frazil, anchor and floating ice).
(a) Under present conditions on river.
(b) After construction of plant.
(c) Without storage.
(d) With storage.
V. Description of Existing Power Developments on the River.
VI. Sites Investigated.
(a) Detailed work at each site investigated,
(1) Scope of the inspection at the site.
(2) Accessibility of site and transportation prob-
lems.
(3) Detailed information and plans at site, —
(a) Contour plan of site.
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658 ECONOMICAL ASPECTS
(6) Cross-sections,
(c) Profiles.
(4) Foundation conditions.
(5) Flooding and pondage.
(6) Existing interests.
(6) Possible Power Developed,
(1) Horse-power at wheel shaft without storage, —
(a) At minimum flow.
(6) For the nine high months.
(2) Horse-power at wheel shaft with storage. Dis-
cuss utilization of local pondage at site for
peak loads.
(c) Estimates.
Cost of power developed, capital and annual.
Cost of storage, capital and annual.
(d) Market for Power.
(1) Present.
(2) Future.
(3) Length of transmission lines, etc.
{e) Recapitulation.
Comprehensive discussion of the foregoing data as
to the individual sites, and a consideration of
the same as a whole or in groups, as local condi-
tions may warrant.
VH. Suggestions and Recommendations.
Vni. Appendices.
(1) Plans pertinent to the actual sites investigated.
(2) Photographs.
(3) Run-oflf records.
(4) Gauge records.
(5) Reports.
(6) Maps and plans of existing power plants and
structm-es, etc.
The details of the data to be covered in each section are in the
main as previously outlined in connection with the report on an
individual site. A careful study of these details is desirable.
In section VI each site investigated should be completely cov-
ered under the headings, a, 6, and c, before discussion on a second
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COMPILATION OF WATER POWER REPORTS 659
site is commenced. The market for power under the heading d
should be discussed with each individual site or with groups of
sites as general conditions may warrant. Plans and photographs
should be suitably numbered in order that they can be referred to,
when necessary, in the text.
Attached as appendices to this Guide are reproductions of the
loose-leaf forms, R-11 to R-22, used in the field by the engineers
of the Water Power Branch. The great flexibiUty of the loose-laef
S}'stem is claimed to be of outstanding advantage to the rapid and
efficient carrying on of the survey work, more especially on those
investigations where the results have been plotted into final
shape in the field. The loose leaves generally lend themselves
most readily to a simple filing system in which the records of
the survey are properly grouped, and are at all time available for
ready reference.
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660
R-11.
ECONOMICAL ASPECTS
O
Diary op.
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Water Power Branch, Dept. of the Interior,
Ottawa
Day of 19
Day of 19
Day of 19
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COMPILATION OF WATER POWSR REPORTS
661
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R-12 Return to
WATER POWER BRANCH, DEPT. OF THE I>
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ECONOMICAL ASPECTS
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R-13 Return to Valuable
WATER POWER BRANCH, DEPT. OF THE INTERIOR, OTTAWA
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COMPILATION OF WATER POWEE REPORTS
663
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R-14 Return to Valuable
WATER POWER BRANCH, DEPT. OF THE INTERIOR, OTTAWA
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ECONOMICAL ASPECTS
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R-15 Return to Valuable
WATER POWER BRANCH, DEPT. OF THE INTERIOR, OTTAWA
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COMPILATION OF WATER POWER REPORTS 665
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R-16 Return to Valuable
WATER POWER BRANCH, DEPT. OF THE INTERIOR, OTTAWA
LEVEL NOTES
Stream
Locality
Party Date 19
station.
B. 8.
Ht. Inst.
F. 8.
Elevation.
Remark!.
No.
.of Sheeta Comp. by Chk. by.
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666 ECONOMICAL ASPECTS
Form R-17 — ^Fbont
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R-17. Return to
WATER POWER BRANCH, DEPARTMENT OF INTERIOR, OTTAWA
DESCRIPTION OP RIVER STATION
^ • {^]"
near PostOflSce, Prov. of
Established 191...., by
Name of observer P. 0. address
pay S occupation distance time of daily observation. . . .
Location of station with respect to towns, bridges, highways, railroads,
tributaries, islands, falls, dams, etc
Description and location of the gauge, also relative to the measuring
station. If chain gauge, give length from end of weight to the marker
Description of the equipment from which measurements are made.
Location and description of initial point for soundings.
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COMPILATION OF WATER POWER REPORTS 667
Form R-17— Back
Channel above the station: straight or curved for about feet,
water swift, sluggish, etc
Channel below the station: straight or curved for about , feet
water s\?if t, sluggish, etc
Right bank: high, rocky or low, liable to overflow, dean or wooded, etc.
Left bank: high, rocky or low, liable to overflow, clean or wooded, etc.
Bed of the stream: rocky, gravel, sandy, clean or vegetation, shifting
Number of channels at low and high water, approximate depth of water,
etc
Note any condition which may affect the measurement, etc
Bench marks: Describe fully, give elevation above zero of the gauge
and above sea level or other datum, if possible; make sketch bringing out
the principal features
Take sufficient soundings to develop a crossHsection of stream bed and, by
use of level, develop banks to above high-water mark. Refer all elevations
to gauge datum.
Make a sketch plan on cross-section paper, showing the relative location
of the station, gauge bench marks, tributaries, towns, etc.
o o
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668
ECONOMICAL ASPECTS
Form R-18— Fbont
R-18 O Return to
WATER POWER BRANCH
Dept. op Interior, Ottawa
Current Meter Notes — Ice Cover
A.M.
o
Valuable
Date.
.19.
P.M.
Stream.
Party Locality
Meter No Gauge height, beg end mean.
Total area Mean velocity Discharge. .
Odseuvatiokh.
COlit»UTATIC}?^S.
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COMPILATION OF WATER POWER REPORTS 669
Form R-IS—Back
Weights used
Wind
Method of supervision of meter (single wire or cable)
Stay wire used or not used
Point of measurement with reference to gauge (i.e., distance above or below)
Length of gauge chain checked and found to be ft. and corrected to ft.
Ckmdition of gauge and equipment at river station
Repairs necessary
Remarks:
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670
ECONOMICAL ASPECTS
R-19
FoBM R-19— Front
Return to
Water Power Q Branch, Department of the Interior Q
Current Meter Notes
Valuable
Ottawa
Date.
.191.
A.M.
'p.m.
Stream.
Party Locality
Meter No. Gauge height, beg end mean
Total area Mean velocity Discharge.
Obbervationb.
COMPUTATIOKB.
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COMPILATION OF WATER POWER REPORTS 671
Form R-19— Back
Weights used
Measurements by reading, from cable, bridge or boat
Wind
Method of supervision of meter (single wire or cable)
Stay wire used or not used y
Point of measurement with reference to gauge (is distant above or below) . . .
Length of gauge chain checked and foimd to be ft. and corrected to ft.
Ck>ndition of gauge and equipment at station
Repairs necessary
Remabeb:
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672
ECONOMICAL ASPECTS
o o
R-20 Return to
WATER POWER BRANCH, DEFT. OF THE INTERIOR, OTTAWA
No
.191....
6
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Photc
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Holder.
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COMPILATION OF WATER POWER REPORTS 673
R-21
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DEPARTMENT OF THE INTERIOR, OTTAWA
water power branch
Discharge Measurebcent Notes
Date , 191 . . No. of Meas
River at
Width Area Mean Vel Cor. M. G. H
Party Disch
Gauge, checked with level and found
Measurement began at Measurement ended at
Date rated
Method of meas
No. meas. pts Coef
Av. width sec Av. depth . .
G. Ht. change (rate per hr.)
First reading of gauge ft. at
Gauge ft. at sta ft. at
Gauge ft. at sta ft. at
Gauge ft. at sta ft. at
Last reading of gauge ft. at
Meter No % error by rating table . .
Meas. from cable, bridge, boat, wading; Meas. at ft. above, below gauge
If not at regular section note location and conditions
Method of suspension Stay wire Approx. dist. to W. S
Arrangements of weights and meter; top hole ; middle hole ;
bottom hole
Gauge inspected, found ; Cable inspected, found
Distance apart of measuring points verified with steel tape and found
Wind upstr., downstr., across. Angle of current
Observer seen and book inspected
Examine station locality and report any abnormal conditions which might
change relation of G. Ht. to disch., e.g., change of control; ice or debris on
control; back water from; condition of station equipment
Sheet No. 1 of sheets. If insufficient space, use back of sheet.
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674 ECONOMICAL ASPECTS
R-22 O O
Return to
WATER POWER BRANCH, DEPARTMENT OF INTERIOR, OTTAWA
Gauge Record
Station No
River at
Old Gauge
Location
Zero 191 Elev .
Kind of gauge. Length. . .
New Gauge
Location
Established 191 ... .by. . .
Zero 191 Elev.
Kind of gaugq
Reading from ft. to. .
Gauge reader Address. . .
Time of observation
Reason for change
Remarks.
Engineer
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AMOUNT OF ENERGY AVAILABLE 675
AMOUNT OF ENERGT AVAILABLE
The two principal factors which enter into the detennination
of the available energy of a stream are the fall or head and the
quantity of water flowing.
The head is usually limited by the cost of the overflowed lands,
and the fall may be either naturally concentrated at one point in a
cascade or it may be artificially concentrated, for the purpose of
development, by combining the fall of several cascades or a series
of rapids. This may be accomplished by either of two methods:
First, by building a dam at the downstream end of the rapids to
impound the water so that the entire fall is concentrated at the
dam; or, second, by building a dam at the upstream end of the
rapids and conducting the water through a closed pipe to the lower
end of the rapids, where the resulting head and pressure will be
exactly the same as in the first instance. A variation in the latter
method consists in diverting the water from the natural channel
at the head of the rapids and carrying it to a canal or flume, on a
slight down grade, along the side of a hill to a suitable point, and
there erect a forebay from which the water is turned into pen-
stocks which run directly down the slope to the stream, where the
power-house may be located. The latter method, involving the
construction of an open canal or flume, is open to the objection
that trouble may be experienced from the accumulation of ice
in the winter time. The first two methods described are the
most common.
The second quantity to be determined was the water flowing
in the stream per unit of time, usually expressed in cubic feet per
second, but for low-head developments the two factors of head-
and stream-flow are, as a rule, inseparable, as the head fluctuates
considerably with the different stages of the stream.
To be of value the stream-flow data should extend over a
period of several years (fifteen to twenty) in order that the min-
imimi as well as the maximum flows which may be expected, and
their duration, may be known, and while the average flow charac-
teristics are of interest they are not of very great value.
The United States Geological Survey and various states have,
for many years, carried on a systematic stream-flow measure-
ments, and data are now available for streams in nearly all sections
of the coimtry. There are, however, a large number of streams,
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676
ECONOMICAL ASPECTS
especially the smaller ones, where few, if any, discharge measure-
ments have been made, and in such cases it is necessary to base
estimates of discharge on the records at other stations in the same
precipitation belt and watershed, and data of other systems of
similar nature may be also used. Rainfall data are also useful as a
check on flow estimates and they also show years of high and low
water, but care should be exercised in their use.
The daily and seasonal distribution of stream-flow is best
shown graphically in the hydrographic curves, as fully explained
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Fig. 398. — Stream-flow-Duration Curves.
under the section of Stream Flow, and by comparing a niunber of
such hydrographs the dryest year, i.e., the year with the minimum
flow, can readily be ascertained.
For convenience in making a scientific analysis and study, the
stream-flows, instead of being arranged chronologically as in the
hydrographs, may be arranged according to magnitude, as in Fig.
398. The discharge is plotted as ordinate and the corresponding
number of days during which the respective discharge has oc-
curred as abscissas. Instead of recording the time in days it
may also be given in percentage of the entire year, and horse-
power values may be substituted for the discharge by making
allowance for any possible variation in the head at the different
discharges.
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POWER DEMAND 677
POWER DEMAND
The market for electric power is of a most widely distributed
character and will always continue to grow with the growth of
the community in which it is located. On the other hand, there
are many instances in which a hydro-electric development will
create its own market by inducing a number of industries to
locate in its inmiediate vicinity, such as at Niagara Falls, etc.
Whether a market can be foimd for the power which is to be
developed and the price at which this power may be disposed of
are two of the first questions to be investigated. This involves a
close canvass of the present power consumption for both public
and private use, the character of the p>ower demand as to periods
of day and season, present and future competition, present rates,
and the cost at which p>ower can locally be generated from fuel.
From these investigations it is p>ossible to anive at a fairly close
estimate of the required capacity, load factor and value of the
service, and future considerations should be based thereon. In
the absence of the above information a fairly close estimate of
the revenue may be made by comparing the possibiUties of the
community to be served with those of similar places already
developed.
A typical power market has three main divisions, namely,
lighting, manufacturing, and traction. If the greatest demand
from each source came at a time different from that of the others,
the total demand would be so distributed as greatly to reduce the
required maximmn capacity of the power plant. As a matter of
fact, however, the demand from no one of these sources is imif orm,
and, furthermore, there is more or less overlapping of these de-
mands. The demand for manufactiuing piu*poses is very nearly
uniform and, except for a few industries and in exceptional cases,
falls between 7 o'clock in the forenoon and 7 o'clock in the after-
noon. Practically all the demand for Ughting is at night, chiefly
in the evening. The period of traction demand is longer than
that for either manufacturing or lighting, and embraces prac-
tically the entire periods of both.
TTie period of lowest combined demand is normally between
the hoiurs of midnight and 4 o'clock in the morning. Traction
demand begins in earnest about 6 o'clock and is immediately
followed by the manufacturing demand. The forenoon period
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678 ECONOMICAL ASPECTS
of active demand is from 6 o'clock to noon. In the middle of the
day manufacturing establishments cease operations for an hour
or less and resume again about 1 o'clock, thus restoring the
demand to the level of the forenoon. Between 4 o'clock and 7
o'clock in the afternoon there is a distinct overlapping of the three
demands. It is during these hours, especially in winter, that
practically all the lights are turned on, manufacturing concerns
have not yet stopped for the day and street cars are carrying,
perhaps, their heaviest loads. It is during this period that the
highest demand of the twenty-four hours is reached.
There is also a seasonal fluctuation in a typical power market.
The demand in winter is usually greater than in summer and the
daily fluctuation is likewise greater. The increased demand grows
out of the increased requirements for Ughting and in some cases
for traction. The greater fluctuation is mainly due to the fact
that between the hours of 4 o'clock and 8 o'clock in the after-
noon more power is required for Ught in winter than in sunmier.
LOAD AND DIVERSIT7 FACTOR
The load factor of a plant or system is the ratio of the average
to the maximmn p)ower during a certain period of time. The
average load may thus be taken over a period of one year, one
month or one day, while the maximum load must necessarily be
limited to very short periods, depending on the overload capacity
of the water wheel or the generator. In other words, it is the
ratio of the actual station output to the maximum possible output
with continuous service.
It is also a measiure of the extent to which the necessary total
investment is being utilized, as a plant with yearly load factor of
50 per cent is turning out just double the energy of another plant
of the same maximum load and with a load factor of 25 peY cent.
This means that, while the fixed charges of both plants are the
same, the gross income of the plant with 50 per cent load factor
should be nearly twice as great as that of the other. The impor-
tance of a good load factor is thus apparent, and everything that
will improve this factor should be sought.
The nature of the load as measured by the load factor forms
necessarily also a very important element in determining the
value of water power as compared to steam power. For load
factors below 50 per cent the former often turns out to be the
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LOAD AND DIVERSITY FACTOR 679
cheaper, but as the load factor increases above this value water
power may show up to the better advantage. This is evident
from the fact that the cost of hydro-electric power is made \ip
chiefly by the fixed charges and is very Uttle dependent on the
operating charges and the amoimt of power used.
There is an enormous variety of uses to which electricity is
applied, the yearly load factors of which also vary widely, as
shown in Table LXI.
The yearly load factor for any class of service is determined
largely by the seasons, the habits of the people, and other con-
ditions which ordinarily do not change very materially. Im-
provement in the load factor must, therefore, be obtained largely
by combining different classes of service, the maximmn demands
of which occur at different times of the day or of the year. Also,
the larger the niunber of customers in any class the better will be
the load factor.
A recognition of the importance of the diversity factor has
imdoubtedly the most marked effect in increasing the load factor
and thereby the economy of production. This factor is the ratio
between the sum of the maximum demands of various classes of
service to the actual simultaneous maximum demand, and the
more non-coincident these peak services are, the greater will be
this factor.
The chief means ot improving the load factor has been the
addition of industrial load. In the early days of electric Ughting
companies, the load factors were very low, due to the absence of
day load. To-day many central stations sell far more energy
for power than for Ught, and this is naturally distributed over a
longer part of the twenty-foiu* hoima. The power load, also, not
being simultaneous with the Ughting load to any great extent,
still further improves the load factor. Residence load has gen-
erally been characterized by a poor load factor, but by the use of
day-load devices such as flat irons, cooking devices, fans, heating
apparatus, vacuum cleaners, etc., a much improved result is
obtained.
Tlie problem of combining electric railway loads and central
station loads on one system has received increasing attention in
recent years, and in some cities of this country great strides have
been made toward effecting such combinations successfully.
Kg. 399 thus shows a typical load curve for a large city.
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680
ECONOMICAL ASPECTS
There are a number of industries which offer ideal loads for
large hydro-electric companies; such as mining, electro-chemical
wdrk, irrigation and farming, while much is expected from the
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Fig. 399. — Typical Daily Load Curve for Large City Service.
railroad field when the time has arrived for the economical elec-
trification of our trunk hnes.
Table LXII gives statistics for 1916 on the outputs, peak load,
and load factors of a number of the largest generating systems in
this country and Canada, and Table LXIII gives the power re-
quired for certain manufacturing industries, as based on the 1909
U. S. Census Report.
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LOAD AND DIVERSITY FACTOR 681
TABLE LXI
Load Factorb
small and medium lighting customers
Per Cent.
BuildingiSy public 17.6
Churches 12.4
Clubs 9.6
Flats 6.9
Halls (public) 6.9
Hotels 24.4
Offices (business) 9.2
Offices (professional) 6.7
Residences 7.8
Restaurants 23.4
Shops (bakery) 13.1
Shops (tailor) 8.4
Schools 7.2
Stores (dry goods) 8.2
Stores (cigar) 16.8
Stores (drug) 19.3
Stores (grocery) 10.3
LARGER POWER AND LIGHTING CUSTOMERS
Per Cent.
Bakeries 12
Blacksmith shops 15
Breweries 45
Boots and shoes 25
Bottling works 10
Candy manufacturing 18
Clothing manufacturing 15
Department stores 30
Furniture manufacturing 28
Foimdries 15
Ice cream manufacturing 20
Ice making 30
Laundries 20
Machine shops 20
Newspapers 18
Packing houses 30
Railroad depots 50
Tanneries 20
TextUe mills 20
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682
ECONOMICAL ASPECTS
TABLE LXII
Data on Output and Load Factor of Largest Generating Stbtems in
America
(From Electrical World, April, 7 1917)
System.
Commonwealth Edison Company.'
Niagara Falls Power Company
Ontario Power Company of Niagara Falls
New York Edison Company & United
Electric Light & Power Company ....
Montana Power Company
Pacific Gas & Electric Company
Hydraulic Power Company
Toronto Power Compaiw
Public Service Electric Co. of N. J
Detroit Edison Company
Tennessee Power Company
Shawinigan Water & Power Company. . .
Duquesne Li^t Company
Philadelphia Electric Company
Penninrlvania Water & Power Company..
Utah Power & Light Company
Great Western Power Company
Mississippi River Power Company
Pacific Lii^t & Power Corporation
Puget Sound TYaction, Light & Power Co.
Cleveland Electric Illuminating Co
Electric Company of Missouri 1
Union Electnc Light & Power Co /
Commonwealth Power, Ry. & Light Co . .
Southern California Edison Company. . .
Buffalo General Electric Company
New England Power Company
Edison Elec. Illuminating Co. of Boston.
Edison Elec. Illuminating Co. of Bklyn.
Wisconsin Edison Company \
Milwaukee Elec. Railway & light Co. /
Portland Railway, Light & Power Co . . .
Sierra & San Francisco Power Company.
Alabama Power Company
Georgia RaOway & Power Company ....
Minneapolis General Electric Company.
Great Northern Power Company
Washington Water Power Company ....
Adirondack Electric Power Corporation .
Rochester Railway & Light Company. . .
Toledo Railways & Light Company
Virginia Railways & Power Company. . .
Southern Sierras Power Company. ... 1
Nevada-California Power Company. . . /
Potomac Electric Power Company
Empire District Electric Company
Southwestern Power & Light Company. .
1916
Peak
Yearly
Yearty
Load,
Kw.
Output.
Kw.-hr.
Factor.
Per Cent.
369,740
1,341,964,000
43.20
143,360
1,015,525,680
80.64
123,900
942,221,900
86.80
254,824
856,385,319
28.30
149,740
867,940,326
84.50
141,008
768,304,907
62.20
89,275
717,079,320
91.50
129,000
660,873,579
58.40
174,000
608,018,729
39.82
130,200
546,925,300
48.70
81,650
483,354,162
67.00
108,000
478,540,000
50.00
101,000
463,537,660
52.30
142,260
444,785,884
35.6
77,000
417,837,600
61.8
68,894
412,726,000
67.8
74,100
408,391,067
62.65
82,400
393,400,000
54.3
82,765
367,308,731
51.76
77.030
353,697,263
51.8
84,999
340,670,721
45.8
88,544
333,964,652
315,964,337
43.1
66,'93d
299,950,513
56.04
65,500
299,306.640
57.00
64,000
246,000,000
44.00
80,539
238.557,144
33.72
67,200
233,452,500
38.1
64,170
218,421,711
39.00
47,335
194,146,555
191,620,000
46.5
46,600
184,345,360
172,000,000
51.07
43,640
171,672,890
44.9
38,200
163,807,560
48.8
30,440
162,825,400
60.80
41,575
151,128,310
41.40
40,250
146,069,428
41.00
36,428
134,842,360
42.2
33.900
132,275,000
44.54
22,400
131,084,265
66.5
38,600
122,158,818
36.1
26,900
119,280.363
49.7
25,600
95,740,000
43.0
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PRIMARY AND SECONDARY POWER
683
TABLE LXIII
Power Rbquirsd for Manufacturing
Based on 1909 U. S. Census
Horse-power
Required per
SI 000 Product.
Horse-power
Used per Person
Engaged in
Industry.
Agricultural implements
Automobiles
Boots and shoes
Brick and tile
Cement
Chemicals
Copper, tin and sheet-iron products. .
Cotton goods
Electrical machinery.
Fertilizers
Flour and grist-mill products
Foundry and machine shops
Manufactured ice
Iron and steel, blast furnaces
Iron and steel, rolling mills
Leather, tanned, curried and finished
Lumber and timber
Paper and wood pulp
Printing and publishing
Packing houses
Copper smelting and refining
Woolen, worsted and felt goods
Total, all industries
0.69
0.30
0.19
3.68
5.90
1.78
0.31
2.07
0.72
0.62
0.97
0.71
7.40
3.00
2.13
0.45
2.46
4.88
0.40
0.15
0.42
0.83
0.91
1.67
0.89
0.45
4.00
12.60
7.50
0.72
3.35
1.50
2.95
12.90
1.41
15.05
27.30
8.06
2.21
3.62
16.05
0.77
1.92
9.41
2.06
2.45
PRIMARY AND SECONDARY POWER
Many companies make two classes of contracts for power,
known as primary and secondary. Under the terms of primary
power it guarantees to supply the amount of p)Ower contracted
for continuously throughout the year, and it is evident that
the maximum amoimt of such power is limited by the minimum
stream-flow and can only be safely increased by providing water
storage or steam auxiliaries to augment the shortage during
low-water periods.
The minimum flow of the stream to be used may be the abso-
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684 ECONOMICAL ASPECTS
lute minimum, the minimum of the average year, the average
minimum, or some other value of low discharge of the stream.
The selection of the particular value to be used depends upon the
degree of insurance of the continuity of the supply that is justified
by the conditions. The added cost of the insurance of the supply
should be equated to the losses, direct and indirect, sustained by
failure of the supply. If it is planned to seciu^ absolute con-
tinuity, in so far as stream-flow is concerned, it will be necessaiy
'to use the absolute minimum of the stream and to use it in con-
nection with the maximum load that can occur upon any day
when the stream-flow may be lowest. This d^ree of insurance is
seldom necessary; usually it will be sufficient to use the stream-
flow which can be depended on for, say four years out of five;
in other words, to eliminate the extraordinary low discharge which
will occur once in every five to ten years. But on this point, as
in all others in connection with the matter, the decision depends
upon the experience and judgment of the engineer, and no hard-
and-fast rule can be laid down. One kind of load demands the
highest degree of insurance, whereas loads of a different character
may be satisfactorily served with a less degree of insurance.
Secondary power is that amoimt which is being developed
above the primary, and which is only available for a certain time
of the year, such as eight or ten months. The continuity of this
power is, as a rule, not guaranteed, and the right is reserved to
cut off such supply upon reasonable notice. The rates for sec-
ondary power are, therefore, much lower than for primary power.
> The question of the sale of secondary p>ower has yet not
reached the proportions to which it is entitled, but there is ever>'
reason to beUeve that by careful planning of certain industries
quite a large amoimt of secondary p)ower could be very econom-
ically utilized.
The question as to what extent a power site should be devel-
oped depends necessarily upon the market conditions for the two
classes of service. It needs no argument to prove that where
power can be sold at a high price and conditions are favorable, the
development can be carried to a higher point of stream-flow than
where the opposite conditions prevail. Over-development, how-
ever, may entail fixed charges which will make the earning of a
surplus only a speculative possibility of the distant future. On
the other hand, the present demand and its probable future
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WATER STORAGE 685
increase may both be done justice by the correct solution of this
factor. As a rule, however, the development of a p>ower site
usuaUy also involves the consideration of an auxiliary power
source, such as a storage reservoir or a steam plant.
If the secondary power can be sold without an auxiliary steam
plant, the amount of secondary power which may be developed
economically depends only upon whether or not the price received
for such power will cover interest and profit on the investment;
that is, the investment which is over and above that for develop-
ing primary power. If a steam plant has to be maintained the
amount of secondary power to be developed depends also upon
the cost of the steam power.
WATER STORAGE
In order to increase the capacity of a hydro-electric plant
at times of low water, the question of storage is one of vit^ im-
portance, and the extent to which the irregular stream-flow can
be equalized depends upon the quantity of storage. It is also
obvious that no considerable amount of money can be judiciously
expended in the construction of storage reservoirs imder average
conditions unless the head available at the plant is considerable,
and this question must be largely determined by local conditions
surroimding each individual development.
Water-storage problems are most readily solved graphically
by means of " mass-curves,'^ and the most economical solution is
fixed by balancing the value in the increase in output as against
the cost of securing the same. From the mass-curve, the available
water for power is obtained and this, under given net heads will
determine the p>ower available.
The application of the " flow-smnmation " or " mass-curve "
to problems of water storage is clearly explained by Mr. E. C.
Jansen in the Engineering News for December 25, 1913, as follows:
" To plot the stream-flow for any period of time, the mean
daily discharges in any convenient unit are added day by day and
plotted as ordinates, the units of time being represented by
abscissas, so that the siun total or ordinate on any date repre-
sents the total quantity of water which has flowed past the gauging
station up to that date (see curve ABODE, Fig. 400). Second-
feet (cubic feet per second) are now most commonly used as units
of flow and, when the mean daily discharges are expressed as such,
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686
ECONOMICAL ASPECTS
the summation of them results in convenient units of day-eecond-
feet or a second-foot flowing for twenty-four hours (1.98 acre-feet)
as in Fig. 400. As the length of the ordinates shows the increase
or decrease of the twenty-four-hour flow, it will readily be seen
that the slope of the curve represents the rate of flow and that a
uniform flow is represented by a straight line as FG."
Fig. 400. — Flow-Summation Curve.
The inclination of a tangent to the curve at any point indicates
the rate of flow at that particular time, and when the tangent is
parallel to the abscissas it illustrates that the flow at that time wHl
just balance the losses caused by evap>orationy seepage, etc., while
a negative incUnation of the curve shows that a loss from the
reservoir is taking place.
''Assume, for example, that FO represents a regulated or
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WATER STORAGE 687
uniform rate of flow of 30 second-feet, then, by applying this
slope as a tangent to the summation cm^e at C, it is observed
that the stream from about October 1st began to .discharge less
than this flow and did not rise above the same until the beginning
of April at D. The flow can be readily interpreted in this way by
drawing a datum and different slopes or tangents on a piece of
tracing linen and applying this at any point on the curve."
Having a certain reservoir capacity and the mean daily dis-
charges of a stream for a period of years, the method of utiUzing
the summation curve for finding the maximum regulated flow
which can be obtained for power purposes, is explained in the fol-
lowing paragraphs.
" ABODE represents the stream-flow in day-second-feet
(usually a period of minimum run-off when water power is con-
templated) ; FG is the desired regulated flow and H is the capacity
of the reservoir ift day-second-feet. Starting with a full reservoir
on or about October 10, 1895 (the smaller units of time are pur-
posely omitted), the sunmiation curve shows that the stream-flow
is below the desired regulated flow ABi, parallel to FG, and that
the ordinates JK, LM, etc., represent the amounts of storage
required to maintain the regulation. Plotting these ordinates
below the high-water level of the reservoir in the storage diagram
as JiKi, L\Mi, etc., the storage curve HiJ\L\ is obtained, showing
the behavior of the reservoir during the uniform rate of dis-
charge for power purposes. At 5, about April 10, 1896, the sum-
mation curve shows that the stream-flow is above the desired
regulated flow; consequently, the ordinates NO, PQ, etc., show
the amount of water which can be stored and these ordinates are
plotted as ATiOi, PiQi, etc., for the remaining portion of the stor-
age curve imtil the reservoir fills about June 1. By continuing
the plotting of these ordinates RS, TU, etc., as RiSi, TiUi, etc.,
in the storage diagram, the cmre SiUiWi is obtained, showing
the quantity of water which passes over the reservoir spillway.
This process is then repeated and in this way is ascertained the
behavior of the reservoir from year to year while a continuous
draft is being made on it. The ordinate X, showing the water
left in the reservoir at the end of the drawing period, enables one
to experiment with differently regulated flows to ascertain just
how much draft the reservoir can stand. Frequently two or three
exceptionally dry years in succession in a long period of obser-
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688 ECONOMICAL ASPECTS
vation will tax the reservoir capacity to its limit and settle the
question conclusively as to the maximum regulated flow obtaio-
able."
Having the mean daily discharges of a stream, it miay also
be required to find how large a reservoir is required to obtain a
maximum regulated flow. This may also be obtained from Fig.
400. By drawing a line from B to D the maximum regulated
flow utilizing all the water is foimd, and the ordinate V2W rep-
resents the capacity of the reservoir in day-second-feet, which
would be required to effect this.
The above method is suitable for determining the power pos-
sibihties of a given development when one or two power-houses
with accompanying reservoirs are involved. When a large num-
ber of related power-houses and reservoirs are involved, this
method of using the mass curve of discharge becomes very long
and tedious. Also, it is only approximate, giving as a result uni-
form flow of water, not uniform power, and it fails to take into
account regulative effect on the power output of the power-houses
situated on the upper sections of the watershed. To solve these
more intricate problems, a method of determination has been
proposed by Mr. L. A. Whitsit, and is described in the Engineering
News for September 11, 1913.*
The utihzation of stored water so as to absolutely insure a
fixed minimmn flow in all years, while, perhaps, best for streams
whose power is not developed up to the limit, leads to a very
uneconomical use of the reservoirs on streams which already are
highly developed as to power. As a condition of high ratio of
development exists on many streams where storage would be most
desirable and valuable, and as this condition will become more
and more pronounced on all power streams, it is apparent that the
subject of this basis of figuring the power benefits is of importance
in securing a proper view of the relation of water storage to water
development.
The conditions may be such that when the method of regu-
lating for a minimum steady flow of water is appUed, it has been
found, for example, that the storage capacity would have been
used to its full extent only once in ten years. Dming six of the
ten years it would not have been used at all, and during two years
^ See also Engineering News, Aug. 24, 1916.
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WATER STORAGE 689
only about one-half of the capacity would have been used. It is,
therefore, evident that capital if invested for use only once in ten
years must when it is used yield a very large return. Such a
method of management of a storage reservoir would call forth
just criticism when it was discovered that after money had been
spent for the auxiliary power during the low-water season, the stor-
age reservoir remains full of water. This has led the Water
Supply Commission of the State of New York to deduce a new
method of computation, which is based on an average rate of
release of stored waters, so that while the assurance of a certain
minimum flow would not be unduly sacrificed, the entire volume
of stored water could be used practically every year. This
method, which has been termed the " utility " method to dis-
tinguish it from the *' insurance " method, has been based on a
knowledge of the conditions of the larger streams of the State,
where the developments can be run at full capacity up to about
60 per cent of the time reckoned over a long period of time, and it
assumes that there is always sufficient demand for power to
absorb any additions and render further development after
regulation as desirable as before.
Figs. 401 and 402 represent graphically the results of an inves-
tigation for the regulation of the Genesee River by providing a
storage reservoir having a capacity of 13.5 billion cubic feet.
The stream-flows are arranged according to magnitude, and
result in the curve marked " Natural Flow of River." Although
the vertical scale is given in horse-power, the power is propor-
tional to the stream-flow as long as the head is not affected, and
the curve would not be changed in any respect if stream-flow
instead of power were used. In order to plot the " Regulated
Flow " curve the mass curve, as previousl;^ explained, is used, and
the regulated flows are also arranged according to magnitude
and the values plotted as for the natural flow.
The results were based on a " present " wheel installation of
29,200 horse-power, and by referring to diagram. Fig. 401, it will
be seen that one-fifth of all the water power with regulated
flow and present wheel capacity will be derived from the stored
water, shown by the vertically sectioned area. Without regula-
tion the present installation can be operated at its full capacity
for only 58 per cent of the time and diminishes to a minimum of
about 7500 horse-power. Similarly the amount of energy neces-
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ECONOMICAL ASPECTS
sary on the average from auxiliary power is shown by the hori-
zontally sectioned area. It amounts to approximately 3000
horse-power, which thus is required to maintain continuously the
full power output equal to the present wheel capacity.
The diagram in Fig. 402 indicates what will be the limit of
111 jo k:u 4i> ^'1
Percentage of Time
Fig. 401. — Power-percentQ.ge of Time Curves of the Genesee River at
Rochester, N. Y.
^u 4L» ^U m iU MJ iHJi i(Mi
Percentage of Time
Fig. 402. — ^Power-percentage of Time Curves of the Genesee River at
Rochester, N. Y.
economic development, it being near the point where the regulated-
flow curve takes the sharp downward bend. As the installation
capacity increases above that amount, the percentage of time
during which further capacity can be .used, diminishes rapidly.
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WATER STORAGE 691
The economic limit of capacity for the particular development in
question, for a steady twenty-four-hour j)Ower after regulation, is
thus seen to be approximately 40,000 horse-j)Ower, based on a'
228-foot head. Such a development would run twenty-four
hour? per day 58 per cent of the time, or seven months per year
on the average. The energy furnished by the natural flow each
year would be 29,000 horse-power-years, from stored water 8400
horse-power-years, and from the auxiliary source 3100 horse-
power-years.
The diagrams also bring out the fact that full economic advan-
tages of the stream cannot be secured even after regulation without
auxiliary power. They also show that a small auxiliary plant
will render more additional energy available from the stream-flow
after regulation than the same amount of auxiliary capacity would
render available before regulation; i.e., after regulation auxiUary
pow^er is more essential to the best economic results than before
regulation.
All the above has been based on a steady twenty-four-hour use
of power; i.e., a load factor of 100 per cent. The general con-
clusions are not, however, affected by a smaller load factor, and
where there is pondage a low load factor simply permits a larger
economic installation. Thus, in the above case, with a load factor
of 62 per cent the economic development would be about 64,000
horse-power.
A point in connection with water-storage problems which is not
always realized is, that while a given quantity of water in stor-
age will raise the minimum flow of the stream a certain definite
amount, a further addition of that same quantity of storage, when
put into the stream, will not raise the minimum flow by any-
thing like the first quantity, because its use will have to be distrib-
uted throughout a longer period of time in the year. Therefore,
as storage reservoirs continue to be built out, the increment in
the minimum flow becomes less and less, which means that as the
development of storage reservoirs progresses, the economical
outlay per unit of storage becomes less and less, and the time
comes when it becomes cheaper to increase the minimum flow
by means of an auxiliary steam plant.
This may be illustrated by the diagram, Fig. 403, which rep-
resents a typical hydrograph or river-flow curve. It will be noted
that the minimum flow shown by this curve is 470 cu. sec. ft.
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692
ECONOMICAL ASPECTS
The introduction of 100 sq. mi. ft. of stored water will raise the
minimum flow to 1100 cu. sec. ft., a difference of 630 cu. sec. ft.
If now further stored water in units of 100 sq. mi. ft. is intro-
duced, the figure clearly shows the decreasing amount by which
the minimum flow is increased. It is, however, to be distinctly
understood that it applies solely to the minimum rate of stream-
1 1 1
ll
Annn
EFFECT OF STORED WATER •
fiOOO -- — ^
°^ ON 1
MINIMUM FLOW OF STREAM 1
^4000 / ! L- _ 1
1 , J. ji 1 L.iL-
._ 'Win - - . - . _ ♦ ^ —
^3000 - ^ - - - —
1 ._....^ +-V---I ^-
(thlOOSj.Mi.Ft. I A
/-' 'j./j'r*/ 2n« ' hT ^^^ ^^ '' ^^v i^f''>
^^f^.^^^J' lit 1 B _| 1 ^'^''^^ ^'^^^^ ) j "^
"^©L t^'piti!-:^
liDimpm Flow W ihoul Storage | ; ' ,
irr 1 iTTT M! ' 1
Mar. Apr. May June July Aug. Sept. Oct. Not. Dec. Jan. Feb.
P'iG. 403. — ^Effect of Stored Water on Minimum Flow.
flow and does not mean a proportionately lower volume of water
available for j)Ower production.
This decrease in minimum flow increment is shown by the curve
Fig. 404, which carries the stored water up to 800 sq. mi. ft.,
resulting, in this particular instance, in the minimum flow of 2000
cu. sec. ft., as against 470 cu. sec. ft. without storage.
AUXILIARY STATIONS
In the previous section it was shown that the full economic
advantage of the stream, even with storage regulation, cannot be
secured without a source of auxiliary power. Such auxiliary
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AUXILIARY STATIONS
693
stations may be divided into four classes according to their utiliza-
tion, although, in reality, they may not differ essentially, as some
stations may serve two or three different purposes simultaneously.
2800
flram
1800
^
^
""
1000
;
1.00
^1200
^
c
V
^
o
^ 800
600
400
/
/
INCREASE OF MINIMUM FLOW
WITH
ADDITIONAL STORAGE
/
'
0
100
aoo
900 400 500
Square Mile Foot of Storage
000
700
800
Fig. 404. — Increase of Minimum Flow with Additional Storage.
Class I. Stand-iy Stations, which are intended to take care of the
load in case of a breakdown to the hydro-electric machinery
or the transmission lines.
Class II. LovMJoaier Stations, which are intended to supplement
the load during low-water periods.
Class III. Peak-load Stations, which are intended to carry peak
loads.
Class IV. Base4oad Stations, which are intended to operate con-
tinuously, the water power being supplemental to the
steam power.
Prime Movers. There are four kinds of prime movers which
may be used for auxiliary stations; the steam turbine, the steam
engine, the gas engine and the oil engine. Of these, the steam-
turbine is used almost exclusively, but the question of deciding
on the most economical and practical equipment is, naturally, a
problem which involves a study of each case individually.
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694 ECONOMIACL ASPECTS
The auxiliary p)Ower can either be secured by op)eratiDg old
steam plants of the power customers which have been shut down
by pm-chase of power from a water-power company or by con-
structing new steam-turbine plants as part of the water-power
system.
Stand-by Stations. Emergency reserve stations are, as a rule,
more necessary in the early days of a hydro-electric develop-
ment than after the operating conditions become settled. They
are, however, essential in order to provide against possible inter-
ruptions to the service and contract provisions are often such
as to make their installation almost imperative.
The size of such stations is naturally governed by the load
which must be maintained under all conditions. Their location
should be close to important distributing centers so as to be use-
ful in case of breakdown of the transmission lines. For large and
extended systems it may be advisable to provide two or more
distributed stations rather than one of the combined capacity.
A quick start is an essential requirement of an emergency
stand-by station. It is, however, not customary to have all
the boilers under fire to take over the load inmiediately in case
of an interruption. Some of the boilers are, as a rule, kept
imder banked fires part of the time to secure the most important
load, and the turbines are operated as synchronous condensers
to improve the power-factor of the entire transmission system,
which may carry a large inductive load.
Under these circumstances it is particularly easy to respond
to sudden load demands because the imit is already up to speed
and in synchronism, the turbine is kept warmed up, and only a
change in the field excitation is necessary to place the unit on the
line, which takes only a few minutes at the most. When storms
are approaching, the entire reserve equipment should be made
ready to respond immediately to any emergency that may arise.
The first cost of the station should be low, while efficiency is
not such an important item. Consideration should, however, be
given to the possibility that it may later be used under other
operating conditions requiring the highest efficiency. It is,
therefore, often advisable to make provision in the design from the
beginning so that economizers and other labor-saving devices may
be installed at a future date, should conditions so demand. With
large steam-turbine units it is, however, practical to obtain the
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AUXILIARY STATIONS 695
moet efficient unit at practically the same cost as one of poorer
efficiency. A less boiler capacity is, of course, needed with a
higher turbine efficiency and consequently a plant of high effi-
ciency can, as a rule, be built at practically the same cost as one
of lower efficiency.
Low-water Stations. The function of the auxiliary plant,
when used as supplemental capacity during low-water periods is
similar to that of the storage reservoir. It converts at least a
part of the secondary power, which would be available only part
of the year, into primary power available at all times, thus increas-
ing its sale value. It is also of value in making up shortage of
water power from loss of head during high back-water caused by
floods. Enough pondage can usually be provided to insure that
daily fluctuations can be taken care of, even though the peak load
is somewhat in excess of the power corresponding to the minimiun
stream-flow. This, of course, necessitates that the average or
integrated load over the twenty-four-hour period must be within
the energy available from the minimum stream-flow.
The problem, therefore, really resolves itself into two ques-
tions: First, in the case of a plant already in operation, to what an
extent shall an auxiliary supply be provided to convert the variable
power supply into a continuous supply? Second, in case of a
new development, for what capacity shall it be bmlt?
Both cases involve a study of the stream-flow and the load
conditions, the first cost and annual operating charges for the
hydro-electric plant of different capacities as well as the cor-
responding charges for auxiliary plants of the required capacities.
In the first case the cost of the auxiliary supply for various degrees
of insurance is determined and compared with the increased earn-
ings obtained by converting the secondary j)ower into primary.
In the second case the problem may be considered from several
different points of view. So, for example, one may start out with
the assumption that the total cost per kilowatt and year shall be a
minimiun, or, if all the power produced can be sold in the market
at a certain price, it should be investigated at what plant capacity
the profit becomes a maximum. In the case of a new develop-
ment, the cost per kilowatt decreases as the capacity increases,
and an increase in the annual cost per kilowatt of the auxiliary
plant is accompanied by a decrease in the annual cost of the
hydraulic plant A point may, therefore, be reached at which
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696 ECONOMICAL ASPECTS
the sum of the two is a minimum, and this would fix the most
economical capacity of the development and, hence, the point of
greatest profit for a given market price of energy. The entire
problem of determining the economical capacity of a combined
hydro-electric and steam-power plant is very complicated. An
excellent treatise on this subject, offering a new method of solution,
was presented by Dr. C. T. Hutchinson before the A.I.E.E.,
February, 1914, and the reader is referred to the same for further
information.^
The size of the auxiliary station is determined by the differ-
ence between the demand curve and the stream-flow curve,
except where storage is available, in which the stream-flow as
affected by the same should be used.
In order to obtain the best results, the method of operation
also deserves a careful consideration. In this connection R. C.
Muir in the General Electric Review for June, 1913, makes the fol-
lowing recommendations: " In order to get the best economy out
of the steam station it must operate at practically a constant load
corresponding to full load on one or more units. In order to get
the best economy out of the water-power station with the water
available during low-water periods, the highest water level attain-
able— ^in other words the maximum head — ^must be maintained at
all times.
" It is impossible to conform to both of these requirements,
especially where the minimum stream-flow capacity and the
steam-station capacity combined are not suflScient to cany the
• peak load. In this case the steam plant can be operated at prac-
tically a constant load, using the water power during the peaks
and storing water during the balance of the time. With high-
head plants the head gained by storage is not of importance;
so that the steam plant can be operated most economically on
constant load, allowing the water power to take the peaks. With
low-head plants having considerable storage capacity both plants
can be operated advantageously dm-ing the low-water period.
Here again the water power should carry the peaks, and the steam-
plant operated at constant load' over a suflScient part of the day
so that the water level will not be materially affected. This
method of operation will prove much more economical, both as
regards fuel used and labor required, than the method of carrying
» See also an article by H. S. Putnam, A.I.E.E. June, 1917.
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AUXILIARY STATIONS 697
heavy loads on the steam plant during the peaks, thereby requir-
ing more boilers and machines in service and, consequently, more
fuel and operators.
" The term ' peaks ' is intended to cover heavy load periods
of the daily load curve, and not the momentary load fluctuations.
Assuming equal governor or speed regulation and equal, fly wheel
effects, these momentary load fluctuations are divided between
the stations in proportion to the total capacities of the generators
operating in each station. The flywheel effect of the steam tur-
bine is usually the larger and the steam turbine governor is the
more sensitive. The steam turbine station will, therefore, ordi-
narily take more of the momentary fluctuation than its propor-
tionate capacity in operation.
" Some fuel can be saved in developments of this kind by
carefully observing the rainfall within the drainage area of the
stream developed. In case of racinfall within this area the steam
plant can be shut down inmiediately and all the load taken over by
the hydraulic plant at the expense of reducing the level of the
reservoir. The increased stream-flow will again fill the reservoir.
Rainfall at the head waters of a large stream would not materially
increase the stream-flow at the development for some time; and,
consequently, a considerable saving in fuel would thus be effected.
During the dry season, water flowing over the dam means fuel
wasted^ and, therefore, if enough reliance could be placed in
weather forecasts to anticipate rainfalls, the steam plant could be
shut down in time, so that the reservoir level would be reduced
suflSciently to take care of the increased flow without wasting any
more over the dam than necessary."
Peak-load Stations. The function of the auxiliary plant used
to carry the daily peaks of load on the system is similar to that of
pondage above the water-power plant, increasing the operating
load factor and, consequently, the output from water. In the
case of the supplemental plant, the first cost and relative economy
of generation must be governed by the proportion of the total
output of the system to be carried by the auxiliary plant, i.e.,
the higher the percentage carried by the auxiliary plant, the
more important becomes the economy of generation and the less
imj)ortant the first cost and resulting fixed charges.
Base-load Stations. Where the conditions are such that the
average power demand exceeds the capacity of the hydraulic
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698 ECONOMICAL ASPECTS
plant it is usually preferable to operate the auxiliary steam plant
continuously, the water power then being supplemental to the
steam power. Low operating costs are essential for this type of
plant and, as far as the operation is concerned, the reconmienda-
tions given for the low-water plants also apply in this case.
INTERCONNECTION OF SYSTEMS
The interconnection of hydro-electric transmission systems
is also a step in the right direction, as demonstrated in our South-
em States, where not less than seven large systems are tied to-
gether, furnishing power to each other on an " interchange " con-
tract basis. The advantages of this are obvious. The peak loads
of the different systems may not coincide, the minimum stream-
flow may occur at different times on the different watersheds,
conunon steam reserve stations may be used, and, in general,
the operation may be so improved that a most efficient and re-
Uable service can be rendered to the customers of all the systems
so tied together.
In some cases groups of established syBtems although located
in vastly different locaUties may be brought together under one
holding company, and to the creation of such companies may,
in many instances, be attributed the high-class service and finan-
cial success of our small and medium-size light and power systems.
The economies due to a central management, the benefit»of the
beK^t technical and expert advice applied even to the smallest
central station, the cumulative effect of active, up-to-date new-
buaness campaigns at every j)oint, all have contributed to an
unpi.')ved and cheaper service to the consumer, and without the
faciUti3s of such a control they could exist only in the larger com-
mimitieb. Another very important advantage is the great prob-
lem of financing all these undertakings and providing funds for
extensions to meet the ever-growing demand of the pubUe for
electric service. It is possibly in providing ready financial facil-
ities for these purposes that the holding company performs its
most important function.
In order to give the people the best service and the lowest rates
all public utiUties must, of necessity, be natural monopolies, and
the pubUc-service regulation is a recognition by the State of the
essentially monopolistic character of these enterprises. The
favorable showing of virtual monopoUes in reducing the cost of
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INVESTIGATION OF AN ENTERPRISE 699
electric power is due mainly to a reduction in the capital expenses,
lower operating costs, and in no less degree to the reduced risk
to the investor. By effective safeguards and a well-considered
policy of public control the electric securities have become one of
the most desirable investments, and there is every indication that
efficient public-service regulation will make possible even further
reductions in the cost of electric-power production of public-service
utilities.
mVESTIGATION OF AN ENTERPRISE
The following points cover broadly the important items upon
which an investor must have information in order to judge in-
telligently of an oflfering to finance an enterprise, and for a more
complete treatise of the subject the reader is referred to Francis
Cooper's book, *' Financing an Enterprise."
I. Nature of Enterprise.
1. Is the basis of the enterprise sound?
2. Is the business or undertaking profitable elsewhere?
3. What competition or opposition will be met?
4. What peculiar advantages does it enjoy over these
others?
5. Can it be conducted profitably under existing condi-
tions?
II. Plan of Organization.
1. In what state organized?
2. What is the capitalization?
3. Is the capitalization reasonable?
4. Has the stock been issued in whole or in part and, if
so, for what?
5. Is the stock offered for sale full-paid and non-assessable?
6. Has any of the stock preferences?
7. Is any of the stock unissued or held in the treasury?
8. Who has stock control?
9. Are the rights of smaller stockholders protected?
10. Are there any imusual features in charter or by-laws?
m. Present Condition of ErUerprise.
As to Property:
1. What properties or rights are controlled?
2. What is their value and how estimated?
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700 ECONOMICAL ASPECTS
3. Are these properties or rights owned, or held under
lease^ license, grant, option or otherwise?
4. If owned, are titles perfect?
5. Are there any incumbrances on the properties or
rights?
6. If not owned, are the holding papers in due form?
7. If not owned, are the terms of holding reasonable,
satisfactory and safe?
8. In event of liquidation, what would be worth of
property?
As to Operation:
1. What operations have been or are now carried?
2. What have been the results?
3. What difficulties, if any, have been encountered?
4. What is demand for the product or operation of
the enterprise?
5. What is present status of the enterprise?
6. Are proper books kept?
As to Finance:
1. What are the present assets and their actual value?
2. What debts, claims, fees, rents, royalties or other
payments or obligations are now due or are to
be met and carried?
3. From what resom^ces are these to be met?
4. Who handles the moneys and under what safe-
guards?
5. What are or will be the running expenses, salaries,
etc.?
IV. Management.
Directors:
1. How many members in the board?
2. Who are these members?
3. What is their past record and present business
status?
4. Who are the active members of the board?
5. Who, if any, are inactive?
6. Are meetings regularly held and attended?
7. Who compose the Executive Committee, if any,
and what are its powers?
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INVESTIGATION OF AN ENTERPRISE 701
8. Are the directors stockholders and, if so, to a
material amount?
Officers:
1. Who are the officers?
2. What are their previous records?
3. What are their special present qualifications?
4. Are they able to work together without friction?
5. What compensation do they receive or are they
to receive?
6. Are they interested in the enterprise beyond their
salaries?
V. Plan of Operation.
1. What is the general plan of operation?
2. What special reasons, if any, led to its adoption?
VI. Disposition of Money Asked for.
1. Does the money from sale of stock go into the
treasury of the company?
2. If any does not go into the treasury, to whom does it
go, and for what purpose?
3. Of money going into the treasury, what proportion
goes into active development and operation?
4. What part goes to pay off existing debts, obligations
and claims?
5. What part, if any, goes to pay for promotion expenses,
conmiissions, etc.?
6. How is the development and operating money to be
applied?
7. Is the amount asked for sufficient to accomplish the
desired results?
8. Will it place the company on a self-supporting or
profitable basis?
VII. The Proposition.
1. Is the general proposition a fair one?
2. Is the price of stock or bonds reasonable?
3. How do these prices compare with any former prices?
4. If common stock is offered, do preferred stock, bonds
or other profit-sharing obligations take precedence
and to what amount?
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702 ECONOMICAL ASPECTS
5. What reserve of profits will be retained before divi-
dends are to be declared?
6. If preferred stock is offered, is it cumulative, does it
vote, when is it redeemable, and at what price,
what sinking fimd provision is made for redemption
and are any peculiar provisions attached? Do any
bonds or other obligations take precedence of the
preferred stock?
7. If bonds are offered, what interest is paid, and when
and where; uj)on what property are they secured
and when and how are they paid; is the trustee
or trust company of repute; imder what conditions
are the bonds foreclosable; when, and how are they
or may they be redeemed; are there any other
securities taking precedence, and are there any
peculiar provisions in deed of trust?
VIII. General.
1. What is the previous history of the enterprise or
the property or undeiiiaking on which it is based?
2. If inventions enter prominently, what is the pre-
vious record of the. inventor?
3. By whom are the statements made and is the party
making them reliable?
4. Are there any contracts or obligations not now effec-
tive by which the enterprise will subsequently be
affected?
COST OF HYDRO-ELECTRIC POWER PLANTS
The cost of water power depends upon a great variety of
factors, the essential feature of the design of the plant being to
keep the cost within reasonable limits, so that the fixed charges,
which constitute by far the greatest part of the power cost, shall not
be excessive. The allowable cost of a water power can obviously
not be more than the cost of producing the same amount of power
by some other means, usually steam. The cost of generating the
power should, furthermore, not be confused with the cost of power
deUvered. Besides the cost of producing the power in the gen-
erating station comes the expenses involved in distributing the
same to the customers, which often amount to several times that
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COST OF HYDRO-ELECTRIC POWER PLANTS 703
of the former, especially with hydraulic developments where the
power must be transmitted for great distances at high voltages
to the market center and there stepped down to a moderate dis-
tributing voltage and again at the point of utilization to the volt-
age required for the power or lighting load. It is the costs of
these transformations, transmission and distributions, besides the
general expense, which makes the cost of power to the customer
so much higher than the cost of actually producing the power at
the generating station bus-bars.
The cost of the plant varies through the widest possible limits,
depending on its location as regards facilities for construction and
for transmission, the quantity of water and regularity of flow,
the total head, conditions of the labor market, both as to quality
and supply, etc.
There are usually more elements of chance and more unknown
factors in a hydraulic development than in a steam plant, and
these facts should be taken into consideration and properly cared
for in making up the cost estimate. In many instances cost
figures must be obtained from similar work under similar condi-
tions, and the dependence to be placed on the source of informa-
tion must be duly considered and weighed. Each case must be
carefully examined and studied from the conditions bearing directly
upon it and the deductions made accordingly. For a very com-
plete classification of the construction and operating accounts the
reader is referred to the report by the N.E.L.A. Accounting
Committee for 1914.
The total cost of a hydro-electric plant may be properly divided
into three parts, viz. :
1. Development expenses.
2. Physical costs.
3. Overhead charges.
Development Expenses. These include all of the preUminary
expenses incidental to the building up of the project and which
are not directly involved in the actual construction of the prop-
erty. They include expenditures on account of promotion, in-
corporation and organization, condemnation and other legal
expenses as well as cost of surveys, expert estimates, etc.
The cost of securing money is also an important item in the
development of a property. By this is not meant the interest
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704 ECONOMICAL ASPECTS
and dividends which are paid on the securities of the company to
the stockholder and bondholder and which are essential to make
future issues marketable, but we are dealing with the actual costs
to the utility of placing its securities in the hands of the public.
This cost of securing the money should be distinguished from pro-
moters' services and from bond discount. The latter is an
adjustment between the amount paid by the public for the bond
and its face value, due to the difference of the interest rate of the
bond and the interest rate prevailing at the time of the sale of the
bond, and it may occur a number of times during the life of the
corporation. The cost of securing money is a very different thing,
and only comes once — when the original capital is acquired. That
such costs are legitimate and must be recc^nized cannot fairly
be denied. The existence of numerous banking and brokerage
houses specializing in public-utility securities shows that it costs
to secure money just as to purchase generators, cable, land or
any of the tangible construction elements of a property.
The losses inciured in the sale of securities, that is, brokerage
and discoimts, should, of course, also be included.
The development expenses will sometimes amount to as high
as 20 per cent of the cost of the physical plant, depending, of
course, on the attractiveness of the undertaking and the rate at
which the securities can be disposed.
Physical Costs. Thes^ should cover the actual costs of con-
structing the plant, including material, apparatus and labor.
The cost of each unit of the plant elements in its final position is
composed not only of its first cost but of all other items of expense
which are necessarily involved. These may be any or all of the
following: Freight, storehouse cost, inspection, assembling or
fitting, transportation from storehouse to work and distribution,
labor of placing element in position, transportation of men and
tools to work, lost time of men during travel or wet weather,
losses on tools and material. After the cost has been estimated
as closely as possible it has become an accepted rule to add a
general percentage of the same to cover contingencies, omissions
and errors. This percentage is frequently estimated as 10 per
cent and sometimes higher, depending on the imcertainties
involved in the proposition.
The physical equipment includes:
Land and water rights.
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COST OF HYDRO-ELECTRIC POWER PLANTS 705
Hydraulic construction:
Dam, intake, forebay, water conductors, etc.
Generating station:
Building, hydraulic and electric equipments, etc.
Transmission lines.
Substations.
Distributing system.
Auxiliary steam station.
Overhead Charges. Besides the above expenses for the de-
velopment and actual construction of the physical plant, there
are others which must be considered as a part of the total cost of
any complete development. These are termed overhead charges
and are as follows:
Engineering and superintendence.
Organization.
Legal expenses.
Taxes and insurance.
Interest during construction.
Working capital.
Engineering and superintendence should cover all costs of
architecture and engineering. This includes all designs and
drafting, plans and supervision of construction, as well as all
other items which properly come under this department. They
vary from 3 to 5 per cent of the construction cost.
Organization expenses should cover the cost of organization
and administration for construction, including general office
expenses. They generally amount to from 3 to 5 per cent.
Legal expenses incurred during the construction period should
be distinguished from those included under development expenses.
They should cover only such legal work which may be necessary
in obtaining such rights as may be needed to carry out the con-
struction.
Taxes must be paid on the property from the time of purchase,
usually months or even years before the development is com-
pleted. Likewise insurance must be paid and should include
not only fire insurance, but casualty insurance, covering both
employees and public liability. The estimate of these expenses
can be accurately made from prevailing rates. Taxes amount to
about one-half of 1 per cent and insurance about the same amount.
Interest during construction accruing on the idle capital, rep-
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706 ECONOMICAL ASPECTS
resented either by cash or plant, must be included in the estimate.
The length of time for which to compute the same will naturally
vary with the time required for the construction, but as a rule it is
figured at the full annual rate for one-half the construction period.
Working capital of a reasonable amount must, of course, be
provided for carrying on the business and must be considered as a
part of the property.
From the above it is seen that the overhead charges form a large
percentage of the cost of developing a system and it may approx-
imately be taken as from 20 to 30 per cent of the physical cost.
Cost data on hydro-electric plants are scarce, and when ob-
tained the greatest caution must be exercised in using them for
estimating other projects. They are greatly affected by local
conditions, as, for example, the nature of the soil in determining
the cost of excavation, the price paid for labor, freight and trans-
portation charges, market value of raw and other material, appa-
ratus, etc.
In order, however, to give the reader an approximate idea of
the costs involved, the following figures are given. They are
based both on actual costs and on estimates under normal con-
ditions, but the authors wish again to repeat their caution as
to a careful discrimination of then: use.
Estimated Cost of 600 Kw. Hydro-electric Power Station
It is proposed to install two units, each comprising a 500-H.P.
turbine operating under a 60-foot head and driving a 300-Kw.
generator. Two separately driven exciter units and complete
switching equipment, but no step-up transformers. The dam is
already provided and is not included in the estimate.
Penstock and flume, including headworks, connections, tunnel, etc. $22,500
Regulating tank, including housing 1,500
Power station; foundation and buildings complete with interior work
and fittings 9,800
Staff house and miscellaneous 3,000
Equipment in power-house, consisting of two 500-H.P. turbines with
governors, generators, exciters, switching, equipment, etc 30,200
Total $67,000
Add for contingencies, engineering, supervision and inspection, 12
per cent, say $8,000
Grand total $76,000
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.COST OF HYDRO-ELECTRIC POWER PLANTS
707
Annual Cost op Opbkation
Overhead charges:
Yearly installment of principal and interest. Debenture
to be retired in thirty years at 5 per cent S4,875
Maintenance account, being an amount set aside yearly
against major repairs, renewals and reasonable ex-
tensions, 2} per cent 1,875
$6,760
Operating charges:
Salary, superintendent and general office expenses $2,000
Wages of operators at power station 2,200
Supplies and minor repairs 900
$5,100
Total annual cost $11,850
Or approximately $20 per Kw.-year.
Municipal Hydro-electric Plant of City op Sturgis, Mich.
Capacity, 1100 Kw.
This development consists of a hollow reinforced concrete
spillway dam, 308 feet long and 24 feet high. This spillway con-
nects with an earth embankment 400 feet long and 24 feet high.
The power-house contains two 550-Kw. 2300-volt generators
driven by two 844-H.P. turbines, and a 40-Kw. exciter driven by
a 67-H.P. turbine. The head is 22 feet. Six 200-Kw. oil-cooled
transformers for stepping up the voltage to 22,000 are provided,
also complete switching equipment and Ughtning arresters. The
ultimate development will include two additional generating units
and one additional exciter.
Cost Data Based on Ultimate Development
Items.
Total Cost.
Cost per
H.P. at
Wheel Shaft.
Cost per Kw.
at Switch-
board.
Power-house and machinery
Spillway
Tailrace
Embankment
Bridge changes
Transmission line
Real estate
Substation and incidentals .
Totals
$110,000
22,000
20,000
8,000
8,000
20,000
50,000
12,000
$32.56
6.50
5.93
2.36
2.36
5.93
14.81
.3.55
$45.90
9.16
8.36
3.33
3.33
8.37
20.90
5.01
$250,000
$74.00
$104.36
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708 ECONOMICAL ASPECTS
Actual Cost of a 4800-H.P. Development Operating tjndeb
90 Feet Head
This plant was designed to utilize the water flowing from a
large storage reservoir primarily built for domestic and industrial
service. It comprises four 48-inch cast-iron penstocks dischai^g
into four 1200-H.P. horizontal turbines, each direct-connected to
a 1000-Kv.A. (800-Kw. 0.8 P.F.), 60-cycle, 13,200-volt generator
operating at a speed of 400 R.P.M. The exciter equipment con-
sists of two 60-Kw. turbine-driven units.
The first cost of the installation was $227,474, itemized as
follows:
Station building $113,786
Foundations of turbines and generators 7,883
Total station cost $121,769
Turbines and generators $70,574
Labor and materials 5,043
Penstocks and valves 1,375
Venturi meters 6,212
Traveling crane 2,500
Total equipment $99,704
Lightning arresters and outgoing line equipment 6,001
Total $227,474
Per H.P $47.50
Per Kw 71.00
Fixed Charqes and Operating Expenses (Yearly)
Labor, 1 electrical engineer, 1 operator, 2 helpers, 1 helper part time $5,531
Fuel for heating building 86
Repairs and appliances 354
Oil and waste 87
Small supplies 262
Taxes 2,675
Interest at 6 per cent 11,374
Depreciation, station and machinery, 4 per cent 4,475
Depreciation on transmission equipment, 2 per cent 120
Total $24,964
Daily output in kilowatt-hours 18,000
Total cost per kilowatt-hour 0.46 cent
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^COST OF HYDRO-ELECTRIC POWER PLANTS 709
Estimated Cost op a 6000-H.P. Development Operating
UNDER A 27-foot HeAD
This development is assumed to comprise two 3000-H.P.
vertical-shaft turbines driving two 2600-Kv.A. (2000-Kw., 0.8
P.F.) 2300-volt generators operating at a speed in the neigh-
borhood of 75 to 80 R.P.M. Two three-phase transformer units
of capacities corresponding to the generators are provided, the
high-tension trajismission voltage being 33,000. Provision is
also made in the building for future installation of a third gener-
ator as well as a transformer unit. It is intended that this plant
is to be erected in connection with an existing dam on a navigable
stream, thus doing away with the necessity of any pipe Une or
similar structures to carry the water to the power-house; neither
do the figures include any allowance for dam or spillway.
Cost Estimate
Electrical equipment $80,000
Delivery and erection 7,500
$87,500
Hydraulic equipment 55,000
Delivery and erection 5,000
60,000
50-ton crane, oil and water piping and misc. equipment
in place 8,500 8,500
Concrete foundations, hydraulic tubes, headrace, etc . . . 55,000
Building, exclusive of foundation 32,000
Excavation 6,000
93,000
5 miles double-circuit line on steel towers 35,000 35,000
Contingencies (10 per cent) 28,400
Interest and insurance during construction 15,000
Engineering and superintendence 20,000
Total $347,400
. • Per H.P $58.00
Per Kw 87.00
Estimated Cost of a 6000-Kw. Hydro-electric Development
Operating under a 47-Foot Head
This development contemplates a hollow reinforced con-
crete dam, 465 feet long and about 55 feet high, including spiUing
and sluiceways. An intake stnicture with controlling devices is
to be provided in connection with the dam and the water is from
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710 ECONOMICAL ASPECTS
there to be led through an open concrete-lined canal, 2600 feet
long and with a cross-sectional area of 525 square feet, to a fore-
bay. The forebay is divided in three sections provided with
gates and trash racks, and there will be three penstocks, 10 feet
6 inches in diameter and 265 feet long.
The power-house equipment comprises three 3500-H.P. tur-
bines with governors, driving three 2000 Kw. generators with
direct-connected exciters. Provision is also made for trans-
formers, switching equipment and necessary station auxiliaries,
such as crane, etc.
Estimated Cost of Plant
Main dam and headworks $313,660
Canal, including lining 62,000
Forebay 23,000
Penstocks 35,750
Power-house 61,000
Machinery:
Turbines and governors 42,000
Generators and exciters 52,000
Transformers and switching apparatus 36,000
Total $626,410
Engineering and contingencies $d4,690
$720,100
Interest during construction 28,000
Grand total $748,100
The total capital cost of the plant, including the proportion of
the cost of creation of storage, also the proportion of the cost of a
duplicate transmission line, and proportion of a transformer sta-
tion and equipment is:
Capital cost of plant $748,100.00
Transmission lines and station equipment 64,700.00
Storage 103,000.00
Total capital cost $916,800.00
Annual charges:
1. Interest on capital invested assuming financing is done
on bonds at 6 per cent sold at par $54,900.00
2. Sinking fund to retire bonds in thirty years reinvested
at 4 per cent, say 1} per cent 16,050.00
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COST OF HYDRO-ELECTRIC POWER PLANTS
711
3. Depreciation on plant adjusted between general works
and equipment to provide for major repairs and re-
newals $13,700.00
4. Operation and maintenance, including management,
superintendence, wages for operators of plant, trans-
mission line, receiving station, storage regulation,
minor repairs, supplies, and upkeep, etc 20,650.00
Total annual charges $105,300.00
Cost per Kw. year, delivered 17.50
Cost op the Minidoka Power Station of United States
Reclamation Service
Capacity, 7000 Kv.A.
The power-house is a reinforced concrete structure with steel
roof trusses and purlins covered by matched liunber and galvanized
corrugated iron. It measures 149 feet in length, 50 feet in width
and 90 feet in height. It contains five 2000 H.P. main turbines
operating imder a head of 46 feet, driving five 1400-Kv.A. 2200-
volt generators at a speed of 200 R.P.M. There are also two 180-
H.P. turbine-driven exciters and each main generator is directly
connected to a three-phase transformer, stepping up the voltage
to 33,000. Complete switching and Ughtning-arrester equip-
ment is included in the estimate, but no allowance is made for the
dam, this forming part of the irrigation system.
Cost of Power-house
Total Cost.
Cost per Kw.
Building. . ,
$82,000
73,000
83,000
26,200
55,500
60,000
7,300
23,200
11,100
15,000
$11.70
Hydraulic machinery
10.40
T*^lf?ctric machinery
11.80
^^ight and hauling, , .
3.75
Erection
7.90
Tailrace
8.60
Roads and telephone lines
1.10
Camo and oermanent Quarters
3.35
Engineering and incidentals
1.55
Administration charges, etc
2.15
Total
$436,300
$62.30
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712
ECONOMICAL ASPECTS
Annual Cost op Operation
Item.
Operation:
Labor
Supplies ,
Repairs:
Labor ,
Supplies and material
Superintendence, clerical, camp, etc.
General expense and administration
Operating expense
Expense per Year.
$5,700
950
900
300
1,700
450
$10,000
A depreciation of 5 per cent ($21,800) has also been charged to
this development. No taxes or interest is charged, the under-
taking being done by the Government. Assuming 7 per cent
for interest and taxes the total operating expenses would amount
to $62,000. A total of about 15,000,000 Kw. hr. were delivered
during one year, thus corresponding to a cost of $0.0041 per
Kw.hr.
Actual Cost op 20,000-Kv.A. Hydro-electric Power Devel-
opment OP THE City op Tacoma, Washington
This development comprises a concrete dam approximately
45 feet high and a spillway of 260 feet. Intake, racks, regulating
gates and a settling channel, the latter being 780 feet long, 40
feet wide and 20 feet deep. From the settling basin the water is
carried through an 8 X 8-foot tunnel, 10,000 feet long, to a reg-
ulating reservoir approximately 500X500 feet, having a capacity
of about 3,000,000 cubic feet available for use during peak loads.
Each main turbine has a separate riveted-steel penstock about
780 feet long and ranging in size from 78 inches at the top to 48
inches at the gate valves in front of the turbines. The two
exciter wheels are supplied from one 24-inch pipe which divides
in the generator room.
The power-house consists of three buildings of the common
wall type of construction of concrete and brick, with galvanized-
iron roof supported by steel roof trusses. There are four 8000-
H.P. horizontal main turbines operating under a 415-foot effective
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COST OF HYDRO-ELECTRIC POWER PLANTS 713
head at 460 R.P.M., driving four 5000 Kv.A. three-phase, 60-
cycle, 6600-volt generators. There are also two 300-H.P., 400-
R.P.M. turbines, two 200-Kw. 125 volts exciters, and twelve
1667-Kw.- gVoVo-volt water-cooled step-up transformers arranged
in four banks. Also the necessary switching and Ughting arrester
equipment.
The entire cost of the development was as follows:
Genebatino Plant
Water rights $30,000.00
Hydro-power plant, land 168,696.50
Building fixtures and grounds 208,621.33
Dam, intake, fliunes, reservoirs, penstocks 1,156,728.24
Equipment 200,640.66
Total $1,764,686.73
Substation
Equipment $85,577.20
Building, fixtures and land 110,619.40
Total $196,196.60
Tbansmibsion
Land $66,226.65
Equipment 118,193.23
Simdry 2.89
"■
Total $184,422.77
Genebal Expenditubes
(During Construction of Plant)
OflSce fumitiwe and fixtures $2,993.91
Engineering and superintendence 95,866.87
Injuries and damages 85.00
Interest '. . . 83,860.47
Miscellaneous 26,872.00
Total $209,678.25
Grand total $2,354,984.35
Cost op Hydro-electric Plants
E. V. Pannell in Electrical News for February 15, 1917, gives
the following capital cost of four undertakings, that of the fifth
being estimated. The costs are separated in five items, which,
for comparison are also shown graphically in Fig. 405, p. 716.
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714
ECONOMICAL ASPECTS
Cost op City op Seattle Municipal Hydro-electric Plant
(Journal Electricity, Power and Gas, July 18, 1914)
Genbral Costs
DiviBlon of Plant.
Cost.
Cost per Kw. on
Basis of 15.500 Kw.
Capacity.
Wood crib dam
$61,863.80
299,471.59
354,387.44
232,629.62
242,096.21
95,550.32
$1,285,998.98
$3.99
Penstocks
19.32
Power station
22 86
Transmission lines
15.01
City substations
15.62
6.16
Total generating system
$82.96
Detail Costs
Division of Plant.
Capacity,
Kw.
Cost.
Unit Cost,
per Kw.
Wood crib dam
Penstocks, combined
No. 1 Penstock, complete
15,407 ft. 49 in. wood stave pipe, com-
plete in place
1,061 ft. 48 in. steel pipe, 308,000 lbs.,
complete
16,468 lineal ft. grading and filling. . .
No. 2 penstock, complete
15,865 ft. 68 in. wood stave pipe, com-
plete
1902 ft. 48 in. steel pipe, with Y-oon-
nection, valves ana cross-over to
smaUer pipe
Two 36-in. standpipes, 65 and 70 ft.
high
16,816 lineal ft. grading and filling. . .
Cedar Falls generating station, total
Power-house buildiings, station, switch
house, transformer house and freight
shed
Emplovees' cottages
Two 8bOO-H.P. turbines with hydraulic
valves, governors and relief valves, com-
plete in place
Two 2400-H.P. Pelton wheels, with valves
and governors, complete
Two 5000-Kw. generators, oomplete in
place
Two 1750-Kw. generators, complete in
place
Two 75-Kw. exciters, with Pelton wheels
and governor
One 150-Kw. exciter with Girard wheel . .
Switchboard, complete
2300-volt wiring, busses and switches . . .
Nine 150a-Kw., 60,000-volt transform-
ers, in place
9,000
11,000
3,600
7,400
13,500
10,000
3,500
10,000
3,500
150
150
13,500
13,500
13,500
$ 61,863.80
299,471.59
84,475.79
33,044.16
14,386.01
37,045.62
214,995.80
131,561.78
19,587.27
2,316.31
61,530.44
354,387.44
47,829.77
10,386.82
53,296.55
28,200.00
39,422.00
23,782.00
5,383.00
4,500.00
11,042.45
30,348.29
74,649.17
$ 6.87
27.23
23.40
29.00
26.30
5.33
8.05
3.94
6.50
35.80
30.00
.82
2.25
5.54
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COST OF HYDRO-ELECTRIC POWER PLANTS
716
CoflT OF CiTT OF Sbattlb Mxtkicipal Htdbo-elbctbic Plant — CanHnued
Division of Plant.
Capacity,
Kw.
Cost.
Unit Cost,
per Kw.
60,000-volt wiring and switches
Transmifflion lines, total
No. 1 transmission line, total. . .
Right of way for both lines
1515 poles and anns, in place. .
4605 insulators
117,500 lbs. No. 2 copper wire. .
Two telephone lines; one of No. 10 cop-
per, one of No. 14 iron, on power line
poles, oomi>lete
No. 2 transmission line
732 poles, with arms, in place
2256 insulators, in place
374,700 lb. No. 4-0 stranded copper wire
Telephone line A in. plow steel cable, on
and
power line poles
Linemen's cottages, incomplete
City substations, total
Main substation, Seventh avenue
Yesler Way, total
Substation building
60,000-volt switches and wiring
Ei[i^t 1500-Kw. 50,000-volt transformers
m place
15,000-volt and 2500-volt wiring and
switches
Station switchboard
Twelve 2500-volt feeder regulators on
commercial circuits
500-Kw. direct-current motor generator
set
Twelve 100-lamp constant-current trans-
formers with switches and wiriqg
500-ampere hour, 500-volt storage bat-
tery
60-Kw. motor generator
Four outlying substations
Seven 15,000 to 2500-volt transformers,
total 3300 Kw
Five constant-current transformers, com-
plete
Three 2500-volt feeder regulators
Station wiring and switches
Four buildings, corrugated iron
Lake Union Auxiliary Station
Buildingcomplete
2500-HJ*. Pelton-Francis water wheel
with governor and valves, complete. . .
1500-Kw., 2500-volt alternator with ex-
citer, complete
Station, wiring, switches and switchboard
3400 ft. 40-in. steel penstock, complete,
400,000 lbs
Special tie-line, 2600-volt, two-phase,
819,000 cm. aluminum, complete
40,000
40,000
13,000
27,000
12,000
12,000
40,000
12,000
12,000
12,000
600
500
720
500
60
3,300
3,300
300
150
3,300
1,900
1,900
1,900
1,900
1,900
1,900
25,547.79
232,629.62
119,012.72
40,490.39
21,584.04
19,938.29
28,480.24
8,519.76
112,889.99
21,943.69
7,699.37
72,044.53
4,475.49
726.91
242,096.21
216,063.89
30,081.26
7,250.00
56,350.00
46,155.83
17,500.00
14,750.00
15,500.00
15,250.00
11,576.80
1,650.00
26,032.32
15,582.26
4,925.00
3,330.00
545.06
1,650.00
95,550.32
10,044.45
8,914.82
10,675.85
8,150.25
41,456.51
16,308.44
.64
5.82
9.18
4.18
20.17
18.00
.18
4.69
3.85
1.46
24.58
31.00
21.20
23.15
27.50
7.90
4.73
16.42
22.20
.16
50.30
5.27
4.80
5.62
4.30
21.80
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716
ECONOMICAL ASPECTS
The different items cover:
1. Dam and forebay, including connecting flumes or tunnels
and all preliminary de-watering, excavation, concrete, masonzy
and sluicing.
2. Penstocks and valves.
3. Generating machinery, including turbines with governors
DamAForabAy
Penatocka Machinerx
Baildlnffs
Enff'g. iBtcTMt EKk 1
a
i-i
a
ToUl
BUM
A 1 88
1 « 1
0
0
I-.
6U0
B 1 « 1
a
H
IIUO
c 1 » 1
1 -» 1
1 « 1
D |u.i 1
i-'i
|.M|
S
mm
1 «« 1
i-i
H
«l
l»l
100.00
E 1 « 1
Fia. 405. — Diagram Showing Cost in Dollars per Kw. of Modem Hydro-
Electric Plants.
Plant A
60.000 kw.
600 ft. head
Plant B
18.000 kw.
90 ft. head
Plant C
30.000 kw.
164 ft. head
Plant D
2.500 kw.
60 ft. head
Plant E (est.)
30.000 kw.
100 ft. head
and regulating gates, generators including exciters, transformers,
switch gear.
4. Building for power-house, switch-house, tailrace, etc.
6. Engineering, interest, contingencies.
ESTIBIATES OF CoST OF HyDRO-ELECTRIC DEVELOPMENTS
Pages 717 to 723 contain, in considerable detail, the cost
of construction and operation of several water-power projects as
contained in Bulletin 5, prepared by* the State Engineer's OflSce
of Oregon.
The unit prices used in the estimates of cost were determined as
follows:
Concrete. Proportions for massive concrete: One part Port-
land cement, two and one-half parts sand, five parts broken
stone of size corresponding to gravel, and two and one-half parts
broken stone corresponding to cobblestone size. For canal lining
and other thin concrete the larger size will not be used.
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COST OF HYDRO-ELECTRIC POWER PLANTS
717
Material.
Price, F.O.B.
Portland.
Local Freight.
Railway and
Wagon and
Storage.
Total.
Cementi per barrel
SI. 60
25.00
S .60
6.00
$2.20
Lumber, per thoiisand
Sftnd. Twr cubic viirrl
31.00
1 50
Broken stone, per cubic yard. . .
(Crushed on the job)
1.50
Estimate op Cost peb Cubic Yard of Concrete
For What Used.
Cement.
Sand.
Stone.
Forms.
Labor.
Total.
Canal lining
Forebay, etc
$3.00
3.00
$.70
.70
$1.40
1.40
$1.90
1.90
$3.00
3.00
$10.00
10.00
Dams
The estimated cost of concrete varied with volume as follows:
More than 200,000 cubic yards $ 6.00
100,000 to 200,000 cubic yards 6.50
50,000 to 100,000 cubic yards 7.00
25,000 to 50,000 cubic yards 8.00
10,000 to 25,000 cubic yards 9.00
Under 10,000 cubic yards 10.00
Rock Excavation
I>am foundations, not including estimate for cofferdam, per cubic yard $1 .25
Canals and forebayti, per cubic yard 1 .25
Tunnels, etc., per cubic yard $8.00 to 15.00
Steel Work
Trash racks (Bessemer-steel rails) :
Factory price, per pound $0 . 01}
Freight, per pound . . , Oil
Fabrication and placing 02
Total $ .05
Pipe work for penstocks:
Factory price, plate, per pound $ .01}
Freight 01}
Fabrication and placing, per pound 03} to .03}
Total $.06i CO .07
Note. See page 724 for unit prices on Hydraulic and Electrical
Equipment.
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718 ECONOMICAL ASPECTS
Oak Springs Power Site
Estimate of Cost:
Power head 32 ft.
Flow used for estimate 3,700 c. f. 8.
Brake horsepower (80 per cent eff.) 10,824 (8100 Ew.)
Dam:
Total height, 50 feet; length of crest. 480 feet;
length of spillway, 200 feet.
Masonry, 15.310 cubic yards, at $9.00 $137.790 .00
Excavation, 6443 cubic yards, at $1.25 8.054 .00
Cofferdam 70.000 .00
Incidentals and special foundation contingencies ... 34,156 .00
$250,000.00
Forebay. etc.:
Excavation, 12,000 cubic yards, at $1.25 15,000 .00
Concrete walls, 1500 cubic yards at $10.00 15,000 .00
Trash raclcs, 12,000 pounds steel, at 5c 600 .00
Stop logs 400.00
81.000.00
Headgates, Penstocks, etc.:
10 sliding headgates, set in place, at $750.00 7,500.00
10 hydraulic relief valves, in place, at $1.200.00 . . . 12,000.00
800 feet ^inch steel penstock. 12 feet diameter,
530 pounds, per foot at 5}c., $34.45 27,560 .00
47.000.00
Power-house and draft tubes:
Power-house, reinforced concrete, 8100 Kw., at $5.00
per Kw 40,500.00 40,500.00
Summation $368,560.00
Engineering and contingencies, 25 per cent 92,140.00
Interest during construction, 5 per cent approx 25.300.00
$486,000.00
Hydro-electrical machinery:
10 horizontal water-wheel units, 1085 H.P., in place.
speed 200 R.P.M.. at $10.000.00 100.000 .00
10 750-Kw. generators. 200 R.P.M. at $8.00 60.000.00
Exciter turbines and exciters, in place, at 80c. per
Kw 6.480 .00
Transformers, at $4.00 Kw 32.400 .00
Switchboard and accessories, cables, etc., at $2.25
per Kw 18,225 .00
Traveling crane, 30-ton 9,(X)0 .00
Quarters, water supply, etc 20,000 .00
Summation 246.105 .00
Engineemg and contingencies, 25 per cent 61.525 .00
Interest during construction, approx 6,370.00
314.000.00
Summation 800,000.00
Railway, realignment. 8 miles, at $50.000.00 400,000.00
Total. construction cost $1,200,000.00
Total amount of power. E.H.P., 10.824.
Construction cost, per E.H.P 110 .87
Assumed right of way cost, per E.H.P 5 .00
Cost of development, per E.H.P $115.87
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COST OF HYDRO-ELECTRIC POWER PLANTS
719
LocKiT Power Site
Estimate of cost:
Power head 70 feet
Flow used for estimate 4,500 c. f. s.
Brake horse-power (80 per cent eff.) 28,630 (21,500 Kw.)
Dam:
Total height, 94 feet; length of crest, 720 feet;
length of spillway, 225 feet.
Masonry, 56.014 cubic yards, at $7.00 $392,008 .00
Excavation, 15,533 cubic yards, at $1.25 19,417 .00
Cofferdam 50,000 .00
Trash racks, 30,0(X) pounds steel, at 5c 1,500.00
Incidentals and special foundation contingencies . . 56,985 .00
Headgates, penstocks, etc.:
10 sUdlng headgates, set in place, at $750.00 7,500.00
10 hydraulic relief valves. In place, at $1.200.00 . . 12,000.00
1,650 feet ^inch steel penstock, 11 feet diameter. .
600 pounds per foot at 6ic., $32.50 53,625.00
1450 feet i^inch steel penstock, 10 feet diameter,
450 pounds, per foot at 7c., $31.50 45,675 .00
Power-house and draft tubes;
Power-house, reinforced concrete, 21,500 Kw., at
$5.00 per Kw 107,500.00
Summation
Engineering and contingencies, 25 per cent
Interest during construction, i of 3 years, at 4 per cent,
6 per cent approz
Hydro-electrical Machinery:
10 horizontal water wheel units, 2860 H.P., In
place, speed 360 R.P.M., at $15,000 150,000.00
10 2500-Kw. generators, 350 R.P.M., at $7.00 per
Kw 175,000.00
Exciter turbines and exciters. In place, at 80c.
per Kw 17,200.00
Transformers, 21,500 Kw., at $4.00 per Kw 86,000.00
Switchboard and accessories, cables, etc., at $2.23
pcrKw 48,000.00
Traveling crane, 30-ton 9,000 .00
Quarters, water supply, etc 20,000. 00
Summation 505,200 .00
Engineering and contingencies, 20 per cent 101,000 .00
Interest during construction, 3 per cent approx 18,800.00
Total construction cost
Total amount of power, E.H.P., 28,630.
Construction cost, per E.H.P 56 .41
Assumed right of way cost, per E.H.P 10 .00
Cost of development, per E.H.P
$520,000.00
118,800.00
107,500.00
$746,300.00
186,575.00
57,125.00
$990,000.00
625.000.00
$1,615,000.00
$66.41
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720 ECONOMICAL ASPECTS
Mecca Power Site
Estimate of cost:
Power head 90 feet
Flow used for estimate. 3,400 c. f . s.
Brake horse-power (80 per cent eflf.) 27.760 (20.750 Kw.)
Dam:
Total height, 110 feet; length of crest. 650 feet;
length of spillway, 160 feet.
Masonry. 64.787 cubic yards, at $7.00 S453.509 .00
Excavation, 10,020 cubic yards, at S1.25 13.650.00
Cofferdam 40,000 .00
Incidentals and special foundation contingencies . . 22.841 .00
$530.000. 00
Forebay, etc.:
Trash racks, 12,000 pounds steel, at 5c 600 .00
Stop logs 400 .00
1,000.00
Headgates, penstocks, etc.:
8 sliding headgates. set in place, at $900 .00 7,200 . 00
8 hydraulic relief valves, in place, at $1,200.00 . . . 9,600.00
1400 feet A-inch steel penstock, 12 feet diameter,
530 pounds per foot at O^c, $34.45 48.230.00
600 feet A-inch steel penstock, 11 feet diameter,
615 pounds, per foot at 7c., $43.05 25,830 .00
90.86000
Power-house and draft tubes:
Power-house, reinforced concrete, 20,750 Kw., at
$5.00 per Kw 103,750 .00 103.750 O^J
Summation $725,610.00
Engineering and contingencies, 25 per cent 181.402.00
Interest during construction, 6 per cent approx 62,988.00
$970,000.00
Hydro-electrical machinery:
8 horizontal water wheel units, in place, 3470 H.P.,
speed 400 R.P.M., at $10,400.00 83,200 .00
8 2500- Kw. generators. 400 R.P.M.. at $6.00 per Kw. 120.000 . 00
Exciter turbines and exciters, in place, at 80 c. per
Kw 16.600.00
Transformers, at $4.00 per Kw 83,000 .00
Switchboard and accessories, cables, etc., at $2.25
per Kw 46.687 .00
Traveling crane, 40-ton 15,000 .00
Quarters, water supply, etc 20,000 .00
Summation $384.487 .00
Engineering and contingencies. 20 per cent 76,895 .00
Interest during construction. 2 per cent approx 8.618.00
470.000 . 00
Summation $1,440,000.00
Railway realigned, 6 miles at $50,000 300.000 00
Total construction cost $1.740,00 .000
Total amount of power, E.H.P., 27,760.
Construction cost, per E.H.P 62.68
Assumed right of way cost, per E.H.P 5.00
Cost of development, per E.H.P $67.68
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COST OF HYDRO-ELECTRIC POWER PLANTS 721
White Horse Rapids Power Site
Batimate of Cost:
Power head 138 feet
Flow used for estimate 3,700 c. f. s.
Brake horse-power (80 per cent eff.) 47,200 (35,100 Kw.)
Dam:
Total height, 122 feet; total length of crest. 440
feet; length of spillway, 160 feet.
Masonry. 56.762 cubic yards, at S7.00 $397,334 .00
Excavation, 13,771 cubic yards, at $1.25 17,214 .00
CofTerdam 40,000 .00
Incidentals and special foundation contingencies. 55.452.00
$610,000.00
Forebay. etc.:
Excavation, 10,000 cubic yards, at $1.25 12,500 .00
Concrete walls, 2500 cubic yards, at $10.00 25,000.00
Trash racks, 120,000 pounds steel, at 5c 600 .00
Stop logs 400 .00
38,500.00
Diversion line:
Canal excavation, 260.000 cubic yards, at $1.25. . . 325,000.00
Canal lining. 4400 cubic yards, at $10.00 44.000 .00
369,000 . 00
Headgates. penstocks, etc. :
10 sliding headgates, set in place, at $900.00 9,000 .00
10 hydraulic relief valves, in place, at $1,200.00 . . . 12,000.00
1100 feet ^inch steel penstock, 11 feet diameter,
500 pounds per foot at 6}c., $32.50 35,750.00
600 feet i-inch steel penstock, 10 feet diameter,
495 pounds per foot at 7c., per foot $34.65 20.790.00
77,640.00
Power-house and draft tubes:
Power-house, reinforced concrete, 35,100 Kw., at
$5.00 per Kw. (made the same as Frieda) . . 176,000.00 176.000 .00
Summation $1,171,040.00
Engineering and contingencies, 25 per cent 292,760 .00
Interest during construction, i of 2 years, 4 per
cent approx 60.200 .00
$1,524,000.00
Hydro-electrical machinery:
10 horizontal water wheel units, in place, 4720 H.P.,
speed 450, at $22,000 220,000.00
10 3500 Kw. generators. 450 R.P. M., at $5.00 . . . 175,000.00
Exciter turbines and exciters, in place, at 80c. per
Kw 28.080.00
Transformers, at $4.00 per Kw 140,400.00
Switchboard and accessories, cables, etc., at $2.25
per Kw 78,975.00
Traveling crane, 40-ton 15,000 .00
Quarters, water supply, etc 20.000 .00
Summation $677.455 .00
Engineering and contingencies, 20 per cent 135,491 .0()
Interest during construction, 20 per cent approx 16,054 .00
829,000.00
Railway realigned, 9 miles, at $50.000 .00 450.000 .00
Total construction cost $2,803,000 .00
Total amount of power. E.H.P., 47.200.
Construction cost, per E.H.P 59 .38
Assumed right of way cost, per E.H.P 5 .00
Cost of development per E.H.P $64 .38
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722
ECONOMICAL ASPECTS
Metouus Power Site
Estiznate of cost:
Power head 210 feet
Flow used for estimate 3.400 c. f. i.
Brake horse-power (80 per cent eO.) 64,060 (48,700 Ew.)
Dam:
Total height, 236 feet; length of crest. 420 feet:
length of spillway. 125 feet.
Masonry, 183.000 cubic yards, at S6.50 $1,189,500.00
Excavation, 37,570 cubic yards, at SI. 25 46.062 .00
Cofferdam 75,000.00
Wagon roads 25,000.00
Incidentals and si;>ecial foundation contingencies. . 164,;38.00
$1,500,500.00
Forebay. etc.:
Excavation, 8000 cubic yards, at $1.25 10.000 .00
Concrete walls, 1500 cubic yards, at $10.00 15.000 .00
Trash racks, 20.000 pounds steel, at 5c 1.000 .00
26.000 . 00
Diversion line:
Tunnel excavation and lining. 300 feet by 15 feet.
by 20 feet, at $150.00 45.000.00
Headgates, penstocks, etc.:
10 sUding headgates, set in place, at $900.00 9,000 .00
10 hydraulic relief valves in place, at $1.200.00.. 12.000.00
500 feet A-iuch steel penstock, 12 feet diameter,
530 pounds per foot, at Ofc, $34.45 17,225 .00
500 feet A-inch steel penstock, 10 feet diameter,
565 pounds per foot at 7c., $39.55 19,775 .00
58,000.00
Power-house and draft tubes:
Power-house, reinforced concrete, 48,700 Ew.. at
$5.00 per Ew 243.500 .00 243.500 00
Summation $1,873,000.00
Engineering and contingencies, 25 per cent 468,250.00
Interest during construction, 8 per cent 208,750 00
$2,550,000.00
Hydro-electrical machinery:
10 horizontal water wheel units, in place, 6496 H.P.,
speed 400 R.P.M., at $24.000 .00 240,000 .00
10 5000-Ew. generators, 400 R.P.M., at $5.00 per
Ew 250,000.00
Exciter turbines and exciters, in place, at 82c.
per Ew 40,000.00
Transformers, at $4.00 per Ew 194,800 .00
Switchboard and accessories, cables, etc., at $2.25
per Ew 109,575.00
Traveling crane, 40-ton 15,000.00
Quarters, water supply, etc 20.000 .00
Summation $869,375 .00
Engineering and contingencies, 20 per cent 173,875 .00
Interest during construction, 30 per cent approx 36,750 .00
1.080.00000
Total construction cost $3,630,000.00
Total amount of power, E.H.P., 64,960.
Construction cost, per E.II.P 55 .88
Assumed right of way cost, per E.H.P 5.00
Cost of development, per E.H.P 160. S8
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COST OF HYDRO-ELECTRIC POWER PLANTS 723
Jefferson Creek Power Site
Estimate of cost:
Power head 400 feet
Flow used for estimate 1,000 c. f. s.
Brake hone-power (80 per cent eff.) 36,363 (27,100 Kw.)
Dam:
Total height, 20 feet ; length of crest. 00 feet ; length
of spUIway. 80 feet.
Masonry. 1000 cubic yards, at $10.00 $10.000 .00
Excavation, 300 cubic yards, at $2.00 600 .00
Cofferdam 800 .00
Incidentals and foundation contingencies 8.600 .00
$20,000.00
Forebay. etc.:
Excavation, concrete walls, trash racks, etc 25.000 .00
Diversion line:
Canal excavation and lining, 8 feet by 30 feet by
41.000 feet, at $30.00 1,230,000.00
Headgates, penstocks, etc.:
4 sliding headgates. set in place, at $900.00 3,600.00
4 hydraulic relief valves, in place, at $1,200.00. . . . 4.800.00
1000 feet A-inch steel penstock. 10 feet diameter,
450 pounds, per foot at 6ic., $29.25 29.250 .00
1000 feet i-inch steel penstock. 9 feet diameter.
440 pounds, per foot at 6}c.. $28.60 28,600 .00
1000 feet, ^inch steel penstock, 8 feet diameter,
500 pounds per foot at 7c., $35.00 35.000 .00
101,250.00
Power-house and draft tubes:
Power-house, reinforced concrete, 27,100 H.P., at
$5.00 per Kw 136.500 .00
Summation $1,511,750.00
Engineering and contingencies, 25 per cent 377,938 .00
Interest during construction, i of 2 years, at 4 per
cent approx 80,812 .00
$1,970,000.00
Hydro-electrical machinery:
4 horizontal water-wheel units, in place, 9091 H.P.,
speed 360 R.P.M., at $31.000.00 124.000.00
4 7000-Kw. generators. 365 R.P.M., at $5.00 per Kw. 140,000 .00
Exciter turbines and exciters, in place, at 80c. per
Kw 21,680.00
Transformers, at $4.00 per Kw 108,400 .00
Switchboard and accessories, cables, etc.. at $2.25
per Kw 60,975.00
Traveling crane. 40-ton 15.000 . 00
Quarters, water supply, etc 20,000 .00
Summation $490,055 . 00
Engineering and contingencies, 20 per cent 98,011 .00
Interest during construction, 2 per cent approx. . . 11,934.00
600.000.00
Total construction cost $2,570,000.00
Total amount of power, E.H.P., 36,363.
Construction cost, per E.H.P 70.67
Assumed right of way cost, per E.H.P 5.00
Cost of development, per E.H.P $75.67
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724 ECONOMICAL ASPECTS
Hydraulic Equipment. Horizontal turbine water wheels in
pairs. Estimate based on figures obtained from two independent
manufacturers. Prices include freight charges and cost of installa-
tion. Relief valves are estimated separately.
Electrical Equipment. Prices on electrical equipment are
based upon estimates of manufacturers of electrical machinery, and
are as follows:
Generators, all of the 3-phase, 2300-volt, 60-cycle type, per Kw. output:
For heads of under 40 feet 18.00
For heads of under 40 to 80 feet 7.00
For heads of 80 to 120 feet. 6.00
For heads of 120 feet 5.00
Exciter turbines and exciters, per Kw. output, whole plant 80
Switchboard and accessories, cables, etc., per Kw. output, whole
plant 2.25
Transformers, oil insulated and water cooled, 2,300-60,000 volts,
per Kw. output, whole plant 4.00
Cost of Georgia Railway and Power Company's Develop-
ment AT Tallulah FallS; Ga.
(A.I.E.E., October 11, 1915)
The development consists essentially of an artificial reservoir
of a capacity of 1,400,000,000 cubic feet formed by^ two reinforced
concrete buttress dams located near near Mathis, Ga., seven
miles from the diverting dam and intake at Tallulah Falls; an
artificial reservoir at Tallulah Falls having an available pondage
of 63,000,000 cubic feet formed by a cyclopean masonry dam of
the gravity type located some 60 feet below the tunnel intake;
a tunnel with a cross-sectional area of 151 square feet 6666 feet
long leading from the intake at the Tallulah reservoir to the
surge or pressure tank at the top of the gorge immediately above
the power-house; five steel penstocks 5 feet in diameter, each of
which serves a 17,000-H.P. Francis type water turbine in the
power-house. Five three-phase, 60-cycle 6600-volt, vertical
generators are direct-connected to these water wheels.
The electrical energy from these machines is stepped up from
6600 volts to 110,000 volts for transmission by five banks of three
3333 Kw. single-phase static transformers of the water-cooled
type and is transmitted over two outgoing lines.
Reservoir, The reservoir covers 834 acres, most of which was
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COST OF HYDRO-ELECTRIC POWER PLANTS 725
heavily timbered prior to the construction period. It was cleared
of timber, brush and other debris before the impounding began,
at a cost of $21 per acre, represented by $8.35 for cutting and
$12.65 for gathering and burning.
Reservoir Dams. There are two reinforced buttressed dams,
the largest is 660 feet in length, 93 feet high to the crest of the
spillway and 114 feet to the top walkway. The other dam is
much smaller. The quantities involved in the construction of
these two dams were 2,200,000 pounds of steel reinforcing, and
38,000 cubic yards of concrete.
The following figures give the cost per cubic yard of these two
dams:
Quarry $1,611
Crushing and mixing 818
Freight and engine service 1 .110
Placing concrete 744
Reinforcement 1.4i7
Placing reinforcement 823
Labor. 3.746
Cement 2.777
Sand 126
Plant, erecting and maintenance 1 .496
Small tools and supphes 1 . 123
Lumber 1 .034
Miscellaneous expenditures 1 .617
Superintendence and overhead 1 .443
Total $19,916
Di erting Dam. This dam is of the gravity type built of
Cyclopean masonry, heavy stone forming a Uttle over one-third of
the mass. The dam is 110 feet high from the stream stratum and
has a length of 426 feet. The spillway section is 280 feet in length,
made up of ten 28-foot openings between concrete piers. There
was used in this dam 39,000 cubic yards of concrete which was
placed by the contractors at $4.80 per cubic yard, the actual cost
possibly being about $3.70 per cubic yard. The cost of bridge
piers and flashboards is additional. The contract price for the
excavation work was $1.50 per cubic yard.
Intake. The intake is a self-contained reinforced structure
divided by partitions into five sections. The construction involved
about 7000 cubic yards of excavation, mostly rock, and 2670
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726 ECONOMICAL ASPECTS
cubic yards of concrete. The detailed cost of excavation and cod-
Crete for the intake was as follows:
Excavation: Per Cubic TanL
Lumber $0,974
Explosives 0.0G5
Miscellaneous supplies 0. 123
Transportation 0.071
Liability insurance 0 .049
Removing debris 0.235
Total $1,517
Concrete:
Labor $3 . 902
Cement 1.982
Lumber 0.794
Freight: 0.042
Transportation 0.203
Liability insurance 0. 136
Erection of plant 0.400
Crusher 1 . 280
Miscellaneous supplies 0.205
Removing debris 0.086
Total $9,030
Tunnel The tunnel is 6666 feet long, and has a net area of
151 square feet inside the concrete lining. About 75 per cent of
the tunnel was driven by the top-heading method and for the
remainder the lower heading or stopping method, which proved
to be much cheaper. The total excavations amounted to 56,000
cubic yards.
The unit cost of excavating 39,831 yards of this tunnel was as
follows:
Per Cubic Yard.
Labor $3,833
Explosives 0.604
Lubricants 0.019
Piping 0.026
Drill repairs 0.172
Miscellaneous supplies 0.237
Freight 0.087
Transportation 0.247
Liability insurance 0. 181
Miscellaneous charges 0.066
Depreciation on equipment 0. 150
Power 0.306
Total $5,928
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COST OF HYDRO-ELECTRIC POWER PLANTS 727
The concrete lining of the tunnel called for the placing of
18,966 cubic yards of concrete, the unit cost of the lining being:
Labor S5.061
Cement 1 .970
Misoellaneous materials 0. 405
Lumber 0. 136
Freight 0.065
Transportation 0 . 155
Liability insurance 0 . 165
Royalty on mixers 0.413
Miscellaneous cost 0 .245
Crushing stone 1 . 991
Quarrying stone 0.858
Plasterers 0.202
Cleaning tunnel 0.376
Total $12,042
The entire tunnel was grouted with grout consisting of one
part cement to one and one-half parts sand. The cost of the
grouting was $1,436 per cubic yard of concrete Uning, made up of
the following unit figures:
Item.
Labor
Cement
Transportation
Liability insurance
Miscellaneous supplies .
Cost per Linear
Foot of Tunnel.
$2,209
1.649
0.001
0.065
0.155
$4,079
The following figures give the approximate total cost of the
tunnel per linear foot:
Excavation $44.44
Concrete lining 34 . 20
Grouting 4.08
Adits and shafts 1 .91
Compressor plants, spur tracks and operation 8.99
Steel forms 2.94
Total $96.56
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728 ECONOMICAL ASPECTS
Forebay, The forebay is a reinforced concrete structure,
30X70 feet and 95 feet deep. The excavation involved some
4750 cubic yards of rock and the thickness of the concrete in the
walls of the tank varied from 3 to 6 feet. Some 700 tons of steel
reinforcement were used.
The cost of the rock excavation at the forebay was as foUows:
Per Cubic Yard.
Labor SI .620
Explosives 0. 106
Transportation 0.089
Liability insurance 0.067
MisceUaneous supplies 0 . 246
Miscellaneous expenses 0.038
$2,166
The concrete Uninjt of the forebay shows the following unit
figures:
Per Cubic Yard.
Labor $1 .680
Cement 1 .920
Lumber 0.117
Freight 0.012
Transportation 0.013
Liability insurance 0.049
Miscellaneous expenses 0 . 178
Crushing stone 1 .569
MisceUaneous supplies 0.033
$5,571
The above figures represent the unit cost of the concrete
below elevation 1500. The thickness of concrete was so small
and the amount of reinforcement so great in comparison with the
concrete below elevation 1500 that no unit copper yard was made.
The concrete used above elevation 1500 cost $1,925 per superficial
square foot surface one side.
Power-plant Builiing. The power-plant buildings are con-
structed with a concrete substructure and a structural steel frame
work enclosed with full brick walls as a superstructure. The gen-
erator building is 186 feet long, 42 feet 3 inches wide and 49 feet
high above generator floor. The switch-house is 277 feet long,
46 feet wide and 103 feet high.
There are five vertical reaction turbines operating under an
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COST OF HYDRO-ELECTRIC POWER PLANTS 729
effective head of 580 feet at a speed of 614 R.P.M., driving five
12,000-Kv.A. 6600-volt generators with direct-connected exciters.
There are also five transformer banks each consisting of three
3333-Kv.A. single-phase transformers for stepping up the voltage
to 110,000.
The unit cost of the power-house buildings and installed equip-
ment is given in the following, the cost of the hydraulic and
electrical equipment being based on the installed capacity of
50,000 Kw. on the original rating and that of the buildings and
other equipment on 60,000 Kw., the ultimate capacity of the
original rating.
Per Kw. Capacity.
Buildings and foundations:
Rock excavation $0,428
Concreting foundations and substructure 2 . 114
Structural steel 0.622
Handling and unloading 0.030
Erecting 0. 109
Brick, sand and cement 0.460
Handling, mixing and laying 7 0.960
Windows and doors 0 . 176
Handling and erecting 0.003
Tile roofing 0. 115
Concrete tile floors 0.400
Miscellaneous material 0. 186
Miscellaneous labor and transportation of men 0 . 234
Painting 0. 124
Plumbing 0.063
Building inspection 0 . 142
Tailrace:
Rock excavation . . ^ 0 . 197
Cribbing .' 0.017
Concreting tailrace walls 0 . 242
Total $6,612
Equipment:
Hydraulic equipment $6,682
Handling and erecting 0. 463
Electrical equipment and erection 6. 236
Auxiliary equipment 0 .999
Handling and erecting auxiliary equipment 0 . 106
High- and low-tension switch and bus structure ... 0 . 445
Water and oil piping system 0.244
Total equipment $16,074
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730 ECONOMICAL ASPECTS
Grouping the above items under a more condensed form, we
have:
Tailrace $0,456
Buildings — substructure 2 . 542
BuUdings — superstructures 3 . 372
Buildings — inspection 0. 142
Total equipment 15.074
Cost per Kw. capacity $21 .586
In addition to this cost there is a certain proportion of the
temporary compressor plant, spur tracks, general tool and utility
equipment, etc., amounting to $1,178, which should be charg^to
this power-plant construction, making the total cost of the power-
plant buildings and equipment $22,764 per kilowatt capacity.
As the foregoing costs do not, in some instances, give the cost
of completed structure under the various headings, the following
table will supply the construction cost per kilowatt capacity of the
entire power production plant, including reservoirs, dams, all
hydraulic conduits, power plant and equipment, and including
temporary construction plant, such as compressor plants, water
system, spur tracks, etc.
Mathis dams and reservoirs $17. 104
Intake dam and bridge 4.660
Intake 1.102
Tunnel 12.379
Forebay 2.395
Penstock tunnels and portal 0.694
Penstocks and foundations 5 . 568
Power plant and equipment 22.764
Total construction cost power production
plant per kilowatt $66,666
The following gives the percentage relation of various ex-
penses on the development as a whole, which might be applicable
to any other development, and therefore does not include the
cost of land or property expense: ^^ ^^
General construction expenditure 75 .575
General engineering expense 3 .078
General legal expense 1 .891
Interest, bonds and advances during construction. 11 .315
General overhead expense 1 . 773
General contract expense 6.368
Total 100.000
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COST OF HYDRO-ELECTRIC POWER PLANTS 731
Estimate of 72,000-Kw. Generating Station at Great Falls,
Potomac River, for Supplying Light and Power for the
Use of United States and the District of Columbia
(From H. R. Document No. 1400)
This proposed project provides for a dam across the Potomac
River at Great Falls, creating a lake or reservoir of some 3000 acres
area and an operating head of 111 feet. The dam is in two
parts, a spillway dam and an intake dam. The former is of
the arched type, somewhat similar to the spillway section of the
Gatun dam, at Panama, and comprises eighteen openings sepa-
rated by piers and provided with Stoney gates. A gatehouse is
arranged for on top of the intake dam, from which nine pen-
stocks convey the water to the tm*bines. These are of riveted
steel from f to f -inch thickness, the inside diameter being 13 feet
and the length 140 feet.
When completed the equipment will comprise nine 12,500-
H.P. single-runner vertical turbines operating at 150 R.P.M.
under a head of 111 feet. These will drive nine 10,000-Kv.A.
(8000 Kw. .8 P.F.) 3-phase, 60-cycle, 13,209-volt generators, with
direct-connected exciters. Provision is further made for com-
plete switching equipment and station auxiUaries.
The allowance in the original estimate for relocating the Ches-
apeake and Ohio Canal has been omitted in the following:
Estimated Ck>ST
Spillway dam:
Piers, superior concrete, 7540 cubic yards, at $9.00 $67,000
Piers concrete, 27,800 cubic yards, at $8.00 222,000
Water-flow guides, concrete, 1850 cubic yards at $8 15,000
Dam, superior reinforced concrete, 37,400 cubic yards, at $9 337,000
Dam, Cyclopean superior concrete, 36,200 cubic yards, at $5.50*. . 200,000
Dam, Cyclopean concrete, 233,550 cubic yards, at $4.50 * 1,050,000
Total masonry $1,891,000
Excavation, rock, 115,400 cubic yards at $2.50 289,000
Stoney gates, 18, erected, weight 1,162,000 pounds, at $0.08 130,000
. Stoney gates, fittings and machinery, etc., 18 sets at $6500 117,000
Floating caisson 5,000
Foot bridge, erected, weight 833,000 pounds, at $0.08 65,000
Railing, 2850 feet, at $1.75 5,000
Total spillway dam $2,502,000
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732 ECONOMICAL ASPECTS
Intake Dam and Power-house
Power-house superstructure, 2,200,000 cubic feet at 15c $330,000
Power-house, substracture, 2,000,000 cubic feet, at 17c 340,000
Intake house, superstructure, 750,000 cubic feet, at 15c 113,000
Intake house, substructure, 471,000 cubic feet, at 17c 80,000
Cranes and raih-oad track 15,000
Turbines, erected, 9, at $51,000 459,000
Central lubrication system 27,000
Electrical units, 9, and switchboard etc., at $90,000 810,000
Intake dam, cyclopean concrete, 107,700 cubic yards, at $4.50 * . 485,000
Excavation, intake dam, power-house, and tailraoe, 475,000 cubic
yards, at $2.50 1,187,500
Penstocks, 10 erected, 1,350,000 pounds, at 8c 108,000
Rack bars, 10 sets, 9350 square feet, at $1.75 16,500
Head gates, 2 5,000
3 pumps and their motors, erected 20,000
Force main, laid, 300,000 pounds, at 14c 42,000
Shore wasteway 25,000
Road and branch railroad 100,000
Total intake dam and power-house $4,163,000
Note. — Prices marked thua (*) are reduced by reason of part cost being borne
by rock excavation.
Summary
Spillway dam $2,502,000
Intake dam and power-house 4,163,000
Land and water rights 1,500.000
Engineering and contingencies 585,000
Total $8,750,000
Cost of P©wer
Estimate for 319.4 millions kilowatt-hours annual output, or 100,000 HP.
effective peak load.
Operation:
Administration and labor $60,000
Maintenance and supplies 20,000
S8O000
Depreciation, headworks and power-house: •^^
1 per cent on masonry $4,910,500 $49,105
2 per cent on steel work 438,500 8,770
3 per cent on machinery 1,316,000 39,480
Fixed charges: »«•«««'«» *^'^
Interest, 3 per cent, sinking fund 3 per cent, or 6 per cent on
above $8,750,000 $525,000
Total $702,355
Or 2.2 mills per kilowatt-hour of output.
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CX)ST OF HYDRO-ELECTRIC POWER PLANTS 733
Estimated Cost op 200,000 and 300,000 Horse-power Hydro-
electric Developments
From Bulletin No. 5. State Engineer's Office. Oregon
Head: 200 feet minimum.
ESTIHATB OF CoST, 200,000 ELECTRICAL HOR8E-POWER INSTALLATION
River diversion:
Temporary diversion channel:
Excavation above elevation 885, 500,000 cubic yards,
at Sl.OO $500,000.00
Excavation below elevation 885, 100.000 cubic
yards, at S1.50 150,000.00
Concrete, lining, 10,000 cubic yards, at S8.00 80,000.00
Concrete walls, 5000 cubic yards, at S8.00 40,000.00
Concrete, miscellaneous, 2000 cubic yards, at SIO. 20,000.00
Steel reinforcing. 100 tons, at SIOO.OO 10,000 .00
$800,000.00
Cofferdams, earth and rock fill: ■
Upper cofferdam, 300,000 cubic yards, at Sl.OO . . . 300.000.00 '
Lower cofferdam (first structure), 100,000 cubic
yards, at Sl.OO 100,000 .00
Lower cofferdam (replacing structure), 100,000
cubic yards, at Sl.OO 100,000 .00
500,000.00
Extraordinary contingency (insurance allowance) . . . 500,000 . 00
Main dam:
Excavation below elevation 885, 350,000 cubic yards,
at S2.00 700,000 .00
Excavation above elevation 885. 50,000 cubic yards,
at Sl.OO 50,000.00
Concrete. 760,000 cubic yards, at S6.00 4,560,000 .00
Movable dam crest 190.000 .00
6,500,000.00
Forebay and penstocks:
Tunnel excavation, 32.000 cubic yards, at S5.00 160,000.00
Tunnel lining concrete, 6000 cubic yards, at S8.00. . . 40,000.00
Open excavation, 200,000 cubic yards, at Sl.OO 200.000.00
Forebay walls, concrete, 20,000 cubic yards, at S7.00 140,000.00
Penstock cradles, concrete. 5000 cubic yards, at S8.00 40,000 .00
Gates, trash racks, etc 200,000, 00
Penstocks, 1500 tons, at S140.00 210,000 .00
Reinforcing steel, 100 tons, at SIOO.OO 10,000.00
1,000,000.00
Power and transformer house:
Excavation, 60,000 cubic yards, at Sl.OO 60,000.00
Concrete, 20.000 cubic yards, at S8.00 160,000.00
Concrete, 5000 cubic yards, at S12.00 60.000.00
Reinforcing steel, 100 tons, at SIOO.OO 10.000 .00
Roof, crane, etc 60,000 .00
350,000 . 00
Right of way (assumed) 150.000 .00
Summation of above items 8,800,000 .00
Engineering and contingencies, 26 per cent 2,200,000.00
Interest during construction, 2 i years at 4 to 10 per cent 1 ,100,000 . 00
$12,100,000.00
Hydro-electric equipment:
Turbines, venerators, exciters, and governors, 7 units,
26,000 Kw. each, at S200.000 .00 1,400,000 .00
Switchboard, plant wiring, etc 200,000.00
Transformers. 1.50,000 Kw 600,000 .00
Freight, erection and installation 400.000 .00
Summation of above items S2,500,000 .00
Engineering and contingencies, 20 per cent 600,000 .00
Interest, } yr. at 4 per cent say 3 J per cent 100,000 .00
3,100,000.00
Total for project SI 6,200,000 .00
200,000 E.H.P. continuous development at S76.00 per
E.H.P.
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734 ECONOMICAL ASPECTS
Estimate of Cost, 100,000 Electrical Horse-power Additional Power
Forebay, penstocks, power-house and tailrace:
Additional, including 25 per cent for engineer-
ing and contingencies and 10 per cent
interest during construction $1,000,000.00
Additional equipment, including 20 per cent for
engineering and contingencies, and 3
per cent for interest, 100,000 H.P 1,500,000.00
Summation ' $2,500,000.00
This is the total additional cost to supply 100,000 horse-power
additional power during the part of the time for which
tHe flow of the river is in excess of 15,000
second-feet.
Estimated cost of storage to maintain a mini-
mum flow of 15,000 second-feet, 500,000
acre-feet 2,000,000.00
Total additional $4,500,000.00
Total for 200,000 H.P. project (preceding esti-
mate) 15,200,000.00
Total for project $19,700,000.00
300,000 E.H.P. at approximately $66.00 per E.H.P.
Estimate of Annual Cost
For 200,000 Electrical Horse-power Continuous Development .
This estimate has been made on the basis of the following assumptioDs:
Interest rate 4 per cent, assumed life of dams, forebay, substructure of power-
house, and tailrace, fifty years. Assumed life of movable crest gates, trash
racks, penstocks, superstructure of power-house and equipment fifteen years.
Annual replacement fund, for fifty-year life portion, $10,800,000
at i per cent $72,000.00
For fifteen-year hfe portion, $4,400,000 at 5 per cent 220,000.00
Aimual interest, $15,200,000.00, at 4 per cent 608,000.00
Annual maintenance and repairs . 60,000.00
Attendance and administration 80,000.00
Total annual cost, 200,000 E.H.P. development. . . $1,040,000.00
Aimual cost per E.H.P. on basis of 100 per cent load
factor $5.20
Additional 25 per cent 1 . 30
Aimual cost, if only 80 per cei^t of the power is used $6.50
These costs are based upon utilization of the power immediately upon
completion of the project.
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COST OF HYDRO-ELECTRIC POWER PLANTS 735
Estimate of Annual Cost
For 300,000 Electrical Horse-power Continuous Development
Based upon similar assumptions to those for the 200,000 E.H.P. development.
' Annual replacement fund, for fifty-year life portion, $13,200,000
at J per cent $88,000.00
For fifteen-year life portion, $6,500,000 . 00, at 5 per cent . 325,000 . 00
Annual interest, $19,700,000.00, at 4 per cent 788,000.00
Annual maintenance and repairs 90,000.00
Attendance and administration 119,000.00
Total annual cost $1,410,000.00
Annual cost per E.H.P. of base load $4.70
Additional 25 per cent 1 . 20
Annual cost if only 80 per cent of the power is used. . $5 .90
Estimated Cost op Proposed Columbia River Project
Capacity:
480,000 horse-power 12 months per year
600,000 horse-power 11 months per year
700,000 horse-power 10 months per year
800,000 horse-power 8 months per year
The following cost estimate on this proposed extensive devel-
opment is taken from an article by Mr. L. F. Harza in the Journal
for Electricity, Power and Gas, for March 18, 1916, €md the readers
interested in this unusual development are referred to the long
series of articles appearing in said journal during 1915 and
1916.
Contingent Margin, The total cost of each item as given in
the estimates which follow all include a margin of 25 per cent to
cover engineering, administration during construction, and con-
tingencies in addition to the amoimts obtained by applying the
foregoing unit prices, except in the case of the generating machin-
ery; in this case only 15 per cent was allowed, as these estimates
are based upon the higher of two or more actual quotations in
nearly all cases, and the manufacturer himself would furnish the
engineering talent except for erection, which item has been in-
cluded in the estimate.
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736 ECONOMICAL ASPECTS
ESTIMATE OF CAPITAL COST
Dam for closing present channel:
Scheme A +26 per cent $3,325,000
Scheme B +25 per cent 2.288,000
Scheme C +26 per cent 3,344,000
Scheme D +26 per cent 3,056,000
Scheme £ +25 per cent 3,485,000
Scheme F +25 per cent 3,419.000
Use for estimate . - $3,350,000
Controlling dam:
Camere type of dam;~approximato quantities as de-
signed for 81 feet controlled depth.
26,000 tons structural steel.
4,000 tons cast steel.
230,000 cubic yards of concrete.
1 traveling gantry crane.
Estimated cost, reduced 25 per cent, for 67 feet con-
trolled depth plus 26 per cent contingent fund $3,861,000
Tainter-gate type of dam, approximate quantities as
designed for 81 feet controlled depth.
41,600 tons structural steel.
21,800 tons cast steel.
480 tons steel cable.
312,460 cubic yards concrete.
Estimated cost, reduced 26 per cent, for 67 feet con-
trolled depth plus 26 per cent contingent fund 8,837,000
Use for estimate of controlling dam 8.837.000
Flood channel:
Approximate quantities:
2,078,000 cubic yards rock excavation, above elevation
84.0 (sill of flood gates) plus 25 per cent 2,078,000
Diversion channel:
Approximate quantities:
1,243,000 cubic yards rock excavation for diversion
channel below elevation 84.0.
140,500 cubic yards concrete.
810,000 F.B.M. timber for cribs.
8,000 cubic yards rock fill in cribs.
Estimated cost of diversion channel and closure of same
plus 25 per cent 2,872,000
Ice and drift sluice, Oregon side:
Approximate quantities:
252,000 cubic yards rock excavation.
28,300 cubic yards concrete.
320 tons structural steel rollers.
Estimated cost plus 25 per cent 452,000
Wing walls for rock fill dam:
Approximate quantities:
42,600 cubic yards concrete plus 25 per cent 266,000
Main floating boom and piers:
Approximate quantities:
11.394,000 f.b.m. of timber.
1,055 tons of rods and drift pins.
3,000 cubic yards concrete.
46,000 cubic yards rock fill in piers.
Estimated cost plus 25 per cent '. . . 493.000
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(X)ST OF HYDRO-ELECTRIC POWER PLANTS 737
Power canal:
Approximate quantities:
4.229,000 cubic yards rock excavation.
136.000 cubic yards rubble walls.
17.960 cubic yards concrete lining.
1,000,000 cubic yards sand excavation.
Two floating booms.
22.000 cubie yards concrete.
1 10 tons structural-steel roller dama.
Estimated cost plus 25 per cent $5,394,000
Jetty at intake to power canal:
Approximate quantities:
4.430,000 f.b.m. of timber.
665.000 pounds rods and drift pins.
2,470 cubic yards reinforced concrete.
164.000 cubic yards rock fill.
73,000 cubic yards sand excavation
Estimated cost plus 25 per cent 285,000*
Rebuilding Five Mile Lock:
Raising walls and gates and building draw span, plus
25 per cent 106,000
Foiebay and power-house substructure:
Approximate quantities
1,584,000 cubic yards dry rock excavation.
137.500 cubic yards rock excavation for removal of cofferdam
429,250 cubic yards concrete.
5,000,000 pounds steel reinforcement.
3.500.000 pounds structural steel for penstock gates.
2,300.000 pounds cast steel for penstock gates.
1,024,000 pounds steel trash racks.
24 filler gates and drain gates.
$375,000 for cofferdamming and pumping.
Estimated cost plus 25 per cent 6.852,000
Power-house superstructure:
76 feet by 1670 feet station building.
Fishway.
Tunnel through building for railroad.
Steel bridges for spanning forebay and tailrace.
Estimated cost plus 25 per cent 1,475.000
Power-house machinery:
23 vertical shaft 35,000-Kw. (50,000 Kv.A.) 25-cycle.
11,000-volt, 75-R.P.M., 3-pha8e generators, including
stator and rotor, but not shaft or bearings.
28 mechanically driven exciters. 500 Kw. each; switch-
b'>ard, low-tension oil switches, busbars, and all mis-
cellaneous electrical equipment.
88 50,000-H.P. vertical shaft 76 R.P.M. turbine units,
including shaft and oil bearings, governors, and oil
system.
2 250-ton traveling cranes in power house and 2 50-ton
traveling gantry cranes serving penstock gates; mis-
cellaneous small equipment.
Estimated cost plus 15 per cent 12,353,000
Reconstruction of railroads:
Total estimated cost plus 25 per cent 687,000
Other property damage 904,000
Total physical cost $45,404,000
Add for interest during one-half of five-year construc-
tion period at 4 per cent equals 10 per cent 4,540.000
Total estimated capital cost $49,944,000
Use for total capital cost 50,000.000
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738 ECONOMICAL ASPECTS
Annual Cost of Generating Primary Power. The following
items are independent of the interest rate on capital investment:
Depreciation — ^Reserve fund assumed to
earn 2 per cent interest and sufficient to
replace all depreciable parts every fifteen
years, and to refund the cost of all nearly
permanent structures, rock excavation,
concrete, etc., every fifty years (average
value 3 per cent) $1,500,000.00
Maintenance and repairs — For maintenance
and repairs on the turbine units, in addi-
tion to depreciation fund, per annum. . . $112,800.00
Maintenance and repairs to generators and
electrical equipment, 1} per cent 74,000.00
Repairs to movable dam 50,000 .00
Painting, average of one coat per annum,
43,700 tons of exposed steel (total in use)
at $1 per ton 43,700.00
Operating suction dredge to prevent possible
accimiulation of sand bar at canal intake,
300 days, $100 per day 30,000.00
Maintenance of building, replacing roof
every five years plus 50 per cent for other
repairs 2,400.00
Contingent maintenance and repair expense 50,000 . 00
Total for maintenance and repairs 362,900.00
Attendance and administration 100,000.00
Total annual expense exclusive of interest $1,962,900 00
The rate of interest to be paid on the capital investment will
depend largely upon the basis of financing. To show the relation
of this to the annual cost of power, interest rates of 3 and 4 per cent
have been assumed as representing public development under dif-
ferent conditions. There has also been assumed a rate of 6 per
cent on securities originally discounted 10 per cent, plus 1 per
cent taxes, this basis being intended to represent approximately
the cost under corporate financing. The results are as follows:
No sinking fimd has been provided, as it is not properly chargeable
to the cost of generation. The depreciation or amortization fund
would provide for keeping the project permanently in first-class
operating condition. A water-power property is of such unques-
tionably permanent value as to make it imnecessary to recover
the principal in a short time as with many industrial enterprises
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COST OF HYDRO-ELECTRIC POWER PLANTS 739
which are subject at any time to the necessity of coxnpiete Uquida-
tion due to unforeseen competition. In the case of corporate
finance, especially, a sinking fund might, however, assist in secur-
ing easier terms in marketing the securities, but in any event is
amply covered by the 25 per cent contingent fund. A 50-year
sinking fimd drawing 2 per cent interest would involve an annual
expense of $1.20 per continuous electrical horse-power.
Three per cent basis:
Depreciation, maintenance and repairs as above . . $1,962,900 . 00
3 per cent interest on $50,000,000 1,500,000.00
Total annual charges $3,462,000.00
Annual cost per peak electrical horse-power year
of base load (480,000 H.P.) $7.22
Add 25 per cent 1 .80
Use $9.02
Four per cent basis:
Depreciation, maintenance and repairs as before. $1,962,900.00
4 per cent interest on $50,000,000 2,000,000.00
Total annual charges $3,962,900.00
Per peak horse-power year 8. 27
Add 25 per cent 2.07
Use $10 . 34
Six per cent basis:
Depreciation, etc., as before $1,962,900.00
Add for 6 per cent on securities originally sold at
10 per cent discount, equivalent to 6.67 per cent 3,340,000 . 00
^dd for taxes 1 per cent 500,000.00
Total annual charges $5,802,900.00
Cost of power on usual basis of private enterprise
per peak horse-power per year 12 . 10
Add 25 per cent 3.03
Use $15 . 13
Cost of Generation Contingent upon Sale of Surplus Power. If
the sale of the surplus power is to be assumed, then an additional
item of depeciation should be added to provide for the possibility
of severe runner erosion for the low-head units when operating at
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740 ECONOMICAL ASPECTS
heads above 80 feet. The value of one runner including freight
and erection would be about $27,000.
About seven low-head units are required to operate at 80 foot-
head to produce 800,000 H.P. with a decreasing number at the
higher heads where the erosion would be most severe. If we
assimie to replace all seven runners every three years, the annual
additional charge would be $63,000, say $75,000. This item is
very small compared with the additional profit which the surplus
power should bring.
It might be assumed roughly that eleven months' surplus
power be worth 80 per cent of the value of continuous power, ten
months' power 60 per cent and eight months' power 30 per cent.
If the various prices now be weighted according to the amount
available, and using the price of primary power as unity, there will
result:
480,000X1.00=480,000
120,000 X .80= 96,000
100,000 X .60= 60,000
100,000 X .30= 30,000
800,000 actual or 666,000 weighted power
The quotient of these, totals or 0.8333, now represents the aver-
age unit value of all power, as a proportion of the value of primary
power, and 666,000 represents the equivalent primary power to
produce the same income. If all power were to be sold at prices
bearing the above ratio to each other, the actual costs of pro-
duction of primary power would then be obtained by first adding
$75,000 to the annual charges and then dividing by 666,000.
Based upon 3 per cent interest:
Former annual charge $3,462,900.00
Add for runner depreciation 75,000.00
Total $3,537,900.00
Add 25 per cent 884,000.00
Use $4,421,900,00
Cost per peak primary- horse-power $6.63
Cost per 11 mo. surplus H.P 5 . 30
Cost per 10 mo. surplus H.P 4.00
Cost per 8 mo. surplus H.P 2.00
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' COST OF HYDRO-ELECTRIC POWER PLANTS 741
Based upon 4 per cent interest:
Former annual charge $3,962,900.00
Add for runner depreciation 75,000.00
Total $4,037,900.00
Add 25 per cent 1,009,500.00
Use $5,047,400.00
Cost per primary horse-power 7.58
Cost per 11 mo. surplus H.P 6.06
Cost per 10 mo. surplus H.P. 4 . 55
Cost per 8 mo. surplus. 2.27
Based upon 6 per cent interest — on securities sold at 90:
Former annual charge $5,802,900.00
Add for runner depreciation 75,000,00
Total $5,877,900.00
Add 25 per cent 1,469,500.00
Use $7,347,400.00
Cost per primary horse-power $11 . 02
Cost per 11 mo. surplus H.P 8.82
Cost per 10 mo. surplus H.P 6.62
Cost per 8 mo. surplus H.P.. 3.31
The computations for the capital cost and cost of power for the
case in which a period of ten years was allowed for building up the
load, were made by starting with the initial investment necessary
to deliver one-tenth of the power, and then progressively adding
for each year the deficit, or difference between interest on the pre-
viously accumulated investment, operating expenses, etc., and
the earnings of the year in question, to the investment of the pre-
vious year. It was necessary first to assume a price of power and
after computing the transactions of the ten-year period, to then
correct this assumption by a process of successive approximations
until an assiunption was made which provided the desired 25 per
cent margin at the end of the ten-year period.
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742 ECONOMICAL ASPECTS
COST OF POWER »
The cost of hydro-electric power can be considered as made
up of two parts: The fixed charges and the operating expenses.
These, in turn are made up as follows:
Fixed Charges:
Interest on investment.
Taxes and insurcknce.
Depreciation.
Operating Expenses:
General administration.
Labor.
SuppUes.
Maintenance and repairs.
In estimating the cost of power a thorough distinction must, as
previously stated, be made between the cost of the same at the
generating station bus-bars and the cost when delivered to the
customer. In the former case the cost should be based on only
such portions of the charges and expenses which are applicable
to the generating station, while in order to obtain the cost of power
delivered, the total expenses must, of course, be considered.
The rate of interest on the investment varies cmd depends on the
risk involved. In risky undertakings the rates of interest are
higher than where greater safety obtains, and if money put into
new enterprises involving risk of loss were not allowed to earn any
more than a normal rate of interest, it would be poor policy for
the inventor to put his money in such undertakings. Bonds,
therefore, should draw the lowest rate of interest because, as a
rule, they are safe, being secured by a mortgage on the property.
So, for example, many government bonds draw only an interest of
3 per cent because there is no risk involved. The rate on public
service bonds, on the other hand, is higher, averaging about 5 per
cent, but, of course, when they are sold at a discount the actual
interest earned by the investor is greater. The interest on the stock,
however, which cannot be declared until the bond interest has
been paid, should be enough higher than the normal interest to com-
pensate for the lesser security. A rate at least 2 per cent higher
than prevailing bank rates seems justifiable and conrniissions are
frequently approving rates of retiu^n of 7 per cent and 8 per cent.
1 See previous section for actual and estimated costs.
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COST OF POWER
743
The second item under the fixed charges is taxes and insurance.
The amount necessarily depends on the rates available, but, for
.estimating purposes it is common practice to allow ^ per cent of
the physical cost for each, making a total of 1 per cent.
Depreciation is the loss in value which occurs during the period
which the property is in service, either due to wear and tear or
obsolescence, and a certain sum of money must be set aside
annually for renewing this property. There are different methods
of providing for depreciation, but the sinking fund or annuity
TABLE LXIV
Property.
Dams, masonry
Pipe lines, iron
Pipe lines, wood-stone
Power-house building, fire-proof. .
Water-wheels
Generators
Transformers
Switching equipment
Miscellaneous auxiliaries
Transmission lines, steel towers . .
Transmission lines, wood poles. . .
Underground cable system
Service transformers
Total Life. Years.
50
30-40
15-25
50-75
20
20
20
12-15
10
25-30
15
20-25
15
method is best applicable to public utility properties. It pro-
vides for setting aside each year a sum that, invested in a certain
rate of interest compounded annually, it will equal the cost of the
property, less its scrap value, at the end of its assumed life. Thus,
if a certain portion of a plant costs S10,000 and has a life of ten
years, with a scrap value of 10 per cent or $1000, and it is desired
to set aside such a sum that, at 5 per cent interest compounded
annually, will accumulate an amount equal to the cost, less the
scrap value, at the end of the life period, it will then be found, by
referring to an annuity table, that $9000X0.0795 or $715.50
annually will produce the required amount. As the life, as well
as the scrap value of the different elements varies to a consider-
able extent, the depreciation should be figured separately for each
item, and thereafter averaged.
The useful life of the plant apparatus or equipments is purely
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744
ECONOMICAL ASPECTS
a speculative matter, and past experience, knowledge of the art
and careful judgment must be exercised in arriving at the prob-
able life of apparatus and property. See Table LXIV.
The operating exp)enses, which include labor, repairs, main-
tenance and supplies, will vary with the amount of power manu-
factured, that is, the load factor. They are, however, by no means,
proportional to it and form a much smaller part of the total cost
than with steam stations, where the fuel expenses come in and
where both labor, repair and supply items are much higher.
Based on a 50 per cent load factor, the operating expenses may
range anywhere from 0.3c. per Kw.-hr. for a small station to
0.02c. or less for a large station. Some approximate representa-
tive values are giyen in the following:
TABLE LXV
Operating Expenses of Hydro-electric Stations
station Capacity
inKw.
Operating Expenses
In Cents per Kw.-hr.
station Capacity
In Kw.
operating ExpeuM
in Cents per Kw.-hr.
2,500
5,000
10,000
15,000
0.1
0.08
0.06
0.05
25,000
50,000
75,000
100,000
0.04
0.03
0.02
0.015
TABLE LXVI
Approximate Cost of Steam Turbine Stations and Power
(Based on Coal at S3.00 per Ton)
Cost per Kw.-hr. in Cents.
Capacity of Station
Cost of Station
Load Factor.
in Kw.
per Kw.
60 Per Cent.
76 Per Cent,
500
S95.00
1.02
0.86
1,000
80.00
0.88
0.74
2,000
75.00
0.77
0.63
3,000
70.00
0.69
0.58
4,000
65.00
0.66
0.54
5,000
62.50
0.62
0,51
7,500
60.00
0.57
0,48
10,000
57.50
0.53
0.45
15,000
55.00
0.51
0.43
25,000
50.00
0.48
0.41
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COST OF POWER
745
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CHAPTER XI
ORGANIZATION AND OPERATION
Management. The measure of financial success attained in a
hydro-electric development is to the greatest extent measured
by the skill and judgment of its management. The department
heads should study the men whom they employ and also the prob-
lem of handling them to the best advantage. It should be the
object of the department chiefs so to dispose both men and
material that their possibiUties will be best realized. An ade-
quate system of records should be kept showing what the several
departments are doing, and promptness and completeness in this
respect should be insisted upon. Regular meetings between the
department heads and their men is advisable, and many com-
panies have inaugiu^ted suggestive systems by which suggestions
for the improvement of the operating and service conditions are
invited, prizes being given at regular intervals for the best sug-
gestions received.
The organization of a hydro-electric company naturally varies
considerably, not only depending on the size of the system, but
also on the nature of the same. An idea of the extensive force
required by a large company such as that of the Great Western
Power Company, is obtained by referring to the chart given in
Fig. 406.
Operating Force. The selection and maintenance of an
efficient and reliable operating force is also essential, as upon the
same dej)ends the quaUty of service rendered. Most modem
systems of any size have a method of operation which corresponds
to that of a train dispatcher on steam railroads, and where many
different plants are attached to the same network, this becomes
practically necessary. A load dispatcher is located at some con-
venient point, which often is not at a power-house, and is phced
in charge of the whole system and personally directs every opera-
tion in all stations. He is in telephone communication \\nth all
operators and keeps a record of the changes and connections made
746
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OPERATING FORCE 747
in each part of the system by means of a system of pins and
markers on a large map or plan of the circuits and apparatus of
the plant. He receives at regular intervals readings of loads,
water conditions, etc., which he marks down on the record sheet
before him, and from these records and recording instruments in
his office he is able to keep close watch on the conditions and
make changes in load generation, voltage, frequency, gate open-
ings, etc., in order to obtain the most satisfactory and efficient
operation.
The real value of a load dispatcher looms up under abnormal
or trouble conditions. When trouble affects the system it is
instantly apparent on the recording instruments. The system
operator inmiediately gets into communication with the station
affected and in case of transmission hne trouble learns what
switches have opened and then, if possible, gives orders to cut
over to duplicate lines. The faulty hne receives one or two
trials, either at full voltage or by bringing the voltage up slowly
on separate generators. If the short or trouble still shows up on
the Une ammeters, the hne is cut up into sections, according to
the judgment of the system operator, and tried until the faulty •
section is located. Patrolmen and repair men, who are on con-
stant call, then receive directions for making the repairs. In the
case of trouble on the distribution system, as, for instance, where a
feeder will not stay in owing to a short on the line, it is imme-
diately reported and turned over to the line department, which
looks after the repairing of the line. In case of trouble with the
underground system, the system operator supervises the locating
and disconnecting of the faulty feeder and then notifies the under-
ground department, whose business it is to repair the trouble.
In case of trouble of a serious nature, the heads of the depart-
ments affected are notified and take active charge of the situation.
The organization of the operating force of a hydro-electric
generating station is necessarily less complicated than in a steam
station. It is determined largely by the location and the arrange-
ment, and there are so many different conditions in such systems
that it is impossible to reconmiend any exact form of organization,
as really no two can be quite alike. If the station is not too large
it is desired to have the hydrauhc superintendent report to the
station superintendent, but if the development is of such a mag-
nitude as to require the entire time of a superintendent for each
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748 ORGANIZATION AND OPERATION
of the departments under consideration, a position is warranted
for a man to whom both electric and hydraulic superintendents
will report, thus still bringing the responsibility of operation of the
two departments under one head.
As a general rule, for the same capacity installed, a plant
having horizontal units can get along with a smaller force than one
using vertical units. It is a general practice to maintain one man
at all times on each of the different levels or floors of the power-
house, such as the switchboard gallery, the main floor and the
basement, where with vertical units the turbines proper, as well
as the oil pumps and other auxiliaries are located. The man in
the basement could, in all probabiUty, be dispensed with in plants
using horizontal units. In addition to these men a chief operator
should be provided for each shift, whose duties should carry him
to all parts of the building. For a very large station the above
force may be entirely inadequate, cmd for small plants the force
may be reduced.
The switching operations are determined by the general method
of operation. It is desirable to eliminate all high-tension switch-
ing under load, due to the fact that such switching may set up
surges which may discharge into the transformers and cause
resonance, resulting in internal disturbances in the same. When
a line is to be cut into service, the high-tension switches in the
main and substation should be closed first, then the low-tension
transformer switch in the generating station should be closed,
energizing the transformers and the Une, after which the low-
tension transformer switch in the substation is closed cmd the load
picked up. In case it becomes necessary to open a high-tension
switch in a loaded line, the circuit should, if possible, first be
parallel with another before opening the switch. If, on the other
hand, transformers are to be paralleled on both high- and low-
tension sides, the low-tension switch should be closed first, assum-
ing that the low-tension bus is energized. Similarly, in cutting
out the transformer the low-tension switch should be opened last.
Operating Records. One of the essential things in connection
with the operation of hydro-electric generating stations is the
keeping of acciu'ate records. Record sheets should contain only
the most important readings, as with complicated forms the
attendant generally reahzes that a large number of the readings
are of no importance and for this reason he becomes very lax in
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OPERATING RECORDS
749
his attention to the readings in general, and as a consequence
the important ones may suffer. The following description applies
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to €m actual record sheet for a medium-size station (Fig. 407),
which has been found to give satisfactory results. The sheet is of
the size of ordinary letter paper and is ruled for hourly records of
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750 ORGANIZATION AND OPERATION
'' Water," /' Main Units," " Cycles," " Power-factor," " Excit-
ers," " Transformers and Floodgates." These items are listed
vertically and the sheet is divided into 24 vertical columns, one
for each hour. At the top are given the " Forebay " readings and
" Tailrace " readings, the difference between which gives the
" Effective Head." Immediately below are listed the indicated
kilowatts and per cent gate opening of each generator in service,
following which are given the " Total Indicated Kilowatts "
and " Total Per Cent Gate." The total kilowatt hom^ during each
hour, as read from the watt-hour meters, is plotted as a block
curve extending across the face of the sheet.
This serves as a better record for the actual station output
than the indicated kilowatts. It has been found necessar>',
however, to follow the indicated kilowatts to serve as a check
on the efficiency and condition of the units in general, from time
to time, as well as to determine what capacity would be required
for short interval peaks. The station voltage is also plotted as a
block curve across the face of the sheet.
The exciters from an individual group, and for each exciter
the voltage current and per cent gate opening are recorded.
Transformer records are Umited to the temperatures. These
are taken hourly, at which time the oil elevation is noted but not
recorded. If the transformer is not in service the column in
which the temperature is listed is left blank. If in service the
temperature is taken and recorded.
Under the item, " Floodgates " the total opem'ng of the flood-
gates in feet is recorded, rather than each one separately. This
record is maintained daily, the flow of the river at each of the
stations being followed very closely.
At the bottom of the sheet appear the daily readings of the
various generator and feeder watt-hour meters taken at mid-
night of each twenty-four hours. The following items are also
recorded at the bottom of the sheet: " Total Generated," or the
total output of the station for twenty-four hours; the " Maximum
Hour Time," or the maximum kw.-hr. of any particular hour
during the day; the " Maximum Kw. Time," or the maximum
indicated kilowatts at any particular instant; the " Average
Load," obtained by dividing the total kilowatt hours generated by
24; the "Load Factor," obtained by dividing the "Average
Load " by the " Max. Kw. Time"; the " Average Flow of the
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DAILY ^
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GENERATOR
H . GFNERATOR
GENFRAl
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LOG
— 191_.
GENERATOR j
GENERATOR I
ENTIRE STATION |
Time
A«»l
Ktlo-
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AMioI
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Kilo-
watt*
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Kmpma
Preaa-
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VMf
Total
PrM6-
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10
11
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Total
Total
Peak
Total
Average
Aver
nge
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*«•
R READINGS
TO LOCAL DWTRIBUTINO 6UB STATION J
STATION USE
ClKQit
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Total
3
lATA
JCHARQE 1
WHEEL DISCHARGE
AIR TEMPERATURE; HUMIDITY
.IL
A.M.
P.M.
1
Max. Temp.
Deg.P.
tim^m
Max. X8.rl
bX
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B^UNUSUAL OCCURRANCES
To face page 761.
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OPERATING AND MAINTENANCE INSTRUCTIONS 751
Hiver in Cubic Feet per Second," calculated each day and con-
verted into *' Available Capacity of River," which is shown in
kw.-hr.; the "Available Capacity of Power House," shown in
kw.-hr., and determined by calculating the capacity of the ma-
chines under the average head for twenty-four hours; the " Kw.-
hr. Lost," or the diflference between what was actually generated
by the machines and what could have been secured from the river
during the same number of hours.
Any important notes of operation are entered on the back
of each day's log sheet. These notes, together with certain rec-
ords for log sheets, are also entered each day in a log book kept
on the operator's desk at all times for reference purposes. Weather
conditions and temperatures are recorded four times daily, at
midnight, 6 a.m., noon, and 6 p.m. A rain guage is provided on
the roof of the station from which records of precipitation covering
each twenty-four hours are obtained.
A record form of a large power gfsrstem in the West is shown
in Fig. 408.
Operating and Maintenance Instructions. Several of the
larger hydro-electric companies have developed very successful
systems of systematizing the operating details and properly
training the operating force, thus obtaining a considerable im-
provement over the methods ordinarily in use. A description of
the practice by one of the larger hydro-electric companies, as
given in the 1917 Report of the N.E.L.A. Committee on Prime
Movers, should therefore be of interest.
Operating Instructions. The operation of the plant is covered
by instructions which express in writing not oply what must
be done in the case of certain emergencies, but also describe how
the plant must be run imder normal conditions.
These " Permanent Instructions," as they are called, are
divided as follows:
General Station Rules, etc.
Safety Rules.
Electrical Operation — Normal and Abnormal.
Hydraulic Operation — ^Normal and Abnormal.
Duties of Operating Men.
Record and Forms.
Electrical Maintenance.
Hydraulic Maintenance.
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752 ORGANIZATION AND OPERATION
The " General Station Rules " govern the employees as a
body and are concerned with such things as wages, hours, leaves
of absence, vacations, and miscellaneous matters regarding the
conduct of the men in the stations.
Under "Safety Rules" come the usual regulations provid-
ing for the safety of the men working aroimd electrical and
mechanical equipment. Safety Rules also include rules for the
" Hold-OflF " system, by which the men are protected while
working on apparatus.
Under the " Electrical Operating Instructions " are two
divisions — normal and abnormal. The normal instructions deal
with every-day conditions, and their aim is to specify how the
apparatus shall be handled, what the connections shall be, and
how the various other routine operations of the station shall be
performed. The abnormal instructions are developed from cases
of trouble that have been experienced in the station, and such as
might occur. They include general instructions on handling
trouble, instructions on various line complications and on gen-
erator, transformer, bus and oil switch trouble. They also in-
clude the handling of the station during lightning storms and
low-water season operation, when particular attention must be
paid to efficiency, as well as instructions for the flood season,
and ice and sleet.
The " Hydraulic Operating " instructions are similwly
divided into normal and abnormal.
The section on " Records and Forms " includes instructions
on the use of the various forms, such as log sheets, graphic meter
records, and also on record and tabulation work. The section
on "Duties" specifies the particular duties of each operating
attendant. The " Electrical and Hydraulic Maintenance "
instructions cover such matters as the cleaning, inspection and
repair of apparatus.
These instructions have been found very valuable in crystal-
lizing the operation of the plant, making it more automatic and
independent of the personal element. They have also made it
considerably easier for those in charge to break in and instruct
new men; under them all operators tend to do given things in
the same way, a way which has been determined by study and
experiment to be the best way. An attendant can be transferred
from one shift to another without having to learn new methods.
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OPERATING AND MAINTENANCE INSTRUCTIONS 753
He will know that all operations, such as the starting and stop-
ping of generators, handling of switches, etc., will be carried
on exactly the same as on any other shift.
A good example of the result of study and system in oper-
ating methods is the comparatively simple matter of starting
up a generator. Before the instructions were put into effect the
time for starting a unit would vary from IJ to 3 or 4 minutes,
depending upon the individual operators and hydraulic attend-
ants. A study was made of the various operations and the time
taken to start a generator, and it was found that by having the
several attendants do their work independently, without waiting
for one another and without waiting for verbal instructions,
operations could be performed simultaneously which were for-
merly done successively. It had been the practice for the gov-
ernor man to make an imspection of the unit and for the opera-
tor to try out the oil switch, before the disconnectors were
closed. These unnecessary precautions were eliminated by in-
sisting that every unit and oil switch, in fact every part of the
equipment, be ready for immediate service at any moment, unless
it was covered by a *' hold-off " tag. The operation of starting
the unit on the governor also took time, and it is now the practice
to start the unit on hand control. The best way of manipulating
the gates to get the unit to accelerate more rapidly was observed,
and the governor attendants instructed accordingly.
It has also been made the practice to always start the units
quickly. The normal time now taken to start a unit is about
sixty seconds. The record time on a stop-watch drill test was
forty-one seconds, while in an actual emergency due to the loss of
a steam turbine unit on the system, and resulting in frequency
disturbance, a unit was paralleled and frequency brought to nor-
mal in thirty-five seconds after the disturbance occurred. In
another case two units were paralleled and frequency brought to
normal IJ minutes after the trouble.
An important feature of this quick starting is that it must
accelerate very quickly at first and pass through the synchronous
point very slowly. While the unit is accelerating the operator
must send his assistant to close the disconnecting switches and
have his synchronizing and voltmeter plugs in position before
the unit comes up to speed, so that as soon as the speed passes
through the synchronous point he gets his " shot." If he misses
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754 ORGANIZATION AND OPERATION
the first " shot " there will be a delay of from fifteen to twenty
seconds in bringing the speed back again, hence it is important
that the governor man manipulate the speed properly and be ready
to take the first shot when it presents itself.
Another point is to have the field rheostat in the proper
position for normal voltage, so that no time is lost in manipu-
lating the voltage. In cases of serious emergency where there
have ahready been interruptions to service or serious fluctuations
of voltage, or where the hydro-electric plant has separated from
the steam plant, the operator is instructed to parallel without the
use of the synchroscope, in order to save time. In this case he
opens the field of the incoming generator while closing its oil
switch and inmiediately closes the field afterwards. Under the
special conditions of high reactance of the tmits employed in the
plant described, this results in a 5 to 8 per cent fluctuation in
voltage in case the incoming unit (of approximately 10,000-kw.
capacity) is 20 per cent less than the capacity already tied in on
the bus.
Maintenance. The first task was to get up a machinery index
wherein is listed the station apparatus. A letter size sheet, or
several of them, are devoted to each piece of apparatus and upon
these sheets are noted data or reference directions in regard to the
apparatus, also references to a machinery repair log book, where
may be obtained detailed information with regard to the repair
history of the piece of apparatus.
In regard to the maintenance of the station, the operating
attendants do a large amount of this work and practically all of
.the inspection. Instructions for cleaning and inspection have
been very carefully drawn up and the operating men instructed
in the proper care of the apparatus. Every piece of apparatus
in the station has been considered individually and it has been
determined just how often it needs to be inspected and how
thorough an inspection is needed. All the equipment is tabulated
on charts, which show the periodicity of the inspections and
provide spaces which are to be filled in with the date and initials
of the attendant who made the inspection. These charts are
posted on the wall in a conspicuous place and make an excellent
graphical record of the status of the inspections of the entire
station up to date. Any delayed inspections are, naturally,
inquired into.
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OPERATING AND MAINTENANCE INSTRUCTIONS 755
In addition to the current inspections by the operating men
chere is also a more thorough inspection made as often as may
be necessary, but at less frequent intervals, by the electrical
inspector and hydraulic inspector. The inspection work for these
men also is laid out on schedule drawn up in the form of charts
and the date of inspection similarly noted. This gfystem of keep-
ing track of inspections has been the result of much experi-
menting and investigation of the methods of other companies.
The card index system, which is ordinarily used, does not have
the advantage of immediate accessibiUty and becomes very bulky
when each individual piece of apparatus in the station is included.
An ordinary manifold note book is used for trouble reports; the
original goes to the office to note that the inspection was made
and later is placed on file. If the apparatus is found to be out of
order a " Trouble Report " is made out on a regular form, space
being provided for the report of the man who is to remedy the
trouble, and also for further report or remarks from the Elec-
trical or Hydraulic Inspector. In these remarks the inspector is
supposed to give assurance that the trouble will not occur again,
or state what is necessary to be done to prevent its reoccurrence.
These reports are filed and later become valuable in eliminating
troublesome features of design, when new apparatus is to be
designed or purchased.
Assignment of Apparatus. Another thing which facilitates the
inspection and cleanliness of the apparatus is the assignment of
every particular piece of apparatus in the station to some particu-
lar person. Each attendant has his own particular apparatus
for which he is responsible, which he must keep clean and in proper
operating condition. When defects occur in this equipment he
will either remedy them himself or report them on a " Trouble
Report." If the apparatus is in bad condition it is this man whose
attention is called to it, and if it is kept in exceptionally good
condition it is he who receives the credit. An attendant who is
inclined to be delinquent in attention to his apparatus soon finds
that his equipment compares unfavorably with the adjacent
equipment and will naturally remedy it without its having to be
brought to his attention by his superior.
Exposed tool boards are mounted at different points in the
station so that attendants have available all they need in the way
of tools for making such repairs as they are able to take care of
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756 ORGANIZATION AND OPERATION
without the assistance of the regular maintenance department.
By being permitted to repair their own apparatus the operating
attendants become more familiar with its details and learn better
how to operate it and take operating care of it, and are given an
interesting occupation, in addition to saving the time of the
maintenance men in attending to minor repairs.
The aim is to substitute preventive maintenance for breaking
down repairs. The result of this inspection and maintenance
system has been that the apparatus is kept in better condition,
and this has been accomplished with the minimum of attention
on the part of superiors, as the system is more or less automatic
in its workings. At the same time, the reports and schedules
give the superior very definite knowledge of the condition of his
equipment. All this work being laid out before the man in the
form of instructions reUeves the superior of continually correcting
new men and instructing them in how things are supposed to
be done. It also eliminates dependence on word-of-mouth
transmission of instructions from one man to another.
This systemization tends to minimize the possibility of
neglect of maintenance work on apparatus, and by scheduling
the work as to time and making necessary the planning of the
work to get it through in that period, there is less time lost in
doing the maintenance jobs or between jobs, and the maintenance
or operating shifts are thus able to turn out more work and better
work.
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APPENDIX I
REFERENCES TO DESCRIPTIONS OF AMERICAN
HYDRO-ELECTRIC POWER SYSTEMS
Abbreviation op Titlfs of Periodicals
American Institute of Electrical Engineers A.I.E.E.
American Institute of Mining Engineers A.I.M.E.
American Society of Civil Engineers A.S.C.E.
American Society of Mechanical Engineers A.S.M.E.
Canadian Electrical News Can. Elec. NewB
Canadian Engineer Can. Engr.
Electrical Age Elec. Age
Electrical Engineering (formerly Southern Electrician) Elec. Engng.
Electrical Record Elec. Rec.
Electrical Review & Western Electrician Elec. Rev.
Electrical World Elec. Wld.
Electric Journal Elec. Jour.
Engineering News Eng. News
Engineering Record Eng. Rec.
General Electric Review Gen. Elec. Rev.
Journal of Electricity, Power & Gas Jour, of Elec.
Power Power
Southern Electrician So. Elctn.
Western Engineering West. Engng.
Alabama Power Company:
Elec. Wld September 13, 1913
Elec. Engng January, 1914
Eng. Rec April 4, 1914
Elec. Wld May 30, 1914
Power August 4, 1914
A.S.C.E September, 1914
Elec. Engng March, 1915
Elec. Engng June, 1915
Gen. Elec. Rev June, 1916
Albany Power & Manufacturing Company, Georgia:
Elec. Wld June 16, 1906
American River Electric Company, California:
Jour, of Elec February, 1904
757
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758 APPENDIX I
Anglo-Newfoundknd Develoiuneiit Company:
Eng. Rec July 22, 1911
Animas Power & Water Company, Colorado:
Eng. News January 4, 1906
Eng. Rec April 14, 1906
Elec. Rev April 21, 1906
Anthony Falls Water Power Company, Minnesota:
Eng. Rec May 29, 1909
Appalachian Power Company, West T^rginia:
So. Electn November, 1912
Elec. Wld November 30, 1912
Power March 25, 1913
Apple River Power Company, Wisconsin:
Elec. Wld December 8, 1800
Eng. News October 12, 1905
Arkansas Valley Railway, Light & Power Company, Colorado:
Jour, of Elec June 5, 1915
Arizona Power Company:
Elec. Wld .August 18, 1910
Elec. Wld. .August 25, 1910
Eng. Rec August 20, 1910
Jour, of Elec June 5, 1915
Athens Railway & Electric Company, Georgia:
Power March 26, 1912
Atlanta Water & Electric Power Company, Georgia:
Eng. Rec April 23, 1904
Elec. Wld December 31, 1904
Auglaize Power Company, Ohio:
Power February 20, 1912
Elec. Wld November 1, 1913
Eng. Rec March 7, 1914
Attgusta-Aiken Railway & Electric Company, South Carolina:
Elec. Engng April, 1914
An Sable Electric Company, Michigan:
Elec. Wld April 13, 1912
Elec. Wd April 20, 1912
Eng. News May 16, 1912
Austin Power Development, Texas:
Elec. Rev May 22, 1915
Elec. Wld June 5, 1915
Eng. News June 10, 1915
Bangor Power Company, Maine:
Elec. Rec May, 1914
Bar Harbor & Union River Power Company, Maine:
Elec. Rec May, 1914
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APPENDIX I 759
Bear Lake Power Company, Idaho:
Jour, of Elec May 17, 1913
Belton Power Company, South Carolina:
Elec. Wld December 15, 1906
Eng. Rec December 15, 1906
Bend Water, Light & Power Company, Oregon:
Jour, of Elec October 11, 1913
Black Hills Traction Company, South Dakota:
Eng. Rec Nov. 16, 1907
Black River Falls Municipal Development, Wisconsui:
Elec. Wld June 1, 1911
Blue Earth Hydro-Electric Development, Minnesota:
Eng. Rec August 26, 1911
Braden Copper Company, Chile:
Eng. Rec September 28, 1912
Eng. News May 22, 1913
British Columbia Electric Railway Company:
Jour, of Elec June 6, 1915
British Railway, Light & Power Company, Oregon:
Eng. Rec .' March 2, 1912
Elec. Wld July 13, 1912
BuU Run Hydro-Electric Development, Oregon:
Eng. Rec January 18, 1913
Burlington Light & Power Company, Vermont:
Elec. Wld Sept. 12, 1914
Calgary Power Company, Canada:
Elec. Wld December 23, 1911
Eng. Rec February 7, 1914
Elec. Wld April 11, 1914
Jour, of Elec December 18, 1916
Eng. Rec January 15, 1916
Eng. Rec January 22, 1916
Power March 14, 1916
California Gas & Electric Company:
See Pacific Gas & Electric Company.
California-Oregon Power Company:
Jour, of Elec February 22, 1913
Eng. Rec June 7, 1913
Jour, of Elec June 5, 1915
Canadian Electric Light Company:
Elec. Wld June 15, 1901
Can. Elec. News June, 1902
Eng. News May 7, 1903
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760 APPENDIX I
Cimadkn Light & Power ComiMmy:
Can. Mec. News September, 1911
Eng. Rec April 6, 1912
Elec. Wld August 3, 1912
Caaadian-Niegiuw Power Company:
Can. Engr November, 19Q2
Elec. Rev January 3, 1903
Elec. Wld January 7, 1905
Elec. Rev December 2, 1905
Can. Elec. News September, 1907
A.S.C.E August, 1908
Elec. Jour June, 1914
Carolina Power & Light Company:
Elec. Wld May 30, 1914
Carp River Hydro-Electric Development, Michigan:
Eng. Rec November 23, 1912
Cedars Rapids Mfg. & Power Company, Canada:
Can. Elec. News February 1, 1913
Eng. Rec October 25, 1913
Can. Elec. News June 15, 1914
Eng. Rec July 18, 1914
Eng. Rec July 25, 1914
Elec. Wld February 13, 1916
Eng. News March 25, 1915
Eng. News April 1, 1915
Can. Elec. News March 1, 1916
Can. Elec. News March 15, 1916
Gen. Elec. Rev June, 1916
Can. Engr Feb. 15, 1917
Central Colorado Power Company:
Eng. Rec June 25, 1910
Elec. Wld June 23, 1910
Elec. Wld June 30, 1910
Elec. Wld July 14, 1910
Eng. Rec July 30, 1910
A.I.E.E June, 1911
Elec. Wld October 7, 1911
Elec. Wld June 1, 1912
Jour, of Elec June 5, 1915
Central Georgia Power Company:
Eng. Rec AprU 17, 1909
Eng. Rec May 14, 1910
Elec. Wld April 27, 1911
So. Electn May, 1911
Elec. Rev July 22, 1911
Elec. Wld. September 16, 1911
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APPENDIX I 761
Hec. Wld Januaiy 26, 1913
Elec. Wld May 30, 1914
Central Maine Power Company:
Elec. Wld December 15, 1019
Elec. Rec June, 1914
Elec. Wld June 3, 1916
Cerro de Pasco Mining Company, Peru:
Eng. & Mining World April 3, 1915
Chasm Power Company, New Tork:
Elec. Wld November 21, 1903
Chattanooga & Tennessee River Power Company:
Eng. Rec February 15, 1913
Elec. Engng August, 1913
Elec. Wld November 15, 1913
Elec. Rev November 22, 1913
Power December 2, 1913
Elec. Wld May 30, 1914
Gen. Elec. Rev August, 1916
Eng. Rec September 23, 1916
Chile Exploration Company:
Elec. Wld January 2, 1915
Elec. Wld January 9, 1915
Chippewa & Flambeau Improvement Company, Wisconsin:
Eng. Rec April 5, 1913
Chippewa Railway, Light & Power Company, ^sconsin:
Elec. Wld December 22, 1910
Chittenden Power Company, Vermont:
Elec. Wld December 2, 1905
Eng. Rec December 9, 1905
Cia Docas de Santos, Brazil:
Elec. Wld March 16, 1912
Gen. Elec. Rev October, 1912
Cleveland Cliffs Iron Company, Michigan:
Eng. & Mining Journal February, 1912
Elec. Engng May, 1913
Coast Counties Gas & Electric Company, California:
Jour, of Elec June 5, 1915
Coast Valley Gas & Electric Company, California:
Jour, of Elec June 5, 1915
Cobalt Power Company, Canada:
Can. Elec. News September, 1910
Eng. Rec March 4, 1910
Cohoes Company, New Tork:
Eng. Rec March 20, 1915
Eng. Rec March 27, 1915
Elec, Wld March 20, 1916
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782 APPENDIX I
Gen. See. Rev! .May, 1916
Eng. Rec May 29, 1915
Power Oct. 6, 1915
Colorado River Power Company, Texas:
So. Electn June, 1911
Elec. Wld June 8, 1911
CoUierBtflle Hydro-Electric Development, New Tork:
Eng. Rec March 7, 1908
Colorado Springs Light, Heat & Power Company:
Elec. Wld October 14, 1911
Coltsmtms Mills Company, South Carolina:
Eng. Rec August 29, 1903
Cohsmtms Power Company, Georgia:
Eng. Rec January 16, 1904
Elec. Engng June, 1913
Elec. Wld May 30, 1914
Concord Electric Company, New Hampshire:
Power May 25, 1909
Connecticut Power Company:
Elec. Wld March 3, 1917
Connecticut River Power Company:
Eng. Rec March 27, 1909
Eng. Rec. April 3, 1909
Elec. Wld September 9, 1909
Power September 28, 1909
Elec. Wld May 25, 1911
Power July 25, 1911
Gen. Elec. Rev October, 1911
Gen. Elec. Rev May, 1916
Connecticut River Transmission Company:
Elec. Wld October 4, 1913
Elec. Wld October 11, 1913
Gen. Elec. Rev June, 1914
Consumers Power Company, Minnesota:
Elec. Wld April 13, 1911
Elec. Wld June 22, 1911
Eng. Rec August 26, 1911
Coquitlam-Buntzen Hydro-Electric Power Development, Canada:
Eng. Rec September 21, 1912
Elec. Wld July 24, 1915
Consolidated Lighting Company of Montpelier, Vermont:
Elec. Wld January 4, 1908
Elec. Rev February 1, 1908
Cumbeiland County Power & Light Company, Maine:
Elec. Rec November, 1914
Elec. Wld February 27, 1915
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APPENDIX I 763
Dakota Power Company:
Elec. Wld August 5, 1911
Dan River Power & Mfg. Company, ^Hrginia:
Eng. Rec September 3, 1904
Desert Power & Water Company, Arizona:
Jour, of Elec June 5, 1915
Diana Paper Company, New Tork:
Eng. Rec January 6, 1912
Dominion Power & Transmission Company, Canada:
Elec. Wld March 9, 1911
Eagle River Electric Power Company, Oregon:
Jour, of Elec June 5, 1915
East Creek Electric Light & Power Company, New Tork:
Eng. Rec May 27, 1911
Elec. Wld August 31, 1912
Gen. Elec. Rev September, 1912
Eastern Oregon Light & Power Company:
Jour, of Elec June 5, 1915
Edison Sault Electric Company, Michigan:
Eng. Rec November 2, 1907
Electric Development Company of Ontario:
Eng. News November 9, 1905
Elec. Rev July 28, 1906
City of EUensbnrg, Washington:
Jour, of Elec January 2, 1916
Empire District Electric Company, Kansas:
So. Electn June, 1911
Empire Gas & Electric Co., Waterloo, N. T.:
Power March 28, 1916
Empire State Power Company, New Tork:
Eng. Rec August 10, 1901
Erindale Power Company, Canada:
Elec. Wld May 4, 1911
Eugene Municipal Power Development, Oregon:
Elec. Wld May 17, 1913
Fall Mountain Electric Company, Vermont:
Elec. Rec October, 1914
Garvins Falls Power Development, New Hampshire:
Elec. Wld January 17, 1903
Eng. Rec January 24, 1903
Eng. Rec May 28, 1904
Elec. Wld May 28, 1904
Elec. Wld June 4, 1904
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764 APPENDIX I
Geofgk-CaroUiia Power Company:
Power January 20, 1914
Elec. Engng April, 1914
Elec. Engng August, 1915
Elec. Wld November, 20, 1915
Elec. Wld November 27, 1915
Geoigia Railway & Power Company:
So. Elctn September, 1912
Elec. Rec April 12, 1913
Elec. Wld December 20. 1913
Elec. Wld December 27, 1913
Power January 27, 1914
Eng. NewB January 29, 1914
Eng. Rec March 21, 1914
Eng. Rec March 28, 1914
Eng. News April 16, 1914
Elec. Engng May, 1914
Elec. Engng June, 1914
Elec. Engng July, 1914
Elec. Wld May 30, 1914
Gen. Elec. Rev June, 1914
Gen. Elec. Rev July, 1914
A.T.E.E October, 1916
Elec. Wld Jan. 8, 1916
Grand Falls Power Company, New Brunswick:
Elec. Wld March 4, 1909
Grand Rapids-Mtiskegon Power Company, Michigan:
Elec. Wld November 3, 1906
Eng. Rec October 19, 1907
Elec. Wld February 4, 1909
Gnmgeville Electric lA0it & Power Company, Idaho:
Jour, of Elec June 5, 1915
Great Falls Power Company, Montana:
Eng. Rec Mareh 12, 1910
Gen. Elec. Rev April, 1910
Gen. Elec. Rev May, 1910
Elec. Wld July 6, 1912
Great Falls Power Development, New Jersey:
Eng. Rec February 22, 1913
Great Northern Paper Company, Maine:
Power February 9, 1909
Great Northern Power Company, Minnesota:
Elec. Wld July 28, 1906
Eng. Rec September 7, 1907
Eng. Rec September 14, 1907
Eng. News December 26, 1907
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APPENDIX I 765
Power August 11, 1908
Elec. Wld March 25, 1916
Great Northern Railway Company, Washington:
Eng. Rec • October 30, 1909
Gen. Elec. Rev August, 1910
Jour, of Elec January 2, 1915
Great Western Power Company, California:
Elec. Wld August 26, 1909
Elec. Wld September 16, 1909
Jour, of Elec April 9, 1910
Eng. Rec July 16, 1910
So. Mectn February, 1913
Elec. Wld May 29, 1915
Jour, of Elec June 5, 1915
Greenville-Carolina Power Company:
Eng. Rec October 6, 1906
Guanajuato Power & Electric Company, Mexico:
Elec. Wld August 6, 1904
Elec. Wld August 13, 1904
Elec. Wld August 20, 1914
Hamilton Cataract Power, Light & Traction Company, Canada:
Elec. Rev September 2, 1905
Hanford Irrigation & Power Company, Washington:
Elec. Rev .July 29, 1911
Jour, of Elec January 2, 1915
Hannawa Water Power Company, New Tork:
Elec. Wld April 21, 1906
Hartford Electric Light Company, Connecticttt:
Elec. Wld March 8, 1902
Holton Power Company, California:
Jour, of Elec June 5, 1915
Holyoke Water Power Company, Massachusetts:
Elec. Wld September 16, 1906
Eng. Rec September 15, 1906
Homestake Mining Company, South Dakota:
Jour, of Elec August 29, 1914
Hortonia Power Company, Vermont:
Elec. Rev August 12, 1916
Hudson River Water Power Company, New Tork:
Eng. Rec March 8, 1902
A.LM.E February, 1903
Eng. News June 18, 1903
Eng. Rec June 27, 1903
Elec. Wld June 27, 1903
Elec. Wld October 24, 1903
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766 APPENDIX I
Elec. Wld May 14, 1904
Elec. Wld June 11, 1904
Eng. Rec March 4, 1905
Haronum Company, Canada:
^g. News July 18, 1907
Eng. Rec August 3, 1907
Hydro-Electric Commission of Ontario, Canada:
Can. Elec. News November, 1910
Elec. Rev December 31, 1910
Elec. Wld January 6, 1912
Elec. Wld January 13, 1912
Elec. Wld January 20, 1912
Elec. Wld January 27, 1912
Can. Engr July 25, 1912
Can. Elec. News April 15, 1914
Eng. Rec June 7, 1917
Conmiission Reports
Idaho Consolidated Power Company:
Elec. Rev June 2, 1906
Idaho Falls Mwiicipal Development:
Elec. Wld Sept. 21, 1902
Idaho Power & Light Company:
Jour, of Elec * June 5, 1915
Elec. Wld Aug. 19, 1916
Indiana & Michigan Electric Company:
Elec. Rev March 4, 1911
Inland Portland Cement Company, Washington:
Jour, of Elec January 2, 1915
Ironwood & Bessemer Railway & Light Company, Michigan:
Eng. Rec February 28, 1914
Isthmian Canal Commission, Gatun, Panama:
Gen. Elec. Rev July, 1914
Jim Creek Water, Light & Power Company, Washmgton:
Joiir. of Elec January 2, 1915
Juniata Water & Water Power Company, Pennsylvania:
Elec. Wld December 22, 1906
Elec. Wld January 20, 1910
Kakabeka Falls Development, Canada:
Elec. Wld January 26, 1907
Can. Elec. News September, 1907
Kaministquia Power Company, Canada:
Elec. Wld January 26, 1907
Can. Elec. News February 15, 1916
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APPENDIX I 767
Kenora Hydraulic Power Developmenty Canada:
Eng. Rec July 18, 1908
Lachine Rapids, Hydraislic & Land Company, Canada:
Elec. Rev November 21, 1903
La Crosse Water Power Company, Wisconsin:
Eng. Rec May 30, 1908
Elec. Wld March 31, 1910
Elec. Wld October 14, 1911
Lanrentian Power Company, Canada:
Can. Engr October 22, 1914
Can. Elec. News August 1, 1916
Can. Elec. News June 15, 1917
Lewiston & Aobum Company, Maine:
Elec. Wld September 20, 1902
Elec. Wld April 8, 1906
Lewiston-Clarkson Improvement Company, Washington:
Elec. Wld March 28, 1914
Jour, of Elec June 5, 1915
Los Angeles Aqueduct:
Eng. News March 24, 1910
Power September 26, 1911
Elec. Wld February 10, 1912
Eng. Rec February 3, 1912
Eng. Rec August 23, 1913
Eng. Rec November 1, 1913
Jour, of Elec June 24, 1916
Madison River Power Company, Montana:
Elec. Wld December 30, 1909
Maumee Valley Electric Company, New York:
Elec. Wld March 2, 1911
Medina Irrigation Company, Texas:
Eng. Rec October 18, 1913
Menominee & Marinette Light & Traction Company:
Eng. Rec January 14, 1911
Elec. Wld January 17, 1914
Metropolitan Water Works, Massachusetts:
Power November 26, 1912
Mexican Light & Power Company:
Eng. Rec June 9, 1906
A.S.C.E January, 1907
Mexico Northern Power Company:
Elec. Wld July 25, 1914
Michigan Power Company:
Elec. Rev December 25, 1909
Digitized by
Google
768 APPENDIX 1
MIchwiein Power Company, Mexico:
Eag. Ree August 27, 1910
Eng. Rec Januaiy 21, 1911
MJimeApolis General Electric Company, Minnesota:
Eng. Rec March 3, 1906
Eng. Rec June 29, 1907
Eng. Rec July 6, 1907
Elec. Wld. July 6, 1907
Elec. Wld September 7, 1907
Mississippi River Power Company, Iowa:
Eng. Rec August 5, 1911
Elec. Wld August 6, 1911
Elec. Wld October 28, 1911
Elec. Wld May 31, 1912
Elec. Wld Sept. 7, 1912
Eng. Rec November 16, 1912
So. Electn JanXiaiy, 1913
Elec. Wld April 26, 1913
Elec. Wld • May 31, 1913
Eng. Rec July 26, 1913
Power August 5, 1913
Elec. Rev Sept. 15, 1913
Eng. News November 13, 1913
Gen. Elec. Rev February, 1914
Gen. Elec. Rev April, 1914
Elec. Engng August, 1914
Eng. Rec September 18, 1915
Eng. Rec October 9, 1915
Missouri River Power Company, Montana:
A.S.C.E 1903
Mokawk Hydro-Electric Company, New Toric:
Elec. Wld October 7, 1911
Eng. Rec November 26, 1911
Montana Power Company:
Jour, of Elec June 5, 1915
Elec. Wld June 12, 1915
Gen. Elec. Rev November, 1916
Elec. Rev July 14, 1917
Mount Hood Railway & Power Company, Oregon:
Elec. Wld March 22, 1913
Elec. Wld March 29, 1913
Mt Whitney Power & Electric Company, California:
Jour, of Elec December 27, 1913
Jour, of Elec June 5, 1915
Elec. Wld June 24, 1916
Digitized by
Google
APPENDIX I 769
»
Keyada-CaliforoiA Power Company:
Eng. Rec March 6, 1909
Elec. Wld October 17, 1914
Elec. Wld October 24, 1914
Hec. Wld October 31, 1914
Elec. Wld , November 7, 1914
Elec. Wld November 14, 1914
Elec. Wld November 21, 1914
Elec. Wld November 28, 1914
Elec. Wld December 5, 1914
Elec. Wld December 12, 1914
Elec. Wld December 19, 1914
Jour, of Elec June 5, 1915
Nevada Power & Milling Company, California:
Elec. Wld June 30, 1906
Eng. Rec June 30, 1906
NevadaValleys Power Company, California:
Jourrof Elec June 6, 1916
New England Fish Company, Alaska:
Elec. Wld January 13, 1910
New England Power Company, Masaachnsetts:
Elec. Wld December 16, 1911
Elec. Wld December 28, 1912
Power February 25, 1913
New River Light & Power Co., North Carolina:
Elec. Wld .June 24, 1916
Now Milford Power Company, Connectioat:
Elec. Wld February 13, 1904
Niagara Falls Hydro-Electric Power & Mfg. Company:
Elec. Wld :;...# November 25, 1905
Niagara Falls Power Company:
Eng. Rec February 16, 1901
A.I.E.E June, 1902
Eng. News October 2, 1902
Elec. Rev Sept. 12, 1903
Eng. Rec November 21, 1903
Eng. Rec October 18, 1913
Nipissing Power Company, Canada:
Elec. Wld "•"• August 12, 1911
North Carolina Electric Power Company:
Elec. Wld February 17, 1912
So. Electn April, 1912
North Coast Power Company:
Jour, of Elec June 16, 1917
Digitized by
Google
770 APPENDIX I
Northern California Power Company:
Elec. Wld September 10, 1904
Elec. Wld September 17, 1904
Elec. Wld ; September 24, 1904
Elec. Wld October 1, 1904
Jour, of Elec August 6, 1910
Jour, of Elec November 4, 1911
Elec. Wld February 3, 1912
Elec. Wld.. . : May 29, 1915
Jour, of Elec June 5, 1915
Northern Colorado Power Company:
Elec. Wld September 30, 1911
Northern Hydro-Electric Power Company, Wisconsin:
Elec. Wld November 24, 1910
Northern Idaho & Montana Power Company:
Elec. Rev March 18, 1911
Jour, of Elec June 5, 1915
Jour, of Elec June 5, 1915
Northern Illinois Light & Traction Company:
Elec. Wld September 29, 1910
Eng. Rec February 24, 1912
Elec. Wld February 24, 1912
North Mountain Power Company, California:
Jour, of Elec February, 1905
Northern Ohio Traction & Light Company:
Elec. Wld August 22, 1914
Northern Ontario Light & Power Company, Canada:
Can. Elec. News 1914
North Washington Power & Reduction Company, Washington:
Jour, of Elec January 2, 1915
Northwestern Electric Company, Oregon:
Elec. Wld August 9, 1913
Eng. Rec October 11, 1913
West. Engng November, 1913
Jour, of Elec December 6, 1913
Jour, of Elec January 2, 1915
Jour, of Elec June 5, 1915
Olympia Light & Power Company, Washington:
Jour, of Elec January 2, 1915
Olympic Power Company, Washington:
Jour, of Elec January 2, 1915
Jour, of Elec June 5, 1915
Jour of Elec October 9, 1915
Jour, of Elec October 16, 1915
Digitized by
Google
APPENDIX I 771
Ontario Power Company, Canada:
A.I.E.E June, 1906
Elec. Wld August 26, 1906
Elec. Wld Sept. 2, 1906
Elec. Wld Sept. 9, 1906
Elec. News November 9, 1905
Can. Elec News November, 1910
Elec. Rev December 31, 1910
Can. Elec. News April 15, 1914
Oregon Power Company:
Jour of Elec June 5, 1915
Oro Electric Corporation, California:
Elec. Wld May 29, 1915
Jour, of Elec June 5, 1915
Ozark Power & Water Company, Missouri:
Eng. Rec August 2, 1913
Elec. Engng November, 1913
Gen. Elec. Rev September, 1914
Pacific Coast Power Company, Washington:
Eng. News April 11, 1912
Eng. News April 18, 1912
Eng. Rec April 13, 1912
Jour, of Elec April 13, 1912
Pacific Gas & Electric Company, California:
Eng. News August 10, 1905
Jour, of Elec , . .April 30, 1910
Power May 21, 1912
Elec. Wld June 1, 1912
Jour, of Elec ' March 15, 1913
Elec. Wld November 22, 1913
Jour, of Elec December 13, 1913
Eng. News December 11, 1913
Elec. Wld May 29, 1915
Jour, of Elec June 6, 1915
Elec. Jour June, 1915
Jour, of Elec September 30, 1916
Jour, of Elec March 15, 1917
Jour, of Elec April 15, 1917
Jour, of Elec May 1, 1916
Elec. Wld June 2, 1917
Jour, of Elec June 1, 2917
Jour, of Elec June 15, 1917
Pacific Light & Power Company, California:
Jour, of Elec November 12, 1910
Elec. Wld December 30, 1911
Jour, of Elec February 24, 1912
Digitized by
Google
772 APPENDIX I
Elec. Wld September 7, 1912
Eng. Rec iSeptember 14, 1912
Eng. News November 7, 1912
Elec. Wld January 3, 1914
Elec. Wld January 10, 1914
Eng. Rec January 10, 1914
Gen. Elec. Rev August, 1914
Elec. Wld December 9, 1916
Pacific Power & Light Company, Oregon:
Elec. Wld September 14, 1912
Jour, of Elec September 14, 1912
Jour, of Elec January 2, 1915
Jour of Elec June 6, 1915
Palmer Mills Development, Massachiisetts:
Eng. Rec June 24, 1911
Palmer Mountain Tnnnel & Power Company, Washington:
Elec. Wld July 21, 1906
Park Dam Conqumy, Iowa:
Eng. Rec July 6, 1912
Parr Shoals Power Company, South Carolina:
Power January 20, 1914
Elec. Engng April, 1914
Elec. Age October, 1915
Patapsco Electric & Mfg. Company, Maryland:
Elec. Wld August 3, 1907
Penn Iron Mining Company, Michigan:
Iron Age July 16, 1908
Peninsular Power Company, Wisconsin:
Eng. Rec May 24, 1913
A.I.M.E February, 1915
Elec. Jour July, 1916
Pennsylvania Water & Power Company:
Eng. News September 12, 1907
Eng. Rec September 21, 1907
Elec. Rev February 27, 1909
Eng. Rec May 28, 1910
Elec. Wld October 20, 1910
Elec. Wld May 4, 1911
Elec. Wld August 24, 1912
Eng. Rec. December 7, 1912
Power May 13, 1913
Eng. Rec March 20, 1915
A.I.E.E May, 1916
Philadelphia Hydro-Electric Company, Pennsylvania:
Elec. Wld December 29, 1910
Digitized by
Google
APPENDIX I 773
Pfabftnka Rivei Power Derelopment, Braxll:
Elec. Wld November 14, 1908
Pikes Peak Hydro-Blectric Company, Colontdo:
Eng. Rec July 19, 1902
Elec. Wld July 26, 1902
Eng. News January 1, 1903
Eng. Rec May 19, 1906
Elec. Wld May 26, 1906
Ffttsford Power Company, Vermont:
Power. April 13, 1915
Elec. Wld May 22, 1916
Eng. News July 1, 1916
Phmfledge River Power DeTelopment» Canada:
Eng. Rec September 20, 1913
Eng. Rec September 27, 1913
Eng. News October 23, 1913
Portfand Electric Company, Maine:
Elec. Wld October 12, 1907
Portland Railway, Light & Power Company, Oregon:
Eng. News June 27, 1907
Elec. Wld April 11, 1908
Elec. Wld April 18, 1908
Elec. Wld April 25, 1908
Elec. Wld December 23, 1911
Elec. Wld July 13, 1912
Jour of Elec April 6, 1912
Jour, of Elec January 4, 1913
Jour, of Elec January 2, 1915
Jour, of Elec June 5, 1915
Preaompscot Electric Company, Maine:
Eng. Rec November 2, 1912
Pueblo and Suburban Traction & Ligliting Company, Colorado:
Elec. Rev January 26, 1907
Paget Sound Ttaction, Liglit & Power Company, Washington:
Elec. Wld October 1, 1904
Elec. Wld October 8, 1904
Eng. Rec March 17, 1910
Eng. Rec January 13, 1912
Jour, of Elec April 13, 1912
Eng. Rec April 13, 1912
Eng. News April 11, 1912
Eng. News April 18, 1912
Elec. Wld June 1, 1912
Jour, of Elec June 1, 1912
Jour, of Elec January 2, 1915
Jour of Elec June 5, 1915
Digitized by
Google
774 APPENDIX I
Quebec-Jacqttes-Cartier Electric Company, Canada:
Elec. Wld June 9, 1900
Can. Elec. News June, 1902
Quebec Railway, Light & Power Company, Canada:
Can. Engr January, 1902
Can. Elec. News June, 1902
Raven Lake Portland Cement Company, Canada:
Elec. Wld April 2, 1904
Raystown Water Power Company, Pennsylvania:
Eng. Rec June 28, 1913
Rio de Janeiro Tramway, Light ft Power Company, Brazil:
Elec. Wld May 13, 1909
Elec. Wld August 12, 1909
Elec. Wld : . .April 26, 1913
Elec. Rev January 5, 1907
Roaring Fork Electric Light & Power Company, Colorado:
Elec. Rev Jan. 6, 1907
Rochester Railway & Light Company, New York:
Elec. Wld January 14, 1909
Elec. Wld January 28, 1909
Elec. Wld February 18, 1909
Power November 14, 1916
Rock Creek Power & Transmission Company, Oregon:
Elec. Wld September 3, 1904
Rockingham Power Company, North Carolina:
Elec. Rev March 14, 1909
Eng. Rec April 4, 1908
Rock River Hydro-Electric Development, Illinois:
Elec. Wld October 26, 1912
Rocky Ford Milling & Power Company, Kansas:
Elec. Wld November 3, 1910
Rogue River Electric Company, Oregon:
Jour, of Elec June 5, 1909
Rumford Falls Power Company, Maine:
Elec. Wld January 9, 1915
Rttsselville Water & Light Company, Arkansas:
Elec. Wld May 26, 1910
Salmon River Power Company, New Tork:
Eng. Rec October 11, 1913
Eng. Rec June 13, 1914
Elec. Wld June 13, 1914
Elec. Wld June 20, 1914
Power March 9, 1915
Digitized by
Google
APPENDIX I 775
Saoitary District of Chicago:
Elec. Rev February 8, 1908
Elec. Wld January 19, 1911
Elec. Rev December 5, 1914
Elec. Wld May 27, 1916
San Joaquin Light & Power Company, California:
Jour, of Elec November 28, 1908
Eng. Rec February 4, 1911
Eng. Rec February 11, 1911
Jour, of Elec May 11, 1912
Power July 16, 1912
Jour, of Elec June 5, 1915
Jour, of Elec June 10, 1916
Sao Paulo Tramway, Light & Power Company, Brazil:
Can. Elec. News May, 1906
Sault Ste. Marie Water Power Development:
Eng. News September 25, 1902
Elec. Wld September 27, 1902
Eng. Rec ' February 21, 1903
A.aC.E February, 1905
Eng. Rec November 2, 1907
Schenectady Power Company, New York:
Elec. Rev March 27, 1909
Gen. Elec. Rev April, 1909
Elec. Wld May 20, 1909
Eng. Rec July 24, 1909
Seattte Municipal Power Development, Washington:
Elec. Wld February 27, 1904
Elec. Wld June 1, 1912
Jour, of Elec .July 27, 1912
Jour, of Elec May 3, 1913
Jour, of Elec .January 2, 1915
Elec. Rev June 9, 1917
Seattle-Tacoma Power Company, Washington:
Eng. Rec March 17, 1910
Eng. Rec January 13, 1912
Sewalls Falls Development, New Hampshire:
Power .May 25, 1909
Shawinigan Water & Power Company, Canada:
Can. Engr April, 1901
Elec. Wld February 8, 1902
Can. Engr May, 1902
Can. Elec. News December, 1904
Elec. Wld May 4, 1912
Elec. Wld May 11, 1912
Digitized by
Google
776 APPENDIX I
Sierra Pacific Company, Nevada:
See Truckee River Gen. Electr. Company:
Sierra San Francisco Power Company, California:
Jour, of Elec August 21, 1909
Jour, of Elec September 4, 1909
Jour, of Elec February 3, 1912
Elec. Wld. . . . May 29, 1915
Jour, of Elec June 5, 1915
Similkameen Power Con^iany, Washington:
Jour, of Elec June 5, 1915
Sioux Falls Light & Power Company, South Dakota:
Elec. Wld April 22, 1909
Power June 22, 1909
So. Electn November, 1911
Snell Hydro-Electric Development, New Tork:
Eng. Rec February 17, 1912
Snow Mountain Water & Power Company, California:
Elec. Wld May 29, 1915
Jour, of Elec June 5, 1915
Sooth bend Electric Company, Michigan:
Elec. Wld May 30, 1903
Southern Aluminum Company, North Carolina:
Eng. News June 11, 1914
Southern California Edison Company:
Elec. Wld February 26, 1905
Elec. Wld March 4, 1905
Elec. Wld March 11, 1906
Elec. Wld March 25, 1905
Elec. Wld April 8, 1905
Elec. Wld August 10, 1907
Elec. Wld August 17, 1907
Elec. Wld August 24, 1907
Elec. Wld August 31, 1907
Eng. News December 24, 1908
Elec. Rev March 26, 1911
Elec. Rev April 1, 1911
Elec. Rev April 8, 1911
Power September 5, 1911
Jour, of Elec June 5, 1915
Elec. Wld Dec. 9, 1916
Southern Indiana Power Company:
Elec. Wld May 18, 1911
Eng. Rec February 10, 1912
Southern Power Company, North Carolina:
Elec. Wld July 23, 1904
Elec. Wld May 25, 1907
Digitized by
Google
APPENDIX I 777
Eng. Rec May 18, 1907
Eng. Rec May 26, 1907
Eng. Rec June 1, 1907
Elec. Jour December, 1907
A.I,E.E June, 1908
Power January 6, 1909
Eng. Rec April 3, 1909
Gen. Elec. Rev December, 1909
Elec. Wld March 24, 1910
Eng. Rec April 2, 1910
Mec. Jour April, 1911
Elec. Rev May 6, 1911
Elec. Wld July 1, 1911
Elec. Wld Sept. 16, 1911
Elec. Wld May 30, 1914
Else. Wld March 27, 1916
Power March 27, 1917
Eng. Rec Feb. 10, 1917
Eng. News Feb. 16, 1917
Soofhem Sierras Power Company, Nevada:
Elec. Wld August 10, 1912
Jour, of Elec July 5, 1913
Jour, of Elec July 12, 1913
Elec. Wld August 2, 1913
Elec. Wld October 17, 1914
Elec. Wld October 24, 1914
Elec. Wld October 31, 1914
Elec. Wld November 7, 1914
Elec. Wld November 14, 1914
Elec. Wld November 21, 1914
Elec. Wld November 28, 1914
Elec. Wld December 6, 1914
Mec. Wld December 12, 1914
Elec. Wld December 19, 1914
Jour, of Elec June 6, 1915
Elec. Wld April 14, 1917
Soufhem Utah Power Company:
Jour, of Elec June 6, 1915
Soufhem Wisconsin Power Company:
Elec. Rev August 28, 1909
Eng. Rec September 4, 1909
Eng. Rec September 18, 1909
Elec. Wld September 23, 1909
Spokane & Inland Empire R. R. Company:
Eng. Rec July 20, 1907
Eng. Rec October 10, 1908
Digitized by
Google
778 APPENDIX I
Elec. Wld October 10, 1908
Jour, of Elec January 2, 1915
Spooner Municipal Hydro-Electric Development, Wisconsin:
Eng. Rec August 29, 1908
Spring River Power Company, Kansas:
Elec. Rev November 18, 1905
St. Anthony Falls Water Power Company, Minnesota:
Eng. Rec. May 29, 1909
St Croix River Power Company, Wisconsin:
A.I.E.E November, 1900
Elec. Rev April, 1914
St Lawrence River Power Company, Canada:
Eng. Rec November 3, 1900
Eng. News February 21, 1901
Elec. Rev July 27, 1901
St Paul Gas & Electric Company, Wisconsin:
Elec. Rev April, 1914
City of Sturgis Municipal Hydro-Electric Development, Michigan:
Elec. Wld August 25, 1910
Eng. Rec March 2, 1912
Superior Portland Cement Company, Washington:
Eng. Rec August 22, 1908
Jour, of Elec January 2, 1915
Tacoma Municipal Power Development, Washington:
Eng. News March 17, 1910
Jour, of Elec March 1, 1913
Elec. Wld August 2, 1913
Jour, of Elec January 2, 1915
Tallassee Power Co., North Carolina:
Elec. Wld Nov. 25, 1916
Telluride Power Company, Utah:
(See also Utah Power & Light Company).
Eng. Rec March 14, 1908
Eng. Rec March 26, 1910
Elec. Wld November 18, 1911
Elec. Wld November 25, 1911
Elec. Wld December 9, 1911
Elec. Wld December 16, 1911
Elec. Wld December 23, 1911
Tennessee Power Company:
Eng. Rec June 22, 1912
Elec. Engng April, 1913
Elec. Engng February, 1914
Elec. Engng March, 1914
Power March 17, 1914
Digitized by
Google
APPENDIX I 779
Eng. Rec April 18, 1914
Eng. Rec May 16, 1914
Elec. Wld May 30, 1914
Elec. Age August, 1916
Towaliga Falls Power Company, Georgia:
Eng. Rec March 9, 1907
Toronto & Niagara Power Company:
Eng. Rec February 13, 1904
Can. Engr July, 1904
Eng. Rec October 8, 1904
Elec. Wld January 7, 1905
Eng. Rec April 8, 1905
Elec. Rev December 2, 1905
Trinity Gold Mining & Refining Company, California: .
Jour of Elec May 27, 1911
T^ckee River General Electric Company, Nevada:
Elec. Rev September 22 1906
Jour, of Elec November 30, 1912
Jour, of Elec June 5, 1915
Tamers Falls Power & Electric Company, Massachusetts:
Elec. Rec September, 1914
Gen. Elec. Rev March, 1917
Elec. Wld April 21, 1917
Elec. Rev February 17, 1917
Twin Falls Hydro-Electric Development, Michigan:
Eng. Rec May 24, 1913
Eng. Rec May 31, 1913
Uncas Power Company, Connecticut:
Eng. Rec November 21, 1908
Elec. Wld October 28, 1909
United Missouri River Power Company:
Eng. Rec August 13, 1 10
Eng. News October 20, 1910
United States Reclamation Service, Boise, Idaho:
Eng. Rec August 24, 1912
Power May 4, 1915
United States Reclamation Service, Snake River, Minidoka, Idaho:
Eng. Rec January 8, 1910
Eng. Rec February 19, 1910
Elec. Rev May 13, 1911
Elec. Rev May 20, 1911
Elec. Wld December 30, 1911
United States Redamation Service, Salt River, Arizona:
Eng. Rea December 31, 1910
Elec. Wld. , March 30, 1911
Digitized by
Google
780 APPENDIX I
A.LE.E April, 1911
Elec. Rev December 30, 1911
Eng. Rec January 1, 1916
Elec. Jour December, 1916
Utah County JAfjbt & Power Company:
Eng. Rec May 9, 1 908
Utah Light & Railway ComjMuiy:
Eng. Rec April 2, 1910
Utah Power & Lififht Company:
(See also Telluride Power Company).
Jour, of Elec May 8, 1914
Elec. Rev October 24, 1914
Elec. Wld June 5, 1915
Jour, of Elec. . .- June 5, 1915
Elec. Wld May 27, 1916
Utah Sugar Company:
Elec. Wld June 18, 1904
Elec. Wld June 25, 1904
Eng. News April 13, 1906
Utica Gas & Electric Company, New Tork:
Elec. Wld May 19, 1906
Elec. Rev February 23, 1907
Vancouver Island Power Company, Canada:
Elec. Wld October 12, 1912
Elec. Wld October 19, 1912
Eng. Rec October 19, 1912
Power November 9, 1916
Elec. Rev August 28, 1916
Elec: Age 9 February, 1916
Vancouver Power Company, Canada:
Eng. Kec July 13, 1907
Eng. Rec September 21, 1912
Elec. Wld July 24, 1916
Ventura Power Company, California:
Jour, of Elec June 6, 1915
Vermont Marble Company:
Elec. Wld July 29, 1911
Virginia Power Company, West Virginia:
Elec. Wld July 31, 1916
Warren Hydro-Electric & Gas Company, Ohio:
Elec. Wld Septemoer 2, 1909
Washhigton-Oregon Corporation:
Jour, of Elec ,,««... . Januaiy 2, 1916
Digitized by
Google
APPENDIX I 781
Washington Water Power Company:
Elec. Wld May 23, 1908
Mac. Wld May 30, 1908
Eng. Rec May 25, 1912
Elec. Wld June 22, 1912
Elec. Wld June 29, 1912
Jour, of Elec April 18, 1914
Jour, of Elec April 25, 1914
Elec. Wld May 2, 1914
Jour, of Elec September 5, 1914
Eng. Rec September 19, 1914
Jour, of Elec January 2, 1916
Jour, of Elec. June 5, 1916
Elec. Rev June 16, 1917
Watab Pulp & Paper Company, Minnesota:
Elec. Rev February 22, 1908
Watauga Power Company, Tennessee:
Eng. Rec November 11, 1911
Power March 26, 1912
Wateree Power Co., South Carolina:
Eng. Rec February 10, 1917
Weber & Davies Counties Company, Utah:
Elec. Wld December 7, 1912
Eng. Rec December 14, 1912
Welland Canal Power Development, Canada:
Elec. Wld January 21, 1906
Elec. Wld January 28, 1906
Wenatchee Valley Gas & Electric Company, Washington:
Jour, of Elec January 2, 1916
Jour, of Elec Jime 6, 1916
Western Canada Power Company:
Eng. Rec February 26, 1911
Elec. Wld July 20, 1912
Elec. Wld September 7, 1912
Jour, of Elec August 30, 1913
Jour, of Elec January 2, 1916
Jour, of Elec June 6, 1916
Western Colorado Power Company, Colorado:
Jour, of Elec June 6, 1915
Western States Gas & Electric Company, California:
Elec. Wld May 29, 1916
Jour, of Elec June 6, 1916
West Kootenay Power & Light Company, Canada:
Eng. Rec October 5, 1907
Elec. Wld July 27, 1912
Jour, of Elec. . . i June 5, 1915
Digitized by
Google
782 APPENDIX I
Whatcom County Railway & Light Company, Washington:
Elec. Wld July 20, 1912
White River Power Company, Wisconsin:
' Elec. Wld May 4, 1911
Winnipeg General Power Company, Canada:
Elec. Wld June 23, 1906
Winnipeg Municipal Hydro-Electric Works, Canada:
Can. Elec. News November, 1906
Eng. Rec October 9, 1909
Elec. Rev December 2, 1911
Eng. News July 4, 1912
Can. Elec. News June 1, 1915
Wisconsin-Minnesota Light and Power Company:
Elec. Rev March 31, 1917
Elec. Wld February 6, 1916
Wisconsin River Power Company:
Elec. Rev May 19, 1917
Yadkin River Power Company, North Carolina:
So. Electn March, 1913
York Haven Water & Power Company, Pennsylvania:
Elec. Wld March 2, 1907
Digitized by
Google
APPENDIX II
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APPENDIX III
STANDARD TESTING CODE FOR HYDRAULIC TURBINES
The following Code has been prepared by a Committee of the Hydraulic
Turbine Manufacturers to assist in avoiding misunderstandings in regard
to stipulated performances of hydraulic turbines. It is subject to such
revision from time to time as will be required by any new developments
in turbine testing methods.
iNTRODnCITON
1. Intended Scope. Hydraulic turbine tests are of two distinct kinds:
First, acceptance tests on completed tiu*bines after installation in the power
plant; second, experimental tests either on full-sized tiu-bines or models,
carried out at manufacturers' laboratories or at a testing flume. Tests of
the first kind are for the purpose of determining the fulfillment or non-
fulfillment of contracts between the turbine builders and the purchasers.
Tests of the second kind are carried out for the purpose of obtaining experi-
mental data on which the design of an installation may be based; for sci-
entific research work; or for the investigation of special problems. This
code is intended to apply only to tests of the first kind. When tests of the
second kind are used for determining the performance of a full-sized in-
stallation, this application should be made only in accordance with principles
which will be stated in section 10, below.
2. Principal Factors, Meaning and Intent of Terms Used. In cod>-
puting the efficiency of an installation a distinction must be made between
the efficiency of the plant and the efficiency of the turbine. The efficiency
of the plant may include all losses of energy up to any stated point of
delivery, such as the delivery of electric power from the transformers, at
the switchboard or at the generator terminals, or may be confined to the
total efficiency of the hydraulic installation, for which purpose the power
is to be computed as that delivered by the turbine to the generator shaft.
For the piurpose of computing the plant efficiency the total or gross head
acting on the plant is to be used, and is to be taken as the difference in
elevation between the equivalent still-water surface before the water has
passed through the racks, to the equivalent still-water surface in the tail-
race after discharge from the draft tube. When the water in the forebay
in advance of the racks flows with sufficient velocity to make its vdocity
head an appreciable quantity, the actual elevation of the water surface shaO
be mcresj^ by the amount of this velocity head. The same process shall
788
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APPENDIX ni 789
apply to the point of measurement in the taihrace; that is, the velocity
head at the point of measurement in the tailraoe shall be added to the actual
elevation of the suif ace, the sum being considered the equivalent still-water
elevation.
Except where specifically stated herein, this code shall be understood
to apply to tests of the turbine proper, and the terms power, efficiency,
effective head, etc., are to be taken as referring to the turbine. In com-
puting the efficiency of the turbine, the losses through the racks, in the
intake to the penstocks, and in the penstocks shall not be charged against
the turbine; nor shall tiie head necessary to set up the velocity required to
discharge the water from the end of the draft tube be charged against the
turbine. The net or effective head acting no the turbine shall be measured
from a point near the intake to the turbine casing in turbines equipped with
casings, or from a point immediately over the turbine in turbines having an
open-flume setting, to a point in the tailrace in the manner set forth below
under the heading ''Measurement of Head." Since the tiu-bine cannot
develop power without discharging water, a correction for the velocity head
required to discharge the water into the tailrace shall be added to the taU-
water elevation; and a similar correction applied at the intake to encased
turbines, as called for under the heading ''Measurement of Head." The
power developed by the turbine shall be taken as the mechanical power
delivered on the turbine shaft and transmitted by the turbine shaft to the
generator or other driven machine or system.
In drawing up a general code it is recognized that under particular cir-
cumstances sometimes occurring, methods of measuring or computing certain
factors entering into the test different from those specified, may appear pos-
sible and reasonable; it is, however, the intent of this code that the meaning
of the terms efficiency, effective head, etc., shall be the efficiency, effective
head, etc., determined as herein specified, and that such terms shall be under-
stood only as thus defined. _^
Genebal
8. Inspection. Careful inspection should be made before, during, and
after the tests to insure the proper operation of the turbine and conditions
of measurement.
The turbine runner, guide vanes, and casing should be inspected before
and after test to guard against obstructions clogging the vanes. Any change
in performance during a test should be investigated.
4. Operating Conditions During Test. Apparatus installed for the pur-
pose of the test shall not affect the performance of the turbine during
the test. When any doubt exists regarding this point, a special experiment
shall be carried out to detect any effect of removing and replacing the
apparatus in question, other conditions being maintained constant.
The unit shall be in normal operating condition throughout the test,
and shall have been operated under load for an aggregate time of at least
three days prior to the test.
4. (a) Leakage. Care should be taken that all air inlets into the draft
tube are closed, and that leakage of air into the tube or drawing of air into
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790 APPENDIX HI
the penstock intake ub not taking place, as indicated by exoessive amounts
of air in the discharge, or presence of vortices in the intake. Precautions
against leakage of water from penstock or turbine casing should be taken,
particularly through drain valves, relief valves or other connections. The
rate of fall of the standing water surface in the turbine casing below the
point of intake through the turbine gates should be observed duhng shut-
down as an indication of possible leakage.
(&) Unsteady Conditions. Tests should not be made under conditions
of changing head, load or speed. Variations of load during an individual
run shall not exceed 3 per cent above or 3 per cent below the average load,
and variations of head shall not exceed 2 per cent above or 2 per cent below
the average head, and variations of speed shall not exceed 1 per cent above
or 1 per cent below the average speed. Instrument calibrations and cor-
rection curves should be prepared in advance of the test, and measures
taken to enable results to be computed as quickly as possible during the
coiu'se of the test or before the work of testing shall be considered to have
been completed.
6. Calibration of Instruments. Important instruments shall be installed
in duplicate and all instruments shall be calibrated both before and after
the test. Only the readings of those instruments in which the two cali-
brations agree shall be used in computing the results. Where results are
appreciably altered by reason of instrument calibrations made after the
test disagreeing with those made before, the test shall be repeated.
6. Conduct of Test. Both parties to the contract shall be represented and
shall have equal rights in determining the methods and conduct of the test.
All points of disagreement shall be settled to the satisfaction of both
parties, and the results of the test be agreed on as acceptable, before the
test shall be considered terminated or the test equipment removed.
The measiu^ment of the various quantities entering into the computa-
tion of tiu*bine power and efficiency shall be in accordance with the follow-
ing regulations:
Measurement of Power Output
7. (a) By Electrical Measurement of Generator Oatpot and Generator
Losses. In turbines direct-connected to electrical generators the power
output of the tiu*bine may be measured as provided below.
The intent of the provisions contained herein is that the power output
of the turbine shall be taken as the power output of the generator plus all
losses supplied by the turbine up to the point of measurement.
The generator may be tested for efficiency either in the shops of the builder
or after installation, the losses being determined either by direct measurem^it
of input and output or by the separate-loss method; the electrical measure-
ments being carried out in accordance with the Standardization Rules of
the American Institute of Electrical Engineers of Septermber, 1916, but
subject to the provisions contained herein.
The generator losses and efficiency as herein defined are for the generator
considered as a dynamometer, and are independent of the performance
guarantees of the generator which are not within the scope of this code.
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APPENDIX III 791
The generator efficiency shall be determined for the values of load, power-
factor, temperature or other conditions existing during the turbine test.
When the generator is run during the turbine test at speeds different from
that used in the generator test, the generator efficiency shall be corrected
for the changes in speed.
When practicable, the generator is to be separately excited during both
generator and turbine tests, and the excitation loss is not to be included
in computing generator efficiency, and is therefore also to be omitted in
computing turbine output during the turbine test.
When determined by the separate-loss method, the generator efficiency
in the case of polyphase alternators when separately excited is to be taken as
(Kilowatt Output at Generator Terminals)
7Kaowatt\^r/'fiar-u|«P«'»''^-K /stray Load-uJ ^7*°' 1
{ Output }+{^tu«}+l-;^-}+{ ws h[-^J
all losses being expressed in kilowatts.
The stray load-losses are to be determined, in accordance with Paragraph
458 of the above Standardization Rules of the A.I.E.E., by operating the
generator on short-circuit and at the current corresponding to the load to
be used in turbine test. This, after deducting the windage and friction and
I^R loss, gives the stray load-loss, the total amount of the loss so determined
being included in the above formula, in place of } or i of this value as some-
times used in former practice. It is, however, understood that whenever
under the special conditions of an installation other losses exist, these are
to be added, in accordance with the second paragraph of this subdivision,
to the stray load-losses determined as here given.
The value of generator windage and friction should be directly measured
in the shop, or after installation. In units containing direct-connected
exciters, the windage and friction may be measured by driving the generator
by the exciter run as a motor. When the windage and friction cannot be
directly measured, it is to be taken either from shop tests of generators of
similar design or from a retardation test made after installation. When
possible more than one method should be used in order to obtain a check.
In making such a retardation test, the turbine shaft and runner, or the
turbine runner, are to be disconnected when practicable from the generator
shaft, in order to enable the windage and friction of the generator alone to
be computed. When the turbine shaft or runner cannot be disconnected,
the generator windage and friction are to be computed by deducting from
the total windage and friction that of the turbine, which for this purpose
may be found with sufficient accuracy from the formula:
Turbine windage and friction in Kw. ^^KBD^N* in which
B = height of distributor in feet ; ^
D= entrance diameter of runner in feet;
iV^= revolutions per second;
K^&n empirical coefficient which may be taken as 0.000115 as deter-
mined from available test data.
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792 APPENDIX ni
In computing the turbine output in the turbine test, this is to be taken
as the kilowatt output of generator divided by the generator eflSdency as
computed above, the result being converted from kilowatts to horse-power.
If an exciter generator is also mounted on the unit shaft and is used to
excite the unit imder test, then to the output of the main generator com-
puted as above without reference to excitation there is to be added the
kilowatt output of exciter divided by the exciter efficiency, this converted
to horse-power. It is recommended, however, for simplicity that when pos-
sible th^exciter shall be run without load and the unit separately excited.
It is recommended to avoid retests and to provide a reliable check, that
the electrical instruments used in all tests be installed in duplicate. These
instruments, together with the instrument transformers, shall be calibrated
both before and after the tests in the same condition as used in the tests.
When tests are made under slightly fluctuating loads, the output shall be
determined both by indicating wattmeters, read at short intervals, and by
recording watt-hour meters. During the turbine test the speed of the unit
shall be observed by accurately calibrated tachometer or by revolution
counter.
(6) By Absorption Dynamometer. When a dynamometer, either of
the Prony brake, friction disc, or other type, is used, the dynamometer is
to be so arranged as to avoid imposing either end thrust or side thrust on
the turbine shaft and bearings, or to avoid adding any friction load which
is not measured.
The brake must be capable of operating with the weighing beam floating
free of the stops during the entire duration of a run. A dash pot or equiv-
alent device may be used to assist this action if so arranged that the accuracy
of measiuing the actual torque acting on the tiu'bme shaft is not impaired.
The dynamometer must be so constructed that the lengths of all lever
arms used for transmitting and reducing the loads can be aocuratdy measured.
The zero load of the dynamometer must be capable of accurate measurement
and should not be large in comparison with the net load to be measured.
When power is determined by dynamometer, particular care is to be
used in obtaining accurate measurement of the speed of the shaft. If ta^
chometers are used these are to be frequently calibrated by counting the revo-
lutions over an ample length of time. Under usual conditions it is recom-
mended that the speed be directly measured by revolution counter, a
tachometer being also used as a check and to indicate variations in speed
during a run.
Mbasubement of Power Input ob Wateb Hobse*foweb
8. Measurement of Head. The intent of the provisions contained herein
for the measurement of head is the true determination of the difference
between the total energy contained in the water immediately before its
entrance into tl^e turbine, and its total energy immediately after its dis-
charge from the draft tube.
The turbine shall be tested if possible under the effective head stated in
the contract, and at the speed specified in the contract. If during the test,
however, the effective head shall differ from the specified head by an amount
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APPENDIX in 793
not exceeding 10 per cent of the latter, the speed of operation of the tur-
bine shall be adjusted to correspond to the head under which the test is
nmde. The principle is recognized and accepted that if the speed is changed
in proportion to the square root of the head, the horse-power output will
change in proportion to the three-halves power of the head, and the turbine
efficiency will remain the same; that is, when the head differs from the
value specified in the contract, the contract guarantees shall be considered
to apply if the hydraulic equivalents of the power and speed of the turbines
are substituted for the power and speed enumerated in the contract. The
hydraulic equivalent of the speed is eqiial to the specified speed multiplied
by the square root of the ratio of the effective head existing during the test
to the specified effective head. The hydraulic equivalent of the horse-
power is equal to the specified horse-power, multiplied by the three-halves
power of the ratio of the effective head existing during the test to the specified
effective head.
The test shall not be carried out if the head differs from the contract
value by more than 10 per cent either above or below, or if, due to an excess
of the head above the contract value, or to a reduction in tailwater eleva-
tion, the total draft head approaches within 5 feet of the limiting value
corresponding to the barometric height. By total draft head is meant the
height of the centerline of the distributor of vertical tiu'bines, or of the
highest point of the discharge space of the runner of horisontal turbines
above tailwater, added to the velocity head at the point of minimum internal
diameter of the runner band.
If during the test it is not practicable to adjust the speed, or if the
final calculation should show the speed to have been incorrectly adjusted
to suit the head, provided that the discrepancy in speed does not exceed
2 per cent either way from the correct value, the values of power and efficiency
fihown by the test shall be corrected on the basis of the test curves, of the
eame or a homologous turbine, made at a testing fliune or on a wheel tested
in place according to the methods of this code, when such curves are available.
(a) Encased Turbines. In turbines having closed casings the head is
to be measured by at least two, and when possible not less than four pie-
zometers located in a straight portion of the penstock near the turbine casing
intake, and by two or more rod or float gauges in the tailrace, placed at points
reasonably free from local disturbances.
Such board, rod or float gauges are to be free of velocity effects, and if
this is not obtainable when the gauges are set in the open channel, they shall
be placed in properly arranged stilling boxes.
All piezometers shall be connected to separate gauges. The conditions
of measurement, including velocity distribution, length of straight run of
penstock, and conditions of piezometer orifices shall be such that no piezom-
eter shall vary in its readings by more than 20 per cent of the velocity head
from the average of all the piezometers in the section of measurement. The
piezometer orifices shall be flush with the surface of the penstock wall, the
passages shall be normal to the wall, and the wall shall be smooth and parallel
with the flow in the vicinity of the orifices. The piezometer orifices shall
be approximately i inch in diameter, If any piezometer shall be obviously
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794 APPENDIX in
in error due to some local cause or other condition, as indicated by its reading,
after the addition of the velocity head, giving a head in excess of the initial
available head corresponding to the elevation of the surface of headwater,
the source of the discrepancy shall be found and removed, or the piezometer
eliminated.
When stilling boxes are used in the tailrace the conununication between
the box and channel shall consist of one or more piezometer openings in a
plane surface parallel to the flow, in order to avoid velocity effects. When
board gauges are used at the side of the channel, they shall be flush with
the wall surface.
The effective head on the turbine is to be taken as the difference between
the elevation corresponding to the pressiu-e in the penstock near the entrance
to the turbine casing, and the elevation of the tailwater at the highest point
attained by the discharge from the unit under test, the above difference being
corrected by adding the velocity head in the penstock at the point of measure-
ment and subtracting the residual velocity head at the end of the draft tube.
The velocity head in the penstock shall be taken as the square of the mean
velocity at the point of meajBurement, divided by 2g; the mean velocity
being equal to the quantity of water flowing in cubic feet per second, divided
by the cross-sectional area of the penstock at the point of measurement
in square feet. The residual velocity head at the end of the draft tube shall
be taken as the square oi the mean velocity at the end of the draft tube,
divided by 2(7, the mean velocity being equal to the quantity flowing in
cubic feet per second, divided by the final croes-eectionai discharge area
of the closed or submerged portion of the draft tube in square feet.
(&) Open Flume Setting. In the case of turbines set iU'Open flumes, the
head is to be measured by board, rod or float gauges located immediately
above the center of the turbine, and by board, rod or float gauges in the
tailrace, all gauges being placed at points reasonably free from local dis-
turbances, and not less than two gauges lieing installed in the flume and not
less than two in the tailrace.
Such gauges are to be free of velocity effects,a nd if this is not obtainable
when the gauges are set in the open channel, they shall be placed in properly
arranged stilling boxes. When stilling boxes are used, the communication
between the box and channel shall consist of one or more piezometer openings
in a plane surface parallel to the flow, in order to avoid velocity effects.
When board gauges are used at the side of the channel, they shall be flush
with the wall surface.
The effective head on the turbine is to be taken as the difference be-
tween the elevation of the free water surface immediately above the center
of the turbine, and the elevation of the tailwater at the highest point attained
by the discharge from the unit under test, the above difference being cor-
rected by subtracting the residual velocity head at the end of the draft tube.
The residual velocity head at the end of the draft tube shall be taken as the
square of the mean velocity at the end of the draft tube, divided by 2g; the
mean velocity being equal to the quantity flowing in cubic feet per second,
divided by the final cross-sectional discharge area of the closed or sub-
merged portion of the draft tube, in square feet.
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APPENDIX ra
795
Measurement op Quantitt op Wateb
9. The quantity of water discharged from the turbine is to be meas-
ured by one of the following methods. It is recommended that whenever
possible -more than one of these methods be used, the quantity being taken
as the average of the results of two or more simultaneous measurements.
(a) By Weir. When the quantity of water is measured by weir, weirs
with suppressed end contractions shall be used.
The weir or weirs shall if possible be located on the tailrace side of the
turbine, and care shall be taken that smooth flow, free from eddies, surface
disturbances or the presence of considerable quantities of air in suspension
exists in the channel of approach. To insure this condition the weir should
not be k>cated too close to the end of the draft tube, and stilling racks and
booms- should be used when required. The channel of approach should be
straight, of uniform cross-section and should be unobstructed, by racks and
booms, for a length of at least 25 feet from the crest. The racks should be
arranged to give approximately uniform velocity across the channel of
appiroach. The uniformity of velocity should be verified by current meter
or otherwise. .
The head <m the weir should be observed by hook gauges placed in stilling
boxes communicating through orifices approximately 1 inch in diameter
in the sides of the channel of approach, approximately 1 foot below the level
of the crest and a distance of not less than 5 or more than 10 times the head
upstream therefrom, the head being observed independently at both sides
of the channel. In measuring quantities of water corresponding to the
loads on which the turbine guarantees are based, the head on .the crest shall
TABLE OF VALUES OF C FOR VARIOUS HEADS AND HEIGHTS
OF CREST P
Head
h
in Feet.
Hbiqht of Cbbbt P
4
5
6
7
S
9
. 10
12
14
16
20
I.O
3.376
3.356
3.344
3.335
3.329
3.325
3.322
3.317
3.314
3.311
3.308
1.2
3.391
3.366
3.350
3.339
3.332
3.326
3.322
3.316
3.311
3.308
3.305
1.4
...
3.379
3.359
3.346
3.336
3.330
3.324
3.316
3.311
3.307
3.303
1.6
. . .
3.370
3.354
3.343
3.334
3.328
3.319
3.312
3.308
3.302
1.8
...
...
3.363
3.350
3.340
3.333
3.322
3.315
3.309
3.303
2.0
...
...
3.358
3.347
3.338
3.325
3.317
3.311
3.304
not be more than two (2) feet or less than one (1) foot, and the velocity of
approach shall not be greater than 1 foot per second.
The discharge shall be computed by the Francis formula in the form given
below, using the accompan3ring table of coefficients. These coefficients are
believed to represent the best available information. The values of turbine
efficiency resulting from weir tests made in accordance with this code are
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796 APPENDIX III
understood to be efficiencies computed by the use of the formula and coef-
ficients here given.
where Q ^quantity in cubic feet per second;
L s length of weir in feet;
^ » observed head above crest in feet.
P is the height of the crest above the bottom of the channel of approach'
in feet.
To facilitate computations, all corrections for velocity of approach have
been included within the coefficients as given; these are therefore to be
used in the formula stated above, the observed head being used without
modification.
Note: The above coefficients are the averages of values computed by
the following three formulas:
(1) Bazin,
(2) Behbock,
(3) Fteley-Steams,
in which h, «head due to velocity of approach.
The weir shall be sharp crested, with smooth, vertical crest wall, complete
crest contraction, and free overfall. Complete aeration of the nappe shall
be secured and observation of the crest conditions and form of nappe shall
be made during the test to avoid defective conditions such as adhering
nappe, disturbed or turbulent flow, or surging. The sidewalls of the channd
shall be smooth and parallel and shall extend downstream beyond the over
fail above the level of the crest.
Weirs of a length exceeding approximately twenty times the head (ex-
cepting in cases where the velocity of approach is extremely low); or weirs
of moderate crest length having high velocities of approach; or those in
which the velocity of approach is irregularly distributed, or in which the
leading channel is subject to action of the wind, should either be subdivided
into a nimiber of sections or the head should be observed not only at both
sides but also at intermediate points across the chamiel of approach. The
elevation of the crest should be measured at short intervals of its length
in determining the zero readings of the hook gauges.
(6) By Current Meter. When the discharge is measured by current
meter, observations shall be taken by two different t3rpes of meter, one type
having preferably such characteristics that it will slightly over-regi»ter
under conditions of turbulent or oblique flow, and the other type having
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APPENDIX III ; 797
characteristics such that it will under-register under similar conditions. The
true velocity obtained by reducing the meter readings on the basis of their
still-water ratings may then be taken as a weighted mean between the two
series of observations.
As a basis for arriving at the proper weighting of diverging meter results,
the instruments in question should, in addition to their regular still-water
ratings, be given simultaneous oscillation or angularity tests at several
velocities near those which will probably be experienced during tests. By
means of the resulting data, curves showing the over- and under-registering
characteristics of each meter may be plotted for varying degrees of obliquity
or velocities of osciUation. The total deviation of the two meters may then
be noted for any obliquity or lateral velocity. When the relative deviation
of the two meters is observed in the field, the curves will then indicate the
proportions in which the total deviation should be divided to give the proper
correction for each meter.
The point method of observation shall be used and sufficient points shall
be obtained to enable both vertical and horizontal velocity curves to be
plotted for all portions of the section of measurement. The average velocity
shall be determined from these curves by planimeter. .
The section of measurement shall be rectangular and smooth flow con-
ditions shall be obtained. It b reconmiended that in order to avoid abnor-
mally long durations of run a number of meters of each type be used simul-
taneously. The elevation of water shall be continuously observed during
the current meter measurement by stilling boxes, piezometers, or other
reliable means. If the supporting rods for the meters are in the same plane
as the meters, the area of these rods shall be subtracted from the wetted
area of the flume in calculating the quantity. The meter should preferably
be supported by rods placed a sufficient distance behind them to avoid any
obstructive effect. When a heavy mast or supporting frame is used, it
should be designed to offer a minimum disturbance, and should be located
several feet downstream from the meters.
(c) By Pitot Tube. When the Pitot tube method is used, the Pitot
tube shall be located in a straight run of penstock or conduit, at a distance
equal to at least ten pipe diameters from any upstream bend and at least
five diameters from a downstream bend. When the observation is made
in a circular pipe or penstock, at least two Pitot tubes shall be arranged
to traverse two relatively perpendicular diameters, but in the case of very
large penstocks or those having imsymmetrical flow, Pitot tubes shall be
arranged to traverse completely or partially the intermediate diameters,
giving traverses at forty-five degree intervals.
In determining the velocity in the penstock by the Pitot tubes the static
pressure over the cross-section shall be measured by from four to eight
carefully constructed piezometers equally spaced around the wall of the pen-
stock at a section 1 foot in advance of the Pitot tube section to avoid the
effect of the Pitot tube supporting structure, the penstock being of uniform
cross-section between the piezometers and the points of the Pitot tubes.
All piezometers shall be connected to separate gauges. The conditions of
measurement, including velocity distribution, length of straight run of pen-
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798 APPENDIX in
stock, and condition of piezometer orifices shall be such that no piezometer
shall vary in its readings by more than 10 per cent of the velocity head
from the average of all the piezometers. The piezometer orifices shall be
flush with the inside surface of the penstock wall, the passages shall be normal
to the wall, and the wall shall be smooth and parallel with the flow in the
vicinity of the onfices. The orifices shall be i inch in diameter.
The velocity at each point in the penstock shall be computed by the
formula V = y/2gh, in which h represents the difference in feet between the
total dynamic pressure recorded by the Pitot tube at that point and the
average static pressure recorded by the piezometers. The velocities so
determined shall be plotted as ordinates against values of the areas of the
sections of the penstock corresponding to the points of measurement aa
abscissas, a smooth curve being drawn through the points obtained. The
mean velocity in the penstock will then be taken as the mean ordinate of
the above curve multiplied by 0.976. This coefficient is based on the average
of various comparative tests, and is required to correct for oblique or sinuous
flow under the usual conditions in straight penstocks.
When the length of straight run of penstock is insufficient or when the
flow is disturbed by a severe bend or obstruction upstream from the tube
or when the average velocity is less than 6 feet per second, the above coef-
ficient will not apply correctly, the correct value being considerably- lower
in such cases, which do not, therefore, come within the scope of this code.
The coefficient corresponds to a tube, the point of which is | inch in diam-
eter with a i inch hole, the face being normal to the axis, and at least 3 inches
from the nearest surface of the supporting pipe.
(d) By the Screen or Diaphragm Method. When the screen method is
used a sufficient length of straight flume of uniform cross-section shall be
constructed with a close-fitting screen filling the cros»-section. Provision
shall be made for accurately observing the velocity of the screen, preferably
by electric contacts and chronograph. The length of run of the screen shall
be sufficiently in excess of the portion used for measurement to orovide
ample space for starting and stopping the screen, so as to insure uniform
conditions over the measured portion of the run. In determining the dis-
charge the velocity of the screen shall be multiplied by an area intermediate
between the net immersed area of the moving screen and the average area
of stream cross-section of the portion of the channel traversed. The varia-
tion of the level in the flume shall be observed during the course of the nm
and the average elevation shall be used in determining the area.
(e) By Titration or Chemical Method. When ^e chemical method is
used in measuring discharge, care shall be taken to insure that at the point
of introducing the dosing solution no portion of the solution shall be carried
off by back currents and shall therefore fail to pass to the sampling station,
and that the sampling station shall be so placed that no pollution shall be
caused by reverse currents, causing fresh water to pass the station from down-
stream. Wlien necessary, owing to a short length of mixing passage or lack
of sufficient disturbance to cause thorough mixing, the dosing pipes shall
be so placed that an equal degree of concentration over the entire section
of the sampling station shall be obtained. Samples shall be taken from
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APPENDIX III 799
points distributed over the entire sampling section. All necessary precau-
tions shall be observed in taking samples, and in observing the end-point
of the reaction during titration.
In short tests, care shall be taken to preserve a uniform rate of intro-
duction of the dosing solution. Preliminary observations shall be made to
determine the time required aft^r the dosing is started for uniform conditions
to become established at the sampling station; and in the actual tests the
dosing shall be continued for double this time before sampling is begun.
Uniformity of dilution of samples both with respect to location in the section
and the time of taking shall be considered essential for an acceptable test.
Power Tests op Turbine Supplemented by Efficiency Tests of a Model
10. When the conditions of an installation are such as to involve serious
difficulty or expense in the application of any of the above methods of water
measurement, the tests of the installed turbine may be made when accept-
able to both parties without measuring the quantity of water, a homologous
model of the turbine being constructed and tested at the expense of the
purchaser, and the power delivered by the installed turbine compared with
that computed from the model tests.
This method must not be confused. with the practice, which has some-
times been followed, of comparing a turbine with a model having a homol-
ogous runner, but dissimilar with respect to setting, draft tube or other parts.
The runner, guide vanes, draft tube, casing, or other adjacent water passages
should be geometrically similar in the turbine and model; and when so
constructed, the power stepped up from the model tests for the hydraulic
equivalent of the speed gives a reliable basis of comparison with the power
actually obtained from the installed unit.
The power of the model when operating at the hydraulic equivalent
of the speed of the large unit in the tests of the latter, at the same propor-
tional gate opening, is to be multiplied by the ratio of the area of the discharge
orifices of the large turbine runner to that of the model, and by the three-
halves power of the ratio of the head existing in the tests of the large unit
to the head in the model tests. When the power so computed agrees exactly
with that obtained from the installed unit, the efficiency of the large unit
shall be considered to be identical with that of the model; and when the
power of the large unit exceeds that thus computed from the model, the
efficiency of the large unit shall be considered to be in excess of that of the
model. In measuring the gate opening the actual opening of the gates shall
be determined, and care shall be taken to avoid errors due to the effect of
the pressure on the vanes.
Appendix
11. Special Methods of Water Measurement. The following methods
of water measurements may sometimes be applied; these are, however,
subject to limitations, and are available only under special conditions.
They have not as a rule been in sufficiently general use in turbine testing
to permit full reliance to be placed on them until opportunities are afforded
for checking them against the methods already given.
(a) By the Bulk or Volumetric Method. Water measurement by weight
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800 APPENDIX m
or volume is not usually available; the fonner is limited to laboratory use,
which is outside the scope of this code. The bulk method is applicable
only when there is available a reservoir of regular form, the volume of which
up to various water levels may be accurately measured, and when the fol-
lowing conditions may be observed:
The draw-down or filling of the reservoir must not cause a variation
in head on the turbine during a run exceeding the limits specified under
section 4 (&), namely, a total of 4 per cent of the head. It must be possible
to shut off completely aU inflow into or outflow from the reservoir. The
tightness of the gates and reservoir walls must be tested by closing aU gates,
and observing over a time of several hours the rate of rise or fall of water
level in the reservoir throughout the full range of variation of level which
will be used in the turbine test. At the same time any leakage through
the turbine head gates is to be measured. The surface elevation in the
reservoir is not to be so affected by velocity or wind effects as to cause local
variations in level of more than 5 per cent of the total draw-down used in
the turbine tests. This variation is to be observed by gauges distributed over
the whole reservoir, which are to be read simultaneously at short intervals
throughout the test. The effect of surface evaporation shall be investigated
and corrections applied to cover it. when local conditions are such that it
becomes appreciable.
(6) By Venturi Meter. When it is possible to install a Venturi meter
not exceeding in dimensions or differing in conditions from meters whose
coefficients have previously been determined in accurate tests, the Venturi
meter may be used. The meter shall be similar in proportions to meter
previously tested.
(c) By Color Velocity Method. When the water used by the turbine
passes through a conduit suited to the purpose, the color method of quantity
determination may be used, depending upon the time of passage between
two points of a mass of color injected into the stream. The distance between
the two points where the passage of the color is observed must be sufficiently
great to render the interval between the times of passage of the color at
the two stations large compared to the time required for all the color to pass
either station. The conduit must be of sufficiently regular form to per-
mit its cro6&-eectional areas to be accurately measured at all points between
the stations.
{d) By Brine Velocity Method. A method similar to 11 (c) adapted to
closed conduits has been used, consisting in the injection of a mass of brine,
the time of passage of which is detected by the variation in electrical resist-
ance between two contacts placed in the stream. . A pair of such contacts
is placed at each station, and the time of passage of the brine between the
stations is chronographically recorded by a specially arranged wattmeter.
The stations should be arranged as imder 11 (c).
(e) By Color Density Method. The coloration or color density may also
be employed for approximate tests, this method depending on the use of
a colored dosing solution in place of a salt solution in a manner similar to
the chemical method of 9 (e), observation of the color density replacing
the titration.
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APPENDIX m 801
if) By Resistance of Salt Soloti<m. A method which has been used ex-
perimentally is similar to the chemical method of 9 (e), except that the
amount of chemical (salt) in solution is detennined by measurement of the
electrical resistance of the solution instead of by titration. Care is required
to guard against changes in resistance due to small temperature variations.
12. Measurement of Water Horse-power in Plants Containing a Fall
Increaser. In case of an installation including a fall increaser or other
device utilizing an auxiliary flow for increasing the effective head, the fol-
lowing provisions shall be observed: In determining the efficiency of the
turbine proper, considered separately from the fall increaser, the faU increaser
shall be closed, and precautions shall be taken that no water except that
passing through the turbine shall enter the system between the points at
which the head is measured.
In order to determine the performance of the combined hydraulic instal-
lation, including both turbine and fall increaser, the total water horse-power
shall be computed from the sum of the turbine discharge multiplied by the
head on the turbine, and the auxiliary discharge multiplied by the head on
the fall increaser. The head on the turbine shall be measured from a point
immediately in advance of the point of intake to the turbine proper, as above
provided, and the head on the fall increaser shall be measured from a point
inmiediately in advance of the intake gates of the increaser, the head in
each case being measured to a point below the junction of the two streams
at the outflow from the plant. For the computation of water horse-power
it will be necessary to determine the division of the total discharge between
the turbine and fall increaser. This may be done when practicable by
separately measuring the water admitted to the tiu'bine during the operation
of the fall increaser.
If, owing to the arrangement of the fall increaser, it is impracticable
to separate the water horse-power of the turbine from that of the fall increaser,
the gross efficiency of the combined installation may be determined by meas-
uring the combined total flow, and the total head from a point common
to the two flows before entering the plant to a point after they are reunited
below the final point of discharge.
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INDEX
A
PAGS
Absorption 49
Agricultural work 28
A.I.E.E. standardization rules 308
Air, reluctance of 289
Air tanks for pressure regulation 142
Air valves 128
Altitude, effect on temperatiure 312
Ammeters 540, 541
Ammeter transfer plugs and receptacles 560
Apparatus, arrangement of 175
exciters 176
general consideration 175
generators 176
governors 176
lightning arresters 192
reactors 178
switching equipment 179, 566
transformers 176
turbines 175
transportation and erection 193
Arcing ground suppressor 618
Area, land and water of United States 14
Armature reactance 286
reaction. . ; 285
Atmospheric pressure 42
Auxiliary stations. See Steam aux. stations 692
B
Banding of wooden-stave pipe 131
Bazin's formula 106, 796
Bearings, generator 331
thrust 333
suspension 333
turbine 241
Bearing value of soils 168
Brakes 348
Breathers, transformers 454
803
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804 INDEX
PAOB
Buft-baw 489, 665
expansion 571
heating 566
mechanical short-circuit stresBes 471
mimic 563
permissible current density 566
reactance 569
sectionalizing 474
skin effect 569
structure 563
supports 569
Bushings, entrance 571
oil circuit breaker 505
transformer 442
C
Cables 625
current-carrying capacity 633
ducts and conduits 628
heating 472, 633
insulation 625
mechanical short-circuit stresses 471
reactance and resistance 642
single vs. multiple conductors 629, 632
sixe 633
troubles 628
voltage tests 634
Calibrating terminals 561
Canals 106
concrete lining 108
cross-section 107
evaporation 110
seepage 110
side slopes 109
Central stations in United States 25
Chezy formula 106, 116
Choke coils 617
Circuit breakers. See Oil circuit breakers 496
Coal production in United States 13
Commercial opportunities 28
agricultural work 28
electro-chemical industries 34
irrigation 30
mining 33
railroad electrification 38
Concrete pipe 137
Conductor spacing 627
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INDEX 805
PAGX
Ck)iiduit 628
Ck)imections, system '. 486
exciter 355
generator armature 282, 295
instrmnents 551
transformers 391
Conservation of natural fuel resources 13
Control switches 561
Cooling water for transformers 381, 457
Corona 639
Corrosion of turbine runners 233
Cost of hydro-electric plant 702
development expenses 703
estimated and actual costs 706
overhead charges 705
physical costs 704
Cost of hydro-electric power 742
Cost of steam power stations 745
Cost of steam power 745
Cranes 171, 195, 197
Current-limiting reactors. See Reactors 458
Current meters 65, 796
Current transformers 546, 563, 638
Curve-drawing instruments 541, 546
D
Dams 74
arched 85
buttressed 85
choice of type 74
classification 74
earth-fill 76
gravity 79
location 74
masonry 79
multiple-arched 88
pressure 79
rock-fill 78
rolling 99
rules governing design 88
timber crib 75
Depreciation » 743
Developments, history 1
electrical 1, 10
hydraulic ; 1, 9
Disconnecting switches 577
Distribution voltage 273
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806 INDEX
/ FAQI
Diversity factor 678
Drainage area 649
Drying, exciters and generators 199
transformers 445
transformer oil 449
Ducts ess
E
Economical aspects ^ 644
auxiliary stations 692
available energy 675
cost of plants 702
cost of power 742
interoonne(;ted systems 698
investigating an enterprise 699
load and diversity factor 678
power demand 677
primary and secondary power 683
water power reports 645
water storage 685
Efficiency, generators 312, 314, 791
installation 788
transformers 384
turbines 211, 217, 791
Electrical developments 1, 10
Electro-chemical industries 34
Energy, available 675
flowing water 66
kinetic 66
potential 66
Entrance bushings 571
Equivalents 68
Erection of apparatus 196
Erosion of turbine runners 233
Evaporation 47, 110, 164
Excitation, synchronous generator 288, 290
Exciters 350
arrangement in power house 176
batteries 361
capacity and rating 351
characteristics i 352
connections 355
control 552
drying 199
insulation resistance 200
mechanical design 353
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INDEX 807
FAOB
Exciters, method of drive 353
separate excitation 350
shunt V8. compound wound 352
speed 353
voltage 351
Expansion joints for pipe lines 128
F
Field control 552
Field discharge switches 554
Field rheostats 556
Financial aspects 644
Fishways 99
Flashboards 91
Float method of stream flow measuring 65
Flood gates 91
Floods, prevention 22
Flow of water, canals 106
flumes, 110
pipe lines 114, 121
tunnels 113
Flow-summation curve 685
Flumes 110
concrete Ill
wood Ill
steel 112
Flux, leakage 286, 377
Flywheel effect 247, 321, 327
Foundations, power house 168
Francis formula 795
Freezing of water in pipe lines 129
Frequency 273
eflfect on generators 275
illumination 280
induction motors 277
railroad electrification 279
synchronous converters 278
transformers 275
transmission lines 276
Frequency changers 274
Frequency, high 596
absorbers 602
indicators 543
Friction, losses in pipe lines 116
coefficient 106. 117
Fuel resources in United States 13
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808 INDEX
G
PAOl
Gas power, relation to steam and water power 27
Gauges, hook 61
Gauging stations 62
Gates. See also Valves 144
gate valves 148
operation and control 149
rolling 97
tainter 97,148
tilting 96
sliding 93
sluice 146
wicket 220,236
Generators, induction 348
comparison with synchronous generators 348
operation 349
output and excitation 348
utilisation 351
Generators, synchronous. 280
A.I.E.E. standardization rules 308
armatiu^ connections 282, 295
armature reactance 286
armature reaction 285
armature self-induction 286
arrangement in power house 176
bearings 330
brakes 348
characteristics 290
determination of efficiency . . .' 314
division of load 321
drying 199
effect of altitude on temperature 312
effect of power factor 284
efficiency 312, 791
excitation range 290
excitation required 288, 290
erection 199
flywheel effect 321, 327
frequency 275
grounding of neutral 304
horizontal o». vertical 324
induced E.M.F 280
insulation resistance 200
leakage flux 286
losses 313
lubrication 338
mechanical design 324
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INDEX 809
PAOB
Generators, synchronous, parallel operation 318
permissible temperatures 309
rating 307
reactance 469
regulation, voltage 291
repair ;. . 172
saturation curves 289
short-circuit current 292
speed 315
83mchronous impedance 292
synchronous reactance 294
temperature measurements 310
ventilation 173, 345
voltage 270, 316
voltage regulation 291
. wave form 282, 301
windings 325, 330
Governors 246
action *. 249
arrangement in power-house 176
arrangement and operation 251
energy output 251
methods of control ^ 254
power cylinders 253
pumping outfit 252
pressure supply 252
speed regulation 220, 246
Grade, hydraulic 106, 117, 119
Grounding, generator neutral 304
lightning arresters 612
transformer neutrals 392, 393, 396, 398, 399, 401, 404, 408,
413,420
transformer secondaries 393, 550, 638
Ground detector, electrostatic 545
Guide vanes 220, 236
H
Head 67, 114, 210
effective or net 114, 789, 794
elevation 114
gross 67, 114, 788
limitations 675
loss 1 16
measurement 792
pressure 114
variation 214
Headworks 74
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810 INDEX
FAOB
Heating of power-house 175
High frequency 596
High-frequency absorbers 602
History of hydraulic and electrical developments 1
Hook gauge 61
Hydraulic gradient 119
Hydtaulic radius 106, 117
Hydro-electric systems, data 783
references to descriptions 757
Hydrograph records 66
Hydrology 39
I
Ice 103
Ice guards 71
lUumination of power-house 174, 538
Impedance, cables 642
effect of parallel operation of transformers 425
natural 597
synchronous 292
transformer 426
Indicators, frequency 543
power factor 542
synchronous 544
temperature 545
transformer cooling water 435
Inductance 467
Insulation, generator 325, 330
transformer 439
wires and cables 625
Insulators, bus-bar 569
Instruments 538
ammeters 540, 541
connections 551
current and potential transformers 546
curve-drawing 641, 546
electrostatic ground detectors 545
frequency indicators 543
indicating wattmeters 542
power-factor indicators 542
reactive volt-ampere indicators 543
synchronism indicators 544
temperature indicators 545
voltmeters 640, 641*
watthour meters 549
Intakes, water 100, 163
Interconnected systems 698
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INDEX 811
FAGS
Investigation of an enterprise 699
Irrigation 30
K
Kutter's formula 106
L
Layouts of power stations 180
Leakage flux, generators 286
transformer 377
Lightning arresters, aluminum cell 604
charging 614
charging current indicator 614
charging resistance 614
choke coils 617
discharge recorder 616
grounding 612
location 192, 609
Line drop compensation 368
Load, division 321
regulation on system 323
curves 680
factor 678, 682
Location of development 644, 652
Lubrication. Sec Oil .^338
M
Magnetizing current, transformers 376
Management 746
Manufacturing, power requirements 27
Market for power 677
Mass curves 685
Mechanical stresses on short circuits 471
Meters, electric. See Instruments 638
price current 65
venturi 262
water flow 262
Mimic buses 563
Mining industry 33
Multi recorder 589
N
Natural impedance 597
Nozzles, auxiliary relief 224
deflecting 222
jet deflecting 222
needle 221
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812 INDEX
O
PAOB
Qfl, lubricating 108, 338, 341
transformcc 46, 178, 443, 449, 451
Oil circuit breakers 496
bushings ' 505
rating 497
rupturing capacity '. . / 470, 497
selection of type 497
structures 563
time of opening 470, 498
types and design 498
Oil circuit-breaker batteries 589
Oil production in United States 15
Organization and Operation 746
management 746
operating force 746
operating and maintenance instructions 754
operating records 748
Oscillations 596
Outdoor stations 192, 577
Overspeed of turbines 226
Over-voltage protection 593
arcing ground suppressor 613
classification of over-voltages 693
^ lightning arresters 604
protection of telephone lines 620
short-circuit suppressor 620
P
Parallel operation, generators 318
transformers 421
Penstocks. See Pipe lines 114
Perimeter, wetted 107
^ezometers 793
Piping, lubricating oil 339,343
transformer oil 466
transformer cooling water 457
Pipe lines 114
anchors 128
concrete pipe 137
economic diameter 121
expansion joints 128
friction loss 116
gradient 119
loss of head 116
number 120
pressure 128, 246, 250
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INDEX 813
PAOa
Pipe lines, sue 120
steel pipe 126
thickness of plates 125, 126
wooden-stave pipe 131
Pitot tube 797
Polarity of transformers 421
Pondage 159
Population of United States 14
Potential transformers 646, 666, 638
Power, cost 742
development 654, 675, 684
market 666, 677
primary and secondary 683
Power factor, effect on generator operation 284
effect of reactance 462
Power factor indicator 542
Power-house 166
arrangemet of apparatus T 176
basement 166
cranes : 171
doors 171
floors 170
foundations 168
general design 166
heating 176
illumination 174
roof 170
typical layouts 180
ventilation 173
windows 171
Power systems, load factor '. 682
peak loads 682
yearly output 682
Power transmission, development 4, 10
Precipitation. See Rainfall 44
Pressing, atmospheric 42
pipe line 122, 126, 138
regulation 246
regulators. See Relief valves 268
Primary power 683
Primary power in United States 24
Q
Quantity of flowing water 67, 795
R
Racks 100
Rack cleaners 101, 147
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814 INDEX
Radius, hydrauHc 106, 117
Railroad electrification 38
Rainf aU 44, 650
disposal 47
records 46
variations 44
Rating, current-limiting reactors 459
exciters 351
generators, synchronous 307
oil circuit breakers 497
transformers 383
Ratio, transformers 375, 424
Reactance, armature 286
bus-bars 569
cables 642
effect on power factor 462
effect on regulation 463
generator, synchronous 292, 294, 469
transformers 377, 469
transmission lines 469
Reaction, armature 285
Reactive volt-ampere indicator 543
Reactors, current-limiting 458
arrangement in power-house 178
bus-bar 466, 474
calculation of three-phase short-circuit currents 460, 468
calculation of single-phase short-circuit currents 480
effect of reactance on regulation 463
effect of reactance on power factor 462
feeder 466, 476
generator 465
inductance '. 467
location 465
losses 467
mechanical design 485
number 468
purpose 458
rating 459
rating as affected by current 461
rating as affected by frequency 461
rating as affected by voltage 461
reactive drop 459
size 468
Stott-system 467
temperature rise 459
Receptacles, ammeter transfer 560
voltmeter and synchronizing 559
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INDEX 815
Register, water stage 265
Regulation, speed of turbines 122, 140
Regulation of stream flow 689
Regulation, voltage 363
effect of reactance 463
generator, 83mchronous 291
hand regulation 363
K. R. system 369
line-drop compensation 368
synchronous condenser 371
T.A. regulator 336
transformer «* 378
Regulators, T. A 363
Relays 507
balanced 521
control 526
differential - 522
high-tension, series 525
high-voltage, high-current 371
interconnected reverse power 518
low voltage r . . . 626
overload 509
over-voltage 525
pilot wire 523
reverse-power 514
selection 492
signal 526
split-conductor 521
time settings 494
trip-free*. 526
underload 526
Relief valves 141, 221, 251
Reluctance, air 289
iron and steel 289
Reports, preparation 645
water power 645
Reservoirs. See Storage reservoirs 159
Resonance 595
Rheostats. See Field rheostats 556
Run-off 51
mean annual 54
records 649
Rupturing capacity of oil circuit breakers 470
S
Saturation curves 289
Secondary power 683
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816 INDEX
PAOp
Seepage 164
canals 110
Shipping limitations 193
Short-circuit currents 458
calculation of three-phase 460, 468
calculation of single-phase 480
mechanical stresses 471
synchronous generators 292
Shori-drcuit suppressors 620
Signal systems 583
Skin effect 569
Slope, hydraulic «. 106, 117, 119
Spacing of conductors 627
Specific speed of turbines 206, 209
Speed, exciters 353
generators , 315
turbines 214
Speed regulation 122, 246
turbines 220
Spillways 83
Stand pipes. See Surge tanks 141
Starting up of station 198
Station wiring. See Wiring 625
Steam auxiliary stations 692
base-load stations 697
cost 745
low-water stations 695
peak-load stations 697
prime movers 693
stand-by stations 694
Steam power, cost 745
relation to water and gas power 27
Steel pipe 125
Storage batteries, excitation 361
oil circuit breaker 589
Storage reservoirs 59, 159
intakes 163
limitations 160
location 160
prevention of floods 22
regulating effect 59
seepage and evaporation 164
storage and pondage 159
Storage of water 650, 685
Stream flow 53
definition of terms 53
duration curves 676
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INDEX 817
PAOB
Stream flow, economical development 645, 684
energy available 676
factors affecting stream flow 56
mass curves , 685
measurements 58, 65, 795
records 66
regulation 689
smxmiation curves 685
variations 53
Supports, bus-bar 569
Surge tanks 141, 251
Switchboards 529
panel type 531
bench boards 535
Switches, control 561
disconnecting 577
field discharge 554
throw-over 561
Switching equipment 485
ammeter transfer plugs and receptacles 560
arrangement in power-house 179
bus-bars 565
bus and switch structures 563
calibrating terminals 561
control switches 561
current and potential transformers 546, 565
disconnecting switches 577
entrance bushings 571
exciter and field control 552
field discharge switches 554
field rheostats 556
instrument equipment 538
mimic bus-bars 563
multi recorder 589
oil circuit breakers 470, 496
oil circuit-breaker batteries 589
outdoor arrangement 577
relays 492, 494, 507
relay protection 486
signal systems 583
switchboards 529
system of connections 486
voltmeter and s3mchronizing plugs and receptacles 559
Switching high-tension circuits 509, 748
S3mchronous condenser regulation 371
S3mchronous generators. See Generators 280
Synchronous impedance 292
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818 INDEX
PAOB
Synchronous reactance 294
S3mchronifian indicator 544
Synchronizing plugs and receptacles 559
T
Taps, transformers 387, 441
Telephone protection '. 620
Temperature, indicators 545
measurements 310
Temperature rise, permissible 309
bus-bars 566
current limiting reactors 459
exciters 351
generators 308
transformers .' • 383, 453, 455
Testing code for turbines 788
Thermometers for transformers 445
Three-wire system, Edison 392, 401, 402, 408, 418, 419
Throw-over switches 561
Thunderstorm records 617
Transformation, phase 409
two- or three-phase to single-phase :,: 409
two-phase to six-phase 410
three-phase to two-phase :•. : 412
three-phase to three-phase, two-phase 415
' three-phase to six-phase 417
Transformation, voltage 391
single-phase 391
two-phase 393
three-phase, delta-delta 397
three-phase, delta-Y and vice ver^. 398
three-phase, Y-Y 403
three-phase, open delta 404
three-phase, T 407
Transformers 373
arrangement in power-house 176
breathers 432
bushings 442
connections 391
cooling coils ; . . .• 433
coo^g water 381, 457
cooling water-indicators 435
cores 437
core type 379, 439
corrosion of cooling coils 434
current and potential 548
drying 445
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INDEX 819
TraDsformen, efficiency . : >....'..' 384
frequency 275
fundamental principles 373
grounding of neutrai . .392, 303, 396, 398, 399, 401, 404, 408, 413, 420
grounding of secondaries 393
grouping 489, 492
impedance 426
induced E.M.F 375
magnetizing current 376
mechanical design 429
method oi cooling 379
number and sixe 390
oil 443, 456
oil drying ; . . 449
oil testing 451
operatKHi 462
parallel operation 421
rating.. ;: 883
ratio 875
reactance 377, 469
regulation, voltage 378
shell-type 379, 437
shipping 445
single and polyphase 381
tanks .- 429
taps 887,441
temperature measurements 383
temperature rise 383, 453, 455
voltage 385
voltage regulation 378
windings 438
Transmission, developments 4, 10
principal data of systems 783
reactance 469
voltage 8, 271
Transportation of apparatus 193
Traveling waves 596
Tunnels 113
Turbines 202
arrangement in power-house 175
bearings 241, 330
brakes 348
buckets 242
casings 237
characteristic curves 214
corrosion 233
draft tubes 239
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820 INDEX
PAOB
Turbinea, efficiency 211, 789
erosion 233
flywheel effect 327
gate mechanism 235
history of developments 1,9
horizontal 227, 242
housing 246
impulse 204
lubrication 338
mechanical design 226, 242
noizles 241, 246
number of units and capacity 204
over-speed 226
reaction 202
regulation 140, 220
runners 231, 242, 244
selection of type 204
speed, actual 214
speed regulation 140, 220
speed rings ^ 237
speed, specific 206
speed variations , 202, 204
test 217, 788
vertical 229, 242
wicket gates 236
windage and friction '. 791
U
Unloading of apparatus 194
V
Valves. See also Gates. . 144
air 128,157
gate 148
Johnson hydraulic 156
operation and control 149
pivot 155
reUef 141, 221, 251, 258
Velocity of water 106, 107, 116, 798
canals 106
flumes 110
pipe lines 114, 246
tunnels 113
Ventilation, generators 173, 345
power-house 173
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INDEX 821
Venturi meten 262
registers 264
manometers 265
Voltage 270
distribution 273
exciter 351
generator 270, 316
induced 280, 375
transformers 386
transmission 4, 271
Voltage drop in conductors 639
Voltage regulation 363
generators 291
transformers 378
Voltage rise. See Over-voltage 525, 593
Voltage test, generators 326, 331
oil circuit breakers 497
transformers 386
Voltmeters 540, 541
Voltmeter plugs and receptacles 559
W
Water 39
critical temperature 40
effect of atmospheric pressure 42
energy of flowing water 67
latent heat 41
measurements 43
properties . . .*. 39
quantity of flowing water 67, 795
safe velocities 107
specific gravity 39
specific heat 42
velocity 66, 106, 110, 113, 114, 116, 121, 798
weight 39
Water conductors 104
canals 106
classification 104
flumes 110
pipe lines 114
tunnels 113
Water hammer 138
Water flow indicators, transformers 435
Water power, history of developments 1
Water power in United States 16, 17
Water power in the world 13
Water power from inland waterways 22
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822 INDEX
Water power, relation to steam and gas 27
Water power reports 645
Water stage registers 265
Water storage. See Storage of water 686
Water supply, source 44
Water supply systems, power from 23
Waterways, power from 22
Water wheels. See Turbines 202
Watthour meters 549
Wattmeters, indicating 542
Waves, form 282, 301
traveling 696
Weir 58
Wetted perimeter 107, 795
William and Hazen formula 116
Windings, generator 282, 285, 295, 325
transformer 391, 438
Wiring, station 626
cables in duct or conduit 628
control and instrument wiring 629, 633
corona limit of voltage 639
• economical considerations 639
exciter and field wiring 631
general practice 631
generator and transformer 631
high-tension 633
insulation 625
open wiring 626
resistance and reactance of cables : 642
single V8. multiple conductors 629, ^
spacing of conductors 627
voltage drop 639
Wooden-stave pipe . . , 131
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