Full text of "Power stations and power transmission; a manual of approved American practice in the construction, equipment, and management of electrical generating stations, substations, and transmission lines, for power, lighting, traction, electro-chemical, and domestic uses; part I.--Power stations, part II.--Power transmission"

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THOMAS A. EDISON,

Inventor of Telegraphic Appliances, Phonograph,
Incandescent Lamp, and Many Other Electrical Devices

Power Stations

and

Power Transmission

A Manual of

APPROVED AMERICAN PRACTICE IN THE CONSTRUCTION, EQUIPMENT,
AND MANAGEMENT OF ELECTRICAL GENERATING STATIONS,
SUBSTATIONS, AND TRANSMISSION LINES, FOR
POWER, LIGHTING, TRACTION, ELECTRO-
CHEMICAL, AND DOMESTIC USES

PART I— POWER STATIONS
PART II— POWER TRANSMISSION

By GEORGE C. SHAAD, E.E

Assistant Professor of Electrical Engineering, Massachusetts
Institute of Technology

ILLUSTRATED

CHICAGO

AMERICAN SCHOOL OF CORRESPONDENCE
M 1908 '"*

f\s

GENERAL

Entered at Stationers' Hall, London
All Rights Reserved

Foreword

N recent years, such marvelous advances have been
made in the engineering and scientific fields, and
so rapid has been the evolution of mechanical and
constructive processes and methods, that a distinct
need has been created for a series of practical
working guides, of convenient size and low cost, embodying the
accumulated results of experience and the most approved modern
practice along a great variety of lines. To fill this acknowledged
need, is the special purpose of the series of handbooks to which
this volume belongs.

C, In the preparation of this series, it has been the aim of the pub-
lishers to lay special stress on the practical side of each subject,
as distinguished from mere theoretical or academic discussion.
Each volume is written by a well-known expert of acknowledged
authority in his special line, and is based on a most careful study
of practical needs and up-to-date methods as developed under the
conditions of actual practice in the field, the shop, the mill, the
power house, the drafting room, the engine room, etc.

C, These volumes are especially adapted for purposes of self-
instruction and home study. The utmost care has been used to
bring the treatment of each subject within the range of the com-

17976G

mon -understanding, so that the work will appeal not only to the
technically trained expert, but also to the beginner and the> self-
taught practical man who wishes to keep abreast of modern
progress. The language is simple and clear; heavy technical terms
and the formulae of the higher mathematics have been avoided,
yet without sacrificing any of the requirements of practical
instruction; the arrangement of matter is such as to carry the
reader along by easy steps to complete mastery of each subject;
frequent examples for practice are given, to enable the reader to
test his knowledge and make it a permanent possession; and the
illustrations are selected with the greatest care to supplement and
make clear the references in the text.

C, The method adopted in the preparation of these volumes is that
which the American School of Correspondence has developed and
employed so* successfully for many years. It is not an experiment,
but has stood the severest of all tests — that of practical use — which
has demonstrated it to be the best method yet devised for the
education of the busy working man,

C. For purposes of ready reference and timely information when
needed, it is believed that this series of handbooks will be found to
meet every requirement.

Table of Contents

PART I— POWER STATIONS
LOCATION OF STATION AND SELECTION OF SYSTEM ' . ... Page 3

Choosing Site — Provision for Future Extensions — Cost of Real Estate
— Location of Substation — Factors Determining Choice of Generating
and Transmission Systems — Advantages of Concentrating the Gener-
ating Plant — Size of Plant.

STEAM AND HYDRAULIC PLANTS Page 10

Boiler Requirements — Types of Boilers — Steam Piping — Interchange-
ability of Units — Size, Location, etc., of Pipes — Loss of Pressure — •
Superheating — Feed-Water and Feeding Appliances — Scale and Other
Impurities — Feed-Pumps and Injectors — Furnaces — Natural and Me-
chanical Draft — Firing of Boilers— Steam Engines — Steam Turbines —
Use of Water-Power — Water Turbines (Reaction and Impulse Types)
— Pelton Wheel — Water-Pressure — Hydraulic Pipe Data — Head and
Horse-Power — Governors — Gas Engines as Prime Movers.

ELECTRICAL EQUIPMENT OF STATIONS Page 36

Generators (Direct-Current, Alternating-Current, Single-Phase, Poly-
phase, Double-Current) — Exciters — Transformers — Storage Batteries
— Switchboards and Connections — Standard Wire and Cable — Panels — •
— Ammeters — 'Voltmeters— Rheostats — Circuit-Breakers — Bus-Bars —
Oil Switches — Tripping Magnets — Lightning Arresters — Reverse-Cur-
rent Relays — Speed-Limit Devices — Substations.

STATION BUILDINGS, RECORDS, AND OFFICE MANAGEMENT . . Page 63

Layout of Structure and Appointments — Station Records — Operating
Expenses — Fixed Charges — Depreciation — Methods of Charging.

PART II— POWER TRANSMISSION
CONDUCTORS Page 1

Materials Used — Temperature Coefficient — Weight — Mechanical
Strength — Effects of Resistance — Current-Carrying Capacity — Insulat-
ing Covering for Wires — Annunciator Wire — Underwriter's Wire —
Weatherproof Wire — Gutta-Percha and India Rubber.

DISTRIBUTION SYSTEMS AND TRANSMISSION LINES. . . . Page 11

Series Systems — Parallel or Multiple-Arc Systems — Feeders and Mains
— Parallel and Anti-Parallel Feeding — Series-Multiple and Multiple-
Series Systems — Multiple-Wire Systems — Voltage Regulation of Par-
allel Systems — Alternating-Current Systems (Series, Parallel) —
Polyphase Systems^ (Two-Phase, Three-Phase)' — Calculation of A. C.
Lines — Wiring Formulae — Transformers — Losses — Efficiency — Regula-
tion— Overhead Lines — Poles — Guying — Cross- Arms — Insulators — Pins
— Temperature Effects — Underground Construction — Vitrified Con-
duit— Fibre Conduit — Manholes — Cables — Protection of Circuit.

INDEX . . Page 75

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wr- 'HE

UNIVERSITY

POWER STATIONS,

With the rapid increase of the use of electricity for power,
lighting, traction, and electro- chemical processes, the powerhouses
equipped for the generation of the electrical supply have increased
in size from plants containing a few low-capacity dynamos, belted
to their prime movers and lighting a limited district, to the mod-
ern central station, furnishing power to immense systems and over
extended areas. Examples of the latter type of station are found
at Niagara Falls, such stations as the Metropolitan and Manhattan
stations in New York City, the plants of the Boston Edison Illu-
minating Company, etc.

The subject of the design, operation, and maintenance of cen-
tral stations forms an extended and attractive branch of electrical
engineering. The design of a successful station requires scientific
training, extensive experience, and technical ability. Knowledge
of electrical subjects alone will not suffice, as civil and mechanical
engineering ability is called into play as well, while ultimate
success depends largely on financial conditions. Thus, with un-
limited capital, a station of high economy of operation may be
designed and constructed, but the business may be such that the
fixed charges for money invested will more than equal the differ-
ence between the receipts of the company and the cost of the gen-
eration of power alone. In such cases it is better to build a cheaper
station and one not possessing such extremely high economy, but
on which the fixed charges are so greatly reduced that it may be
operated at a profit to the owners.

The designing engineer should be thoroughly familiar with
the nature and extent of the demand for power and with the prob-
able increase in this demand. Few systems can be completed for
their ultimate capacity at first and, at the same time, operated
economically. Only such generating units, with suitable reserve
capacity, as are necessary to supply the demand should be installed
at first, but all apparatus should be arranged in such a manner
that future extensions can be readily made.

POWER STATIONS

The subjects of power stations, as here treated, will consider
the following general topics :

Location of station and substation3 with choice of system to be em-
ployed.

Steam plants, boilers, piping, prime movers, etc.

Hydraulic plants.

The use of other prime movers.

The electrical plant, generators, and exciters, switching apparatus, etc.

Buildings.

Station records, methods of charging for power, etc.

LOCATION OF THE GENERATING STATION.

The choice of a site for the generating station is very closely
connected with the selection of the system to be used, which sys-
tem, in turn, depends largely on the nature of the demand, so that
it is a little difficult to treat these topics separately. Several possi-
ble sites are often available, and we may either consider the require-
ments of an ideal location, selecting the available one which is

ct>

nearest to this in its characteristics, or we may select the best system
for a given area and assume that the station may be located where
it would be best adapted to this system. Wherever the site may
be, it is possible to select an efficient system, though not always
an ideal one.

The following points should be considered in the location of
a station, no matter what the system used :

1. Accessibility.

2. Water supply.

3. Stability of foundation.

4. Surroundings.

5. Facility for extension.

6. Cost of real estate.

The station should be readily accessible on account of the
delivery of fuel and stores, and of the machinery, while it should
be so located that ashes and cinders may be easily removed. If
possible, the station should be located so as to be reached by both
rail and water, though the former is generally more desirable. If
the coal can be delivered to the bunkers directly from the cars, the
very important item of the cost of handling fuel may be greatly
reduced. Again, the station should be in such a location that it

O "

may be readily reached by the workmen.

POWEK STATIONS

Cheap and abundant water supply for Loth boilers and con-
densers is of utmost importance in locating a steam station. The
quality of the water supply for the boiler is of more importance
than the quantity. It should be as free as possible from impuri-
ties which are liable to corrode the boilers, and for this reason
water from the town mains is often used, even when other water is
available, as it is possible to economize in the use of water by the
selection of proper condensers. The supply for condensing pur-
poses should be abundant, otherwise it is necessary to install ex-
tensive cooling apparatus which is costly and occupies much
space.

The machinery, as -well as the buildings, must have stable
foundations, and it is well to investigate the availability of such
foundations when selecting the site.

In the operation of a power plant using coal or other fuels,
certain nuisances arise, such as smoke, noise, or vibration, etc.
For this reason it is preferable to locate where there is little lia-
bility to complaint on account of these causes, as some of these
nuisances are costly and difficult or even impossible to prevent.

A station should be located where there are ample facilities
for extension and, while it may not always be advisable to pur-
chase land sufficient for these extensions at first, if there is the
slightest doubt in regard to being able to purchase it later, it
should be bought at once, as the station should be as free as possi-
ble from risk of interruption of its plans. Often real estate is too
high for purchasing a site in the best location, and then the next
best point must be selected. A consideration of all the factors
involved is necessary in determining whether or not this cost is
too high. In densely populated districts it is necessary to econo-
mize greatly with the space available, but it is generally desirable
that the. machinery may all be placed on the ground floor and that
adequate provision may be made for the storage of fuel, etc.

The location of substations is usually fixed by other con-
ditions than those which determine the site of the main power
house. Since, in the simple rotary converter substation, neither
fuel or water are necessary and there is little noise or vibration, it
may be located wherever the cost of real estate will permit, pro-
vided suitable foundation may be constructed. The distance

POWER STATIONS

between substations depends entirely on the selection of the sys-
tem and the nature of the service.

Where low voltages are used it is essential that the station
be located as near the center of the system as possible. This cen-
ter is located as follows:

Having determined the probable loads and their points of
application for the proposed system, these loads are indicated on a
drawing with the location of the same shown to scale. The center
of gravity of this system, considering each load as a weight, is
then found and its location is the ideal location, as regards amount
of copper necessary for the distributing system.

Consider Fig. 1, which shows the location of five different
loads, which in this case are indicated by number of amperes.
Combining loads A and B, we have Ax = By. x -f y — a. Solv-
ing these equations we find that

,,*---- -3^" *B4 A and B may be considered as

*• C-*--*"*"" """ f

a load of A + B amperes at F.

,<H9 Similarly, C and D, E and F,

/ NXN /*C3 and G and II may be combined

SN^IS / giying us I> the center of the

/ NSN / system. The amount of copper

/3 Nxyo9 necessary for a given regulation

/ runs up very rapidly as the dis-

/ tance of the station from this

point increases.

Selection of System. Gen-
eral rules only can be stated for the selection of a system to be
used in any given territory for a certain class of service.

For an area not over two miles square and a site reasonably
near the center, for lighting and ordinary power purposes, direct-
current, low-pressure, three-wire systems may be used. Either 220
or 440 volts may be used as a maximum voltage, and motors should,
preferably, be connected across the outside wires of the circuits.
Five-wire- systems with 440 volts maximum potential have been
used, but they require very careful balancing of the load if the
service is to be satisfactory. 220-volt lamps are giving good satis-
faction; moderate-size, direct-current motors may be readily built
for this pressure and constant-potential arc lamps may be operated

POWER STATIONS

on this voltage though not BO economically as on 110 volts, if
single lamps are used. For direct-current railway work, the limit
of the distance to which power may be economically delivered with
an initial pressure of GOO volts is from live to seven miles, depend-
ing on the traffic.

If the area to be served is materially larger than the above,
or distances for direct-current railways greater, either of two dif-
ferent schemes may be adopted. Several stations may be located
in the territory and operated separately or in multiple on the va-
rious loads, or one large power house may be erected and the en-
ergy transmitted from this station at a high voltage to various
transformers or transformer substations which, in turn, transform
the voltage to one suitable for the receivers. Local conditions
usually determine which of these two shall be used.
;:_, . The use of several .low- tension stations operating in multiple
is recommended only under certain conditions, namely, that the
demand is very heavy and fairly uniformly distributed throughout
the area, and suitable sites for the power house can be readily ob-
tained. Such conditions rarely exist and it is a question whether
or not the single station would not be just as suitable for such
cases as where the load is not BO congested.

One reason why a large central station is preferred to several
smaller stations is that large stations can be operated more eco-
nomically, owing to the fact that large units may be used and they
can be run more nearly at full load. There is a gain in the cost
of attendance, and labor-saving devices can be more profitably in-
stalled. The location of the power plant is not determined to such
a large extent by the position of the load, but other conditions,
such as water supply, cheap real estate, etc., will be the governing
factors. In several cities, notably Xew York and Boston, large
central stations are being installed to take the place of several sep-
arate stations, the old stations being changed from generating
power houses to rotary- converter substations. Both direct-cur-
rent low-tension machines, to supply the neighboring" districts,
and high-tension alternating-current, for supplying the outlying
or residence districts, are often installed in the one station

As examples of the central station being located at some dis-
tance from the center of the load, we have nearly all of the large

POWER STATIONS

hydraulic power developments. Here it is the cheapness of the
water power which determines the power house location. The
greatest distance over which powrer is transmitted electrically at
present is in the neighborhood of 200 miles.

If a high-tension alternating-current system is to be installed,
there remains the choice of a polyphase or single-phase machine as
well as the selection of voltage for transmission purposes. As
pointed out in " Power Transmission ", polyphase generators are
cheaper than single-phase generators and, if necessary, they can be
loaded to about 80% of their normal capacity, single-phase, while
motors can be more readily operated from polyphase circuits. If
synchronous motors or rotary converters are to be installed, a poly-
phase system is necessary. 'The voltage will be determined by the
distance of transmission, care being taken to select a value consid-
ered as standard, if possible. Generators are wound giving a volt-
age at the terminals as high as 15,000 volts, but in many districts
it is desirable to use step-up transformers for voltages above 6,600
on account of liability to troubles from lightning.

With the development of the single-phase railway motor, cen-
tral stations generating single-phase current only, will be built in
larger sizes than previously, as their use heretofore has been lim-
ited to lighting stations.

Size of Plant. A few general notes in regard to the design
of plants will be given here, the several points being taken up
more in detail later.

Direct driving of apparatus is always superior to methods of
gearing or belting as it is efficient, safe, and reliable, but it is not as
flexible as shafting and belts, and on this account its adoption is
not universal.

Speeds to be used will depend on the type and size of the
generating unit. Small machines are always cheaper when run at
high speeds, but the saving is less on large generators. For large
engines, slow speed is alwrays preferable.

It is desirable that there be a demand for both power and
lighting, and a station should be constructed which will serve both
purposes. The use of power will create a day load for a lighting
station which does much to increase its ultimate efficiency and, as
a rule, its earning capacity.

POWER STATIONS

In addition to generator capacity necessary to supply the load,
a certain amount of reserve, either in the way of additional units
or overload capacity, must be installed. The probable load for say
three years can be closely estimated and this, together with the
proper reserve, will determine the size of the station. The plaat
as a whole, including all future extensions, should be planned at
the start as extensions will then be greatly facilitated. Usually it
will not be desirable to begin extensions for at least three years
after the first part of the plant has been erected.

Enough units must be installed so that one or more may be
laid off for repairs, and there are several arguments in favor of
making this reserve in the way of overload capacity, for the gen-
erators at least. Some of these arguments are: .Reserve is often
required at short notice, notably in railway plants. With overload
capacity, rapid increase of load, such as occurs in lighting stations
when darkness comes on suddenly, may be more readily taken care
of. There is always a factor of safety in machines not •running to
their fullest capacity. Reserve capacity is cheaper in this form
than if installed as separate machines. As a disadvantage, we
have a lower efficiency, due to machines not usually running at
full load, but in the case of generators this is yery slight.

With an overload capacity of 33 J%, four machines should be
the initial installment since one can be laid off for repairs if neces-
sary, the total load being readily carried by three machines. In
planning extensions, the fact that at least one machine may require
to be laid off at any time should not be lost sight of, while the
units should be made as large as is conducive to the best operation.

TABLE 1.
Permissible Overload 33 per cent.

Machines
one at a

added
time.

Machines
two at a

added
time.

Machines
three at i

added
i time.

Initial installment.

Size.
500

No..
4

Size.
500

No.
4

Size.
500

First extension

666

1000

2000

Second '

888

2000

5000

Third '

lias

4000

5000

Fourth '

1577

4000

Fifth '

2103

4000

Sixth '

2804

10 POWER STATIONS

Table- 1 is worked out showing the initial installment fora
2,000-K.AV. plant with future extensions. It is seen from this
table that adding two machines at a time gives more uniformity in
the size of units — a very desirable feature.

The boilers should be of large units for stations of large
capacity, while for small stations they must be selected so that at
least one may be laid off for repairs.

STEAM PLANT.
BOILERS.

The majority of power stations have their machinery driven
by either steam or water power, though there are many using gas
engines as prime movers. If a steam plant is being considered.
one of the first subjects to be taken up is the generation of the
steam. The subject of boilers is one of vital importance to the
successful operation of steam-driven central stations. The object
of the boiler with its furnace is to abstract as much heat as possi-
ble from the fuel and impart it to the water. The various kinds
of boilers used for accomplishing this more or less successfully are
described in books on boilers, and we will consider here the merits
of a few of the types only as regards central-station operation.

The requirements are: First, that steam be available through-
out the twenty-four hours; the amount required at different parts
of the day varying considerably. Thus, in a lighting station, the
demand from midnight to 6 a. in. is very light, but toward eve-
ning, when the load on the station increases very rapidly, there is an
abrupt increase in the rate at which steam must be given off. The
maximum demand can be readily anticipated under normal weather
conditions, but occasionally this maximum will be equaled or even
exceeded at unexpected moments. For this reason a certain num-
ber of boilers must be kept under steam constantly, more or less
of them running with banked fires during light loads. If the
boilers have a small amount of radiating surface, the loss during
idle hours will be decreased.

Second, the boilers must be economical over a large range of
rates of firing and must be capable of being forced without detri-
ment. Boilers should be provided which work economically for the
hours just preceding and following the maximum load while they

POWER STATIONS • 11

may be forced, though running at lower efficiency, during the peak.

Thvrd, coining to the commercial side of the question, we have
first cost, cost of maintenance, and space occupied. The first cost,
as does the cost of maintenance, varies with the type and pressure
of the boiler. The space occupied enters as a factor only when
the situation of the station is such that space is limited, or when the
amount of steam piping becomes excessive. In some city plants,
space may be the determining feature in the selection of boilers.

The Cornish and Lancashire boilers differ only in the num-
ber of cylindrical tubes in \vhich furnaces are placed. As many
as three tubes are placed in the largest sizes (seldom used) of the
-Lancashire boilers. They are made np to 200 pounds steam pres-
sure and possess the following features:

1. High efficiency at moderate rates of combustion.

2. Low rate of depreciation.

3. Large water space.

4. Easily cleaned.

5. Large floor space required.

6. Cannot be readily forced.

The Galloway boiler differs from the Lancashire boiler in that
there are cross tubes in the flues.

In the Multitubular boiler the number of tubes is greatly
increased and their size diminished. Their heating surf ace is large
and they steam rapidly. They are used extensively for power-
station work.

The chief characteristics of the water-tube boilers, of which
there are many types, are:

1. Moderate floor space.

2. Ability to steam rapidly.

3. Good water circulation.

4. Adapted to high pressure.

5. Easily transported ami erected.

6. Easily repaired.

7. Not easily cleaned.

8. Rate of deterioration greater than for Lancashire boiler.

9. Small water space, hence variation in pressure with varying
demands for steam.

10. Expensive setting.

Marine boilers require no setting. Among their advantages
and disadvantages may be mentioned:

12 POWER STATIONS

1. Exceedingly small space necessary.

2. Radiating surface reduced.
8. Good economy.

4. Heavy and difficult to repair.

5. Unsuitable for bad water.

6. Poor circulation of water.

Another type of boiler, known as the Economic, is a combi-
nation of the Lancashire and multitubular boilers, as is the marine
boiler. It is set in brickwork and arranged so that the gases pass
under the bottom and along the sides of the boiler as well aa
through tne tubes. It may be compared with other boilers from
the following points:

1. Small floor space.

2. Less radiating surface than the Lancashire boiler,

3. Not easily cleaned.

4. Repairs rather expensive.

5. Requires considerable draft. ,

As regards first cost, boilers installed for 150 pounds pressure
and the same rate of evaporation, will run in the following order:
Galloway and Marine, highest first cost, Economic, Lancashire, Bab-
cock & Wilcox. The Increase of cost, with increase of steam pres-
sure, is greatest for the Economic and least for the water-tube type.

Deterioration is less with the Lancashire boiler than with the
other types.

The floor space occupied by these various types built for 150
pounds pressure and 7,500 pounds of water, evaporated per hour,
is given in Table 2.

TABLE 2.

Kind of Boiler.

Lancashire ........................... ............. / ...... 408

Galloway ................................................. 371

Babcock and Wilcox ..................................... 200

Marine wet-back .......................................... 120

Economic ................................................. 210

The percentage of the heat of the fuel utilized by the boiler
is 01 great importance, but it is difficult to get reliable data in re-
gard to this. Table 8 is taken from Donkin's "Heat Efficiency of
Steam Boilers", and will give some idea of the efficiencies of the
different types. Economizers were not used in any of these tests,
but they should always be used with the Lancashire type of boiler.

POWER STATIONS

TABLE 3.

Kind of Boiler.

No. of Ex-
periments.

Mean Effi-
ciency of
two best
Experi-
ments.

Lowest
Efficiency.

Mean Effi-
ciency of
all Experi-
ments.

Lancashire hand-lired .

107

79.5

42 1

62 8

Lancashire machine-fired

78.0

51 9

64 2

Cornish hand-lired

81.7

53.0

68 0

Babcock and \Vilcox hand-lired... .
Marine wet-back hand-lired
Marine dry-back hand-lired

49
6
24

77.5
69.6
75.7

50.0
62.0
64.7

64.9
66-0

69.2

. It is well to select a boiler from 20 to 50 pounds in excess of
the pressure to be used, as its life may thus be considerably ex-
tended, while, when the boiler is new, the safety valve need not
be set so near the normal, pressure, and there is less s.team wasted
by the blowing off of this valve. Again, a few extra pounds of
steam may be carried just previous to the time the peak of the
load is expected. For pressures exceeding 200 or, possibly, 150
pounds, a water- tube boiler should be selected.

In large stations, it is preferable to make the boiler units of
large capacity, to do away as much as possible with the extra
piping and fittings necessary for each unit. Water-tube boilers
are best adapted for large sizes. These may be constructed for
150 pounds pressure, large enough to evaporate 20,000 pounds of
water per hour, at an economical rate.

To sum up — For stations of moderate size and with medium
pressures with plenty of space, use Lancashire or fire- tube boilers;
for high pressure or large units, select water-tube boilers; where
space is limited, install marine boilers, although they are not as
safe as water-tube boilers for high pressures.

Steam Piping. The piping from the boilers to the engines
should be given very careful consideration. Sieam should be
available at all times and for all engines. Freedom from serious
interruptions due to leaks or breaks in the piping is brought about
by very careful design and the use of good material in construction.
Duplicate piping is used in many instances. Provision must
always be made for variations in length of the pipe with variation
of temperature. For plants using steam at 150 pounds pressure,
the variation in the length of steam pipe maybe as high as 2.5

POWER STATIONS

inches for 100 feet, and at least 2 inches for 100 feet should always
be counted upon.

Arrangement. Fig. 2 shows a simple diagram of the " ring"
system of piping. The steam passes from the boiler by two paths
to the engine and any section of the piping may be cut out by

VALISE.
Fig. 2.

the closing of two valves. Simple ring systems have the following
characteristics:*

1. The range, as the main pipe is called, must be of uniform size and
large enough to carry all of the steam when generated at its maximum rate.

2. A damaged section may disable one boiler or one engine.

3. Several large valves are required.

4. Provision may be readily made to allow for expansion of pipes.

Cross connecting the ring system, as showrn in Fig. 3, changes
these characteristics as follows:

1. Size of pipes and consequent radiating surface is reduced.

2. More valves needed but they are of smaller size.
8. Less easy to arrange for expansion of the pipes.

POWER STATIONS

If the system is to be duplicated, that is, two complete sets of
main pipes and feeders installed .(see Fig. 4), two schemes are in use:

1. Each system is designed to operate the whole station at maxi-
mum load with normal velocity and loss of pressure in the pipes, and only
one system is in use at a time. This has the disadvantage that the idle

BO/LZFIS

Fig. 8.

section is liable not to be in good operating condition when needed. Large
pipes must be used for each set of mains.

2. The two systems may be made large enough to supply steam at
normal loss of pressure when both are used at the same time, while either
is made large enough to keep the station running should the other section
need repairs. This has the advantages of less expense, and both sections
Of pipe are normally in use; but it has the disadvantages of more radiating
surface to the pipes and consequent condensation for the same capacity
for furnishing steam.

POWER STATIONS

Complete interehangeability of units cannot be arranged for
if the separate engine units exceed 400 to 500 horse power. Since
engine units can be made larger than boiler units, it becomes nec-
essary to treat several boiler units as a single unit, or battery, these
batteries being connected as the single boilers already shown. For
still larger plants the steam piping, if arranged to supply any
engines from any batteries of boilers, would be of enormous size.
If the boilers do not occupy a greater length of floor space than
the engines, Fig. 5 shows a good arrangement of units. Any

Fig. 4.

engine can be fed from either of two batteries of boilers and the
liability of serious interruptions of service due to steam pipes or
boiler trouble is very remote.

Material. Steel pipe, lap welded and fastened together by
means of flanges, is to be recommended for all steam piping. TLe
flanges may be screwed on the ends of sections and calked so as to
render this connection steam tight, though in large sizes it is better
to have the flanges welded to the pipes. This latter construction

POWER STATIONS

costs no more for large pipes and is much more reliable. All
valves and fittings are made in two grades or weights, one for low
pressures, and the other for high pressures. The high -pressure
fittings should always be used for electrical stations. Gate valves
should always be selected and, in large sizes, they should be pro-
vided with a by-pass.

Asbestos, either alone or
with copper rings, vulcan-
ized india rubber, asbestos
and india rubber, etc., are
used for packing between
flanges to render them
steam tight. Where there
is much expansion, the ma-
terial selected should be one
that possesses considerable
elasticity. Joints for high-
pressure systems require
much more care than those
where steam is used at a
low pressure, and the num-
ber of joints should be re-
duced to a minimum by-
using long sections of pipe.
A list of the various fit-
tings required for steam
piping, together with their
descriptions, is given in
books on boilers. One pre-
caution to be taken is to
see that such fittings do not
become too numerous or
complicated, and it is well
not to depend too much

Fig. 5.

on automatic fittings. Steam separators should be large enough
to serye as a reservoir of steam for the engine and thus equalize,
to a certain extent, the velocity of flow of steam in the pipes.

18 POWER STATIONS

In providing for the expansion of pipes due to change of
temperature, " IT " bends made of steel pipe and having a radius
of curvature not less than six times, and preferably ten times the
diameter of the pipe, are preferred. Copper pipes cannot be rec-
ommended for high pressures, while slip expansion joints are most
undesirable on account of their liability to bind.

The size of steam pipes is determined by the velocity of flow.
Probably an average velocity of 60 feet per second would be better
than 100 feet per second, though in some cases where space is
limited a velocity as high as 150 feet per second has been used.

The loss in pressure in steam pipes may be obtained from the
following formula:

QVL

*.-*.*' Tgr

where j?, — p.2 = loss in pressure in pounds per sq. in.

Q = quantity of steam in cu. ft. per minute.
d = diameter of pipe in inches.
.L = length in feet.

w = weight per cu. ft. of steam at pressure JP,.
c — constant depending on size of pipe.

Values of c are as follows:

Diameter of pipe.. %" v' -" B" 4" 5" 6" 7" 8" 9" 10"

Value of c 36.8 45.3 52.7 56.1 57.8 58.4 59.5 60.1 60.7 61.2 61.8

Diameter of pipe 12" 14" 16" 18" 20" 22" 24"

Value of c. 62.1 62.3 62.6 62.7 62.9 63.2 63.2

In mounting the steam pipe, it should be fastened rigidly at
one point, preferably near the center of a long section, and allowed
a slight motion longitudinally at all other supports. Such sup-
ports may be provided with rollers to allow for this motion, or the
pipe may be suspended from wrought-iron rods which will give a
flexible support. Practice differs in the location of the steam pip-
ing, some engineers recommending that it be placed underneath
the engine room floor and others that it be located high above the
engine room floor. In any case it should be made easily access-
ible, and the valves should be located so that nothing will inter-
fere with their operation. Proper provision must be made for
draining the pipes.

PO\YER STATIONS 1U

All piping &s well as joints should be carefully covered with a
good quality of lagging as the amount of steam condensed in a bare
pipe, especially if of any great length, is considerable. In select-
ing a lagging the following points should be noticed. Covering for
steam pipes should be incombustible, should present a smooth sur-
face, should not be easily damaged by vibration or steam, and
should have as large a resistance to the passage of heat as possible.
It must not be too thick, otherwise the increased radiating surface

will counterbalance the resistance to the passage of heat.

The loss of power in steam pipes due to radiation is given as
follows:

II = loss of power in heat units.
(I — diameter of pipe.
L = length of pipe in feet.
r — constant depending on steam pressure and pipe covering.

Steam pressure in pounds (absolute) ...... 40 65 90 115

Values of r for uncovered pipe ............. 437 555 620 684

Value ofr for pipe covered with 2 inches of

hair felt .............................. 48 58 66 73

Referring to table in books on boilers, the relative values of
different materials used for covering steam pipes may be found.

Superheated Steam reduces condensation in the engines as
well as in the piping? and increases the efficiency of the system.
Its use was abandoned for several years, due to difficulties in
lubricating and packing the engine cylinders, but by the use of
mineral oils and metallic packing, these difficulties have been done
away with to a large extent, while steam turbines are especially
adapted to the use of superheated steam. The application of heat
directly to steam, as is done in the superheater, increases the
efficiency of the boilers. Table 4 shows the increase in boiler
efficiency for a certain boiler test, the results being given in
pounds of water changed to dry, saturated steam. Tests on vari-
ous engines show a gain in efficiency as high as 9% with a super-
heat of 80° to 100° F, while special tests in some cases show even
a greater gain.

POWER STATIONS

TABLE 4.

Amount of superheat.

Water evaporated per Ib.
of coal.

Without
superheat.

With super-
heat.

40 degrees F

7.82
6.42
6.00
6.78
7.15

9.99
7.06
7.00
8.66
8.65

42 " ..

55 "

56.5 "

5.5.2 " ...

Superheaters are very simple, consisting of tubular boilers
containing steam instead of water, and either located so as to util-
ize the heat of the gases, the same as economizers, or separately
fired. They should be arranged so that they may be readily cut
out of service, if necessary, and provision must be made for either
flooding them or turning the hot gases into a by-pass, as the tubes
would be injured by the heat if they contained neither water nor
steam.

FEED WATER AND FEEDING APPLIANCES.

All water, such as can be obtained for the feeding of boilers,
contains some impurities, among the most important of which as
regards boilers are soluble salts of calcium and magnesium. Bicar-
bonates of the alkaline earths cause precipitations on the interior
of boilers, forming " scale ". Sulphate of lime is also deposited
by concentration under pressure. Scale, when formed, not only
decreases the efficiency of the boiler but also causes deterioration,
for if sufficiently thick, the diminished conducting power of the
boiler allows the tubes or plates to be overheated .and to crack or
burst. Again, the scale may keep the water from contact with
sections of the heated plates for some time and then, giving way,
large volumes of steam are generated very quickly and an explo-
sion may result.

Some processes to prevent the formation of scale are used,
which affect the water after it enters the boilers, but they are not
to be recommended, and any treatment the water receives should
affect it previous to its being fed to the boilers. Carbonates and
a small quantity of sulphate of lime may be removed by heating

POWER STATIONS

ECONOM/ZERS

in a separate vessel. Large quantities of sulphate of lime must
be precipitated chemically.

Sediment, small particles of matter in suspension, must be
remove*! by allowing the water to settle. Vegetable matters are
sometimes present, which
cause a film to be deposited.
Certain gases, in solution-
such as oxygen, nitrogen,
etc. — cause pitting of the
boiler. This effect is neu-
tralized by the addition of
chemicals. Oil, from the
engine cylinder, is particu-
larly destructive to boilers
and when present in the
condensed steam must be
carefully removed.

Both feed pumps and
injectors are used for feed-
ing the water to the boilers.
Feed pumps may be either
steam or motor-driven.
Steam-driven pumps are
very inefficient, but they are
simple and the speed is easily
controlled. Motor-driven
pumps are more efficient and
neater, but more expensive and more difficult to regulate efficiently
over a wide range of speed. Direct-acting pumps may have feed-
water heaters attached to them, thus increasing the efficiency of
the apparatus as a whole. The supply of electrical energy must
be constant if motor-driven pumps are to be used.

Feed pipes must be arranged so as to reduce the risk of fail-
ure to a minimum, and for this reason they are almost always du-
plicated. More than one water supply is also recommended if there
is the slightest danger of interruption on this account. One com-
mQn arrangement of feed-water apparatus is to install a few large
pumps supplying either of two mains from which the boiler con-

Fig. 6.

POWER STATIONS

TABLE 5.

Giving Rate of Flow of Water, in Feet per Minute, through Pipes
of Various Sizes, for Varying Quantities of Flow,

Gallons
per Min.

% in.

1 in.

1% in

Itt in.

Sin.

2VS in.

3 in.

4 in.

218

122%

78%

54%

30%

19%

13%

'**&

436

245

157

109

653

367%

235%

163%

91%

58%

40%

23 3

872

490 "

314

218

122

30%

1090

612%

392%

272%

152%

97%

67%

38%

735

451

327

183

117

81 "

857%

549%

3813^

213%

136%

94%

53%

980

628 "

436 "

244 "

156 "

108

61%

1102%

706%

490%

274%

175%

121%

785

545 "

305

195

135

76%

1177%

817%

457%

292%

202%

115

100

1090

610 "

380

270

153%

125

762%

487%

337%

191%

160

915

585

405

230

175

1067%

682%

472%

268%

200

1220 "

780

540

306%

nections are taken. This is a complicated and costly system of
piping. Fig. 6 shows a scheme used for feeding two boilers in
which each pump is capable of supplying both boilers. Pipes
should be ample in cross-section, and, in long lengths, allowance
must be made for expansion. Cast iron or cast steel is the mate-
rial used for their construction, while the joints are made by means
of flanges fitted with rubber gaskets.

Table 5 gives the rate of flow of water in feet per miniHe
through pipes of various sizes. A flow of 10 gallons per minute
for each 100 H. P. of boiler equipment should be allowed without
causing an excessive velocity of flow in the pipes.

BOILER FOUNDATIONS, FURNACES AND DRAFT.

The economical u.se of coal depends, to a large extent, on the
setting of the boiler and proper dimensions of the furnaces.
Internally-fired boilers require support only, while the setting of
externally-fired boilers requires provision for the furnaces. Com-
mon brick, together with fire brick for the lining of portions
exposed to the hot gases, are used almost invariably for boiler
settings. It is customary to set the boiler units up in batteries
of two, using a 20-inch wall at the sides and a 12-inch wall be-
tween the two boilers. The instructions for settings furnished by

POWER STATIONS 23

the manufacturers should be carefully followed out as they are
based on conditions which give the best results in the operation of
their boilers.

Natural Draft is the most commonly used and is the most
satisfactory under ordinary circumstances. In determining the
size of the chimney necessary to furnish this draft, the following
formula is given by Kent:

.06 F .06 Fv

A— — — — orA= ( — -)2
V h A

A == area of chimney in sq. ft.
k = height of chimney in ft.
F = pounds of coal per hour.

The height of chimney should be assumed and the area calcu-
lated, remembering that it is better to have the chimney too large
than too small.

The chimney may be of either brick or iron, the latter having
a less first cost but requiring repairs at frequent intervals. Gen-
eral rules for the design of a chimney may be, given as follows:
The external diameter of the base should not be less than ^ of
the height. Foundations must be of the best. Interiors should
be of uniform section and lined with fire brick. There must be an
air space between the lining and chimney proper. The exterior
should have a taper of from TX6 to \- i'nch to the foot. Flues
should be arranged symmetrically.

Fig. 7 shows the construction of a brick chimney of good
design, this chimney being used with boilers furnishing engines
which develop 14,000 H. P.

Mechanical Draft is a term which may be used to embrace
both forced and induced draft. The different systems of mechan-
ical draft are described in books on boilers. The first cost of
mechanical -draft systems is less than that of a chimney, but
the operation and repair are much more expensive and there is
always the risk of break-down. Artificial draft has the advan-
tage that it can be varied within large limits and it can be increased
to any desired extent, thus allowing the use of low grades of coal.

Firing of Boilers and Handling of Fuel. Coal is used for
fuel to a greater extent than any other material, though oil, gas,

POWER STATIONS

wood, etc., are used in some localities. Local conditions, such as
availability, cost, etc., should determine the material to be used
and no general rules can be given. Data regarding the relative

heating values of different
fuels show the following
general iigures: One .pound
of petroleum, about \ of a
gallon, is equivalent, when
used with boilers, to 1.8
pounds of coal and there is
less deterioration of the fur-
nace with oil. 7it to 12 cubic
feet of natural gas are re-
quired as the equivalent of
one pound of coal, depending
on the quality of the gas. 2i
pounds of dry wood is as-
sumed as the equivalent of
one pound of coal.

When coal is used, it
requires stoking and this
may be accomplished either
by hand or by means of me-
chanical stokers, many forms
of which are available. Me-
chanical stoking has the ad-
vantage over hand stoking
that the fuel may be fed to
the furnace more uniformly
and the fires and boilers are
not subjected to sudden
blasts of cold air as is the
case when the fire doors are
opened ; a poorer grade of
coal may be burned, if nec-
essary, and the trouble due
to smoke is much reduced. It may be said that mechanical
stokers are used almost universally in the more important elec-

Spo.ce

Ground Line

Fig. 7.

POWER STATIONS 25

trical plants. Economic use of fuel requires great care in firing,
especially if it is done by hand.

Where gas is used, the tiring may be made nearly automatic,
and the same is true of oil tiring, though the latter requires more
complicated burners, as it is necessary that the oil be vaporized.

In large stations, operated continuously, it is desirable that,
as far as possible, all coal and ashes be handled by machinery,
though' the difference in cost of operation should be carefully con-
sidered before installing extensive coal-handling machinery. Ma-
chinery for automatically handling the coal will cost from $7.50 to
$10 per horse-power rating of boilers for installation, while the ash-
handling machinery will cost from $1.50 to $3.00 per horse power.

The coal-handling devices usually consist of chain -operated
conveyors which hoist the coal from railway cars, barges, etc., to
overhead bins from which it may be fed to the stokers. The
ashes may be handled in a similar manner, by means of scraper
conveyors, or small cars may be used. Either steam or electricity
may be used for driving this auxiliary apparatus.

It is always desirable that there be generous provision for the
storage of fuel sufficient to maintain operations of the plant over
a temporary failure of supply.

STEAM ENGINES AND TURBINES.

The choice of steam prime movers is one which is governed
by a number of conditions which can be treated but briefly here.
The first of these conditions relates to the speed of the engine to
be used. There is considerable difference of opinion in regard to
this as both high and low-speed plants are in operation, which are
giving good satisfaction. Slow-speed engines have a higher first
cost and a higher economy. Probably in sizes up to 250 K.W.
the generator should be driven by high-speed engines, above which
the selection of either type will give satisfaction until sizes of say
above 500 indicated horse power, when the slow-speed type is to
be recommended. Drop valves cannot be used with satisfaction
for speeds above about 100 revolutions per minute, hence high-
speed engines must use direct-driven valve gears, usually governed
by shaft governors. Corliss valves are used on nearly all slow-
•peed engines.

26 POWER STATIONS

The steam pressure used should be at least 125 pounds per
square inch at the throttle and a pressure as high as 150 to 160
pounds is to be preferred.

Close regulation and uniform angular velocity are required

O v

for driving generators, especially alternators which are to operate
in parallel. This means sensitive and active governors, carefully
designed fly-wheels and proper -arrangement of cranks when more
than one is used.

For large plants or plants of moderate size, compound con-
densing engines are almost universally installed. The advantage
of these engines in increased economy are in part counterbalanced
by higher first cost and increased complications, together with the
pumps and added water supply necessary for the condensers.
The approximate saving in amount of steam is shown in table 0,
which applies to a 500 horse-power unit.

TABLE 6.

Pounds or Steam
per H. P. hour.

Simpler non-condensing 30

Simple condensing 22

Compound non-condensing 24

Compound condensing in

Triple expansion engines are seldom used for driving electrical
machinery as their advantages under variable loads are doubtful.
Compound engines may be tandem or cross compound and either
horizontal or vertical. The use of cross-compound engines tends
to produce uniform angular velocity, but the cylinder should be so
proportioned that the amount of work done by each is nearly equal.
A cylinder ratio of about 3J to 1 will approximate average condi-
tions. Either vertical or horizontal engines may be installed, each
having its own peculiar advantages. Vertical engines require less
floor space, while horizontal engines have a better arrangement of
parts. Either type should be constructed with heavy parts and
erected on solid foundations.

Recently steam turbines have come into use, and the number
of stations at present under process of design or construction which
will use steam turbines is very large. Several types of turbines
are described in the books on engines. In addition to these, a

POWER STATIONS 27

short review of the Curtis turbine will not be out of place since
this is one of the types which is. coming into extended use.

The Curtis turbine is divided into sections, each section of
which may contain one, two, or more, revolving sets of buckets
and stationary vanes supplied with steam from a set of expansion
nozzles. By this arrangement of parts the work is divided into
stages, the nozzle velocity is reduced in each stage, and the energy
of the steam is effectively given up to the rotating parts. This
type admits of lower speeds than the other forms of turbines.
Fig. 8. shows the arrangement of nozzles, buckets, and stationary
blades or guiding vanes for two stages. Governing is accom-
plished by shutting off "the steam from some of the nozzles. A
complete Curtis turbine of the vertical type, direct connected to a
5,000 K.W. three-phase alternating-current generator, is shown
in Fig. 9.

The advantages claimed for this turbine are:

1. High steam economy at all loads

2. High steam economy with rapidly fluctuating loads.

' 3. Small floor space per K.W. capacity, reducing to a minimum
the cost of real estate and buildings.

4. Uniform angular velocity.

5. Simplicity iii operation and low expense for attendance.

6. Freedom from vibration.

7. Steam economy not appreciably impaired by wear or lack of
adjustment in long service.

8. Adaptability to high steam pressure and high superheat without
practical difficulty and with consequent improvement in economy.

9. Condensed water is kept entirely free from oil and can be
returned to the boilers.

Many of these advantages apply equally well to the other
types of turbines now on the market. All turbines are especially
adapted to operation with superheated steam.

Engines should preferably be direct-connected as already
stated, but this is not always feasible, and gearing, belt, or rope
drives must be resorted to. Countershafts, belt or rope driven,
arranged with pulleys and belts for the different generators, and
with suitable clutches, are largely used in small stations. They
consume considerable power and the bearings require attention.

Careful attention must be given to the lubrication of all run-
ning parts, and extensive oil systems are necessary in large plants.

POWER STATIONS

In sucli systems a continuous circulation of oil over the bearings
and through the engine cylinders is maintained by means of oil
pumps. After passing through the bearings, the machine oil goes
to a properly arranged oil-filter where it is cleaned and then
pumped to the bearings again. A similar process is used in cyl-

ill! I i

DIAGRAM OF NOZZLES AND BUCKETS IN CURTIS STEAM TURBINE.

Fig. 8.

inder lubrication, the oil being collected from the exhaust steam
and only enough new oil is added to make up for the slight amount
lost. The latter system is not installed as frequently as the con-
tinuous system for bearings. In the Curtis turbine, vertical type,
the oil is forced in between the two plates, forming the step bear-
ing, at such a pressure that a thin film of oil is constantly main-
tained between these plates. It may be arranged so that if, for
any reason, this pressure fails, the steam will be cut off from the

T&^A^^

OFTHt

UNIVERSITY

POWER STATIONS

turbine automatically. The bearings which support the shafts
used with the generators at the Niagara Falls Power Companies'
plants are generously flooded with oil and the turbines are arranged
so as to remove a great deal of the weight of the rotating part
from this bearing.

HYDRAULIC PLANTS.

Because of the relative ease with which electrical energy may
be transmitted long distances, it has become quite common to locate

Fig. 9.

large power stations where there is abundant water power, and to
transmit the energy thus generated to localities where it is needed.
This type of plant has been developed to the greatest extent in the
western part of the United States, where in some cases the trans-
mission lines are very extensive. The power houses now completed,
or in the course of erection at Niagara Falls, are examples of the
enormous size such stations may assume.

POWER STATIONS

Water

Before deciding to utilize water power for driving the ma-
chinery in central stations, the following points should be noted:

1. The amount of water power available.

2. The possible demand for power.

o. Cost of developing this power as compared with cost of plants
using other sources of power.

4. Cost of operation compared with other plants and extent of
transmission lines.

Hydraulic plants are often much more expensive than steam

plants, but the first cost is
more than made up by the
saving in operating ex-
penses.

Methods for the devel-
opment of water powers
vary with the nature and
amount of the water supply,
and they may be studied
best by considering plants
which are in successful
operation, each one of
which has been a special
problem in itself. A full
description of such plants

LOW Water would be too extensive to

be incorporated here, but

Fig. 10. they can be found in the

various technical journals.

Water Turbines used for driving generators are of two general
classes, reaction turbines and impulse turbines. The former may be
subdivided into Parallel-flow, Out ward -flow, and Inward-flow tur-
bines. Parallel-flow turbines are suited for low falls, not exceeding
30 feet. Their efficiency is from 70 to 72%. Outward-flow and
inward-flow turbines give an efficiency from 79 to 88%. Impulse
turbines are suitable for very high falls and should be used from
heads exceeding say 100 feet, though it is difficult to say at what
head the reaction turbine would give place to the impulse wheel,
as reaction turbines are giving good satisfaction on heads in
the neighborhood of 200 feet, while impulse wheels are operated

-I

POWER STATIONS

with falls of but 80 feet. The Pelton wheel is one of the best
known types of impulse wheels. .An efficiency as high as 86% is

Fig. 11.

claimed for this type of wheel under favorable conditions. Fig.
10 shows a reaction wheel and Fig. 11 illustrates a Pelton wheel.

TABLE 7.
Pressure of Water.

Feet
Head.

Pressure
Pounds per
Square Inch.

Feet
Head.

Pressure
Pounds per
Square Inch.

Feet
Head.

Pressure
Pounds per
Square Inch.

Feet
Head.

Pressure
Pounds per
Square Inch.

4. .33

105

45.48

200

86. 63

295

127.78

6.49

110

47.64

205

88.80

300

129.95

8.66

115

49.81

210

90.96

310

134.28

10.82

120

51.98

215

93.13

320

138.62

12.99

125

54.15

220

95.30

330

142.95

15.16

130

56.31

225

97.46

340

147.28

17.32

135

58.48

230

99. a3

350

151.61

19.49

140

60.64

235

101.79

360

155.94

21.65

145

62.81

240

103.90

370

160.27

23.82

150

64.97

245

106.13

380

164.61

25.99

155

67.14

250

108.29

390

168.94

28.15

160

69.31

255

110.46

400

173.27

30.32

165

71.47

260

112.62

500

216.58

32.48

170

73.64

265

114.79

600

259.90

34.65

175

75.80

270

116.96

700

303.22

36.82

180

77.97

275

119.12

800

346.54

38.98

185

80.14

280

121.29

900

389.86

41.15

190

82.30

285

123.45

1000

433.18

100

43.31

195

84.47

290

125.62

The fore bay leading to the flume should be made of such size
that .the velocity of water does not exceed 1J feet per second, and

POWER STATIONS

TABLE 8.
Riveted Hydraulic Pipe.

Diam. of Pipe
in inches.

Area of Pipe
in sq. inches.

Thickness of
Iron by wire
gauge.

Head in Feet
the Pipe will
safely stand.

Cu. ft. Water
Pipe will con-
vey per min.
at vel. 3 ft.
per sec.

Weight per
lineal ft. in Ibs.

400

350

525

825

8V7

500

675

296

487

743

. 36

254

419

640

367

560

854

327

8%.

9
9

14
12

499
761

80
80

10%
14%

295

100

10
10
10
10

78
78
78
78

14
12
11
10

450

687
754
900

100
100
100
100

11%
lo%

17%
19%

269

120

412

120

13 4

626

120

ll¥

. 11

687

120

820

120

21 4

113

246

142

113

377

142

12
12

113
113

12
11

574

630

142
142

18%
19%

113

753

142

22%

132

228

170

132

348

170

132

530

170

132

583

170

132

• 696

170

24%

153

211

200

153

324

200

14
14

153
153

12
11

494
543

200
200

21%

23%

153

648

200

176

197

225

13%

176

302

225

176

460

225

176

507

225

24%

176

606

225

28 2

201

185

255

14%

201

283

255

l?g

201

432

255

201

474

255

26%

POWER STATIONS

Riveted Hydraulic Pipe. (Continued.)

Diam. of Pipe
in inches.

Area of Pipe
in sq. inches.

Thickness of
Iron by wire
gange.

Head in Feet
the Pipe will
safely stand.

Cu. ft. Water
Pipe will con-
vey per niin.
at vel. 3 ft,
per sec.

Weight per
lineal ft, in Ibs

201

567

255

29%

254

165

320

254

252

320

20%

254

385

320

254

424

820

30 *

254

10 -

505

320

314

148

400

314

227

400

22%

314

346

400

314

380

400

82%

314

456

400

36%

380

135

480

380

206

480

24%

380

316

480

82%

380

347

480

35%

380

415

480

452

188

570

27%

452

290

570

85%

452

318

570

452

379

570

43%

452

466

570

530
530

14
12

175

267

670
670

29%
38%

530

294

670

530

352

670

530

432

670

57%

615

102

775

31%

615

247

775

41%

615

278

775

615

327

775

50%

615

400

775

61%

706

231

890

706

254

890

706

304

890

706

375

890

706

425

890

36,

1017

141

1300

1017

155

1300

1017

192

1300

1017

210

1300

1256

141

1600

1256

174

1600

1256

189

1600

1256

.213

1600

108

• 40

1256

250

1600

126

1385

135

1760

74%

1385

165

1760

1385

180

1760

102

. 42

1385

210

1760

114

42 -

1385

240

1760

133

1385

270

1760

137

1385

300

1760

145

1385

321

1760

177

42 j 1385

363

1760

216

POWER STATIONS

it should be free from abrupt turns. The same applies to the tail
race. The velocity of water in wooden flumes should not exceed
7 to 8 feet per second. Riveted steel pipe is used for the penstocks
and for carrying water from considerable distances under high
heads. In some locations it is buried, in others it is simply
placed on the ground. Wooden -stave pipe is used to a large extent
when the heads do not much exceed 200 feet. Table 7 gives the
pressure of water at different heads, while Table 8 gives considera-
ble data relating to riveted -steel hydraulic pipe.

Governors are required to keep the speed constant under
change of load and change of head. Various governors are manu-
factured which give excellent satisfaction.

TABLE 9.
Horse Power per cubic foot of water per minute for different heads.

Heads
in
Feet.

Horse
Power.

Heads
in
Feet.

Horse
Power

Heads
in
Feet.

Horse
Power.

Heads
in
Feet.

Horse
Power.

.0016098

170

.273666

330

.531234

-490

. 788802

.032196

180

.289764

340

.547332

500

.804900

.048294

190

.305862

350

.563430

520

.837096

.064392

200

.321960

360

.579528

540

.869292

.080490

210

.338058

370

.595626

560

.901488

.096588

220

.354156

380

.611724

580

.933684

.112686

230

.370254

390

.627822

600

.965880

.128784

240

.386352

400

.648920

650

1.046370

.144892

250

.402450

410

.660018

700

1.126860

100

.160980

260

.418548

420

.676116

750

1.207350

110

.177078

270

.434646

430

.692214

800

1.287840

120

.193176

280

.450744

440

.708312

900

1.448820

130

.209274

290

.466842

450

.724410

1000

1.609800

140

.225372

300

. .482940

460

.740508

1100

1.770780

150

.241470

310

.499038

470

.756606

160

.257568

320

.515136

480

.772704

GAS ENGINES.

There are at present, in the United States, several successful
electrical installations using gas engines as prime movers, while

they have been operated abroad for a greater length of time,
advantages for gas engines are given as follows:

1. Minimum fuel and heat consumption.

2. Light-load efficiency is higher than for the steam engines.

3. Low cost of operation and maintenance.

The

POWER STATIONS

4. Simplification of equipment and small number of auxiliaries.

5. No heat lost due to radiation when engines are idle.

0. Quick starting.

7. Extensions may be easily made.

8. High pressures are limited to the engine cylinders.

Fig. 12 shows the efficiency and amount of gas consumed by
a 550 K.P. engine, Pittsburg natural gas being used.

The only auxiliaries needed are the igniter generators and the

air compressors, with a pump for the jacket water in some cases.

These may be driven by a motor or by a separate gas engine.

"The jacket water may be utilized for heating purposes in many

plants. Cooling towers may be installed where water is scarce.

MENCY TEST OF A 5?0 aH.R FOUR CYCLfc GAS ENGINE
25"x30" 3 CYLINDER VERTICAL SINGLE-ACTING VvPF I

Fig. 12.

Parallel operation of alternators when direct-driven by gas
engines has been successful, a spring coupling being used between
the engines and generators in some cases to absorb the variation in
angular velocity.

The fact that no losses occur, due to heat radiation when the
machines are not running, and the lack of losses in piping, add
greatly to the plant efficiency. If producer gas or blast furnace
gas is used, a larger engine must be installed, to give the same
power, than when natural or ordinary coal gas is used Electric

36 POWER STATIONS

stations are often combined with gas works, and gas engines can
be installed in such stations to particular advantage in many cases.

THE ELECTRICAL PLANT.
GENERATORS.

The first thing to be considered in the electrical plant is the
generators, after which the auxiliary apparatus in the way of
exciters, controlling switches, safety devices, etc., will be taken up.
A general rule which, by the way, applies to almost all machinery for
power stations is to select apparatus which is considered as "stand-
ard" by the manufacturing companies. This rule should be fol-
lowed for two reasons. First, reliable companies employ men who
may be considered as experts in the design of their machines, and
their best designs are the ones which are standardized. Second,
standard apparatus is from 15 to 25% cheaper than serni-standard
or special work, owing to larger production, and it can be fur-
nished on much shorter notice. Again, repair parts are more
cheaply and readily obtained.

Specifications should call for performance, and details should
be left, to a very large extent, to the manufacturers. Following
are some of the matters which may be incorporated in the specifi-
cations for generators:

1. Type and general characteristics.

2. Capacity and overload with heating limits.

3. Commercial efficiency at various loads.

4. Excitation.

5. Speed and regulation.

6. Floor space.

7. Mechanical features.

As to the type of machine, this will be determined by the
system selected. They may be direct-current, alternating-current^
single or polyphase, or as in some plants now in operation, they
may be double-current generators. The voltage, compounding,
frequency, etc., should be stated. Direct-current machines are sel-
dom wound for a voltage above 600, but alternating-current genera-
tors maybe purchased which will give as high as 15,000 volts at the
terminals. As a rule it is well not to use an extremely high volt-
age for the generators themselves, but to use step-up transform-
ers in case a very high line voltage is necessary. Up to about
75000 volts generators may be safely used directly on the line.

POWER STATIONS 37

Above this local conditions will decide whether to connect the
machine directly to the line or to step up the voltage. Machines
wound for high potential are more expensive for the same capacity
and efficiency, but the cost of step-up transformers and the losses
in the same are saved by using such machines, so that there is a
slight gain in efficiency which may be utilized in better regulation
of the system, or in lighter construction of the line. On the other
hand, lightning troubles are liable to be aggravated when trans-
formers are not used, as the transformers act as additional protec-
tion to the machines, and if the transformers are injured they
may be more readily repaired or replaced.

The following voltages are considered standard:

Direct-current generators 125, 250, 550-600.

Alternating-current systems, high pressure, 2,200, 6,000, 10,000,
15,000, 20,000, 30,000, 40,000, 60,000.

The generators, with transformers when used, should be capa-
ble of giving a no-load voltage 10% in excess of these figures.
25 and 60 cycles are considered as standard frequencies, the
former being more desirable for railway work and the latter for
lighting purposes.

The size of machines to be chosen has been briefly considered.
Alternators are rated for non-inductive load or a power factor of
unity. Aside from the overload capacity to be counted upon as
reserve, the Standardization Report of the American Institute of
Electrical Engineers recommends the following for the heating
limits and overload capacity of generators :

Maximum values of temperature elevation,

Field and armature, by resistance, 50° C.

Commutator and collector rings and brushes, by thermometer, 55° C.

Bearings and other parts of machine, by thermometer, 40° C.

Overload capacity should be 25% for two hours, wTith a tem-
perature rise not to exceed 15° above full load values, the machine
to be at constant temperature reached under normal load, before
the overload is applied. A momentary overload of 50% should be
permissible without excessive sparking or injury. Some com-
panies recommend an overload capacity of 50% for two hours
when the machines are to be used for railway purposes.

38 POWER STATIONS

As a rule, generators should have a high efficiency over a con-
siderable range of load, although the nature of the load will have
much to do with this. It is always desirable that maximum effi-
ciency be as high as is compatible with economic investment.

Table 10 gives reasonable efficiencies which may be expected
for generating apparatus. In order to arrive at what may be con-
sidered the best maximum efficiency to be chosen, the cost of power
generation must be known, or estimated, and the fixed charges on
capital invested must also be a known quantity. From the cost
of power, the saving on each per cent increase in efficiency can be
determined, and this should be compared with the charges on the
additional investment necessary to secure this increased efficiency.
A certain point will be found where the sum of the two will be a
minimum.

If a generator is to be run for a considerable time at light
loads, one with low " no-load " losses should be chosen. These
losses are not rigidly fixed but they vary slightly with change
of load. It is the same question of " all-day efficiency" which
is treated, in the case of transformers, in " Power Transmission ".
Under no-load losses may be considered, in shunt-wound gener-
ators, friction losses, core losses, and shunt-field losses. PR losses
in the series field, in the armature, and in the brushes, vary as the
square of the load.

Table 10.
Average Maximum Efficiencies.

K.W.
5

Per Cent
85

150 .

. 93

200 94

500 , 95

1000 96

Dynamos, if for direct current, may be self-excited, shunt- or
compound-wound, or separately excited. Separate excitation is not
recommended for these machines. Alternators require separate
excitation, though they may be compounded by using a portion of
the armature current when rectified by a commutator. Automatic
regulation of voltage is always desirable, hence the general use of

POWER STATIONS 39

compound-wound machines for direct currents. Many alternators
using rectified currents in series fields for keeping the voltage
nearly constant are in service in small plants as well as several of
the so-called " compensated " alternators, arranged with special
devices which maintain the same compounding with different
power factors. The latter machine gives good satisfaction if
properly cared for, but an automatic regulator, governed by the
generator voltage and current, which acts directly on the exciter
field, is taking its place. The capacity of the exciters must be
such that they will furnish sufficient excitation to maintain normal
voltage at the terminals of the generators when running at 50%
overload. Table 11 gives the proper capacity of exciter for the
generator listed.

TABLE ii.

Exciters for Single=Phase Alternating=Current Generators.

60 Cycles.

Alternator
Classification.

Exciter
Classification.

y' • 1J

P-i W J/}

'It I

8- 60-900
8- 90-900
8 - 120 - 900
12 - 180 - 600
16 - 300 - 450

2
o

- 1.5 - 1900
- 1.5 - 1900
- 1.5 - 1900
-2.5-1900
-4.5-1800

If direct-connected, the speeds of the generators will be
determined by the prime mover selected. If belt-driven, small
machines may be run at a high speed, as high-speed machines are
cheaper than slow- or moderate -speed generators. In large sizes,
this saving is not so great.

When shunt- wound dynamos are used, the inherent regula-
tion should not exceed 2 to 3% for large machines. For alterna-
tors, this is much greater and depends on the power factor of the
load. A fair value for the regulation of alternators on non-
inductive load is 10 per cent.

Exciters may be either direct -connected or belted to the shaft
of the machine which they excite, or they may be separately

POWEK STATIONS

driven. They are usually compound-wound and furnish current
at 125 or 250 volts. Separately driven exciters are preferred
for most plants as they furnish -a more flexible system, and any
drop in the speed of the generator does not affect the exciter
voltage. Ample reserve capacity of exciters should be installed,
and in some cases storage batteries, used in conjunction with
exciters, are recommended in order to insure reliability of service.

Motor-generator sets, boosters, frequency changers, and other
rotating devices come under
the head of special apparatus
and are governed by the same
general rules as generators.

Transformers for step-
ping the voltage from that
generated by the machine up
to the desired line voltage, or
vice versa, at the substation,
may be of three general types,
according to the method of
cooling. Large transformers
require artificial means of
cooling, if they are not to be
too bulky and expensive.
They may be air-cooled, oil-
cooled, or water-cooled.

Air-cooled transformers are usually mounted over an air-
tight pit fitted with one or more motor-driven blowers which feed
into the pit. The transformer coils are subdivided so that no part
of the winding is at a great distance from air and the iron is pro-
vided with ducts. Separate dampers control the amount of air
which passes between the coils or through the iron. Such trans-
formers give good satisfaction for voltages up to 20,000 or higher,
and can be built for any capacity. Care must be taken to see that
there is no liability of the air supply failing, as the capacity of the
transformers is greatly reduced when not supplied with air. Fig.
13 shows a three-phase air-blast transformer.

POWER STATIONS

Oil-cooled transformers have their cores and windings placed
in a large tank filled with oil. The oil serves to conduct the heat
to the case, and the case is usually either made of corrugated sheet
metal or of cast iron containing deep grooves, so as to increase the
radiating surface. These transformers do not require such heavy

— c

Fig. 14. 150 K.W. Self-Cooled Oil Transformer.

insulation on the outside of the coils as air-blast machines because
the oil serves this purpose. Simple oil-cooled transformers are
seldom built for capacities exceeding 250 K.W. as they become
too bulky, but they are employed for the highest voltages now in
use. Fig. 14 shows a transformer of this type.

POWER STATIONS

^Water-cooled transformers. When large transformers for high
voltages are required, the water-cooled type is usually selected.
This type is similar to an oil-cooled transformer, but with water

Fig. 15. Water-Cooled Transformer.

tubes arranged in coils in the top. Cold water passes through
these tubes and aids in removing heat from the oil. Some types
have the low- tension windings made up of tubes through which
the water circulates. Water-cooled transformers must not have

POWER STATIONS

the supply of cooling water shut off for any length of time when
under normal load or they will overheat. Fig. 15 shows a water-
cooled transformer.

For connections of transformers, see "Power Transmission".

Fig. 15. 400 K. W. Water Cooled Oil Transformer.

One or more spare transformers should always be on hand and
they should be arranged so that they can be put into service on
very short notice.

Three-phase transformers allow a considerable saving in floor
space, as can be seen by referring to Fig. 16; they are cheaper than
three separate transformers which make up the same capacity, but
they are not as flexible as a single-phase transformer and one

POWER STATIONS

complete unit must be held for a reserve or "spare" transformer.
Storage Batteries. The use of storage batteries for central
stations and substations is clearly outlined in " Storage Batteries ".
The chief points of advantage may be enumerated as follows:

/^V^VAYAVAVAVAVAV

Single-Phase Air-Blast Transformers. Total Capacity 3,000 K.W.

Three-Phase Air-Blast Transformers. Total Capacity 3,000 K.W.
Fig. 16.

1. Reduction in fuel consumption due to the generating machinery
being run at its greatest economy.

2. Better voltage regulation.

3. Increased reserve capacity and less liability to interruption of
service.

The main disadvantage is the high cost.

Switchboards. The switchboard is the most vital part of
the whole system of supply, and should receive consideration as
such. Its objects are: to collect the energy as supplied by the gen-
erators and direct it to the desired feeders, either overhead or

POWER STATIONS 45

under ground; furnish a support for the various measuring instru-
ments connected in service, as well as the safety devices for the
protection of the generating apparatus; and control the pressure
of the supply. Some of the essential features of all switch-
boards are:

1. The apparatus aiid supports must be fire-proof.

2. The couductiug parts must iiot overheat.

3. Parts must be easily accessible.

4. Live parts except for low potentials must not be placed 011 the
froiit of the operating panels.

5. The arrangement of circuits must be symmetrical aiid as simple
as it is convenient to make them.

6. Apparatus must be arranged so that it is impossible to make a
wrong connection that would lead to serious results.

7. It should be arranged so that extensions may be readily made.

There are two general types — in the first, all of the switching
and indicating apparatus is mounted directly on panels, and in the
second, the current-carrying parts are at some distance from the
panels, the switches being controlled by long connecting rods; op-
erated electrically or by means of compressed air. The first may
again be divided into direct-current and alternating-current switch-
boards. It is from the first class of apparatus that the switchboard
gets its name and the term is still applied, even when the board
proper forms the smallest part of the equipment. Switchboards
have been standardized to the extent that standard generator, ex-
citer, feeder, and motor panels may be purchased for certain classes
of work, but the vast majority of them are made up as semi-stand-
ard or special.

The leads which carry the current from the machines to the
switches should be put in with very careful consideration. Their
size should be such that they will not heat excessively when carry-
ing the rated overload of the machine, and they should preferably
be placed in fire-proof ducts, although low-potential leads do not
always require this construction. Curves showing sizes for lead-
covered cables for different currents are given in " Power Trans-
mission ". Table 12 gives standard sizes of wires and cables to-
gether with the thickness of insulation necessary for different
voltages. Cables should be kept separate as far as possible so
that if a fault does occur on one cable, neighboring conductors

46 POWER STATIONS

will not be injured. For lamp and instrument wiring, such as
leads to potential and current transformers, the following sizes of
wire are recommended :

No. 16 or No. 14, wiring to lamp sockets.

No. 12 wire, &" rubber iiisulatioii, all other small wiring under <>00
volts potential.

No. 12, 3V rubber insulation for primaries of potential transformers
from 600 to 3,500 volts.

No. 8, 3y rubber insulation for primaries of potential transformers
up to 6,600 volts.

No. 8, 375 rubber insulation for primaries of potential transformers
up to 10,000 volts.

No. 4, |i rubber insulation for primaries of potential transformers
up to 15,000 volts.

No. 4, jf rubber insulation for primaries of potential transformers
up to 20,000 volts.

No. 4, 45 rubber insulation for primaries of potential transformers
up to 25,000 volts.

Where high-tension cables leave their metallic shields they
are liable to puncture, so that the sheath should be flared out at
this point qnd the insulation increased by the addition of com-
pound. Fig. 17 shows such cable "bells, as they are called, as
recommended by the General Electric Company.

Central -station switchboards are usually constructed of panels
about 90 inches high, from 16 inches to 86 inches wide, and 1^
inches to 2 inches thick. Such panels are made of Blue Vermont,
Pink Tennessee, or White Italian marble, or of black enameled
slate. Slate is not recommended for voltages exceeding 1,100. The
panels are in two parts, the sub-base being from 24 to 28 inches
high. They are polished on the front and the edges are beveled.
Angle and tee bars, together with foot irons and tie rods, form the
supports for such panels, and on these panels are mounted the in-
struments, main switches, or controlling apparatus for the main
switches, as the case may be, together with relays and hand wheels
for rheostats and regulators. Small panels are sometimes mounted
on pipe supports.

The usual arrangement of the panels is to have a separate
panel for each generator, exciter, and feeder, together with what is
known as a station or total-output panel. In order to facilitate
extensions and simplify connections, the feeder panels are located

POWER STATIONS

at one end of the board and the generator panels are placed at the
other end, and the total-output panel between the two. The main
bus bars extend throughout the length of the generator and feeder
panels, and the desired connections are readily made. The instru-
ments required are very numerous and a brief description only of
a few of the more important can be given here.

TABLE 12.
Standard Wire and Cable.

Wire (Solid).

Area.

Diam.
Inches.

Amps.

Thickness of Rubber
Insulation.

Gauge.

Circular

Bare.

Con.
Current

1§ | | | 1 1 |

B. & S

Mils.

Capacity.

> « ' _ S 1 «

Special Insulation.

2,582

.051

No. 30 Dr.

4,106j .064

6,530

.081

16,510

.128

3*2

26,2511 .162

41,743

.204

66,373

.257

T5ff

- 90

83,695 .289
105,593; .325

8 8

110
130

1 4
32

1
0

133,079
167,805

.365
.410

170

205

t!4~

000

211,600

.460

250

til

i< ¥

0000

Cable.

(Stranded.)

Circular
Mils.

Diameter.
Inches
Bare.

Terminal
Drilling

Con. Curr.
Capacity.
Amps.

Thickness of Rubber
Insulation.
(For 6000 V. only.)

250,000

.568

290

300,000

.637

it"

340

350,000

.680

380

400,000

.735

420

500,000

.820

i!'

500

600,000

.900

1''

575

800,000

1.037

710

1,000,000

1.157

830

1,500,000

1.412

1100

2.000,000

1.65

1350

POWER STATIONS

Wiped joint

alberene soapstone
x or wood

-me—*

H 9

JZ3

o.67compoun

iextra insulation

I -------- Q ----- yj X -3-150. -f-2. 15 Y-t-4.3d

Three-Conductor Cable Without Joints.

Wiped joint

alberene soapstone
-'• or wood A--
C--+,

t- - -5ssss-~

Jextra insulation

X =3.150. +2.. 15 Y+4.3d

Three-Conductor Cable With Joints.

Wiped joint

Two-Conductor Cable With Joints.

Wiped joint

alberene soapstone
3*^ or wood *

no 67 compound

rF*

lextroi insulation •x.-s.o.+y-

Single-Conductor Cable With Joints.

VOLTS.

6600

-/2

13200

26400

i -inch Lead or jVinch Brass Bells..
Fig. 17.

POWER STATIONS

Circuit
Breaker

For direct current generator panels there are usually re-
quired:

1 Main switch

1 Field switch.

1 Ammeter.

1 Voltmeter.

1 Field rheostat with controlling mechanism.

1 Circuit breaker

Bus bars and various connections.

These may be arranged in any suitable order, the circuit
breaker being preferably located at the top so that any arcing
which may occur will not injure other instruments. Fig. 18 gives
a wiring diagram of such a panel.

The main switch may be single or double throw, depending

on whether one or two sets of bus •_

bars are used. It may be triple
pole as shown in Fig. 18, in
which the middle bar serves as
the equalizing switch, or the equal-
izing switch may be mounted on a
pedestal near .the machine, in
which case the generator switch
would be double-pole.

The field switch for large ma-
chines should be double-pole fitted
with carbon breaks and arranged
with a discharge resistance con-
sisting of a resistance which is
thrown across the terminals of the field just before the main cir-
cuit is opened. One voltmeter located on a swinging bracket at
the end of the panel, and arranged so that it can be thrown across
any machine or across the bus bars by means of a dial switch, is
sometimes used, but it is preferable to have a separate meter for
each generator.

Small rheostats are mounted on the back of the panel, but
large ones are chain operated and preferably located below the
floor, the controlling hand wheel being mounted- on the panel.

The circuit breaker may be of the carbon break or the mag-
netic blow-out type. Fig. 19 shows circuit breakers of both

Ammeter

Voltmeter

D.P. Field

Discharqe
Resistance

Rheostat

Generator
Fig. 18.

POWER STATIONS

types. Lighting panels for low potentials are often fitted with
fuses instead of circuit breakers, in which case they may be open
fuses on the back of the panel or enclosed fuses on either the
front or back of the panel.

Direct=Current feeder panels contain:

1 Ammeter.

1 Circuit Breaker.

1 or more main switches, single-pole, and single- or double-throw.

1 recording wattmeter, not always used

Apparatus for controlling regulators when such are used.

Fig. 19.

One voltmeter usually serves for several feeder panels, such a
meter being mounted above the panels or on a swinging bracket
at the end. Switches should preferably be of the quick-break
type. Fig. 20 shows some standard railway feeder panels.

Exciter Panels are nothing more than generator panels on a
small scale.

POWER HOUSE OF NUW YOrtK SUBWAY.

Showing Five of the Nine 12,000 Horse-Power Allis-Chalmers Engines.

OF THE

UNIVERSITY

POWER STATIONS

Total Output Panels contain instruments recording the total
power delivered by the plant to the switchboard. Alternatiog-
current panels for potentials up to 1,100 volts follow the same
general construction. Synchronizing devices are necessary on the
generator panels, and additional ammeters are used for polyphase
boards. Sometimes the exciter and generator panels are combined

Fig. 19.

in one. Fig. 21 shows such a combination. The same construction
is sometimes used for voltages up to 2,500, though it is not usually
recommended. The paralleling of alternators is treated in " Man-
agement of Dynamo Electric Machinery".

For the higher voltages, the measuring instruments are no
longer connected directly in the circuit, and the main switch is not
mounted directly on the panel. Current and potential trans-

POWER STATIONS

formers are used for connecting to the indicating voltmeters and
ammeters, and the recording wattmeters and potential transformers
are used for the synchronizing device. These transformers are
mounted at some distance from the panel, while the switches may

RAILWAY FEEDER PANELS

NO. 13559

Engineering Dept.

General Electric Co.

I May I9OO

Fig. 20.

be located near the panel and operated by a system of levers, or
they may be located at considerable distance and operated by elec-
tricity or by compressed air.

Oil Switches are recommended for all high potential work
for the following reasons: By their use it is possible to open cir-
cuits of higher potential and carrying greater currents than with

POWER STATIONS

any other type of switch. They may be made quite compact. They
may readily be made automatic and thus serve as circuit breakers
for the protection of machines and circuits when overloaded.

SWITCHBOARD PANEL FOR

ONE THREE-PHASE ALTERNATING CURRENT GENERATOR
TO 2500 VOLTS

ASSIFICATK

Type

Volts

Amperes

Form

Switch

Field
Ammeter

synchronizing
Device

2500

I3O

. with

25OO

I3O

with

withoot-

2300

130

without

with

2500

I3O

without

23OO

I3O

with

without

2500

130

without

Without -

Transformer is calibrated with Voltmeter only. Therefore Synchronizing Piuj must be removes*
•for correct Voltmeter reodinj

Fig. 21.

There are several types on the market. One constructed for
three-phase work, to be cloned by hand and to be electrically
tripped or opened by hand, is shown in Fig. 22. This shows the
switch without the can contain ing the oil. Fig. 23 shows a similar
switch hand-operated, with the can in place. Both of these
switches are arranged to be mounted on the panel. Fig. 24 shows
how the same switches are mounted when placed at some distance
from the panel. For high voltages, they are placed in brick cells
and often three separate single-pole switches are used, each placed
in a separate cell so that injury to the contacts in one leg will in

POWER STATIONS

no way affect the other parts of the switch. A form of oil switch
used for the very highest potentials and currents met with in prac-
tice, is shown in Fig. 25. This particular switch is operated by
means of an electric motor, though it may be as readily arranged to
operate by means of a solenoid or by compressed air. General
practice is to place all high-tension bus bars and circuits in separate
compartments formed by brick or cement, and duplicate bus bars
are quite common.

Fig. 22.

Oil switches are made automatic by means of tripping mag-
nets, which are connected in the secondary circuits of current
transformers, or they may be operated by means of relays fed
from the secondaries of current transformers in the main leads.
Such relays are made very compact and can be mounted on the

POWER STATIONS

front or back of the switchboard panels. The wiring of such trip-
ping devices is shown in Fig. 26.

With remote control of switches, the switchboard becomes in
many instances more properly a switch house, a separate building
being devoted to the bus bars, switches, and connections. In other
cases a framework of angle bars or gas pipe is made for the support
of the switches, bus bars, current and potential transformers,, etc.

Fig. 23.

Additional types of panels which may be mentioned are trans-
former panels, usually containing switching apparatus only; rotary
converter panels for both the alternating current and direct -current
sides; induction -motor panels and arc- board panels. The latter

AAA

Form K Oil Switches Located Above and Form K Oil Switches Located Below and Back

Back of Operating Panel. of Operat ing Panel.

AA1

-3

Form K Oil Switches Located Above Form K Oil Switches Located Back of Operating

Operating Panel. Panel.

Fig. 24,

W a

B I

POWER STA110NS

are arranged to operate with plug switches. A single panel used
in the operation of series transformers on arc-lighting circuits is
shown in Fig. 27.

Safety Devices. In addition to the ordinary overload trip-
ping devices which have already been considered, there are various
safety devices necessary in connection with the operation of cen-
tral stations. One of the most important of these is the liyhtning
arrester. For direct-current work, the lightning arrester takes the
form of a single gap connected in series with a high resistance and
fitted with some device for destroying the arc formed by discharge

Red Indicatinq Lamp
/(Oil Switch Closed)

losinq Contact

XDpeninq Contact
^reen Indicatinq La
(Oil Switch Open)

Automatic Contact Finqers
Cam Actuated

Oil Switch in Closed Position

Fig. 25.

to the ground. One of these is connected between either side of
the circuit and the ground, as shown diagrammatically in Fig. 28.
A " kicking ?> coil is connected in circuit between the arresters and
the machine to be protected, .to aid in forcing the lightning dis-
charge across the gap. In railway feeder panels such kicking
coils are mounted on the backs of the panels.

For alternating-current work, several gaps are arranged in
series, these gaps being formed between cylinders of " non-arcing"
metal. High resistances and reactance coils are used with these,

POWER STATIONS

Source

Overload Coil R

Source

Load

I Current .
Transformer:
tomatic:
Oil Switch

Double Pole Relay
. Circuit Normally Closed

Source

O pen Ci re u i ti ncj Switch

Trip Coil

Relay

To Continuous
Current Supply

Fig. 20.

as in direct-current arresters.
Fig. 29 shows connections
for a 10,000-volt lightning
arrester. Lighting arresters
should always be provided
with knife blade switches so
that they can be discon-
nected from the circuit for
inspection and repairs. A
typical installation of light-
ning arresters is shown in
Fig. 30.

He verse-current relays are
installed when machines or
lines are operated in parallel.
If two or more alternators
are running and connected
to the same set of bus bars,
and one of these should fail
to generate voltage by the
opening of the field circuit,
or some other cause, the
other machine would feed
into this generator and
might cause considerable
damage before the current
flowing would be sufficient
to operate the circuit breaker
by means of the overload trip
coils. To avoid this, re-
verse-current relays are used.
They are so arranged as to
operate at say J the normal
current of the machine or

line, but to operate only wThen the power is being delivered in the
wrong direction.

Speed limit devices are used on both engines and rotary con-
verters to prevent racing in the one case and running away in the

POWER STATIONS

second. Such devices act on the steam supply of engines and on
the direct-current circuit breakers of rotary converters, respectively.

Complete wiring diagram for a railway switchboard is shown
in Fig. 81.

Substations. Substations are for the purpose of transform-
ing the high potentials down to such potentials as can be used on

motors or lamps, and in many cases to convert alternating current
into direct current. Step-down transformers do not differ in any
respect from step-up transformers. Either motor-generator sets
or rotary converters may be used to change from alternating to
direct current. The former consist of synchronous or induction
motors, direct connected to direct-current generators, mounted on

POWER STATIONS

the same bedplate. The generator may be shunt or compound
.wound, as desiretl. Rotary converters are direct-current genera-
tors, though specially designed; they are fitted with collector rings
attached to the winding at definite points. The alternating cur-
rent is fed into these rings and the machine runs as a synchronous

Connections for series arc liahtincj circuits up to eooo volts
qenerator ,reacta.nce coil

cjround

Connections forliqhtinq or power circuits
uptoQ50 volts (metallic circuits) J

qenercttor ^ reactance coil

motor

Connections for railway circuits up to eso volts
reactance coil (one side a rounded)

qenercL-

~ tor

Reaction coil is
composed ofes of
conductor wound
in acoil of two or
more turns as con
venient-

Fig. 28.

motor, while direct current is delivered at the commutator end.
There is a fixed relation between the voltage applied to the alter-
nating-current side and the direct-current voltage, which depends
on the shape of the wave form, losses in the armature, pole pitch
of the machine, method of connection, etc. The generally accepted
values are as follows:

MANHATTAN 74th ST. POWER STATION, NEW YORK.

Showing Carey's Carbonate of Magnesia Pipe Coverings. Steam Connections.

POWER STATIONS

TABLE 13.

Full Load Ratios.

Current. Potential.

Continuous : 100

Two-phase ( 550 volts . 72.5

and Six-phase
(diametrical)
Three-phase
and Six-phase
( Y or delta)

•{ 250
(125
( 550
1 250
( 125

78.5

IOOOOV

The increase of capacity of six-phase machines over other
machines of the same size is given in Table 14.

This increase is due to

the fact that, with a greater Alternator^^Reactance Coil
number of phases, less of the
winding is traversed by the
current which passes through
the converter. The saving
by increasing the number of
phases beyond six is but
slight and the system be-
comes too complex. Ilotary
converters may be over-com-
pounded by the addition of
series fields, provided the re-
actance in the alternating cir-
cuits be of a proper value.
It is customary to insert re-
actance coils in the leads from
the low-tension side of the
step-down transformers to
the collector rings to bring

the reactance to a value which will insure the desired compounding.
Again, the voltage may be controlled by means of induction regu-

TABLE 14.
Capacity Ratios.

Continuous-current generator 100

Single-phase converter 85

Two-phase converter 164

Three-phase converter 184

Six^phase converter 196

POWER STATIONS

POWER STATIONS 63

lators placed in the alternating-current leads. Motor-generatoiM
are more costly and occupy more space than rotary converters, but
the regulation of the voltage is much better and they are to be
preferred for lighting purposes.

Buildings. The power station usually has a building devoted
entirely to this work, while the substations, if small, are often
made a part of other buildings. While the detail of design and
construction of the buildings for power plants belongs primarily
to the architect, it is the duty of the electrical engineer to arrange
the machinery to the best advantage, and he should always be con-
sulted in regard to the general plans at least, as this may save
much time and expense in the way of necessary modifications.
The general arrangement of the machinery will be taken up later,
but a few points in connection with the construction of the build-
ings and foundations will be considered here.

Space must be provided for the boiler, — this may be a sepa-
rate building — engine and dynamo room, general and private
offices, store rooms and repair shops. Very careful consideration
should be given to each of these departments. The boiler room
should be parallel with the engine room, so as to reduce the neces-
sary amount of steam piping to a minimum, and if both rooms
are in the same building a brick wall should separate the two, no
openings which would allow dirt to come from the boiler room to
the engine room being allowed. The height of both boiler and
engine rooms should be such as to allow ample headway for lifting
machinery and space for placing and repairing boilers, while pro-
vision should be made for extending these rooms in at least one
direction. Both engine and boiler rooms should be fitted with
proper traveling cranes to facilitate the handling of the units. In
some cases the engines- and dynamos occupy separate rooms, but
this is not general practice. Ample light is necessary, especially
in the engine rooms. The size of the offices, store rooms, etc., will
depend entirely on local conditions.

The foundations for both the walls and the machinery must
be of the very best. It is well to excavate the entire space under
the engine room to a depth of eight to ten feet so as to form
a basement, while in most cases the excavations must be made to a
greater depth for the walls. Foundation trenches are sometimes

D.P.S.T.D.R.SW. D.P.S.T.Diseh. Res
RH'. Exciter Rheostat.

POWER STATIONS

filled with concrete to a depth sufficient to form a good under-
footing. The area of the foundation footing should be great enough
to keep the pressure within a safe limit for the quality of the soil.

The walls themselves may be of wood, brick, stone, or concrete.
Wood is used for very small stations only, while brick may be
used alone or in conjunction with steel'f raining, the latter con-
struction being used to a considerable extent. If brick alone is

POWER STATIONS

used, the walls should never be less than twelve inches thick, and
eighteen to twenty inches is better for large buildings. They
must be amply reinforced with pilasters. Stone is used only for
the most expensive stations. The interior of the wralls is formed
of glazed brick, when the expense of such construction is war-
ranted. In iireproof construction, which is always desirable for
power stations, the roofs are supported by steel trusses and take a
great variety of forms. Fig. 32 shows what has been recommended
as standard construction for lighting stations, showing both brick
and wood construction. The floors of the engine room should be

made of some material which will not form grit or dust. Hard
tile, nnglazed, set in cement or wood floors, is desirable. Storage
battery rooms should be separate from all others and should have
their interior lined with some material which will not be affected
by the acid fumes. The best of ventilation is desirable for all parts
of the station, but is of particular importance in the dynamo room
if the machines are being heavily loaded. Substation construction
does not differ from that of central stations when a separate build-
ing is erected. They should be fireproof if possible.

The foundations for machinery should be entirely separate
from those of the building. Not only must the foundations be
stable, but in some locations it is particularly desirable that no

POWER STATIONS

vibrations be transmitted to adjoining rooms and buildings. A
loose or sandy soil does not transmit such vibrations readily, but
drm earth or rock transmits them almost perfectly. Sand, wool,
tiair, felt, mineral wool, and asphaltum concrete are some of the
materials used to prevent this. The excavation for the foundation is
made from two to three feet deeper and two to three feet wider on
all sides than the foundation, and the sand, or whatever material
is used, occupies this extra space.

for bncK foundation a 1 2" footing of
concrete should be laid. Depth orfoondL-
ation must, be aoverr»eo' toy t-he char-
acter of the soil Batter Ito6.

Foundation timbers and flooring snould.
be independent of station floor.

Fig. 34.

Brick, stone, or concrete is used for building up the greater
part of machinery foundations, the machines being held in place
by means of bolts fastened in masonry. A template, giving the
location of all bolts to be used in holding the machine in place,
should be furnished, and the bolts may be run inside of iron pipes
with an internal diameter a little greater than the diameter of the
bolt. This allows some play to the bolt and is convenient for the
final alignment of the machine. Fig. 33 gives an idea of this con-
struction. The brickwork should consist of hard-burned brick of
the best quality, and should be laid in cement mortar. It is well
to fit brick or concrete foundations with a stone cap, forming a
level surface on which to set the machinery, though this is not
necessary. Generators are sometimes mounted on wood bases to

POWER STATIONS

furnish insulation for the frame. Fig. 34 shows the foundation
for a 150 K.W. generator, while Fig. 85 shows the foundation for
a rotary converter.

For brick foundation a I2"footing of concrete should
be lai.d Depth of foundation must, be governed by the
character of the soil- Batter I to 6-

Fig. 35.

Station Arrangement. A few points have already been
noted in regard to station arrangement, but the importance of the
subject demands a little further consideration. Station arrange-
ment depends chiefly upon two
facts — the location and the ma-
chinery to be installed. Un-
doubtedly the best arrangement
is with all of the machinery on
one floor with, perhaps, the oper-
ating switchboard mounted on a
gallery so that the attendants
may have a clear view of all the
machines. Fig. 36 shows the
simplest arrangement of a plant
using belted machines. Fig. 37
shows an- arrangement of units
where a jack shaft is used. Direct -current machines should be
placed so that the brushes and commutators are easily accessible
and the switchboard should be placed so as to not be liable to
accidents, such as the breaking of a belt or a fly-wheel.

£/VG/A/£'S DYNAMOS

SWtTCH BOAFU3

CNG/NE. ROOM

Fig. 36.

POWER STATIONS

BOtLEF* HOUSE

ENGtNE ROOM

Fig. 37.

When the cost of real estate prohibits the placing of all of
the machinery on one floor, the arrangements shown in Fig. 38
may be used when the machines are belted. It is always desirable
to have the engines oh the main floor, as they cause considerable
vibration when not mounted
on the best of foundations.
The boilers, while heavy, do
not cause such vibration and
they may be placed on the
second or third floor. Belts
should not be run vertically,
as they must be stretched too
tightly to prevent slipping.

Fig. 39 shows a large
station using direct-connected
units, while Fig. 40 shows the arrangement of the turbine plant
of the Boston Edison Electric Illuminating Company. This sta-
tion will contain twelve such 5,000 K.W. units when completed.
Note the arrangement of boilers when several units are required
for a single prime mover. The use of a separate room or building

for the cables, switches, and
operating boards is becoming
quite common for high-tension
generating plants. The remark-
able saving in floor space brought
about by the turbine is readily
seen from Fig. 41. The total
floor space occupied by the new
Boston station is 2.64 square
feet per K0W. This includes
boilers — of which there are eight,
each 512 H.P. for each unit-
turbines, generators, switches,
and all auxiliary apparatus.

When transformers are used
for raising the voltage, they may

be placed in a separate building, as is the case at Niagara Falls, or
the transformers may be located in some part of the dynamo room,
preferably in a line parallel to the generators.

BOfL £H HOUSE.

ENGfNE ROOM

Fig. 39.

POWER STATIONS

Fig. 42 shows the arrangement of units in an hydraulic plant.
Fig. 43 is a good example of the practice in substation arrange-
ment. Here the switchboard is mounted at one end of the room,
while the rotary converters and transformers are arranged along

either side of the building.

L/NE

ENG//VE

GROUND

ENG/NE

Fig. 38.

Large cable vaults are
installed at the stations
operating on underground
systems, the separate ducts
being spread out, and
sheet-iron partitions erect-
ed to prevent damage be-
ing- done to cables which

t~)

were not originally de-
fective, by a short circuit
in any one feeder.

Station Records. In

order to accurately deter-
mine the cost of gener-
ating power and to check
up on uneconomical or
improper methods of oper-
ation and lead to their im-
provement, accurately
kept station records are of
the utmost importance.
Such records should con-
sist of switchboard rec-
ords, engine-room records,
boiler-room records, and
distributing-system rec-
ords. Such records accu-

rately kept and properly plotted in the form of curves, serve admir-
ably for the comparison of station operations from day to day and
for the same periods for different years. It pays to keep thesn
records even when additional clerical force must be employed.

Switchboard records consist, in alternating stations, of daily
readings of feeder, recording wattmeters, and total recording watt-

POWER STATIONS

meter, together with voltmeter and ammeter readings at intervals
of about 15 minutes in some cases to check upon the average
power factor and determine the general form of the load curve.
For direct-current lighting systems volt and ampere readings serve
to give the true output of the sta-
tions, and curves are readily plotted
from these readings. The voltage
should be recorded for the bus bars
as well as for the centers of distri-
bution.

Indicator diagrams should be taken from the engines at fre-
quent intervals for the purpose of determining the operation of
the valves. Engine-room records include labor, use of waste oil
and supplies, as well as all repairs made on engines, dynamos and
auxiliaries.

POWER STATIONS

Boiler-room records include labor and repairs, amount of
coal used, which amount may be kept in detail if desirable, amount
of water used, together with steam-gauge record and periodical
analysis of flue gases as a check on the methods of firing.

Records for the distributing system include labor and ma-
terial used for the lines and substations. For multiple- wTire

POWER STATIONS 75

systems, frequent readings of the current in the different feeders
will serve as a check on the balance of the load.

The cost of generating power varies greatly with the rate at
which it is produced as well as upon local conditions. Station
operating expenses include cost of fuel, water, waste, oil, etc., cost
of repairs, labor, and superintendence. Fixed charges include,
insurance, taxes, interest on investment, depreciation, and general
office expenses. Total expenses divided by total kilowatt hours
gives the cost of generation of a kilowatt hour. The cost of dis-
tributing a kilowatt hour may be determined in a similar manner.
The rate of depreciation of apparatus differs greatly with different
machines, but the following figures may be taken as average values,
these figures representing percentage of first cost to be charged up
each year :

Fireproof buildings from 2 to 3 per cent.

Frame buildings from 5 tc 8 per cent.

Dynamos from 2 to 4 per cent.

Prime movers from 2% to 5 per cent.

Boilers from 4 to 5 per cent

Overhead lines, best constructed, o to 10 per cent.

More poorly constructed lines 20 to HO per cent

Badly constructed lines 40 to (50 per cent

Underground conduits 2 per cent.

Lead covered cables 2 per cent.

flethods of Charging for Power. There are four methods
used for charging consumers for electrical energy, namely, the fiat-
rate or contract system, the meter system, the two-rate meter sys-
tem, and a system by which each customer pays a fixed amount
depending on the maximum demand and in addition pays at a
reasonable rate for the power actually used. In the flat-rate
system, each customer pays a certain amount a year for service,
this amount being based on the estimated amount of power to be
used. These rates vary, depending on the hours of the day during
which the power is to be used, being greatest if the energy is to
be used during peak hours. It is an unsatisfactory method for
lighting service, as many customers are liable to take advantage
of the company, burning more lights than contracted for and at
different hours, while the honest customer must pay a higher rate
than is reasonable in order to make the station operation profitable.

POWER STATIONS

This method serves much better when the power is used for driving
motors, and is used largely for this class of service.

The simple meter method of charging serves the purpose
better for lighting, but the rate here is the same no matter what
hour of the day the currenHs used. Obviously, since machinery

Fig. 43.

is installed to carry the peak of the load, any power used at this
time tends to increase the capital outlay from the plant, and users
should be required to pay more for the power at such times.

The two-meter rate accomplishes this purpose to a certain
extent. The meters are arranged so that they record at two rates,
the higher rate being used during the hours of heavy load.

There are several methods of carrying out the fourth scheme.
In the Brighton System, a fixed charge is made each month,
depending on the maximum demand for power during the previous
month, a regular schedule of such charges being made out, based
on the cost of the plant. An integrating wattmeter is used to
record the energy consumed, while a so-called " demand meter "
records the maximum rate of demand.

POWER TRANSMISSION,

ELECTRICAL.

The subject of power transmission is a very broad one ; deal-
ing with the transmission and distribution of electrical energy, as
generated by the dynamo or alternating-current generator, to the
receivers. The receivers may be lamps, motors, electrolytic cells,
etc. Electric distribution of power is better than other systems
on account of its superior flexibility, efficiency, and effectiveness ;
and we find it taking the place of other methods in all but a very
few applications. For some purposes the problem is compara-
tively simple, while for other uses, such as supplying a large
system of incandescent lamps, scattered over a comparatively large
area, it is quite complicated. As with other branches of electrical
engineering, it is only in recent years that any great advances
have been made in the means employed for transmission of elec-
trical power, and wrhile this advance has been very rapid, there is
still a large field for development.

In a study of this subject the different methods employed
and their application, the most efficient systems to be installed for
given service, the preparation of conductors and the calculation
of their size, together with the proper installation of the same,
should be considered.

CONDUCTORS.

Material Used. Power, in any appreciable amount, is trans-
mitted, electrically, by the aid of metal wires, cables, tubes, or bars.
The materials used are iron or steel, copper and aluminum. Other
metals may serve to conduct electricity but they are not applied
to the general transmission of energy. Of these three, the two
latter are the most important, iron or steel being used to a consid-
erable extent only iii the construction of telephone and telegraph
lines, and even here they are rapidly giving way to copper. Steel
may be used in some special cases, such as. extremely long spans
in overhead construction or for the working conductors for rail-
way installations using a third rail. Phosphor bronze has a lim-
ited use on account of its mechanical strength.

POWER TRANSMISSION

Copper and aluminum are used in the commercially pure state
and are selected on account of their conductivity and comparatively
low cost. The use of aluminum is at present limited to long-dis-
tance transmission lines or to large bus-bars, and is selected on
account of its being much lighter than copper. It is not used for
insulated conductors because of its comparatively large cross-sec-
tion and consequent increase in amount of insulation necessary.

TABLE I.
Copper Wire Table.

Dimensions.

Resistance.

A. W. G.
or

B. &S.

Diameter.

Area.

Ohms per foot.

Inches.

Circular
Mils.

At 20° C.

At 50° C.

At 80° C.

0000

.460

211,600

.00004893

•.00005467

.00006058

000

.4096

167,800

.00006170

.00006893

.00007640

.8648

133,100

.00007780

.00008692

.00009633

.3249

105,500

.00009811

.0001096

.0001215

.2893

83,690

.0001237

.0001382

.0001532

.2576

66,370

.0001560

.0001743

.0001932

.2294

52,630

.0001967

.0002198

.0002435 .

.2043

41,740

.0002480

.0002771

.0003071

.1819

33,100

.0003128

.0003495

.0003873

.1620

26,250

.0003944

.0004406

.0004883

.1443

20,820

.0004973

.0005556

.0006158

.1285

16,510

.0006271

.0007007

.0007765

.1144

13,090

.0007908

.0008835

.0009791

.1019

10,380

.0009972

.001114

.001235

.09074

8,234

.001257

.001405

.001557

.08081

6,530

.001586

.001771

.001963

.07196

5,178

.001999

.002234

.002476

.06408

4,107

.002521

.002817

.003122

.05707

3,257

.003179

.003552

.003936

.05082

2,583

.004009

.004479

.0049(54

.04526

2,048

.005055

.005648

.006259

.04030

1,624

.006374

.007122

.007892

Resistance. The resistance of electrical conductors is ex
pressed by the formula:

where R = total resistance of the conductors considered.

L = length of the conductors in the units chosen.
A = area of the conductors in the units chosen.
f = a constant depending on the material used and on the
units selected .

POWER TRANSMISSION

For cylindrical conductors, L is usually expressed in feet and
A in circular mils. By a circular mil is meant the area of a circle
.001 inches in diameter. A square mil is the area of a square
whose sides measure .001 inches and is equivalent to 1.27 circular
mils. Cylindrical conductors are designated hy gauge number or
by their diameter. The Brown & Sharpe (B. & S.) or American
wire gauge is used almost universally and the diameters corre-
sponding to the different gauge numbers are given in Table I.
Wires above No. 0000. are designated by their diameter or by
their area in circular mils.

TABLE II.
Resistances of Pure Aluminum Wire.

A. W. G.
or
B. & S.

Resistance at 75^ F.

R
Ohms 1,000 ft.

Ohms per mile.

0000

.08177

.43172

000

.10310

.54440

.13001

.(58345

.16385

.86515

.20672

1.09150

.26077

1.37637

.32872

1.7357

.41448

2.1885

.52268

2.7597

.65910

3.4802

.83110

4.3885

1.06802

5.5355

1.32135

6.9767

1.66667

8.8000

2:1012

11.0947

2.6497

13.9900

3.3412

17.642

4.3180

22.800

5.1917

27.462

6.6985

35.368

8.4472

44.602

10.6518

56.242

A convenient way of determining the size of a conductor from
its gauge' number is to remember that a number 10 wire has a
diameter of nearly one-tenth of an inch and the cross-section is
doubled for every three sizes larger (Nos. 7, 4, etc.) and one-half
as great for every three sizes smaller (Nos. 13, 10, etc.)

1,000

6 POWER TRANSMISSION

feet of number 10 copper wire has a resistance of 1 ohm and
weighs 31.4 pounds.

"Wheny is expressed in terms of the mil foot, a wire one foot
in length having a cross-section of one mil, its value for copper of
a purity known as Matthiessen's Standard, or copper of 100%
conductivity, is 9.586 at 0° C.* For aluminum its value is given
as 15.2 for aluminum 99.5% pure. Table II gives the resistance
of aluminum wire.

This shows the conductivity of aluminum to be about 63% of
that of copper. The conductivity of iron wire is about \ that
of copper.

Matthiessen's standard is based on the resistance of copper
supposed, by Matthiessen, to be pure. Since his experiments, im-
provements in the refining of copper have made it possible to produce
copper of a conductivity exceeding 100%. Copper of a conductivity
lower than 98% is seldom used f or power transmission purposes.

Temperature Coefficient. The specific resistance (resistance
per mil foot) is given for copper as 9.586 at 0° Centigrade. Its
resistance increases with the temperature according to the approx-
imate formula:

Et == K0 (1 + at)

where Iit = Resistance at temperature tf°, Centigrade.
R0 - 0J C.

a = .0042, commercial value.

The value of a for aluminum does not differ greatly from
this. It is given by Kempe as .0039.

Weight. The specific gravity of copper is 8.89. The value
for aluminum is 2.7, showing aluminum to weigh .607 times as
much as copper for the same conductivity or resistance. It is this
property wilich makes its use desirable in special cases. Iron, as
used for conductors, has a specific gravity of 7.8. .

Mechanical Strength. Soft-drawn copper has a tensile
strength of 25,000 to 35,000 Ibs. per sq. in. Hard-drawn copper
has a tensile strength of 50,000 to 70,000 Ibs. per sq. in., depending
on the size; the lower value corresponding to Nos. 0000 and 000.

*The commercial values given for the mil foot vary from 10.7
to 11 ohms.

POWER TRANSMISSION

Aluminum Las a tensile strength of about 33,000 Ibs. per sq.
in. for bard-drawn wire ^ incb in diameter.

Effects of Resistance. The effect of resistance in conductors
is three-fold.

1. There is a drop ju voltage, determined from Ohm's law,

I=-EorE=IB.

2. There is a loss of energy proportional to the resistance and the

TT2

square of the current flowing. Loss in watts = I2R = -^-

3. There is a heating of the conductors, due to the energy lost, and
the amount of heating allowable depends on the material surrounding the
conductors. The drop in voltage or the heating limit is usually more im-
portant in the design of a transmission system than the loss of energy.

Capacity of Conductors for Carrying Current. The tem-
perature of a conductor will rise until heat is lost at a rate equal
to the rate it is generated so that a conductor is only capable of
carrying a certain current with a given allowable temperature rise.
The limit of this rise in temperature is determined by tire risk, or
injury to insulation. A general rule is that the current density
should not exceed 1,000 amperes per square inch of cross-section
for copper conductors. This value is too low for small wire and
too high for heavy conductors, and it is governed by the way in
which the conductors are installed. This value serves for bus-bars
where the thickness of the copper used is limited to -J-inch.
Curves shown in Fig. 1 are applicable to switchboard wiring, and
Table YII of " Electric Wiring" gives safe carrying capacity of
conductors for inside wiring. Perrine gives the following table
showing the class of conductors to be used under various conditions:

TABLE III.
Conductors for Various Conditions.

PART I.

Reference Reference

No. Remarks. No. Remarks.

1. Not allowed. 8. In insulating tubes.

2. Clear spaces.^ 9. In wood moldings.

3. Through trees. ](). Without further precaution.

4. On glass insulators. 11. If necessary.

5. On porcelain knobs. 12. Below 350 volts.

6. In porcelain cleats.* 13. Above 350 volts.

7. In wood cleats^

POWER TRANSMISSION

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Insulation, in the form of a covering, is required for elec-
trical conductors in all cases with the exception of switchboard bus-
bars and connections and wires used on pole lines, and even these
are often insulated. It may serve merely to keep the wires from
making contact, as is the case with cotton or silk-covered wire.
Again, the wire may be covered with a material having a high

POWER TRANSMISSION

specific resistance but being weak mechanically, and this combined
with a material serving to give the necessary strength to the insu-
lation. For this purpose yarns are used as the mechanical sup-
port, and waxes and asphaltum serve for the insulation proper.

Fig- 1.

Annunciator wire is covered with heavy cotton yarn saturated with
parath'ne. The so-called Underwriter's wire is insulated with cot-
ton braid saturated with white paint. Asphaltum or mineral wax
is used for insulating Weatherproof wire. It may be applied in
several ways, the best insulation being made by covering the con-
ductor with a single braiding laid over asphaltum and then passing

POWER TRANSMISSION

the covered wire through the liquid insulation, at the same time
applying two cotton braids, and finishing by an external application
of asphaltum and polishing. The most complete insulation is made
up of a material which gives the most perfect insulation and which
is strong enough, mechanically, to withstand pressure and abrasion
without additional support.

Fig. 1.

Qutta Percha and India Rubber, Gutta percha is used for
submarine cables, but rubber is the insulating material most used
for electrical conductors. Gutta percha cannot be used when ex-
posed to air, as it deteriorates rapidly under such conditions.

POWER TRANSMISSION 11

Rubber, when used, is vulcanized, and great care is necessary in
the process. This vulcanized rubber is usually covered with braid
having a polished asphaltum surface. The insulation of high-tension
cables will be considered in the topic, " Underground Construction."

DISTRIBUTION SYSTEMS.

Distribution systems may be divided into series systems, par-
allel systems, or combinations, such as series-parallel or parallel -
series systems. Various translating devices may be connected in
circuit, changing from one system to the other, and the parallel
system may be divided into single and multiple-circuit systems
commonly known as two-wire and three-, or Jive-wire systems.

Series Systems are applied to series arc lighting, series incan-
descent lighting, and to constant-current motors driving machin-
ery, or generators feeding secondary circuits. They serve for both
alternating and direct currents. Fig. 2 shows the arrangement of
units in this system. The current,
generated by the dynamo D, passes
from the positive brush A (in direct-
current systems) through the units
L in series to the negative brush B. „. 9

r ig. Z.

For lighting purposes, this current

has a constant value and special machines are used for its gener-
ation. The voltage at the generator depends on the voltage required
by the units and the number of units connected in service. As an
example, the voltage allowed for a direct-current open-arc lamp
and its connections may be taken as 50 volts. If 40 lamps are
burning, the potential generated will be 50 X 40 = 2,000 volts.
The number of units is sometimes great enough to raise this poten-
tial to 0,000 volts; but by a special arrangement of the Brush arc
machine, known as the multiple-circuit arc machine, the potential
is so distributed that its maximum value on the line is but 2,000
volts, provided the lamps are equally distributed, while the total
electromotive force generated is 6,000 volts, when the machine is
fully loaded.

The machine is supplied with three commutators and the
lamps connected as shown in Fig. 3, which also shows the distri-
bution of potential.

POWER TRANSMISSION

All calculations for series systems are simple. The drop in

voltage is obtained from Ohm's law, I = ~. A wire smaller than

No. 8 should never be used for line construction, as it would not
be strong enough mechanically, even though the drop in voltage
with its use should be well within the limit.

The current taken by arc lamps seldom exceeds 10 amperes.
For series incandescent lighting, the current may be lower than

Fig. 3.

this, having a value from 2 to 4 amperes. Special devices are used
to prevent the breaking of a single filament from putting out all of
the lights in the system and automatic short-circuiting devices are
used writh series arc lamps for accomplishing the same purpose.

As an example of the calculation of series circuits, required
the drop in voltage and loss of energy
in a line four miles long and composed
of No. 8 wire, when the current flowing
in the line is 9.6 amperes. From Table
1 we have a resistance of .0007007 ohm
per foot for N"o. 8 wire at 50° C. This
gives a resistance of 3.7 ohms per mile,
or a resistance of 14.8 ohms for the cir-
cuit. The drop in voltage from Ohm's
j(1j 4 law equals current times resistance or

equals 9.6 X 14.8 = 142 volts. The

loss in energy equals the square of the current times the resistance,
equals 9.62 X 14.8 = 1,364 watts. If the circuit contains 80 lamps,
each taking 50 volts, the total voltage of the system is 4,142 volts,

142

and the percentage drop in pressure is TTTo ™ 3.43%.

,)JFE.LDERS

-o

-0

POWER TRANSMISSION 13

Parallel Systems of Distribution. In the parallel or "mul-
tiple-arc" system of distribution, the lamps or motors are supplied
with a constant potential, and^the current supplied by the generators
is the sum of the currents taken by each translating device. There
are several methods of distribution applicable to this system, each
one having some characteristic which makes its use desirable for
certain installations. The usual arrangement is to run conductors
known as " feeders" out from the station, and connected to these
feeders are other conductors known as mains, to which, in turn,
the receivers or translating devices are connected. * Fig. 4 is a
diagram of such a "feeder and main" system.

The feeders may be connected at the same ends of the mains,
known as parallel feeding; or they may be connected at the opposite
ends of the main, giving us the an ti -parallel system of feeding.
The mains may be of uniform cross-section throughout, or they
may change in size so as to keep the current olensity approximately
constant. The above conditions .give rise to four possible combi-
nations, namely :

I. Cylindrical conductors, parallel feeding. Fig. 5.

II. Tapering conductors, parallel feeding. Fig. 6.

III. Cylindrical conductors, anti-parallel feeding. Fig. 7.

IV. Tapering conductors, anti-parallel feeding. Fig. 8.

The regulation of the voltage of a system is of particular im-
portance when incandescent lamps are supplied; and the calcula-
tion of the drop in voltage to lamps connected to mains supplied
with a constant potential should be considered. Without going into
detail as to the methods of derivation, we have the following for-
mulae which apply to the above combinations when the receivers are
uniformly distributed and each taking the same amount of current.
Cylindrical conductors, parallel feeding,

Tapering conductors, parallel feeding,

D = 2 RLr. II

Cylindrical conductors, anti-parallel feeding,

It I'//' ,. TTT

D=-y-(L-a?) Ill

Tapering conductors, anti -parallel feeding,

D = O. IV

14 POWER TRANSMISSION

where D = difference between potentials applied to different lamps.
•R = resistance of conductors per unit length at feeding
point. This will be a constant quantity for cylindrical conductors,
but will change for tapering conductors, having its minimum value
at the feeding point, and its maximum value at the end of the main.

I = current in main at feeding point, or point at which the
feeders are connected to the mains. In Figs. 5, 6, 7, and 8 the
mains only are shown in detail.

ce = distance from feeding point to the particular lamps at
which the voltage is being considered.

L = length of main.

For Cases I and II the maximum difference of potential is

found where % -- L, that is,
at the lamps located at" the
O> (|) (|) C|) CJ) (|) (|) (|) end of the mains.

For Case III the maxi-
mum difference of potential

(j) (JX^CJ) (^ is found, where x ----- , or

Fig. 6. at the lamp located at the

middle point of the mains.

9 9 9 9 y 9 For Case IY the potential

on all of the lamps is the

Fig. 7. same, but the difference be-

S\ A A A A A A A tween the voltage on the

X T T 9 V V T V feeders and the voltage on

' - — ' the lamps is equal to RI L.

For unequal distribution of
receivers and special feeding

points the drop in voltage can be calculated by the aid of Ohm's
law, but this calculation becomes quite complicated for extensive
systems. It usually is sufficient to keep the maximum drop writhin
the desired limits when designing electrical conductors for lighting,
being careful not to exceed the safe carrying capacity of the wires.
The drop in voltage on the feeders may be calculated directly
from Ohm's law when direct current is used, knowing the cur-
rent flowing and the dimensions of the conductors used.

POWER TRANSMISSION 15

Additional formulae are given in u Electric "Wiring," whicn
will aid in determining the size of wire to be vised for a given
installation.

As examples of calculation we have the following:
System consists of 20 lamps, each taking .5 amperes. L = 80
feet. R = .01 ohm per foot at feeding point. Find the maximum
difference of potential on the lamps in each of the first three cases.

I = 20 X .5 = = 10 amperes.

Case I. D = -Q1 X 10 X 8Q x /160 _'80) = 8 volts.

Case II. D = 2 X .01 X 10 X 80 == 16 volts.

.01 X 10 X -g-

Case III. D = — -.XlSO - r)= 2 volts.

oU \ &'

In Case IV the difference in potential applied to the lamps and
the potential of the feeders would be .01 X 10 X 80 = 8 volts.

Again, with the maximum allowable drop given, the resist-
ance of the wires at the feeding point may be determined. For
tapering conductors, the current density is kept approximately con-
stant by using wire of a smaller diameter as the current decreases.
Thus supposing, as in the case considered, that the resistance at
the feeding point was .01 ohm per foot. At a distance of 40 feet
from the feeding point the current would be only ^ of 10 or 5
amperes and the size of the wire would be one-half as great, giving
it a resistance at this point of .02 ohm per foot.

Feeding Point, In order to determine the point at which a
system of mains should preferably be fed, that is, the point where
the feeders are attached to the mains, it is necessary to find the
electrical center of gravity of the system. The method employed
is similar to that used in determining the best location of a power
plant as regards amount of copper required, and consists of sepa-
rately obtaining the center of gravity of straight sections and then
determining the total resultant and point of application of this
resultant of the straight sections to locate the best point for feed
ing. Actual conditions are often such that the system cannot be

16 POWER TRANSMISSION

fed at a point so determined, but it is well to run the feeders as
close to this point as is practical, as less copper is then required
for a given drop in potential.

Consider, as an example, a system such as is shown in Fig. 9.
The number of lamps and location of the same are shown in this
figure. The loads, ABC I), may be considered as concentrated
at A', a point 33.8 feet from I arid equal to A -f- B -f C + D.
This point is obtained as follows:

Kx = By. 10 y = 20 x. x + y = 400.
A + B = 30.
Cx' = Dy'. 15^ = 20//. x' + y = 500. x == 285.7 feet.

c + D = 35.

(A + B)^ = (0 + D)y". «" + ,/' = 632.4. __
30a?" = 35y".

A + B + C + D = 65

A' is 6.2 feet from C or 33.8 feet from I.

E and F may be combined to form a group of 30 lamps and
the resultant of E, F, G, and II is 70 lamps located at B', a point
310 feet from J, this point being located in the same manner as
A'. Similarly we find the resultant of the loads at A' and B' to
be 135 lamps located at C', a point 331.1 feet from I, and the
proper feeding point for the system.

A' = 65 lights, 33.8 feet from I.

B' = 70 lights, 310 feet from J.

Distance IJ = 360 feet.

Distance from A' to B' == 360 -f 310 -f 33.8 == 703.8 feet.

x -f y = 703.8 feet.

x = 364.9 feet.

364.9 - 33.8 == 331.1 feet.

The above is a simple definite case. Should the load be
variable, the proper feeding point will change with the load, and,
in extensive systems, the location of this point can be obtained
approximately only. The same method of calculation is employed
in locating the points from which sub-feeders are run out from-
the terminals of the main feeders as is the case in large systems,

POWER TRANSMISSION

the voltage being maintained constant at the point where the sub-
feeders are connected to the feeders.

Good practice shows the drop in potential to be within the

following limits:

•*w
From feeding points (points where sub-feeders

or mains are attached) to lamps 5 per cent.

Loss in sub-feeders o

Loss in mains l.o

Loss in service wires . . . O.o "

The actual variation in voltage should not exceed 3

I A C

-y- -

Fig. 9.

In Series=MultipIe and Multiple=Series Systems, groups of
units, connected in multiple, are arranged in series in the circuit, or
groups of units are connected in series and those, in turn, con-
nected in multiple, respectively. The application of such systems
is limited. They are used to some extent in street-lighting when
incandescent lamps are used.

18 POWER TRANSMISSION

MULTIPLE=WIRE SYSTEMS.

The Three=Wire System. AVe have seen that in any system
of conductors the power lost is equal to PR. For a given amount
of power transmitted (IE) the current varies inversely with the
voltage and consequently the amount of power lost, which is
directly proportional to the square of the current, is inversely pro-
portional to the square of the voltage. Hence, for the same loss
of power and the same percentage drop in voltage, doubling the
voltage of the system would allow the resistance of the conductors
to be made four times as great, and wire of one-fourth the cross-
section or one-fourth the
amount of copper would be
required. The voltage for
which incandescent lamps,
Fig. 10. having a reasonable efficiency,

can be economically manu-
factured is limited to 220, while the majority of them are made
for 110. In order to increase the voltage on the system, a special
connection of such lamps is necessary. The three-wire and five-
wire systems are adopted for the purpose of increasing this voltage.
Fig. 10 shows a diagram of a three-wire system. Consider the
conductor B removed, and we have a series-multiple system with
two lamps in series. This arrangement does not give independent
control of individual lamps, and the third wire is introduced to
take care of any unbalancing

of the number of lamps or A _^^ _^3 _+a

units connected on either side Q KJ • i(S i(Si(S

of the system, and to allow ± (^ ? '6'6'cJ) 1616 16
more freedom in the location - ^_6
of the lights. The current Fig. 11.

flowing in the conductor B,

known as the neutral conductor, depends on the difference of the
currents required by the units on the two sides of the system.
Fig. 11 shows a system in which the loads on the two sides are
unequal, an unbalanced system, with the value of the current in
the neutral wire at different points. Each unit is here assumed
to take one ampere.

POWER TRANSMISSION

As stated above, were no neutral wire required, the amount
of copper necessary for a system with the lamps connected, two in
series, for the same percentage drop in voltage would be one-fourth
the amount necessary for the parallel connection. This may be
shown as follows: The current in the wire in the first case is one-
half as great, so that the voltage drop would be divided by two for
the same size wire.
The voltage on the sys-
tem is twice as great,
so that, with the same
percentage regulation,
the actual voltage drop
would be doubled.
Consequently wire of
one-fourth the cross -
section and weight may
be used. If the neutral
wire is made one-half
the size of the outside
conductor, as is usually
the case in feeders, the
amount of copper re-
quired is -fft of that
necessary for the two-
wire system. For
mains it is customary
to make all three con-
ductors the same size,
increasing the amount

Fig. 12.

of copper to | of that required for a two-wire system. For a five-
wire system with all conductors the same size, the weight of copper
necessary is .156 times that for a two-wire system.

Multiple-wire systems have no advantage other than saving
of copper, except when used for multiple-voltage systems, while
among their disadvantages may be mentioned:

Complication of generating apparatus.

Complication of instruments and wiring.

Liability to variation in voltage, due to unbalancing of load.

20 POWER TRANSMISSION

Fig. 12 shows some of tlie methods employed in generating
current for a three-wire system.

A. Two dynamos connected in series, the usual method

B. A double dynamo.

C. Bridge arrangement, using a resistance R with the neutral con-
nection arranged so as to change the value of resistance in either side of
the system. Has the disadvantage of continuous loss of energy in R.

D. Storage battery connected across the line with neutral connected
at middle point.

E. Special dynamo supplied with three brushes.

F. Special machine having collector rings, across which is con-
nected an impedance coil, the neutral wire being connected to the middle
point of this coil.

G. Compensators or motor-generator set used in connection with
generator. The motor-generator set is known as a balancer set.

Compensators are usually wound for about 10% of the capac-
ity of the machine with which they are used. In the motor-gen-
erator set, one side becomes a motor or generator depending on
whether the load on that side is less or greater than the load on
the opposite side.

Voltage Regulation of Parallel Systems. It is customary to
keep the voltage on the mains constant, or as nearly so as possible,
at the point where the feeders are attached. Where but one set
of feeders is- run out from the station, this may be readily accom-
plished by the use of over-compounded dynamos, adjusted to give
an increase of voltage equal to the drop in the feeders at different
loads. Again, the field of a shunt-wound generator may be con-
trolled by hand, the pressure at the feeding points being indicated
by a voltmeter connected to pilot wires running from the feeding
point back to the station.

When the system is more extensive, separate regulation of
different feeders is necessary. A variable resistance may be placed
in series with separate feeders, but this is undesirable on account
of a constant loss of energy. Feeders may be connected in along
a system of mains and one or more of these switched in or out of
service as the load changes. Bus-bars giving different voltages
may be aranged so that the feeders can be v changed to a higher
voltage bar as the load increases. Boosters — series dynamos — may
be connected in series with separate feeders and these may be ar-
ranged to regulate the voltage automatically. The use of boosters is

POWER TRANSMISSION

not to be recommended except for a few very long feeders, and then
the total capacity of boosters should equal but a small percentage
of the station output if the efficiency of the system as a whole is
to remain high. Fig. 13 is a diagram of a system using different
methods of voltage regulation.

Alternating=Current Systems of Distribution may be classi-
fied in a manner similar to direct-current systems, that is, as series
and parallel systems; but in addition to these we have a classifica-
tion depending on the number of phases used, such as single-phase,
quarter- or two -phase and three-phase systems.

The Series System may consist of a simple series circuit fed
by a constant-current generator, or it may be fed by a constant-

Fig. 13.

current transformer, the primary of which is supplied with a con-
stant potential, the secondary furnishing a constant current. For
a description .of such a transformer, see "Electric Lighting".
Again, the current may be maintained constant by means of a con-
stant-current regulator, such as is described in "Electric Light-
ing". Constant-current alternators are seldom used, the two latter

forms of regulation being applied to most series installations. The
principal application of series alternating-current systems is to
street-lighting. Parallel -series alternating-current systems are
sometimes used for street-lighting with incandescent lamps.

Parallel Systems, using alternating current are also analo-
gous to parallel systems using direct current, though the receivers,
especially if lamps, are seldom connected directly to the leads com-
ing from the station, but are fed from the secondaries of constant-

22 POWER TRANSMISSION

potential transformers, which are connected to the lines in parallel,
and step down the voltage. The readiness with which the voltage
of such systems may be changed by means of suitable transformers
is the chief advantage of the single-phase systems. The voltage
may be generated at, or ' transformed* up to, a" high value at the
station, transmitted over a considerable distance over small con-
ductors with a small loss of energy, and then transformed to the
desired value for the connected units. Transformers may be readily
constructed to furnish voltage for a three-wire secondary distribu-
tion. Fig. 14 is a diagram of a single-phase system supplying
power to both two-wire and three-wire systems. Two separate
transformers are used for obtaining the three-wire system, in one
case, and a transformer, supplied with a tap connected to the mid-
dle ppint of the secondary, is used in the other case.

The regulation of voltage for alternating-current systems may
be accomplished, as in direct -current installations, by means of
compounding (" composite- wound alternators"), hand regulation,
or resistance or reactance connected in series with the feeders. In
addition, the feeders may be controlled by means of special regu-
lators such as the Stillwell Regulator, or the " C R " Regulator,
which consist of transformers with the primary coil connected
across the line and the secondary in series with the line, and so
arranged that the number of turns in one or both windings may
be varied; other forms of regulators are the magnetic regulator
and the induction regulator.

Polyphase Systems. Polyphase systems of distribution are
used where motors are to be run from the circuits; also for long-
distance transmission lines partly on account of the saving in cop-
per, polyphase generators may be constructed more cheaply, for
a given output, than single-phase machines because of a better
utilization of the winding space on the armature; while single-
phase motors, except in small sizes, or series motors as applied to
railway work, are not entirely satisfactory. Two-phase and three-
phase systems are the only ones that are in common use for power
transmission, three phases being used for long-distance transmis-
sion lines. Six phases are used for rotary converters only, the
capacity of the machines being greatly increased when connected
six-phase.

POWER TRANSMISSION

The amount of copper required for the different systems,
assuming the weight of copper for a single phase two- wire system
to be 100%, is as follows:

Single-phase two-wire systems — .100 per cent

" " three-wire " (Neutral wire same

size as outside wires). 37.5

Two-phase four-wire system ; 100

" " three-wire " 72.9

Three-phase three-wire system 7.5

11 " four-wire " 33.3

This assumes the voltage on the receivers to be the same in
every case, the maximum voltage having different values, depend-
ing on the system used. The three-
phase three-wire system is preferable \

to the two-phase three-wire system ^

for most purposes. In the three-

-O-
-O
-O-

-0-0
O--O-
-0-0
L0L0J
Fig. 14.

00
00

Fig. 15.

phase four-wire system the maximum voltage is V 3 times the
voltage on the receivers. Were the same maximum voltage allow-
able as in the three-phase three- wire system, the amount of copper
for the three-phase four-wire system would be f that required for
the three-phase three-wire system. Fig. 15 shows, diagram mat ic-
ally, the connections of the different systems.

As an example of the way in which the relative amounts of
copper are calculated, take the three-phase three-wire system.
Assume the amount of power transmitted to be P and the percent-

24 POWER TRANSMISSION

age loss of energy to be^>. Let E = the voltage on the receiver,
I = the current flowing in a single conductor, single-phase system,
and I' - - current in a single conductor, three-phase system. We
have for the single-phase two-wire system,

P == IE,

\
for the three-phase three-wire system,

P == 1/3TE

IE = 1/3 PE
I

T' __

1/3

The loss in energy in the two- wire system = j> P = 2 PR,
when R = resistance of one conductor. The loss in energy in the

three-phase system = ^> P - 3 I'2R'.
Substituting - ^ for I', we have

2 PR = ^--°r 2 R == R'-

The amount of copper is inversely proportional to the resist-
ance of the conductor, so that if W -= weight of one conductor for
single-phase system and W = weight of one conductor for three-
phase system, W : = 2 W.

Two conductors are required in the first case = 2 W.

Three conductors are required in the second case = 3 W.

3 W == .8 W.

2 W = 2 W.

3 W * W
^=2W^^75%-

TRANSniSSION LINES.

Capacity. Conductors used for the transmission of power
form, with their metallic shields, with the ground, or with neigh-
boring conductors, condensers, which, when the line is long, have
an appreciable capacity. The capacity of circuits is quite readily
calculated, the following formula applying to individual cases.

POWER TRANSMISSION

TABLE IV.

Capacity in nicro=Farads Per Mile of Circuit for Three-Phase

System.

Size
B. & S.

Diain.
in
inch.

Distance
A
in inches.

Capacity
C
in M. F.

Size
B. & S.

Diain.
in
inch.

Distance
A
in inches.

Capacity
in M. P.

0000 .4(> 12

.0226

.204

.01874

.0204

.01726

.01922

.01636

.01474

.01452

000

.41

.0218

.182

.01830

.01992

.01690

.01876

.01602

.01638

.01426

.886

.0124

.1(52

.01788

.01946

.01654

.01832

.01560

.01604

.0140

.825

.02078

.144

.01746

.01898

.01618

.01642

.01538

.01570

.01374

.289

.02022

.128

.01708

.01952

.01586

.01748

.01508

.0154

.01350

•>

.258

.01972

.114

.01660

.01818

.01552

.01710

.01478

.01510

.01326

.229

.01938

.102

.01636

.01766

.01522

.01672

.01452

.01480

.01304

38-88 & 10

. Insulated cable with lead sheath.

C —

C =

38.83 X 10-

~~4A~
JOLT -__

19.42 >: 10-
2A

jle. Siiigle conductor with earth return.

per mile of circuit. ParaHel conductors forming
a metallic circuit.

POWER TRANSMISSION

C = Capacity in micro-farads. (Divide by 1,000,000 to give
capacity in farads.)

k — specific inductive capacity of insulating material = 1 for

air — 2.25 to 3.7 for rubber.
D = inside diameter of lead sheath.
d = diameter of conductor.
li — distance of conductors above ground.
A = distance between wires.

Common logarithms apply to these formulae and C for a
metallic circuit is the capacity between wires.

TABLE V.
Inductance Per Mile of Three=Phase Circuit.

Size
B. &S.

Diameter
in inch.

Distance
d in inches.

Self-induct-
ance L.
henrys.

Size
B. &S.

Diameter
in inch.

Distance
d in inches.

Self-induct-
ance L
henrys.

0000

.46

'.00234

.204

.00280

.00256

.00300

.00270

.00315

.00312

.00358

000

.41

.00241

.182

.00286

.00262

.00307

.00277

.00323

.00318

.00356

.365

.00248 •

.162

.00291

.00269

.00313

.00285

.00329

.00330

- .00369

.325

.00254

.144

.00298

.00276

.00310

.00293

.00336

.00331

.00377

.289

.00260

.128

.00303

.00281

.00325

.00308

.00341

.00338

.00384

.258

.00267

.114

.00310

.00288

.00332

.00304

.00348

.00314

.00389

.229

.00274

.102

.00318

.00294

.00340

.00310

.00355

.00351

.00396

POWER TRANSMISSION 27

If the capacity be taken between one wire and the neutral point
of a system, or the point of zero potential, the capacity is given as:

C (in micro-farads) = — ^-r— per mile of circuit.

Table IY gives the capacity, to the neutral point, of different
size wire used for three-phase transmission lines.

The effect of this capacity is to cause a charging current, 90'
in advance of the impressed pressure, to flow in the circuit, and
the regulation of the system is affected by this charging current as
will be seen later. Capacity may be reduced by increasing the
distance between conductors or in lead-sheathed cables, by using
an insulating material having a low specific inductive capacity,
such as paper.

Inductance. The self -inductance of lines is very readily cal-
culated. Following is a formula applicable to copper or alumi-
num conductors:

L = .000558 |~2.303 log (— ) + .25] per mile of circuit when

L = inductance of a loop of a three phase circuit in henrys. The
inductance of a complete circuit, single phase, is equal to the
above value multiplied by 2 -f- ;/ 3.

Self-inductance is reduced by decreasing the distance between
wires and it disappears entirely in concentric conductors. Sub-
dividing the conductors decreases the drop in voltage due to self-
inductance but it complicates the wiring. Circuits formed of
conductors twisted together have very little inductance. When
alternating-current wires are run in iron pipes, both wires of the
circuit must be run in the same pipe, inasmuch as the self-induc-
tance depends on the number of magnetic lines of force passing
between the conductors or threading the circuit, and this number
will be increased when iron is present between the conductors.

The effect of self-inductance in a circuit is to cause the current
to lag behind the impressed voltage and it also increases the impe-
dance of the circuit.

The effect of self -inductance may be neutralized by capacity
or vice-versa. The relative value of the two must be as follows:

POWER TRANSMISSION

° ~ (^/)2L

an(i L are in farads and henrys respectively,

• A

and/1 is the frequency of the system.

Mutual=Inductance. By mutual-inductance is meant the in-
ductive effect one circuit has on another sep-
: arate circuit, generally a parallel circuit in
power transmission. An alternating current
flowing in one circuit sets up an electromotive
force in a parallel circuit which is opposite in
direction to the E.M.F. impressed on the first
^ circuit, and is proportional to the number of
the lines of force set up by the first circuit
which thread the second circuit.
The effects of mutual inductance may be reduced by increas-
ing the distance between the circuits, the distance between wires
of a circuit remaining the same. This is impractical beyond a

•D

Pig. 16.

-«1300fl300 ~«-1

Upper cross arm

certain extent, if the circuits are to be run on the same pole line,
so that a special arrangement of the conductors is necessary.

Figs. 16 and 17 show such special arrangements. In Fig. 10
AB forms the wires of one circuit and CD the wires of the other

POWER TRANSMISSION 29

circuit. Lines of force set up by the circuit AB do not thread the
circuit CD, provided ABC and D are arranged at the corners of
a square so that there is no effect on the circuit CD. In Fig. 17
assume an E.M.F. to be set up in the portion of the circuit CD in
the direction of the arrows. The E.M.F. in the section DE will
then be in the direction of the arrows shown and the effects on the
circuit AB will be neutralized, provided the transposition, as the
crossing of the conductors is called, is made at the middle of
the line. Such transpositions are made at frequent intervals on
transmission lines to do away with the effects of mutual inductance
which, at times, might be considerable. When several circuits
are run on the same pole line, these transpositions must be made
in such a manner that each circuit is transposed in its relation to
the other circuits. Thus in Fig. 17 is also shown the transposi-
tion of the circuits of a line composed of ten two-wire circuits.

CALCULATION OF ALTERNATING=CURRENT LINES.

In dealing with alternating currents, Ohm's law can be applied
only when all of the effects of inductance and capacity have been
eliminated, and, since this can seldom be accomplished, a new for-
mula must be used which takes such capacity and inductance
effects into account. Not only the inductance or capacity of the
line itself must be considered, but the nature of the receiver must
be taken into account as well, when the regulation of the system
as a whole is being considered. The following quantities must be
known in the complete solution of problems relating to alternatintr-
current systems.

1. Frequency of the current used.

2. Self-induction and capacity of the receivers.

3. Self-induction and capacity of the lines.

4. Voltage of, and current flowing in, the lines.

5. Resistance of the various parts.

Following is a set of formulae and an appropriate table for cal-
culating transmission lines proper when using direct or alternating
current and for frequencies varying from 25 to 125, and for single
and polyphase currents. This table is issued by the General Elec-
tric Company.

30 POWER TRANSMISSION

GENERAL WIRING FORMULA.

D X W X C1

Area of conductor, Circular Mils =

W X T
Current in main conductors = -

X E2

AV = Total watts delivered.

D = Distance of transmission (one way) in feet.

j) - Loss in line in per cent of power delivered, that is, of AY.

E = Voltage between main conductors at receiving or con-
sumer's end of circuit.

For continuous current C' = 2,160, T = 1, B = = 1, and
A == 6.04.

X E X B

ir n/

V olts loss in lines =

Lbs.

— — —
100

D2 X W X C" X A
— x E. >( 1)(NK)>fluo

The following formula will also be found convenient for cal-
culating the copper required for long-distance three-phase trans-
mission circuits:

M2X K.W. X 300,000,000
Lbs. Copper — —

• p X E'

M is the distance of transmission in miles, K.W. the power
delivered in kilowatts, and the power factor is assumed to be
approximately 95%.

APPLICATION OF FORMUL/E.

"The value of C' for any particular power factor is obtained by
dividing 2,160, the value for continuous current, by the square of
that power factor for single-phase, by twice the square of that
power factor for three-wire three-phase, or four-wire two-phase.
The value of B depends on the size of wire, frequency, and
power factor. It is equal to 1 for continuous current, and for
alternating current with 100 per cent power factor and sizes of wire
given in the following table of wiring constants.

"The figures given are for wires 18 inches apart, and are suffi-
ciently accurate for -all practical purposes provided the displacement
in pliase between current and E.M.F. at the receiving end is not

POWER TRANSMISSION

TABLE VI.

System.

Values
of A.

Values of C'.

Per Cent Power Far tor.

100

5)0

Single-phase

6.04
12.08
9.06

2,160
1,080
1,080

2,400
1,200
1,200

2,660
1,880
1,880

8,000
1,500
1 ,500

8,880
1,690
1,690

Two-phase (four-wire) ....
Thre-phase (three-wire) . . .

System.

Values of T.

Per Cent Power Factor,

100

Single-phase

1.00
.50

.58

1.05
.53
.61

1.11

.55
.64

1.17
.59

.68

1.25
.62
.72

Two-phase (four-wire)

Three-phase (three-wire)

VALUES OF B.

60 Cycles.

125 Cycles.

Per Cent Power Factor.

ft*

0000
000

1.62
1.49

1.84
1.66

1.99
1.77

2.09
1.95

2.35

2.08

2.86
2.48

3.24

2.77

3.49
2.94

1 34

1.52

1.60

1.66

1.86

2.18

2.40

2.57

1.31

1.40

1.46

1.49

1.71

1.96

2.13

2.25

1.24

1.30

1.34

1.36

1.56

1.75

1.88

1.97

1.18

1.23

1.25

1.26

1.45

1.60

1.70

1.77

1.14

1.17

1.18

1.17

1.35

1.46

1.53

1.57

1.11

1.12

1.11

1.10

1.27

1.35

1.40

1.43

1 08

1.08

1.06

1.04

1.21

1.27

1.30

1.31

1.05

1.04

1.02

1.00

1.16

1.20

1.21

7
" .' 8

1.03
1.02

1.02
1.00

1.00
1.00

1.12
1.09

1.14
1.10

1:14

1.09

1.13
1.07

9
10

1.00
1.00

1.06
1.04

1.06
1.03

1.04
1.00

1.02
1.00

POWER TRANSMISSION

Values of B.

Per Cent Power Factor.

££ ££ "ES • JS8 88 83 83

S3 88 S3 S8 88 88 88

Sis ggj £2 gg gg 88 33

S5.SS SS SS SS S8 88

Per Cent Power Factor.

^^ Sg Sg 88 88 83 88

'eg

• §g?| S2 §g 83 88 88 88

g§1 $Sq SS §g 88 83 88

i— 1 rH rH 1— I i— 1 TH 1— ( i— 1 r-l i— 1 i— 1 r-l rH r— 1

SS SS gJS S§ gg 88 88

•suiqo -0 o<&
TB jaajooo'l^d
8JIAV jo 90tnnsis8H

O5 CO •rfi 1-—
O5 <M O5 O2 CO Ol C-1 -^ Oi CC O >C CC
•^ CD 1^ OS <M »O O "O r- 1 O r-l CC i— I T-H
OO OO rH T-H 01 <M CCf 10 CD GOO

T— 1

•sqi-'lJOOO'l J3<I
f)JTAV a^SI JocmSpAV

LO X Tt< -^f 10

T-HO5 COO CC (M O5CD OO5 <MO OlrH
'sf O O (M "CO iO <M O 1- CD ^O CC CC
CD »O "tf<CC <M<M rHrH rH

SUK roinoJK)
a.ii.M. jo -eaav

O1GO CCCD CCCD (MrH CCCD OCD CCO
rHCD CCO OOCO 'O"^1 CCC^I Oli— 1 rH i— I
(M rH rH rH

•aSni?£) -g sy -g
9JIM jo -OK

§O OO i— IC-1 CO ^ 1OCD i-> 00 CiO
O O rH

very much. greater than that at the generator; in other words, pro-
vided that the reactance of the line is not excessive or the line
loss unusually high. For example, the constants should not be
applied at 125 cycles if the largest conductors are used and the
loss 20% or more of the power delivered. At lower frequencies,
however, the constants are reasonably correct even under such
extreme conditions. They represent about the true values at 10%
line loss, are close enough at all losses less than 10%, ancf often,
at least for frequencies up to 40 cycles, close enough for even
much larger losses. Where the conductors of a circuit are nearer
each other than 18 inches, the volts loss will be less than given by

POWER TRANSMISSION 33

the formula?, and if close together, as with multiple-conductor
cable, the loss will be only that due to resistance.

<'• The value of T depends on the system and power factor. It
is equal to 1 for continuous current and for single-phase current
of 100 per cent power factor. The value of A and the weights of
the wires in the table are based on .00000302 pound as the weight
of a foot of copper wire of one circular mil area.

" In using the above formulae and constants, it should be particularly
observed thatp stands for the per cent loss in the line of the delivered power,
not foi the per cent loss in the line of the power at the generator; and that
E is the potential at the delivery end of the line and not at the generator.

" When the power factor cannot be more accurately determined
it may be assumed to be as follows for any alternating system oper-
ating under average conditions: Incandescent lighting and syn-
chronous motors, 95%; lighting and induction motors together,
85%; induction motors alone, 80%.

" In continuous -cur rent three-wire systems, the neutral wire for
feeders should be made of one- third the section obtained by the for-
mulas for either of the outside wires. In both continuous and alter-
nating-current systems, the neutral conductor for secondary mains
and house wiring should be taken as large as the other conductors.

u The three wires of a three-phase circuit and the four wires of
a two-phase circuit should all be made the same size, and each
conductor should be of the cross-section given by the first formula".

Numerical examples of the application of this table, as well
as of other formulae, are given later.

A better idea of the way in which the different quantities in-
volved affect the regulation of an alternating-current line may be
obtained from graphical representation or from formulae which are
not so empirical. Before taking up other methods of calculation,
however, let us consider the meaning of power factor.

By power factor we mean the cosine of the angle by which
the current lags behind or leads the electromotive force producing
that current. It is the factor by which the apparent watts (volts
times amperes) must be multiplied to give true power. The formula
for po\ver in a single-phase circuit is then,

Power = IE cos 0 when 6 is the lag or lead angle; and for
three-phase circuits,

34 POWER TRANSMISSION

Power == IE cos 0 V 3 when I is the current flowing in a
single conductor.

For two-phase circuits, balanced load, this "becomes,

Power = 2 IE cos 0; and,

Power = 2 1/3 IE cos 0, for six-phase circuits.

For single and three-phase circuits E is the voltage between
lines. For two-phase circuits it is the voltage across either phase,
and for six-phase circuits it is the voltage across one phase of what
corresponds to a three-phase connection.

Considering the formula for single phase, we find that the
current flowing in the line may be taken as made up of two com.
ponents, one in phase with the voltage and one 90° out of phase,
lagging, or leading, depending on conditions. In Fig. 18 let OE

equal the impressed pres-
sure and OC the current
flowing. 6 = angle of lag.
The current OC may be
resolved into two compo-
nents, one in phase with
OE = OB, and one 90 de-
grees behind OE = BC.

OB = OC cos 6 and is known as the active component of the
current.

BC = OC sin 0 and is known as the wattless component of
the current.

The capacity and inductance are distributed throughout the
line, that is, the line may be considered as made up of tiny con-

j— — ^OTiP — I — n^Tt — I — nrftp — I — nnp — i — IWF — i — ifflp — i — <IRR^ — \

O 1 ll 1 111 If 1:1

2= — — nm^ — I — nffln — ' — -^w^ — ' — nmp — I — nnn^J oj^p — I — ^^ — I

Fig. 19.

densers and reactance coils, connected at short intervals as shown
in Fig. 19. Considering the inductance and capacity as distributed
in this manner, the regulation of a syistem may be calculated, but
the process is very difficult, and simpler methods, which give very
close results, have been adopted for practical work. Probably the

POWER TRANSMISSION 35

methods presented by Perrine and Baum are as simple as any ex-
cept those based on purely empirical 'formulae.

Tables giving the capacity and inductance of lines, together
with the formulae for the calculation of these quantities, have
already been given. It has also been stated that the effect of the
capacity of a line is to cause a charging current to flow in the line,
this current being 90° in advance of the impressed voltage. The
value of this charging current i-s:

Charging current per wire = Z, single-phase.

C = capacity in micro-farads of one wire to neutral point.
f = frequency o£ the circuit.
E = voltage between wires.

Charging current, three-phase, = r or 1.155 X charging

1/3

current, single-phase.

Since the voltage across the lines is not the same all along
the line, the value of the charging current will not be the same,
but the error introduced by assuming it to be constant is not great.
For our calculation, then, we assume that the charging current in
an open-circuited line is constant throughout its length, and also
that the capacity of the line may be taken as concentrated at the
center of the line.

Fig. 20.

Consider a single-phase line such as is shown diagrammatically
in Fig. 20.

Let EO = the voltage at the generator end of the line.
E = the- voltage at the receiver.
L = self induction of the line.
Ic = charging current per wire.

I = current flowing in the line due to the load on the
line.

36 POWER TRANSMISSION

6 = angle by which the load current differs frOm the

impressed voltage.
R — resistance of the line.
e = drop in voltage in the line.

w — 2 77 f.

+ ,;' is a symbol indicating that the current is 90° in

advance of the pressure.
-j indicates that the current is 90° behind the pressure.

The expression, 1/R2 + (2 7T/L)2 = 1/R2 + <ya L2 may be
represented by R + ^'L &>, the factor -f ,/ indicating that the square
root of the sum of the squares of these two quantities must be
taken to obtain the numerical result. The quantity/2 may be con-
sidered as - 1.

Taking the capacity of the line and considering it as a con-
denser located at the middle of the line, we may assume the charg-
ing current as flowing over only one-half of the line, or one-half the
charging current may be considered as flowing over all of the line.

The im-pedance of the line is equal to 1/R2 -f- co2 L2 = R -j- jLw.
The power factor of the load = cos 6.
The active component of the current is I cos 6.
The wattless component of the current is -jl sin 6 (-j indicat-
ing that the current lags 90° behind the pressure).

The charging current may be represented by -f j ~j~-

Then the drop due to the active component of the load is

I cos 6 (K + fLo>).

The drop due to the wattless component of the load is
-jl sin 0(R -h/Lcu).

The drop due to the charging current is + j-jj~(R +/L®)

The total drop is equal to the sum of these three values = 0,
so that,

Eo = E + e = I cos 9 (R + jLu) -jl sin 6 (R +

Expanding this and substituting - 1 for/2 we have,

POWER TRANSMISSION

E0 = E + I cos 6 R -f jl cos 0 Lo> -jl sin 0 R + I sin 6 Lo>

Referring to Fig. 21 \ve have these various values plotted
graphically.

. ICR IpL<y

oa = E, aJ = -j -_-, fo = -

— -f- ./I cos 6 Lw,

sin #

cd = -f- I cos # R?

ef = — ^'IR sin 0,

off = E0.

«J is plotted 90° in advance of oa on account of the symbol

Jc is plotted in the opposite direction from oa on account of
the negative sign.

ef is plotted downward on account of the symbol —j.

"xi*
Fig. 21.

If we let oa', Fig. 21, represent the current vector, then 6 =
angle of lag, and eg which equals IR is plotted parallel to oa' and
ce = ILw is plotted perpendicular to oa'.

It is seen from this that the charging current tends to pro-
duce a rise in E.M.F. instead 'of a drop in pressure.

The above takes into account only the constants of the line.
In order to determine the regulation of a complete system, the

38 POWER TRANSMISSION

resistance, capacity, and inductance of the translating devices must
be considered as well. In Fig. 22 is shown a diagram of a com-
plete system with both step-up and step-down transformers con-
nected in service. The charging current may be considered as
flowing through half of the system only, namely, the generator,
the step- up transformers, and one -half of the line.

L R

Fig. 22

Let Kj = the equivalent resistance of the step-down trans-
formers.

B2 = the equivalent resistance of the step-up trans-
formers.

Lj = inductance of the step-down transformers.

L2 = inductance of the step-up transformers.

Kg = equivalent resistance of the generators.

Lg = equivalent inductance of the generators.

R = resistance of the line.

L = inductance of the line.

1*=!^ + L2 + Lg + L.

KT = Ps + E2 + Eg + R.

All quantities should be converted into their equivalent
values for the full line pressure. Thus the generator and re-
ceiver voltages should be multiplied by the ratio of transforma-
tion of the step- up and step-down transformers, respectively, to
change them to the full line pressure. The resistance and induc-
tance of the transformers must include the resistance and inductance
of both windings, and the value must correspond to the line voltage.
Thus the resistance of the step- up transformers will be i\ n2 -f- 7*2,

when rt = resistance of primary coil,
r2 = resistance of secondary coil,
11 = the ratio of transformation. In the same way, the

equivalent resistance of the step-down transformers will be ^-f- n2
rr The generator resistance and inductance must be multiplied by

to bring them to equivalent values for the full line pressure.

POWER TRANSMISSION 39

Our formula then becomes: —

E0 == E + I cos e (KT +JLTo>) -j I sin 0 (KT + t/LTo>) +

* l* [(I + ** + Es) +> (t + L> +

Plotted graphically we have, Fig. 21:

6»t£ — E 6Y/ = I COS 0 Km

de = I cos 0 L

The numerical value of E and E0 may be determined, from a
diagram such as is shown in Fig. 21, wThen constructed to scale;
or it may be calculated analytically, remembering that the quan-
tities affected by j are to be combined, geometrically, with the
quantities not affected by the symbol.

The above formulae apply to single-phase circuits directly.
If to be used for the calculation of three-phase circuits, the follow-
ing points must be .observed:

1. Charging current ( Ic ) three-phase = ,— x charging current

v o

single-phase.

'2. The voltage should, preferably, be considered as the voltage be-
tween one line aud the neutral point. The voltage to the neutral point
will be the line voltage divided by ]/ 3.

3. The resistance of one line only is considered, not the resistance
of a loop.

4. The inductance of one line only is used. The inductance of one
line equals the inductance of a loop divided by j/j£

Examples of AIternating=Current Line Calculation.

1. What is the capacity, in micro-farads, between wires of a
single-phase transmission line 10 miles in length composed of
number 6 copper wire spaced 15 inches apart ? AVhat is the
capacity to the neutral point ?

19 42 X 10"9
(J in farads = -^ -- per mile of circuit.

, £ A.

log -j

A =15' inches d -- .1<>2 inches. .

9 \

~' =185 log 185 == 2.2072

40 POWER TRANSMISSION

19 4^ y 10~9

0 in farads = - ' " : - X 10 - .000000085

C in micro-farads = .000000085 X 1,000,000 == .085

r\ Wt+J />

0 in micro-farads with respect to the neutral point — - -

/\^V W/>

C iii micro-farads — o ^

This shows that the capacity to the neutral point is twice the
capacity to the other wire.

2. What is the self inductance of the above circuit ?

>er mile of

L = .000558 X -=f 2.303 log -T -f /*„ ,

I/ 3 \ ' d ) circuit.

L = .000644 (2.303 X 2.2672 + .25) X 10
- .000644 X 5.47 X 10 = .0352 henrys.

3. A circuit has a capacity of .2 micro-farads. What must
be the value of its inductance to compensate for this capacity at

60 cycles ?

C = .0000002 farads

(27T/7 = (2 X 3.1416 X CO/ == 142122

-0000002 =

L = 1 -5- (142122 X 0000002) === 35.2 lienrys

4. It is desired to transmit 1,000 K.W. a distance of 25
miles at a voltage of 20,000, a frequency of 60 cycles, and a power
factor of 85%. Transmission is to be a three-phase three-wire sys-
tem. Allowing 10% loss of delivered power in the line, required:

a Area of cond uctor.

b Current in each conductor.

c Volts lost in line.

d Pounds of copper.

1) X W X C'

Circular mils =

—
p X E

D = 25 X 5,280 == 132,000

W = 1,000 X 1,000 =± 1,000,000

POWER TRANSMISSION 41

C' = 1,500 for three-phase three wire system and 85% power
factor.

p = = 10

E == 20,000 E2 = = 400,000,000

132000 X 1000000 X 1500

Circular mils =

= 49,500.

Number 8 wire has a cross-section of 52,400 cir. mils.

W X T
b Current in each conductor = -- ~ — = 34.

T = .68 for three-phase system, 85% power factor.

•^ , p X E X B

c v olts lost in line = - — ^- —

B = 1.18 for number 3 wires, 60 cycles and 85% power
factor.

10 X 20,000 X 1.18

Volts lost = - - = 23(50

1UU

D3 x W X C- X A

*>pp« = -; or ]t ma be cal-

culated directly from the weight of wire given in the tables after
the size of wire has been determined by other formulae. Thus 75
miles of number 3 wire is required. This weighs 159 pounds
per 1,000 feet.

159 X 5.280 X 75 == 62,964 pounds.

5. A single-phase line 20 miles in length is constructed of
number 000 wire strung 24 inches apart. It is desired to trans-
mit 500 K.W. over this line at a frequency of 25 cycles and a
power factor of 80%, the voltage at the receiver end being 25,000.
Considering the line drop only, what must be the voltage at the
generator end of the line?

E0 = E + I cos -0 II + j I cos eisto—jl sin 0 II + I sin 0

T • J p ~l ^ 1 f » -W-

A ft) -}- J -~ K — • 1-- ft).

>5 (Power == IE cos 0)

E =: 25,000

500,000

25,000 X .80

42 POWER TRANSMISSION

Cos 6 = .80

Sin 0 = .60 (from trigonometric tables)

R = resistance of 40 miles of number 000 wire = 14.56
ohms at 50° C.

L = .00277 X ~L X 20 = .064 (calculated from Table V).

a>-=2'nf= 27rX 25 = 157

E X C X 2 TT X-/ 25,000 X .3752 X 157
ic " 2 X 10« 2 x 1,000,000

C = .3752 (Table IV or calculated).

Substituting these values in the above formula we have,
E0 = 25,000 + 291.2 +j 200.8 -j 218.4 -f 150.6 -f e/5.36 - 8.7
E0 = 25,000 -f 291.2 + 150.6 -'3.7 + j (200.8 - 218 4 + 5.36)
E0 = 25,000 + 291.2 + 150.6 - 3.7 -j (218.4 - 200.8 - 5.36)

E0 = V (25,000 + 291.2 + 150.6 - 3.7)2 -f (218.4 - 200.8 - 5 36)2
Since the symbol j indicates that the quantities must be com-
bined geometrically.

E0 = l/(25;438.1)2 + (12.24)2 — 25,438.1 volts.

6. A three-phase line 20 miles in length is constructed of
number 000 wire strung 24 inches apart. We wish to transmit
1,000 K.W. over this line at a frequency of 25 cycles and a power
factor of 85%, the voltage at the receiving end being 2,000. Three
Y-connected 500 K.W. transformers having a ratio of 10 : 1 step
the voltage up and down at either end of the line. The resistance
of the high-tension winding of each transformer is 4 ohms. The
resistance of the low-tension windings is .04 ohms. The induc-
tance of each transformer is 4 henrys. Neglecting the generator
constants, what must be the voltage applied to the low-tension
windings of the step-up transformers?

E0 = E + I cos 6 (RT + j LTe») -jl sin 0 (KT -J- j LTo>) -f j Ic

Since this is for a three-phase circuit we will work with the
voltage to the neutral 'point and will change all values to corre-
spond to the line voltage. Hence,

POWER TRANSMISSION 43

, x 10 = x 10 +

1/3 V 3

1 — 34 amperes. Since 1 3 IE Cos 6 -- 1.000,000

E =-- 10 X 2,000 == 20,000
Cos 6 = .85
I — 34.

IIT == Resistance of one line + equivalent resistance of one
transformer at each end of the line.

KT = 7.28 ohms + 4 + 100 X .04 + 4 + 100 >( .04.

= 23.28 ohms.

LT = .0554 -*• 1/3"+ .4 + .4 == .832 henrys.
o> == 157

sin 6 = .52

2
Ic = .589 X - = .(377 amp. = charging current single-

2
])hase X -

1/3

R ^ PA .

-y = 3.64

It, ==' 8

^ — .010 L2 = .4

Hubstituthig these values in our formula we have,

+ ^'7.88-44.2
= 11,550 + 672.8 + 2,309-44.2 + j (3,774 - 411.6 + 7.88)

-- V 14,487.^ + 3370.32 == 14,874
£0 = 2,573 volts.

TRANSFORMERS.

A transformer consists of two coils made up of insulated wire,
the coils being insulated from each other and from a core, made
up of laminated iron, on which they are placed. One of these
coils, known as the primary coil, is connected across the circuit, in
constant-potential transformers, and the other coil, known as the

44 POWER TRANSMISSION

secondary coil, is connected to the lamps or motors, or whatever
makes up the receivers. As a matter of fact, these coils are each
usually made up of several sections. The voltage induced in the
secondary windings is equal to the voltage impressed on the pri-
mary winding multiplied by the ratio of the number of turns in
the secondary to the number in the primary coil, less a certain drop
due to impedance of the coils and to magnetic leakage. This drop
is negligible on no load. If transformers are used to raise the
voltage, they are termed step -up transformers. If used to lower
the voltage, they are called step-down transformers.

Losses of power occurring in transformers are of two kinds
namely:

Iron or core losses which are made up of hysteresis and eddy-
current losses in the iron making up the core, and

Copper losses which are due to the I2R losses in the windings
with the addition, in some cases, of eddy currents set up in the
conductors themselves.

The efficiency of a transformer depends on the value of these
losses and may be expressed as the ratio of the watts output to
the watts input.

W, W..-IW, + Wh + We)

WP " Wp

"W"s = watts secondary.
Wp = watts primary.
Wc = copper losses.
Wh = hysteresis losses.
We = eddy current losses.

The iron losses remain constant for any given voltage regard-
less of the load, while the copper losses are proportional to the
square of the current. The efficiencies of transformers are high,
varying from 94 to 95% at ^ load to 98% at full load for sizes
above 25 K.W.

By All=Day Efficiency is meant the efficiency of a trans-
former, taking into consideration its operation for twenty. four
hours, and it is calculated for the ratio of watt-hours output to
watt-hours input for this length of time when in actual service.
For calculation, the transformer is often assumed to be fully loaded

POWER TRANSMISSION

WWWWW

vVv VWWWWv

nwVWWAM ^WWWWVj
I

for five hours and run with no load for the remaining nineteen.
The all-day efficiency is then determined as follows:

Output, K.W. hours == watts output at full load X 5.
Input, K.W. hours : = watts output at full load X 5 + 12E
loss at full load X 5 -f core loss at normal voltage X 24.

A11 ,. «, . output, watt-hours

All-day efficiency = -. — i- —

input, watt-hours.

The assumption that a lighting transformer is fully loaded
five hours out of the day is not always a correct one. On many
circuits from two to three hours of full load would be more nearly
the proper value to use in calculating the all-day efficiency.

By Regulation of a transformer
is meant the percentage drop in the
secondary voltage from no load to full
load when normal pressure is im-
pressed on the primary. This drop is
due to the IH drop in the windings
and to magnetic leakage. In well
designed transformers the loss due to
magnetic leakage is about 10%, or
less, of that due to the resistance drop.
For non-inductive load (power factor
= unity) the regulation is from 1 to
3% in good transformers. With in-
duction load this is increased co 4 or
5%, or even more. p. oo

Both the efficiency and the reg-
ulation should be considered in selecting a transformer for given
service. Thus, if a transformer is to be used for lighting, its reg-
ulation should be of the best, since drop in voltage due to the trans-
former is in addition to that due to the conductors. In the same
way the regulation of any system as a whole depends to a certain
extent on the regulation of the transformer installed.

If the efficiency of a transformer is low, it means a direct loss
of considerable energy as well as greater heating of the transformer
and consequent deterioration. If a transformer is to be used for
lighting purposes, or is lightly loaded, a large portion of the time,

POWER TRANSMISSION

a type should be selected which has a relatively low core loss so as
to increase the all-day efficiency. If fully loaded "all day, the
losses should be divided about equally between the copper and the
iron losses.

Transformer Connections. Transformers for three-phase
work may be connected in two ways. Where three transformers
are used, they may be connected in Y or star, that is, with one
terminal of each primary brought to a common point and the other

terminal connected to a line wire
(see Fig. 23), or they may be con-
nected in A or mesh when the three
primaries are connected in series and
the line wires are connected to the
three corners of the. triangle so
formed (see Fig. 24). The second-
aries may be connected in Y the
same as the primaries or the second-
aries may be connected in Y when
the primaries are in A, or vice versa.
The voltage relation may be best de-
termined from vector diagrams as
shown in Fig. 25, which gives the
voltage relation of step-down trans-
when the voltage across the primary

WvA^AAA^V~^\A/\AAAA^AAAT-*-\^\AWAAAA'
^WAVWWj N/VWWWVVM ^/VWVWWM

Fig. 24.

formers with a ratio of 10
lines is 1,000,

Changes may be made from two to three phases, or from three
to two phases, with or without a change of voltage, by means of
transformers having the required ratio of transformation by use of
what is known as the Scott connections. Fig. 26 shows such a
connection together with a corresponding vector diagram showing
the relations when the change is from two to three-phase with a
10 : 1 transformation of voltage. The main transformer is fitted
with a tap at the middle point of the secondary wiring to which
one terminal of the teaser transformer is connected. The teaser
has a ratio of transformation differing from that of the main trans-
former, as shown in the figure.

Six Phases are obtained from three phases for use with
rotary converters by means of transformers having two secondary

POWER TRANSMISSION

windings or by bringing both ends of each winding to opposite
points on the rotary-converter winding, utilizing the. converter
winding for giving the six phases. The latter, shown in fig. 27,
is known as a diametrical connection. When transformers with

1000

- 1000 -^t- 1000

'WVA/WW

VAVvVWWv|

100 -^-100
100

AAA^AAA*

100

578

1000

^-1000 -H

1000J-1000

+— 1000 -,
LOOO-^1000*

V^v/^A/^AA^^~^v^AA^AA^A^^AAAAAA^^A/ WV\MAAA/^-AAA/\AWWV~*~AA/WWWV

^VWNAAAA/|

100

1000

. 25.

two secondaries are used, the secondaries may be connected in six-
phase Y or six-phase A as shown in Figs. 28 and 29. When the
Y -connection is used, the common connection of each set of sec-
ondaries is made at the opposite ends of the coils. This leaves the
free ends directly opposite or 180° different in phase. The way in

POWER TRANSMISSION

which these ends are brought out to give six phases is best illus-
trated by means of the two triangles arranged as shown in Fig. 30,
which have their points numbered corresponding to the connec-

TEASER

'' §

MAIN

1000
Fig. 26.

100

tion in Fig. 28. In Fig. 29 one A is reversed with respect to the
other, and six phases are brought about in this manner.

Single transformers, constructed for three-phase and six-phase
work, are now being manufactured in this country, and they are

— wvwvw

|>/vWWW

-^AA/WVM

~ WWWA/1

K/WVWV

K/WWWV/

Fig. 27.

43 65 2

Fig. 28.

being used to an increasing extent. They are a little cheaper to
build for the same total output, and save floor space, but are not
so flexible as three single-phase transformers.

Where other conditions allow, a A to A-connection is prefer-
able, for with this connection, if one transformer is injured, it

PO\YER TRANSMISSION

may be taken out of circuit and the remaining two will maintain

«' t~>

the service, and may be loaded up to § of the former capacity of
the system. In the Y-connection, however, the voltage impressed

on the transformer winding is only = .58 times the volt-

age of the line, thus making it possible to construct a transformer
with a fewer number of turns. The windings must be insulated
from the case, however, for a potential equal to the line potential,
unless the neutral point be grounded when the potential strain to
which the transformer is liable to be subjected, under ordinary

conditions, is reduced to ~*~r~ of its value when the neutral is not

grounded. For small transformers
wound for high potential the cost is in
favor of the Y -connection.

k/wwv

K/VWVWj

kW>

/WW1

1 634-52

Fig. 29.

Choice of Frequency. The frequencies in extended use at
present in this country are 25, 40, and 00 cycles, 25 or <50 cycles
being met with more frequently than 40 cycles. Formerly, a fre-
quency of 125 or 133 cycles per second was quite often employed
for lighting purposes, but these are no longer considered standard.

The advantages of the higher frequency are:

1. Less first cost and smaller size of generators and transformers for
a given output.

2. Better adapted to the operation of arc or incandescent lamps.
Lamps, when run below 40 cycles, especially low candle-power incandes-
cent lamps at 110 volts or higher, are liable to be trying to the eyes on
account of the flicker.

50 POWER TRANSMISSION

Its disadvantages are:

1. Inductance and capacity effects are greater, hence a poorer regu-
lation of the voltage. The charging current is directly proportional to the
frequency arid this amounts to considerable in a long line.

2. There is greater difficulty in parallel operation of the high-fre-
quency machines due to the fact that the armature reactions of the older
types of high-frequency machines are .high.

3. Machines for high frequencies are not so readily constructed for
operation at slow speeds. This, however, will cease to be an objection
with the increasing use of the steam turbine.

4. Not well adapted to the operation of rotary converters and single-
phase series motors on account of added complications in construction and
increased commutator troubles.

A frequency of BO cycles is usually adopted if the power is to
be used for lighting only, and 25 cycles are better for railway work
alone. By the use of frequency changers the frequency of any sys-
tem may be readily changed to suit the requirements of the service.

OVERHEAD LINES.

Having considered the calculation of the electrical constants
of a transmission line and distributing system, we turn next to the
mechanical features of the installation of the conductors and find
two general methods of running the wires or cables.

In the first method the conductors are run overhead and sup-
ported by insulators attached to pins in cross-arms which, in turn,
are fastened to the supporting poles. In the other methods the
cables are placed underground and are supported and protected by
some form of conduit.

Overhead construction is used when the lines are run through
open country or in small towns. It forms a cheap method of pro-
viding satisfactory service and is reliable when carefully installed.
It has the advantage that the wires may be placed some distance
apart and, being air-insulated, the capacity of the line is much less
than that of underground conductors.

The old practice in overhead line construction has always been
to consider the design and erection of the line as work that anyone
could do, it being taken as the simplest part of the electrical
system. As a result, the line was a source of a great deal of trouble
which was laid to almost any other cause than poor construction.
The overhead line, when used, must be considered as a part of the

POWER TRANSMISSION 51

power plant and it should receive as careful attention as any part
of the central station or substation. It often has to meet much
more severe conditions than the power plant itself and it is respon-
sible to a very large extent for the reliability of service.

The new way of treating the question of overhead lines is to
consider them as structures which must be designed to meet cer-
tain strains just as a bridge or similar structure is designed. This
is especially true when steel or iron poles are used as is the case
in nearly all transmission lines abroad.

The design of an overhead line may be divided into five parts:

1. Location of line.

± Supports for the line, pole, and cross-arms.

Insulators and pins.

Stresses sustained by the pole line.

Conductors, material, size.

Some of these are purely mechanical features while others are
both mechanical and electrical. Let us take them up in the order
named.

Location of Line. The location of the line takes into account
the territory over which the line must be run with respect to
contour, direction, and freedom from obstructions as well as pos-
sible right of way. Width of streets, kind and height of buildings,
liability to interference with or from other systems must be con-
sidered, when such are present. The right of way for electric lines
may be secured, in some cases, along a railway or public road when
its location is comparatively simple, provided it is not necessary
to interfere with adjoining property. When adjoining property
must be interfered with, or when the line is to run over sections
containing no roads, it is usually possible to form contracts with
the property owner such as shall free the line from future inter-
ference by the property owner. In general, the cost of such con-
tracts will be comparatively low. Again, the right of way may
be purchased outright as is preferable when right of way is being
secured for high-speed electric railways. When the demands for
right of way are in excess of a reasonable amount, the process of
condemnation of property may be resorted to or the direction of
the line may be changed so as to avoid such locations. A prelimi-
nary survey of the line should be made at the time the route is

•V*

POWER TRANSMISSION

being located, such a survey consisting of the approximate location
of the poles, notes of the changes in direction and level of the
ground as well as of its character. This survey aids in the selec-
tion of. material to be delivered to the different parts of the line.
Changes in level are compensated for as much as possible by
selecting long poles for the low places and short poles for the
higher elevations, thus reducing the unbalanced strains in the line.
The heavier poles should be used where there is a
change in direction, where the line is especially ex-
-^Tf!*— posed to the wind or where branch lines are taken off.
It is sometimes necessary that power lines be run on
the same poles as telephone wires, in which case the
power conductors should, preferably, be located above
the telephone wires.

Supports, Poles. In this country, the support
for ferial lines consists almost universally of wooden
poles to which the cross-arms, bearing the insulator
pins, are attached. These poles may be either natural
grown or sawn. Abroad, the use of metal poles pre-
vails. In order to determine the proper cross-section
of a pole it may be regarded as a beam fixed at one
end and loaded at the other, this load consisting of the
weight of the wire, with attendant snow or sleet, which
tends to produce compression in the pole, and the
tension of the wires together with the effect of wind
pressure, which tends to produce flexure. Only the
Fig. 31. latter stresses need be considered in selecting a pole
for ordinary transmission lines. The poles are in the
shape of a truncated cone or pyramid, the equation of which is:

d{ and
spectively.

y ~- diameter of any section.

x == distance from the top of the pole.

I — length of pole.

72 = diameter of the pole at the top and bottom re-

POWER TRANSMISSION 53

The proper taper for a pole should be such that d, = J of </,.
If d.} > | dt the pole is heavier than need be as it would tend to
break below the ground. If less than | <:/,, the pole will tend
to break above the ground and the material is not distributed to
the best advantage.

In calculating the size of pole necessary to stand a certain
stress, we have, from the principles of Mechanics,

M — moment of resistance.
I = moment of inertia.

S — stress in the section at </2 at which point the pole is
least able to withstand the strain which comes on it.

M = P/ where P is the tension in the wires and / = length

of pole in inches.

For a round pole, I = -

()4r

S1JY/8.

and we have

Solving for 8, S — ^ /3

For a sawn pole with square cross-sections the value of I is:

Sd\ 6 PI

and PI •= -^ or b = —^~

The value for S should not exceed a certain proportion of the
ultimate strength of the material. If T represents the ultimate

strength in pounds per square inch, then P = — where n is known

as the factor of safety and is ordinarily not taken less than 10 for
wooden structures. A high factor of safety is necessary on account

54 POWER TRANSMISSION

of the material not being uniform, and the uncertainty of the
value of T.

Following are commonly accepted values of T:

Yellow pine: 5,000 - 12,000 pounds

Chestnut 7,000-18,000 '<

Cedar 11,500

Redwood 11,000

The value of — should not be over about 800 for natural poles
u>

and GOO for sawn poles.

d., is measured at the ground line of the pole, not at the base.

Consider a pole of circular cross-section having a length of
35 feet and a diameter at the ground line of 12 inches. Using

- 000, what is the maximum allowable stress that should be

applied at the end of the pole ?
327V

7Td\

P = 600

I = =35 >[ 12 ^ 420 inches.
d2 = 12

32 X 000 X 420
S - 3.1410 X 1728 = i'480 lbs-

It is customary to select a general type of pole for the whole
line determined from calculations based on the above formulae,
after the tension in the wire has been found, and not to apply
such calculations to every section of the line. The line is then
reinforced, where necessary, by means of guy wires or struts.

Following are some of the general requirements for poles:

Spacing should not exceed 40 to 45 yards.

Poles should be set at least five feet in the ground with an addi-
tional six inches for every five feet increase in length over thirty-five feet.
Special care in setting is necessary when, the ground is soft. End and
corner poles should be braced and at least every tenth pole along the line
should be guyed with % or %-inch stranded galvanized iron wire.

Regular inspection of poles, at least yearly, should be main-
tained and defective poles replaced. The condition of poles is best
determined by examination at the base.

POWER TRANSMISSION 55

Poles should preferably be of good, sound chestnut, cedar, or
redwood. Other kinds of wood are sometimes used, the material
depending largely on the section of the country in which the line
is to be erected and the timber available. Natural poles should be
shaved, roofed, gained, and given one coat of paint before erecting.

Special methods of preserving poles have been introduced,
chief among which may be considered the process of creosoting.
Creosoting consists of treating the poles with live steam at a tem-
perature of 225 to 250°, so as to thoroughly heat the timber, after
which a vacuum is formed and then the containing cylinder is
pumped full of the preserving material, a pressure of about 100
pounds per square inch being used to force the desired amount of
material into the wood. The butts of poles are often treated with
pitch or tar, but this should only be applied after the pole is
thoroughly dry.

Guying of pole lines is one of the most important features of
construction. Guys consist of three or more strands of wTire,
twisted together, fastened at or near the top of the pole, and car-
ried to the ground in a direction opposite to that of the resulting
strain on the pole line. The lower end is attached to some form
of guy stub or guy anchor. This may be a tree, a neighboring
pole, a short length of pole set in the ground, or a patent guy
anchor. Guy stubs are set in the ground at an inclination such
that the guy makes an angle of 90° with the stub or with the axis
of the stub in the direction of guy, the stub in the latter case being
held in place by timber or plate fastened at right angles to the
bottom of the stub. Such a timber is known as a " dead man ".

The angle the guy wire makes with the pole should be at least
20°. When there is not room to carry the guy far enough away
from the base of the pole to bring this angle to 20° or more, a
strut may be used. This consists of a pole slightly shorter and
lighter than the one to be reinforced. It is framed into the line
pole near the top and set in the ground at a short distance from
the base of the pole on the opposite side of the pole from that on
which a guy would be fastened.

Stranded galvanized steel guy wire is used for guys. There
are two general methods of attaching the guys to the top of the
pole. In the one, a single guy is run, attached at or near the

POWER TRANSMISSION

middle cross-arm, while in the other, known as " Y" guying, two
wires are run to the top of the pole, one at the upper the other at
the lower arm, and these united into a single line a short distance
from the pole.

Head guying, guying-in the direction of the line, is used when
the line is changing level and for end poles. The guys are attached

Fig. 3i>.

near the top of one pole and run to the bottom of the pole just
above. Fig. 32 shows several methods of reinforcing pole lines.
Special methods are adapted as necessary.

Cross-Arms. The best cross-arms are made of southern yellow
pine. Oak is also used to a large extent. They should -be of
selected well-seasoned stock. The iisual method of treatment is to
paint them with white lead and oil. The size of cross-arms and
spacing of pins have not been thoroughly standardized. For cir-

POWER TRANSMISSION

cuits up to 5,000 volts, 3^ X ±^ or 3| X 4J;" cross-arms with
spacing between pins of 16 inches, the pole pins being spaced 22
inches, are recommended. For higher voltages, special cross-arms
and spaciijgs are necessary. The cross-arms should be spaced at
least 2-4 inches between centers, the top arm being placed 12 inches
below the top of the pole. They
are usually attached to the pole by
means of two bolts and are braced
by galvanized iron braces not less
than 11 X f\ inch and about 2<S

inches long-.

Cross-arms are placed on al-
ternate sides of the poles so as to
prevent several of them from being
pulled off should one become
broken or detached. On corners
or curves double arms are use'd
In European practice, the cross-arm
is done away with to a large extent,

the wire beino1 mounted on inSUla-
^D

tors attached to iron brackets
mounted one above the other. Fig.
33 gives- an idea of this con-
struction.

Insulators. Electrical leak-
age between wires must be pre-
vented in some way and various
forms of insulators are depended
upon for this purpose. The ma-
terial used in the construction of
these insulators should possess the
following properties: high specific
resistance; surface not readily de-
stroyed and one on which moisture

Fig. 33.

does not readily collect; mechanical strength to resist both strain
and vibrating shocks. Its design must be such that the wire can
be readily fastened to it and the tension of the wire will be trans-
mitted to the pin without producing a strong strain in the insu-

POWER TRANSMISSION

HEIGHT 3|"TESTED AT 50,000V HEIGHT 3" TESTED AT 30,000V.

HEIGHT 4^ TESTED AT 70,000V. HEIGHT 7\ TESTED AT 80,000V.

HEIGHT 4| TESTED AT 5QOOOV. HEIGHT 4$ TESTED AT 50,000V.

Ti r _, w

HEIGHT 3i TESTED AT 40,000V. HEIGHT 4^ TESTED AT 40,000 V.

Fig. 34.

POWER TRANSMISSION

f Diet.

Cut Eccentric in
Bolt Cutter

Composite Pin

for
Hiqh Tension Insulator

lator. Leakage surface must be ample for the voltage of the line
and so constructed that a large portion of it will be protected from
moisture during rainstorms. The principal materials used are
glass and porcelain.

Porcelain has the advantage over glass that it is less brittle
and generally stronger and that it is less hygroscopic, that is, mois-
ture does not so readily collect on and adhere to its surface. Glass
is less conspicuous and is
cheaper for the smaller in-
sulators. Both materials
are freely used for the con-
struction of high-tension
lines, while the use of glass
prevails for the low-tension
circuits.

All line insulators are
of the petticoat type and
are made up in various
shapes and sizes. The
larger size porcelain insu-
lators are made up in two
or more pieces which are
fastened together by means
of a paste formed of lith-
arge and glycerine. The
advantages of this form of
construction are greater
uniformity of structure,
and each part may be tested separately. 1< "ig. 34 shows several
forms of insulators now in use with the voltage at which they
are tested. The test applied to an insulator for high-tension lines
should be at least double the voltage of the line, and some engineers
recommend three times the normal voltage.

Pins. Pins made of locust wood boiled in linseed oil are pre-
ferred for voltages up to 5,000. Above this special pins are used.
Wood pins are often objected to on account of the burning or
charring which takes place in certain localities, and iron pins are
being used to a large extent. Fig. 35 shows the dimensions of such

60 POWER TRANSMISSION

a pin used on a (30, 000- volt line. The insulator is fastened to the
pin by means of a thread in a lead lug which is cast on top of the
pin. The insulators in the construction shown in Fig. 33 are
cemented to. the iron brackets.

The Stresses sustained by the line may be classified as
follows :

1. Weight of wire, which includes insulation, and snow and sleet
which may be supported by the wire.*

2. Wind pressure upon the parts of the line.

The strain produced by the weight of the \vire on the pole
itself need not be considered except in exceptional cases, because
if the pole is sufficiently strong to withstand the bending strains,
it is more than strong enough to withstand the compression due
to the weight of the wires.

8. Tension in the wire itself.

Langley shows the pressure of the wind normal to Hat sur-
faces to be equal to:

, = .0030 * = -.

j> = pressure in pounds per sq. ft.
v -- velocity in miles per hour.

For cylindrical surfaces the amount of pressure is § that ex-
erted on a flat surface of a width equal to the diameter of the
cylinder. Without great error we may assume that* the maximum
wind pressure, and that for which calculation is necessary, is that
at right-angles to the line, and a value of thirty pounds per square
foot is sufficient allowance for exposed places, while twenty pounds
]>er square foot is considered sufficient where the line is par-
tially sheltered.

Example. What is the pressure, due to the wind, on the
wires of a pole line containing three number 0000 wires, the poles
being spaced 45 yards and the velocity of the wind such that the
pressure may be taken as 30 pounds per square foot.

The diameter of a number 0000 wire is .400 inch. The area
against which the wind exerts its force may be considered as:

'2 3 X 45 X 3 X 1'2 X .400
-77-) ~iTT~ ~ °-l()<) square feet.

POWER TRANSMISSION 61

5.100 )( 30 = 155 pounds pressure due to wind on wires.

The most important strain-producing factor in a line is that
due to the tension in the wire itself. A wire suspended so as to
hang freely between two supports assumes the form of curve known
as a catenary, but for ordinary work the curve may be taken as a
parabola the equation of which is simple and from which the fol-
lowing equations are derived :

"=i

~8D~

L = n + S

When I) — deflection or sag at lowrest point in feet.

L := actual length of wire between supports in feet.

II : = distance between supports in feet.

W — weight of wire in pounds per foot.

Pc — horizontal tension in the wire at the middle point.

Pc = - where T = tensile strength of the wire and n -

factor of safety, n = 2 to 0 under the conditions existing when
the wire is erected. The temperature changes in the wire affect
the" value of this factor, it being greatest when the temperature is
a maximum, and a minimum when the temperature is lowest, and
calculation should be for the maximum strain that may come on
the wires.

If Lt = length of a wire at a given temperature, t" (1.
and L^ == length of a wire at a given temperature, 20 J C.
Then, Lt ;= L,0 [1 + k (t - 20)].

k == .000012 for iron.

.0000108 to .0000114 for aluminum.
.0000172 for copper.

The following table gives the deflection of spans of wire in
inches for different temperatures and different distances between
poles, a maximum stress of 30,000 pounds per square inch being
allowed at - 10° F, which gives a factor of safety of 2 for hard-
drawn copper wire.

POWER TRANSMISSION

TABLE VII.
Temperature Effects in Spans.

Spans

in
Feet.

TEMPERATURE IN DKGKKKS KAHKKNHK1T.

-10 30 '' 40 - o()

70"

80 •' 90°

Deflection in. Im-hes.

1.2

1.6

100

1.9

2.3

120

2.8

140

3.7

.33

160

4.9

180

6.2

200

7.7

The above formulae apply directly to lines in which the poles
are the same distance apart and on the same level, and any number
of spans may be adjusted at one time by applying the calculated
stress at the end of the wire and the line will be in equilibrium;
that is, there will be no strain on the poles in the direction of the
wires. Special care must be taken to preserve this equilibrium when
the length of span changes or when the level of the pole tops varies,
and this is accomplished by keeping Pc and ti constant for every. span.

What is the tension in pounds per square inch at. the center
of a span of number 0000 wire when the poles are 120 feet apart
and the sa is 16 inches ?

^TT

II : = 120
I) :

"W = .(>4 pounds.

(120)2 X .64

P, =

8 X

= 864 pounds

The cross-section of number 0000 wire is,—
77" X (.23)2 == .1662 square inches.
864 -T- .1662 == 5200 pounds per square iach.

POWER TRANSMISSION

The regulation of the system and the amount of power lost in
transmission together determine the cross-section of the conductors
to be used. The amount of power lost, for most economical opera-
tion can be determined from the cost of generating power and the
fixed charges on the line investment. Either copper or aluminum
wire or cables may be used. The latter is lighter in weight but
more care must be taken in erecting and it is more difficult to
make joints.

UNDERGROUND CONSTRUCTION.

In large cities or other localities where, if overhead construc-
tion be used, the number of conductors becomes so great as to be
objectionable, not alone on account of appearance but also on
account of complication and danger, the lines are run underground.
The expense of installing underground systems is very great com-
pared with that of overhead construction, but the cost of mainten-
ance is much less and the liability to interruption of service, due
to line troubles, greatly reduced. The essential elements of an
underground system are the conductor, the insulator, and the pro-
tection. The conductor is invariably of copper, the insulator may
be rubber, paper, some insulating compound, or individual insu-
lators, depending on the system, while the protection takes one of
several forms. The system, as a whole, may be divided into

, Bolid or built-in systems.

Trench systems.
Drawing-iii systems.

As an example of the first, we have the Eflixon, Tnbe xyxttin*
which is especially adapted to house-to-house distribution and is
used to a large extent for direct-current three-wire distribution in
congested districts. It is made up of copper rods as conductors
(three of equal size for mains and the neutral but \ the size of the
main conductors in feeders), which are insulated from each other
by an asphaltum compound. This compound also serves as an
insulation from the protecting case, which consists of wrought-
iron pipe. Pilot wires are also often installed in the feeder tubes.
This tube is built up in sections about twenty feet long. In insu-
lating the conductors, they are first, loosely wrapped with jute
rope so as to keep them from making contact with each other,

POWER TRANSMISSION

Fig. 36.

POWER TRANSMISSION r,r,

and with the pipes, and the heated asphaltum forced into the tube
from the bottom, when the tube is in a vertical position. Tlie
ends of the conductors and the tubes must be joined and properly
insulated in a completed system. Special connectors are furnished
for the conductors, and cast-iron coupling boxes are fitted to the
ends' of the tube as shown in Fig. 30. After the conductors are
properly connected, the cap is put on this coupling box and the
inside space then filled with insulating compound through a hole
in the cap. This hole is later fitted with a plug to render the box
air-tight. The system is a cheap one, though the joints are expen-
sive. It is not adapted to high potentials.

The Siemens-IIdlske system of iron -taped cables consists of
insulated cables encased in lead to keep out moisture, this lead
sheathing being in turn wrapped with jute which forms a bedding
for the iron tape. The iron tape is further protected by a wrap-
ping thoroughly saturated with asphaltum compound. These
cables may be made up in lengths of from 500 to 000 feet.

In unexposed places, such as across private lands, the steel
taping may be omitted and the lead sheathing simply protected by
a braid or wrapping saturated with asphaltum.

The Trench system consists of bare or insulated conductors
supported on special forms of insulators as in overhead construc-
tion, the whole being installed in small closed trenches. As this
system is not used to any extent in America, but one system, the
Crompton system, will be described.

In the Crompton system, bare copper strips are used, each 1
to li inches wide and | to ^ inch thick. These strips rest in
notches on the top of porcelain or glass insulators, supported by
oak timbers embedded in the sides of the cement-lined trench.
This trench is covered with a layer of flagstone. These insulators
are spaced about 50 feet and about every 800 feet a straining
device is installed for takinor up the sag in the conductors. Hand-

01 O

holes are located over each insulator.

There are several of the drawing -in systems, and certain of
these have come to be considered standard underground construc-
tion in the United States. It is no longer deemed advisable to
construct ducts which will serve as insulators, but they are de-

POWER TRANSMISSION

pended on for mechanical protection only, and should fulfill the
following requirements:

They must have a smooth interior, free from projections, so that the
cables may be readily drawn in and out.

They must be reasonably water-tight.

They must be strong enough to resist injury due to street traffic and
accidental interference from workmen.

Among the materials used for duct construction may be men-
tioned: iron or steel, wood, cement, and terra cotta. Wood is
used in the form of a trough or box, or in the form of wooden

TO STREET SURFACE

A MINIMUM-OF 3'
PLANKS

"-KVI

-2'APPROX-
Fig. 37.

pipes. The latter is known as "pump log" conduit. The wood
used for this purpose must be very carefully seasoned and then
treated with some antiseptic compound, such as creosote, in order
for the duct to give satisfactory service. If improperly treated,
acetic acid is formed during the decay of the wood, and this attacks
the lead covering of the cable, destroying it and allowing moisture
to deteriorate the insulation. Wood offers very little resistance to
the drawing in of the cables, and it is a cheap form of conduit,
though it cannot be depended on for long life.

One of the best and at the same time most expensive systems
is the one using wrought-iron pipes, laid in a bed of concrete.
The ordinary construction of the duct consists of digging a trench

POWER TRANSMISSION 07

of the desired size and covering the bottom, after it is carefully
graded, with a layer of good concrete from two to four inches thick.
Such a cement may consist of Rosendale cement, sand, and broken
stone in the ratio of 2, 3, 5, the broken stone to pass through a
sieve of H-inch mesh. The sides of the trench are lined with 1A-
inch planks. The first layer of pipes consisting of wrought-iron
pipes 3 to 4 inches in diameter, 20 feet long, and £ inch thick,
joined by means of water-tight .couplings, is laid on this concrete,
and the space around and above them filled with concrete. A sec-
ond layer of pipes is laid over this, and so on. A covering of con-
crete 2 to 3 inches thick is placed over the last layer, and a layer
of 2-inch plank is placed over all, to protect against injury by
workmen. Fig. 37 shows a cross-section of such duct construc-
tion. The pipe should be reamed so as to remove any internal
burs which might injure the insulation during the process of
drawing in.

A modification of this system consists of the use of cenient-
liiH'd wroucjht-irou pipes. This usually consists of eight-foot
lengths made of riveted sheet-iron, pipes. Rosendale cement is
used for the lining, this lining being -about | inch thick. .The
external diameter of the pipe is about 4| inches. The outside of
the pipe is coated with tar to prevent rusting. The sections have
a very smooth interior and are light enough to be easily handled.
They are embedded in concrete, similar to the system previously
described. Connections between the sections are made by means
of joints, constructed on the ball-and-socket principle, moulded in
the cement at the ends of the sections. This forms a cheaper con-
struction than the use of full -weight pipe.

Earthenware Conduits. This form of conduit is being ex-
tensively used for underground cables. The sections may be of
the single-duct or multiple-duct type. The former consists of an
earthenware pipe from 18 to 24 inches in length. The internal
diameter is from 2^ to 3 inches. These are laid on a bed of con-
crete, the separate tiles being laid up in concrete in such a manner
as to break joints between the various ducts. In .the multiple-
duct system the joints are wrapped with burlap and the whole
embedded in concrete. This form of conduit has a smooth inte-
rior and the cables are readily drawrn in and out. The single-duct

POWER TRANSMISSION

type lends itself admirably to slight changes of direction that
may be necessary. Fig. 38 shows both forms of duct, while Fig.
39 shows a cement-lined iron -pipe duct system, laid in concrete,
in course of construction.

Other forms of conduits are ducts formed in concrete, earthen-
ware troughs, cast-iron troughs, and libre tubes.

Manholes. For all drawing-in systems, it is necessary to
provide some means of making connections between the several
lengths of cable after they are drawn in, as well as for attaching
feeders. Since the cables cannot be handled in lengths greater

Fig. 38.

than about 500 feet, and less than this in many cases, vaults or
junction boxes must be placed at frequent intervals. Such vaults
are known as splicing vaults or manholes. The size of the man-
hole depends upon the number of ducts in the system, as well as
on the depth of the conduit. If the ducts be laid but a short dis-
tance from the surface of the street and traffic is light, the cables
may be readily spliced with a manhole but 4 feet square and 4
feet deep. The smaller vaults are often called " hand-holes ".
Deeper vaults are from 5 to 6 feet square, and the floor should be
at least 18 inches below the lowest ducts on account of convenience
to the workmen and to serve as collecting basins for water which
gets into the system. The ducts should always be laid with a
gentle slope toward such manholes.

POWER TRANSMISSION 09

Common construction consists of a brick wall laid upon a con-
crete floor, the brick being laid in cement and being coated inter-
nally with cement. The cables follow the sides of the manhole
and they are supported on hooks set in the brickwork. This
causes quite a waste of cable in large manholes. Care should be
taken that workmen (Jo not use the cables, so supported, as ladders

Fig. 39.

in entering and leaving the manhole, as the lead sheathing maybe
readily injured when the cables are so used.

Conductors are drawn into place by the aid of some form of
windlass. Special jointed rods, 3 to 4 feet long, may be used for
making the first connection between manholes or a steel wire or
tape may be pushed through. A rope is drawn into the duct and
the cable is attached to this rope. Fig. 40 shows one way in which
the cable may be attached to the rope. Care must be taken to see
that no sharp bends are made in the cable during this process.
Cable should not be drawn in during extremely cold weather un-
less some means are employed for keeping it warm, owing to the
liability of the insulation to be injured by cracking.

POWER TRANSMISSION

Conduit systems must be ventilated in order to prevent ex-
plosion due to the collecting of explosive mixtures of gas. Many
special ventilating schemes' have been tried, but the majority of
systems depend for their ventilation on holes in the manhole cov-
ers. This prevents excessive amounts of gas from collecting but
does not always free the system from gas so completely as to make
it safe for workmen to enter the splicing vault until the impure
air has been pumped out.

The above applies to the main conduit system. Auxiliary
ducts are laid over the main ducts and distribution accomplished
from hand -holes in this system.

It is customary to ground the lead sheaths of the cables at
frequent intervals, thus in no way depending on the ducts even
when made of insulating material, for insulation.

IRON WIRE

ROPE

SHACKLE:

Fig. 40.

YARN SERVING

Cables. Well insulated copper cables are used for under-
ground systems. On account of the fact that various materials,
such as acids and oils which are injurious to the insulation, come
in contact with the cable, it is necessary that it be protected in
some manner. A lead sheath is employed for this purpose. This
sheath is made continuous for the whole length of the conductor,
and with its use it is possible to employ insulating materials such
as paper which, on account of being readily saturated by moisture,
could not be used at all without such a hermetically sealed sheath.
Lead containing a small percentage of tin is usually employed for
this purpose. The sheath may consist of a lead pipe into which
the cable is drawn, after which the whole is drawn through suitable
dies, bringing the lead in close contact with the insulation or the
casing may be formed by means of a hydraulic press.

Yarns thoroughly dried and then saturated with such materials
as paraffin, asphaltum, rosin, etc., paper, both dry and saturated,

POWER TRANSMISSION

anil rubber are the materials more generally employed for insula-
tion. When paper is employed, it is wound on in strips, the cable
being passed through a die after each layer is applied, after which
it is dried at a temperature of 200° F to expel moisture. After
being immersed in a bath of the saturating compound it is taken
to the hydraulic presses where the lead sheath is put on.

When rubber insulation is used, the conductors are tinned to
prevent the action of any uncqmbined sulphur which may be
present in the vulcanized rubber. The Hooper process consists of

usincr a layer of pure rubber next to the conductors and usim** the

o J i r>

vulcanized rubber outside of this. One or two layers of pure rub-
ber tape are put on spirally,
the spiral being reversed for
each layer. Rubber com-
pound in two or more layers
is applied over this in the
form of two strips which pass
between rollers which fold
these strips around the core
and press the edges together.

INSULATION

(. STRANDED CONDUCTOR

Fig. 41.

Prepared rubber tape is ap-
plied over this, after which
the insulator is vulcanized
and the cable tested. If sat-
isfactory the external protection is applied.

Cable for polyphase work is made up of three conductors in
one sheath. Fig. 41 shows a cross-section of cable manufactured
for three-phase transmission at 6,600 volts. The conductors of
this cable have a cross-section equivalent to a number 0000 wire,
to which an insulation of rubber --^-inch thick is applied. These
three conductors are twisted together with a lay of about 20
inches. Jute is used as a tiller, and a second layer of rubber insu-
lation gV-inch thick is then applied. The lead sheath employed is
J-inch thick, and is alloyed with 3% of tin.

Joints in cables must be carefully made. Well- trained men
only should be employed. The insulation applied to the joint
should be equivalent to the insulation of the cable at other points,
and the joint as a whole must be protected by a lead sheath made

POWER TRANSMISSION

continuous with the main covering by means of plumbers' joints.

Some engineers prefer rubber, some paper insulation, but
both types are giving good service, and are used up to voltages of
22,000. It is customary to subject each cable to twice its normal
potential soon after it is installed. This voltage should not be
applied or removed too suddenly as unnecessary strains might be
produced in this manner.

Rubber-insulated cables should never be allowed to reach a
temperature exceeding 65° to 70° C (149° to 158° F). Paper
will stand a temperature of 90° C (194° F), but it is neither desirable
nor economical to allow such a temperature to be reached. The
following table is of interest in connection with underground
cables. The dimensions here given are only general.

TABLE VIII.
Typical Cable Construction.

Cables.

No. of Conductors.

Character
of
Conductor

Sizes
of
Individual
Wires.

Electric light less than 500 volts. .
Arc lighting

Single
Single

Stranded
Solid

No. 10 B.&S.
or smaller.
No. 6 or 4

High-tension power transmission .

Single, concentric,
duplex, or three
conductors

Stranded

B.&S.
No. 10 B.&S.
or smaller.

Thickness of Insulation.

Rubber.

Saturated
Fiber.

Saturated
Paper.

Dry

Paper.

Thickness
of Lead.

Electric light less than 500
volts

Inch.
A

Inch,
i

Inch.
JU

Inch.

Tff t0 TO

Arc lighting

A- to A-

High-tension power trans-
, mission

-A to A

H
Tl¥

H
31

»¥

Selection of Voltage to be Used. The voltage to be selected
for a given system depends on the distance the power is to be
transmitted as well as its amount, and on the use to be made of
the power. If a lighting load is concentrated in a small district,
a '2'20- volt three-wire system will give very good service. If the

POWEK TRANSMISSION 73

region is a little more extended, possibly a 44:0 -volt three-wire
system using 220-volt lamps would serve the purpose without an
excessive loss of power or a prohibitive outlay for copper. For
location when the service is scattered, a distribution at from 2,200
to 4,000 volts alternating current is used, transformers being
located as required for stepping down the voltage for the units
which may be fed from a two- or three- wire secondary system.

2,300 volts (alternating) is a standard voltage for lighting
purposes and for polyphase systems; 2,300 volts is often taken as
the voltage between the outside wires and the neutral wire of a
four-wire three-phase distribution.

For railway work, 550 to 600 volts direct current is used up
to distances of about 5 or 6 miles, beyond which it becomes more
economical to install an alternating-current main station and sup-
ply the line at intervals from substations to which the power is
transmitted at voltages of from 6,600 to 30,000 or even higher,
depending on the distance it is to be transmitted. At present,
the highest voltage used in long-distance transmission is 60,000,
though higher values are contemplated. Such voltages are used
only on very long lines, and each one becomes a special problem.
It is always well to select a voltage for apparatus which may be
considered as standard by manufacturing companies, as standard
apparatus may always be purchased more cheaply and furnished
in shorter time than special machinery.

Protection of Circuits. Lightning arresters are installed at
intervals along overhead lines for the protection of connected
apparatus. For ordinary lighting circuits, such arresters are in-
stalled for the protection of transformers, and are located preferably
on the first pole away from the one on which the transformer is
installed. Care should be taken to see that there are no sharp
bends or turns in the ground wire and that there is a good ground
connection. For the high-tension lines, lightning arresters at
either end of the circuit are relied on to afford the greater part of
the protection. In some localities, a wire strung on the same pole
line at a short distance from the power wires and grounded at very
frequent intervals has been found to reduce troubles due to lightning.

The grounding of the neutral of three-wire secondary systems
forms a means of protection of such circuits against high potentials

74 POWER TRANSMISSION

which might arise from accidental contact with the primaries, and
is recommended in some cases. The grounding of the neutral of
high-tension systems reduces the potential between the lines and
the ground, but a single ground will cause a short-circuit on the
line with any grounded system. Grounding, through a resistance
which will limit the flow of current in such a short-circuit, has
been recommended and is employed in some instances. Spark
arresters are installed at the ends of high-tension underground
systems to prevent high voltages which might injure the insulation
in case of sudden changes in load, grounds, and short-circuits.

INDEX

Part I — POWEH STATIONS; Part //— POWKK TRANSMISSION

Part Page

All-day efficiency II, -44

Alternating-current line calculation II, 29

examples of II, 39

Alternating-current systems of distribution II, 21

Annunciator wire II, 9

Boiler efficiencies, table I, 13

Boiler foundations I, 22

Boilers I, 1()

Cornish I, 11

economic I, 12

Lancashire I, 11

marine I, 11

multitubular I, 11

water-tube I, 11

Boilers, firing of '. I, 23

Cable, standard, table I, 47

Cable construction, table II, 72

Cables II, 70

Capacity of conductors for carrying current II, 7

Capacity ratios, table I, 61

Central station I, 3

Charging for power, methods of I, 75

Circuits, protection of II, 73

Conductors II, 3

capacity of for carrying current. II, 7

for various conditions, table. . II, 7

Copper losses : II, 44

Copper wire table II, 4

Cornish boilers I, 11

Cross-arms II, 56

Curtis turbine , : . . . . I, 27

Direct-current feeder panels I, 50

Distribution systems II, 11

multiple-series

parallel

series II, H

series-multiple II, 17

II INDEX

Part Page
Draft

mechanical I, 23

natural , . . I, 23

Earthenware conduits II, 67

Economic boiler I, 12

Efficiency of transformer II, 44

Electric distribution of power II, 3

Electrical plant I, 36

Engines, gas , I, 34

Exciter panels I, 50

Exciters I, 39

Feed water I, 20

Feeding appliances I, 20

Feeding point II, 15

Firing of boilers. I, 23

Formula, general wiring II, 30

Frequency, choice of II, 49

Fuel, handling of. I, 23

Full load ratios, table I, 61

Galloway boiler I, 11

Gas engines. I, 34

Generating station, location of.. I, 4

Generator efficiencies, table. . I, 38

Generators " I, 36

Governors I, 34

Gutta percha.. II, 10

Handling of fuel I, 23

Hydraulic plants I, 29

Increase in boiler efficiency, table I, 20

India rubber it, 10

Inductance II, 27

per mile of circuit, table II, 26

Insulation • II, 8

Insulators II, 57

Iron or core losses.... II, 44

Lancashire boilers , I, 11

Location of generating station. I, 4

Loss of power in steam pipes I, 19

Loss in pressure in steam pipes, formula for I, 18

Manholes II, 68

Marine boilers • • • • I, 11

Matthiessen's standard • • • • • II, 6

Mechanical draft I, 23

Mechanical strength of different materials... II, 6

Multiple-series system of distribution II, 17

Multiple wire system II, 18

parallel.... II, 21

polyphase II, 22

INDEX 111

Part Page
Multiple wire system

series n , 21

three-wire 1 1 , i #

Multitubular boiler I, n

Mutual inductance H, 28

Natural draft I, 23

Oil-cooled transformer? I, 41

Oil switches I, 52

Overhead lines II, 50

cross-arms II, 56

insulators : II. 57

location of II, 51

pins II, 59

stresses sustained by II, 60

supports for.. II, 52

Panels

direct-current I, 50

exciter I, 50

total output I, 51

Parallel systems of distribution II, 13, 21

voltage regulation of II, 20

Power factor.... II, 33

Power station buildings.. I, 63

Pressure of water, table I, 31

Plant, size of I, 8

Pump log conduit II, 66

Regulation of a transformer II, 45

Resistance, effects of II, 7

Resistance of electrical conductors II, 4

Riveted hydraulic pipe, table I, 32

Safety devices I, 57

Selection of system I, 6

Series system of distribution •. II, 11

Series-multiple system of distribution. '. II, 17

Size of plant I, 8

Station arrangement I, 68

Station records I, 70

Steam engines I, 25

Steam piping I, 13

arrangement I, 14

material for I, 10

Steam plant I, 10

Steam turbines I, 25

Storage batteries I, 44

Stresses sustained by pole line • • • • II, 60

Substations. . . '. I, 59

Superheated steam • • • I, 19

Switchboards I, 44

II INDEX

Part Page
Draft

mechanical I, 23

natural I, 23

Earthenware conduits II, 67

Economic boiler I, 12

Efficiency of transformer.. II, 44

Electric distribution of power II, 3

Electrical plant I, 36

Engines, gas , . I, 34

Exciter panels I, 50

Exciters I, 39

Feed water I, 20

Feeding appliances I, 20

Feeding point II, 15

Firing of boilers I, 23

Formula, general wiring II, 30

Frequency, choice of II, 49

Fuel, handling of I, 23

Full load ratios, table I, 61

Galloway boiler I, 11

Gas engines . I, 34

Generating station, location of.. I, 4

Generator efficiencies, table I, 38

Generators I, 36

Governors I, 34

Gutta percha II, 10

Handling of fuel I, 23

Hydraulic plants I, 29

Increase in boiler efficiency, table I, 20

India rubber it, 10

Inductance II, 27

per mile of circuit, table II, 26

Insulation. •• II, 8

Insulators II, 57

Iron or core losses.... II, 44

Lancashire boilers I, 11

Location of generating station. I, 4

Loss of power in steam pipes I, 19

Loss in pressure in steam pipes, formula for I, 18

Manholes • II, 68

Marine boilers • • • • I, 11

Matthiessen's standard • • • • II, 6

Mechanical draft I, 23

Mechanical strength of different materials... II, 6

Multiple-series system of distribution II, 17

Multiple wire system II, 18

parallel.... II, 21

polyphase II, 22

INDKX 111

Part I'iitfe

Multiple wire system

series n, 21

three-wire II, is

Multitubular boiler I? n

Mutual inductance. II, 28

Xatural draft I, 23

Oil-cooled transformers I, 41

Oil switches I, 52

Overhead lines II, 50

cross-arms II, 50

insulators .' II. 57

location of II, 51

pins II, 59

stresses sustained by II, 60

supports for.. II, 52

Panels

direct-current I, 50

exciter I, 50

total output I, 51

Parallel systems of distribution II, 13, 21

voltage regulation of II, 20

Power factor II, 33

Power station buildings.. I, 63

Pressure of water, table I, 31

Plant, size of I, 8

Pump log conduit II, 66

Regulation of a transformer II, 45

Resistance, effects of II, 7

Resistance of electrical conductors II, 4

Riveted hydraulic pipe, table. I, 32

Safety devices I, 57

Selection of system I, 6

Series system of distribution •. II, 11

Series-multiple system of distribution '. II, 17

Size of plant . I, 8

Station arrangement. I, 68

Station records I, 70

Steam engines I, 25

Steam piping I, 13

arrangement. I, 14

material for I, 16

Steam plant I, 10

Steam turbines I, 25

Storage batteries I, 44

Stresses sustained by pole line • • • • II, 60

Substations. . . '. I, 59

Superheated steam I, 19

Switchboards I, 44

IV INDEX

Part Page

System, selection of I, 6

Tables

boiler efficiencies I, 13

boiler efficiency, increase in I, 20

boilers, floor space for , I, 12

cable, standard I, 47

cable construction II, 72

capacity in Micro-Farads per mi. of circuit for three phase

system II, 25

capacity ratios I, 61

conductors for various conditions II, 7

conductors for various positions.... II, 8

copper wire II, 4

exciters for single-phase A. C. generators I, 39

full load ratios I, 61

generator efficiencies. I, 38

horse-power per cu. ft. of water per m in. for different heads.. . . I, 34

inductance per mile of circuit. II, 26

permissible overload 33 per cent I, 9

rate of flow of water, in ft. per min., per pipes of various sizes. .1, 22

resistances of pure aluminum wire II, 5

riveted hydraulic pipe I, 32

temperature effects in spans II, 62

transmission line calculation II, 31

water, pressure of I, 31

wire, standard I, 47

Temperature coefficient.. II, 6

Three-wire system of distribution II, 18

Total output panels I, 51

Transformer connections II, 46

Transformer regulation II, 45

Transformers I, 40; II, 43

efficiency of II, 44

oil-cooled • I, 41

water-cooled I, 42

Transmission lines. • II, 24

capacity... •• II, 24

Turbines I, 25

Curtis.. I, 27

steam I> 25

water • I, 30

Underground construction II, 63

Crompton system II, 65

Edison tube system II, 63

Siemens-Halske system II, 65

French system II, 65

Underwriter's wire II,

Variation in voltage • II, 17

INDEX

Part Page

Voltage, selection of II, 72

Voltage regulation of parallel systems II, 20

Water-cooled transformers I, 42

Water-tube boilers I, 11

Water turbines I, 30

Weatherproof wire II, 9

Weight of materials. II, (5

Wire, standard, table I, 47

Wiring formula.... II, 30

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