The Brevard Street mercury arc rectifier substation of the Baltimore and Ohio Railroad / Joseph Kaminski

THE BREVARD STREET

MERCURY ARC RECTIFIER

SUBSTATION
of the

BALTIMORE AND OHIO RAILROAD

TfU BET? FT INITIATION THESIS

Joseph ka:,:tnski

college of engineering

electrical

CLASS OF 1940

SUMMARY

The subject of this paper is a modern mercury arc rectifier sub-
station constructed to replace a rotating substation which had to be moved
or abandoned.

The paper opens with the "Early History" designating the events
leading up to the construction of the substation. This is followed by a
description of the building and operating equipment, illustrated with pic-
tures. The theory of operation of a mercury arc rectifier is given with a
brief description of a rectifier tank unit which is also illustrated by s
picture showing the operating parts. A discussion of the essential features
of Mercury ere rectification, such as:

Efficiency.

Voltage Regulation, and power factor are drawn out followed by a
mention of the inspection and maintenance of the substation.

In the Conclusion, the inherrent advantages of the rectifier unit
is brought out by a comparison with rotating equipment.

BIBLIOGRAPHY

Mr. J. H. Davis Chief Engineer of Electric Trection

Baltimore and Ohio Railroad

Mr, R. L, Erring

Substation Operator

Brevard Street Rectifier Substation

General Electric Review

Rail?.-py Electric Journal

festinghouse Electric Engineer

Bryant and Johnson

Alternating Current Machinery

iv^ gnus son

Alternating Currents

I

TABLE OF CONTENTS

CONSTRUCTION OF THE RECTIFIES SUBSTATION 6-19

THEORY OF OPERATION C* THE MERCURY ARC RECTIFIER 20 - 22

P SCRIPTION OF THE RECTIFIER 52-27

REGULATION , 29

EFFICIENCY 29 - 30

INSPECTION AND MAINTENANCE 32

CONCLUSION 52 - 54

-1-

EaRLY RTSTORY

The Brevard Street Mercury *rc Rectifier SubstFtion of the Balti-
more and Ohio Railroad is the first substation of this type in the South.
The substation represents the latest design anr] application of engineering
principles in accordance with American Railroad progress, towards vhich the
Baltimore and Ohio Railroad has been a leading contributor.

Going back to the year 1888, the Baltimore and Ohio Railroad pfs
seeking a means to serve it's customers more readily. At this time the
railroad had no facilities thru the city of Baltimore for it's merchandise
and passenger traffic, fill trains over the Philadelphia division of the
Baltimore and Ohio entered and left Baltimore by ferry transfer across the
v. est branch of the petspsco river, from Canton to Locust Point. The trains
were then conducted thru the railway yards along the streets of South Bal-
timore to Camden Station.

A franchise was secured from the city of Baltimore in the early
part of l? f J0 in accordance with the provision of a special act passed by
the Maryland legislature, March 18, l-'90 providing for the construction of
a railroad thru the city. This road was known as the Belt Line and was to
furnish a direct rail connection between the main line West of Baltimore
and that East of Baltimore. The ordinance required that the trains be
operated electrically, end since the railroad was to be underground, elec-
tric motive power provided the most satisfactory solution.

Thus the electrified Belt Line of the Baltimore and Ohio in the
cit;, of Baltimore is historically famous as it marked the first use of
electric locomotives by any trunk line railroad.

The electrified portion of the Belt Line which lies within the

-g-

E/RLY HISTORY

city limits of Baltimore begins at Camden Station on the rest to the raver-
ly interlocking tower on the erst, a distance of ',75 miles. Forty-eight
per cent of the totFl distance is thru tunnels. The longest section is the
Howard Street tunnel from Camden Station to Mt. Royal Station comprising 8
length of 7500 feet.

Design and construction of a suitable power plant to furnish the
necessary power was an interesting problem. The entire portion of the road
to be handled by (lectric locomotives is upgrade, the difference in eleva-
tion amounting to 150 feet, giving an average grade of 0.9^, the ruling
grade being 1,5$ and maximum curvature 10° 16'.

A power plant for supplying the necessary load was constructed at
the western end of the line in 1894. The equipment consisted of five 500-
k.w., 700 volt, direct-current generators direct connected to tandem-com-
pound, non-condensing Corliss engines. This installation represented the
largest direct connected generators ever installed up to that time. Tn
addition to this layout, there was constructed a storage battery station
near the Mt. Royal passenger station, one and three-quarter miles from the
power house, (The site of the present rectifier substation.) The purpose
of the battery substation was to improve voltage conditions by a booster
system of control. The first trip with electric locomotive Number 1 was
made June ?7, 1R94, and the line was opened for traffic May 1, 1895. One
of the first electric locomotives used is still presented for exhibition as
being the first electric locomotive used in this country under steam rail-
road conditions.

*(See picture showing map, profile and curvature of Belt Line on following
P^ge.)

I
t

_4_

EARLY HISTORY

With increased traffic it soon became necessary to increase the
power for the Belt Line end in 1909, the old power plant was found to be of
insufficient capacity. This led to the construction of a rotary converter
substation pt the Mt. Royal end, near the battery station, in 1S10. The
converter substation consisted of three 1000 k.w., 650 volt synchronous
converters with the necessary auxiliaries with space being provided for
additional ma chines. The power was supplied by a local electric light sad
power comppny in the form of three phase, 12,000 volt, ?5 cycle current.
The bpttery stetion was retained, for peak loads. In 1914, a 2000 k.w, con-
verter was added and due to addition? 1 electrical improvements the battery
station was dismantled. In 1915, the originpl power plant at the Camden
Station end was abandoned.

In 1924, plans for the Howard Street extension were approved by
the Maryland legislature. The rotary substpticn would then be in the cen-
ter of the new street location. Since actual construction of the Howard
Street extension wss not scheduled to begin until some fourteen yeers later
the railroad began planning for a new substation to supply the Belt Line.

Space was available for a new substption on ad joining property
owned by the Baltimore and Ohio Railroad. However, this space was located
directly above the Howard Street tunnel, and to construct s rot? ting sub-
station on this site would subject the old walls of the tunnel to the vi-
bration set up by rotating machines which, in all probability, they could
not withstand.

Moving the substation to a more substantial site would involve
considerable expense since additional units would h-vc- to be operated in

I

The original Baltimore and Ohio Belt Line power plant, built in 1894 and abandoned in 1915. In the far end of the building are the five
500-kw direct-current generators driven by direct-connected compound steam engines and supplying power to the railroad electrification.
In the foreground are belted single-phase, 125-cycle, 120-kw generators for supplying power for lights and other station necessities.

-6-

EARLX HISTORY

order to supply the load while the remainder of the equipment was moved .

CONSTRUCTION OF THE RECTIFIER SUBSTATION

The Mercury Arc Rectifier seemed to offer a solution to this
series of conflicting problems and in November 1357, construction of the
Breverd Street Mercury Arc Rectifier Substation was under way.

It was possible to construct the Rectifier Substation directly
over the tunnel since the foundation requirements Fere considerably less
for rectifiers then for rotating machines. A much smaller and hence 8 less
expensive building would be required. Fhile construction on the new sub-
station was being carried out, the old synchronous station continued to
serve the load demand.

The new substation was designed to supply 670 volts direct cur-
rent to the tunnel feeders with no interruption to service.

The substation capacity Is 6000 k,w, rhich consists of tvo 3000-

k.w. Testinghouse sectional mercury arc rectifier units. The mercury arc

rectifier Is at itte best in the smaller sizes because the arc path is

smaller, hence a lower arc voltage, thereby decreasing the possibility of

p. breakdown voltage in the reverse direction. Therefore, each £000 k.w.

sectional unit is composed of four 750 k.w. rectifier tanks equipped with

the necessary auxiliaries for operation.

*(See picture on following page showing comparison of sizes of the old and
new substation. Also picture showing sectional units.)

-7-

On the left is the new Mercury Arc Substation.
The old Rotary Substation is shwqn st the right.

-8-

I

c

-9-

CONSTRUCTION OF THE RECTIFIER SUBSTATION

Each unit may be operated ith tvo, three, or four tanks r na the 3000 k.w,
units may be operated independently or in multiple. Each unit Fill deliver
4478 amperes at 670 volts d.c. continuously, 150^ load for two hours, and
Z00% load for five minutes. The auxiliary power supply is 240 volts, 3
phase 60 cycles. The tot el weight of each unit is 30,000 pounds when in
operation. (The pdded operating weight being due to the necessary circu-
lating water.)

Power is supplied to each 5000 k.w, rectifying unit by a "esting-
house 3 phase rectifier transformer rated at 3240 kva, 17,200 volts to 613
volts, 60 cycle, impedance 4.85?, 12 phase, »nd zig zag secondary connections.
This transformer is oil insulated, water cooled and has a total weight of
42,500 pounds. In conjunction with each main transformer is supplied a
^estinghouse SL interphase transformer. The purpose of the interphase
transformer is to give six or twelve phase operation of the rectifier v. ith
the advantages of three phase operation where the windings carry current
for 120 electrical degrees or more. The interphase transformer is placed
between the wye or zig-zag groups of the main transformer secondary so that
the groups operate as three phase.

The interphase transformer is oil insulated, water cooled, and
rated at 4473 amperes d.c. in the negative lead. The weight is 10,310
pounds.

Since the Mercury Pre Rectifier must be maintained at r definite

tempera ture above a certain minimum value for best operation a recirculst-

*(See picture on folloT^ing page showing main and interphase transformers.
Also a schematic diagram of a typical t*o section Mercury Arc Rectifier
Installation shovring main transformer, interphase transformer and essen-
tial auxiliaries.)

o

Supply Line

Disconnect I
Smtch |

Oil Circuit r
Breaker

Power

Transformer

Insulating

Transformer

Current
..Transformer

-To Section A

( Rotary i Mercury j
s Pump d Vacuum
'Motor 5 Pump i
ik» . 1 Heater

. llano- Vacuum
[ meter Pumping
Equipment
\^ Section "8"

S-C Reactor

Excitation ,
for Section "A

Excitation
Equipment

Section 8 '

\ Phase
Position

Controller

interphase
I Transformer ^

-Mam Anode

I J, J, lEhminatoiS/

Heaters Pump'Hclor
Impulsing Transformer
— Negative Bus

Starting
Anode

\Emtinq

I Anode

D-C Reverse
1 Current Breaker

Cathode

Section A '

- Positive Bus

-12-

COBSTRUCTICN 0^ THE RECTIFIER SUBSTATION

ing water system works In conjunction ^ith a heat exchanger. Under normal
operating condition?, the vfter is used to cool the rectifier below e cer-
tain maximum permissible operating temperature; but during periods of ex-
tremely low temperature it becomes necessary to hert the water in the beet
exchanger. Each rectifying unit is provided with a Meetinghouse heat ex-
changer. The heat exchanger has 135 square feet of heating surface. Cir-
culation is provided by a 2h.u, 2°0-440 volt, 5 phase, 60 cycle motor
direct connected to a Gould centrifugal pump capable of delivering 35 gal-
lons per minute, operating at 1750 r.p.m. — the maximum head being 66 feet.
Above each heat exchanger is provided an expansion tank. The heater tank
contains three Testinghouse C7-148, 4500 watt, 250 volt electric heaters.
An accurate temperature control being maintained automatic- lly. That is,
the pump runs continuously and as soon as the temperature crops to a cer-
tain value the heaters are turned on autcmatic r lly and cut out when the
water Is at the proper temperature.

Three phase, 60 cycle power is supplied to the substation, by
the Consolidated Gas and Flee trie Company of Baltimore, thru t?.o 15,200
volt underground feeders. The feeders enter the high tension oil circuit
breakers — rated at 15,000 volts and 600 amperes. This also feeds two 25
kva, 15,200 volts - 220/ll0 volt 5 phase, 60 cycle transformers used for
an auxiliary iorer supply. The main feeder circuits may be connected in-
dividually or in parallel to the rectifier equipment by means of a "dummy
breaker" which is used as a disconnect switch. These five units are housed
separately as metal clad units,
*(See picture on following pege showing a view of the heat exchanger units,)

This picture shows the rear of the rectifier
units showing the heat ey changer units and the high speed
breaker as well as the conduit layout.

In front is a view of the metnl clad srltchgear
and control panel.

I

CM
I

-14-

CONSTRUCTICN OF THE RECTIFIER SUBSTATION

Alongside the metal clad svitchgear is located the control panel.
This panel contains two Ester line graphic wattmeters giving a graphic indi-
cation of the load on erch unit during the day. There is also a d.c, volt-
meter, 0-800 volt scale, for indicating the d.c, potential. Two ?.c. kilo-
volt-meters for indicating the bus potentials, tvo a.c. ammeters, d.c. load
ammeters, .watthour meters, and overcurrent protective relays.

On the d.c. switchboard is mounted tv,o 4 pole - 2000 ampere - 750
volt d.c. type CHR air circuit breakers arid one 6000 ampere 650 volt d.c.
breaker. Below this is mounted °, - 6000 ampere 600 volt single throw knife
switches.

For protection of the outgoing d.c. feeders rnd equipment against
high momentary overloads due to some abnormal condition, it is desireable
to disconnect the load as soon as possible. For this purpose the Vesting -
house Electric Manufacturing Company developed s high speed water cooled
breaker of 10, )00 amperes and 750 volts. There are two such breakers
mounted behind the d.c. panel.

Also included in the equipment is e "Degassing Unit" consisting
of a SL ^estinghouse degassing transformer of 30 kva capacity and a port-
able register en wheels, for use in connection ^ith the unit. The de-
gassing unit is necessary as all of the foreign gases must be removed from
the rectifier unit before it is suitable for operation at it's rated volt-
age.

An interesting feature is the method of heating the substation.

*(See picture on following page showing both rectifier units end d.c.
panel. Also picture showing view of high speed breaker.)

I

I

-15-

-17-

CONSTRUCTION OF THE RECTIFIER SUBSTATION

It is hefted entirely electrics lly by tvo ?0 k.r. Chrome lox motcr driven
electric heaters and the transformer room by two 7^ k.? . electric heat-
ers contained in each transformer vault. The o^ice is heated by p. 5 k.w,
208 volt heater.

For lighting the substation and supplying lighting current for
the Mt, Royal Station, there are three 50 kva single phase 60 cycle f
4160/l?0/?08 volt transformers. Also to supply current for car battery
charging purposes at Mt, Royal station, there is included a SO k.w. 60
volt d.c. motor generator set.

; The substation battery which supplies control current for var-
ious operating oevices in connection with the substation operation, is
charged thru rectox units from ?08 volts s.c.

Also included in the construction and equipment of the substa-
tion is sn "Electrolysis Bus" mounted in a cabinet on the wall. The pur-
pose of this bus is to aid in studying electrolytic problems. The sub-
station ground is connected directly to the bus and connections of all
the water mains, gas lines, and conauits are also made to the bus. In
order to determine the flow of current between any of these circuits ana
ground, the desired circuit is removed from it'n bus connection and sn
instrument is inserted.

*(See picture on foLlowing page showing Electrolysis Bus. Also section-
el and floor plan of the substation showing location of ell equipment.)

-18-

-30-

THEGRY 0? OPERATION CE THE iiiERCURY SRC RECTIFIER

In gaseous conduction of electricity, the movement of electrons
toward an anode and of the positive ions towards the cathode, constitutes
the flow of current between the electrodes. The voltage required for gas-
eous conduction between two electrodes depends primarily «n the gas or vs-
por pressure, ;=nd on the temperature of the material of the electrodes.

In the Mercury pre rectifier, the cathode or electron emitting
material is mercury. The advantages of mercury when used for this purpose
are;

(1) The voltage required to release the electrons from the mercury
surface at the operating temperatures is less than that required
by ether materials,
(p) Mercury vapor in the vacuum chamber increases ionization by

collision.
(?) Ionized mercury <=toms pre attracted to the mercury pool cathode
and the heat produced by collision increases the cathode tempera-
ture.

(4) Any condensation or change ^n the quantity of mercury vapor in the
chamber is automatically adjusted by the cathode mercury pool,

(5) The mercury arc terminating on the cathode surface produces an in-
tensely hot cathode spot which moves rapidly over the surface of
the mercury pool. The high temperature (approximately ?000°C) of
the cathode spot is of importance in producing the rapid emmission
of electrons without causing deterioration of the cathode surface.

The unidirectional flow of current thru the rectifier is due
largely to the difference in temperature o** the two electrodes. The cathode

-"■S..L™

THEORY OF OPERATION OF THE MERCURY JRC RECTIFIER

being brought to e state of rapid electronic emission while the anode is
maintained at a temperature at which electrons cannot be emitted.

The anode or positive terminal of the rectifier is usually
graphite because grpphite is capable of rithstanding the high operating
temperatures more readily than other available materials.

Gases other than mercury vapor in the rectifier prove to be
detrimental to the efficient operation. Collisions with electrons are not
elastic with common gases, consequently power losses are higher. The
presence of oxygen is particularly undesireable since this gas combines
with mercury under arc conditions and produces compounds which would inter-
fere with the operation and in time destroy the mercury cathode.

*(3ee diagram on following page.)

Figure 1. Shows a single phase full wave rectifier. Then the
current in the primary of the single phase transformer is in one direction,
to the right, on the positive half of the cycle \ the current in the sec-
ondary flows to the left in the opposite direction thru anode 1 to the load.
On the next half of the cycle, the current in the primary Is reversed caus-
ing the current in the secondary to flow thru anode 2 and thru the load in
the same direction as before. Thus a pulsating direct current is produced
from alternating current.

Figure Z m Shows a three phase rectifier. The primary of the
transformer is delta connected and each leg of the wye secondary is con-
nected to an anode. In three phase rectification there will be three cur-
rents differing in conduction periods by 120 electrical degrees. Hence, a

-22-

THEORI OF OPERATION OF THE MERCURY ARC RECTIFIER

smoother direct current is produced. For s greater number of phases, the
conduction period of each anode is decreased end less pronounced becomes
the ripple in the d.c. voltage produced. This c^n readily be seen by com-
paring figure 1 and Figure 2 with figure g.

DESCRIPTION OF THE RECTIFIER

The metal tank mercury arc rectifier of the t;'pe used in the con-
struction of the substation consists essentially of a gas tight steel con-
tainer which contains solid electrodes, or anodes, and a single electrode
of mercury. The tenk itself is constructed of special steel plates which
are welded tight. All seams p.re welded on the inside, and the tank is con-
structed so that there is access to all of the interior parts for proper
maintenance. The joints that are made separable are fitted with speclsl
gaskets to prevent leakage. The main and auxiliary anodes, as well as the
control grid leads, enter the vacuum chamber thru porcelain bushings, sol-
dered tight to the tank by a specif 1 process. The anodes '■-re of 8 high
quality graphite. The cathode, or mercury pool, is contained in a steel
dish which is insulated from the tank by an insulating ring and vacuum
sealed to the tank.

The tank Is surrounded with a steel water jacket for maintaining
the proper temperature of the rectifier for efficient operation.

In order to maintain the mercury arc rectifier at the proper
vacuum which is of prime Importance, there is included a mercury vapor

7^

'III

r\ O n /"\

Diagrams ohoyvng the Principle of C/>era~~ion

^r- ^..^ KAr-„~ ,„ , A^ DU

3F TH : MERCURY ARC KECTI " EE.

.

r.,. 4

Fgi

Conduce -'erioo o r Each Ancoe is ISO Degrees

■ i /

LOAD VOLTAGE ^ ,

.;._,»_

/~\ /"*\ /His. S/WNA/VW

/ di \ / \ / /it \

/ ll> \ / 111 / (1> \

/ \/ \/ \ AA/WWV\

* . . * *

.■' ; - .- -i I i i— i

« ; i • • t! ' f jJ p r J * *r

- •" '". •* *■ _ t i.\ f*%\

's,-' ••.••■ *--*' LJH> (1) U , K)

E, v |

1 '

u — i — — i —

_

,

— f- i i i rr r t ii *

ClJRREf^TIN ftHOPE NO-1

Single rHASE i-ull Wave Kectifiex

_L_ _ .. _U 1 .^ _

J\

Fi s. 2 v ^,

'r *? 7 7

Conduction ?eroc> ok Each Anode is 120 Degrees A^^i

AAAA

. * **t\ _?

_oad Voltage ^A X

L j L ^ ..- . \ «.*aa

\/\ i'N /N/^s/^/^v/^ »>/VVV

V in V v V t « v v v /*» ^^

" a) s X .-. U) a X i /^

» 1 »| ■ «> it ■ • * l m i* # A

' ' r" *, ■' '■ ** '■ t* *,../.._;.._ c

', . '. .* '. ; \ : ■ ■ IV [f I'T \

j-i

V V V V v V V _ %

• : . A . -. A A A A _ S

..,.-• •...•■ '...-• ■....• •■.[.»■ ,%.../ V.V*

,_ aiJ>

n ii i ii

j U * ■ '

El n t~i rn

13 LJ _ U

E, \ . /

3 V \ I / /

4 \ \ J /

\ * 1 / /

\ /

-. 1 1

1 1

n , rt l J rt ^

Currevt n Anode NO.i

HREE rHASE KECTIFUR;

1 1 Y

:.\

-24-

I -n-rn

}iagrams Showing the Principlf

;c Kect fier

of Operation

DlAGRAM SHOMtfG THE EfFFECT OF f:H£RGIZE» GRIDS IN C0NTROLLI1HG THE OutPUf VoOAGEOFA (feCffFIK

rTTTIT

1 t . ■ ■ ■ J , ■ ■ ■ J . ■ ■ ■ ■ ■ . |- rr , , 1

^*„o—

DESCRIPTION 0^ THE RECTIFIER

vacuum pump. This vacuum pump pumps gas from the section and discharges
it thru e barometric tube Into an interstage reservoir. From here the gas
Is pumped thru a float operated vacuum valve into a rotary oil-sealed back-
ing pump which discharges it at Atmospheric pressure.

The mercury vapor pump is ca.ab?ble of evacuating the vessel to
a very low pressure which is in the order of a fraction of a micron. (A
micron is that iressure which will support a column of mercury 0.001 milli-
meter high. Since atmospheric pressure is 760 millimeters. One micron is
1/760,000 of an atmosphere.) The pump will not pump against a high back
pressure. The pressure maintained within the section is indicated by vacu-
um gauges of special construction and the proper pressure is maintained by
means of contact making pressure gauges. This equipment Is classed as the
rectifier auxiliaries.

In the process of loading a mercury arc rectifier, the first step
is to bring the cathode into an active stat^ of electronic emission. This
is accomplished by me ens of the ignition and excitation equipment vhich
starts the arc In the vacuum chamber. The starting is accomplished by de-
pressing a steel rod into the mercury by action of a solenoid and v itinerat-
ing it. The solenoid is comvetpd In parallel with the starting rod, Vhen
the solenoid circuit is energized thru the control transformer end relay
contacts the steel rod is plunged into the mercury. This short circuits
the solenoid and by the action of a spring, the rod Is "Ithdrewn, thereby
drawing an arc. As ~oon as this happens, the excitation anodes which ere
supplied by s small transformer, pick up and maintain the cathode siot.

*{See following page showing a schematic diagram of connections of the con-
trol end eycitation system.)

a a

2 "

6

*

B

ri

z

-26-

! I I 1 1 1 ! 1 Ml

Schematic Diagram of Connections of the

— (_ jMk

Starting and Excitation System

k a An

of a Mercury Arc Kectifiek

A *

II j II

flWLiflR^wr -l^ E

i L rfMJTYMiT — HCt JlY

^ C 3

Scleiqid c;

L

e

O A

H t UX.

d—. „^-

Jji „ •f feu,r

S < 1 L ^^Ojil

^ >^

AC. SUPPLY S <i t F

J» <f U k*l f n

5 ^ Tt *te Pewr

s < "~~ L J •' cprnwCTa

i i s 5*

s <?

,, r l

r"\ n t il

^ ,, ^ f t

M

T T

(UtWOpF ' t ' ii

o

A

L r, . ,,

uv iA ii

Current KtLAY 1 a t"

Coil

■ — -

_

-27-

DESCRTFTION 0^ THE RECTIFIER

The excitation anodes maintain the cathode spot in absence of the main
load. In case the pre is extinguished for some reason, it is started af-
ter p. time delay automatically — requiring no restprting by fn operator,

THEORY QV OPERATION OF THE MERCURY ARC RECTIFIER

Although during operation, the enodes of a rectifier wHl with-
stand apprecirble negative voltage without formation of a cathode spot on
the mode, which will cause a breakdown in the reverse direction, they will
not reliably withstand the high voltage of operation unless some provision
is msde to establish the required gradient and to deionize the gss surround-
ing the anodes pfter a conduction period. For this purpose, the anodes are
surrounded by shields and energized grids. The grids rve in the arc path
to each anode, and by placing a potential on the grid thpt is negative * . i.th
respect to the cathode, pn pnode may be prevented from picking up current.
Changing the grid potential from negative to positive, the anode is re-
leased to crrry currentj and by controlling the time of this change, the
anode pick up may be delayed beyond it's normrl time in each cycle. (:~ee
figure 4 on page ^A.)

*(See diagram on followin page shoving a crosst-ctional view of the
rectifier section showing operating parts.

-?8-

Dome Water Jacket Bulb for Thermometer^- Starting Anode
- , . r , MalnAnode\ \ ^-^— Porcelain r ,
Solder Seats - \. \\ \ — rrTn Abiufl , &»4™? *»*

Water Jacket

Rubber Seal ->.

Bulbs for under-,
temperature relay
and relay for neat-
er control -

Main Anode Shield -

Three Tank_
Heaters

mmufe

Head W „
„ . . . Cooler
fwnAiwfc

' Grid

Starting Rod | | Ignition Anode .

Flashing Valv e /

and Drain Porcelain —

Mercury

Flushing
Valve

Welded
Steel Tank

Jfam Water
Jacket

Rubber Seals

- Cathode

Water Jacket

CIross-sectlonpl View of Rectifier
Section.

750 k.iF. f 600 volt
Mercury *rc Rectifier.

-39-

REGULATI01S

The normsl rectifier unit has a slightly drooping voltage char-
acteristic. The output voltage being determined by the transformer secon-
dary voltage and the connections used. However, it is influenced by the
arc drop in the rectifier and the reactive drop in the transformer supply
circuit. The arc drop is nearly constant throughout the load range end
the regulation Ls in the order of 5*? to 6^.

The normal characteristics are altered by the use of control grids,
mentioned previously. This control is accomplished by the application, to
the grids, of impulse voltages that are synchronized "dth the power supply
to the main anodes. The transformer is designed to provide the highest
voltage desired and the d.c. output is reduced from that value by delaying
the point of pick up by shifting the phase position of the impulsing supply,
or by applying a bias voltage to alter the point on a sine v-ave impulse at
vhich pick up takes place. Thin delay action is brought about automatic-
ally vith a. voltage regulator. This method of control provides an extreme-
ly smooth variation of voltage output,

E^TCTENCI

The efficiency of a mercury ere rectifier unit is the ratio of
the po^er output fit the d.c. terminal to the power input at the high ten-
sion terminals of the transformer. The component losses of the unit in-
cluded in the efficiency calculations are, copper and iron transformer
losses, loss in the rectifier arc and the power for operation of the rec-

-31-

II 1 1 II | II ( Il 1 II II 4. ,

j-N <*• 1-1

Curves Showing the kelatio/>

— c-,-,-,,-,,-.. *~ -r.. ^ -T- ~r «u*

OF tFFlCIENcy OF THKEE TYPtS OF

A /

Conversion /^fak/itus with vaei^tion

in ?, c. Voltage .

tec

oP v ARC RECT/P/ir*

wvtS-^- q "~— ~

.— -*» < ^NpHrm^,,, /-

L-- ^ »g. ^''3 1 ?A*yfcM7y-p

^"i POOTOE UENfcKflTOk. oET

^ ^-' j**"

^**"**^ j/S^

i ■***'^ j***^^

^^

U ^^^

z

n

Qrt U

ElL FT

u.

UJ

.

1—

u

L>

t* 3000 tw PC jr its

u

s.

60

■

.

)C VOLTAGE

200 400 bOO 800 1000

. [_^_ h |_... __j_ _.. ^ ^ ^

INSPECTION /NT MAINTENANCE

Inspection of apparatus tn s completely automatic substation,
as described, is pn important •factor towards continued service without de-
lays. The frequency of inspection depends primarily upon the nature of
the equipment and the quality of inspection. Tt has been the practice of
the operators In the Brevard Street substation to make detailed inspections
at least once a week, in order that ell apparatus receives the best pos-
sible attention and care. Pt the substation, there are ell of the circuit
diagrams find schematic diagrams suitably framed, to enable the operator to
locate any trouble that might develop during regular operation. Of course,
certain routine inspections ere carried out by each operator in turn dur-
ing regular operation. In such E manner, all parts that begin to v.eer ere
noted and repaired when time permits.

In the maintenance of the equipment is included the cleaning of
relay contacts ancl operating devices. Keeping moveable parts well lubri-
cated and replacing worn contacts and faulty wiring. Ml protective de-
vices are frequently tested and adjusted whenever necessary.

CONCLUSION

The Brevard Street Mercury Rectifier Substation was opened for
traffic in March 1958, An average of 7,000,000 gross ton miles is handled
over the Belt Line each month, the electric locomotive mileage being about
19,500 and the totel k.w. load used each month being about 500,000.

Today, to supply such e load, the mercury arc rectifier is re-
placing the rotating equipment because it offers a reliable means of con-

-53-

CONCLUSION

version of flternating current to direct current. Such applications in-

■
elude direct current for railways, end many industrial uses.

Because of the eycellent performance due to design improvements,
making it possible to supply loads of severs 1 thousand kilowatts fit high
d.c, potentials ranging up to ?0,000 volts, the rectifier is faster be-
coming more widely used.

As brought out by the efficiency curves and discussion covering
the comperison of rotating machines to rectifiers — the rectifier gives a
much lower operating cost. Few replacement parts give low maintenance cost.

Noiseless operation and the ability of the rectifier unit to take
on and deliver a power dem?nd immediately, without the need of synchroniza-
tion or switching, is definitely an "Engineering .Achievement."

As a final comparison, the Table following gives a summary of the
Engineering Economic involved, leading up to the present installation.

-54-

CONCLUSION

Belt Line

Power Plant

(1894)

Rotery
Converter
Substation
(1 910)

Mercury /re
Rectifier
Substation
(1958)

Capacity of Equipment, k.?.. 2,500

5,000

6,000

+—

Size of Building -
Electric Power

126 ft, 7 55 . 36.6 x SI. 5ft
ft. x 24.5ft.: x 56.2ft.

61.6 x 41ft.
x25,2ft.

Floor Space - Sq, Ft.
Generators

6,950

6,090

2,749

Cubic Contents (cu. ft.)
Electric Power only

169,785

110,581

58,788

Cu. Ft, per k.w. Capacity
Electric Power

68

22.2

9.8

Relative Unit Size (Cu. ft,
per k.w.) in %

100

M 7

14.5

This tabulation brings out the fact thft it is now possible to
concentrate more power in a much smaller space. Using the old Belt Line
power plant as a basis of 100^, denoting the floor space in cubic feet per
kilowatt, it follows the fact that the Rotary Substation required only
52.7 % compared to the present installation of 14. 5t.