SYSTEM OF ELECTRICAL SUPPLY
[Sidenote: _Energy from
Engine Shaft
to Third Rail_]
The system of electrical supply chosen for the subway comprises
alternating current generation and distribution, and direct current
operation of car motors. Four years ago, when the engineering plans
were under consideration, the single-phase alternating current railway
motor was not even in an embryonic state, and notwithstanding the
marked progress recently made in its development, it can scarcely yet
be considered to have reached a stage that would warrant any
modifications in the plans adopted, even were such modifications
easily possible at the present time. The comparatively limited
headroom available in the subway prohibited the use of an overhead
system of conductors, and this limitation, in conjunction with the
obvious desirability of providing a system permitting interchangeable
operation with the lines of the Manhattan Railway system practically
excluded tri-phase traction systems and led directly to the adoption
of the third-rail direct current system.
[Illustration: SIDE AND END ELEVATIONS OF ALTERNATOR.]
[Illustration: SIDE ELEVATION AND CROSS SECTION OF ALTERNATOR WITH
PART CUT AWAY TO SHOW CONSTRUCTION.]
It being considered impracticable to predict with entire certainty the
ultimate traffic conditions to be met, the generator plant has been
designed to take care of all probable traffic demands expected to
arise within a year or two of the beginning of operation of the
system, while the plans permit convenient and symmetrical increase to
meet the requirements of additional demand which may develop. Each
express train will comprise five motor cars and three trail cars, and
each local train will comprise three motor cars and two trail cars.
The weight of each motor car with maximum live load is 88,000 pounds,
and the weight of each trailer car 66,000 pounds.
The plans adopted provide electric equipment at the outstart capable
of operating express trains at an average speed approximating
twenty-five miles per hour, while the control system and motor units
have been so chosen that higher speeds up to a limit of about thirty
miles per hour can be attained by increasing the number of motor cars
providing experience in operation demonstrates that such higher speeds
can be obtained with safety.
The speed of local trains between City Hall and 96th Street will
average about 15 miles an hour, while north of 96th Street on both the
West side and East side branches their speed will average about 18
miles an hour, owing to the greater average distance between local
stations.
As the result of careful consideration of various plans, the company's
engineers recommended that all the power required for the operation of
the system be generated in a single power house in the form of
three-phase alternating current at 11,000 volts, this current to be
generated at a frequency of 25 cycles per second, and to be delivered
through three-conductor cables to transformers and converters in
sub-stations suitably located with reference to the track system, the
current there to be transformed and converted to direct current for
delivery to the third-rail conductor at a potential of 625 volts.
[Illustration: OPERATING GALLERY IN SUB-STATION]
[Illustration: GENERAL DIAGRAM OF 11,000 VOLT CIRCUITS IN MAIN POWER
STATION]
Calculations based upon contemplated schedules require for traction
purposes and for heating and lighting cars, a maximum delivery of
about 45,000 kilowatts at the third rail. Allowing for losses in the
distributing cables, in transformers and converters, this implies a
total generating capacity of approximately 50,000 kilowatts, and
having in view the possibility of future extensions of the system it
was decided to design and construct the power house building for the
ultimate reception of eleven 5,000-kilowatt units for traction current
in addition to the lighting sets. Each 5,000-kilowatt unit is capable
of delivering during rush hours an output of 7,500 kilowatts or
approximately 10,000 electrical horse power and, setting aside one
unit as a reserve, the contemplated ultimate maximum output of the
power plant, therefore, is 75,000 kilowatts, or approximately 100,000
electrical horse power.
[Sidenote: _Power
House_]
The power house is fully described elsewhere in this publication, but
it is not inappropriate to refer briefly in this place to certain
considerations governing the selection of the generating unit, and the
use of engines rather than steam turbines.
[Illustration: OIL SWITCHES--MAIN POWER STATION]
The 5,000-kilowatt generating unit was chosen because it is
practically as large a unit of the direct-connected type as can be
constructed by the engine builders unless more than two bearings be
used--an alternative deemed inadvisable by the engineers of the
company. The adoption of a smaller unit would be less economical of
floor space and would tend to produce extreme complication in so large
an installation, and, in view of the rapid changes in load which in
urban railway service of this character occur in the morning and again
late in the afternoon, would be extremely difficult to operate.
The experience of the Manhattan plant has shown, as was anticipated in
the installation of less output than this, the alternators must be put
in service at intervals of twenty minutes to meet the load upon the
station while it is rising to the maximum attained during rush hours.
After careful consideration of the possible use of steam turbines as
prime-movers to drive the alternators, the company's engineers decided
in favor of reciprocating engines. This decision was made three years
ago and, while the steam turbine since that time has made material
progress, those responsible for the decision are confirmed in their
opinion that it was wise.
[Illustration: PART OF BUS BAR COMPARTMENTS--MAIN POWER STATION]
[Sidenote: _Alternators_]
The alternators closely resemble those installed by the Manhattan
Railway Company (now the Manhattan division of the Interborough Rapid
Transit Company) in its plant on the East River, between 74th Street
and 75th Street. They differ, however, in having the stationary
armature divided into seven castings instead of six, and in respect to
details of the armature winding. They are three-phase machines,
delivering twenty-five cycle alternating currents at an effective
potential of 11,000 volts. They are 42 feet in height, the diameter
of the revolving part is 32 feet, its weight, 332,000 pounds, and the
aggregate weight of the machine, 889,000 pounds. The design of the
engine dynamo unit eliminates the auxiliary fly wheel generally used
in the construction of large direct-connected units prior to the
erection of the Manhattan plant, the weight and dimensions of the
revolving alternator field being such with reference to the turning
moment of the engine as to secure close uniformity of rotation, while
at the same time this construction results in narrowing the engine and
reducing the engine shafts between bearings.
[Illustration: REAR VIEW OF BUS BAR COMPARTMENTS--MAIN POWER STATION]
[Illustration: DUCT LINE ACROSS 58TH STREET 32 DUCTS]
Construction of the revolving parts of the alternators is such as to
secure very great strength and consequent ability to resist the
tendency to burst and fly apart in case of temporary abnormal speed
through accident of any kind. The hub of the revolving field is of
cast steel, and the rim is carried not by the usual spokes but by two
wedges of rolled steel. The construction of the revolving field is
illustrated on pages 91 and 92. The angular velocity of the
revolving field is remarkably uniform. This result is due primarily to
the fact that the turning movement of the four-cylinder engine is far
more uniform than is the case, for example, with an ordinary
two-cylinder engine. The large fly-wheel capacity of the rotating
element of the machine also contributes materially to secure
uniformity of rotation.
[Illustration: MAIN CONTROLLING BOARD IN POWER STATION]
[Illustration: CONTROL AND INSTRUMENT BOARD--MAIN POWER STATION]
The alternators have forty field poles and operates at seventy-five
revolutions per minute. The field magnets constitute the periphery of
the revolving field, the poles and rim of the field being built up by
steel plates which are dovetailed to the driving spider. The heavy
steel end plates are bolted together, the laminations breaking joints
in the middle of the pole. The field coils are secured by copper
wedges, which are subjected to shearing strains only. In the body of
the poles, at intervals of approximately three inches, ventilating
spaces are provided, these spaces registering with corresponding air
ducts in the external armature. The field winding consists of copper
strap on edge, one layer deep, with fibrous material cemented in place
between turns, the edges of the strap being exposed.
[Illustration: DUCTS UNDER PASSENGER STATION PLATFORM
64 DUCTS]
The armature is stationary and exterior to the field. It consists of a
laminated ring with slots on its inner surface and supported by a
massive external cast-iron frame. The armature, as has been noted,
comprises seven segments, the topmost segment being in the form of a
small keystone. This may be removed readily, affording access to any
field coil, which in this way may be easily removed and replaced. The
armature winding consists of U-shaped copper bars in partially closed
slots. There are four bars per slot and three slots per phase per
pole. The bars in any slot may be removed from the armature without
removing the frame. The alternators, of course, are separately
excited, the potential of the exciting current used being 250 volts.
As regards regulation, the manufacturer's guarantee is that at 100 per
cent. power factor if full rated load be thrown off the e. m. f. will
rise 6 per cent. with constant speed and constant excitation. The
guarantee as to efficiency is as follows: On non-inductive load, the
alternators will have an efficiency of not less than 90.5 per cent. at
one-quarter load; 94.75 per cent. at one-half load; 96.25 per cent. at
three-quarters load; 97 per cent. at full load, and 97.25 per cent. at
one and one-quarter load. These figures refer, of course, to
electrical efficiency, and do not include windage and bearing
friction. The machines are designed to operate under their rated full
load with rise of temperature not exceeding 35 degrees C. after
twenty-four hours.
[Illustration: THREE-CONDUCTOR NO. 000 CABLE FOR 11,000 VOLT
DISTRIBUTION]
[Sidenote: _Exciters_]
To supply exciting current for the fields of the alternators and to
operate motors driving auxiliary apparatus, five 250-kilowatt direct
current dynamos are provided. These deliver their current at a
potential of 250 volts. Two of them are driven by 400 horse-power
engines of the marine type, to which they are direct-connected, while
the remaining three units are direct-connected to 365 horse-power
tri-phase induction motors operating at 400 volts. A storage battery
capable of furnishing 3,000 amperes for one hour is used in
co-operation with the dynamos provided to excite the alternators. The
five direct-current dynamos are connected to the organization of
switching apparatus in such a way that each unit may be connected at
will either to the exciting circuits or to the circuits through which
auxiliary motors are supplied.
The alternators for which the new Interborough Power House are
designed will deliver to the bus bars 100,000 electrical horse power.
The current delivered by these alternators reverses its direction
fifty times per second and in connecting dynamos just coming into
service with those already in operation the allowable difference in
phase relation at the instant the circuit is completed is, of course,
but a fraction of the fiftieth of a second. Where the power to be
controlled is so great, the potential so high, and the speed
requirements in respect to synchronous operation so exacting, it is
obvious that the perfection of control attained in some of our modern
plants is not their least characteristic.
[Sidenote: _Switching
Apparatus_]
The switch used for the 11,000 volt circuits is so constructed that
the circuits are made and broken under oil, the switch being
electrically operated. Two complete and independent sets of bus bars
are used, and the connections are such that each alternator and each
feeder may be connected to either of these sets of bus bars at the
will of the operator. From alternators to bus bars the current passes,
first, through the alternator switch, and then alternatively through
one or the other of two selector switches which are connected,
respectively, to the two sets of bus bars.
[Illustration: INSIDE WALL OF TUNNEL SHOWING 64 DUCTS]
Provision is made for an ultimate total of twelve sub-stations, to
each of which as many as eight feeders may be installed if the
development of the company's business should require that number. But
eight sub-stations are required at present, and to some of these not
more than three feeders each are necessary. The aggregate number of
feeders installed for the initial operation of the subway system is
thirty-four.
Each feeder circuit is provided with a type H-oil switch arranged to
be open and closed at will by the operator, and also to open
automatically in the case of abnormal flow of current through the
feeder. The feeders are arranged in groups, each group being supplied
from a set of auxiliary bus bars, which in turn receives its supply
from one or the other of the two sets of main bus bars; means for
selection being provided as in the case of the alternator circuits by
a pair of selector switches, in this case designated as group
switches. The diagram on page 93 illustrates the essential
features of the organization and connections of the 11,000 volt
circuits in the power house.
[Illustration: MANHOLES IN SIDE WALL OF SUBWAY]
Any and every switch can be opened or closed at will by the operator
standing at the control board described. The alternator switches are
provided also with automatic overload and reversed current relays, and
the feeder switches, as above mentioned, are provided with automatic
overload relays. These overload relays have a time attachment which
can be set to open the switch at the expiration of a predetermined
time ranging from .3 of a second to 5 seconds.
[Illustration: CONVERTER FLOOR PLAN
SUB-STATION NO. 14]
The type H-oil switch is operated by an electric motor through the
intervention of a mechanism comprising powerful springs which open and
close the switch with great speed. This switch when opened introduces
in each of the three sides of the circuit two breaks which are in
series with each other. Each side of the circuit is separated from the
others by its location in an enclosed compartment, the walls of which
are brick and soapstone. The general construction of the switch is
illustrated by the photograph on page 94.
[Illustration: CROSS SECTION SUB-STATION NO. 14]
[Illustration: INTERIOR OF SUB-STATION NO. 11]
[Illustration: LONGITUDINAL SECTION SUB-STATION NO. 14]
Like all current-carrying parts of the switches, the bus bars are
enclosed in separate compartments. These are constructed of brick,
small doors for inspection and maintenance being provided opposite all
points where the bus bars are supported upon insulators. The
photographs on pages 95 and 96 are views of a part of the bus bar
and switch compartments.
[Illustration: TWO GROUPS OF TRANSFORMERS]
The oil switches and group bus bars are located upon the main floor
and extend along the 59th Street wall of the engine room a distance of
about 600 feet. The main bus bars are arranged in two lines of brick
compartments, which are placed below the engine-room floor. These bus
bars are arranged vertically and are placed directly beneath the rows
of oil switches located upon the main floor of the power house. Above
these rows of oil switches and the group bus bars, galleries are
constructed which extend the entire length of the power house, and
upon the first of these galleries at a point opposite the middle of
the power house are located the control board and instrument board, by
means of which the operator in charge regulates and directs the entire
output of the plant, maintaining a supply of power at all times
adequate to the demands of the transportation service.
[Illustration: MOTOR-GENERATORS AND BATTERY BOARD FOR CONTROL
CIRCUITS--SUB-STATION]
[Illustration: 1,500 K. W. ROTARY CONVERTER]
[Sidenote: _The Control
Board_]
The control board is shown in the photograph on page 97. Every
alternator switch, every selector switch, every group switch, and
every feeder switch upon the main floor is here represented by a small
switch. The small switch is connected into a control circuit which
receives its supply of energy at 110 volts from a small motor
generator set and storage battery. The motors which actuate the large
oil switches upon the main floor are driven by this 110 volt control
current, and thus in the hands of the operator the control switches
make or break the relatively feeble control currents, which, in turn,
close or open the switches in the main power circuits. The control
switches are systematically assembled upon the control bench board in
conjunction with dummy bus bars and other apparent (but not real)
metallic connections, the whole constituting at all times a correct
diagram of the existing connections of the main power circuits. Every
time the operator changes a connection by opening or closing one of
the main switches, he necessarily changes his diagram so that it
represents the new conditions established by opening or closing the
main switch. In connection with each control switch two small
bull's-eye lamps are used, one red, to indicate that the corresponding
main switch is closed, the other green, to indicate that it is open.
These lamps are lighted when the moving part of the main switch
reaches approximately the end of its travel. If for any reason,
therefore, the movement of the control switch should fail to actuate
the main switch, the indicator lamp will not be lighted.
[Illustration: MOTOR-GENERATOR SET SUPPLYING ALTERNATING CURRENT FOR
BLOCK SIGNALS AND MOTOR-GENERATOR STARTING SET]
The control board is divided into two parts--one for the connections
of the alternators to the bus bars and the other for the connection
of feeders to bus bars. The drawing on page 97 shows in plain view
the essential features of the control boards.
[Sidenote: _The
Instrument
Board_]
A front view of the Instrument Board is shown on page 97. This
board contains all indicating instruments for alternators and feeders.
It also carries standardizing instruments and a clock. In the
illustration the alternator panels are shown at the left and the
feeder panels at the right. For the alternator panels, instruments of
the vertical edgewise type are used. Each vertical row comprises the
measuring instruments for an alternator. Beginning at the top and
enumerating them in order these instruments are: Three ammeters, one
for each phase, a volumeter, an indicating wattmeter, a power factor
indicator and a field ammeter. The round dial instrument shown at the
bottom of each row of instruments is a three-phase recording
wattmeter.
A panel located near the center of the board between alternator panels
and feeder panels carries standard instruments used for convenient
calibration of the alternator and feeder instruments. Provision is
made on the back of the board for convenient connection of the
standard instruments in series with the instruments to be compared.
The panel which carries the standard instruments also carries ammeters
used to measure current to auxiliary circuits in the power house.
For the feeder board, instruments of the round dial pattern are used,
and for each feeder a single instrument is provided, viz., an ammeter.
Each vertical row comprises the ammeters belonging to the feeders
which supply a given sub-station, and from left to right these are in
order sub-stations Nos. 11, 12, 13, 14, 15, 16, 17, and 18; blank
spaces are left for four additional sub-stations. Each horizontal row
comprises the ammeter belonging to feeders which are supplied through
a given group switch.
This arrangement in vertical and horizontal lines, indicating
respectively feeders to given sub-stations and feeders connected to
the several group switches, is intended to facilitate the work of the
operator. A glance down a vertical row without stopping to reach the
scales of the instruments will tell him whether the feeders are
dividing with approximate equality the load to a given sub-station.
Feeders to different sub-stations usually carry different loads and,
generally speaking, a glance along a horizontal row will convey no
information of especial importance. If, however, for any reason the
operator should desire to know the approximate aggregate load upon a
group of feeders this systematic arrangement of the instruments is of
use.
[Illustration: SWITCHBOARD FOR ALTERNATING CURRENT BLOCK SIGNAL
CIRCUITS--IN SUB-STATION]
[Illustration: EXTERIOR OF SUB-STATION NO. 18]
[Sidenote: _Alternating
Current
Distribution
to Sub-Stations
Power House
Ducts and
Cables_]
From alternators to alternator switches the 11,000 volt alternating
currents are conveyed through single conductor cables, insulated by
oil cambric, the thickness of the wall being 12/32 of an inch. These
conductors are installed in vitrified clay ducts. From dynamo switches
to bus bars and from bus bars to group and feeder switches, vulcanized
rubber insulation containing 30 per cent. pure Para rubber is
employed. The thickness of insulating wall is 9/32 of an inch and the
conductors are supported upon porcelain insulators.
[Sidenote: _Conduit
System for
Distribution_]
From the power house to the subway at 58th Street and Broadway two
lines of conduit, each comprising thirty-two ducts, have been
constructed. These conduits are located on opposite sides of the
street. The arrangement of ducts is 8 x 4, as shown in the section on
page 96.
[Illustration: EXTERIOR OF SUB-STATION NO. 11]
The location and arrangement of ducts along the line of the subway are
illustrated in photographs on pages 98 and 99, which show
respectively a section of ducts on one side of the subway, between
passenger stations, and a section of ducts and one side of the subway,
beneath the platform of a passenger station. From City Hall to 96th
Street (except through the Park Avenue Tunnel) sixty-four ducts are
provided on each side of the subway. North of 96th Street sixty-four
ducts are provided for the West-side lines and an equal number for the
East-side lines. Between passenger stations these ducts help to form
the side walls of the subway, and are arranged thirty-two ducts high
and two ducts wide. Beneath the platform of passenger stations the
arrangement is somewhat varied because of local obstructions, such as
pipes, sewers, etc., of which it was necessary to take account in the
construction of the stations. The plan shown on page 98, however,
is typical.
The necessity of passing the cables from the 32 x 2 arrangement of
ducts along the side of the tunnel to 8 x 8 and 16 x 4 arrangements of
ducts beneath the passenger platforms involves serious difficulties in
the proper support and protection of cables in manholes at the ends of
the station platforms. In order to minimize the risk of interruption
of service due to possible damage to a considerable number of cables
in one of these manholes, resulting from short circuit in a single
cable, all cables except at the joints are covered with two layers of
asbestos aggregating a full 1/4-inch in thickness. This asbestos is
specially prepared and is applied by wrapping the cable with two
strips each 3 inches in width, the outer strip covering the line of
junction between adjacent spirals of the inner strip, the whole when
in place being impregnated with a solution of silicate of soda. The
joints themselves are covered with two layers of asbestos held in
place by steel tape applied spirally. To distribute the strains upon
the cables in manholes, radical supports of various curvatures, and
made of malleable cast iron, are used. The photograph on page 100
illustrates the arrangement of cables in one of these manholes.
[Illustration: OPERATING BOARD--SUB-STATION NO. 11]
In order to further diminish the risk of interruption of the service
due to failure of power supply, each sub-station south of 96th Street
receives its alternating current from the power house through cables
carried on opposite sides of the subway. To protect the lead sheaths
of the cables against damage by electrolysis, rubber insulating pieces
1/6 of an inch in thickness are placed between the sheaths and the
iron bracket supports in the manholes.
[Sidenote: _Cable
Conveying
Energy from
Power House to
Sub-Stations_]
The cables used for conveying energy from the power house to the
several sub-stations aggregate approximately 150 miles in length. The
cable used for this purpose comprises three stranded copper conductors
each of which contains nineteen wires, and the diameter of the
stranded conductor thus formed is 2/5 of an inch. Paper insulation is
employed and the triple cable is enclosed in a lead sheath 9/64 of an
inch thick. Each conductor is separated from its neighbors and from
the lead sheath by insulation of treated paper 7/16 of an inch in
thickness. The outside diameter of the cables is 2-5/8 inches, and the
weight 8-1/2 pounds per lineal foot. In the factories the cable as
manufactured was cut into lengths corresponding to the distance
between manholes, and each length subjected to severe tests including
application to the insulation of an alternating current potential of
30,000 volts for a period of thirty minutes. These cables were
installed under the supervision of the Interborough Company's
engineers, and after jointing, each complete cable from power house to
sub-station was tested by applying an alternating potential of 30,000
volts for thirty minutes between each conductor and its neighbors, and
between each conductor and the lead sheath. The photographs on
page 98 illustrates the construction of this cable.
[Sidenote: _Sub-Station_]
The tri-phase alternating current generated at the power house is
conveyed through the high potential cable system to eight sub-stations
containing the necessary transforming and converting machinery. These
sub-stations are designed and located as follows:
[Illustration: DIAGRAMS OF DIRECT CURRENT FEEDER AND RETURN CIRCUITS]
Sub-station No. 11--29-33 City Hall Place.
Sub-station No. 12--108-110 East 19th Street.
Sub-station No. 13--225-227 West 53d Street.
Sub-station No. 14--264-266 West 96th Street.
Sub-station No. 15--606-608 West 143d Street.
Sub-station No. 16--73-77 West 132d Street.
Sub-station No. 17--Hillside Avenue, 301 feet West of
Eleventh Avenue.
Sub-station No. 18--South side of Fox Street (Simpson
Street), 60 feet north of Westchester Avenue.
[Illustration: SWITCH CONNECTING FEEDER TO CONTACT RAIL]
[Illustration: CONTACT RAIL JOINT WITH FISH PLATE]
The converter unit selected to receive the alternating current and
deliver direct current to the track, etc., has an output of 1,500
kilowatts with ability to carry 50 per cent. overload for three hours.
The average area of a city lot is 25 x 100 feet, and a sub-station
site comprising two adjacent lots of this approximate size permits the
installation of a maximum of eight 1,500 kilowatts converters with
necessary transformers, switchboard and other auxiliary apparatus. In
designing the sub-stations, a type of building with a central air-well
was selected. The typical organization of apparatus is illustrated in
the ground plan and vertical section on pages 101, 102 and 103 and
provides, as shown, for two lines of converters, the three
transformers which supply each converter being located between it and
the adjacent side wall. The switchboard is located at the rear of the
station. The central shaft affords excellent light and ventilation for
the operating room. The steel work of the sub-stations is designed
with a view to the addition of two storage battery floors, should it
be decided at some future time that the addition of such an auxiliary
is advisable.
[Illustration: CONTACT RAIL BANDS]
The necessary equipment of the sub-stations implies sites
approximately 50 x 100 feet in dimensions; and sub-stations Nos. 14,
15, 17, and 18 are practically all this size. Sub-stations Nos. 11 and
16 are 100 feet in length, but the lots acquired in these instances
being of unusual width, these sub-stations are approximately 60 feet
wide. Sub-station No. 12, on account of limited ground space, is but
48 feet wide and 92 feet long. In each of the sub-stations, except No.
13, foundations are provided for eight converters; sub-station No. 13
contains foundations for the ultimate installation of ten converters.
[Illustration: DIRECT CURRENT FEEDERS FROM MANHOLE TO CONTACT RAIL]
The function of the electrical apparatus in sub-stations, as has been
stated, is the conversion of the high potential alternating current
energy delivered from the power house through the tri-phase cables
into direct current adapted to operate the motors with which the
rolling stock is equipped. This apparatus comprises transformers,
converters, and certain minor auxiliaries. The transformers, which are
arranged in groups of three, receive the tri-phase alternating current
at a potential approximating 10,500 volts, and deliver equivalent
energy (less the loss of about 2 per cent. in the transformation) to
the converters at a potential of about 390 volts. The converters
receiving this energy from their respective groups of transformers in
turn deliver it (less a loss approximating 4 per cent. at full load)
in the form of direct current at a potential of 625 volts to the bus
bars of the direct current switchboards, from which it is conveyed by
insulated cables to the contact rails. The photograph on page 102
is a general view of the interior of one of the sub-stations. The
exterior of sub-stations Nos. 11 and 18 are shown on page 107.
[Illustration: CONTACT RAILS, SHOWING END INCLINES]
The illustration on page 108 is from a photograph taken on one of
the switchboard galleries. In the sub-stations, as in the power house,
the high potential alternating current circuits are opened and closed
by oil switches, which are electrically operated by motors, these in
turn being controlled by 110 volt direct current circuits. Diagramatic
bench boards are used, as at the power house, but in the sub-stations
they are of course relatively small and free from complication.
The instrument board is supported by iron columns and is carried at a
sufficient height above the bench board to enable the operator, while
facing the bench board and the instruments, to look out over the floor
of the sub-station without turning his head. The switches of the
direct current circuits are hand-operated and are located upon boards
at the right and left of the control board.
A novel and important feature introduced (it is believed for the first
time) in these sub-stations, is the location in separate brick
compartments of the automatic circuit breakers in the direct current
feeder circuits. These circuit breaker compartments are shown in the
photograph on page 93, and are in a line facing the boards which
carry the direct feeder switches, each circuit breaker being located
in a compartment directly opposite the panel which carries the switch
belonging to the corresponding circuit. This plan will effectually
prevent damage to other parts of the switchboard equipment when
circuit-breakers open automatically under conditions of short-circuit.
It also tends to eliminate risk to the operator, and, therefore, to
increase his confidence and accuracy in manipulating the hand-operated
switches.
[Illustration: ASSEMBLY OF CONTACT RAIL AND PROTECTION]
The three conductor cables which convey tri-phase currents from the
power house are carried through tile ducts from the manholes located
in the street directly in front of each sub-station to the back of the
station where the end of the cable is connected directly beneath its
oil switch. The three conductors, now well separated, extend
vertically to the fixed terminals of the switch. In each sub-station
but one set of high-potential alternating current bus bars is
installed and between each incoming cable and these bus bars is
connected an oil switch. In like manner, between each converter unit
and the bus bars an oil switch is connected into the high potential
circuit. The bus bars are so arranged that they may be divided into
any number of sections not exceeding the number of converter units, by
means of movable links which, in their normal condition, constitute a
part of the bus bars.
Each of the oil switches between incoming circuits and bus bars is
arranged for automatic operation and is equipped with a reversed
current relay, which, in the case of a short-circuit in its
alternating current feeder cable opens the switch and so disconnects
the cable from the sub-station without interference with the operation
of the other cables or the converting machinery.
[Illustration: CONTACT RAIL INSULATOR]
[Sidenote: _Direct Current
Distribution
from
Sub-Stations_]
The organization of electrical conductors provided to convey direct
current from the sub-stations to the moving trains can be described
most conveniently by beginning with the contact, or so-called third
rail. South of 96th Street the average distance between sub-stations
approximates 12,000 feet, and north of 96th Street the average
distance is about 15,000 feet. Each track, of course, is provided with
a contact rail. There are four tracks and consequently four contact
rails from City Hall to 96th Street, three from 96th Street to 145th
Street on the West Side, two from 145th Street to Dyckman Street, and
three from Dyckman Street to the northern terminal of the West Side
extension of the system. From 96th Street, the East Side has two
tracks and two contact rails to Mott Avenue, and from that point to
the terminal at 182d Street three tracks and three contact rails.
[Illustration: CONTACT SHOE AND FUSE]
Contact rails south of Reade Street are supplied from sub-station No.
11; from Reade Street to 19th Street they are supplied from
sub-stations Nos. 11 and 12; from 19th Street they are supplied from
sub-stations Nos. 12 and 13; from the point last named to 96th Street
they are supplied from sub-stations Nos. 13 and 14; from 96th Street
to 143d Street, on the West Side, they are supplied from sub-stations
Nos. 14 and 15; from 143d Street to Dyckman Street they are supplied
from sub-stations Nos. 15 and 17; and from that point to the terminal
they are supplied from sub-station No. 17. On the East Side branch
contact rails from 96th Street to 132d Street are supplied from
sub-stations Nos. 14 and 16; from 132d to 165th Street they are
supplied from sub-stations Nos. 16 and 18; and from 165th Street to
182d Street they are supplied from sub-station No. 18.
Each contact rail is insulated from all contact rails belonging to
adjacent tracks. This is done in order that in case of derailment or
other accident necessitating interruption of service on a given track,
trains may be operated upon the other tracks having their separate and
independent channels of electrical supply. To make this clear, we may
consider that section of the subway which lies between Reade Street
and 19th Street. This section is equipped with four tracks, and the
contact rail for each track, together with the direct current feeders
which supply it from sub-stations Nos. 11 and 12, are electrically
insulated from all other circuits. Of each pair of track rails one is
used for the automatic block signaling system, and, therefore, is not
used as a part of the negative or return side of the direct current
system. The other four track rails, however, are bonded, and together
with the negative feeders constitute the track return or negative side
of the direct current system.
The diagram on page 109 illustrates the connections of the contact
rails, track rails and the positive and negative feeders. All negative
as well as positive feeders are cables of 2,000,000 c. m. section and
lead sheathed. In emergency, as, for example, in the case of the
destruction of a number of the cables in a manhole, they are,
therefore, interchangeable. The connections are such as to minimize
"track drop," as will be evident upon examination of the diagram. The
electrical separation of the several contact rails and the positive
feeders connected thereto secures a further important advantage in
permitting the use at sub-stations of direct-current circuit-breakers
of moderate size and capacity, which can be set to open automatically
at much lower currents than would be practicable were all contact
rails electrically connected, thus reducing the limiting current and
consequently the intensity of the arcs which might occur in the subway
in case of short-circuit between contact rail and earth.
The contact rail itself is of special soft steel, to secure high
conductivity. Its composition, as shown by tests, is as follows:
Carbon, .08 to .15; silicon, .05; phosphorus, .10; manganese, .50 to
.70; and sulphur, .05. Its resistance is not more than eight times the
resistance of pure copper of equal cross-section. The section chosen
weighs 75 pounds per yard. The length used in general is 60 feet, but
in some cases 40 feet lengths are substituted. The contact rails are
bounded by four bonds, aggregating 1,200,000 c. m. section. The bonds
are of flexible copper and their terminals are riveted to the steel by
hydraulic presses, producing a pressure of 35 tons. The bonds when in
use are covered by special malleable iron fish-plates which insure
alignment of rail. Each length of rail is anchored at its middle point
and a small clearance is allowed between ends of adjacent rails for
expansion and contraction, which in the subway, owing to the
relatively small change of temperature, will be reduced to a minimum.
The photographs on pages 110 and 111 illustrate the method of
bonding the rail, and show the bonded joint completed by the addition
of the fish-plates.
The contact rail is carried upon block insulators supported upon
malleable iron castings. Castings of the same material are used to
secure the contact rail in position upon the insulators. A photograph
of the insulator with its castings is shown on page 113.
[Sidenote: _Track
Bonding_]
The track rails are 33 feet long, of Standard American Society Civil
Engineers' section, weighing 100 pounds a yard. As has been stated,
one rail in each track is used for signal purposes and the other is
utilized as a part of the negative return of the power system.
Adjacent rails to be used for the latter purpose are bonded with two
copper bonds having an aggregate section of 400,000 c. m. These bonds
are firmly riveted into the web of the rail by screw bonding presses.
They are covered by splice bars, designed to leave sufficient
clearance for the bond.
The return rails are cross-sectioned at frequent intervals for the
purpose of equalizing currents which traverse them.
[Sidenote: _Contact Rail
Guard and
Collector Shoe_]
The Interborough Company has provided a guard in the form of a plank
8-1/2 inches wide and 1-1/2 inches thick, which is supported in a
horizontal position directly above the rail, as shown in the
illustration on page 113. This guard is carried by the contact
rail to which it is secured by supports, the construction of which is
sufficiently shown in the illustration. This type of guard has been in
successful use upon the Wilkesbarre and Hazleton Railway for nearly
two years. It practically eliminates the danger from the third rail,
even should passengers leave the trains and walk through a section of
the tunnel while the rails are charged.
Its adoption necessitates the use of a collecting shoe differing
radically from that used upon the Manhattan division and upon the
elevated railways employing the third rail system in Chicago, Boston,
Brooklyn, and elsewhere. The shoe is shown in the photograph on
page 114. The shoe is held in contact with the third rail by
gravity reinforced by pressure from two spiral springs. The support
for the shoe includes provision for vertical adjustment to compensate
for wear of car wheels, etc.