is on each car a controller of some kind which controls the current
flowing to the motors on that car. This controller is operated from
a distance by means of electro-magnetic or electro-pneumatic devices
controlled by circuits called _pilot circuits_, which circuits are
connected to the motorman’s controller. All the pilot circuits of a
train are connected together by means of train plugs which make the
connections between the cars. The pilot circuits of each car are
connected to a motorman’s controller on that car and this makes it
possible to operate the train from any controller.
=Sprague Multiple-Unit System.= In the earliest form of multiple-unit
control—which was that devised by F. J. Sprague—the motors on each car
were controlled by an ordinary Type K controller, which had geared to
its shaft a small pilot motor. The pilot motor was controlled by the
pilot circuits connected with the motorman’s controller.
In the more recent forms of multiple-unit control, the use of main
controllers having contact cylinders has been practically abandoned.
The contacts are made instead by a number of electro-magnetic or
electro-pneumatic contact devices sometimes called _contactors_.
=General Electric Train Control.= In the General Electric train-control
system each contact for the motor circuits is made by a solenoid magnet
which draws together two heavy copper contact fingers to establish the
circuit. A magnetic blow-out coil in series with the contact is also
provided. The contactors make contact only when energized by a small
amount of current from the master or motorman’s controller. In Fig.
28_a_ is a diagram of the car wiring for a motor car equipped with
this system. The motorman’s controller is a drum controller, but is
comparatively small since it has to handle only the small amount of
current necessary to operate the solenoid magnets of the contactors.
It is evident that by connecting together the pilot circuits, which
are connected to the motorman’s controller, so that the pilot circuits
will be continuous for the entire length of the train, any number
of cars equipped with the train-control system can be operated; and
similar contacts will be made by the contactors under all the cars
simultaneously, by virtue of the circuits established by the master
controller at any platform.
Besides controlling the contactors, the master or motorman’s controller
must control an electro-magnetic reversing switch, or _reverser_, to
change the direction of car travel.
The handle of the motorman’s controller is provided with a push button,
which must be depressed while the current is turned on. Should the
motorman release this push, the circuit through the controller will be
opened and all the contactors will fall open. This handle is called the
_dead man’s handle_ because it is put there to provide for cutting off
the current should the motorman fall dead or in a faint at his post.
The flow of the current in the control circuits, which operates the
reverser and picks up the contactors on the several points may be
followed in the diagram Fig. 28_a_. With the reverse handle in the
forward position and the controller on the first point, current passes
from the main circuit through a single-pole fused switch called the
control switch and through the auxiliary blow-out coil to a finger
bearing on the upper section of the master controller cylinder by which
connection is established to the adjacent finger and thence to the
reverse cylinder. It leaves this over wire No. 8, passing by way of the
connection board and control cut-out switch to the forward operating
coil of the reverser, thence through the forward blow-out coil and over
wire 81, through the switch underneath contactor No. 2 and to ground G,
by way of wire B 2 after passing through the fuse shown. The current
through the operating coil of the reverser, having thrown this, the
path is changed somewhat. The current then instead of passing from
the reverser over wire 81, is conducted through wire 15, through the
operating coils of contactors No. 1, 2, 3, and 11 in series, through
the switch under contactor No. 12, and to ground through finger 1 of
the controller. Contactors 1 and 2 are in multiple and when raised
connect the trolley with the contactors controlling the resistance
leads. Contactor 3 connects R to the line while contactor 11 places
the two motors in series. The motors then operate with all of the
resistance in circuit. When contactor 2 raises, it opens the switch
immediately below it, making it impossible for the reverse to operate
while current is flowing through the motors. On the second notch of
the controller an additional path is opened by way of finger 3 of the
controller. This path leads from finger 3 through four of the control
circuit rheostat coils, through contactor No. 5 and to ground over 32.
On the 3rd, 4th and 5th points contactors 6, 7 and 9 respectively are
raised. The motors are then in full series. Between the 5th and 6th
points all the control circuits are broken preparatory to starting the
multiple connections of motors. On the 6th or the first multiple point
the ground through finger 1 of the master controller is opened while a
ground through finger 3 is established. The current from the reverser
then, after raising contactors 1 and 2 as before, instead of passing
through contactors 3 and 11, passes through the coils of 4, 12 and 13,
through the switch under contactor 11 and to ground over finger 2.
Contactor 12 connects motor No. 2 to R₇, while contactor 13 grounds No.
1 motor. The motors now operate in parallel and on successive notches
of the controller, contactors 6, 7, 8, and 9 are raised, cutting out
all of the resistance. The switches underneath contactors 11 and 12
make it impossible for 11 to raise with 12 and 13 or vice versa. The
reason for this arrangement is very evident, as a direct ground for R₇
would result.
=The Westinghouse Electro-Pneumatic System of Control.= In this system
of multiple unit or train control, the current to the motors is
supplied through a set of unit switches or circuit breakers which are
sometimes placed in a circular case or turret underneath the car and in
other cases are ranged in a row under the car. The opening and closing
of these unit switches is done with compressed air acting on a piston
in an air cylinder. When the circuit is to be closed, compressed air
is admitted behind the piston and forces it down against the tension
of a seventy-pound spring, and the contacts are brought together.
When the switch is to be opened, the air is let out of the cylinder
and the spring forces the piston back. The air supply is obtained
from the storage tanks of the air brake system. The valve controlling
the air supply to the cylinder of each unit switch is operated by
electromagnets which derive current from a seven cell, fourteen-volt,
storage battery. The small master controller operated by the motorman,
makes and breaks the battery connections to the magnets controlling the
air valves.
[Illustration: Fig. 28b. Car Wiring for Westinghouse Control System.]
An advantage of this over other multiple-unit systems is that by
the use of battery current the control system is not disturbed by
interruptions of the main supply of current. The chief advantage of
this is that it makes it possible to reverse the motors and operate
them as brakes in emergencies at all times.
The battery is charged from the main line through lamps as resistance,
or may be charged by being connected in series with the air compressor
motor.
In the accompanying diagram, Fig. 28_b_, there are two batteries
shown which are charged in series with the compressor motor. By means
of two double-pole, double-throw switches, first one and then the
other battery is connected for charging and for service. The battery
is charged in shunt with a resistance and a relay is connected in
the circuit as shown, so as to open the battery circuit whenever
the current through the motor stops, and thus prevent the battery
discharging through the resistance.
The master controller has a double set of segments in order to decrease
the length of the shaft. The handle, therefore, is moved only one-sixth
of a revolution from off to full speed. The various circuits can be
traced by the letters and numbers each wire bears, so that the circuits
will not be gone over in detail. The first position of the master
controller throws the reverser switch in the proper direction and
also closes the main circuit breaker. On the second point the motors
are connected in series with all resistance in circuit, and these
resistances are automatically cut out one by one. On the next point
of the controller the motors are in multiple and the resistances are
automatically cut out in a similar manner. The automatic cutting out
of resistances is accomplished by a limit switch in conjunction with
operating and holding coils on the electro-pneumatic valves. This
limit switch is a kind of a relay which has the current from one of
the motors flowing through its coil and which acts to open a certain
battery circuit which operates the electro-pneumatic valves whenever
the current in the motor circuit in question exceeds the amount for
which the limit switch is set. The automatic acceleration or cutting
out of resistance is accomplished as follows:
Each electro-pneumatic valve has two magnet coils, one of which is
an operating coil and the other a holding coil for holding the valve
open after it is operated. When first the current flows through a
circuit to one of the electro-pneumatic valves, it flows through the
operating coil and operates the valve to close the corresponding
switch or switches of the main circuit by turning the air into the
cylinders. As soon as the main switch is closed, it cuts into circuit
the holding coil of its corresponding electro-pneumatic valve and
this coil will, with the battery current, hold the switch closed even
though the circuit to the operating coil may be opened momentarily by
the limit switch as each step of resistance is cut out. This prevents
the switches from opening when they are once closed and allows the
operating coils to open an air valve each time the current through
the limit switch coil falls below the amount for which it is set. The
contacts which close the holding coil circuit on each valve whenever a
main switch is closed, are called interlocks and are indicated on the
diagram.
[Illustration: Fig. 29. Diagram of Electric Heaters.]
The main line circuit breaker, which is electro-pneumatically operated,
will open automatically on overload and can be reset by the motorman
on all the cars of a train by closing a switch located beside each
controller.
CAR HEATERS.
=Electric Heaters= for warming cars in winter, consist of iron wire
coils which are warmed by the passage of electric current through
them. The heat so evolved varies as the resistance multiplied by the
square of the current. The iron wire coils of the heater are mounted on
non-combustible insulating supports, and are arranged so that there is
a free circulation of air through them. The coils are surrounded with
a perforated metal case, the object of which is to prevent injury to
the coils and to prevent persons or clothing coming in contact with the
hot, live wires of the coils. Heaters are sometimes arranged so that
they can be connected in series or parallel to give different degrees
of heat.
The diagram, Fig. 29, shows the most common arrangement of electric
heaters recently. The tap from the trolley should be taken off on the
trolley side of the circuit breaker. After passing through a fuse the
circuit goes to the switch. Each of the heaters contains two coils,
one of higher resistance than the other. Two independent circuits
are run from the switch, through the heaters and to the ground. One
circuit passes through the high resistance coils of the several heaters
while the other goes through the low resistance coils. The switch
has three points. On the first point a circuit is made through the
high resistance coils. The second point connects the low resistance
coils while the third point puts both circuits in service. With this
arrangement three gradations of heat may be obtained.
To avoid complicated wiring sometimes but one circuit is employed. In
such a case the heat must either be all on or off, no gradations being
possible.
The chief difficulty encountered with electric heaters is the breaking
of the wires because of the scale of oxide that forms gradually when
they are run at a high temperature or because of water striking them
from passengers’ clothing on wet days, which causes the wires to snap.
The Consolidated Car Heating Company gives the following data on the
current required to heat cars:
====================+=================+=================
| Length of Car | Amperes.
| Body. +-----------------
| |Switch Positions.
| +-----------------
| | 1 2 3
--------------------+-----------------+-----------------
| { 14 to 20 feet | 3 4 7
Average conditions | { 20 to 28 ” | 3 6 9
| { 28 to 34 ” | 4 7 11
| |
Severest conditions | { 18 to 24 feet | 4 7 11
| { 28 to 34 ” | 6 8 14
--------------------+-----------------+-----------------
In his Electrical Engineers’ Hand Book, Mr. Foster gives results of
tests made on Brooklyn cars as follows:
=========================+================+====================
Cars. | Temperature F. | Consumption.
-------+--------+--------+----------------+--------------------
Doors. |Windows.|Contents|Outside.|Average|Watts.| Amperes
| | cu. ft.| |in car.| |at 500 volts.
-------+--------+--------+--------+-------+------+-------------
2 | 12 | 850½ | 28 | 55 | 2295 | 4.6
2 | 12 | 850½ | 7 | 39 | 2325 | 4.6
2 | 12 | 808½ | 28 | 49 | 2180 | 4.3
2 | 12 | 913½ | 35 | 52 | 2745 | 4.5
4 | 16 | 1012 | 7 | 46 | 3038 | 6.
4 | 16 | 1012 | 28 | 54 | 3160 | 6.3
-------+--------+--------+--------+-------+------+-------------
When not watched carefully considerable current may be wasted by
allowing the heaters to remain turned on when not needed. Many
companies hang out signs where motormen may observe them, indicating
when the heaters shall be turned on and to what point.
[Illustration: Fig. 30. Electric Heater.]
The best practice in electric heating is to have plenty of heaters and
run the wire at a low temperature, rather than attempt to heat with a
few at high temperature. The greater the number of heaters the larger
the radiating surface around which the air can circulate and a given
amount of car heating can be accomplished with less current than with a
few high temperature heaters. The depreciation of the heater wires is
less the lower the temperature at which they are operated. An electric
heater is shown in Fig. 30.
=Hot-Water Heaters= are frequently used on large electric cars.
Hot-water pipes are placed along the sides of the car, and connected
with a stove containing hot-water coils at one end of the car.
The water, as it is heated in the stove or heater, expands, and
consequently becomes lighter per cubic inch or other unit of volume;
it therefore tends to rise when balanced against the colder water in
the car pipes. Hot water leaves the top of the heater, flows up to
an expansion tank and then down through the car piping, and back to
the bottom of the heater. The car piping slopes continuously down from
the top connection to the bottom connection of the heater. At the top,
an opening to the atmosphere is provided through a small water tank,
called an _expansion tank_. This prevents water pressure bursting the
pipes as they become heated, and allows any steam that may have formed
to escape. The most modern hot-water heaters for cars are completely
closed except as to the ash pit at the bottom and a small feed door in
the top. The latter is locked so that the fire cannot come out even
if the car is tipped over in a wreck. Fig. 31 shows the pipes of a
hot-water heating installation.
[Illustration: Fig. 31. Pipes for Hot-Water Heating.]
CAR WIRING.
The wires from motors to controllers, when placed in exposed position
under the car, are bunched in cables or covered with hose. In some
cases special runways are provided in the bottom of the car to
accommodate the car wiring. All the wiring in a car should be heavily
insulated with moisture-proof rubber-covered wire, and further
protected from mechanical abrasion by a tough outer covering.
Stranded rubber insulated wire is used almost exclusively for wiring
all parts of the car. A general idea of the path of the motor circuit
wiring may be obtained by reference to Fig. 22. The main lead after
leaving the trolley stand is cleated to the trolley board on top of
the car. At the end of the car it passes through the roof and to the
circuit breaker. On leaving the breaker it is led down a post, through
the floor and to the choke coil and lightning arrester underneath the
car. It then passes to the trolley terminal of the controller.
The tap for the light wiring (although shown otherwise in the drawing)
is usually taken off the main circuit before the circuit breaker is
reached. This arrangement allows the lamps to be burned when the
circuit breaker is open. After passing through fuses and switches in
the motorman’s cab the circuit for the lights is led through the car in
moulding concealing it.
The wires running between the motors, controllers and resistance
frames underneath the car, as has been stated, are often carried in
canvas hose. Usually two cables are made up, for should all the wires
necessary be placed in one cable this would become too bulky to be
properly cleated up. To make the canvas hose waterproof and to prolong
its life it is usually given several coats of asphaltum paint.
The wiring of the new cars of the New York subway is an example of
the most advanced practice. All the wires under the cars are carried
in “loricated” conduit, which consists of a wrought-iron tube heavily
enameled both inside and out. The motor leads and the other larger
wires are carried in separate conduits. The conduits are usually hung
to the steel beams of the floor framing by strap bolts. This method of
wiring gives a reasonable assurance that it will not become defective.
Moreover, it lessens fire risk. The conduits are all grounded and
should one of the wires come in contact with the conduit carrying it,
the dead ground resulting would cause the fuse to blow instantly, and
all danger would cease.
RESISTANCES.
The type of resistance now most common for heavy motor equipment is in
the form of cast-iron grids, which are assembled together and connected
in series. These grids are sufficiently stiff to render unnecessary any
solid insulation between them, and hence they can radiate heat to the
best advantage. The only difficulty experienced with them is from the
warping or cracking. Resistances for lighter equipment are composed of
sheet-steel ribbons wound in coils. Each turn of a coil is insulated
from the next by asbestos. Other forms of sheet-steel resistance with
asbestos insulation between the turns, have also been used. In Fig. 32
is shown a Westinghouse grid type diverter for street railway equipment.
ELECTRIC CAR ACCESSORIES.
=Canopy Switch.= An overhead switch, sometimes called a “canopy
switch,” is commonly placed over each street-car platform where
a controller is located, usually in the deck or canopy above the
motorman’s head. This is simply a single-point switch that may be used
by the motorman to cut the trolley current off from the controller
wiring so that the controllers will be absolutely dead. When two such
switches are used, one on each end of the car, they are connected in
series.
[Illustration: Fig. 32. Grid Type of Resistance.]
=Car Circuit Breaker.= Frequently on large equipments an automatic
circuit breaker is provided instead of this overhead switch. This
circuit breaker can be tripped by hand to open the circuit whenever
desired; and is also equipped with a solenoid magnet, which can
be adjusted so that it will trip or open the circuit breaker at
approximately whatever current it is set for. This circuit breaker
protects the motor and car wiring from excessive current, such as would
occur in case of a short circuit in motors or car wiring, or in case
the motorman turned on current so rapidly as to endanger the windings
of the motors. Circuit breakers, however, are most commonly used on
cars having controllers located at only one end in a motorman’s cab.
=Wiring of Circuit Breakers and Canopy Switches.= Figs. 33, 34, and 35
show the methods of wiring circuit breakers and canopy switches for
double-end cars.
[Illustration: Fig. 33.]
In the parallel connection as shown in Fig. 33, the trolley leads after
passing through the choke coils go directly to the blow-out coil of the
controllers. Aside from the fact that two lightning arresters and choke
coils are required, this method is preferable for automatic circuit
breakers.
[Illustration: Fig. 34.]
Fig. 34 shows the hand-operated circuit breakers connected in series.
This method is used where non-automatic breakers are employed, but for
automatic breakers it has the objection that an overload would throw
the breaker set at the lowest point. This might be the breaker on the
opposite end to that occupied by the motorman and in such an event
would necessitate a trip to the other end to set the breaker. Fig.
35 shows a method of parallel connection requiring but one lightning
arrester. This method has the objection that the motorman on the front
end would have no assurance that by throwing the breaker over him the
power would be cut off. The rear breaker might have been carelessly
left set.
[Illustration: Fig. 35.]
[Illustration: Fig. 36.]
=Fuses.= A fuse is placed in series with the motor circuit before it
enters the controller wiring, but where circuit breakers are used
instead of canopy switches, the fuse box may sometimes be dispensed
with. The fuse box on street cars is usually located underneath one
side of the car body where it is accessible for replacing fuses, but
where a motorman’s cab is used, the fuse may be placed in the cab. The
fuse may be of any of the types in common use, either open or enclosed.
In the Westinghouse fuse box it is necessary only to open the box
and drop in a piece of straight copper wire of the right length and
size. The closing of the box clamps this wire to the terminals and
establishes a circuit through the copper wire as a fuse. Of course this
copper wire is of small enough size to be fused by a dangerously heavy
current.
=Lightning Arresters.= A lightning arrester is used on all cars taking
current from overhead lines. The lightning arrester is connected to
the main circuit as it comes from the trolley base, before it reaches
any of the other electrical devices on the car, so that it may afford
them protection. A common type of lightning arrester is shown in Fig.
36. One terminal of the lightning arrester is connected to the motor
frame so as to ground it, and the other is connected with the trolley.
In most forms of lightning arrester, a small air gap is provided, not
such as to permit the 500-volt current to jump across, but across which
the lightning will jump on account of its high potential. To prevent
an arc being established across the air gap by the power house current
after the lightning discharge has taken place and started the arc, some
means of extinguishing the arc is provided. In the General Electric
Company’s lightning arrester, the arc is extinguished by a magnetic
blow-out, which is energized by the current that flows through the
lightning arrester. The instant the discharge takes place the current
flows across the air gap. The magnetic blow-out extinguishes the arc,
and this opens the circuit, leaving the arrester ready for another
discharge. In the Garton-Daniels lightning arrester a plunger contact
operated by a solenoid opens the circuit as soon as current begins to
flow through the arrester. This plunger operates in a magnetic field,
which extinguishes the arc. A choke coil, consisting of a few turns
of wire around a wooden drum, is placed in the circuit leading to the
motors at a point just after it has passed the lightning arrester tap.
This choke coil is for the purpose of placing self-induction in the
circuit, so that the lightning will tend to branch off through the
lightning arrester and to ground, rather than to seek a path through
the motor insulation to ground.
[Illustration: Fig 37. Diagram of Light Circuit.]