1.42.
MULTIPLE- UNIT EQUIPMENT
When locomotives are connected but their power systems remain independent, the process is
known as doubleheading. However, if electrical connections are made and all locomotives are
controlled from one cab, it is called multiple-unit operation. Equipment for connecting units in multiple
consists of a jumper with the following control wires: control switch, forward-reverse control, throttle,
sanding, and alarm and indicating circuits, and emergency shutdown switches. The wires are connected
to a plug which is keyed in such a way that it can be inserted in the end receptacle of the locomotive in
the correct position only. The locomotive from which operation is controlled is called the leading unit
and the others trailing units. On all trailing units, engines are started and battery switches closed before
operation begins.
1.43.
AUXILIARY POWER SYSTEM
The auxiliary generator is used to charge the storage battery and to power the low-voltage circuits
for lighting, control equipment, fuel pump motor, and field excitation. It may be driven by belt or gear
from the shaft of either the engine or the main generator and is usually mounted on the generator's frame.
The auxiliary generator assumes the load after the battery has supplied power for starting the engines.
A breaker-type switch or a fuse disconnects the auxiliary generator; if this switch or fuse is open,
the battery must supply all low-voltage requirements. Many locomotives also have an auxiliary
generator field switch; it is opened when the locomotive is shut down and kept open until after the
engines are started again. On locomotives having both these switches, the field switch is in the
equipment cabinet.
a. Voltage regulation. The auxiliary generator output is regulated by changing the strength of
the auxiliary generator field; if the speed of the auxiliary generator increases, the shunt field strength
must be decreased to maintain a constant voltage. A regulator may consist of a small torque motor or of
relays which are sensitive to changes in voltage. The movement of these elements changes the resistance
in the field circuit. The operating principle of the voltage regulator is that the voltage generated is
proportional to the shunt field strength. The voltage regulator increases the resistance of the field,
thereby reducing the flux. If such external conditions as generator speed, load, or internal shunt field
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