APT-P Motor-Alternator

A Motor-Alternator type ASEA GH355MB is fitted in each Van Trailer car to accomodate the electrical loading of approximately 300 KVA of a six vehicle rake of APT-P Trailer Cars, in addition a 50 KVA supply is fed to each Power Car from a Van Trailer car respectively to supply its Tilt and H-K Brake System in a similar manner.

The Motor-Alternator provides the normal auxiliary electrical supply of 415 volts and 250 volts A.C. and has a continous rating of 430 KVA, the input to the M-A is derived from the 25 KV overhead supply which is transformed down to 800 volts single phase A.C. and rectified by means of a thyristor bridge, located in the Power Car, to 510 volts D.C. All the motor controls are in the Power Car.

The 510 volt D.C. supply for the motor is passed to the Van Trailer by means of jumpers using standard 600 amp E.T.H. plug and sockets, due to the current capacity these are paralleled. All controls for the alternator are mounted in the Van Trailer car.

There is a small control panel at the driver's left hand side for control of the M-A and D-A sets. It consists of an on and off switch with indicator for each M-A set Local/Remote and for each D-A set Local/Remote.

M-A and D-A Set Controls
M-A and D-A Control Panel in APT-P Cab.


A 382 KW series wound D.C. motor is used to drive the alternator, the normal motor speed is 1500 r.p.m. with only a ±2% speed variation.


The Alternator is a 430 KVA brushless type, fitted with an Automatic Voltage Regulator to maintain its output voltage to ±6% of 415 volts under normal operating conditions, with varying load. A supply voltage of 415 volts ±6%, 50 Hz ±2% 3 phase is distributed along a 4 wire system, which is the same as the standard industrial supply specification.

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Last Revised: 23.05.2021 10:05
by R G Latham
© 1998