GENERAL MOTOR DIESEL LOCOMOTIVE. Manual - part 14

IRCAMTECH/2006/M/D/GM loco/1.0

Introduction hand book on GM locomotive February 2006

Emergency Application:

An emergency application means to apply brakes at

the maximum rate. When the brake valve handle is placed in
the emergency position, ER reduces at the faster rate to zero
pressure and also the brake valve mechanically opens a vent
valve. In addition the brake controller is provided with a switch
which opens sending an emergency signal to the computer.
Then the computer energizes an emergency magnet valve
(MVEM). The opening of MVEM vents the pilot port of the high
capacity BP relay pneumatic valve (PVEM) exhausting BP
pressure.

Automatic Brake Application on Loco:

The brake pipes transducer (BPT) provided in the BP

pipe detects the reduction in BP and sends signal to computer.
The computer calculates the required brake cylinder pressure
and commands the BC analog converter to maintain the
desired rate of pressure level in the brake cylinder. The brake
cylinder analog converter operates a BC magnet valve. The
output pressure of the BC magnet valve work as a pilot
pressure for the BC relay valve. BC relay valve is a self
lapping pressure maintaining pneumatic valve which will come
to the lap position when matches with the BC pilot air
pressure. The application is complete if the BC pressure is
maintained at the level commanded by the computer until the
brake valve handle is again moved.

Bail-Off Automatic Application:

When the automatic brake is applied lifting the bail-off

ring provided in the independent brake valve handle in any
position will release the brake cylinders of the loco.

On the LEAD UNIT, the CCB computer commands the

BC analog converter to release the pilot air pressure which in
turn drives the BC relay valve to release the BC pressure, if an
emergency brake has been mad, the brake will reapply to
maximum as soon as the bail off ring is released.

IRCAMTECH/2006/M/D/GM loco/1.0

Introduction hand book on GM locomotive February 2006

NOTE;-If the bail-off continuous for longer than 50 seconds
the BC pressure will be restored and a fault will be
displayed on the EM 2000 display screen. The crew
messages the center point of display and it will indicate
fault condition that required immediate attention.

Independent Brake Operation:

According to the independent brake valve controller

handle position, signals from the brake valve handle will go to
the fibre optic receiver (FOR) and then to he computer.
Computer will send signals to the BC analog converter. The
analog converter operates the BC relay valve. BC relay valve
is a self lapping pressure maintaining pneumatic valve which
will come to the lap position when matches with the BC pilots
air pressure.

Any leakage in the BC pipe will be noticed by the BC

transducer (BCT) and the feed back signals will go to CCB
computer. Then computer will in turn take corrective action to
maintain BC pressure. The BC equalizing pipe (BCEP) is used
to supply air to end from all the trailing units of the locomotive
consist to control application and release of both automatic
and independent brakes. The only exception to this operation
is locomotive consist separation.

According to the service positions of the brake

controller valve handles, CCB computer gets signals from the
FOR. Then the computer sends the signals to BCEP analog
converter to supply piloting air pressure to BCEP relay valve.
When the BC pressure equalizes BCEP, the BCEP relay valve
moves to LAP position.
Maximum BCEP = 3.7Kg/Cm

Introduction Of Blended Brake System

The passenger service locomotive is equipped with a

blended brake system. It simultaneously applies dynamic
braking and air braking when the driver operates the automatic
air brake handle in the service zone.
The Knorr CCB air brake system controls the air brakes on the
locomotive and carriages coupled in trains, and requests the

IRCAMTECH/2006/M/D/GM loco/1.0

Introduction hand book on GM locomotive February 2006

required amount of dynamic braking from EM 2000 computer
for blended brake operation.

IRCAMTECH/2006/M/D/GM loco/1.0

Introduction hand book on GM locomotive February 2006

ELECTRICAL SYSTEM

Power Distribution system in GT46MAC locomotives

The diesel engine is the source of locomotive power,

when the engine is running it directly drives three electrical
generators:

1.  Main generator (traction alternator)
2.  Companion alternator
3.  Auxiliary generator

Main generator (traction alternator)

The main generator (traction alternator) rotates at

engine speed generating AC power. Rectifiers are covered
within the generator assembly. The rectifiers convert the AC
power to DC, and the DC output is applied to DC link. Switch
gear and contractors supply DC voltage to traction inverter
circuits. The traction inverters convert the DC link voltage to 3-
phase AC power for the traction motors. There are two
separate computers TCC1 and TCC2 which control the
traction motors by varying the voltage and frequency which is
fed to traction motors to get the proper torque and speed i.e.,
the out put from traction motors.

Companion alternator

The companion alternator is directly coupled to the

traction alternator and is within the main generator assembly
itself. Output is utilized for the following:

• To excite the main generator (traction alternator) field.

• To drive the two rectifier cooling fan motors.

• To drive the inertial blower motors.

• To drive the traction inverter blowers.

• Various transducers and control devices.

Auxiliary generator

The auxiliary generator is driven by engine gear train.

The output of aux. Gen. is converted to74V DC in a rectifier
&output from the rectifier is utilized for the following:

• To excite the companion alternator fields.

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