TM 55-1520-240-23-7
9-30
ALTERNATING CURRENT (AC) POWER DISTRIBUTION
(Continued)
9-30
MAIN AC GENERATOR
Each of the two 40 kilovolt ampere (kva) 3-phase
400 Hz ac generators (alternators) is mounted on and
driven by the aft transmission. The generators are oil
cooled and brushless. Phase rotation of the generators
is A-B-C, with phase-to-phase potential of 208 volts,
regulated to 200 volts. The phase-to-neutral (ground)
potential is 120 volts, regulated to 115 volts. These
generators produce all the ac power required for flight
operation of the helicopter. Oil to cool windings and
lubricate splines and bearings is provided by the main
pump in the transmission oil system.
APU GENERATOR
A 20 kva 3-phase brushless generator (alternator) is
mounted on and driven by the auxiliary power unit
(APU). The generator is air cooled by a built-in fan. As
with the main generators, phase rotation is A-B-C, with
potential between phases of 208 volts, regulated to 200
volts. The potential between each phase and neutral
(ground) is 120 volts, regulated to 115 volts. The APU
generator provides helicopter electrical power during
ground operations.
GENERATOR CONTROL UNITS
The ac electrical system has two main generator control
units (GCU), one for each system. The No. 1 unit is
located in the electrical compartment at the forward
end of the left pod. The No. 2 unit is in the electrical
compartment of the right pod.
NO BREAK - WORK HARDER
Each GCU monitors its generator for under voltage,
over voltage, under-frequency and feeder faults. It also
regulates generator output voltage and controls the
connection of the generator to the distribution system.
NO BREAK - WORK HARDER
When an abnormal condition is detected, the generator
is shut down and disconnected from the ac bus. The
condition also trips an annunciator on the front panel of
the GCU, changing the normal black flag to white. Each
control unit is connected to the helicopter wiring through
one plug and one receptacle.
APU GENERATOR CONTROL UNIT
The APU generator control unit (GCU) is located in the
electrical compartment of the right pod, directly aft of the
No. 2 GCU. It monitors and regulates generator output in
the same manner as the GCU for each main generator.
NO BREAK - WORK HARDER
The control unit is connected to the helicopter wiring
through a receptacle (J9) on the front. A second
receptacle (J6) is connected to a conversion plug to
make the GCU compatible with the brushless APU
generator.
EXTERNAL POWER MONITOR
An external power monitor is located in the electrical
compartment of the left pod. It monitors the applied
input from an external power source for correct voltage,
frequency, and phase sequence. When an abnormal
condition is detected, the external power is disconnected
from the No. 1 and No. 2 ac buses.
NO BREAK - WORK HARDER
The monitor is connected to the helicopter wiring
through one receptacle.
9-88
