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The Generator Control Unit (GCU) also provides generator
feeder fault protection. If a fault occurs between the
feeder and the airframe, the GCU will disable the generators.
This prevents structural damage to the airframe
when a ground fault occurs.
The Permanent Magnet Generator (PMG) section within
the generator is used to power the main contactors (relays)
in the distribution system. A pickoff coil within the
PMG provides an RPM signal for the rotor tachometer
indicators. This tachometer signal is available whenever
the rotor are turning.
2-11-3. Generator Control Switches.
The generator control switches are located on the ELEC
panel of the overhead switch panel (fig. 2-11-2). The
three switches are labeled GEN 1, GEN 2, and GEN
APU. The switch positions are TEST, OFF RESET, and
ON.
TM 1-1520-240-10
2-11-2
When the switches are ON, the respective main relay
operates, which energizes and connects the generator to
the buses. At OFF RESET, the generator is deenergized
and disconnected from the bus. This position is also used
to reset a generator. The TEST position is provided to
allow the generator to be energized but disconnected
from the bus to determine whether the AC produced is of
proper frequency and voltage, except the APU generator.
Figure 2-11-2. Electrical Power Panel
2-11-4. GEN OFF Cautions.
Two generator caution capsules labeled 712 NO. 1
GEN OFF and NO. 2 GEN OFF, 714A GEN 1 AND GEN
2 are on the master caution/advisory panel ( 712 fig.
2-14-5 714A fig. 2-14-6).These caution capsules illuminate
whenever the generators are in operative.The capsules
are controlled by the main generator contactors
when the generator control switches are in either ON or
OFF RESET.In TEST, the capsules are controlled by the
generator control switch and will extinguish if generator
output has the proper frequency and voltage.Power to
operate the generator capsules is supplied by the DC
essential bus through the LIGHTING CAUTION PNL circuit
breakers on the No. 1 PDP.
2-11-5. EXT PWR Caution.
CAUTION
When external power is used, a visual
check shall be made by the crew to ensure
that the external power unit has been disconnected
from the helicopter before taxiing.
An external power caution capsule labeled EXT PWR is
on the master caution panel (fig. 2-14-5 and fig.
2-14-6).This capsule illuminates and remains illuminated
whenever external power is connected.The light is controlled
by the AC external power contactor and the DC
power relay.The capsule extinguishes when the generators
are supplying current to the buses.Power to operate
the external power caution capsule is supplied by the DC
essential bus through the LIGHTING CAUTION PNL circuit
breaker on the No. 1 PDP.
2-11-6. DC System.
The direct current (DC) power supply system supplies
28-volt DC from the No. 1 transformer rectifier (RECT) to
No. 1 DC bus and the No. 2 RECT supplies power to the
No. 2 DC bus (fig. FO-4 and FO-7).RECT convert 200
VAC power to 28-volt DC power for use in the DC distribution
system.
Cooling air for the RECTS is obtained from within the
cabin.The air inlets are located at sta. 176 on the left and
right side of the cabin behind the troop seats.If the inlets
are blocked, the RECTS will overheat.
A bus-tie relay is between No. 1 and No. 2 DC buses.If
either RECT fails, the respective RECT failure relay operates
and the bus-tie relay closes automatically to connect
the unpowered bus to operating RECT.In addition to
No. 1 and No. 2 DC buses, the DC system includes an
essential bus, a switched battery bus, and a hot battery
bus.
During normal operation, the essential bus and the
switched battery bus are energized by No. 1 DC bus.If
both DC buses fail or if NO. 1 DC bus fails and does not
bus-tie to No. 2 DC bus, the essential bus, the switched
battery bus, and the hot battery bus will be energized by
the battery as long as the BATT switch is ON.These
buses provide power to emergency, ground maintenance,
and communications components.The hot battery
bus and switched battery bus are energized as long
as the battery is connected.The hydraulic reservoir level
indicators and the emergency APU control circuits and
cabin and maintenance lights are on these buses.
The 24-volt nickle cadmium battery is located in the left
forward electrical compartment.The battery capacity is
11 ampere-hours.A battery charger is connected to the
battery.The battery charger receives power from No. 1
AC bus, rectifies the AC and applies the DC to the battery
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