TM 55-1520-240-23-7
9-30
ALTERNATING CURRENT (AC) POWER DISTRIBUTION
(Continued)
9-30
POWER DISTRIBUTION PANEL
Two power distribution panels (PDP) are the electrical
load centers for the ac power distribution system. The
panels contain circuit breakers, relays, and transformers
associated with both power systems.
NO BREAK - WORK HARDER
The No. 1 PDP is outboard of the copilot seat on the
left side of the cockpit. Its contents are associated with
the No. 1 ac system and it services the left side of the
helicopter.
NO BREAK - WORK HARDER
The No. 2 PDP is outboard of the pilot seat on the right
side of the cockpit. Its contents are associated with
the No. 2 ac system. It services the right side of the
helicopter.
NO BREAK - WORK HARDER
The following major components are in one or both PDP:
NO BREAK - WORK HARDER
Circuit Breakers (No. 1 and No. 2 PDP): All of
the helicopter ac circuit breakers are on one or
the other PDP. All 5 through 50 ampere circuit
breakers are single-hole mounted. The 70 ampere
ac and 100 ampere dc bus tie circuit breakers are
mounted with screws, nuts, and washers.
NO BREAK - WORK HARDER
Main Generator Current Transformer (No. 1
and No. 2 PDP): Feeder current from the main
generators passes through coils in the transformer,
inducing voltages that are routed to the generator
control unit, where they are used to detect ground
fault currents.
NO BREAK - WORK HARDER
APU Generator Feeder Current Transformers
(No. 2 PDP): Feeder current from the APU
generator passes through coils in the three current
transformers, inducing voltages that are routed
to the APU generator control unit in the right
electrical compartment, where they are used to
detect ground fault currents.
NO BREAK - WORK HARDER
Instrument Transformer (No. 1 and No. 2 PDP):
This transformer steps down 115 vac to 26 vac to
operate cockpit instruments.
NO BREAK - WORK HARDER
Lighting Transformer (No. 1 and No. 2 PDP): This
transformer steps down 115 vac to 26 vac to
operate instrument lamps. It is installed only on
helicopters without 17 .
NO BREAK - WORK HARDER
Generator Contactor (No. 1 and No. 2 PDP):
This contactor connects generator output to
its associated ac bus. It also controls various
monitoring and control functions through sets of
auxiliary contacts.
NO BREAK - WORK HARDER
External Power Contactor (No. 1 PDP): When
energized in one mode, this contactor connects
ac external power to the No. 1 ac bus. In another
mode, it provides part of the crosstie connection
between No. 1 and No. 2 ac buses.
NO BREAK - WORK HARDER
APU Generator Contractor (No. 2 PDP): When
energized in one mode, this contactor connects
power from the APU generator to the No. 1 ac
bus. In another mode, it provides part of the
crosstie connection between No. 1 and No. 2
when external power is applied.
NO BREAK - WORK HARDER
APU Generator Slave Relay (No. 2 PDP): This relay
disconnects the APU generator from the ac buses
when either main generator is operating. It also
provides a portion of the logic that determines the
operating mode of the external power contactor
and the APU generator contactor.
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