TM 55-1520-240-23-7
9-30
ALTERNATING CURRENT (AC) POWER DISTRIBUTION
9-30
DESCRIPTION
Alternating current (ac) is the primary source of electrical
power for the helicopter. The ac power distribution
system has four power sources: two main generators, a
secondary generator, and external power.
NO BREAK - WORK HARDER
The two main generators are mounted on and driven
by the aft transmission. The secondary generator is
mounted on and driven by the auxiliary power unit.
A receptacle for connecting external power to the
helicopter is at the forward end of the left pod.
NO BREAK - WORK HARDER
Each power source delivers 115 volt 3-phase power to
one or both of two ac buses. The buses distribute the
power to all ac electrical components on the helicopter.
Each of the power sources has its own control unit,
panel, or monitor that ensures that it is operating
properly before its output is delivered to the buses.
NO BREAK - WORK HARDER
During normal operation, with rotors turning minimum of
85 percent, the No. 1 generator, driven off the left side
of the aft transmission, supplies power to the No. 1 ac
bus. The No. 2 generator, driven off the right side of the
transmission, powers the No. 2 bus. When either main
generator is running, output from the auxiliary power unit
(APU) and external power is blocked from the buses.
NO BREAK - WORK HARDER
If the main generators are not operating, but the auxiliary
power unit is running, the APU generator supplies power
to both ac buses. When the APU generator is operating,
the external power circuits are blocked from the ac bus.
Only if both the main and the secondary generators are
not operating can external power be used to supply the
ac buses.
NO BREAK - WORK HARDER
Control switches for each of the three generators are on
the overhead ELECT panel in the cockpit. The master
caution panel has lights to indicate the status of the
system.
NO BREAK - WORK HARDER
Most of the electrical connectors used on the aircraft
have a fully-coupled indicator which is utilized to
prevent over or under engagement of the connector
by the installer, and is also utilized during inspection
as a quick visual indication of proper installation. This
indicator consists of three axial stripes, usually blue
in color, placed on the plug shell which will align with
three corresponding stripes on the coupling ring when
completely coupled. Do not over-tighten the coupling
ring beyond the blue stripes.
9-84
