TM 1-1520-238-10
Change 3
2-67
to the ac essential buses. The No. 1 ac contactor con-
nects the No. 1 generator output to the No. 1 essential ac
bus, and the No. 2 ac contactor connects the No. 2 gener-
ator to the No. 2 essential ac bus. If one generator fails, its
load is automatically connected to the remaining genera-
tor.
a. Generators.
Two generators, located on the
main transmission accessory gearbox, supply 115 vac,
three-phase power for operating the helicopter electrical
equipment. Generator operation is controlled from the pi-
lot ELEC PWR control panel (fig 2-37). When a generator
control switch is in GEN 1 or GEN 2 position, the selected
generator(s) are brought on-line. When the switch is
placed to OFF/RESET, the generator is taken off-line and
fault sensing is reset. Two caution lights, GEN 1 and
GEN 2 on the pilot caution/warning panel illuminate when-
ever the generator control unit senses a fault. These lights
receive 28 vdc from the emergency dc bus through the
CAUT circuit breaker on the pilot overhead circuit breaker
panel (fig 2-39).
b. External Power Receptacle.
The external pow-
er receptacle is located aft of the aft avionics bay. It pro-
vides a means of connecting external power to the heli-
copter. A microswitch, which is actuated by opening the
external power access door, informs the pilot when the
door is open by illuminating the EXT PWR caution lamp
on his caution/warning panel. The system is controlled
from the ELEC PWR control panel. When the BATT/EXT
PWR switch is at EXT PWR position, the external power
monitor checks the GPU for proper phase sequence, volt-
age, and frequency. The power monitor also inhibits con-
necting and charging of the battery. The EXT PWR cau-
tion light receives 28 vdc from the emergency dc bus
through the CAUT circuit breaker on the pilot overhead
circuit breaker panel (fig 2-39).
M01-203
Figure 2-37.
Pilot Electrical Power Control Panel
