*
TRU C1 & C2 supply power

*
The two flight instrument buses lose power.

All of the conditions that energize the captain-F/O bus tie relay also enable the flight instrument bus fault logic. The dc subsystem card monitors TRU current and bus voltage to detect a bus fault. If the card detects a fault, the relay is de-energized and the fault logic latches. The logic is reset at system power-up or with the MAT special function test: INITIATE P310 EU SELF TEST.
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TRU -FUNCTIONAL DESCRIPTION -CAPT & F/O FLIGHT INSTRUMENT DC BUSES

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STANDBY POWER -GENERAL DESCRIPTION

General
The standby power system operates when the normal electrical power sources do not supply power to the left and right transfer buses. Standby power goes to these buses:
*
Captain’s flight instrument bus

*
First officer’s flight instrument bus

*
Battery bus

*
Battery bus #2

*
Hot battery bus

*
AC standby bus.

Standby power comes from either the RAT generator or the main battery. ELMS controls the standby system relays. The battery switch and the standby power switch send control signals to the ELMS.
Rat Generator
The RAT generator supplies 7.5 kva of ac power to the two center TRUs. The RAT GCU monitors and controls the output of the RAT. The TRUs change the ac power into 28v dc power and supply it to the captain’s and first officer’s flight instrument buses.
The captain’s flight instrument bus supplies power to the battery bus and battery bus #2.
EFFECTIVITY
BEJ ALL

The battery bus supplies power to the hot battery bus and the ac standby bus. Power to the ac standby bus goes through the static inverter. The static inverter changes 28v dc power into one phase of 115v, 400 Hz, ac power.
Main Battery
The main battery supplies 28v dc power to the standby system if the RAT generator does not.
To supply power to the standby system, the main battery supplies power to the hot battery bus. The hot battery bus supplies power to the battery bus.
The battery bus supplies power to the captain’s flight instrument bus. The captain’s flight instrument bus supplies power to battery bus #2.
The battery bus supplies power to the static inverter, so that the ac standby bus has power.
Operation
The standby power switch on the P61 overhead maintenance panel has three positions:
*
OFF

*
AUTO

*
BAT.

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STANDBY POWER -GENERAL DESCRIPTION

The BAT position is a momentary position. The standby power switch permits you to do these functions on the ground only:
*
De-energize the ac standby bus (OFF position)

*
Arm the standby system for automatic operation (AUTO position)

*
Energize the standby buses when ac power is not available (BAT position, when the battery switch is in the ON position)

*
Start a self-check of the dc/standby system (BAT position, when ac power is available).

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777 AIRCRAFT MAINTENANCE MANUAL

STANDBY POWER -GENERAL DESCRIPTION

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STANDBY POWER -RAT GENERATOR

General
The RAT generator supplies ac power when normal power sources are not available. The RAT generator supplies power to TRU C1 and TRU C2 for the standby system buses.
Physical Description
The generator capacity is 7.5 kva. It has two electrical connectors. One connector carries RAT GCU signals and power. The other carries the generator output to TRU C1 and TRU C2.
The generator contains these parts:
*
Permanent magnet generator (2)

*
Exciter

*
Main generator

*
Heater (2).

The main generator makes three-phase ac power. The voltage is 115 volts. The frequency is the result of the rotational speed of the of the RAT propeller/governor unit. The frequency range is from 392 Hz to 510 Hz.
There are two heaters in the RAT generator that prevent ice. The hydraulic interface module (HYDIM) cards control the heaters through the ELMS. See the ram air turbine system section for more information on the heaters (SECTION 29-20).
Location
Eight bolts attach the RAT generator to the RAT strut. The RAT propeller/governor unit attaches to the front side of the generator. The hydraulic pump attaches to the aft side of the generator. See the ram air turbine system section for more information on the RAT (SECTION 29-20).
　
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