757 MAINTENANCE MANUAL
ELECTRICAL POWER - GENERAL -
____________________________ DESCRIPTION AND OPERATION
_________________________
1. General (Fig. 1)_______
A. The electrical power system consists of a 115-volt ac system, and a 28-volt dc system.
B. AC Electrical Power
(1)
The electrical power system generates and controls 115/200-volt, 3-phase, 400-Hz ac power. Two integrated drive generators (IDGs), one mounted to and driven by each engine, supply main ac power (Ref 24-11-00). An auxiliary power unit driven generator provides inflight backup to the IDGs (Ref 24-21-00). System control is by three generator control units (Ref 24-22-00), and one bus power control unit (Ref 24-41-00).
(2)
The system normally provides two, non-parallelable ac power channels. During a category III autoland, the static inverter is powered from the hot battery bus to provide a third independent ac power channel (Ref 24-33-00).
C. DC Electrical Power
(1)
Two main 28-volt dc power channels are supplied by two transformer rectifier units (TRUs). The TRUs convert main 115-volt ac power (Ref 24-32-00).
(2)
The main battery and its charger provide a backup source for the standby power system (Ref 24-33-00). During a category III autoland, the main battery and its charger provide a third independent dc power channel (Ref 24-33-00).
(3)
GUN 051; The main and APU batteries are paralleled if power is lost at the left 28 volt dc bus. This provides a 90 minute standby power source.
D. GUN 006-103; an independent non-time-limited standby power system is installed on extended range airplanes. 115-volt ac and 28-volt dc power is provided by a hydraulic motor-driven generator which is activated automatically when power is lost at both main ac buses.
E. GUN 104-999; an independent non-time-limited standby power system is installed on the extended range airplanes. 115-volt ac power is supplied by a hydraulic motor generator which is activated automatically when power is lost at both main ac buses. A part of the ac power is transformed and rectified by a transformer/rectifier unit to supply dc power for the dc essential loads.
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757 MAINTENANCE MANUAL
GENERATOR DRIVE SYSTEM - DESCRIPTION AND OPERATION
__________________________________________________
1. General_______
A. The purpose of the generator drive system is to convert mechanical power into electrical power. The major components are two integrated drive generators (IDGs), one mounted to each engine. Each IDG has a corresponding air/oil heat exchanger.
2. Component Details (Fig. 1)_________________
A. Integrated Drive Generator
__________________________
(1) An integrated drive generator (IDG) is located on the left aft side of each engine, and is mounted on the engine accessory gearbox. The IDG converts the varying input speed of the engine into 115/200-volt, 3-phase, 90-KVA, 400|4-Hz power. The IDG weighs 118 pounds.
B. Scavenge Filter
_______________
(1) The scavenge filter is a replaceable component, which filters oil flowing out of the integrated drive generator (IDG). The oil then goes to the air/oil heat exchanger. The scavenge filter is located in the aft end of the IDG housing.
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