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747-400 MAINTENANCE MANUAL
 115-VOLT AC POWER GENERATION AND PROTECTION -
_____________________________________________ DESCRIPTION AND OPERATION
_________________________
General
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 A.  115-volt ac power is supplied to the ac load buses by four integrated drive generators, one installed on each engine.
 B.  The load buses may also be powered from the two auxillary power unit generators for ground operation.
 C.  Lightning protectors are installed to assure that transient voltages
 remain within design limits even during a lightning strike.Integrated Drive Generator (Fig. 1)
__________________________
 A.  The primary electrical power system is 115/200 volt, 400 Hz, three phase, Wye (Y) connected, with the neutral point connected to the airplane structure. An oil-spray-cooled brushless generator, driven at a constant speed is installed on each engine. Each generator channel is rated at 90 KVA at continuous operation. For further information on the integrated drive generator, refer to Generator Drive System, 24-11-00/001.
APU-Driven Generator (Fig. 2)
____________________
 A.  For ground operation, the APU generators, which are rated at 60 KVA each, are capable of providing 90 KVA continuous electrical load capacity at the generator terminals with sufficient cooling air. The generators are brushless permanent-magnet type, driven at a constant speed of 8000 RPM to provide 120/208 volts, 400 Hz. For further information on the auxillary power unit, refer to Auxilliary Power Unit, 49-11-00/001.
APU Driven-Generator Quick Attach-Detach (QAD) Ring (Fig. 2)
___________________________________________________
 A.  A quick attach-detach (QAD) ring allows rapid installation and removal of the ac generator to and from the auxillary power unit load gearbox. The ring assembly includes a QAD ring and an adapter plate. The ring mates along the outside edge of the adapter plate, which is mounted to the load gearbox.
 B.  A generator mounting flange (on the generator), mates the generator with the QAD ring. The QAD ring secures the generator in a breech-type lockup.
Lightning Protectors (Fig. 3)
____________________
 A.  Lightning strikes on the aircraft induce transients on the feeders between load busses and the generators. The purpose of the lightning protectors is to attenuate these transients to a level consistent with the electrical equipment capability. One protector is connected to each phase of each main ac bus while electrical power is supplied by its respective IDG. These protectors serve to limit induced voltage on the IDG feeders to |252-275 volts.
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747-400
MAINTENANCE MANUAL

SEE A
INTEGRATED DRIVE GENERATOR
SEE B
MAIN GEARBOX
A
MAIN GEARBOX
QAD
RING

INTEGRATED DRIVE GENERATOR
OIL-IN LINE
TERMINAL
BLOCK
OIL-OUT B LINE
Integrated Drive Generator Location Figure 1
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747-400
MAINTENANCE MANUAL

SEE B
SEE A
CONNECTORS ELECTRICAL 
A  FWD 
APU GENERATOR 2 
ADAPTER QAD RING PLATE  BLOCK TERMINAL  WITH CONNECTOR PHASE LEAD 

CONNECTORS ELECTRICAL 
APU GENERATOR 1 
B  APU LOAD GEARBOX  WITH CONNECTOR PHASE LEAD 
Figure 2 APU-Driven Generator Location 

L97017
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747-400 MAINTENANCE MANUAL
　
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