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 C.  External power or auxiliary power unit (APU) generator power is used during ground operations and maintenance.
 D.  The EPGS is controlled with switches provided on the flight deck control panel which directs the automatic and manual operation of the system.
 E.  The bus control units (BCUs), generator control units (GCUs), and the auxiliary generator control units (AGCUs) control, protect, and regulate the EPGS in the automatic and manual modes of operation.
 F.  Standby power provides ac and dc power to the fight critical loads when the primary source is lost.
 G.  The main and APU batteries and the transformer rectifier units (TRUs) supply the dc voltage required for all dc loads.
 H.  Both ac and dc power is distributed to the many loads throughout the
 airplane from the EPGS buses.Generator Drive System (AMM 24-11-00)
______________________
 A.  The integrated drive generator (IDG) is attached to the engine-driven gearbox by means of a quick-attach detach (QAD) ring. Each IDG consists of a constant speed drive (CSD) and a generator all within the same housing.
 (1)  
The CSD is used to convert the variable engine speed to a constant 12,000 RPM to drive the generator.

 (2)  
The generator is a spray oil cooled, salient-pole, brushless, rotating rectifier, synchronous generating device which supplies the 115 volt ac three phase power.

AC Generation (AMM 24-20-00)
_____________
 A.  The 115 volt ac power is provided to the main ac buses by the IDGs. The APU generators may also power the main ac buses for ground operation and maintenance.
 B.  The two APU generators are connected to the APU load gearbox by QAD rings.
 C.  Protection from transient voltages is provided by lighting protectors installed on each main IDG feeder.
 D.  Manual and automatic control of the EPGS is accomplished by the switches provided on the flight deck control panel. These switches then direct the BCU, GCU, and AGCU to perform automatic control and regulation of the EPGS system.
 E.  The 115 volt ac single phase standby power is provided by the static inverter to power the flight critical loads if the primary power is lost.
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MAINTENANCE MANUAL

 F.  The APU static inverter provides 115 volt ac power and shares the flight critical loads with the ac standby bus.
 4.  DC Generation (AMM 24-30-00)
_____________
 A.  The main battery/battery charger system provides 24/28 volt dc power for the main hot battery bus.
 B.  The APU battery/battery charger system provides 24/28 volt dc power for the APU hot battery bus.
 C.  The main and the APU hot battery buses are the source of dc standby power if the primary power is lost.
 D.  Four main TRUs provide the 28 volt dc power to the four main dc buses.
 E.  A main deck cargo handling TRU is used to supply 28 volts dc power for control and relay operation associated with loading and unloading the main cargo deck.
 5.  AC External Power (AMM 24-41-00)
_________________
 A.  The 115 volt ac three phase power, from a ground power source connected to the two airplane external power receptacles, supplies power to all the load buses for ground operations and maintenance.
 B.  The external power also supplies the ac ground handling bus through external power recptacle No. 1.
 C.  External power TRUs utilize power from the ac ground handling bus and convert it to 28 volts dc for the dc ground handling bus.
 6.  AC Electrical Load Distribution (AMM 24-50-00)
_______________________________
 A.  The four main ac buses are powered by their own IDG through the generator circuit breaker (GCB) or by the other IDGs through the sync bus via the bus tie breaker (BTB) and the split system breaker (SSB) for parallel operation. The APU generators or external power supplies power to the sync bus via the auxiliary power breakers (APB), or the external power contactors (XPCs) to provide power to the four main ac buses when all four BTBs are closed.
 B.  The 115 volts ac is supplied from the main ac buses to the three main ac distribution centers.
 C.  Protection and control of the ac power distribution is provided by electrical load control units (ELCUs) for the galley and utility power and by thermal circuit breakers (TCBs) for all other circuits.
　
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