H20863
CSD Sight Glass Installation 501
24-11-51 Figure 401 Jan 20/82
Page 402
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
AC GENERATION SYSTEM - DESCRIPTION AND OPERATION
1. General
A. Energy for operation of all electrical loads on the airplane except when external power is used is provided by three 3-phase, 115/200 volt, 400- cycle, alternating current systems (See figure 1.) Two of these electrical generating systems are driven from the accessory gearbox on the engines by a hydromechanical constant speed drive unit (CSD), to supply constant frequency ac electrical power. When the engine is operating within its normal speed range, power of the correct frequency is delivered through the CSD to the electrical system. Neither of the engine driven systems is arranged to be operated nor connected in parallel with the other system and attempts should not be made to alter connections to obtain parallel operation. A third power unit (auxiliary power unit ) is mounted to the airplane structure in the tail cone. For further details on the auxiliary power unit (APU), refer to Chapter 49. An external power receptacle is installed which enables using a conventional ground power unit for furnishing ac power on the ground. Switching is provided so that external power may be fed throughout the airplane by closing the external power contactor, which ties the ground power unit to the tie bus. Alternatively, external power may be fed only to selected ground servicing circuits. The APU generator cannot be operated in parallel with external power, nor can either of the ground power sources be operated in parallel with the airplane generators
B. Standby ac power is available when no other 400 cycle source is operating. An inverter, energized by 28 volt dc power from the storage battery, supplies single-phase 400-cycle 115 volt power for critical communication and navigation equipment. This inverter and standby power transfer relays No. 1 and No. 2 connect to ac and dc busses to make up the standby power system. The inverter is located adjacent to the battery charger in the E3 electrical/electronic equipment racks in the electronic compartment. (See figure 1.)
C. There are certain dc components required for control of the generation systems which are located in the electrical equipment racks. Except for circuit breakers on the P18 panels, most of the ac electrical power control components are located on the P6 panels. (See figure 1.) The space adjacent to and forward of equipment racks E3-1, E3-2, E3-3 and E3-4 contain the battery, the battery shunt and the battery charger thermal switch. The battery charger, T-R units No. 1, No. 2 and No. 3, and the standby static inverter are on equipment rack E3-1 to the right of the electronic compartment access door in the lower forward fuselage. The APU control unit module (M280) is beneath the No. 1 T-R unit on the E3-3 rack. (See figure 1.)
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May 15/68 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 24-21-0 Page 1
H20939 H21188
AC Generation System Component Location 500
24-21-0 Figure 1 (Sheet 1) Nov 15/68
Page 2
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
525 AC Generation System Component Location
Feb 15/71 Figure 1 (Sheet 2) 24-21-0
Page 3
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
D. The generator control unit (GCU) is a multi-purpose device for regulating voltage, supplying exitation power, limiting power output, and protecting the generating system against a variety of electrical faults. The GCU contains protection circuits which shut down a generator when a deviation from normal operation occurs. The unit also contains an anticycling feature for instances when a control switch is manually held ON by a crew member. The GCU for each generator and for the APU generator are the same. A separate bus protection panel provides for the external power circuits and equipment and contains protective features for negative sequence, high phase overvoltage, undervoltage, and anticycling. The generator control units and bus protection panel are in the P6 panel on the control cabin aft bulkhead. (See figure 1.) A functional block diagram of the generator control unit is shown on figure 4.
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