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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
757
MAINTENANCE MANUAL
(c)
Tighten the terminal nuts (7) to 144-168 pound-inches (16-19 Newton-meters).
(d)
Install the terminal block cover (6). Tighten the screws (3) to 20-22 pound-inches (2.3 - 2.5 Newton-meters).
CAUTION: ALIGN THE ELECTRICAL CONNECTOR PINS BEFORE INSTALLATION.
_______ IF THE PINS DO NOT ALIGN DAMAGE TO THE CONNECTORS CAN OCCUR.
(e) Install the APU wire harness to the generator electrical connector.
S 614-019
(3)
Fill the APU with oil (AMM 12-13-04/301).
S 414-020
(4)
Close the APU access doors.
S 864-021
(5)
Remove the DO-NOT-CLOSE tag and close this circuit breaker on the E6 rack in the aft equipment center.
(a) APU PRIME CONT
S 864-022
(6) Remove the DO-NOT-CLOSE tags, and close these P11 panel circuit breakers:
(a) 11B34, APU ALTN CONT or APU MN BAT CONT
H. Do the Generator Installation test
S 734-038
(1)
Do this task: APU Generator Operation Test (AMM 24-21-00/501).
(2)
Remove external power if it is not necessary (AMM 24-22-00/201).
S 864-030
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
757 MAINTENANCE MANUAL
CONTROL - DESCRIPTION AND OPERATION
___________________________________
1. General_______
A. Flight compartment switches and indicators work with control units to provide manual and automatic distribution of ac power. The major components are three generator control units (GCUs), and a bus power control unit (BPCU).
2. Component Details (Fig. 1)_________________
A. Generator Control Unit (GCU)
______________________
(1)
The electrical power system contains three GCU's. Each GCU regulates the output voltage of its generator, and coordinates system protection with the bus power control unit (BPCU). The GCU's isolate faults and show failure information on the BPCU BITE display. (The GCU's are connected to the BPCU by a serial data link.) The left and right GCU's work with flight compartment switches to control one relay and two contactors associated with each generator: The generator field control relay, generator circuit breaker, and bus tie breaker. The APU GCU works with flight compartment switches to control the APU generator field control relay, and the auxiliary power breaker.
(2)
Each GCU receives 95-volt ac power from the permanent magnet generator (PMG) in its IDG. This ac power goes through a transformer-rectifier in the GCU to produce 28-volt dc power. The dc power is used for GCU control. The left, right, and APU GCU's get 28-volt dc backup power from the battery bus, through circuit breakers on main power distribution panel P6.
(3)
The left and right GCU's receive additional dc power for their generator disconnect drive functions. This power is from the battery bus through circuit breakers on P6.
(4)
The left GCU is on shelf 1 of equipment center rack E5. The right GCU is on shelf 2 of E5. The APU GCU is on shelf 3 of E5. The front of each GCU has a nameplate, and two circuit breakers. An electrical connector is mounted on the rear of the unit.
B. GCB/APB/BTB
___________
(1) The generator circuit breakers (GCB's), auxiliary power breaker (APB), and bus tie breakers (BTB's) are identical. Each breaker contains three main contacts along with seven normally open and seven normally closed auxiliary contacts. The main contacts are rated for continuous operation of 115/200-volt, 400-Hz, 275-amp ac power. Main ac power flows through these contacts. Six terminal studs on the breaker provide main contactor connections. The auxiliary contacts provide control to the breaker, and breaker status information to the GCU and BPCU. An electrical connector provides continuity to the auxiliary contacts and power to the trip and close coils.
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