757 MAINTENANCE MANUAL
RIGHT 28 VOLT AC AUTOTRANSFORMER, T124
INBD FWD
MISCELLANEOUS RELAY PANEL, P33 B
28V AC GROUND SERVICE
AUTOTRANSFORMER, T126
APU/EXT POWER PANEL, P34
C
28-Volt AC Power Distribution Component Location Figure 1 (Sheet 2)
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MAINTENANCE MANUAL
EXT APU L GEN R GEN
PWR GEN
28 - Volt AC Power Distribution Block Diagram
Figure 2
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FAULT ISOLATION/MAINT MANUAL
28 VOLT AC POWER DISTRIBUTION
* SEE THE WDM EQUIPMENT LIST
28 Volt AC Power Distribution - Component Index
Figure 101
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E45047
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757 FAULT ISOLATION/MAINT MANUAL
MAIN EQUIPMENT CENTER
28 Volt AC Power Distribution - Component Location Figure 102
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757 MAINTENANCE MANUAL
28-VOLT DC POWER DISTRIBUTION - DESCRIPTION AND OPERATION
_________________________________________________________
1. General_______
A. Twenty-eight volt DC power distribution involves buses. These are: left and right main DC buses, the 28-volt DC center, standby, battery, and hot battery buses, and 28-volt DC ground handling bus. The main system components include two transformer-rectifier units for the main dc buses and one ground handling transformer-rectifier unit.
2. Component Details (Fig. 1)_________________
A. Transformer-Rectifier Units
___________________________
(1) Two identical TRUs convert nominal 115-volt, 3-phase AC power into unregulated 28-volt DC power. Each TRU is capable of providing 120 amps continuous current with forced-air cooling. Internal protection circuits prevent TRU damage due to a shorted output. An internal meter shunt allows measurement of TRU output current by the EICAS computers. The main TRUs are located in left forward equipment center rack E1.
B. Ground Handling Transformer-Rectifier Unit (TRU)
__________________________________________
(1) The ground handling TRU converts 115 volt, 3-phase AC power from the ground handling bus to unregulated 28-volt DC power. The TRU can provide output currents up to 20 amps continuous. The TRU is cooled by natural convection. The TRU is in APU/external power panel P34.
3. Operation (Fig. 2)_________
A. Functional Description
______________________
(1)
Main DC Buses
(a) The left and right main DC buses are powered by transformer-rectifier units connected to the main AC buses. The buses can be joined by a DC tie relay if one bus loses power (AMM 24-32-00/001).
(2)
28-Volt DC Hot Battery Bus
(a) The hot battery bus supplies 28-volt DC power to the most critical flight loads. The hot battery bus is connected directly to the main battery through a thermal circuit breaker. The hot battery bus is not switched.
(3)
28-Volt DC Battery Bus
(a) The battery bus supplies power to critical DC flight loads. The battery bus is normally powered by the left main DC bus through the main battery transfer relay. If the left DC bus is unpowered, the main battery relay will automatically switch to hot battery bus power. 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：757 AMM 飞机维护手册 电源 ELECTRICAL POWER 2(99)
