787 Flight Crew Operations Manual
DO NOT USE FOR FLIGHT
Electrical -
System Description
Copyright © The Boeing Company. See title page for details.
6.20.8 D615Z003-TBC
28 Vdc Bus Distribution System
There are multiple 28 Vdc buses. To distribute power, the 28 Vdc system uses both
primary power system buses located in the forward E/E bay, and RPDUs located
throughout the airplane. The higher amperage (greater than 10 amps) loads are
distributed directly by the bus system. The lower amperage (10 amps or less) loads
are distributed by the RPDUs.
The 235 Vac system provides power to the 28 Vdc system through power
conversion devices.
Four electrical brake power supply units regulate power for the exclusive use of
the airplane electric brake system. Each of the four power supplies receive two
separate 28 Vdc inputs. One from the 28 Vdc bus system, and one from the main
battery. The 28 Vdc bus system is the primary power source, and the main battery
provides the backup power source. (Refer to Electric Brake System
in Chapter 14,
Section 20, for additional information.)
Large Motor Power Distribution System
The airplane’s use of variable frequency power requires large motor loads to be
energized by motor controllers, which conditions that power for use. A dedicated
large motor power distribution system in the aft E/E bay power panels energize the
motor controllers.
The main 235 Vac distribution system energizes the large motor power system
through power conversion devices. In addition, portions of the large motor power
system are energized by the APU battery and aft external power through power
conversion devices. The APU battery energizes only the motor controller required
to perform an APU battery start. The aft external power system energizes only the
motor controller required to perform a right engine start using external power as
the sole power source.
The Power Electronics Cooling System (PECS) dissipates heat created by these
high voltage motor controllers. (Refer to Power Electronics Cooling System
in
Chapter 2, Section 20, for additional information.)
February 15, 2010
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