787 Flight Crew Operations Manual
DO NOT USE FOR FLIGHT
Electrical -
System Description
Copyright © The Boeing Company. See title page for details.
6.20.4 D615Z003-TBC
For additional information, refer to:
• Electrical – Modes of Operation
, Ch. 6, Sec. 20
• Hydraulics – Hydraulic Panel
, Ch. 13, Sec. 10
• Hydraulics – Ram Air Turbine (RAT)
, Ch. 13, Sec. 20
Battery Power
The airplane has two primary batteries; main and APU. The main battery power
switch is located on the overhead electrical panel. The APU battery functions
automatically, and has no power switch. Operating indications for the main and
APU batteries are provided on the electrical synoptic.
The main battery provides power for:
• airplane power-up
• APU start (assists APU battery)
• refueling operations
• towing operations
• electric braking (as backup power source)
• captain’s flight instruments (energizes essential instruments until RAT
deployment)
(Refer to Modes of Operation
in Chapter 6, Section 20, for additional
information.)
The APU battery provides power on the ground for:
•APU start
• navigation lights (during battery-only towing operations)
Permanent Magnet Generators
Three engine driven Permanent Magnet Generators (PMG) are the primary source
of power for the flight control electronics. These power sources are independent
from the main airplane electrical system, and are also independent from each
other.
A secondary source for flight control power is provided by the airplane’s 28 Vdc
bus distribution system, and the main battery. In addition, a backup system is
provided by dedicated batteries to assure positive flight control operation during
temporary power interruptions.
February 15, 2010
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