ELECTRICAL POWER – GENERAL
The electrical power system is a 28 VDC system that has the purpose to:
• Generate and distribute DC electrical power
• Store electrical energy into batteries for:
• In-flight emergency operations, and
• Autonomous engine starting and ground operations
• Distribute DC electrical power provided by an external power source on
the ground
The major components of the system are listed in the figure.
ELECTRICAL POWER – GENERAL ARRANGEMENT
The electrical power system consists of two similar subsystems, no.1 (LH)
and no.2 (RH), each consisting of:
• A Starter-Generator and the relevant Generator Control Unit (GCU)
• A Battery (Main on LH; Auxiliary on RH)
• A set of bus bars ranked – from the most important – as:
• Essential bus ............................................................ (ESS)
• Main bus ................................................................... (MAIN)
• Non-Essential bus ..................................................... (NON ESS)
A Battery bus – directly powered by the Auxiliary Battery – is also available.
The Battery bus is only to supply power to the on-board recorders
(FDR/CVR and CMC) for proper shut-down when power is removed from the
Essential busses.
ESS BUS 1 and ESS BUS 2 are interconnected via a circuit breaker and
protected by diodes so as they cannot feed any other bus bar.
MAIN BUS 1 and MAIN BUS 2 are normally isolated; a BUS TIE contactor
permits interconnection to allow transfer of power in case of generator failure
or when generators are not operating.
The external power – when available – is connected to the MAIN BUS 1;
however, external power is distributed to all bus bars.
In the following pages two diagrams show the general arrangement of the
electrical power system with the major components highlighted:
• the Synoptic Diagram, which can be displayed on the MFD, both on the
ground and during flight
• the Simplified Diagram, which is used in this training manual to
describe the system operation