12-04-2014, 04:55 PM
Aircraft Electrical Systems
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Aircraft Electrical Systems
The function of the aircraft electrical system
is to generate, regulate and distribute
electrical power throughout the aircraft
New-generation aircraft rely heavily on
electrical power because of the wide use of
electronic flight instrument systems
Electrical Power Uses (cont.)
Essential power is power that the aircraft
needs to be able to continue safe operation
Passenger services power is the power that
used for:
– Cabin lighting
– Operation of entertainment systems
– Preparation of food
Power Sources
There are sever different power sources on large
aircraft to be able to handle excessive loads, for
redundancy, and for emergency situations.
These power sources include:
– Engine driven AC generators
– Auxiliary Power Units
– External power
– Ram Air Turbines
APU Power
Most often the APUs power is used while
the aircraft is on the ground during
maintenance or for engine starting
However, most aircraft can use the APU
while in flight as a backup power source
– One exception to this is the B272, which only
allows APU operation in the ground
Aircraft Batteries
The aircraft’s nickel cadmium battery is
final source of backup power
The battery provides 28 VDC
It is also possible to change the 28 VDC
into 115 VAC 400Hz with the use of a static
inverter
When using the battery, power usage is
limited by the short life of the battery
Constant Speed Drive
The purpose of the Constant Speed Drive (CSD) is
to take rotational power from the engine and, no
matter the engine speed, turn the generator at a
constant speed
This is necessary because the generator output
must be 400Hz
CSD Operation
– The engine turns the CSD which uses a differential
assembly and hydraulic pumps to turn the generator