Electrics

Question 1

The backup electrical system is designed to automatically provide power to selected airplane systems. The backup electrical system automatically powers one or both transfer busses when:

Answer 1

1) only one main AC generator (including APU) is available
2) power to one or both of the main AC busses is lost
3) approach (APP) mode is selected for autoland
4) the system is automatically tested after engine starts.

The system transfers power without interruption.

Question 2

The ground service bus is normally powered by the right main bus. Alternate sources of power for the ground service bus are:

Answer 2

the APU generator

primary external power.

Question 3

The ground service bus is used on the ground and in flight. It powers:

Answer 3

the main battery charger
the APU battery charger
miscellaneous cabin and system loads.

Question 4

The ground handling bus can be powered on the ground only from the APU generator or from the primary external power source. It is provided for loads such as

Answer 4

cargo handling, fueling/defueling operations, and other equipment energized only during ground operations.

Question 5

The main DC electrical system uses ……transformer–rectifier units (TRUs) to produce DC power.

Answer 5

4

Question 6

You get the EICAS message : ELEC GEN DRIVE L. What does it mean and what will happen

Answer 6

It either indicates low pressure in the gen drive, so the IDG must be manually disconnected.
Or it indicates a high temp, in which case, the IDG will automatically disconnect with the same messages.

The Backup gen will immediately connect to the Left transfer bus and the Right engine generator will power the the Left Main AC bus.

Start the APU for a second generator. (Backups are not considered part of the big 3 Gens)

Question 7

The TRUs are powered by the

Answer 7

AC Transfer buses