Questions

Question 1

A twin engined aircraft has 1 main generator per engine and another for the APU. It has a split busbar AC electrical system. After an engine failure what would be the normal condition of the bus tie breaker?

Answer 1

Closed unless the APU is running

Question 2

What would be the purpose of the consumers powered by an emergency bus?

Answer 2

Equipment that might be needed at any point during operation, even on the ground with all engines shut down, such as a portion of the cabin lighting to assist during an evacuation

Question 3

What is the main type of battery currently used in aircraft?

Answer 3

Lead acid and NiCad

Question 4

The voltage of a fully charged lead-acid battery is:

Answer 4

2.2v

Question 5

What are the advantages of three phase AC compared to single phase AC?

Answer 5

• It gives three outputs from one generator, this reduces the required RPM of the rotor while maintaining a high frequency output
• simpler distribution and wiring
• greater efficiency in generation
• three phase motors have better characteristics
• can supply both single and three phase loads

Question 6

Frequency (Hz) in AC generator=

Answer 6

(Poles x RPM)/120 or (Pole Pairs x RPM)/60

Question 7

In a three phase, star wound, generating system how do phase voltage and line voltage differ?

Answer 7

Phase voltage is the voltage measured between any output line and the neutral point (115v).
Line voltage is the vector sum being measured between two different output lines. Equal to 1.73 (root 3) multiplied by phase voltage (approx 200v)

Question 8

What is the function of the GCU?

Answer 8

The generator control unit houses the voltage regulator and monitors the generator output voltage, frequency(if required) and phase sequence. Only if generator is within parameters will it allow the generator to be brought online.

Question 9

What is the function of the CSDU?

Answer 9

A constant speed drive unit provides constant generator speed irrespective of engine speed (which is variable)

Question 10

The CSDU of an AC generator may be disconnected in flight. The primary reason for disconnection are:

Answer 10

Low oil pressure and/or high oil temperature of the generator drive.

Question 11

A current limiters is used to:

Answer 11

Limit the current in the distribution system

Question 12

A current limiter operates by

Answer 12

Allowing a short term overload before rupturing

Question 13

In a paralleled AC distribution system how is the real load balanced?

Answer 13

Torque from the CSDU

Question 14

In a paralleled AC distribution system how is the reactive load balanced?

Answer 14

Field excitation via the voltage regulator

Question 15

If the mechanical load on a 3-phase AC induction motor is increased, its RPM will:

Answer 15

Decrease