AET AET Aircraft Power Systems 4 — Questions and Answers
Question 1: What is the primary purpose of a voltage regulator in an aircraft electrical system?
- Increase generator output frequency
- Maintain constant output voltage despite load variations (Correct answer)
- Convert AC to DC power
- Protect against reverse current flow
Correct answer: Maintain constant output voltage despite load variations
A voltage regulator maintains a constant output voltage from the generator regardless of changes in engine speed or electrical load.
Question 2: In a three-phase AC aircraft generator, the phases are separated by how many electrical degrees?
- 90 degrees
- 60 degrees
- 120 degrees (Correct answer)
- 180 degrees
Correct answer: 120 degrees
In a three-phase AC generator, the three windings are physically and electrically spaced 120 degrees apart to produce balanced three-phase power.
Question 3: Which type of battery is most commonly used as a primary backup power source in modern transport-category aircraft?
- Lead-acid
- Nickel-cadmium (NiCd) (Correct answer)
- Lithium-ion
- Silver-zinc
Correct answer: Nickel-cadmium (NiCd)
Nickel-cadmium batteries are preferred in transport-category aircraft for their high discharge rate capability, long cycle life, and reliability under extreme temperatures.
Question 4: What does the term 'paralleling' mean when applied to aircraft AC generators?
- Connecting generators in series to increase voltage
- Synchronizing and connecting multiple generators to share load equally (Correct answer)
- Switching between generator and APU power
- Isolating a failed generator from the bus
Correct answer: Synchronizing and connecting multiple generators to share load equally
Paralleling AC generators means synchronizing their frequency, phase, and voltage so they can be connected together and share the electrical load equally.
Question 5: A current transformer (CT) in an aircraft AC power system is primarily used for:
- Stepping up voltage for high-power equipment
- Measuring load current without breaking the circuit (Correct answer)
- Converting single-phase to three-phase power
- Filtering harmonic distortion from the bus
Correct answer: Measuring load current without breaking the circuit
Current transformers allow current monitoring by inducing a proportional secondary current, enabling measurement without interrupting the high-current circuit.
Question 6: What is the nominal frequency of AC power produced by most commercial aircraft generators?
- 50 Hz
- 60 Hz
- 400 Hz (Correct answer)
- 800 Hz
Correct answer: 400 Hz
Aircraft AC generators produce power at 400 Hz, which allows smaller, lighter transformers and motors compared to the 60 Hz used in commercial ground power.
Question 7: In an aircraft bus tie system, what is the function of a Bus Tie Breaker (BTB)?
- Regulate voltage between two AC buses
- Connect or isolate AC buses to allow power transfer between sources (Correct answer)
- Convert AC bus power to DC for avionics
- Protect the bus against overvoltage conditions
Correct answer: Connect or isolate AC buses to allow power transfer between sources
A Bus Tie Breaker connects two AC buses together, allowing one generator to power both buses if one generator fails.
AET AET Aircraft Power Systems 4
What is the primary purpose of a voltage regulator in an aircraft electrical system?