DGCA Technical General: AC Electrics Questions
301 exam-style AC Electrics questions for the DGCA Technical Generalpaper (CPL & ATPL). The first 12 are free below with answers and explanations — sign up free to practise all of them with progress tracking.
- Q1
what is the speed of rotation of a four pole induction motor it is operating at a frequency of 400 Hz?
- A1800 RPM.
- B3400 RPM.
- C6000 RPM.
- D12000 RPM.
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Correct answer: D. 12000 RPM.
This Explanation is Coming Soon
- Q2
The output of an AC generator is rated in?
- AKW and volts.
- BKVA or KW.
- CVolts and amperes.
- DKVA and amps.
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Correct answer: D. KVA and amps.
This Explanation is Coming Soon
- Q3
In a paralleled AC distribution system what regulates the real load
- A Torque from the CSDU (CSD)
- B Field excitation from the voltage regulator
- C Synchronising circuits in the BTB
- D A potentiometer on the Flight Engineers panel
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Correct answer: A. Torque from the CSDU (CSD)
In a paralleled AC system the real (kW) load sharing is governed by the input drive torque delivered through each generator's constant-speed drive, since real power comes from mechanical shaft power. Reactive load, by contrast, is trimmed with field excitation.
- Q4
What frequency is commonly used in aircraft electrical distribution systems
- A 200Hz
- B 400 Hz
- C 100Hz
- D 50Hz
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Correct answer: B. 400 Hz
Aircraft AC electrical systems are standardised on 400 Hz, a frequency high enough to allow lighter, smaller transformers and motors than the 50/60 Hz used on the ground, while remaining practical for aircraft generators.
- Q5
AC busbar loads are connected?
- AIn series so that current is proportional to load.
- BIn parallel so that current is proportional to load.
- CIn series so that voltage is proportional to load.
- DIn parallel so that voltage is proportional to load.
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Correct answer: B. In parallel so that current is proportional to load.
This Explanation is Coming Soon
- Q6
If the oil temperature gauge of the CSD is in the red what would action is required
- A Throttle back and allow to cool down
- B Auto disconnect
- C Manually disconnect and reconnect on the ground
- D Disconnect, then when cooled reconnect
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Correct answer: C. Manually disconnect and reconnect on the ground
A CSD (constant-speed drive) oil temperature in the red indicates overheating, so the drive should be manually disconnected to protect it; it cannot be re-engaged in flight and must be reconnected only on the ground after it has cooled and been checked.
- Q7
A busbar is.
- AA common connection to a number of loads.
- BA common connection for a number of power supplies.
- CAn integral part of a generator.
- DFed by a circuit breaker.
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Correct answer: A. A common connection to a number of loads.
This Explanation is Coming Soon
- Q8
345.An alternator normally used to supply an aircraft's power system would be:
- A single phase
- Bthree phase
- C two phase
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Correct answer: B. three phase
Aircraft main alternators are three-phase machines, typically 115/200 V at 400 Hz, because three-phase generation gives the best power-to-weight ratio and a smooth supply for motor loads.
- Q9
What is a transistorised static inverter in a DC circuit used for
- A Convert AC to DC
- B Provide field excitation current
- CProvide AC for instruments
- D To supply power to the emergency lights
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Correct answer: C. Provide AC for instruments
A transistorised static inverter converts the aircraft's DC supply into AC, and is used to provide the alternating current needed to run certain instruments and equipment, particularly as a standby AC source.
- Q10
The frequency of the output of an AC generator is determined by?
- ARPM.
- BNumber of poles.
- CField excitation amplitude.
- DNumber of poles and RPM.
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Correct answer: D. Number of poles and RPM.
This Explanation is Coming Soon
- Q11
If the load increases on a ‘constant speed AC generator’ what does the voltage regulator do
- A Increases generator speed
- BDecreases field excitation
- C Remains the same
- D Increases field excitation
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Correct answer: D. Increases field excitation
With the drive holding speed and therefore frequency constant, an increase in electrical load tends to pull the generator output voltage down. The voltage regulator responds by increasing the field excitation, restoring the output voltage to its regulated value.
- Q12
If the fire handle is pulled in an aeroplane with an AC generator system what disconnects.
- A Exciter control relay and GCB
- BGCB and BTB
- CBTB and GCU
- D Exciter control relay only
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Correct answer: A. Exciter control relay and GCB
Pulling the fire handle isolates the affected engine's electrical generation by tripping the generator field (exciter) control relay and opening the generator circuit breaker. This de-excites the generator and disconnects it from its busbar, removing electrical energy from the fire zone.
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