40 Questions
What is the term used to refer to the number of cycles of AC that occur every second?
Hertz
In aircraft, what is the standard frequency for AC power supply?
400 Hz
What type of AC waveform is represented by a single sine wave?
Single-phase
Which term refers to the electrical bus that is non-essential for flight?
Non-essential bus
How does the frequency of AC power impact aircraft equipment?
Increases output power
What is the primary function of an inverter in an aircraft electrical system?
Convert DC voltage into AC voltage
In the event of all AC generators failing, how are essential aircraft electrical systems powered?
By an inverter
What is the main difference between rotary and static inverters in aircraft electrical systems?
Static inverters are solid state electronic devices
Why is supplying aircraft with external AC power essential on the ground?
To avoid running the engines for AC generation
What does a TRU do in an aircraft electrical system?
Converts AC into DC
What determines the output frequency of an aircraft's AC generator?
Engine speed
Which component ensures that the generator's output frequency is maintained close to 400 Hz?
Constant Speed Drive Unit (CSDU)
What function does the Generator Control Unit (GCU) perform?
All of the above
What is the main purpose of Transformer Rectifier Units (TRUs) in an aircraft's power supply system?
Convert AC to DC
In an aircraft's AC system operation, what ensures that the generator's frequency output remains stable even if the engine speed varies?
Constant Speed Drive Unit (CSDU)
What is the main advantage of using Alternating Current (AC) over Direct Current (DC) in aircraft power supply systems?
AC generators do not require a commutator and brushes like DC generators, reducing complexity and eliminating arcing of brushes.
In an aircraft, what design feature of AC generators makes them ideal for high altitude flight?
Elimination of arcing of brushes by not requiring a commutator in the generator design.
What feature of AC allows it to achieve higher electrical efficiency in comparison to DC in aircraft systems?
Transmission with lower electrical losses due to its nature compared to DC.
What component allows AC power in aircraft to be adjusted as required for different equipment?
Transformers that can step up or down the AC voltage.
Why are AC generators preferred over DC generators in aviation applications?
AC generators eliminate arcing of brushes by not requiring a commutator, reducing complexity.
What is the fundamental operation for an AC tied bus system?
Starting number 2 engine and synchronising it with number 1 generator.
What are the components of a tied bus system?
Generator Circuit Breakers (GCBs), Bus Tie Breakers (BTBs), Frequency control adjustment, Voltmeter.
How is the synchronization of number 2 generator to number 1 generator achieved in an AC tied bus system?
By fine adjusting the frequency and voltage of number 2 generator.
What happens after number 2 generator is synchronized to number 1 generator in an AC tied bus system?
Number 2 generator is connected to the AC distribution system by closing number 2 GCB.
Which system uses GCBs and BTBs with the same construction as the ones used in a split bus system?
AC tied bus system.
What is the main purpose of a current limiter in a generator system?
To reduce the generator output voltage when a safe load is exceeded
What will happen if an aircraft generator's armature burns out due to excessive current flow?
The batteries will overcharge
When would a Transformer Rectifier Unit (TRU) be used as a secondary DC supply in an aircraft?
When the AC generating system fails
What is the primary function of an RCR in an aircraft electrical system?
To prevent overcharging of the batteries
How does a Transformer Rectifier Unit (TRU) contribute to an aircraft's power supply?
By converting power from AC to DC
If a DC generator operating within limits supplies the essential bus with a regulated 28 VDC, what action does the RCR take if the generator fails?
Disconnects the generator from the essential bus
Which bus in an aircraft would typically power some lighting systems and mission control when a generator fails?
Non-essential bus
In an aircraft, what role does the essential bus play in the DC distribution system?
Re-distributes power to all loads
If an AC waveform is represented by a single sine wave, what type of waveform does it indicate?
Sinusoidal wave
When an aircraft's AC power frequency increases, how does it impact the operation of equipment connected to it?
Alters performance characteristics
What action does the RCR take if a DC generator fails and its output voltage remains above the battery's voltage?
Disconnects the generator from the essential bus
Which term describes an electrical bus that is necessary for aircraft operation?
Essential bus
What component disconnects a DC generator from the essential bus when it fails?
RCR
If an AC system operates with a sawtooth waveform, what does this indicate about its output?
It is pulsating and irregular
What type of electrical wave has a triangular shape and is commonly used in certain AC applications?
Triangular wave
Study Notes
Tied Bus Distribution System
- A tied bus AC distribution system includes GCBs, BTBs, CSDUs, frequency control adjustment, GCUs, voltmeter, and frequency meter.
- The system operates by starting and synchronizing generators, then bringing them online by closing GCBs.
Generator Circuit Breaker (GCB) and Bus Tie Breaker (BTB)
- GCBs and BTBs used in a tied bus system are the same construction as those used in a split bus system.
AC System Operation
- AC waveform is a single-phase sine wave that periodically rises and falls on a regular time basis.
- Frequency is the number of cycles of AC that occur every second, and aircraft AC equipment requires a constant frequency of 400 Hz.
Transformer Rectifier Units (TRUs)
- TRUs convert AC generator output into 28 VDC required for the aircraft's DC loads.
- TRUs can be used as the primary DC supply or as a secondary DC supply if a DC generator fails.
Inverters
- Inverters change DC voltage into AC voltage, and can be used as a primary AC supply in aircraft with DC generators.
- Inverters can also be used as a backup power supply if all AC generators fail.
External Power Supply
- External power supply is essential for engine starting and servicing, and is usually provided by a constant frequency AC generator.
- Larger aircraft require only AC external power, while smaller aircraft typically use DC external power only.
Constant Speed Drive Unit (CSDU)
- CSDU ensures the output frequency of the generator is maintained close to 400 Hz, despite engine speed variations.
Generator Control Unit (GCU)
- GCU performs functions such as voltage regulation, current limiting, system protection, and crew alerting.
Advantages of Alternating Current
- AC has advantages over DC, including simpler generator design, higher electrical efficiency, and the ability to be stepped up or down by transformers.
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