Podcast
Questions and Answers
What type of generators are used as the principal source of electric power in almost all transport-category aircraft?
What type of generators are used as the principal source of electric power in almost all transport-category aircraft?
- Alternators
- Transformer Rectifier Units
- AC generators (correct)
- DC generators
What type of generator is used on light aircraft due to being lighter than an AC generator?
What type of generator is used on light aircraft due to being lighter than an AC generator?
- AC generator with constant-speed drive
- Auxiliary battery charger
- DC alternator (correct)
- Transformer Rectifier Unit
What is the purpose of the internal rectifiers in a DC alternator?
What is the purpose of the internal rectifiers in a DC alternator?
- Produce AC voltage
- Control engine speed
- Produce DC output (correct)
- Convert AC to DC
Which component is responsible for changing engine-driven AC-generated 115-V AC to 28-V DC on larger aircraft?
Which component is responsible for changing engine-driven AC-generated 115-V AC to 28-V DC on larger aircraft?
In the event of other power sources failing, what serves as the backup DC source on aircraft?
In the event of other power sources failing, what serves as the backup DC source on aircraft?
What is the function of Auxiliary batteries in aircraft electrical systems?
What is the function of Auxiliary batteries in aircraft electrical systems?
What is the function of the shunt connected in series with the output of the transformer rectifier units?
What is the function of the shunt connected in series with the output of the transformer rectifier units?
How is the cooling typically provided for Transformer Rectifier Units (TRUs) in modern aircraft?
How is the cooling typically provided for Transformer Rectifier Units (TRUs) in modern aircraft?
What is the ripple frequency of the DC voltage produced when 400 Hz, three-phase AC is full wave rectified by six diodes?
What is the ripple frequency of the DC voltage produced when 400 Hz, three-phase AC is full wave rectified by six diodes?
In a star-to-star transformer, are the input and output in phase or out of phase?
In a star-to-star transformer, are the input and output in phase or out of phase?
What is the purpose of the thermal switch mentioned in the text?
What is the purpose of the thermal switch mentioned in the text?
How many silicon diodes are typically connected in parallel in each bridge rectifier assembly mentioned in the text?
How many silicon diodes are typically connected in parallel in each bridge rectifier assembly mentioned in the text?
What happens when the output voltage of a generator rises above a critical value?
What happens when the output voltage of a generator rises above a critical value?
How does a vibrating-type voltage regulator ensure a maintained average voltage with load changes?
How does a vibrating-type voltage regulator ensure a maintained average voltage with load changes?
What role does the dashpot P play in a vibrating-type voltage regulator?
What role does the dashpot P play in a vibrating-type voltage regulator?
What occurs when contact B closes in a vibrating-type voltage regulator?
What occurs when contact B closes in a vibrating-type voltage regulator?
Why is a capacitor C placed across contact B in a vibrating-type voltage regulator?
Why is a capacitor C placed across contact B in a vibrating-type voltage regulator?
In what scenario does additional force need to be applied to turn the armature of a generator?
In what scenario does additional force need to be applied to turn the armature of a generator?
What is the role of the current coil in the relay described in the text?
What is the role of the current coil in the relay described in the text?
How is the contactor coil energized in the relay system?
How is the contactor coil energized in the relay system?
What initiates the opening of the pilot contacts in the relay system?
What initiates the opening of the pilot contacts in the relay system?
Why does the reverse current circuit breaker remain in a 'locked-out' condition?
Why does the reverse current circuit breaker remain in a 'locked-out' condition?
What leads to the de-energization of the contactor coil in the relay system?
What leads to the de-energization of the contactor coil in the relay system?
How do the main and auxiliary contacts behave when the pilot contacts open in the relay system?
How do the main and auxiliary contacts behave when the pilot contacts open in the relay system?
What is the purpose of the reverse polarity diode in the external DC power circuit?
What is the purpose of the reverse polarity diode in the external DC power circuit?
How is the external AC power receptacle identified?
How is the external AC power receptacle identified?
What happens if the external power plug is disconnected while 'live' from the aircraft?
What happens if the external power plug is disconnected while 'live' from the aircraft?
Which component prevents incorrect polarity power from reaching the aircraft in the external DC power system?
Which component prevents incorrect polarity power from reaching the aircraft in the external DC power system?
What is the function of the two smaller pins in the external AC power receptacle?
What is the function of the two smaller pins in the external AC power receptacle?
Why is it important for the external power supply to be correct before connecting AC to the aircraft?
Why is it important for the external power supply to be correct before connecting AC to the aircraft?
Study Notes
DC Power Generation
- DC alternators are used in light aircraft to produce electric power, producing an AC voltage that is then converted to DC using internal rectifiers.
- Larger aircraft use Transformer Rectifier Units (TRUs) to convert AC power to 28-V DC.
- Aircraft have multiple DC power sources, including main batteries, main battery chargers, and auxiliary batteries and chargers.
- These batteries act as a backup DC source if other power sources fail.
AC Power Generation
- AC generators (alternators) are used in transport-category aircraft to produce electric power.
- Modern aircraft (e.g. 787) have generators that produce 235-V AC, with a frequency governed by engine rotational speed.
- The generator consists of a transformer and two three-phase bridge rectifier assemblies, which produce a DC output with a ripple frequency of 2400 Hz.
Voltage Regulation
- A vibrating-type voltage regulator uses a solenoid to connect or remove a field rheostat from the circuit, maintaining a consistent output voltage.
- When the output voltage rises above a critical value, the solenoid opens the contact, inserting the field rheostat and reducing the field current.
- When the output voltage falls below a certain value, the solenoid closes the contact, shorting the field rheostat and increasing the field current.
Reverse Current Circuit Breakers
- These circuit breakers protect power supply systems from fault currents greater than those at which cut-outs normally operate.
- They remain in a "locked-out" condition until the fault is cleared.
External Power Systems
- External DC power systems have a short pin connected to a positive voltage, with a reverse polarity diode to prevent incorrect polarity power being supplied to the aircraft.
- External AC power receptacles have six pins: four for phases (ABC) and neutral, and two for interlock sensing.
- The external power supply must be correct before connecting to the aircraft, and the system is designed to prevent arcing at the receptacle pins during disconnection.
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Description
Test your knowledge on electrical systems used in modern light aircraft, including DC power generation and DC alternators. Understand the importance of using DC alternators over AC generators in light aircraft.
