Chapter 5 - Aircraft Electrical Systems 2 Flashcards
What is the purpose of the CSDU (Constant Speed Drive Unit)?
Fitted between the engine accessory gearbox and the generator.
Maintains the generator at a constant RPM irrespective of engine RPM.
What is a generator called if it has a built in CSDU?
Integrated Drive Generator (IDG)
What does a voltage regulator do?
Maintains a constant generator voltage output to cope with changing generator loads.
A voltage regulator within a Generator Control Unit (GCU) samples the output voltage. If it drops, the voltage regulator increases the voltage to the Excitor Field coils, which creates a stronger Main Field and subsequently increases the Main Armature voltage to the busbars.
Works the other way if output voltage is too high.
This is a constant process as components are switched on and off.
Where is the voltage regulator (VR) housed?
In the GCU
What is the role of a Voltage Protection Unit and how does it work?
Opens the Field Contactor, cutting off generator output if the voltage exceeds its limits. Protects the electrical systems.
What is an LSCU?
Load Sharing Control Unit
Used when you have multiple generators connected through a Bus Tie Contactor.
Samples the output from both generators and increases the output of the more lightly loaded machine until balance is achieved.
What is frequency regulation and how is it achieved?
With more than one generator, the AC sine wave frequencies must be synchronised with each other.
Frequency control unit varies generator speed through the CSDUs to ensure that generator phases are synchronised.
CSDU and IDG systems able to control f within 1%.
What the most common issues electrical circuit protection devices protect against?
Over volt/under volt
Over-current
Reverse current
If an electrical fault is allowed to persist without protection measures, what are the major risks?
Damage to equipment
Failure of essential power supplies
Fire or loss of life
How do circuit protection devices work?
Disconnect the relevant generator from the distribution busbar and can also de-excite the generator.
What are three common methods of circuit protection?
Circuit Breakers (CBs)
Reverse Current Cut-Out (RCCO)
Fuses
How do CBs work?
Isolate faulty circuits by means of a mechanical trip.
How do RCCOs work?
Senses the difference in voltage between the generator and its busbar.
Its contacts remain closed whilst the voltage of the generator is higher than that of the busbar, but opens if busbar voltage exceeds generator voltage.
How do fuses work?
A thermal device which protects cables and components from short circuits and overload currents by providing a weak link in the circuit.
Ruptures and protects the circuit/component from damage by cutting off the current.
