Electrical Flashcards
What power sources can cross tie on the ground?
The engine generators.
What is the electrical source priority?
On side engine generator
APU generator
External power unit
Off side generator cross tie
What does the reset position of the generator control switch do?
Closes the generator control relay.
When only the battery switch is on what buses are powered?
DC Transfer Bus
Battery Direct Bus
Battery Bus
What are the two purposes of the ground service bus?
To provide power to those circuits necessary for ground service, and to provide an alternate means of battery charging. (B2 8-120)
Is there a way to monitor external power?
No AC load meter exists for external power.
At what RPM should you disconnect a CSD?
A higher speed to allow for a smoother disconnect.
Can a CSD be reconnected?
Yes, but only on the ground by a mechanic.
What is the electrical power source for the pneumatic pressure gauge?
Emergency AC bus
What is the electrical power source for the augmentation valve?
Respective DC bus
What is the power source for the start valve solenoid?
The DC Transfer bus
How do you verify an AC EMER BUS OFF light?
By looking for a “GYRO” flag in the captains ADI
What normally powers the DC Transfer bus?
The Left AC Bus through the Left DC Bus
How would you identify a differential fault in the “feeder” zone?
Move Generator switch to reset and off and observe no volts and frequencies.
What is needed for battery charging to occur?
Ground Service AC bus powered, battery switch on, emergency switch off.
How would you verify the DC TRANSFER BUS OFF light?
By doing a fire warning test.
Is the DC cross tie automatic?
No
How many circuit breakers must be pulled to disconnect a Transformer Rectifiers from its power source?
3, one for each phase of the AC input.
What is the power source for the #2 Transformer Rectifier on the right side?
The Ground Service Bus
What happens if you turn off the Battery Bus if you have the Emergency Power switch on?
You will lose the DC Transfer Bus and the Battery Bus, along with battery charging.
List some items (3) powered by the Battery Direct Bus
Emergency Inverter
DC Emergency Bus
Fuel Fill and Transfer Valves
How many batteries are on board?
Two 14 volt NICAD batteries.
What are the Major Faults in the Electrical System? (2)
Generator Bus Differential Feeder Fault
Generator Bus Short
(B2 8-127)
What are the Minor Faults in the Electrical System? (5)
Overvoltage Undervoltage Underfrequency Overspeed Incorrect phase sequence
(B2 8-127)
What will cause the AC Crosstie to lock open?
A major fault
After a Major Fault how would you know that it is a Generator Differential Feeder Fault? Can the associated bus be powered and if so by what?
If zero voltage and zero frequency are observed on the associated voltmeter for that bus. Yes it can be powered by the APU.
After a Major Fault how would you know that a Generator Bus Short has occurred? Can the associated bus be powered and if so by what?
If good voltage is observed on the voltmeter for the associated bus. No it must not be powered by the APU as a short exists on the bus.
During a Minor Fault will the AC Crosstie automatically close?
Yes
What does the Ground Service AC Bus receive power from?
Right Generator Bus
APU
External Power
Generally what kind of items do the Generator Buses supply power to? Where do these buses get their power from?
High current draw items. They receive their power directly from the generator.
Generally what kind of items do the L/R AC Buses supply power to? Where do these buses get their power?
Low current draw items and the DC power distribution system. They receive power directly from the onside Generator Bus.
What is the purpose of a Generator Relay?
To provide a means of disconnecting the generator’s output from the Generator Bus. (B2 8-124)
What is the purpose of the Generator Control Relay?
Often referred to as the Field Relay this provides a means of controlling the generator field, or the way for the generator to produce current.
If the Generator Control Relay opens what other relay opens?
The Generator Relay will also open. The reason both switches exist is because you need a way to disconnect the power to the system (Generator Relay) and you need a way to stop the generator from producing power (Generator Control Relay).
What normally powers the Emergency DC Bus?
The Left DC Bus which is in turn powered by the Left AC Bus.
What gauges will work on Emergency Power?
Airspeed Cpt ADI without the FD Cpt Altimeter Cpt VSI EGT N1 N2 Oil pressure low lights
Can one TR power the entire airplane?
Yes
What indicates that the Emergency DC Bus is unpowered?
Captains pitot heat is inoperative.
What do the blue APU and External Power Available lights mean?
Power is available, meets frequency/voltage requirements, and the phase sequence is correct.
All temperature readings are powered by what?
AC power
All direct reading items are powered by what?
DC power
All pressure reading items are powered by what?
AC power
