06 - Electrical Flashcards
ELECTRICAL
- What are the sources of DC power?
3 TRUs
Main battery
main battery charger
- What happens when an IDG is decoupled?
The splined IDG drive shaft is retracted out of the gearbox for complete drive decoupling from engine rotation
- What causes the illumination of the DRIVE light?
IDG experiencing low oil pressure caused by:
- Engine shutdown
- IDG mechanical failure
- IDG disconnected by DISCONNECT switch
- IDG auto-decouple due to high oil temperature
- When is the GRD POWER AVAILABLE light illuminated?
External power cord is connected to the aircraft and the power is checked to be within tolerances and available for connection to the AC buses
- What are the basic principles of operation of the 737 electrical system?
- There is no paralleling of AC power sources
- The source of power being connected to a transfer bus automatically disconnects an existing source
- How is the AC standby bus normally powered?
By transfer bus 1
- What is indicated by a GEN OFF BUS light?
An IDG is not supplying power to the transfer bus
- Is it possible to power one AC transfer bus with external power and the other AC transfer bus with APU power?
No. As soon as the GRD PWR switch is selected ON (with GRD POWER AVAILABLE illuminated), the BTB will close supplying external power to both transfer buses
- What is the load shedding logic when only one source of AC power is available?
APU;
- on ground it attempts to carry the full electrical load
- in flight, if the APU is the only source of power, all main and galley buses are automatically shed
Single IDG;
- sheds transfer bus 2 main and galley buses
- sheds transfer bus 1 main and galley buses
- IFE buses
- What is the automatic generator on-line feature?
In the event an aircraft takes off with the APU powering both transfer buses and the APU is subsequently shut down or fails, the IDGs are automatically connected to their related transfer buses. This feature only occurs once per flight cycle.
- How long can two fully-charged batteries provide standby power?
A minimum of 60 minutes
- When does the DC cross bus tie relay open?
With the BUS TRANS switch in AUTO, the cross bus tie opens when Glide Slope is active during a FD or AP ILS approach
- How is the DC standby bus normally powered?
By TR1, TR2, or TR3
- The BAT switch controls which bus(ses)?
The switched hot battery bus and battery bus
- What does the illumination of the BAT DISCHARGE light on the AC and DC Metering panel indicate?
An excessive discharge of the main battery and/or auxiliary battery
- What does the illumination of the TR UNIT light indicate?
- On ground; failure of TR1, TR2, or TR3
- In flight; failure of TR1, or TR2 and TR3
- With the loss of all AC power, if automatic switching does not occur, how can the standby power buses be powered?
By placing the STANDBY POWER switch to BAT
- What causes the illumination of the STANDBY PWR OFF light?
One or more of the following buses are unpowered;
- AC Standby bus
- DC Standby bus
- Battery bus
