Electrical Flashcards
What are the two “basic principles of operation” for the 737 Electrical System?
No paralleling of power & the source of power being connected to a Transfer Bus automatically disconnects an existing source
What could cause the illumination of the Generator DRIVE light?
Respective IDG has low oil pressure.
What happens when positioning the GRD PWR switch ON?
Removes previously connected power and connects external power to both Transfer Busses.
What does the BUS TRANSFER switch, in the AUTO (guarded) position, allow?
Allows the Bus Tie Breakers (BTB) to operate automatically to maintain power to the AC Transfer Busses from any operating generator or external power.
Which light(s) indicate(s) the APU is ready-to-load, but not powering a bus?
APU GEN OFF BUS
If the AC Transfer Buses are powered by External Power, momentarily positioning either APU GEN switch ON will cause the APU to power which bus(es)? What lights would you see?
Both transfer busses will be powered by the APU & APU GEN OFF BUS light goes away and SOURCE OFF light on opposite side of triggered switch illuminates.
When the APU is powering a Transfer Bus, how can you power the opposite Transfer Bus?
APU or IDG.
What buses are shed when the APU is operating in flight as the single electrical source?
All Galley Busses and Main Busses are automatically shed.
Moving a GEN (Generator) switch to ON powers which bus? What lights would you see?
Respective Transfer Bus. GEN OFF BUS goes out & SOURCE OFF on the opposite side.
Describe the Automatic Generator Online Feature.
If the aircraft takes off with the APU powering both transfer busses power will be automatically transferred if the APU shuts down.
What does the ELEC light (amber) indicate?
Fault exists in DC Power System or Standby Power System.
When does the Cross Bus Tie Relay open and isolate DC Bus 1 from DC Bus 2?
At Glide Slope capture during a Flight Director or Autopilot ILS approach or bus transfer switch off.
Which Bus is always connected to the battery?
Hot battery bus.
When does the BAT DISCHARGE light (amber) illuminate?
Excessive battery discharge is detected in the Main Battery and/or Auxiliary Battery.
What is/are the alternate power source(s) for AC standby power?
Static inverter from the batteries to AC standby bus.
