Electrical Flashcards
What are the sources of DC power?
- Three Transformer Rectifier Units (TRU’s).
- Main Battery.
- Main Battery Charger.
What happens when an IDG is decoupled?
When the Generator Drive Disconnect Switch is placed to DISCONNECT, with the Engine Start Lever in Idle, A solenoid operated pawl mechanically interfaces with a worm-gear. The worm gear retracts the splined IDG drive shaft out of the gearbox for a complete de-coupling from engine rotation.
(Can only be reset on ground by MX)
What causes the illumination of the DRIVE light?
An IDG has experienced low oil pressure caused by:
-Engine Shutdown.
-IDG mechanical failure.
- DISCONNECT switch.
-auto-decouple due to
high oil temperature
When is the GRD POWER AVAILABLE light illuminated?
When the external power is connected, and the power is within tolerances and available for connection to the AC buses.
This light remains illuminated so long as those conditions are met, regardless of whether external power is powering the AC System.
What are the basic principles of operation of the 737 Electrical System?
Two basic principles of the 737 Electrical System:
-There’s no paralleling of AC power sources
- Source of power being connected to a Transfer Bus automatically disconnects an existing source.
How is the AC standby bus normally powered?
The AC standby bus is normally powered by Transfer Bus 1.
What is indicated by a GEN OFF BUS (blue) light?
An IDG is not supplying power to the respective Transfer Bus.
Is it possible to power an AC bus with External power and the other AC transfer bus with APU power?
No. It is not possible to power one transfer bus with external power and the other transfer bus with APU power. Reference schematic Figure 7 on 6.010 page 8.
What is the load shedding logic when only one source of AC power is available?
Load shedding occurs by:
*Transfer Bus 2
main and Galley Busses
*Transfer Bus 1
Main and Galley Busses
*IFE Busses
What is the automatic generator on-line feature?
In case the aircraft takes off with the APU powering both Transfer Busses.
If the APU is either shutdown or fails, the IDG (engine generators) are automatically connected to their related transfer busses.
- This feature only occurs one 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-tie relay is normally closed except
When the glide slope is active during a Flight Director or Auto Pilot ILS approach.
How is the DC standby bus normally powered?
The DC standby bus is normally powered by TR1, TR2, or TR3.
The BAT switch controls which bus(ses)?
Selecting BAT Switch ON powers both the switched hot battery bus and the battery bus.
What does the illumination of the BAT DISCHARGE amber light on the AC and DC panel indicate?
Excessive discharge of the main battery and/or auxiliary battery.
(Starting the APU with battery power may ill’ the BAT DISHCARGE light during start)
What it the purpose of the static inverter?
Convert of DC to AC power.
What does illumination of the TR UNIT amber light indicate?
On the ground:
Failure of TR1, TR2, or TR3
In flight:
Failure of TR1
or Failure of TR2 AND TR3.
With the loss of all AC power, if automatic switching does not occur, how can the standby busses be powered?
Setting STANDBY POWER switch to BAT.
-This overrides the automatic relay and
places the AC standby bus, DC standby bus, and Battery Bus on battery power regardless of BAT switch position.
What causes the illumination of the STANDBY PWR OFF light?
One or more of the following busses are
un-powered:
* AC Standby bus.
* DC Standby bus.
* Battery Bus.
What causes the illumination of the ELEC light, and when is it armed?
When a fault is in the Standby Power or
DC Power System occurs.
*The ELEC light is inhibited in flight
Armed on the ground
If all generators are inoperative, and the main battery and the auxiliary battery are the only sources of power, which Display Units are available?
- CA outboard DU, (display unit) with PFD.
- CA inboard DU, (display unit) with ND
- Captains clock.
- Left EFIS control panel.
- Standby Instruments.
