Electrical Flashcards
TRU light logic (when it will illuminate)
- Ground
- Flight
Ground:
- any failure means a TR Unit light.
Flight:
- TR 1 Fails or
- TR 2 AND 3 Fails
AC Transfer Buses switch
What does each option do?
AUTO:
- Allows BTB’s to configure to allow AC power AC Transfer Buses via IDG’s, APU, or External Power. DC Cross Tie also will provide isolation as required.
*Usually an IDG powers it’s onside Transfer Bus.
OFF:
- Isolates AC Transfer Bus 1 from 2 (in the case one IDG is powering both)
What does this light indicate?
Dim?
Bright?
Bright?
- APU Generator is operating above 95% RPM and NOT powering a bus.
Dim?
- APU GEN is powering the respective bus
What does moving the 3 position APU switches to ON do when the AC transfer busses are unpowered (Dark Airplane, other than BAT ON)?
What would the light brightness be before and after?
- Spring loaded to neutral
- ON:
Connects APU GEN to BOTH buses
Disconnects GRD PWR
Opposite Source of light illuminates until other APU GEN switch is selected ON, then dark.
LIGHTS
- Bright when OFF bus, Dark when ON bus
Remember 737 electrical rule! Only 1 source, and the previous source is kicked off.
If the TRANSFER buses are unpowered can you select one bus to power with the APU and one with External (GRD PWR)?
No, an APU switch selected to ON actually connects both Transfer buses to the APU GEN when on external power
What do the 3 position GEN 1 and GEN 2 switches do on the AC Transfer panel?
ON
- Powers respective transfer bus by IDG as long as the power is deemed good. Takes previous source off the bus.
OFF
- Terminates power to respective bus
What does the GEN OFF BUS light indicate when BRIGHT or Dark
Bright: IDG not supplying power
Dark: IDG IS providing power to bus
What does the TRANSFER BUS OFF light indicate?
The transfer bus is not powered.
It will cause a ELEC annunciator on the recall panel and MASTER CAUTION
What does the SOURCE OFF light indicate?
- No manually selected source to the respective transfer bus (could be disconnected manually)
It will cause a ELEC annunciator on the recall panel and MASTER CAUTION
What does the STANDBY POWER switch ‘AUTO’ position do?
AUTO: In the event of all engine or APU electrical failures the Batteries power the Standby Buses. This also occurs with the loss of power from AC Transfer Bus 1 or DC Bus 1.
- Standby Bus - Powered by Batteries via an inverter
- DC Standby, Battery Bus, Hot Battery Bus, & Switched Hot Battery Bus are powered by batteries
What does the STANDBY POWER switch ‘OFF’ position do?
OFF: Removes power from both AC and DC Standby buses, which illuminates the STANDBY POWER OFF Light and associated annunciator.
What does the STANDBY POWER switch ‘BAT’ position do?
Overrides automatic switching and connects the Stanby busses as well as the battery bus to batteries.
