Electrical Flashcards
What are the basic principles of operation of the 737 Electrical System?
There is no paralleling of the AC sources of power
The source of power being connected to a Transfer Bus automatically disconnects an existing source
What are the sources of AC and DC power?
AC power: 2 Engine-Driven Generators, APU, External Power, Static Inverter
DC power: 3 TRUs, Main Battery, Main Battery Charger, Auxiliary Battery, Auxiliary Battery Charger
What happens when an IDG is decoupled?
A worm-gear will retract the splined IDG drive shaft out of the gearbox for complete drive decoupling with engine rotation.
What does a generator DRIVE (amber) light indicate?
Indicates the respective IDG has experienced low oil pressure caused by:
-IDG failure
-engine shutdown
-IDG disconnected by activation of the DISCONNECT switch
-IDG auto-decouple due to high oil temperature (182C)
What does the GRD POWER AVAILABLE (blue) light indicate?
Indicates the external power cord is connected to the aircraft and power (checked within tolerances) is available for connection to the aircraft busses.
Through the Bus Transfer system, how can a transfer bus be powered if normal power is lost?
The Transfer bus can be powered by any available source through the Tie Bus with the Bus Tie Breakers (BTB)
What does the GEN OFF BUS (blue) light indicate? APU GEN OFF BUS (blue) light?
GEN: Indicates an IDG is not supplying power to the respective Transfer Bus.
APU GEN: Indicates the APU is operating above 95% RPM (ready-to-load condition) and not powering a bus
What does the BUS TRANSFER switch allow?
If the source powering the Transfer Bus is disconnected or fails, the source powering the opposite Transfer Bus automatically pics up the unpowered Transfer Bus with the BTBs
What is the load shedding logic for single generator operation?
Shed electrical load incrementally based on load sensing.
-Galleys and Main Bus on Transfer Bus 2 are shed first
-Galleys and Main Bus on Transfer Bus 1 second
-IFE Busses third
What is the Automatic Generator Online Feature?
In case the aircraft takes off with the APU powering both Transfer Busses, if the APU is either shut down or fails, the engine generators are automatically connected to their related Transfer Busses.
What does an ELEC (amber) light indicate?
illuminates to indicate a FAULT exits in DC Power System or Standby Power System
What is the TR UNIT (amber) light logic.
The light illuminates on the ground for any TRU failure.
In flight the light illuminates if:
TRU 1 Fails or;
Both TRU 2 and 3 Fail
What is the Cross Bus Tie Relay and what does it do?
The Cross Bus Tie Relay automatically opens, isolating DC Bus 1 from DC Bus 2 under the following conditions.
-Glide Slope capture during a Flight Director or Autopilot ILS approach. This isolates the DC Busses during approach to prevent a single failure from affecting both navigation receivers and Flight Control Computers
-Bus Transfer Switch positioned to OFF
What does the BAT switch do?
-Provides power to the Battery Bus and Switched Hot Battery Bus
-Energizes relays to provide automatic switching of the Standby Electrical System to battery power with the loss of normal power.
What does the BAT DISCHARGE (amber) light indicate?
Illuminates when excessive battery discharge is detected in the Main Battery and/or Auxillary Battery.
