Which of the following is FALSE concerning the B737NG electrical system?
The AC power sources are paralleled by an auto-paralleling system.
The purpose of the AC ground service bus is to power:
- The cabin lighting.
- The utility outlets.
- The battery charger.
The TRs (Transformer rectifier) convert:
115 volts AC to 28 volts DC.
Which is the power source for the AC standby bus?
Transfer bus 1 under normal conditions.
If the AC source powering a transfer bus fails, the transfer bus will remain unpowered.
False.
A high oil temperature in the IDG would cause an automatic disconnect of the IDG.
True.
The TR3 cross bus tie relay automatically opens at glide slope capture to:
Prevent a single bus failure from affecting both navigation receivers and Flight Control Computers (FCCs).
In flight, if the APU is supplying both AC Transfer busses, positioning the BUS TRANS switch to OFF will:
Cause AC Transfer bus No.2 to lose power.
The TR3 Disconnect Relay:
Automatically opens at glide slope capture during a Flight Director or Autopilot ILS approach.
The Engine Integrated Drive Generators (IDGs):
Allow the generator to maintain a constant speed throughout the normal range of operation.
After the loss of all generators, a fully charged battery can furnish power to the STANDBY Bus equipment for a minimum of:
30 minutes.
The cross bus tie relay:
Opens up if BUS TRANSFER switch is moved to OFF.
Illumination of the GND POWER AVAILABLE light indicates
Ground power is connected and meets airplane power quality standards.
For ground service, a ground service switch is placed:
On forward attendant´s panel.
The GROUND POWER AVAILABLE light will extinguish when:
The AC ground power cart has been disconnected.
The 115V AC Standby Bus is powered by:
Transfer Bus No.1 under normal conditions and Battery through Static Inverter with failure of both engine driven generators.
One basic principle of operation for the B737 electrical system is:
There is no paralleling of the AC power sources.
Because engine generators power the transfer busses directly, and transfer busses are connected by a bus tie system, the loss of an engine driven generator will not necessarily result in the loss of any bus(es).
True.
The modified DC system architecture resulted in the TR3 disconnect relay found in the B737-300 thru 500 being replaced with a cross bus tie relay. The cross bus tie relay opens automatically under the same circumstances as did the TR3 disconnect relay.
True.
The SOURCE OFF light will illuminate:
- When the source selected to power the transfer bus has failed and the automatic bus transfer
function has closed the BTBs to power the transfer bus from another source. - When the source selected to power the Transfer bus and the automatic transfer function have both failed, resulting in the transfer bus being unpowered.
- When the TRANSFER BUS OFF light is illuminated.
When the STANDBY POWER Switch is OFF:
The STANDBY PWR OFF light will be illuminated.
Illumination of the BAT DISCHARGE light indicates:
Excessive battery discharge is detected with the battery switch ON.
In the event that the airplane battery is depleted, the APU can be started using DC external power.
True.
Illumination of the blue GEN OFF BUS light indicates:
The IDG is not supplying power to its associated transfer bus.
