Chapter 6: Electrical Flashcards
Describe the function of the GROUND SERVICE switch on the Forward F/A panel.
Provides manual control of ground service busses. Enables servicing of airplane using external power without activating AC transfer busses.
ON – connects external power to ground service bus.
OFF – disconnects external power from ground service bus.
Explain the meaning of the blue GRD POWER AVAILABLE light.
Illuminated (blue)-
Ground power is connected and meets airplane power quality standards.
Explain the meaning of the blue APU GEN OFF BUS light.
Illuminated (blue)-
APU is running and not powering a bus.
Explain the meaning of the blue GEN OFF BUS light.
Illuminated (blue)-
IDG is not supplying power to the related transfer bus.
Recall where to read voltage, frequency and amps.
AC and DC Metering panel on the Forward Overhead panel.
Explain the meaning of the amber DRIVE light.
Illuminated (amber)-
Integrated Drive Generator (IDG) low oil pressure.
Explain the meaning of the amber TRANSFER BUS OFF light.
Illuminated (amber)-
- Related Transfer Bus is not powered.
Extinguished-
-Related Transfer Bus is powered
Explain the meaning of the amber SOURCE OFF light.
Illuminated (amber)-
No source has been manually selected to power the related transfer bus, or the manually selected source has been disconnected.
Note: SOURCE OFF light triggers ELEC light and Master Caution to alert crew of change to source of power to associated Transfer Bus.
Explain the meaning of the amber BAT DISCHARGE light.
Illuminated (amber)-
With BAT switch ON, excessive battery discharge detected.
Explain the meaning of the amber TR UNIT light.
Illuminated (amber) – TR failure.
Explain the meaning of the amber ELEC light.
Illuminated (amber)-
fault exists in DC power system or standby power system.
Note: Operates only with airplane on ground.
Explain the meaning of the amber STANDBY PWR OFF light.
Illuminated (amber)-
One or more of the following busses are unpowered:
- AC standby bus.
- DC standby bus.
- Battery bus.
Recall the number of minutes available on standby power with two fully charged batteries.
60 minutes
Recall the function of the Ground Power (GRD PWR) switch.
Three position switch, spring loaded to neutral
OFF – disconnects ground power from AC transfer busses.
ON – if momentarily moved to ON position and ground power is available:
- removes previously connected power from AC transfer busses.
- connects ground power to AC transfer busses when power quality is correct.
Recall that it is not possible to use APU power and GRD power at the same time.
There are two basic principles of operation for the 737 electrical system:
- No paralleling of AC sources of power.
- The source of power being connected to a transfer bus automatically disconnects the existing source.
Recall the function of positioning the APU Generator (GEN) Switches to ON.
Three position switch, spring loaded to neutral
Neither AC transfer bus powered by an IDG…
Moving an APU GEN switch to ON:
- Powers both AC transfer busses from the APU generator.
- Disconnects external power, if connected.
-opposite SOURCE OFF light illuminates until the APU GEN switch is moved ON.
Both AC transfer busses powered by IDGs…
Moving an APU GEN switch to ON:
- Powers the related AC transfer bus from the APU generator.
- Other AC transfer bus continues to receive power from the IDG.
Recall the location of the GROUND SERVICE Switch
The forward flight attendant control panel.
Recall the function of the Generator (GEN) Switches
Three position switch spring-loaded to
neutral
OFF – disconnects IDG from related AC transfer bus by opening generator circuit breaker.
ON – connects IDG to related AC transfer bus by disconnecting previous power source and closing generator circuit breaker.
Recall the function of the BUS TRANSFER Switch.
AUTO (guarded position) – bus tie breakers operate automatically to maintain power to AC transfer busses from any operating generator or external power.
OFF – isolates AC transfer bus 1 from AC transfer bus 2.
Recall the function of the Generator Drive Disconnect (DISCONNECT)
Switches. (guarded)
Disconnects IDG if electrical power is available and engine start lever is in IDLE. IDG cannot be reconnected in the air.
Explain the function of the BAT (battery) switch.
ON –
- Provides battery power.
- Provides automatic switching of standby electrical system to battery power with loss of normal power.
OFF –
-Removes battery power.
