Electrical Flashcards
Describe the function of the GROUND SERVICE switch on the fwd 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 fwd ovhd panel
Explain the meaning of the amber DRIVE light
Illuminated (amber): 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 GRD PWR switch
Three position switch, spring loaded to neutral:
- OFF: disconnects ground power from AC transfer bus
- 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
Is it possible to use APU and GRD power simultaneously?
No
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 power
Recall the function of positioning the APU GEN switches ON
3 position switch, spring loaded to neutral
Neither AC transfer bus power 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
Explain the function of the BAT switch
ON:
- Provides battery power
- Provides automatic switching of standby electrical system to battery power with loss of normal power
OFF:
- Removes battery power
Recall the components powered by the ground service bus
- Utility outlets
- Cabin lighting
- Battery chargers
Recall the components powered by the ground service bus
- Utility outlets
- Cabin lighting
- Battery chargers
Recall the location of the GROUND SERVICE switch
The fwd flight attendant control panel
Recall the function of the 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: 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
Disconnects IDG if electrical power is available and engine start lever is in IDLE
IDG cannot be reconnected in the air
