Electrical System *** Flashcards
What does the “AVAIL” light indicate on the External and APU PWR switches?
• The related power source (APU or EXT) is plugged in and the power quality is acceptable and available.
What bus is powered on the ground when the APU generator 1 or external power 1 is available?
• Ground handling bus
When is the main deck cargo handling bus powered?
• When the “AVAIL” light is displayed on the APU 2 or EXT 2 switches.
What electrical power source would you select if ground handling is required?
• The number one auxiliary or external power
When is the ground service bus powered?
• When A/C bus 1 is powered, either on the ground or in flightWhen the Ground Service Switch is on and Ext or APU power is Avail
What is the function of the Standby Power Switch in the Auto Position?
• Allows the main and APU standby busses to be powered from available sources.
Where would you find the Electrical Power-up procedure?
Note:Refer to the FCOM, Vol. 1, Supplemental Procedures
What does a Bus Isolation (ISLN) light illuminated indicate?
- BTB open
* AC bus isolated from synchronous bus
What happens when you push a Generator Drive Disconnect (DRIVE DISC) switch?
- Disconnects IDG from engine when above idle speed
* Open related Generator Control Breaker
What condition would automatically disconnect the IDG if not manually disconnected by the flight crew?
• Excessively high drive oil temperature
How do you reconnect an IDG that has been disconnected?
- Maintenance action is required
* The IDG cannot be restored by flight crew action
What does a Generator DRIVE light indicate?
- IDG oil pressure low, or
- IDG oil temperature high, or
- GCB open due to uncorrectable generator frequency fault
What are some of the equipment items powered by the Utility busses?
- APU T/R
- Forward main pumps 2 and 3
- Forward override/jettison pumps 2 and 3
- Center override/jettison pump
- Galley equipment (freighter)
Describe the electrical load shedding process.
• Utility bus loads are shed one at a time through the electrical load control unit (ELCUs) in a programmed sequence until the overload condition is relieved.
What is the purpose of the electrical system overload protection?
• To ensure power is available to critical and essential equipment.
During load shedding, would you expect to see an EICAS Advisory message ELEC UTIL BUS L, R?
• No, this message is inhibited during load shedding
What are the main AC electrical power sources?
- Four IDGs
- Two auxiliary power sources (APU generators)
- Two external power sources
Describe the function of the Split System Breaker (SSB).
• Divides the synchronous bus, allowing each side of the AC electrical system to be powered by separate auxiliary or external power sources.
Describe the electrical system sequence of events during engine start with the SSB open.
- The IDG powers its side of the synchronous bus when voltage and frequency are acceptable.
- The previous power source is disconnected.
Describe the electrical system sequence of events with a single power source powering the synchronous bus, when an engine is starting, SSB closed.
- The IDG powers the entire synchronous bus when voltage and frequency are acceptable.
- The SSB remains closed and the original power source is disconnected
Which bus powers the Captain’s transfer bus?
- AC bus 3
* If AC bus 3 is unpowered, AC bus 1 powers the Captain’s Transfer bus
Which bus powers the First Officer’s transfer bus?
- AC bus 2
* If AC bus 2 is unpowered, AC bus 1 powers the First Officers transfer bus.
Which bus provides backup power for both transfer busses captain and FO transfer ?
1 is all you need
• AC bus 1
What are some of the equipment items powered by the ground service bus?
- Main and APU battery chargers
- Fuel pumps for APU start
- Flight deck flood, navigation, and service lights
- Miscellaneous service outlets a
