ELECTRICAL SYSTEM Flashcards
What does “AVAIL” light indicate on the External and APU PWR switches?
Power connected (EXT) and quality acceptable.
What Bus is powered on the ground when APU GEN 1 or EXT PWR 1 is available?
Ground handling bus
When is the Main Deck Cargo Handling Bus powered?
APU GEN 2 or EXT PWR 2 avail.
What electrical power source would you select if cargo handling is required?
EXT 1
When is Ground Service Bus powered?
On ground and in flight when AC Bus 1 is powered
What is the function of the Standby Power Switch in the auto position?
Allows Main and APU standby busses to be powered from available sources.
Where would you find the Electrical Power-up procedure?
Supplementary procedures 6.1
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. Opens related GCB
What condition would automatically disconnect the IDG if not manually disconnected by the flight crew?
Excessively high drive oil temp.
How do you reconnect an IDG that has been disconnected?
Maintenance action on ground.
What does a Generator DRIVE light indicate?
IDG Oil pressure low. IDG oil temp high. GBC open due to uncorrectable generator frequency fault.
What are some of the equipment items powered by the Utility busses?
Fwd Main fuel Pump 2&3. Fwd override/jettison pump 2&3. Centre override/jettison pump. Galley equipment. APU TR.
Describe the electrical load shedding process
If electrical loads exceed power available the load management system sheds AC loads by priority until the loads are within the capacity of airplane or ground power generators. Util bus loads are shed one at a time by ELCU’s in a programmed sequence until the overload condition in relieved. When an additional AC source is available the loads are restored in reverse order.
What is the purpose of the electrical system overload protection?
Load management system is configured 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, messages inhibited.
What are the main AC electrical power sources?
Four IDGs. Two APU Gens, Two external ground power sources.
Describe the function of the Split System Breaker (SSB)?
The SSB divides the synchronous bus allowing each side of the AC electrical system to be powered by seperate APU or EXT 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
Describe the electrical system sequence of events with a single power source powering the synchronous bus, when an engine is starting, SSB closed.
IDG powers the entire synchronous bus when voltage and frequency are acceptable. SSB remains closed, previous source is disconnected.
Which bus powers the Captain’s transfer bus and the main standby bus?
AC Bus 3
Which bus powers the First Officer’s transfer bus?
AC Bus 2
Which bus provides backup power for both transfer buses?
AC Bus 1
What are some of the equipment items powered by the ground service bus?
Main and APU generators. Fuel pumps for APU start. Flight deck flood, navigation and service lights. Misc service outlets and equipment.
How can the ground service bus be powered when AC bus 1 is not powered, while on the ground?
By pushing the ground service switch on the cabin panel at door 1L
What are some of the equipment items powered by the ground handling bus?
Lower cargo doors, lower cargo handling equipment.
Lower cargo lights, Fuelling system.
Aux HYD pump 4.
What bus powers the APU standby bus?
CAPT XFER
How is the electrical system configured during an automatic ILS approach (auto-land)?
AC and DC busses 1,2,3 are isolated from the synchronous bus to provide independent power sources for the three autopilots. AC bus 4 continues to power the synchronous bus.
What are some of the major components of the AC standby power system?
Main and APU standby busses.
Main and APU batteries. Main and APU standby inverters.
Standby power selector
What is the normal source of power for the main standby bus?
AC bus 3.
How does the main standby bus get power if AC bus 3 becomes unpowered in flight, all other conditions normal?
Powered by the main standby inverter, normally unpowered, is activated and receives its power from the main battery charger thru the main hot battery bus. Main battery charger is normally powered by AC bus 1 thru the ground service bus.
If both AC bus 3 and AC bus 1 are not powered, all other conditions normal, how is the main standby bus powered, and for how long can it be powered?
Powered by the main standby inverter, (normally unpowered) is activated and receives its power from the main battery thru the main hot battery bus for a minimum 30 minutes.
What are some of the equipment items on the main standby bus?
Primary EICAS. L CDU, EIU, ILS, VOR, Xponder, EFIS control, RMI, Sby instrument lights, Various flight control components.
What are the equipment items on the APU standby bus?
L PFD, ND, FMC
How is DC power provided by the electrical system?
Four TRU’s powered by its related AC bus
What is the normal power source for the main and APU battery busses?
DC Bus 3
If either AC bus 3 or DC bus 3 is unpowered, how is each battery bus powered?
By its related hot battery bus.
What are some examples of individual equipment items on the main battery bus?
Alt. APU controller, ENG fuel valves, xfeed valves, DOME, Storm & selected cockpit lights, IDG disconnect, manual pressurisation, trailing edge flap control, CA’s intern-phone, L VHF, & tuning panel
How is each hot battery bus normally powered?
By the ground service bus through its related battery charger.
What are some examples of equipment items on the main hot battery bus?
APU fuel SOV, All eng SPAR valves. APU, Engine, lwr cargo fire extinguishers. Fire sw unlock.
What are some examples of equipment items on the APU hot battery bus?
IRU L,C,R DC power, L&R outflow valves. APU inlet door, PRI APU controller.
