ELECTRICAL SYSTEM Flashcards
What systems do you have if powered by ONE Generator only ?
Both Main AC Busses will still operate but Load shedding may occur:
Electrical load shedding occurs automatically to ensure power is available to critical and essential equipment.
The load shedding is galley power first, then utility busses. Utility busses are followed by individual equipment items powered by the main AC busses. When an additional power source becomes available or the load decreases, the electrical system automatically restores power to the shed systems (in the reverse order).
Examples of load shedding that may be observed during NORMAL operations include:
an electric hydraulic pump prior to engine start
center tank fuel pumps prior to engine start
utility busses during engine start.
Examples of load shedding that may be observed during NON-NORMAL operations include:
utility busses after a generator failure
center tank fuel pump after an engine failure
cabin ceiling lights after an engine failure.
If you lose all Generators what instruments do you have ?
If you lose IDGs, APU Generator and HDG you are down to Battery Power only.
The battery/standby power electrical system can supply DC and AC power to selected flight instruments, communications and navigation systems, and other critical systems, if there are main AC and DC electrical power system failures.
How long will the battery provide power to the Standby Bus ?
The main battery can provide power to the standby bus for a minimum of 90 minutes
What power sources are available in flight ?
Left and Right IDGs and the APU Generator
In the generator control (GEN CONT )switch
What does the White ON bar indicate
What does the Amber OFF light indicate ?
The switch is ON to arm the generator breaker for automatic operation
The generator breaker is open
Which FOUR buses can be powered by the Batteries ?
Hot Battery Bus
Battery Bus
Standby AC Bus
Standby DC Bus
What causes the HDG to start operating ? **
When both Right and Left main AC Buses are unpowered.
How are the DC buses powered?
By right and left TRUs supplied by the AC Buses
Name the Aircraft batteries ?
Main and APU batteries
Which units charge the Main and APU batteries ?
The battery chargers
Which Bus provides the power for the Battery Chargers ?
The Ground Service Bus
Which sources can power the Ground handling Bus ?
APU or External Power
Can the Ground Handling Bus be powered in flight ?
No
Is the Ground Service Bus powered in flight ?
Yes
Which Main Bus normally supplies the Ground Service Bus ?
Right main AC Bus
What are the Left and Right AC Transfer Busses for ? **
Left and right AC transfer busses power items considered necessary for ETOPS flights, which are not powered by the battery/standby system. Transfer busses are normally powered by their associated main AC busses, but also can be powered by the Hydraulic Driven Generator when both AC busses are unpowered.
Does the RAT have any Electrical function ? **
No.
When deployed, the RAT, provides hydraulic power to the flight controls portion of the center hydraulic system. The RAT provides adequate hydraulic power at speeds above 130 knots. In flight, the RAT deploys automatically when both engines fail. The RAT is inhibited from auto deployment on the ground.
What does the Flight Instrument Bus Power switch do? **
ALTN – allows hydraulic driven generator to power first officer’s flight instruments
OFF (ALTN not visible) – allows hydraulic driven generator to power captain’s flight instruments
How is the STANDBY AC BUS powered ?
The APU battery and main battery are paralleled and power the Standby inverter to energise the STANDBY AC BUS
How is the STANDBY DC BUS powered ?
By the APU battery and main battery working in parallel.
What does the HDG power ?
The HDG is powered by the Centre Hydraulic System and provides both AC and DC power
It provides AC power to 4 items
Left AC transfer Bus
Right AC Transfer Bus
Standby AC Bus through the Left AC Transfer Bus
The Captains or First Officer’s Flight Instruments through the Flight Instrument Transfer Bus
It provides DC Power to:
Hot Battery bus
Battery Bus
The DC Standby Bus
What needs to fail for the Aircraft to be on Battery Power only ?
When both main AC buses fail, and the Hydraulic Driven Generator fails, (IF INSTALLED), the battery is the only source of electrical power.
What THREE sources of power can supply the Main AC Buses ?
IDGs
APU gen
External power
What does the DRIVE light indicate on the IDG ?
High Oil temperature
Low oil pressure
Engine shutdown - light on due Low oil Press
What is the function of the GENERATOR CONT SWITCH ?
Controls associated Generator Breaker automatically. The Gen control light will come on anytime the Generator breaker opens
How are the Left and Right buses linked ?
By the Bus Tie Breakers
When an engine is started what happens to associated
a. Generator Control breaker
b Bus tie breaker
a. Closes
b. Opens
APU Generator breaker switch
Has an off light which illuminates for TWO reasons.
If the Gen has a fault with the APU running
Or
The switch is off.
