ELECTRICAL SYSTEM

Question 0

What systems do you have if powered by ONE Generator only ?

Answer 0

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.

Question 1

If you lose all Generators what instruments do you have ?

Answer 1

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.

Question 2

How long will the battery provide power to the Standby Bus ?

Answer 2

The main battery can provide power to the standby bus for a minimum of 90 minutes

Question 3

What power sources are available in flight ?

Answer 3

Left and Right IDGs and the APU Generator

Question 4

In the generator control (GEN CONT )switch
What does the White ON bar indicate
What does the Amber OFF light indicate ?

Answer 4

The switch is ON to arm the generator breaker for automatic operation

The generator breaker is open

Question 5

Which FOUR buses can be powered by the Batteries ?

Answer 5

Hot Battery Bus
Battery Bus
Standby AC Bus
Standby DC Bus

Question 6

What causes the HDG to start operating ? **

Answer 6

When both Right and Left main AC Buses are unpowered.

Question 7

How are the DC buses powered?

Answer 7

By right and left TRUs supplied by the AC Buses

Question 8

Name the Aircraft batteries ?

Answer 8

Main and APU batteries

Question 9

Which units charge the Main and APU batteries ?

Answer 9

The battery chargers

Question 10

Which Bus provides the power for the Battery Chargers ?

Answer 10

The Ground Service Bus

Question 11

Which sources can power the Ground handling Bus ?

Answer 11

APU or External Power

Question 12

Can the Ground Handling Bus be powered in flight ?

Answer 12

No

Question 13

Is the Ground Service Bus powered in flight ?

Answer 13

Yes

Question 14

Which Main Bus normally supplies the Ground Service Bus ?

Answer 14

Right main AC Bus

Question 15

What are the Left and Right AC Transfer Busses for ? **

Answer 15

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.

Question 16

Does the RAT have any Electrical function ? **

Answer 16

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.

Question 17

What does the Flight Instrument Bus Power switch do? **

Answer 17

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

Question 18

How is the STANDBY AC BUS powered ?

Answer 18

The APU battery and main battery are paralleled and power the Standby inverter to energise the STANDBY AC BUS

Question 19

How is the STANDBY DC BUS powered ?

Answer 19

By the APU battery and main battery working in parallel.

Question 20

What does the HDG power ?

Answer 20

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

Question 21

What needs to fail for the Aircraft to be on Battery Power only ?

Answer 21

When both main AC buses fail, and the Hydraulic Driven Generator fails, (IF INSTALLED), the battery is the only source of electrical power.

Question 22

What THREE sources of power can supply the Main AC Buses ?

Answer 22

IDGs
APU gen
External power

Question 23

What does the DRIVE light indicate on the IDG ?

Answer 23

High Oil temperature
Low oil pressure

Engine shutdown - light on due Low oil Press

Question 24

What is the function of the GENERATOR CONT SWITCH ?

Answer 24

Controls associated Generator Breaker automatically. The Gen control light will come on anytime the Generator breaker opens

Question 25

How are the Left and Right buses linked ?

Answer 25

By the Bus Tie Breakers

Question 26

When an engine is started what happens to associated

a. Generator Control breaker

b Bus tie breaker

Answer 26

a. Closes

b. Opens

Question 27

APU Generator breaker switch

Has an off light which illuminates for TWO reasons.

Answer 27

If the Gen has a fault with the APU running

Or

The switch is off.