Electrical Power

Question 1

If the IDG has a fault with Low oil pressure, high oil temp, or a frequency fault, what would the flight deck effect be?

Answer 1

Electrical system sources and distribution system detects and isolates faults automatically. When a power source is not available the system reconfigures automatically to ensure electrical power loads are within the capacity of the operating power source.

Question 2

Can the IDG be reconnected in flight after disconnection?

Answer 2

No

Question 3

What electrical system parameters are displayed on the status page?

Answer 3

• Main battery voltage and current.
• APU battery voltage and current.
• whether they are being charged or discharged.

Question 4

What system ensures power availability to critical equipment during electrical overload?

Answer 4

Load Management System.

Electrical Load Control Unit (ELCU)

Question 5

What happens when load shedding occurs?

Answer 5

Load management system sheds AC loads by priority until loads are within the capacity of the aircraft or ground power generators.

Question 6

What are the indications shown during load shedding?

Answer 6

FUEL PUMP 3 FWD
FUEL OVRD 2 FWD
FUEL OVRD 3 FWD
FUEL OVRD CTR L
FUEL PUMP 2 FWD

Question 7

What occurs when two different power sources are connected to the same sync bus? (On ground)

Answer 7

Split system breaker divides the synchronous bus allowing each side of AC electrical system to be powered by separate auxiliary or external power sources.

Question 8

What power condition during start allows the whole synchronous bus to be powered by the first IDG coming online?

Answer 8

Split system breaker closes and power is provided to the synchronous bus by the IDG.

Question 9

If the aircraft is using dual ground power sources, which busses will be powered by the first IDG coming online?

Answer 9

The IDG powers it’s side of the synchronous bus.

Question 10

During engine start, power transfer occurs with or without a break?

Answer 10

Without:

-Output from IDG and another power source momentarily synchronised before one source is disconnected.

Question 11

What powers AC Bus 2 when Number 2 IDG fails?

Answer 11

AC synchronous bus:

-Bus tie breaker closes to provide power from the synchronous bus.

Question 12

What is the effect of excessive oil temperature on the IDG if not manually disconnected?

Answer 12

Disconnects IDG automatically and is not done manually by the crew. EICAS advisory message GEN OFF is displayed and loss of generator power output causes GCB to open.

Question 13

Can an APU generator be used in flight?

Answer 13

No- Ground use only.

Question 14

Which component allows connection between the AC buses and the sync bus?

Answer 14

Bus tie breaker

Question 15

How is a tripped bus tie breaker reset?

Answer 15

Pushing BTB off, then AUTO, resets logic circuitry and allows BTB to close if fault is corrected?

Question 16

How is the Ground Service Bus usually powered?

Answer 16

On ground and inflight whenever AC bus 1 is powered.
-When AC bus 1 is not powered, GSB can be connected to the same source at GHB by pushing Ground Service Switch on Main Deck Panel door L1.

Question 17

List the normal and alternate power sources for the captains transfer bus and the first officers transfer bus.

Answer 17

Captain: AC Bus 3 (ALTN AC Bus 1)

First officer: AC Bus 2 (ALTN AC Bus 1)

Question 18

How can the external power be connected to the ground service bus?

Answer 18

When AC Bus 1 is not powered, GSB can be connected to the same source at GHB (PWR by EXT PWR 1) by pushing Ground Service switch on main deck panel door L1.

Question 19

Which are the two power sources for the ground handling bus and what are their priorities?

Answer 19

EXT PWR 1 and APU GEN 1 (EXT PWR 1 has priority)

Question 20

List the users of ground handling bus.

Answer 20

• Lower cargo handling equipment and Compartment lights.
• Fuelling System.
• Aux hydraulic pumps 1 and 4.

Question 21

List the users of utility busses.

Answer 21

• Forward main fuel pump 2 and 3.
• Forward OVRD/jettison pump 2 and 3.
• Centre OVRD/Jettison pump.
• Galley equipment.

Question 22

How is ELEC UTIL BUS fault reset?

Answer 22

Cycling the Utility Power switch OFF, then ON, restores power to the effected bus of the fault is corrected.

Question 23

With EXT 2 or APU 2 AVAIL lights illuminated, which bus can be powered?

Answer 23

Main Deck Cargo Handling Bus.

Question 24

During a normal Autoland electrical power isolation, which AC bus powers the synchronous bus?

Answer 24

AC bus 4

Question 25

Can you view the Electrical Synoptic Oage during Autoland below 1500 feet RA?

Answer 25

No

Question 26

What is the normal and alternate power sources for the main standby bus and the time limitation?

Answer 26

Normally powered by AC Bus 3.

Main battery can supply main standby bus through main hot battery bus for 30 minutes minimum.

Question 27

List the users of the main AC standby bus

Answer 27

-Left EIU, CDU, ILS, VOR.
-Various flight control components.
-Standby ignition for all engines.
Primary EICAS display, standby instrument lights.
-Left ADC, Transponder, EFIS control panel.

Question 28

What is the normal and alternate power source for the APU standby bus and the time limitation?

Answer 28

Normally powered by Captains transfer bus (AC bus 1 and 3).

APU standby inverter from APU battery through APU hot battery bus (30 minutes minimum)

Question 29

List the users of the APU standby bus.

Answer 29

Left FMC
Left ND
Left PFD

Question 30

Describe the selections available for the standby power selector.

Answer 30

OFF- standby power not available.
AUTO- main bus and APU standby bus powered from available sources.
BATT- ground maintenance use only.

Question 31

How long can the main and APU battery supply power?

Answer 31

Minimum 30 minutes.

Question 32

Which switch selection is required to isolate both BTB and DCIR?

Answer 32

Pushing Bus Tie Switch to OFF

Question 33

HOT BAT bus is normally powered from what source?

Answer 33

AC bus 1/GSB