B777 Electrical

Boeing 777 Electrics

Boeing 777 Electrics

1 / 15

What does the green EXTERNAL POWER AVAIL light indicate?

External power is disconnected from the airplane.

External power is connected to the airplane, correct and ready to power the electrical busses.

Electrical power is available to the electrical busses but may not be correct.

External power is connected to all the airplane's electrical busses.

2 / 15

What is the primary source of power for the transfer busses?

Ram Air Turbine.

Engine generators.

Main DC busses.

Backup generators.

3 / 15

Which condition(s) cause the ELEC GEN DRIVE L EICAS message to display?

GENERATOR CONTROL switch selected to OFF.

Either A or B is correct

Generator drive oil temperature is high.

Generator drive oil pressure is low.

4 / 15

The standby inverter converts DC power to AC power. The inverter powers the AC standby bus if the right transfer bus is not powered.

False.

True.

The standby inverter converts DC power to AC power. The inverter powers the AC standby bus if the left transfer bus is not powered.

5 / 15

Which one of the following is not a reason for the backup electrical system to automatically power one or both transfer busses?

One engine shutdown.

Approach (APP) mode is selected for autoland.

Only one main AC generator (includes APU) is available.

Power to one or both of the main AC busses is lost.

6 / 15

What is the secondary source of power for 'fly-by-wire' if one or more PMGs are unpowered?

Hot battery bus.

DC busses.

Main AC busses.

Left transfer bus.

7 / 15

Primary power for the flight control DC electrical system comes from permanent magnet generators (PMGs) housed within each backup generator. Variable frequency PMG AC power is used by individual power supply assemblies (PSAs) to provide DC power to the three flight control DC busses. To ensure a high level of system reliability, each PSA also has multiple AC power sources.

False.

True.

To ensure a high level of system reliability, each PSA also has multiple DC power sources (No AC power!). If primary PMG AC power is not available, secondary power for the left and right PSAs is provided by the related main DC bus. Secondary power for the center PSA is provided by the captain’s flight instrument bus. The hot battery bus provides additional backup power for the left and center PSAs only. Each PSA also uses a dedicated battery to prevent power interruptions to the related flight control DC bus. The batteries have limited capacity and are incorporated to supply power for brief periods during PSA power source transfers.

8 / 15

What provides DC power on the B777?

Standby inverters.

DC generators.

Transfer busses.

Transformer rectifier units.

9 / 15

Which one of the following is not true about the ram air turbine (RAT) generator?

The RAT can supply electrical and hydraulic power simultaneously.

The RAT is deployed automatically if both AC transfer busses lose power in flight.

The RAT cannot be manually deployed by pushing the RAM AIR TURBINE switch if any of the AC transfer busses powered.

The RAT generator provides standby power to the C1 and C2 TRUs.

10 / 15

Which bus operates only on the ground?

The left main AC bus.

The ground handling bus.

The ground service bus.

The right transfer bus.

11 / 15

Which one of the following is not true about the backup electrical system?

Right and Left backup generators power the converter at the same time.

Backup power is provided by one variable speed, variable frequency generator mounted on each engine.

If both IDGs and the APU generator are inoperative, a backup generator powers essential airplane equipment to reduce electrical loading on the backup generator, some of the systems becomes inoperative such as TCAS, Centre tank override/jettison pumps (centre tank fuel is unusable).

A frequency converter converts the generator frequency to a constant 400 Hz.

12 / 15

How are the busses powered if the right engine is started with the APU powering the left bus system and external power powering the right bus system?

External power continues to supply the right main bus.

The right engine generator powers both main busses.

The right engine genrator automatically powers the right main bus.

There is no automatic switching till the left engine is started.

13 / 15

You have a cold airplane (no power connected). Which items will be powered if you push the BATTERY switch ON?

The hot battery bus will be powered.

Only the main battery bus will be powered.

The APU controller and the DC fuel pump will be powered.

14 / 15

Which one of the following is not true about Electrical Load Management System (ELMS)?

When an additional power source becomes available or the loads decrease, ELMS restores power to shed systems in the same order of shedding(First shed system restored first).

If the electrical loads exceed the power available (airplane or external), ELMS automatically sheds AC loads by priority until the loads are within the capacity of the airplane or ground power generators.

The ELMS provides load management and protection to ensure power is available to critical and essential equipment.

Priority for shedding is galleys first, then utility busses. Utility busses are followed by individual equipment items powered by the main AC busses.

15 / 15

Which one of the following is not true about the DC electrical system?

The main DC electrical system uses four transformer-rectifier units (TRUs) to produce DC power.

The left TRU powers the left main DC bus.

The DC electrical system includes the main DC electrical system and the flight control DC electrical system.

The C1 TRU powers the first officer's flight instrument bus.

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