B777 Electrical

Boeing 777 Electrics

Boeing 777 Electrics

1 / 15

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

Main DC busses.

Ram Air Turbine.

Backup generators.

Engine generators.

2 / 15

During autoland, the busses isolate to allow three independent sources to power the three autopilot. In this case which one of the following is the power source for the right AC transfer bus, the right DC bus, and the first officer's flight instrument bus?

APY Generator

Backup System

Right IDG

Left IDG

3 / 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.

4 / 15

When will the RAT auto-deploy?

Both transfer busses unpowered, and both engines fail.

Both transfer busses unpowered, all three hydraulic systems low, both engines fail and C hydraulic system low

Both transfer busses unpowered, both engines fail and C hydraulic system low

Both transfer busses unpowered, all three hydraulic systems low, and both engines fail.

5 / 15

What is the primary source of standby power if all normal AC and DC power source fail?

Backup generators.

Main battery.

RAT generator.

APU.

6 / 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.

7 / 15

Backup power is provided by one variable speed, variable frequency generator mounted on each engine. A frequency converter converts the generator frequency to a constant 400 Hz. Only one backup generator can power the converter at a time.

False.

True.

8 / 15

What is the correct source order for powering left and right main busses in flight?

Respective IDG - APU generator - opposite IDG.

APU generator - respective IDG - opposite IDG.

Opposite IDG - APU generator - respective IDG.

Respective backup generator - APU generator - opposite backup generator.

9 / 15

Which one of the following is not true about the Primary External Power?

If both busses are powered from secondary external power, pushing the PRIMARY EXTERNAL POWER switch ON connects primary external power to the both main busses.

When the Primary power source voltage and frequency are within limits, the primary external power AVAIL (available) light illuminates.

If a single IDG powers both busses, pushing the PRIMARY EXTERNAL POWER switch ON connects primary external power to both busses and removes the IDG source.

If the APU generator is running, pushing the PRIMARY EXTERNAL POWER switch ON connects primary external power to the right main bus, leaving the previous source connected to the left main bus.

10 / 15

How many total AC sources of power does the B777 accommodate?

7

5

6

4

Seven (2 IDG, APU, PRI and SEC external power, 2 BUG).

11 / 15

Which one of the following is not true about the Secondary External Power?

If a single IDG powers both main busses, pushing the SECONDARY EXTERNAL POWER switch ON connects secondary external power to both busses and removes the IDG source.

Secondary external power can only power the left main bus.

When the secondary external power source voltage and frequency are within limits, the secondary external power AVAIL (available) light illuminates.

If the BATTERY switch is ON and no other source is powering the main busses, pushing the SECONDARY EXTERNAL POWER switch ON connects secondary external power to both main busses.

12 / 15

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

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).

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

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

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

13 / 15

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

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

Only the main battery bus will be powered.

The hot battery bus will be powered.

14 / 15

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

Priority for shedding is galleys 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 loads decrease, ELMS restores power to shed systems in the same order of shedding(First shed system restored first).

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

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.

15 / 15

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

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

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

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