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Boeing 777-200 Systems > Electrical > Flashcards

Electrical Flashcards

1
Q

The electrical system is comprised of

A

Main AC power

Backup AC power

DC Power

Standby power

Flight control power

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2
Q

ELMS

A

Electrical Load Management System

  • Detects and isolates faults ensuring power is available to critical and essential equipment
  • If the electrical loads exceed the power available ELMS automatically sheds AC loads
  • When an additional power source is available or the loads decrease, ELMS restores power
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3
Q

What are the normal sources of AC power?

A

Two engine-driven integrated drive generators

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4
Q

What is the third source of AC power?

A
  • APU generator
  • Available for use on the ground or in flight
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5
Q

What is the purpose of the two engine driven backup generators?

A

Ensure electrical power is available for essential loads during non-normal situations.

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6
Q

What does the main DC electrical system use?

A

Four transformer rectifier units (TRUs) to produce DC power.

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7
Q

How is standby power made available?

A

Through either a ram air turbine driven generator or the ship’s battery.

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8
Q

What do the two permanent magnet generators (PMGs) provide a primary source of power to?

A

The flight controls and are housed within each backup generator

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9
Q

The main AC electrical power sources are:

A
  • Left and right IDGs
  • APU generator
  • Primary and secondary external power
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10
Q

How many main AC power systems can power the entire plane’s electrical load?

A

Any two main AC power sources

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11
Q

With both the PRIMARY EXT PWR and SECONDARY EXT PWR selected ON, when the APU generator is available which external power source does it automatically replace?

A

SECONDARY EXT PWR

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12
Q

What does the Generator Control Unit (GCU) provide?

A

Automatic control functions and system protection.

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13
Q

When does the DRIVE light illuminate?

A

When IDG oil pressure is low?

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14
Q

What happens when the DRIVE DISC switch is pushed?

A

The IDG input is disconnected from the engine and maintenance action on the ground is required to reconnect it.

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15
Q

With the L and R BUS TIE switches in auto, power to the main busses automatically comes from what power sources in priority order?

A
  • Associated engine generator
  • APU generator
  • Opposite engine generator
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16
Q

In what order does the ELMS shed AC loads?

A
  • Galleys
  • L and R utility busses
  • Individual equipment powered by the Main AC Busses
17
Q

How many backup generators can power the frequency converter?

A

1 at a time

18
Q

When does the BACKUP GEN power the AC transfer buses

A
  • Only one AC generator is available
  • Power to one or both Main AC buses is lost
  • APP mode is selected for autoland
  • Automatically testing the system after engine start
19
Q

What are the two sources of power for the ground handling bus?

A
  • Primary external power
  • APU generator (when primary external power is not available)
19
Q

If the APU is running and the primary external power is plugged in, which source of power has priority on the ground handling bus?

A

Primary external power

20
Q

What does the Ground Handling Bus power?

A
  • Cargo handling systems
  • Fueling/defueling operations
  • Other equipment energized only during ground operation
21
Q

What does the ground service bus power?

A
  • Main and APU battery chargers
  • Miscellaneous cabin system loads
21
Q

What normally powers the ground service bus?

A

Right main bus

22
Q

If the right main bus is not powered but the primary external power is plugged in, how is the ground service bus powered

A

A switch near the 1L door can be used to power the ground service bus

23
Q

How many batteries does the 777 have?

A

2 (main battery and APU battery)

24
Q

What does the main battery power?

A
  • APU control circuits
  • APU fuel valves
  • APU inlet and exhaust doors
  • Standby buses
  • Emergency lighting
  • LH inboard, outboard, and upper center displays
  • LH CDU
25
Q

How many Transformer Rectifier Units (TRUs) provide DC power?

A

4

26
Q

What provides power to the TRUs?

A

L and R transfer busses

27
Q

What are the four DC buses the TRUs provide power to?

A
  • L main DC bus
  • R main DC bus
  • Captain’s flight instrument bus
  • FO’s flight instrument bus
28
Q

The permanent magnet generators are the source of power for what?

A

The flight controls.
L, R, C power supply assemblies (PSAs) as well as their flight control DC busses

29
Q

If one or more PMG fail in flight, what powers the flight control DC busses?

A

The main DC busses, or the captain’s flight instrument bus.

30
Q

Why does each PSA have a one minute battery?

A

To ensure uninterrupted power during a transfer of power from one source to another.

31
Q

What are the critical AC equipment?

A
  • Center ILS
  • Center radio altimeter
  • Left marker beacon
  • Left ATC transponder
  • Left VOR
  • Engine ignitors
32
Q

What are the critical DC equipment?

A
  • Captain’s PFD and ND
  • FO’s PFD and ND
  • Standby instruments
  • Left FMC
  • Left CDU
  • VHF 1 and ACP 1
  • Flight interphone
  • APU DC fuel pump
  • Upper EICAS
33
Q

What does the standby system consist of?

A
  • Main battery
  • Ram air turbine (RAT)
34
Q

What does the standby system power?

A
  • Battery buses
  • Captain and FO flight instrument buses
  • AC standby buses
35
Q

What happens if both transfer buses lose power?

A
  • RAT deploys automatically
  • APU starts automatically regardless of switch position

Boeing 777-200 Systems (21 decks)

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