Main electrical Components

Question 1

Electrical components

Answer 1

Two engine driven generators
Two back ups
APU
AC needs two sources for normal ops

Question 2

Electrical load management system

Answer 2

Comes into play when only one source available

Automatically shuts down low priority items, such as the galleys

Question 3

Schematic

Answer 3

Left and right buses distribute AC power to all systems

Bus tie and and two isolation relays ensure both main buses remain powered at all times

Question 4

All electrical power switched off

Answer 4

Main battery still continues to power a few important items through the hot battery bus even with battery switch off
Fire eq bottles
APU eq bottles
And the ADIRU as long as it is switched on

When AC shutdown main battery if on will power
Standby power systems
Captains display
Left AIMS

Question 5

Primary external power

Answer 5

If Available light on this indicates primary external power is connected to the airplane and is useable quality

Question 6

Secondary external power

Answer 6

Gives full electrical load capacity for most ground situations

Question 7

Both primary and secondary power on

Answer 7

Primary powers right main bus

Secondary powers left main bus

Question 8

APU POWER WHEN ON

Answer 8

APU powers left main bus and secondary light will annunciate available

Question 9

APU ON and primary and secondary off

Answer 9

APU powers both buses

Question 10

Each main engine generator

Answer 10

Housed in a single case
Share common oil supply
Combined unit called a IDG
Integrated drive generator

Question 11

IDG

Answer 11

controlled by a general control unit (see schematic)

Which provides automatic control functions and system protection

Question 12

Generator off switches

Answer 12

Breaker open and on means armed if off light is visible

Question 13

Starting engine

Answer 13

IDG begins to rotate at operating speed
Breaker closes
Generator off and drive lights extinguish
This generator will now power its applicable bus (right engine start=right bus)

Question 14

When generator comes on line

Answer 14

Primary and secondary external power automatically disconnect from the main buses and the applicable side generator will power both buses
After a few seconds APU will power left main bus until the left engine is started

Question 15

Each main AC bus powers

Answer 15

One utility bus (see schematic)

Question 16

Priority power order

Answer 16

Keep buses powered

1. Associated engine generator
2. APU Generator
3. Opposite engine generator

Question 17

ELMS if only one power source

Answer 17

First galleys
Galley chiller
Then left and right utility buses

Question 18

Shut down of left engine example

Answer 18

Fuel control switch moved to cutoff
The IDG synchronises with the bus tie
The left tie breaker closes
Engine generator breaker opens
APU powers that bus