Main Electrical Components Flashcards
In normal inflight ops, all electrical power is provided by?
2 engine driven generators
There’s a 3rd generator available in flight. What is it driven by?
APU. (It’s equal in size & capacity to either engine driven generator)
How many generators are required in flight to meet all electrical demands?
Any 2 of the 3
What happens if only 1 generator is available in flight?
An electrical load management system automatically shuts down some low priority items (e.g galleys)
What distributes power to all airplane electrical systems?
2 main AC power busses (L&R)
What ensures both main busses remain powered at all times?
A bus tie & 2 isolation relays
Where are the controls for the electrical system located?
On the overhead panel (above the captain)
With all electrical power switched off, the main battery still continues to power a few important items through?……
The Hot Battery Bus
What important items does the Main Battery continue to power, through the Hot Battery Bus, even with all electrical power switched off?
- Engine fire extinguisher bottles
- APU fire extinguisher bottle
- ADURU - as long as the ADIRU switch is on
How many external power switches are there?
2 - primary & secondary
What does the ‘AVAIL’ light on the external power switch indicate?
External power is connected to the airplane & is of usable quality.
With a single external power source, on the ground, will every electrical item be powered?
No, some non-essential electrical items e.g galleys May be unpowered if loads are high
Connecting secondary external power to the airplane gives ……….. electrical load capacity for most ground situations
Full
When both primary & secondary external power are available primary power powers the ………. Bus & secondary power powers the ……… Bus
Primary powers the right main bus
Secondary powers the left main bus
How many power sources support full electrical load?
Any 2
When the APU is running & primary external power is online, the APU powers the …….. main bus & the primary external source powers the …….. main bus
APU - Left Main Bus
Primary External power - Right Main Bus
What position is the APU GEN switch normally left in?
ON.
The APU GEN breaker opens & closes automatically.
There’s no interruption of power when switching power sources except when ?
Switching between 2 external sources.
Each main generator & its drive unit are housed in a single case & share a common oil supply. What is this unit called?
An Integrated Drive Generator (IDG)
What controls the IDG & what does it provide?
Controlled by a generator control unit.
Provides automatic control functions & system protection.
The generator control switches automatically connect the IDG to ?
The Main Busses (L &R)
What does the ‘OFF’ light mean on the APU GEN switch?
Means Fault or switch is off
What does the ‘OFF’ light mean on the GEN CTRL switch mean?
Means “Breaker Open”
What happens to the electrical system when you start the #2 engine?
- IDG rotates to operating speed
- The generator breaker closes
- The right Gen now powers the right main bus
- Simultaneously, Primary & Secondary ext power auto disconnect from Main busses, the Right Gen also powers the Left Main Bus
- After a few seconds with the APU running, APU power replaced Right Gen power on the Left main bus.
Each main AC bus powers how many utility busses?
1 utility bus
The bus tie breakers are normally left in AUTO, why?
The bus tie breakers keep both main busses powered at all times from any available source in a priority order
Bus Tie Breakers keep busses powered in what priority order?
- Associated engine generator
- APU Generator
- Opposite engine generator
External power is the only AC power source which is ?
Not automatically selected.
You must apply it manually.
What position are the bus tie breakers in whenever the IDGs are powering their respective busses?
Open
If the L BUS TIE switch is selected to ‘ISLN’ can the R BUS TIE close? What effect does this have if both engines are running & both engine generators are powering their associated bus?
No.
None.
One generator can power…….
All essential flight loads
If there’s only 1 power source available, the ELMS does what?
The Electrical Load Management System load sheds non-essential loads.
1st - Galleys & galley chillers
2nd - L & R utility busses
The Main Battery powers ?
- The standby power system
- Captains displays & CDU
- The left AIMS (Airplane Information Management System)
You have an unpowered airplane. Which items will be powered if you push the BATTERY switch to ON?
The Battery Bus
Power is removed from which items when the battery switch is pushed OFF during power down?
Power is removed from the standby bus, Captain’s flight instruments, & left AIMS.
