3. Electrical Flashcards
(31 cards)
What are the normal sources of AC power?
AC power is supplied by
2 integrated drive generators (IDG’s),
1 APU generator, and
1 external power receptacle = 4 sources
What are the normal sources of DC power?
DC power is supplied by
4 TRU’s (TRU1, TRU2, ESS TRU, and GND SERVICES TRU),
2 batteries, and
1 DC external receptacle. = 7 sources
What busses does AC normally supply?
AC normally supplies 7 buses:
- AC BUS 1
- AC BUS 2
- ESS AC BUS
- EMER AC BUS
- GALLEY BUSSES 1 & 2
- GND SERVICES AC BUS
What busses does DC normally supply?
Dc normally supplies 7 busses:
- DC BUS 1
- DC BUS 2
- ESS DC BUS
- EMER DC BUS
- DUAL DC BUS
- DC GROUND HANDLING BUS
- DC GROUND SERVICES BUS
If all AC generator power is lost, what power is available?
If all AC generator power is lost, batteries will power the EMER DC BUS which then powers the EMER AC BUS via the EMER INVERTER.
In case of total AC power loss, batteries power DC EMER BUS and AC EMER BUS via EMER INV.
What alert is presented in this situation and where will the alert be shown?
AC SUPPLY in red is displayed on the SAP when only battery power is available.
How long would you expect the batteries to last if you lost all generators?
In case all generator power is lost, the batteries should last for at least 30 minutes.
When external AC is plugged in but not switched on, what is powered and what indication do you get?
When external power is plugged in but not online the AC GROUND SERVICES BUS will be powered. The white AVAIL light will be on the EXT PWR push button.
The DC GROUND SERVICE BUS and the DC GROUND HANDLING BUS will also be powered through the GROUND SERVICES TRU. There are no indications for these buses.
On engine start, when do engine generators normally come on line?
On engine start, when voltage and frequency are within predetermined limits, the GCU automatically connects the generator to the line.
What is an IDG?
An IDG is and AC generator with an integrated constant speed drive, used to provide constant frequency (400Hz) AC POWER.
What is a GCU and what does it do?
A GCU is a generator control unit. Its functions are:
- regulate the generator output
- control connection of the generator to the line
- Automatically disconnect the generator in case of a fault
If an IDG overheats, what happens, and what indications do you get?
If an IDG overheats a level 1 alert is issued (IDG TEMP). If the temperature continues to rise, the IDG is automatically disconnected.
Is the APU generator equipped with a constant speed drive?
The APU generator is not equipped with a CSD because the APU itself operates at a constant speed.
If external power is online and the parameters go out of limits?
If external power is online and goes out of limits, the ground power control unit (GPCU) automatically disconnects external power.
From which generators do AC busses 1 and 2 normally receive power?
AC BUS 1 is normally powered by IDG 1. AC BUS 2 is normally powered by IDG 2.
They can also be powered by either the APU or EXT PWR).
When is automatic AC cross tie inhibited?
The auto-cross tie is inhibited automatically in case of a short circuit on an AC bus.
It can also be manually inhibited by pushing the AC X-TIE push button.
What busses remain powered after the ESS+EMER PWR ONLY push button is pressed?
When the ESS+EMER PWR ONLY push button is pressed the following buses remain powered:
a. ESS AC + EMER AC
b. ESS DC + EMER DC
What are the power source priorities for the ESS AC bus?
The power source priority for the CAC ESS BUS is
1. IDG 1
2 IDG 2
3. APU
4. EXT PWR
From where can the EMER AC bus obtain power?
The EMER AC BUS is normally powered by the ESS AC BUS. If the ESS AC BUS is unpowered , the EMER AC BUS will be powered by the EMER DC BUS via the EMER INV.
The EMER AC BUS will be powered by the batteries for a minimum 30 minutes.
When is the galley power shed automatically?
In flight, galley power is automatically shed during single generator operation.
The galley busses can also be manually depowered by pushing the galley power push buttons
You are airborne and GEN 1 goes offline. The APU generator is not available. What happens?
The AC busses are automatically tied and GEN 2 powers AC BUS 1 and 2 and the ESS AC BUS. The galley busses are shed and remain offline.
You are airborne and GEN 1 goes offline. The APU generator is available. What happens?
If the APU is available, the APU will power AC BUS 1. GEN 2 will power AC BUS 2 and the ESS AC BUS.
How can the DC busses be tied together?
The DC busses can be tied together by pushing the DC X-TIE push button.
What happens if a TRU fault occurs? What might the fault be?
If a TRU fault occurs a level 2 alert is issued and a local fault light illuminates.
The fault is probably caused by a TRU overheat or a reverse current flow.
