8_ELECTRICAL SYSTEM Flashcards
What is the primary power source for the aircraft and what is it rated at?
primary power is generated by 2 IDGs
3 phase 115vac 400 cycle AC power
What is the source of DC power on the aircraft?
TR units, main battery and battery charger supply DC power.
How many sources of electrical power are there?
external
APU
2 IDGs
Battery
What are the 2 basic principles of the electrical system?
- No paralleling of AC power sources
- the source of power being connected to a transfer bus AUTOMATICALLY disconnects an existing source.
What are the 3 main divisions of the electrical system?
AC
DC
Standby
Do the IDGs maintain a constant speed?
Yes through a CSD.
Can the APU provide power to BOTH AC transfer busses on the ground and in flight?
Yes.
Where is the external AC power receptical?
lower right side of fuselage - near the nose gear wheel well
How do you provide power for ground servicing equipment in the plane?
there is a ground service switch on the fwd attendants panel - provides ground power to the AC ground service busses for utility outlets, cabin lights, and the battery charger.
What busses make up the AC system?
Each AC systems contains:
Transfer bus
main bus
2 galley busses
ground svc bus
Is it possible on the ground to power one transfer bus with external power and the other with the APU?
No.
What does moving the Gen Switch do?
it closes the related Gen CB and connects gen to associated transfer bus.
What happens if external power or APU is running the transfer busses and you connect 1 generator?
the Generator will power the associated transfer bus BUT the APU or External power will continue to power the other bus.
What is the Automatic Generator On-Line Feature and how does it work?
this is used if the airplane takes off with the APU powering BOTH transfer buses….
Operations:
if the APU is either shut down or fails, the engine generators are AUTOMATICALLY connected to their related transfer bus - it occurs ONLY ONCE in flight and ONLY under the above conditions.
How does the automatic load shedding work for ENG GENERATORS?
for SINGLE GEN ops:
- designed to shed incrementally -
ORDER.
Galleys & Main Bus (transfer bus 2) - THEN
Galleys & Main Bus (transfer bus 1) - THEN
IFE busses
How does electrical load shedding occur if the APU is the sole source of electrical power?
Order (in flight).
All Galley and Main Busses - THEN -
Both IFE busses
Order (ground)
the APU tries to carry the full load - if not - THEN
Galley Busses and Main Busses.
How do you restore power to the galley and main busses after load shedding occurs?
you move the CAB/UTIL power switch to OFF then ON.
What is an IDG?
it contains a generator and a drive in a common housing - self contained oil system.
When is frequency only indicated on the AC voltmeter?
Only when the generator is electrically excited.
What positions on the DC switch only indicate DC voltage?
Standby Power and battery bus - all others show volts and amps.
How is 28v DC power supplied to the airplane?
through 3 TR units that are energized from the AC transfer buses.
What do the TRUs do?
they convert 115vAC to 28v DC
Where do each of the TRs get their power from?
TR 1: transfer bus 1
TR 2: transfer bus 2
TR 3: transfer bus 2 (Normally) but has transfer bus 1 (backup)
How many TRs are the minimum for full electrical operation?
Any 2 TRs are capable of supplying the total connected load.
