Electrics Flashcards
What type of AC and DC is used on the aircraft?
115V AC and 28V DC
What provides AC and what procides DC?
AC= Engine driven VFGs (Variable frequency generators), APU, RAT, GROUND
DC= TRU, batteries
How are VFGs cooled?
Using lubrication oil from oil/air cooler on the engine

What is GCU and what is its function
Generator Control Unit (GCU)
The Generator Control Unit (GCU) does the functions that follow:
* Regulates VFG voltage,
* Electrically connects or disconnects the VFG to the main AC
busses,
* Protects the electrical circuits from generator faults, and
* Supplies status information to the Bus Power Control Units
(BPCUs).
Primary power for the GCU is the associated PMG, backed up by
aircraft DC power.
Explain the function of Overvoltage Protection Unit OPU
The Overvoltage Protection Unit (OPU) is an additional
independent backup to the GCU overvoltage protection. The OPU
electrically disconnects the VFG if it produces excessive voltage
and the GCU has not acted. The PMG powers the OPU.
How to engage the Ground Power Ground Service mode?
By pressing on the Ground service panel press SERV button from green AVAIL to white IN USE
What type of electrical power is provided by the RAT, and when does it deploy automatically?
Supplies AC power and deploys automatically when all AC power is lost
What is the minimum speed IAS for RAT to start working?
148 kts
To where does the RAT supply power?
To the AC ESS BUS
- What is FBWPCs?
Fly by whire power converters. They supply DC power to the EFCS (electronic flight control system) and the engine FADECs. The two Permanent Magnet Alternator/Generators (PMAGs), one on each engine accessory gearbox, supply dedicated AC power to two FBWPCs and the Electronic Engine Control (EEC) of each FADEC.
What do the BATTERIES supply
They supply power for the components that follow:
* BATT DIR busses at all times,
* DC EMER bus at all times,
* DC ESS busses when BATT selector is in AUTO and TRUs are not
functioning, and
* Electric brakes when all other DC sources are not available
When is the BATT DISCHARGING caution message displayed?
If only batteries supply the power for more than 5 minutes.
At what minimum speed RAT still can supply hydraulic power?
115kts
What happens when with help of RAT one VFG is recovered?
If a single VFG is recovered while the RAT is deployed, the VFG
supplies the entire electrical system except for the AC ESS and DC
ESS 3 busses. The RAT continues to supply these two busses.
The RAT DPLY advisory message replaces the EMER PWR ONLY
warning message on the EICAS page (refer to
How do the TRUs work?
Three Transformer Rectifier Units (TRUs) are the primary source of DC
power, and are each rated at 350 amperes. The TRUs receive 115 VAC
power from the AC busses, convert it to 28 VDC, and distribute it to the
DC busses.
Can you draw the elecrical system?
What does the batteries supply when in AUTO mode on ground with no AC power available?
Power for refueling, APU start, CB reset for maintenance
How are BATT 1 and BATT2 charged during EMER POWER mode?
How is DC power supplied to FLY BY WIRE and FADEC systems?
Engine GEN -> PMAG -> AC CONVERTER -> 28V DC power supply for FBW SYSEM
What is the function of AC ESS BUS and when is it used?
AC ESS BUS is used in case of a major electrical failure, is normally powered by AC ESS BUS 2, in emergency powered by RAT
What does EPC stand for?
Electrical Power Center
Where are EPCs located and what do they contain?
Located in Mid nad FED equipment bays. The EPCs contain the AC and
DC busses, the TRUs, the line and bus tie contactors, and most of
thermal circuit breakers on the aircraft.
What is the function of Bus Power Control Units and Emergency Power Control?
Is part of DC sictribution system, BPCU and EPC monitor and control Electrical Power distribution is EPCs. EPCs are responsible for load shedding and power redistribution in case some BUS etc is lost
What does CDC stand for?
Control and Distribution Cabinet
When does load shedding occur.
When exxessive demand is placed on VFG or TRU
How are TCBs Thermal Circuit breakers marked in the CB Symoptic page.
With a circle around the CB
What are the possible CB status indications?
What happens when BUS ISOL is switched to MAIN?
MAIN − Inhibits automatic reconfiguration in EPC 1 and EPC 2.
When the BUS ISOL switch is selected to MAIN, AC busses can only
be powered by their on-side VFG. The ELEC BUS ISOL MAIN
status message is displayed on the EICAS page.
The only ones powered remain AC BUS1 AC ESS BUS, and DC BUSES except DC BUS
What happens when BUS ISOL is switched to ESS.
ESS − Inhibits automatic reconfiguration in EPC. AC ESS BUS AND DC ESS BUS 3 re isolated
What is CAB PWR guarded switch used for?
The CABIN PWR guarded switch is used to deactivate electrical loads
from flight compartment outlets and selected cabin systems to isolate
sources of smoke in the cabin, such as the galley(s) and in-flight
entertainment systems.
