ELECTRICAL SYSTEM

Question 1

Where can the aircraft receive its power from?

Answer 1

Variable Frequency Generators (VFG)
APU Generator
External AC Power
Ram Air Turbine (RAT)

Question 2

Variable Frequency Generator (VFG)

Answer 2

Two VFGs, mounted on the accessory gearbox.
Supplies 115VAC. Rated to 75kVA continuous. 112.5kVA for 5mins. 150kVA for 5sec.
Contains Permanent Magnet Generator (PMG), which supplies power to a GCU and an Over-voltage Protection Unit
Lubricating oil for the VFG is cooled by a dedicated air/oil cooler
VFGs controlled by L GEN & R GEN switches

Question 3

Generator Control Unit (GCU)

Answer 3

Regulates VFG voltage
Connects or disconnects the VFG to the main AC busses
Protects the electrical circuits from generator faults
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

Question 4

Over-voltage Protection Unit (OPU)

Answer 4

Is an additional independent backup to the GCU over-voltage protection
Electrically disconnects the VFG if it produces excessive voltage and the GCU has not acted
PMG powers the OPU

Question 5

APU Generator

Answer 5

115 VAC, VFG mounted on the APU accessory gearbox.
Rated to 75 kVA for continuous up to FL365. 58 kVA at FL410

Question 6

APU Generator Control Unit (AGCU)

Answer 6

Regulates the APU generator voltage
Connects or disconnects the APU generator to the aircraft busses
Protects the electrical channel from APU generator faults
Supplies status information to the Bus Power Control Units (BPCUs)
Primary power is the APU PMG, backed up by aircraft DC power

Question 7

External AC Power

Answer 7

Can supply AC power in two different modes:
Ground service mode
External power mode

When connected, checked for frequency, voltage, & phase.

In ground service mode, AC BUS 1, AC BUS 2, & DC BUS 1 are powered

Question 8

Which busses are always powered?

Answer 8

DC EMER BUS and BATT DIR BUS

Question 9

Which bus is not shown on ELEC synoptic page?

Answer 9

BATT DIR BUS

Question 10

Ram Air Turbine (RAT)

Answer 10

If there is a total loss of AC power, RAT deploys automatically and supplies emergency AC power and hydraulics.
115 VAC, rated at 10 kVA.
Air cooled
Also drives a hydraulic pump

Question 11

Which busses are supplied by the RAT generator?

Answer 11

AC ESS BUS, which powers Electrical Power Center 3 (EPC 3)
DC ESS 3 bus through TRU 3

Question 12

At what aircraft speed will the RAT supply electrical and hydraulic power?

Answer 12

148 knots or more for electrical power
115 knots for hydraulic power

Question 13

What busses are the batteries connect to?

Answer 13

DC ESS 1 & DC ESS 2 busses. All three DC ESS busses are connected in parallel

Question 14

What happens if a VFG is recovered while RAT is deployed?

Answer 14

The VFG will supply the entire electrical system except for:
AC ESS & DC ESS 3 busses. RAT powers these.

Question 15

How is DC power supplied?

Answer 15

Transformer Rectifier Units (TRUs)
Nickel-Cadmium (NiCad) batteries
Battery chargers

DC power generated by two Fly-By-Wire Power Converters (FBWPCs) supplies the Electronic Flight Control System (EFCS)

Question 16

Transformer Rectifier Units (TRU)

Answer 16

3 TRUs.
Primary source of DC power
Rated at 350 amperes
Receives power from AC busses, converts it to 28 VDC and distributes it to the DC busses

Question 17

Batteries

Answer 17

2 24 VDC NiCads
Rated at 42 ampere-hours

Supplies power to:
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
Electric brakes when all other DC sources are not available

Question 18

What happens if only batteries are supplying power?

Answer 18

After 5 minutes, the BATT DISCHARGING caution message is displayed &
A horn sounds until AC power is available, or batteries are switched off

Question 19

Fly-By-Wire power generation and FADEC power

Answer 19

Two PMAGs, installed on the accessory gearbox. Supplies dedicated AC power to 2 FBWPCs and the EEC of each FADEC
Converts AC to DC and supplies dedicated DC power to FBW system as an alternate source when DC BUS is not available

Question 20

When will the DC EMER bus show on ELEC synoptic page?

Answer 20

When it is not powered

Question 21

What do the BATT 1 & BATT 2 switches do?

Answer 21

Allows the BPCU to connect the BATT DIR bus to its corresponding DC ESS
Allows the battery chargers to operate if AC power is available

AUTO position: the BATT DIR bus will power the corresponding DC ESS bus until the DC ESS bus receives power from a TRU

Question 22

APU GEN Switch

Answer 22

FAIL: APU GCU removes generator from the bus due to a fault

Question 23

CABIN PWR guarded switch

Answer 23

Deactivates electrical loads from:
Flight compartment outlets
Cabin systems, such as, galleys and in-flight entertainment systems

Used to isolate sources of smoke in the cabin

Question 25

What happens when you push the RAT GEN switch with the RAT deployed?

Answer 25

RAT GCU will reset

Question 26

L DISC & R DISC guarded switch

Answer 26

Allows crew to disconnect the generator shaft from engine gearbox cannot be reset in-flight OIL: low oil pressure or high oil temperature Engine VFG high oil temperature has two threshold: When the first threshold is reached, the amber OIL light come on When the second higher temperature limit is reached, the VFG automatically disconnects from the engine accessory gearbox

Question 27

Cockpit Voice Recorder

Answer 27

Records all voice, digital comms, & aural alerts Starts recording when beacons or strobes On or weight off wheels Stops recording when lights off plus 10mins Records last 2 hours

Question 28

How long will the Under Water Beacon last?

Answer 28

90 days