System Electrical

Question 1

DC sources (4)

Answer 1

Batteries 2
External DC power
DC starter/generator 2
TRU 2

Question 2

AC sources 4

Answer 2

APU
AC generators 2
Inverters 9
External AC

Question 3

Batteries

Answer 3

2x24 volt DC
Engine/APU start
Backup power source

Question 4

DC starter/Generator

Answer 4

One per engine
Starters to crank engine
Revert to generator when engine reaches idle speed
Produce 28V DC limited to 300 amps

Question 5

TRU

Answer 5

Convert AC to DC
Ensure DC available even if both generators fail
Both can run off one generator through cross-feed bus
In the nose

Question 6

APU

Answer 6

115 volt 400hz variable frequency
Cannot start engine
Provides AC power for ATS via AC generator, charging battery and hydraulic system
Supplies air conditioning via bleed air
Fuel from left main
Extinguisher automatic, Temperatures above 182-227°, APU is shut down. 15 seconds later, the extinguisher is discharged. Red doll eye

Question 7

AC generators

Answer 7

Do not work until prop unfeathered
Produce 3 phase 115V variable freq AC power
Each phase output powers different bus
Variable freq AC used to power: TRU, Anti-icing, Sby aux fuel pumps

Question 8

Inverters 9

Answer 8

DC to AC
ATS: fixed frequency power to the NIM, Doppler and cooling (in the floor)
Radar (nose)
Avionics

Question 9

Electrical anti-icing
Kind of power
Areas

Answer 9

Powered by Freq AC
prop blade (not on ground and below 900RPM)
pitot tubes
static ports
Stall warning transducers (DC on ground and AC in air after PSEU)
Engine intakes
Windshields 
Pilot side window (42°)
elevator horn

Question 10

Can all DC and AC services be operated from the AC generators or from external AC

Answer 10

Yes

Question 11

What is the ESU with regard to the APU?

Answer 11

Electronic Sequence unit provides automatically-controlled APU start sequencing and malfunction indication
Also has built-in fault monitoring which automatically shuts down APU if detection of faults occurs

Question 12

Fixed frequency

Answer 12

Provided by 3 Inverters

• 2 for NAV interface Module, Doppler and computer rack cooling fans
• 1 to maintain the AC power synchronization