Electrical

Question 1

How many VAC and what are the sources?

Answer 1

115VAC

• 2 variable freq generators (VFGs, Engines) - primary
• APU VFG - aux power
• RAT - low rated emerg power
• external connection for gnd pwr

Question 2

How many VDC and what sources?

Answer 2

28VDC

• 3 TRU - primary
• 2 nickel cadmium batteries - emerg DC and all APU starts with no ext power
• 2 permanent magnet alternator generators (PMAGs) - pwr for fly by wire and FADEC (42ah)

Question 3

Engine generator description: ie KVA’s, lube/cooling

Answer 3

75KVA VFG on Eng accessory gearbox, cooled and lubricated by a self contained oil system

Question 4

APU generator description

Answer 4

75 KVA on APU accessory gearbox. Power up to FL365 and amperage output gradually decreases at higher alt.

Question 5

What do the generator control units do? 4 things

Answer 5

1. Regulate VFG voltage
2. Control contractors connect/discon of VFGs to/from main AC buses
3. Protect circuits from Gen faults
4. Provide Gen status

Question 6

RAT description

Answer 6

10 KVA. Emerg pwr to AC ESS BUS and DC ESS BUS 3 through TRU3 at 148KIAS and above.

Question 7

When will you get a BATT DISCHARGING caution msg?

Answer 7

5 mins of battery power only

Question 8

Can a single VFG power everything?

Answer 8

Everything except AC ESS BUS and DC ESS BUS 3 (RAT powers them, even if second VFG comes back online)

Question 9

What does the battery power at all times?

Answer 9

• BATT DIR BUSES
• DC EMERG BUS
• DC ESS BUS when TRUs not functioning

Question 10

AC BUS structure

Answer 10

• 1 and 2 powered by VFGs or ext
• AC ESS BUS normally powered by AC BUS 2 but can be powered by 1 or the RAT
• each powers a TRU

Question 11

AC BUS power source priority

Answer 11

AC BUS 1 AC BUS 2
L Gen R Gen
Ext power APU Gen
APU Gen Ext Pwr
R Gen L Gen

Question 12

How many DC buses are there and what are they?

Answer 12

8 DC buses (6 shown on synoptic

• 1, 2 main buses, powered by TRU 1,2
• DC ESS 1,2 powered from main DC buses
• DC ESS 3 powered by TRU 3
• BATT DIR BUS 1,2 not shown, powered by batteries

Question 13

What are the electrical power centers?

Answer 13

Power isolation and distribution infrastructure for the electrical system.
EPC 1 - left power channel and ext pwr
EPC 2 - right power channel and APU Gen
EPC 3 - essential/emergency power

Question 14

What do the bus/emergency power control units do/manage?

Answer 14

They control AC/DC line contactors and bus tie contactors.

BPCU1 –> EPC1
BPCU2 –> EPC2
EPCU –> EPC3

Question 15

What do the 5 Control and Distribution cabinets (CDCs) do?

Answer 15

Receive AC/DC power from the EPCs and redistribute that power to components not essential for flight.

CDC1/2 are masters
CDC3/4/5 are slaves