Electrical Questions

Question 1

How man networks make up the electrical system on the airplane? Why?

Answer 1

• 2 independent networks

- Redundancy and fault isolation

Question 2

What happens if a power generating source fails?

Answer 2

• BUS ties automatically connect to provide no system degradation

Question 3

What components power the AC system?

Answer 3

• 2 integrated drive generators (IDG)
• Auxiliary power unit (APU)
• Inverter
• Ram Air Turbine (RAT)
• AC GPU receptacle

Question 4

What components power the DC system?

Answer 4

• 2 NiCad batteries
• 3 transformer rectifier unit (TRU)
• DC GPU receptacle

Question 5

How does the IDG maintain a stable power output?

Answer 5

• A constant speed drive (CSD) attaches the IDG to the AGB (Accessory Gear BOX)

Question 6

What monitors and controls the IDG’s?

Answer 6

• Each has a Generator control unit (GCU)

Question 7

Can one IDG supply the entire electrical system?

Answer 7

Yes

Question 8

What will cause the amber IDG light on the overhead panel to illuminate?

Answer 8

• High oil temperature

- Low oil pressure

Question 9

If an IDG is manually disconnected can it be reconnected by the flight crew?

Answer 9

• No. This is a maintenance function

Question 10

What is the primary purpose of the AC Generators?

Answer 10

• To power the AC BUSSES and AC ESS BUS

- Power the 3 transformer rectifier units (TRU) 1,2 and ESS

Question 11

What is the purpose of the transformer rectifier unit?

Answer 11

• To convert 115 VAC to 28 VDC

Question 12

Can the APU replace a failed IDG?

Answer 12

• Yes

Question 13

What is the AC electrical system priority?

Answer 13

• Onside (IDG)
• Inside (APU)
• Outside (GPU)
• Cross-side (other IDG)

Question 14

How is it known that an AC GPU is hooked up to the airplane and ready to provide electricity?

Answer 14

• GPU button displays AVAIL and the GPU icon is presented on the electrical synoptic page
• Once the GPU button is pushed in, the button will display IN USE provided another AC power source is not available

Question 15

What does it mean if the AC GPU is plugged in and the outside GPU panel button displays IN USE?

Answer 15

• Ground service bus is in use

- Cockpit GPU button will display AVAIL even though the ground service bus is in the use

Question 16

If the airplane is using the AC GPU and the APU is started what should the pilot be use to do?

Answer 16

• Deselect the GPU button before the next GPU connection

Question 17

What will charge the batteries?

Answer 17

• Any AC power source

Question 18

How long will the aircraft’s batteries last with no recharging?

Answer 18

• 10 min

Question 19

What is the purpose of the DC GPU receptacle?

Answer 19

• For APU start when batteries < 22.5 VDC or

- If battery temp os < -20 C

Question 20

What is the minimum battery temp for APU start?

Answer 20

-20 C

Question 21

What is the minimum battery voltage to close the battery’s-ties?

Answer 21

18 Volts

Question 22

What battery is used for the inverter?

Answer 22

• BATT 2 powers the APU start BUS

- BATT 1 powers the FADEC & EICAS for monitoring

Question 23

What is the purpose of the inverter?

Answer 23

• Converts 28 VDC from the batteries to 115 VAC to power the AC STANDBY BUS when and AC source is not available

Question 24

What is the AC STANDY BUS?

Answer 24

• Engine exciters 1A and 2A

Question 25

What powers the Ram Air Turbine (RAT)?

Answer 25

Airflow turns the RAT propeller which spins the turbine inside

Question 26

When will the RAT deploy?

Answer 26

- Automatically deploys if AC BUSSES are not powered | - Manually by pilot

Question 27

How long after deployment before the RAT will supply power?

Answer 27

- 8 Seconds

Question 28

Is there a total loss of power during the 8 second RAT deployment?

Answer 28

- No. Batteries supply power to the DC BUSSES and AC STANDBY BUS

Question 29

What does the RAT power?

Answer 29

- ESS BUSSES

Question 30

What is minimum airspeed for the RAT?

Answer 30

- 130 Kias | - Load shedding occurs below 130 Kias

Question 31

When is the RAT icon displayed on the electrical synoptic page?

Answer 31

- When the RAT is deployed

Question 32

What manages the electrical system?

Answer 32

- 4 Integrated Control Centers (ICC) | - 2 Secondary power distribution assembles (SPDA)

Question 33

What is an ICC?

Answer 33

- An electrical control device, which provides power distribution and protection for electrical loads.

Question 34

What is an SPDA?

Answer 34

- An electrical load-management unit (powered by the ICC's) that distributes electrical loads to the aircraft systems according to distribution logic.

Question 35

Can the flight crew reset the ICC and SPDA remote electronic CB's?

Answer 35

- ICC CB's can only be reset by maintenance | - SPDA CB's can be reset via the MCDU