Electrical

Question 1

How does the IDG maintain a stable power output?

Answer 1

A Constant Speed Drive (CSD) attaches the IDG to the AGB (Accessory Gear Box) (this supplies a constant frequency AC power to the aircraft).

Question 2

Can one IDG supply the entire electrical system?

Answer 2

Yes.

Question 3

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

Answer 3

Low Oil Pressure, or Hi Oil Temperature in the CSD.

Question 4

If an IDG is manually disconnected, can it be reconnected by the flightcrew?

Answer 4

No.

Question 5

Can the APU replace the failed IDG?

Answer 5

Yes, below 33,000 ft.

Question 6

What is normal AC electrical priority?

Answer 6

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

Question 7

Does the APU gen have the same power output as the IDG’s?

Answer 7

Yes.

Question 8

How do you manually disconnect an IDG?

Answer 8

Hold the rotary knob to DISC position for at least 1 second.

Question 9

When does the IDG come online?

Answer 9

When an engine starts; it will power the respective AC buses.

Question 10

Whats the RAT?

Answer 10

Ram Air Turbine. An AC electrical device installed in the nose section, which converts the kinetic energy of airflow across the turbine into AC power.

Question 11

When will the RAT deploy and what will it provide power for?

Answer 11

Total AC power loss or manually by the pilot, it will take 8 seconds to deploy. The following essential systems: AC ESS BUS (3,2,2,1; Hyd Pump 3A, AC Fuel Pump 2, Slat Ch 2, Flap Ch 1)

Question 12

What is minimum airspeed for the RAT?

Answer 12

130 KIAS. Load shedding occurs below this speed. You need 150 kts minimum to get the RAT spinning. Once it’s spinning it will remain spinning down to 130 kts.

Question 13

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

Answer 13

When the RAT is deployed.

Question 14

How long does the RAT take to deploy and what happens in the meantime?

Answer 14

8 seconds. Batteries are used as backup power to power DC ESS BUS & AC STBY BUS.

Question 15

Whats an Inverter?

Answer 15

AC/DC Inverter converts 28v DC power from batteries, to 115v AC power to supply the AC STBY BUS when an AC power source is not available.

Question 16

Name the AC BUSES (4). How do they work in conjunction with each other?

Answer 16

AC BUS 1, AC BUS 2, AC ESS, AC STBY. If one of the AC BUSES fails, the AC BUSES are automatically connected by buis tie contractors (BTCs). One AC source is sufficient to supply the whole system without degradation or added workload.

Question 17

In an electrical failure, what does the system do to protect against an overload?

Answer 17

The system will load shed the galleys and right windshield heat.

Question 18

Whats on the AC ESS BUS?

Answer 18

Essential items for safe operation in case of an electrical emergency, powered by the RAT. 3, 2, 2, 1: Hyd Pump 3A, AC Fuel Pump 2, Slat Ch 2, Flap Ch 1.

Question 19

How and when is the AC STBY BUS powered? What does it power?

Answer 19

Powered from a DC BUS through an inverter. Powered as soon as DC BATs are turned ON; this allows for an engine start without AC power! Engine ignitors 1A & 2A.

Question 20

Whats a TRU?

Answer 20

Transformer Rectifier Unit. 115V 400 Hz AC power to 28V 300amp DC power.

Question 21

If one TRU 1 or 2 fails, can the other still power all the DC busses?

Answer 21

Yes! (as long as the DC BUS TIES toggle switch is set to AUTO).

Question 22

Whats on TRU1?

Answer 22

DC BUS 1, DC ESS BUS 1, DC GND SVC BUS, HOT BATT BUS 1, battery #1 charging.

Question 23

Whats on TRU2?

Answer 23

DC BUS 2, DC ESS BUS 2, HOT BATT BUS 2, battery #2 charging.

Question 24

Whats on TRU3?

Answer 24

DC ESS BUS 3.

Question 25

What kind of batteries do we have? What do they power?

Answer 25

Two 24V SLABs (sealed lead acid batteries). Power the DC ESS BUSES (when no AC power source is available).

Question 26

How are the batteries charged?

Answer 26

Any AC Power Source. (charged through the TRU’s).

Question 27

What battery is used for the APU start?

Answer 27

BATT 2 powers the APU Starter, BATT 1 powers the FADEC and EICAS for monitoring.

Question 28

The batteries are rated to provide ___ volts fully charged.

When the batteries are being charged, they will typically display ___ volts.

Answer 28

24, 28.

Question 29

BATT 1:
OFF, provides power to?
ON, provides power to?

Batt 2:
OFF, provides power to?
AUTO, provides power to?

Answer 29

BATT 1: OFF = Hot Battery Bus 1. ON = Hot Batt Bus 1 and DC Bus 1.

Batt 2: OFF = Hot Battery Bus 2 , AUTO = Hot Batt Bus 2 and DC Bus 2, OR the APU Start Bus.

Question 30

How long will the batteries provide DC power to the aircraft (as long as they are above 22.5 V)?

Answer 30

10 minutes. “It’s a 10 minute airplane”.

Question 31

(T or F)

LOAD SHED EICAS message may be displayed on ground when an airplane is powered by only one AC power source and indicated airspeed is at or above 50 kt.

Answer 31

True.

Question 32

When is a DC GPU used?

Answer 32

When the #2 battery is N/A. To assist with APU start if batteries < 22.5vDC or if battery temp is

Question 33

AVAIL light for GPU indicates?

Answer 33

Proper voltage, amps, and frequency.

Question 34

What’s ICC?

Answer 34

Integrated Control Center. Provides power distribution and protection for the electrical loads, SPDAs and CBs. 4 ICCs total.

Question 35

Whats SPDA?

Answer 35

Secondary Power Distribution Assemblies; electrical load management unit, which receives power from the ICC AC/DC electrical buses and distrubitues it to the airplane systems.

Question 36

What kind of CBs are there?

Answer 36

Electronic (MCDU) and thermal (cockpit) CBs.

Question 37

What happens if a power generating source fails with the Bus Ties in Auto?

Answer 37

Bus ties automatically connect to provide no system degradation.