Electrical

Question 1

You Taxi and Park at the Gate.
Ground crew plugs in Externalnpower and you Select GPU.

-With both Engines running what powers AC bus 2?

• Shutdown Engine 2. Now, How is AC BUS 2 powered?

Answer 1

Engine 2- IDG 2

GPU via AC Bus Tie.

Question 2

In Cruise, you receive an IDG 1 off bus caution message. Where does AC BUS 1 now receive its power ?

You start the APU. Where does the AC BUS TIE now receive its power?

Answer 2

1.) IDG 2 via bus tie

2.) APU

Question 3

During Descent you receive an
IDG 1 OIL message on the EICAS. What indication will you expect to see on the Electrical Panel?

Answer 3

An Amber Disc light on IDG 1

No

Question 4

When will GPU AVAIL light Illuminate?

Answer 4

When connected to External power but it’s NOT powering the BUS TIE.

Button can be both pushed in or out

Question 5

If QRH instructs you to deselect the APU GEN switch, what would this do?

Answer 5

Opens the APU GEN contactor isolating it from the AC BUS TIE.

Disconnects the APU GEN

Question 6

During OET (one engine taxi) to the gate. With #2 and APU off. What is AC BUS 1 power source?

Answer 6

IDG 1

IDG 1 vía The AC BUS TIE

Question 7

In Flight: ( APU not Available )

What Normally powers AC BUS 1?

What if IDG 1 was not Available?

Answer 7

IDG 1

IDG 2 via the Bus Tie

Question 8

What Does the (GPU) IN USE light indicate?

Answer 8

GPU is powering the AC BUS TIE

Question 9

During cruise QRH directs you to turn AC BUS TIE Selector Switch to
“1 Open” .

What does this Action do?

Will we lose anything.

Answer 9

Opens Bus Tie 1 Contactor- isolating , AC BUS TIE from AC BUS 1

The ability to power AC BUS 1 if IDG 1 fails

Question 10

What is the priority of the AC BUS TIE

Answer 10

APU, GPU, IDG

Question 11

What Happens if AC BUS TIE Switch is moved to “2 open”

Answer 11

BUS TIE Contactor 2 opens and isolates AC BUS TIE from AC BUS 2

Question 12

What does the Yellow light 🟡 below DISC on the IDG switch indicate?

Answer 12

Indicates which IDG to disconnect

Associated with an IDG OIL caution EICAS

Question 13

How can you Disconnect IDG 1?

Can it be Reconnected in Flight?

Answer 13

Holding the IDG knob in the DISC position for 1 sec.

No, only tech ops can reconnect on the ground.

Question 14

What happens if a TRU Switch is moved to “OFF”

Would that DC BUS still receive Power?

Answer 14

Isolates TRU from its associated DC Bus

Yes, the DC TIE Contactor will close to provide power.

Question 15

QRH directs you to move the DC BUS TIE switch to OFF position. How does this affect the DC system?

Answer 15

Opens all DC BUS TIE Contactors
-Restricts the DC system’s capability to Tie DC Buses automatically.

Question 16

Power Down with NO EXTERNAL power available:

-BATT 1 and BATT 2 are placed into the OFF Position.
….. Have you removed power from ALL the buses on the Aircraft?

Answer 16

NO

HOT BATT BUS 1 and 2 will still be powered through the batteries.

Question 17

Why is there an AUTO position on BATT 2?

Answer 17

“Auto” allows BATT 2, to power either the:

DC ESS 2 BUS or APU START BUS

Question 18

How does the AUTO Position of the IDG 1 or IDG 2 Rotary Knob work?

Answer 18

“AUTO” allows IDG Contactor to close, connecting the IDG to it’s AC BUS automatically, according to system logic.

Question 19

What is the “OFF” function of the IDG rotary knob?

Answer 19

“OFF” opens the IDG Contactor. Isolating the IDG from it’s AC BUS

Question 20

When will the AVAIL Light ( on the GPU Push Button ) illuminate ?

Answer 20

When AC GPU is connected, but not powering the AC BUS TIE. Regardless of switch position ( In or Out )

Question 21

Describe the operation of the Essential TRU when in AUTO.

Answer 21

Allows automatic connection of the TRU ESS to the ESS BUS 3

Question 22

What is the difference between OFF and AUTO on the BATT 2 selector?

Answer 22

OFF- Only the HOT BATT BUS 2 is powered by the BATT 2

AUTO- connects BATT 2 to either the DC ESS BUS 2 or APU START BUS Automatically, according to system logic.