Electrical Systems

Question 1

List all AC power sources

Answer 1

IDGs
APU
External power
Battery (for standby) via inverter

Question 2

List all DC power sources

Answer 2

TRUs

Battery

Question 3

Does the battery need to be on for the Hot Battery Bus to be powered? What about the
Switched Hot Battery Bus?

Answer 3

NO/ YES

Question 4

Can the battery be charged with external AC?

Answer 4

YES

Question 5

What does Ground Power Available light mean?

Answer 5

Ground power available but not selected

Question 6

What is the difference between the Ground Power Switch in the flight deck and the
Ground Service Switch on the Forward Attendant Panel?

Answer 6

Ground power supplies power to both transfer busses

Ground power service provides power to AC ground service busses

Question 7

What does the GEN Off Bus illuminated light mean?

Answer 7

IDG is not supplying power to the related transfer bus.

Question 8

Is there any automatic source transfer from APU to Engine IDG? If so, when?

Answer 8

in case the airplane takes off with the APU powering both transfer busses. If the APU is either shut down or fails, the engine generators are automatically connected to their related transfer busses.

Question 9

When does automatic load shedding differ when aircraft is in flight and on the ground
with APU running?

Answer 9

In flight if APU only all galley busses and main busses are automatically shed, if still overloaded, IFEs are shed.
On ground, sheds galley and then main busses until within limits

Question 10

What would happen if we were to turn the Battery Master off in flight?

Answer 10

Battery buss and switched hot battery buss would not be powered

Question 11

When do the BTB’s close in the AUTO position?

Answer 11

If source powering the transfer bus is disconnected or fails, the source powering the opposite transfer bus automatically picks up the unpowered transfer bus through the BTBs.

Question 12

When does the Cross-Bus Tie Relay open?

Answer 12

• At glide slope capture during a flight director or autopilot ILS approach. This isolates the DC busses during approach to prevent a single failure
from affecting both navigation receivers and flight control computers
• Bus transfer switch positioned to OFF.

Question 13

What condition(s) would cause the DRIVE light to illuminate?

Answer 13

• IDG failure
• engine shutdown
• IDG automatic disconnect due to high oil temperature
• IDG disconnected through generator drive DISCONNECT switch

Question 14

Can an IDG be reconnected in flight?

Answer 14

NO

Question 15

How many TR units are there? Which bus powers TR 3?

Answer 15

3.

TR3 normally receives AC power from transfer bus 2 and has a backup source of AC power from transfer bus 1

Question 16

What indication would you have if there was fault in the DC power system or standby system on the ground? How would a fault be indicated in the air?

Answer 16

On the ground, an amber ELEC light comes on to indicate that a fault exists in DC
power system or standby power system. The ELEC light is inhibited in flight.

Question 17

What powers the AC standby bus and DC standby bus when on standby power?

Answer 17

The AC standby bus is powered from the battery via the static inverter. The DC
standby bus, battery bus, hot battery bus, and switched hot battery bus are powered
directly from the battery.

Question 18

What display units will be powered when on standby power?

Answer 18

• Captain’s outboard display unit with primary flight display.
• Captain’s inboard display unit with navigation display.