REVIEW QUESTIONS – ELECTRICAL

Question 1

1. What are the two “basic principles of operation” for the 737 Electrical System?

Answer 1

• There is no paralleling of the AC sources of power

* The source of power being connected to a Transfer Bus automatically disconnects an existing source

Question 2

2. What are all the sources of AC power?

Answer 2

AC Power:
• two Engine-Driven Generators
• one APU Generator
• external power

Question 3

3. What could cause the illumination of the Generator DRIVE light?

Answer 3

-The IDG has low oil pressure caused by: IDG failure, Engine shutdown, IDG has been disconnected by the DISCONNECT switch, or IDG auto-decoupled due to high oil temp (182C)

Question 4

4. What happens when positioning the GRD PWR switch ON?

Answer 4

-External power is connected to both Transfer Buses.

Question 5

5. What does the BUS TRANSFER switch, in the AUTO (guarded) position, allow?

Answer 5

-Allows the Bus Tie Breakers (BTB) to operate automatically to maintain power to the AC Transfer Buses.

Question 6

6. Which light(s) indicate(s) the APU is ready-to-load, but not powering a bus?

Answer 6

-the APU GEN OFF BUS (Blue) Light

Question 7

7. If the AC Transfer Buses are powered by External Power, momentarily positioning either APU GEN switch ON will cause the APU to power which bus(es)? What lights would you see?

Answer 7

-Both Transfer Buses
-The opposite side source light and GRD POWER AVAILABLE (blue) light

Question 8

8. When the APU is powering a Transfer Bus, how can you power the opposite Transfer Bus?

Answer 8

-With either the APU generator or the other IDG

Question 9

9. What buses are shed when the APU is operating in flight as the single electrical source?

Answer 9

-Galley Buses and Main Buses, if needed the IFE Buses.

Question 10

10. Moving a GEN (Generator) switch to ON powers which bus? What lights would you see?

Answer 10

-It’s own Transfer Bus
-Depends on what was powering it before, maybe the GRD PWER AVAILABLE, APU GEN OFF BUS

Question 11

11. Describe the Automatic Generator Online Feature.

Answer 11

-If you takeoff with APU powering both Transfer Busses and APU is shutdown or fails, the engine generators are automatically connected to their Transfer Bus.

Question 12

12. What does the ELEC light (amber) indicate?

Answer 12

-There is a fault in the DC Power system or Standby Power System

Question 13

13. When does the Cross Bus Tie Relay open and isolate DC Bus 1 from DC Bus 2?

Answer 13

-At Glide Slope capture during a FD or AP ILS approach or Bus Transfer Switch positioned to OFF

Question 14

14. Which Bus is always connected to the battery?

Answer 14

-Hot Battery Bus

Question 15

15. When does the BAT DISCHARGE light (amber) illuminate?

Answer 15

-During an excessive battery discharge: 5 amps for 95 seconds, 15 amps for 25 seconds, or 100 amps for 1.2seconds

Question 16

16. What is/are the alternate power source(s) for AC standby power?

Answer 16

-the batteries via static inverter

Question 17

17. How long will two fully-charged batteries provide standby power?

Answer 17

-a minimum of 60 minutes

Question 18

18. With the loss of all engine or APU electrical power, the battery will be powering which buses if the STANDBY POWER switch is in AUTO? Is this the same in flight and on the ground?

Answer 18

-AC Standby Bus (via the Static Inverter), DC Standby Bus, Battery Bus, Hot Battery Bus, and Switched Hot Battery Bus.