737 Systems: Electrical

Question 1

What are the basic principals of the 737 electrical system?

Answer 1

-There is no paralleling of AC sources for power

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

Question 2

What happens when a IDG is decoupled?

Answer 2

A solenoid-operated pawl that mechanically interfaces with a worm-gear that retracts the splined IDG drive shaft out of the gearbox for complete drive decoupling with engine rotation

Question 3

What does a generator DRIVE (amber) light indicate?

Answer 3

The IDG has experienced Low Oil Pressure due to:
-IDG Failure
-Engine shutdown
-IDG disconnected via DISCONNECT switch
-IDG auto decouple due to high oil temperature

Question 4

What does the GRD POWER AVAILABLE (blue) light indicate?

Answer 4

That external power is connected and checked within tolerance and is available for use

Question 5

Is it possible to power AC Transfer Bus 2 with APU power and AC Transfer Bus 1 with External Power?

Answer 5

No, it is one or the other

Question 6

What does positioning the BUS TRANSFER switch to OFF do?

Answer 6

This isolates AC Transfer Bus 1 from AC Transfer Bus 2 if one IDG is supplying power to both Transfer Busses

Question 7

What is the load shedding logic for single generator operation?

Answer 7

-First the Galley and Main Bus for the associated Transfer Bus ( 2 for IDG, both for APU)
-Then the In-Flight Entertainment systems

Question 8

What does the GEN OFF BUS (blue) light indicate?

Answer 8

That the associated IDG is not powering the Transfer Bus

Question 9

What is the Automatic Generator Online feature?

Answer 9

If the aircraft takes off with the APU supplying power to BOTH transfer busses and is shut down or fails, the IDGs will automatically connect to their associated Transfer Bus. (Only happens In-Flight)

Question 10

What are the sources of DC power?

Answer 10

-Main Battery
-AUX Battery
- 3 TR Units

Question 11

What does an ELEC (amber) light indicate?

Answer 11

On the ground indicates a fault with the DC Power system OR Standby power system

Question 12

What would cause the illumination of a TR UNIT (amber) light to illuminate?

Answer 12

On the ground:
Any TR Unit Failure

In Flight:
-Failure with TR1
Or
-Failure with TR2 AND TR3

Question 13

When will the Cross Bus Tie Relay open automatically?

Answer 13

At Glidelsope capture during a Flight Director or Autopilot ILS approach
-Bus Transfer Switch positioned OFF

Question 14

Positioning the BAT Switch to OFF deenergizes which electrical busses?

Answer 14

-Battery Bus and Switched Hot Battery Bus with normal sources available

-Battery Bus, Switched Hot Battery Bus, DC Standby Bus, Static Inverter, and AC Standby Bus when battery is the ONLY power source

Question 15

What does the BAT DISCHARGE (amber) light indicate?

Answer 15

When excessive battery discharge is detected in the Main Battery and/or AUX Battery

Question 16

Under normal conditions, how is the AC Standby Bus powered?

Answer 16

By AC Transfer Bus 1

Question 17

Under normal conditions how is the DC Standby Bus powered?

Answer 17

By TR1, TR2, OR TR3

Question 18

With two fully charged batteries, how many minutes of standby power are available?

Answer 18

60 minutes

Question 19

What causes the STANDBY PWR OFF (amber) light to illuminate?

Answer 19

One or more of the following busses are unpowered:
-AC Stanby Bus
-DC Standby Bus
-Battery Bus

Question 20

What does the STANDBY POWER switch do?

Answer 20

Provides automatic or manual control of power to the Standby Busses

Question 21

Which displays are available on Standby Power?

Answer 21

Captains Outboard DU with PFD, Inboard DU with NAV Display and Upper DU for engine indications

Question 22

What does the Static Inverter do?

Answer 22

It converts DC power from the batteries to AC power, so the AC Standby Bus remains powered during a loss of all normal electrical power