Electrical

Question 1

How much and what type of electrical power do each of the IDGs provide?

Answer 1

115V AC.

Question 2

What are the 2 operating principles of the 737 electrical system?

Answer 2

1. AC power sources do not run in parallel.
2. Connecting a new source of power, automatically disconnects the current source.

Question 3

What bus does the AC transfer bus 1 power, that bus 2 does not?

Answer 3

AC Standby Bus.

Question 4

What is the purpose of the generator “on-line” feature?

Answer 4

It automatically connects the engine generators in the event the APU is accidentally powering both transfer busses at takeoff, and subsequently fails.

Question 5

With regards to Automatic Load Shedding (during single generator operation); what is the order of bus shedding?

Answer 5

(1) Galleys & Main Bus on TB2.

If an overload is still sensed:
(2) Galleys & Main Bus on TB1.

Overload still exists:
(3) IFE Bus.

Question 6

When the APU is the only source of electrical power, what sequence does Automatic Load Shedding follow if an overload is sensed?

Answer 6

(1) All Main & Galley Busses.
(2) Both IFE Busses.

Question 7

During a flight, the generator DRIVE light illuminates. What does this indicate?

Answer 7

Low oil pressure on the associated generator.

Question 8

During a flight you have had to disconnect a generator using the drive disconnect switch.
Can you reconnect the generator in flight?

Answer 8

No.

Question 9

How much DC power do each of the TRs provide?

Answer 9

28V.

Question 10

Where does TR3 normally receive power from? And where can it receive back-up power from?

Answer 10

Transfer Bus 2.
Back-up from Transfer Bus 1.

Question 11

What connects DC bus 1, DC bus 2 and the DC STBY bus to each other?

Answer 11

The Cross Bus Tie Relay.

Question 12

Which bus does TR3 provide power to?

Answer 12

The battery bus.

Question 13

Under what conditions will the Cross Bus Tie Relay move to open?

Answer 13

(i) Glideslope capture during a FD/AP ILS/GLS approach.
(ii) Bus Transfer switch positioned to OFF.

Question 14

During a flight, the TR UNIT light illuminates, what could this indicate?

Answer 14

Either:
(i) TR1 has failed.
or
(ii) Both TR2 & TR3 have failed.

Question 15

What is the capacity and type of battery on the aircraft?
What is the batteries voltage range?
What is the minimum standby power time available from the battery?

Answer 15

(i) 24V Nickel-Cadmium Battery.
(ii) Range of 22 - 30V
(iii) A minimum of 30 minutes.

Question 16

How long can the ISFD remain powered on after loss of power?

Answer 16

Up to 150 minutes.

Question 17

Which bus powers the AC Standby Bus?

Answer 17

AC Transfer Bus 1.

Question 18

What powers the DC Standby Bus?

Answer 18

TR1, TR2 & TR3.

Question 19

What powers the battery bus?

Answer 19

TR3.

Question 20

What powers the hot battery bus and switch hot battery bus?

Answer 20

Battery/Battery Charger.

Question 21

What does placing the standby power switch to BAT do?

Answer 21

It overrides automatic switching and sets the standby busses and battery bus on battery power.

Question 22

During taxi, the TR UNIT light illuminates. What does this indicate?

Answer 22

At least one of the TR UNITS have failed.

Question 23

Will the overhead ELEC light only illuminate on the ground, or in the air?

Answer 23

On the ground.

Question 24

What other battery bus is also powered whenever the battery switch is ON?

Answer 24

The Switched Hot Battery Bus.

Question 25

What components are used to convert the AC power to DC power?

Answer 25

The Transformer Rectifier Units (TRs).

Question 26

In the event of a loss of all engine and APU electrical power, how is power provided to the AC STBY BUS?

Answer 26

Power is provided from the Battery via an Inverter.

Question 27

During a total electrical failure; if the standby power switch is positioned OFF, which busses are de-energised?

Answer 27

The AC STBY BUS and DC STBY BUS.

Question 28

What is the alternate power source for standby power?

Answer 28

The Battery.

Question 29

How are the IDGs lubricated and cooled?

Answer 29

By a self-contained oil system.

Question 30

With STANDBY POWER SWITCH in AUTO, if there is a complete electrical failure, how does the system receive electrical power? And how does the AC STANDBY BUS receive its power then?

Answer 30

From the BATTERY, and the INVERTER converts the DC power from the battery to AC for the AC STANDBY BUS.

Question 31

What does the the STANDBY POWER OFF light illuminated indicate?

Answer 31

That the AC and DC STANDBY bus are not powered.