737 Electrical

Question 1

Describe function of the Ground Service switch on the Forward Flight Attendant Panel

Answer 1

Provides manual control of ground service busses. Enables servicing of airplane using external power without activating AC transfer busses - no need to go up in cockpit.

Question 2

Explain meaning of the blue GROUND POWER AVAILABLE light

Answer 2

Ground power is available and meets airplane quality standards

Question 3

Explain the meaning of the blue APU GEN OFF BUS light.

Answer 3

APU is running and not powering a bus

Question 4

Explain the meaning of the blue GEN OFF BUS light

Answer 4

IDG or generator is not supplying power to the related transfer bus

Question 5

Where can the voltage, frequency and amps be read?

Answer 5

AC DC metering panel on the forward overhead panel

Question 6

What is the meaning of the amber DRIVE light?

Answer 6

• Integrated Drive Generator (IDG) low oil pressure
• An under frequency position. ie. putting out bad power.

Question 7

What is the amber TRANSFER BUS OFF light?

Answer 7

Related transfer bus not powered.

Question 8

What is the meaning of the amber SOURCE OFF light

Answer 8

No source has been manually selected to power the related transfer bus, or the manually selected source has been disconnected.

Question 9

What is the meaning of the TR UNIT light?

How many TR Units are on the aircraft.

Answer 9

Transformer Rectifier UNIT failure

Three.

Question 10

What is the meaning of the ELEC lights

Answer 10

It will only illuminate on the ground

It means that a fault exists in the DC power system or standby power system

Question 11

What is the meaning of the amber STANDBY PWR OFF light?

Answer 11

One or more of the following busses are unpowered:
AC Standby bus
DC standby bus
Battery bus

Question 12

How many minutes are available on standby power?

Answer 12

60 mins

Question 13

What does the GRD PWR switch do?

Answer 13

OFF - disconnects ground power from AC transfer busses

ON - If it is momentarily moved to ON position and ground power is available:
* removes previously connected power from AC transfer busses
* connects ground power to AC transfer busses when power quality is correct

Question 14

Can APU and GRD power be used at the same time?

What are the two basic principles of the Electrical System?

Answer 14

NO

Two basic principles of the Electrical system:
1. there is no paralleling of AC sources of power
2. The source of power being connected to a transfer bus automatically disconnects the existing source.

Question 15

What happens when one of the APU GEN switches is turned on?

Answer 15

1. Powers both AC transfer busses from the APU generator
2. Disconnects external power if connected
3. Opposite amber SOURCE OFF light illuminates until the second APU GEN switch is turned on.

Question 16

What components are powered by the ground service bus?

Answer 16

• Utility outlets
• Cabin Lighting
• Battery Chargers

Question 17

Where is the GROUND SERVICE switch?

Answer 17

Forward flight attendant’s control panel

Question 18

What do the GEN switches do?

Answer 18

Normally spring loaded to neutral position but also have an:
OFF - disconnects IDG from AC transfer busses
ON - connects IDG to AC transfer bus and disconnects previous power source

Question 19

What does the BUS TRANSFER switch do?

Answer 19

AUTO - bus tie breakers automatically close to maintain power to AC transfer busses in the event that one of them loses power source

OFF - Isolates AC transfer bus 1 from AC TB 2

Question 20

What does the Generator drive Disconnect (DISCONNECT) do?

Answer 20

Disconnects generators from system. Cannot be reset in flight.

Question 21

What are the three main divisions in the electrical power system?

Answer 21

1. AC Power
2. DC Power
3. Standby Power

Question 22

Which Transfer Bus supplies power to the AC standby bus?

Answer 22

Transfer Bus 1

Question 23

What is the automatic on-line feature?

Answer 23

If the APU is providing all electrical power and the crew forgets to connect the engine generators to the system. The Bus Tie Breakers will automatically transfer power supply to the generators at life off.