Electrical

Question 1

Electrical) What are the 3 main divisions of the Electrical System?

Answer 1

• AC Power System
• DC Power System
• Standby Power System

Question 2

(Electrical) What are the two principles of the AC Electrical System?

Answer 2

• No paralleling of AC sources of power

* Source of power connected to a transfer bus automatically disconnects an existing source

Question 3

(Electrical) With External Power available, how would you energize the Ground Service Busses?

Answer 3

By activating the Ground Service Switch on the Forward Attendant Panel.

Question 4

(Electrical) What does an illuminated (Blue) GRD POWER AVAILABLE light indicate?

Answer 4

Ground Power is connected and meets the airplane power quality standards.

Question 5

(Electrical) Moving the GRD PWR switch momentarily to ON does two things - what are they?

Answer 5

• Remove any previously connected power from the AC Transfer Busses and
• Connect Ground Power

Question 6

(Electrical) What does the illuminated (Blue) APU GEN OFF BUS light indicate?

Answer 6

The APU is running, but the APU Generator in not powering a Bus

Question 7

(Electrical) What does an illuminated DRIVE light on the Overhead Panel indicate?

Answer 7

IDG Low Oil Pressure or an Under Frequency condition (Caused by one of the following:
• IDG Failure
• Engine Shutdown
• IDG Automatic Disconnect due to High Oil Temperature
• IDG Disconnected through Generator Drive DISCONNECT switch

Question 8

(Electrical) What does an illuminated (Blue) GEN BUS OFF light indicate?

Answer 8

That the respective IDG is not supplying power to it’s Transfer Bus

Question 9

(Electrical) What does an illuminated SOURCE OFF light on the Overhead Panel indicate?

Answer 9

• No source has been manually selected to power the related Transfer Bus or
• The manually selected source has been disconnected

Question 10

(Electrical) In addition to each AC Transfer Bus supplying power to a Main Bus, Galley Bus, and Service Bus what other bus is powered by AC Transfer Bus 1?

Answer 10

AC Standby Bus

Question 11

(Electrical) What does an illuminated TRANSFER BUS OFF light on the Overhead Panel indicate?

Answer 11

The related Transfer Bus is not powered

Question 12

(Electrical) When the BUS TRANS switch on the Overhead Panel is in AUTO (Guarded) and one of the sources powering a Transfer Bus is disconnected or fails what happens?

Answer 12

The source powering the opposite Transfer Bus automatically picks up the unpowered bus

Question 13

(Electrical) What would moving the BUS TRANS Switch (Normally Guarded to Auto) to OFF accomplish?

Answer 13

Inhibit the automatic switching of Bus Tie Breakers (BTB’s)

Question 14

(Electrical) How does automatic Load Shedding work?

Answer 14

• In Flight (if the APU is the ONLY source of Electrical Power, all Galley Busses and Main Busses are automatically shed)
• On Ground (if APU is the ONLY source of Electrical Power, it will attempt to carry a full electrical load. If an overload condition is sensed, the APU will start shedding Galley Busses and Main Busses until the load is within limits)

Question 15

(Electrical) What does an illuminated TR UNIT light on the Overhead Panel indicate?

Answer 15

• In Flight (TR 1 has failed or TR2 AND TR3 have failed)

* On the Ground (any TR Unit has failed)

Question 16

(Electrical) When does the Cross Bus Tie Relay (normally connecting TR1 to TR2) automatically open?

Answer 16

• at G/S capture with the flight director or auto pilot selected to ILS approach
• BUS TRANSFER switch to OFF (this isolates the DC buses and prevents a failure of DC bus from affecting both navigation receivers and FCCs

Question 17

(Electrical) Normally the AC Standby Bus is powered by AC Transfer Bus 1 and the DC Standby Bus is Powered by TR1, 2, and 3. If these are NOT available, what would it’s secondary Power Source be?

Answer 17

Battery (AC standby through the static inverter)

Question 18

(Electrical) What does an illuminated BAT DISCHARGE light on the Overhead Panel indicate?

Answer 18

an excessive battery discharge is detected

Question 19

(Electrical) What are the three battery busses connected to the Battery?

Answer 19

• hot battery bus
• switched hot battery bus
• battery bus

Question 20

(Electrical) What does an illuminated ELEC light on the Overhead Panel indicate?

Answer 20

ONLY ON THE GROUND:

• fault in the DC power system
• fault in the standby power system

Question 21

(Electrical) What Busses comprise of the Standby Power System?

Answer 21

• AC standby bus
• DC standby bus
• battery bus
• switched hot battery bus
• hot battery bus

Question 22

(Electrical) What does an illuminated STANDBY PWR OFF light on the Overhead Panel indicate?

Answer 22

that either one of the three buses is NOT powered

• AC standby
• DC standby
• battery bus

Question 23

(Electrical) What happens when you moved the Standby Power (Guarded) Switch to the OFF position?

Answer 23

removes power from the

• AC standby bus
• static inverter
• DC standby bus

Question 24

(Electrical) What happens when you move the Standby Power (Guarded) Switch to BAT?

Answer 24

overrides the automatic switching of the standby power - the switch position manually places the AC standby bus, DC stanby bus and battery bus on battery power