8_ELECTRICAL SYSTEM

Question 1

What is the primary power source for the aircraft and what is it rated at?

Answer 1

primary power is generated by 2 IDGs

3 phase 115vac 400 cycle AC power

Question 2

What is the source of DC power on the aircraft?

Answer 2

TR units, main battery and battery charger supply DC power.

Question 3

How many sources of electrical power are there?

Answer 3

external

APU

2 IDGs

Battery

Question 4

What are the 2 basic principles of the electrical system?

Answer 4

1. No paralleling of AC power sources
2. the source of power being connected to a transfer bus AUTOMATICALLY disconnects an existing source.

Question 5

What are the 3 main divisions of the electrical system?

Answer 5

AC

DC

Standby

Question 6

Do the IDGs maintain a constant speed?

Answer 6

Yes through a CSD.

Question 7

Can the APU provide power to BOTH AC transfer busses on the ground and in flight?

Answer 7

Yes.

Question 8

Where is the external AC power receptical?

Answer 8

lower right side of fuselage - near the nose gear wheel well

Question 9

How do you provide power for ground servicing equipment in the plane?

Answer 9

there is a ground service switch on the fwd attendants panel - provides ground power to the AC ground service busses for utility outlets, cabin lights, and the battery charger.

Question 10

What busses make up the AC system?

Answer 10

Each AC systems contains:

Transfer bus

main bus

2 galley busses

ground svc bus

Question 11

Is it possible on the ground to power one transfer bus with external power and the other with the APU?

Answer 11

No.

Question 12

What does moving the Gen Switch do?

Answer 12

it closes the related Gen CB and connects gen to associated transfer bus.

Question 13

What happens if external power or APU is running the transfer busses and you connect 1 generator?

Answer 13

the Generator will power the associated transfer bus BUT the APU or External power will continue to power the other bus.

Question 14

What is the Automatic Generator On-Line Feature and how does it work?

Answer 14

this is used if the airplane takes off with the APU powering BOTH transfer buses….

Operations:

if the APU is either shut down or fails, the engine generators are AUTOMATICALLY connected to their related transfer bus - it occurs ONLY ONCE in flight and ONLY under the above conditions.

Question 15

How does the automatic load shedding work for ENG GENERATORS?

Answer 15

for SINGLE GEN ops:

• designed to shed incrementally -

ORDER.

Galleys & Main Bus (transfer bus 2) - THEN

Galleys & Main Bus (transfer bus 1) - THEN

IFE busses

Question 16

How does electrical load shedding occur if the APU is the sole source of electrical power?

Answer 16

Order (in flight).

All Galley and Main Busses - THEN -

Both IFE busses

Order (ground)

the APU tries to carry the full load - if not - THEN

Galley Busses and Main Busses.

Question 17

How do you restore power to the galley and main busses after load shedding occurs?

Answer 17

you move the CAB/UTIL power switch to OFF then ON.

Question 18

What is an IDG?

Answer 18

it contains a generator and a drive in a common housing - self contained oil system.

Question 19

When is frequency only indicated on the AC voltmeter?

Answer 19

Only when the generator is electrically excited.

Question 20

What positions on the DC switch only indicate DC voltage?

Answer 20

Standby Power and battery bus - all others show volts and amps.

Question 21

How is 28v DC power supplied to the airplane?

Answer 21

through 3 TR units that are energized from the AC transfer buses.

Question 22

What do the TRUs do?

Answer 22

they convert 115vAC to 28v DC

Question 23

Where do each of the TRs get their power from?

Answer 23

TR 1: transfer bus 1

TR 2: transfer bus 2

TR 3: transfer bus 2 (Normally) but has transfer bus 1 (backup)

Question 24

How many TRs are the minimum for full electrical operation?

Answer 24

Any 2 TRs are capable of supplying the total connected load.

Question 25

How are DC Bus 1, 2 and Standby bus connected?

Answer 25

Under normal conditions, they are connected via the cross bus tie relay.

Normal.

TR 1 and TR 2 each power DC Bus 1, 2 and DC Standby Bus

TR 3 will power the Battery Bus and serves as backup power for TR 1 & 2.

Question 26

When does the cross bus tie relay automatically OPEN? What does it do?

Answer 26

when it opens, it isolates DC bus 1 from DC bus 2

Conditions.

• opens at glideslope capture on ILS (AP or FD appr)

[this is to isolate the DC Buses during approach preventing a single failure from affecting BOTH nav receivers and FCCs]

• Bus Transfer Switch - OFF

Question 27

What is the power rating of the battery?

Answer 27

24V Nicad battery - 1 with the option for 2

Question 28

How is battery charging controlled?

Answer 28

it is controlled automatically.

Question 29

What is the battery voltage range?

Answer 29

22-30 V

Question 30

What DC busses are powered from the Battery with a loss of both generators?

Answer 30

Batt Bus

DC Standby Bus

Hot Batt Bus

Switch Hot Bat Bus.

Question 31

What is the purpose of the battery chargers?

Answer 31

to restore and maintain the batteries at full electrical charge.

Question 32

How is the main battery charger powered?

Answer 32

AC Ground service bus 2.

Question 33

What happens after the battery is fully charged?

Answer 33

The main battery reverts to a constant voltage TR mode - which means it powers loads connected to the hot battery bus and the switched hot batt bus.

The main battery charger TR also powers the battery bus if TR3 fails.

Question 34

The standby power system provides what power?

Answer 34

115Vac and 24V DC to the essn services in case of loss of all engine or APU driven AC power.

Question 35

What is the standby electric system consist of?

Answer 35

AC