B737 Electrical (Old)

Front 1

Describe the primary electrical power source

Back 1

Two engine integrated drive generators (IDGs) which supply three-phase, 115 volt, 400 cycle alternating current

Front 2

What are the two basic principles of operation for the 737 electrical system?

Back 2

•There is no paralleling of the AC sources of power. •The source of power being connected to a transfer bus automatically disconnects an existing source.

Front 3

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

Back 3

The AC power system, the DC power system, and the standby power system.

Front 4

What will the APU generator supply when it is the only power source?

Back 4

All electrical power requirements on the ground and most of them in flight

Front 5

What does each AC power system consist of?

Back 5

A transfer bus, a main bus, two galley busses, and a ground service bus. Transfer bus 1 also supplies power to the AC standby bus.

Front 6

What happens if the AC source powering either transfer bus fails or is disconnected?

Back 6

The transfer bus can be powered by any available source through the tie bus with the bus tie breakers (BTBs).

Front 7

On the ground with both generator switches OFF (or engines not running), will ground power or APU power take precedence?

Back 7

Neither, the source selected last powers both transfer busses

Front 8

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

Back 8

No

Front 9

What powers the transfer busses if ground or APU is supplying power and an engine generator is switched to ON?

Back 9

The respective transfer bus is powered by the engine generator and the other transfer bus is still powered by the ground or APU

Front 10

What happens in flight if one engine generator fails?

Back 10

The bus tie breakers will close allowing the remaining generator to power both transfer busses

Front 11

What happens if you takeoff with the APU supplying power to the transfer busses and the APU fails or is shutdown?

Back 11

There is an automatic generator on-line feature that will automatically connect the engine generators to their respective transfer bus.

Front 12

In regards to the AC system, what does placing the BUS TRANSFER switch in the AUTO position allow for?

Back 12

If the the source powering the transfer bus is disconnected or fails, the source powering the opposite transfer bus automatically picks up the unpowered transfer bus through the BTBs

Front 13

Describe the engine generators automatic load shedding process

Back 13

For single generator operation, if the load it too high, it will automatically shed first the galleys and main bus on transfer bus 2, then the same on 1, and then the IFE buses.

Front 14

Describe the APU generator automatic load shedding process

Back 14

In flight, all galley busses and main buses are automatically shed. If load is still too high, both IFE busses are automatically shed. On the ground, the APU attempts to carry a full electrical load. If there is an overload, the APU sheds galley busses and main busses until the load is within limits.

Front 15

Describe the Integrated Drive Generators

Back 15

IDGs contain the generator and drive in a common housing, and are lubricated and cooled by a self–contained oil system. An integral electro–mechanical disconnect device provides for complete mechanical isolation of the IDG

Front 16

What does the DRIVE amber caution light indicate?

Back 16

IDG low oil pressure is 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

Front 17

What does the generator drive disconnect switch do?

Back 17

If electrical power is available and engine start lever is in idle, it disconnects the generator from the engine in the event of a generator drive malfunction.

Front 18

Can the the generator be reactivated after it has been disconnected through the switch?

Back 18

No, only on ground by maintenance

Front 19

What is the source of power for the DC power system during normal operation?

Back 19

28 volt DC power is supplied by three TR units, which are energized from the AC transfer busses

Front 20

What does an amber ELEC light indicate?

Back 20

On the ground and there is a fault in the DC power system or standby power system (light is inhibited in flight)

Front 21

What do the transformer rectifier units (TR's) do?

Back 21

They convert 115V AC into 28V DC

Front 22

How many TR's are there?

Back 22

3

Front 23

How many TR's do you need to supply the total load?

Back 23

2

Front 24

Where does each TR receive it's AC power?

Back 24

TR1 from transfer bus 1, TR2 from transfer bus 2, TR3 from transfer bus 2 with transfer bus 1 as a backup

Front 25

Under normal conditions, which TR's power which busses?

Back 25

TR1 and TR2 powers DC Bus 1, DC Bus 2, and the DC standby bus. TR3 powers the battery bus and serves as backup power for TR1 and TR2

Front 26

Under normal conditions, are the bus ties for the AC and DC system open or closed?

Back 26

AC Bus Tie Breakers (BTB's) are open, DC cross bus tie relay is closed

Front 27

What would cause the cross bus tie relay to automatically open?

Back 27

•At glide slope capture during a flight director or autopilot ILS approach. This isolates the DC busses during approach to prevent a single failure from affecting both navigation receivers and flight control computers, •Bus transfer switch positioned to OFF

Front 28

What does an amber TR light indicate?

Back 28

Ground, any TR fault. Flight, TR1 has failed or TR2 and TR3 has failed

Front 29

Describe the battery('s)

Back 29

For single battery aircraft, one 24V Ni-Cad battery in the electronics compartment. For dual batteries, 2 24V Ni-Cad batteries

Front 30

What is the battery voltage range?

Back 30

22 to 30 volts

Front 31

How long will a fully charged battery(ies) supply standby power?

Back 31

30 minutes for single battery, 60 minutes for dual batteries

Front 32

Which DC busses are powered following a loss of all generators?

Back 32

Battery Bus, DC Standby Bus, Hot Battery Bus, Switched Hot Battery Bus

Front 33

What does an amber BAT DISCHARGE light indicate?

Back 33

With the BAT sItch ON, there is excessive battery discharge.

Front 34

What is the purpose of the battery charger?

Back 34

To restore and maintain the battery at full electrical power

Front 35

What powers the battery charger?

Back 35

AC ground service bus 2

Front 36

What happens to the battery charger after the completion of the battery charge cycle?

Back 36

It reverts to a constant voltage Transformer Rectifier.

Front 37

What does the battery charger do when it is in the TR mode?

Back 37

It powers loads connected to the hot battery bus and the switched hot battery bus. It also powers the battery bus if TR3 fails

Front 38

For dual battery aircraft, what charges the auxiliary battery?

Back 38

The auxiliary battery charger is powered through AC ground service bus 1.

Front 39

What does the standby power system provide?

Back 39

115V AC and 24V DC power to essential systems in the event of loss of engine generators and APU generator

Front 40

What does the standby power system consist of?

Back 40

•static inverter, •AC standby bus, •DC standby bus, •battery bus, •hot battery bus, •switched hot battery bus, •main battery

Front 41

What powers the standby power system during normal operations?

Back 41

The AC standby bus is powered from AC transfer bus 1. The DC standby bus is powered by TR1, TR2, and TR3; the battery bus is powered by TR3; the hot battery bus and switched hot battery bus are powered by the battery/battery charger.

Front 42

With the STANDBY POWER switch in AUTO, what would cause the automatic switching from normal to standby power?

Back 42

Loss of power from either AC transfer bus 1 or DC bus 1

Front 43

What does positioning the standby power switch to BAT do?

Back 43

It overrides automatic switching and places the AC standby bus, DC standby bus, and battery bus on battery power.

Front 44

Does the battery switch position have any effect when the standby power switch is in BAT?

Back 44

Yes, the switched hot battery bus will turn on or off

Front 45

When the APU generator is powering both AC transfer busses and the BUS TRANSFER switch is in AUTO, what does placing the APU GEN switch in OFF do?

Back 45

-Moving a single switch to OFF illuminates the related SOURCE OFF light, APU continues to power AC transfer busses. Subsequently moving the other switch to OFF disconnects APU generator from tie bus and removes APU power from AC transfer busses

Front 46

When the APU generator is powering one or both AC transfer busses and the BUS TRANSFER switch is in OFF, what does placing the APU GEN switch in OFF do?

Back 46

The BTB opens if it's related switch is set to OFF

Front 47

When the APU generator is powering one AC transfer bus, the IDG is powering the other, and the BUS TRANSFER switch is in AUTO, what does placing the APU GEN switch in OFF do?

Back 47

Disconnects APU generator from tie bus and AC transfer bus. IDG powers the other AC transfer bus through the BTB

Front 48

What does placing the APU GEN switch to ON do if neither AC transfer bus is being powered by IDG's and BUS TRANSFER switch is in AUTO?

Back 48

APU powers both transfers busses, ground power automatically disconnects, opposite SOURCE OFF light illuminates until the other APU GEN switch is placed to ON

Front 49

What does placing the APU GEN switch to ON do if both AC transfer busses are being powered by IDG's and BUS TRANSFER switch is in AUTO?

Back 49

Related AC transfer bus is powered by APU, opposite is powered by IDG

Front 50

What does placing the APU GEN switch to ON do if there is a Loss of All Generators and BUS TRANSFER switch is in OFF?

Back 50

Related AC transfer bus powered by APU, opposite side still unpowered because the BTB is open.

Front 51

What does placing the battery (BAT) switch in the OFF position do?

Back 51

-Normal power sources available: removes power from battery bus and switched hot battery bus. -Battery only power source: removes power from battery bus, switched hot battery bus, DC standby bus, static inverter, and AC standby bus

Front 52

What does placing the battery (BAT) switch in the ON position do?

Back 52

-Provides power to switched hot battery bus, -Energizes relays to provide automatic switching of standby electrical system to battery power

Front 53

What is powered by the CAB/UTIL switch?

Back 53

-All 115V AC galley busses, -Left and right recirculation fans, -Fwd and aft door area heaters, -Drain mast heaters, -Lavatory water heaters, -Logo lights, -Potable water compressor, -115V shaver outlets, -(for FDJ and later) LED cabin lighting

Front 54

What is powered by the IFE/PASS SEAT switch?

Back 54

-115V audio/video entertainment equipment, -Cabin telephone equipment, -FAX machine, -28V DC video equipment and pax seat electrical outlets, -flight deck door surveillance system

Front 55

What does the STANDBY PWR OFF light indicate?

Back 55

AC standby bus, DC standby bus, and/or battery bus unpowered

Front 56

What does positioning the STANDBY POWER switch to AUTO do?

Back 56

-If AC transfer busses powered: AC standby bus is powered by AC transfer bus 1, DC standby bus is powered by TR 1, 2, and 3. -If loss of all AC power: AC standby bus powered by battery static inverter, DC standby bus powered by battery, Battery bus powered by battery

Front 57

What does positioning the STANDBY POWER switch to OFF do?

Back 57

-AC standby bus, static inverter, and DC standby bus are not powered, -STANDBY PWR OFF light illuminates

Front 58

What does the GRD POWER AVAILABLE light indicate?

Back 58

Ground power is connected and meets quality standards

Front 59

What does placing the GRD PWR switch to OFF do?

Back 59

Disconnects ground power from AC transfer busses

Front 60

What does placing the GRD PWR switch to ON do?

Back 60

If power quality is correct, connects ground power to AC transfer busses.

Front 61

What does the TRANSFER BUS OFF light indicate?

Back 61

Related transfer bus is not powered

Front 62

What does the SOURCE OFF light indicate?

Back 62

-No source has been manually selected to power the related transfer bus, OR -The manually selected source has been disconnected.

Front 63

What does the GEN OFF BUS light indicate?

Back 63

IDG is not supplying power to the related transfer bus

Front 64

What does placing the GEN switch in the OFF position do?

Back 64

Disconnects IDG from related AC transfer bus by opening generator circuit breaker

Front 65

What does placing the GEN switch in the ON position do?

Back 65

Connects IDG to related AC transfer bus by disconnecting previous power source and closing generator circuit breaker

Front 66

What does placing the BUS TRANSFER switch in AUTO do?

Back 66

-BTB's operate automatically to maintain power to AC transfer busses from any operating generator or external power. -DC cross tie relay automatically provides normal or isolated operation as required

Front 67

What does placing the BUS TRANSFER switch to OFF do?

Back 67

-If one IDG is supplying power to both AC transfer busses, it isolates AC transfer bus 1 from bus 2, -If the APU generator is the only available power source, the OFF position arms each bus tie breaker to open if it's related APU GEN switch is set to OFF, -DC cross tie relay opens to isolate DC bus 1 from DC bus 2

Front 68

What does the APU GEN OFF BUS light indicate?

Back 68

APU is running and not powering a bus

Front 69

What does the GROUND SERVICE switch do?

Back 69

Provides manual control of ground service buses, allows ground service buses to be powered by ground power without AC transfer buses being powered.

Front 70

If automatic load shedding has occurred with the engine generators, is there a way to manually attempt to restore the main and galleys bus?

Back 70

Yes, by recycling the CAB/UTIL switch.

Front 71

If automatic load shedding has occurred with the APU generator, is there a way to manually attempt to restore the main and galleys bus?

Back 71

Yes, by recycling the CAB/UTIL switch.