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B737-800 > Electrical System > Flashcards

Electrical System Flashcards

1
Q

BAT DISCHARGE light (amber)

A

with BAT switch on, there is excessive battery discharge detected

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2
Q

TR UNIT light (amber)

A

on ground- any TR has failed

in flight-

  • TR 1 failed OR
  • TR2 and TR3 failed
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3
Q

ELEC light (Amber)

A

fault exists in DC power system or standby power system (operates only on ground)

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4
Q

BAT SWITCH (OFF, On)

A

OFF- removes power from battery bus and switched hot battery bus with normal power

  • removes power from battery bus, switched hot batt bus, DC standby bus, static inverter and AC standby bus when battery is only source

ON-

  • provides power to switched hot battery bus
  • energizes relays to provide auto switching of standby electrical system to battery power with loss of normal power
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5
Q

what does the CAB/UTIL switch control?

A

power to:

all AC galley busses

FWD and AFT door area heaters

drain mast heaters

lav water heaters

logo lights

potable water compressor

115V AC shaver outlets

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6
Q

Generator DRIVE lights (amber)

A

IDG low oil pressure caused by:

  • IDG failure
  • engine shutdown
  • IDG auto disconnect due to high oil temp
  • IDG disconnect through generate drive DISCONNECT switch
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7
Q

Generate drive disconnect switch

A

disconnects IDG if electrical power is available and engine start lever is IDLE

IDG can’t be reconnected in flight

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8
Q

STANDBY Power OFF light (amber)

A

illuminates when one or more of the following busses are unpowered:

-AC standby bus
‘
DC standby bus

battery bus

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9
Q

STandby power switch (AUTO, OFF, BAT)

A

AUTO:

W/ AC transfer busses powered:
.
-AC standby bus powered by AC transfer bus 1

-DC standby bus powered by TR1, TR2, and TR3

W loss of all AC power:

  • AC standby bus powered by battery thru static inverter
  • DC standby bus powered by battery
  • Battery bus powered by battery

OFF

  • standby power OFF light illuminates
  • AC standby bus, static inverter, and DC standby bus not powered

BAT:

  • AC standby bus powered by battery through static inverter
  • DC standby bus and battery bus powered by battery
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10
Q

GRD POWER AVAILABLE (blue)

A

ground power available and meets power quality standards

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11
Q

GRD PWR switch

A

OFF-disconnects ground power from AC transfer busses

ON-

-‘removes previously connected power from AC transfer busses and connects ground power to AC transfer busses if power quality is correct

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12
Q

TRANSFER BUS OFF lights (amber)

A

associated transfer bus not powered

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13
Q

SOURCE OFF light (Amber)

If a source is powered the opposite transfer bus, will both transfer busses be powered?

A

no source has been manually selected to power the related transfer bus or manually selected source was disconnected

Yes– if a source has been selected to power the opposite transfer bus, both transfer busses are powered

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14
Q

Gen Off Bus light (blue)

A

IDG not supplying power to related transfer bus

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15
Q

GEN switch

A

OFF- disconnects IDG from related AC transfer bus by opening gen CB

ON- connects IDG to related AC transfer bus by disconnecting previous source and closing gen CB

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16
Q

Bus transfer switch (AUTO, OFF)

A

AUTO:

  • BTBs operate automatically to maintain power to AC transfer busses from any operating generator or external power
  • DC cross tie relay provides normal or isolated operation as required

OFF-

  • isolates AC transfer bus 1 from AC transfer bus 2 if one IDG is supplying power to both AC transfer busses
  • DC cross tie relay opens to isolate DC bus 1 from DC bus 2
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17
Q

APU GEN OFF BUS (blue)

A

APU running and not powering bus

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18
Q

APU GEN switch (OFF, On) with APU powering both AC transfer busses

A

OFF:

  • moving a single APU GEN switch to OFF illuminates related SOURCE OFF light but APU continue to power AC transfer busses
  • if you also move the other APU gen switch OFF, the APU gen disconnects from tie bus and removes APU power from AC transfer busses
19
Q

what happens if you select APU GEN off when the APU is powering one AC transfer bus and IDG powering one transfer bus?

A

the APU gen will disconnect from tie bus and AC transfer bus and the IDG will power both AC transfer busses

20
Q

What happens when you move a single APU gen switch to ON with no IDGs powering transfer busses?

A

both AC transfer busses will connect to APU gen

External power is disconnected

Opposite source off light illuminates until other APU gen switch is moved on

21
Q

if both AC transfer busses are powered by IDGs, what will moving the APU GEN switch to ON do?

A

it will power the related AC transfer bus from the APU gen and
the other AC transfer bus will continue to receive power from the IDG

22
Q

What provides the primary electrical power to the Aircraft

A

TWo integrated drive generators (IDGs) which supply three phase, 115V, 400 cycle AC

23
Q

What supplies DC power to the Aircraft?

A

TR units and battery/battery charger

24
Q

what are the two basic principles of the operation of the 737 electrical system?

A
  • there is no paralleling of AC sources of power (i.e. two generators would not power the same bus at the same time)
  • the source of power being connected to a transfer bus automatically disconnects the existing source
25
Q

AC power system components

A

Each system consists of:

transfer bus

main bus

two galley busses

ground service bus

26
Q

Which transfer bus supplies power to AC standby bus?

A

Transfer bus 1

27
Q

If the AC source powering either transfer bus fails or is disconnected, how does the disconnected transfer bus receive power?

A

it can be powered by any available source through the tie bus with the BTBs

28
Q

Can you power one transfer bus with external power and one with APU power?

A

NO

29
Q

What is the automatic generator on line feature in case the airplane takes off with APU powering both transfer busses?

A

If the APU is shut down or fails, the engine generators are automatically connected to their related transfer busses.

30
Q

Load shedding with single generator operations

A

1.galleys and main bus on transfer bus 2
if overload is still sensed

  1. galleys and main bus on transfer bus 1 shed
    if overload still sensed
  2. IFE buses shed
31
Q

If APU is only source of power in flight, what is automatically shed?

A

Galley busses and main buses

32
Q

DC power system consists of:

A

three TR units, energized from AC transfer busses.

Battery provides DC power to loads required to be operative with no other source available

33
Q

What does a TR unit do?

A

Converts 115V AC to 28 V DC

34
Q

Where does TR1 normally receive AC power from?

A

transfer bus 1

35
Q

Where does TR2 normally receive AC power from?

A

transfer bus 2

36
Q

Where does TR3 normally receive AC power from? what is the backup source?

A

TR3 normally gets AC power from transfer bus 2 but has a backup source of AC power from transfer bus 1.

37
Q

Are DC bus 1, DC bus 2, and DC standby bus normally connected? if so, how?

A

they are normally connected through the cross bus tie relay. TR1 and TR2 are normally powering these busses.

38
Q

TR3 is normally powering which bus?

A

battery bus

39
Q

when does cross bus tie relay automatically open to isolate DC bus 1 from DC bus 2?

A
  • Glide slope capture during F/D or AP ILS. Isolates the DC busses during approach to prevent a single failure from affected both nav receivers/flight control computers
  • bus transfer switch positioned to OFF
40
Q

For single battery airplanes, what kind of battery is it and how long will it provide standby power?

A

24V NiCad with a power minimum of 30 minutes

41
Q

For two battery airplanes, what kind of battery and how long will it provide standby power?

A

two 24V NiCad with a minimum of 60 minutes

42
Q

Which DC busses are powered from the battery if you have a loss of all gens?

A

battery bus

DC standby bus

hot battery bus
switched hot battery bus

43
Q

STandby power system consists of:

A

Main battery

Aux battery (as applicable)

Static inverter

DC standby bus

AC standby bus

Battery bus

Switched hot battery bus

Hot battery bus

44
Q

what does the static inverter do?

A

converts 24V DC from battery to 115V AC power to supply AC standby bus with loss of normal electrical power

B737-800 (21 decks)

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