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NEW Alaska B737 Systems > Electrical > Flashcards

Electrical Flashcards

1
Q

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

A

No paralleling of AC power sources, and

A power source connected to a Transfer Bus automatically disconnects an existing source

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2
Q

How is AC power supplied?

A

Engine IDGs
APU Generator
External Power

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3
Q

How is DC power supplied?

A

3x TRUs
Main Battery
Main Battery Charger

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4
Q

How is Standby Power supplied?

A

Normal Operations
–AC Transfer Bus 1
–DC Bus 1

Standby Power
–Main Battery
–Auxiliary Battery
–Battery Chargers
–Static Inverter

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5
Q

What does the STANDBY PWR switch do? When would you expect it to be used?

A

Provides automatic or manual control of power to the Standby Busses

AUTO – power source switches to batteries if AC power lost

OFF – removes power to Standby Busses

BAT – forces Standby Power to batteries

Used during the STANDBY POWER OFF QRH

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6
Q

How is the AC Standby Bus powered?

A

Normally – AC Transfer Bus 1

Standby Power – Batteries via Static Inverter

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7
Q

How is the DC Standby Bus powered?

A

Normally – DC Bus 1

Standby Power – Batteries (also battery chargers)

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8
Q

What is the Standby Power duration with fully charged batteries?

A

60 minutes minimum

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9
Q

What does the Static Inverter do?

A

Converts 24 VDC battery power to 115 VAC power for AC Standby Bus

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10
Q

What is the Cross Bus Tie relay and what does it do?

A

Connects or isolates DC Bus 1 from DC Bus 2

Normally closed (DC Bus 1/2 connected)

Opens if
–BUS TRANS switch OFF, or
–G/S capture on F/D or A/P ILS approach

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11
Q

What is the APU automatic generator online feature?

A

APU powering both Transfer Busses, and
APU is shut down or fails, then
Each engine IDG is automatically connected to respective AC Transfer Bus

Can only occur once per flight and in-flight

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12
Q

What does the BUS TRANSFER switch do?

A

Auto
–Allows Bus Tie Breakers (BTBs) to operate automatically
–Maintains power to the AC Transfer Busses

OFF
–Isolates left and right AC and DC

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13
Q

Through the Bus Transfer system, how can the transfer busses be powered?

A

Powers AC Transfer Busses from any operating generator or external power

APU generator and external power cannot power AC Transfer Busses at the same time!

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14
Q

What does the STANDBY PWR OFF light indicate?

A

One or more of the following Standby Busses are not powered
–AC Standby Bus
–DC Standby Bus
–Battery Bus

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15
Q

What Display Units are available on Standby Power?

A

Captain PFD
Captain ND
Upper DU

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16
Q

What does the BAT switch do?

A

Powers the Battery and Switch Hot Battery Busses

Allows Standby Busses to be powered with loss of normal power

17
Q

What does an ELEC (amber) light indicate?

A

Fault in DC Power system or Standby Power system

Inhibited in-flight

18
Q

What does BAT DISCHARGE (amber) indicate? When might you see it?

A

Excessive battery discharge in Main or Auxiliary battery

Usually illuminates during APU battery start

May briefly illuminate (rarely) in changes of TR charger mode

19
Q

What is the TR UNIT (amber) light logic?

A

Ground
–Failure of ANY TRU

In-Flight
–Failure of TR 1, or
–Failure of both TR 2 AND TR 3

20
Q

What do the generator DRIVE (amber) lights indicate?

A

IDG low oil pressure due to:

–Engine shutdown,
–IDG failure,
–IDG manual disconnect,
–IDG auto disconnect due high oil temperature

21
Q

What happens when an IDG is decoupled?

A

IDG physically disconnects

Can only be reset on the ground by maintenance

22
Q

How is the electrical system designed to work with a single generator online?

A

Maintain power to the AC Transfer Busses

Incremental load shedding as needed based on actual load

23
Q

What does the GEN OFF BUS (blue) light indicate?

A

IDG is not powering the respective AC Transfer Bus

24
Q

What does the APU GEN OFF BUS (blue) light indicate?

A

APU RPM > 95% RPM and NOT powering an AC Transfer Bus

25
Q

What is the load-shedding process for the APU?

A

In-flight
–AC Galley and Main Busses automatically shed
–IFE Busses shed if load still too high

Ground
–Attempts to carry full load, then
–AC Galley and Main busses shed if overload

26
Q

What is the load-shedding process for the generators?

A

Incrementally as needed based on load sending

AC Galley and Main Bus 2 shed, then
AC Galley and Main Bus 1 shed, then
IFE Busses shed

Automatic restoration if another generator comes online, or

Manual restoration via cycling CAB/UTIL switch

27
Q

What does the GRD POWER AVAILABLE (blue) light indicate?

A

Ground power is connected and quality is good

NEW Alaska B737 Systems (16 decks)

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