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Alaska 737 > Electrical > Flashcards

Electrical Flashcards

1
Q

What are the basic principles of the 737 electrical system?

A

No paralleling of AC sources of power

The source being connected to a transfer bus automatically disconnects the existing source

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2
Q

What happens when an IDG is decouples?

A

That generator is offline (mechanically decoupled)

Can only be reset by maintenance on the ground

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3
Q

What does a generator DRIVE (amber) light indicate?

A

The respective IDG has experienced low oil pressure caused by:
-IDG failure
-engine shutdown
-IDG disconnect (DISCONNECT switch)
-IDG auto-decouple (high oil temp >182 C)

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4
Q

What does GRD POWER AVAILABLE (blue) light indicate?

A

External power cord connected to aircraft and and power (checked within tolerances) is available for connection to aircraft busses

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5
Q

Is it possible to power AC Transfer Bus 2 with APU power and AC Transfer Bus 1 with External Power?

A

No

Momentarily positioning either APU GEN switch ON:
-connects APU power to both transfer busses
-disconnects external power, if connected
-the opposite SOURCE OFF (amber) light illuminates until the other APU GEN switch is moved to ON

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6
Q

What does positioning the BUS TRANSFER switch OFF do?

A

Isolates AC Transfer Bus 1 from AC Transfer Bus 2 if one IDG is supplying power to both Transfer Busses.

*AUTO allows the bus tie breakers (BTB) to operate automatically to maintain power to the AC Transfer Busses from any operating generator or external power.
-if the source powering the Transfer Bus is disconnected or fails, the source powering the opposite side automatically picks up the unpowered Transfer Bus through the BTBs

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7
Q

What is the load shedding logic for single generator operation?

A

1 Engine Gen only:
-designed to incrementally shed load based on actual load sensing.
—1st. Galleys+Main Bus on Transfer Bus 2
—2nd. Galleys+Main Bus on Transfer Bus 1
—3rd. In-Flight Entertainment (IFE) Busses
-auto restoration (two gen operation)
*manual restoration can be attempted (on the ground) CAB/UTIL OFF then ON

APU Gen only:
-in flight, all Galley+Main Busses shed
—then both IFE Busses if overloaded
-on ground, APU attempts to carry full load
—if overloaded, sheds Galley+Main Busses until within limits
*manual restoration on ground, CAB/UTIL

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8
Q

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

A

That an IDG is not supplying power to the respective Transfer Bus.

*whenever external power or APU is powering both Transfer Busses, and engine generator power is applied to its onside Transfer Bus, external power or APU continues to power remaining Transfer bus

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9
Q

What is the Automatic Generator Online feature?

A

If aircraft takes off with APU powering both Transfer Busses, APU fails/shutdown, engine generators automatically connect to their related Transfer Busses.

*only in flight under these circumstances

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10
Q

What are the sources of DC power?

A

Three Transformer Rectifier Units (TRU), powered by the AC Transfer Busses, provide DC power

Dual NICAD batteries provide DC power to loads required to be operative when no other source is available

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11
Q

What does an ELEC (amber) light indicate?

A

A fault exists in the DC or Standby power system

Inhibited in flight

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12
Q

What would cause the illumination of a TR UNIT (amber) light?

A

Ground
-failure of any TR

In flight
-TR1 fails, or
-TR2 and TR3 fail

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13
Q

When will the Cross Bus Tie Relay open automatically?

A

At glide slope capture during flight director or autopilot ILS approach. Isolates DC busses to prevent single failure from affecting both navigation receivers and FCCs

Or when bus Transfer Switch positioned OFF

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14
Q

Positioning the BAT switch to OFF deenergizes which electrical busses?

A

Removes power from:

Battery Bus and Switched Hot Battery Bus when normal power sources available

Battery Bus, Switched Hot Battery Bus, DC Standby Bus, Static Inverter, and AC Standby Bus when only battery power available

*switching BAT on
-powers battery and switched hot battery
-energizes relays to auto switch Stby elec system to batt power with loss of normal power

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15
Q

What does the BAT DISCHARGE (amber) light indicate?

A

Excessive battery discharge in Main and/or Aux battery

-5 amps for 95 sec
-15 amps for 25 sec, or
-100 amps for 1.2 sec

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16
Q

Under normal conditions, how is the AC standby bus powered? DC standby bus?

A

AC Standby from AC Transfer Bus 1
DC Standby from TR1, TR2, or TR3

Battery Bus from TR3

Hot Battery/Switched Hot Battery Bus from battery and battery charger

17
Q

With two fully charged batteries, how many minutes of standby power are available?

A

Minimum of 60 minutes

18
Q

What causes the STANDBY PWR OFF (amber) light to illuminate?

A

Indicates one or more of the following are unpowered:
-AC Standby Bus
-DC Standby Bus
-Battery Bus

19
Q

What does the STANDBY POWER switch do? Which displays are available on Standby Power?

A

Provides automatic or manual control of power to Standby Buses

Displays:
-upper: engine gauges
-captains outboard/PFD
-captains inboard/ND
-clocks
-Stby instruments
-left FMC CDU

-In the air or ground, the switch in AUTO (guarded) loss of all engine/APU power causes batteries to power standby loads:
—AC Standby Bus powered by batteries from static inverter
—DC Standby Bus, Battery Bus, Hot Battery Bus, and Switched Hot Battery Bus powered directly from batteries

*positioning the STBY PWR switch to BAT overrides auto switching and places AC Standby, DC standby, and Battery Buses on battery power even if BAT switch is off

*if BAT switch is OFF, Switched Hot Battery Bus not powered

*Stby PWR switch to OFF removes power from AC Standby and DC Standby Buses and illuminates STANDBY PWR OFF light

20
Q

What does the static inverter do?

A

Converts 24 volt DC power from battery to 115V 400 Hz single phase AC power for the AC Standby Bus (normally powered by AC Transfer Bus 1) during loss of normal electrical power

*BATT must be on or Stby PWR Switch to BATT

Alaska 737 (15 decks)

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