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United 737 > Electrical > Flashcards

Electrical Flashcards

1
Q

737 draws DC power from _______ and a single______.

A

transformer rectifiers. Battery

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2
Q

IDGs provide power in the form of three phase, ________ alternating current.

A

115V, 400 cycle.

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3
Q

T/F: when one IDG is inop, the other can power the other bus as well.

A

True.

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4
Q

The APU generator can power both transfer buses on the ________ or in flight.

A

ground.

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5
Q

Which aircraft have auxiliary batteries?

A

tail 751 & 752.

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6
Q

Where is the hook up for the ground cart?

A

right side near nose gear.

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7
Q

What are two important principles for power on the 737?

A

different sources of AC power cannot be paralleled.

connecting a different source automatically disconnects and existing electrical power source.

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8
Q

What is the purpose of the AC and DC metering panel?

A

display AC and DC voltage and amperage and AC freq. Test functions are used by mx.

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9
Q

When does the BATT DISCHARGE light illuminate?

A

excessive discharge detected.

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10
Q

When does the TR UNIT light illuminate?

A

Ground: any TR unit has failed.
Flight: either TR1 has failed or both TR2 and TR3 have failed.

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11
Q

When does the ELEC light illuminate?

A

on the ground only: a fault in the DC power system or the stby power system.

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12
Q

When the BATTERY switch is off, and no other power sources connected, power is removed from which buses?

A 
Battery Bus
Switched Hot Battery Bus
DC Stby Bus
Static inverter
AC Stby Bus
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13
Q

When the BATTERY switch is off, and other power sources are connected, power is removed from which buses?

A

Battery Bus and switched hot battery bus.

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14
Q

What does the CAB/UTIL switch do?

A

switches power on or off to galleys and cabin equipment when the AC transfer busses are powered.

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15
Q

When does the generator DRIVE disconnect light happen?

A

drive has been disconnected through use of the Generator drive DISCONNECT switch
IDG failure
engine shutdown
IDG automatic disconnect due to high oil temp

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16
Q

Can and IDG be reconnected in the air?

A

no

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17
Q

What are the conditions for the disconnect switch to work?

A

power is available

engine start lever in IDLE

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18
Q

If STANDBY POWER switch is in AUTO, how are busses transfered if all AC power lost?

A

AC stby bus powered by battery through static inverter
DC standby bus powered by battery
battery bus powered by battery

19
Q

If you move the STANDBY POWER switch to off, what happens?

A

STANDBY POWER OFF light illuminates

AC standby bus, static inverter, and DC standby bus are not powered.

20
Q

If you move the STANDBY POWER switch to BAT, what happens?

A

AC standby bus is powered by battery through static inverter

DC standby bus and battery bus are powered directly by battery

21
Q

If the STANDBY POWER OFF light is illuminated, what busses are unpowered?

A

AC standby
DC standby
Battery bus

22
Q

The DC cross tie opeartes as req’d to provide normal operations of the DC busses, or to isolate DC bus 1 from DC bus 2 _________.

A

when conducting an ILS approach.

23
Q

What does TRANSFER BUS OFF light mean?

A

associated bus is not powered.

24
Q

What does SOURCE OFF show?

A

no source has been manually selected to power the associated transfer bus.
manually selected source has been disconnected.

25
Q

What does the ground service switch do?

A

allows the airplane to be serviced using external power by manually activating the ground service busses without energizing the AC transfer busses.

26
Q

The AC STANDBY bus receives power from which bus?

A

AC TRANSFER BUS 1

27
Q

When one generator fails or is disconnected, the system automatically ____________ in increments to bring the total load in line with capacity.

A

sheds electrical loads

28
Q

With 1 IDG inop, what is the order of load shedding?

A

Galley on Trans Bus 2
Galley on Trans Bus 1
Main Bus 1
Main Bus 2

29
Q

With the APU as the only elec source, which buses are shed?

A

galley busses and main busses are shed. If needed the IFE busses are also shed.

30
Q

How many TRs are there? Where does their power come from?

A

3, AC Transfer buses
TR 1- AC Trans 1
TR 2& 3= AC Trans 2

31
Q

How much power do the TRs supply?

A

28V DC power

32
Q

How many volts is the battery?

A

24V DC power

33
Q

What is the backup source of power for TR3?

A

AC Transfer bus 1.

34
Q

The total DC load can be supplied by any ____ TRs.

A

2

35
Q

Voltage range for the batteries is___ to ____ .

A

22V ; 30 V.

36
Q

How long does power last for a single charged battery? Dual charged batteries?

A

30 min; 60 min

37
Q

Which bus is always powered by the battery?

A

Hot Battery Bus, however, battery voltage must be above a specified minimum.

38
Q

What bus powers the battery charger?

A

GND Service BUS 2. If 2 batteries installed, Aux battery powered by Batt Chgr on Gnd Service Bus 1

39
Q

For batteries in TR mode what is being powered?

A

Hot battery bus and switched hot battery bus

40
Q

The STBY power system provides _____AC and _____DC power to essential systems

A

115V; 24V

41
Q

What are the components of the STBY power system?

A 
Static inverter
AC Stby bus
DC stby bus
battery bus
Hot battery bus
switched hot battery bus
main battery
(aux battery) if installed
42
Q

If a/c is secured, to power down the a/c you do what?

A 
APU switch OFF
External power (if used) OFF
BAT switch OFF
43
Q

If both SOURCE OFF lights stay illuminated, what should you do?

A

Avoid icing conditions
Plan to land at nearest suitable airport
Fully charged battery will supply 30 min of power

44
Q

If a TR UNIT light illuminates, what are you restricted to?

A

Don’t use AFDS Approach Mode

Autoland is not available

United 737 (25 decks)

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