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PEGS Homework > ELECTRICS > Flashcards

ELECTRICS Flashcards

1
Q

What is the primary electrical power system on the aircraft?

A

28VDC run by 2 DC generators on the engines and one on the APU

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2
Q

Where is DC power obtained from?

A

2 DC generators, APU gen, ground power, Main and AUX battery and 2 TRUs from the AC generators.

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3
Q

What is a TRU? What do they do? Where are they located? What does the left TRU supply?

A

Transformer Rectifier Unit, they transform and rectify 115VAC to 28VDC. They are located in the nose compartment. The left TRU runs the left secondary feeder bus.

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4
Q

Where do TRU’s get their power from?

A

From the L,R, 115 Variable AC bus.

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5
Q

What type of batteries are fitted? How many are there?

A

2, main and aux, lead acid type in the nose compartment (only lead acid on SM a/c)

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6
Q

What does the MAIN BAT supply? How is it charged?

A

The main battery supplies the essential busses and the right main feeder via the Batt switch. It also supplies the hot battery bus.

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7
Q

What does the AUX BAT supply? How is it charged?

A

The aux battery supplies the essential busses and battery bus, it is charged form the left main feeder bus. if switched on.

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8
Q

What do the DC generators feed? Do they have any other function?

A

The DC generators feed the L,R, main feeder busses. They also act as starter motors.

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9
Q

Where is the receptacle for external DC?

A

Lower left nose compartment.

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10
Q

What buses are directly fed by external DC power?

A

L,R main feeder busses

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11
Q

What is the function of the Battery Master switch?

A

The battery master connects the AUX and main battery to the Essential busses.

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12
Q

What do the other battery switches do?

A

The AUX battery allows the L main bus to charge it, The main battery switch connects the R main bus so that that the battery can charge or the battery supply the bus

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13
Q

What is a GCU and what is it responsible for?

A

Generator Control Unit. It monitors and controls generator output and will shut it down if a malfunction occurs.

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14
Q

What is the function of the BBPU?

A

Provides batteries and generators protection from a fault on one of the main feeder buses.

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15
Q

When external DC is selected ON; how is the aircrafts electrical system protected from a faulty external power unit?

A

A voltage protection relay run by the essential bus will disconnect external DC if a fault is detected >31.5V

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16
Q

What happens if there is a short circuit on a main bus?

A

The BBPU will try and isolate the bus by opening all ties. if it is a local issue it could just trip a circuit breaker.

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17
Q

How can we restore normal operation following activation of the BBPU?

A

We can press the bus fault reset switch.

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18
Q

Can the main bus tie be manually closed after the BBPU has reacted to a bus fault?

A

No

19
Q

What should the DC BUS VOLTS L.E.D display read during flight?

A

28V

20
Q

How is a battery discharge condition indicated to the crew?

A

The DC panel will show a flashing negative sign with a decimal fraction indicating % discharge of max discharge.

21
Q

What is the indication of battery over-temperature? Following an indication of battery over temperature is the affected battery automatically or manually isolated from the generating system?

A

The battery temperature monitor shows battery temperature, green to 50deg, yellow to 65deg, BATT HOT caution illuminates above 65. the battery must be manually disconnected.

22
Q

What buses in the DC system can be manually tied by the crew?

A

The left and right main feeder busses.

23
Q

Are the batteries charged on surveillance Australia aircraft when external DC power is applied and selected on?

A

No however some have a modification which allows it, battery switch must of course be on.

24
Q

What drives the DC generators?

A

the L,R engine accessory drives.

25
Q

What are the sources of AC power?

A

The two AC generators on the propeller gearboxes. 3 inverters which run off the essential busses. also external AC.

26
Q

What do the inverters supply?

A

Through the paralleling control box they supply, 115VAC constant frequency, stepped down to 26VAC

27
Q

What are the power sources for each inverter? What does the AUX inverter switch on the AC CONTROL allow?

A

Primary runs off the left essential bus.
Secondary runs off the right essential bus.
Auxiliary runs off the left main bus.
The aux switch allows the left or right main bus to be powered.

28
Q

What type of electrical power is used to power anti-icing systems? Is this power available to anything else?

A

115VAC variable, it is also used for the standby hydraulic pumps and standby fuel pumps and the TRUs

29
Q

What drives the AC generators?

A

L,R propeller gearboxes

30
Q

Is DC power required prior to connecting AC external power to the aircraft?

A

Yes, the battery switches must be on.

31
Q

If a DC GEN is off-line, what is the effect on the electrical system?

A

The main bus tie will close enabling the remaining generator to power both sides.

32
Q

If a DC GEN and a TRU both fail, what is the effect on the electrical system?

A

The main busses will tie and the secondary busses will tie, allowing full power to all services.

33
Q

If both DC generators fail, what is the effect on the electrical system?

A

The TRUs will supply the secondary feeder busses which in turn will power the main feeder busses. After completing the checklist the batteries will be isolated from the main busses to avoid draining.

34
Q

If the Number 1 GCU isolates the Number 1 AC generator will the left AC bus be powered?

A

Yes the generators can supply either bus by switching in the GCU, if the GCU fails then that side AC is lost.

35
Q

Will fixed frequency AC power be available following a double inverter failure?

A

Yes as there will be one left, however may not be powerful enough to power the entire system.

36
Q

What do the inverters power?

A

Navigation instruments, communication equipment, flight instruments and certain system indicators.

37
Q

Where do the inverters get their power from?

A

Left and right from the left and right essential busses, the aux from the left main DC

38
Q

What is the function of the battery master switch?

A

to connect the batteries to the essential busses and therefore power the inverters which power the instruments etc.

39
Q

If the main bus is tied with the switch, will a bus fault still cause it to be isolated?

A

Yes, the BBPU can override the bus tie switch.

40
Q

Can a DC generator still function if selected off?

A

only as a starter unit.

41
Q

What is the GCU responsible for?

A

Monitoring output from the starter/generators, controls the start cycle, voltage and current regulation, paralleling and generator shutdown if an abnormal condition detected.

42
Q

What is the purpose of the BBPU?

A

Protect the starters/generators and batteries from overload from a bus fault.

43
Q

During flight what should the R MAIN and R SEC voltage display?

A

28V

PEGS Homework (18 decks)

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