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Powerplant elextrical > Final > Flashcards

Final Flashcards

0
Q

What is the principle of operation that the generator exists upon?

A

The theory of electromagnetic induction.

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1
Q

What is a generator?

A

A device with converts mechanical energy into electrical energy through the principal of electromagnetic induction.

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2
Q

Explain the theory of electromagnetic induction.

A

As a conductor is passed through a flux field, an electrical potential is created in that conductor.

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3
Q

What is the polarity of the potential based on?

A

The left hand rule.

  • thumb direction of conductor motion
  • First finger flux direction
  • second finger direction of current flow
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4
Q

The amount of potential produced is based on what two things?

A

The strength of the flux field

The rate at which the flux are cut

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5
Q

What are the components of the generator?

A

Armature, field assembly, brush assembly, structural parts.

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6
Q

What is the purpose of the field assembly?

A

To provide the lines of flux for the conductor to cut.

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7
Q

Describe the contruction of the field assembly?

A

Soft iron cores wrapped with copper wire.

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8
Q

What is sometimes used to keep the neutral plane in the same position as the system load varies?

A

Inter poles

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9
Q

What is the purpose of the armature?

A

It acts as the conductor which cuts the lines of flux in which the voltage is induced to produce system current

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10
Q

Describe the construction of the armature.

A

Consists of windings of wire and laminated soft cores to hold the windings in place

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11
Q

What do DC systems use as a mechanical rectifier to turn the generator produced AC into DC?

A

A commutator.

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12
Q

What is the purpose of the brush assembly?

A

To transfer the system current from the commutator to the terminals of the generator housing

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13
Q

Description of brush assembly?

A

Carbon brushes held against the commutator with springs

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14
Q

What is the purpose of structural parts?

A

To support the field and armature

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15
Q

Describe the construction of the structural parts

A 
End frame
Field frame
Brush frame
Bearings 
Shock mounts 
Cooling devices
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16
Q

Why are generators self exciting?

A

Due to residual magnetism.

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17
Q

Where is the residual magnetism in a generator stored?

A

In the case.

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18
Q

What is the purpose of the residual magnetism?

A

To provide a weak flux field for the armature to cut to provide enough current to begin to energize the field assembly (this is known as initial excitation)

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19
Q

What are types of armature field connections?

A

Series wound
Shunt wound
Compound wound

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20
Q

What are types of generator circuits?

A

A type and B type

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21
Q

A type=

A

Volt reg located between the field assembly and ground

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22
Q

B type=

A

Volt reg is located between the armature and the field assembly

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23
Q

What is the type of generator circuit based on?

A

It is based on voltage regulator location

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24
Q

What are three basic controls required for a generator?

A

Voltage regulator
Current limiter
RCCR

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25
Q

What does the current limiter do?

A

It prevents the armature from producing more than it’s rated current

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26
Q

What does a voltage regulator do?

A

It maintains system voltage within it’s specified range

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27
Q

What does an RCCR do?

A

It provides some method of disconnecting the generator/armature from the battery/bus to prevent battery discharge through the armature.

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28
Q

What type of GCU do low output generators use?

A

Vibrator type

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29
Q

What does a typical GCU consist of?

A

Three sets of relays that are rapidly opening and closing

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30
Q

How do DC generators control voltage and current?

A

By controlling the amount of excitation current

31
Q

What must the GCU type match?

A

The circuit type, either A or B

32
Q

What is the purpose of two resistors in a type A circuit?

A

To keep the field from collapsing completely and to prevent the points from burning/arcing

33
Q

What is different about the control requirements of a high output DC system compared to a low output?

A

In a high output system the components are separate, located at different points in the aircraft.

34
Q

What form is a current limiter in for a high output DC system?

A

A slow blow fuse or circuit breaker

35
Q

What are the control requirements of a multiple engine system?

A

The same as basic systems with the addition of a parallelizing or equalizing control.

36
Q

What does a parallelizing or equalizing control consist of?

A

It consists of a differential coil that senses the output voltage of each generator

37
Q

Where does the G terminal of the GCU go to?

A

The A terminal of the generator.

38
Q

Where does the F terminal of the GCU go to?

A

The bus.

39
Q

When will generator servicing and inspection be performed?

A

100 hour or annual intervals

40
Q

What would be done when looking for

An open in the armature?

A

Use an ohmmeter between each segment of commutator. There should be continuity

41
Q

When looking for shorts to ground in an armature what must be done?

A

Between segments of commutator and shaft there should not be continuity

42
Q

How would one check for an integral short in an armature?

A

Use a growler tester, hacksaw should not vibrate.

43
Q

What should be done when looking for an open in the field assembly?

A

Check between the F terminal of the generator and the ground lead.
There should be continuity

44
Q

What should be done when looking for a short to ground in a field assembly?

A

Check between the f terminal and case, should not have continuity, unless generator has g terminal or of b type generator

45
Q

Alternator components?

A

Stator
Rotor
Rectifier
Structural parts

46
Q

What do the structural parts of the alternator consist of?

A

Main frame, end frame , bearings and cooling devices

47
Q

Where does the excitation current come from for an alternator?

A

Excitation current comes from the battery via the bus through the brushes and slip rings

48
Q

How does initial excitation for the alternator come about?

A

After it reaches the bus it goes to the rotor to produce the electro magnetic field

49
Q

How are the lines of flux in an alternator cut?

A

They are cut by the stator and that induces a three phase AC into the stator

50
Q

How is the AC in an alternator turned to DC?

A

Through the rectifier and sent to the bus as system voltage

51
Q

What kinds of output controls are used with an alternator?

A

A voltage regulator and a switch field relay

52
Q

What is a typical alternator circuit?

A

There are no typical alternator circuits

53
Q

When is servicing and inspection of an alternator done?

A

In 100 hour or annual inspections

54
Q

When are AC electrical systems used?

A

On large commercial aircraft

55
Q

What is the industry standard for AC electrical systems?

A

110 volt 400 hertz AC

56
Q

What are the advantages of an AC electrical system?

A

AC systems offer significant weight savings
Easier to generate in large quantities
Easier to change current & voltage without substantial power loss which makes it easier to be carried over large distances
AC is easily rectified to DC

57
Q

What are disadvantages AC electrical systems?

A

Not storable unless first rectified to DC

Frequency must be kept constant

58
Q

Why are brushless alternators used?

A

To prevent arcing ( they are a cross between generators and alternators)

59
Q

Describe the construction of a brushless alternator.

A

The main output winding is stationary and the exciter field is stationary, armature is rotating

60
Q

Three main parts of a brushless alternator?

A

Permanent magnet generator
Exciter generator
Main generator

61
Q

What is an IDG?

A

A CSD and generator all in one

62
Q

Why are generators or alternators driven by constant speed drives?

A

To maintain a constant frequency, it utilizes an engine driven variable displacement hydraulic pump and motor to turn the generator or alt at constant rpm to maintain constant frequency

63
Q

How is the maintenance to AC systems different from DC?

A

Higher voltage and complexity

64
Q

What is the purpose of a starter motor?

A

To concert electrical energy to mechanical energy to turn the engine until the ignition system is able to start the combustion process

65
Q

What principle of operation does the starter motor operate under?

A

Electromagnetic repulsion.

66
Q

What is electromagnetic repulsion?

A

The reactions of two magnetic fields, if a conductor carrying current is passed through a flux field, it will be impelled outward.

67
Q

Components of a starter motor?

A

Armature
Field assembly
Brush assembly
Structural parts

68
Q

What does the armature do?

A

It is the rotating conductor, it is being repelled by the field windings,
Producing motion.

69
Q

What is the purpose of the field assembly?

A

It is the electromagnetic field to repel and turn the armature

70
Q

What is the principal of operation for a starter generator?

A

Electromagnetic repulsion

71
Q

Where are starter generators used?

A

Only used on turbine/ turboprop engines

72
Q

In addition to the basic starter or generator components, what extra
Components will there be in a starter generator?

A

A starter winding and a generator winding

And possibly an under current controller

73
Q

What is the purpose of a under current generator?

A

To ensure positive action of the starter and keep it operating until the engine sustains combustion

74
Q

What does an ignition solenoid do?

A

Controls igniter circuit during start up process

75
Q

Basic operation of a starter generator?

A

Close battery and engine master switches
Close start switch, causing starter solenoid and ignition solenoid to close
Current begins flowing through motor
Under current solenoid closes and motor begins turning
As motor speed increases, current draw decreases, once below 200 amps the undercurrent solenoid opens, stopping current flow to the starter and ignition exciters
Once engine successfully starts, the sg begins to function as a normal generator

Powerplant elextrical (2 decks)

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