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ATV Electives > Motors And Generators > Flashcards

Motors And Generators Flashcards

1
Q

1.1 Outline the properties of permanent magnets

A

• Magnet that does not lose its magnetic force

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2
Q

Detail the handling precautions for permanent magnets

A

- don’t drop it
- No sharp blows
- Don’t influence with other magnets
- must be fitted with a keeper

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3
Q

2.1 Identify the factors that influence the magnitude of induced EMF in a DC generator

A

The strength of the induced voltage is dependant on the speed of the conductor and the strength of the magnetic field

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4
Q

2.2 Name the components of a dc generator

A

• Carcass, frame or yoke
• Field Coils
• Field pole
• Armature
• Commutators

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5
Q

2.3 Describe the operation of the components of a DC generator

A

• Carcass, frame or yoke is used to:
◦ Complete the magnetic circuit between the poles
◦ Mechanically support the other parts of the generator
• Field coils
◦ Produce the magnetic field by allowing current to flow through the coils
• Armature
◦ Cuts through the magnetic field
◦ Produces the electric current
• Commutators
◦ Converts the AC current into DC current
◦ Different sections of the commutator come into contact with the brushes and will alternate between each other

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6
Q

2.4 Identify the neutral plane of a DC generator

A

The point where the current in the armature produced is equal to zero

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7
Q

2.5 Explain armature reaction in DC generators

A

• The current flowing through the armature creates a seperate magnetic field which affects the magnetic flux of the generators poles, bending and disturbing them
• This distortion increases with an increase in load
• Geometric neutral plane is the position where the plan of two opposite armature coils is perpendicular to the undistorted magnetic field

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8
Q

2.6 Describe the methods of overcoming armature reaction in DC generators

A

• Brush positioning
◦ Moving the brushes so they align with the new disturbed field
• Compensating windings
• Interpoles

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9
Q

3.1 Determine the direction of resultant conductor movement through a magnetic field from an applied current

A

• Conductors will move in a way that they combine or subtract from each other, almost in a super positioning sense, when multiple coils are used in the armature
• Magnetic fields occur around the conductor, with areas of strong force and weak force
◦ This difference creates torque which spins a motor, converting electrical force into mechanical force

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10
Q

3.2 Explain the right hand rule

A

• Motion goes up with thumb
• Magnetic flux goes out with index finger
• Current points left from middle finger

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11
Q

3.3 Identify the construction features of DC motor components

A

• Armature assembly
◦ Laminated to reduce eddy currents
◦ Contains the commutator as well
• Field assembly
• Field poles and field coils
• Brushes
• End bells and bearings

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12
Q

3.5 Describe the construction features of common DC motor designs

A

• Series DC Motor
◦ High starting torque
◦ High starting current
• Shunt DC Motor
◦ Resistance is very high
◦ Current is constant through the field
◦ Suitable for when constant speed is required and high starting torque is not required
• Compound DC Motor
◦ Combination of the two previous motors

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13
Q

3.6 Identify typical aircraft applications for common DC motor designs

A

• Series motors are used in aircraft as engine starters, land gears, cowl flaps and wing flaps
• Shunt motors are ideal when constant speed is desired and when high starting torque isn’t
• Compound required when both characteristics are required

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14
Q

3.7 Explain the advantage of using DC starter-generators in aircraft

A

• Saves weight by eliminating a seperate starter that is only used during the start

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15
Q

3.8 Explain the effect of counter-EMF in DC motors

A

• Counter EMF opposes the current and the rotation of the armature
• The polarity of counter EMF is opposite the torque of the armature
• A build up of eddy currents that oppose the armatures magnetic field

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16
Q

3.9 Describe methods of speed control in DC motors

A

• Varying the current in the field windings
◦ A motor in which speed can be controlled is called a variable speed motor

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17
Q

3.10 Detail common DC motor maintenance checks

A

• Operation of motor
• Wiring, connection and terminations etc
• Clean and mounting bolts tight
• Check brushes for minimum length and spring tension
• Inspect commutator

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18
Q

4.1 State the common aircraft alternator design configurations

A

Rotating armature
Rotating field

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19
Q

4.2 Describe the operation of the components of an aircraft alternator

A

Slip rings
Brush block
Stator
Rotor

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20
Q

4.3 Identify physical characteristics of three phase aircraft alternators

A

Has three single phase windings spaced with 120 degrees between

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21
Q

4.4 List the common output connection methods for three phase aircraft alternators

A

Star/Wye
Delta

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22
Q

4.5 Describe line and phase voltage relationships of three phase aircraft alternators

A

Star connections have an increase in voltage
Delta connections have an increase in current

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23
Q

4.6 Describe the output phase sequence of three phase aircraft alternators

A

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24
Q

4.7 Identify the advantages of brushless aircraft alternators

A

More efficient and produces less wear as brushes, commutators are not required
Won’t arc at high altitudes with no brushes

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25
Q

4.8 Describe the operation of a brushless aircraft alternator

A

Uses multiple generators in the one alternator to induce and amplify a current

26
Q

4.9 Explain aircraft alternator output frequency production

A

27
Q

4.10 Detail common aircraft alternator maintenance checks

A

Secure attachment
Terminal board covers fitted and secured
Alternator clean from oil and grease
Electrical connections to the alternator are tight and correct phase sequence has been maintained

28
Q

4.11 Explain the operation of an aircraft generator control unit

A

Regulates, senses and protect the AC generation system

Can regulate the generator output

29
Q

4.12 Identify the purpose of constant speed drive units in aircraft

A

30
Q

What are the two types of AC motors

A

Induction and synchronous

31
Q

The three types of AC generators may be:
(hint: phase)

A

Single, two, three phase

32
Q

What is three phase induction used for

A

Where large amounts of power are required

33
Q

What is the purpose of single phase AC induction motors

A

Much smaller devices that require less power output

34
Q

What is the characteristic and purpose of three phase synchronous AC motors

A

Operate at constant speed and are used for flux grate compasses and propeller synchroniser systems

35
Q

What are the two sections of an inductive AC motor

A

Rotor and Stator

36
Q

What is the plane of commutation

A

The resulting neutral plane that occurs after armature reaction

37
Q

How do you reduce eddy currents

A

Laminate shit

38
Q

What is the geometric neutral plane

A

position where the plane of the two opposite armature coils is perpendicular to the undistorted magnetic field in the generator.

39
Q

What are generators rated with

A

Amps

40
Q

What is the speed of frequency in AC motors called

A

Synchronous speed

41
Q

What is a capacitive start motor

A

Uses two windings and a parallel circuit to create a split phase. A centrifugal switch will activate once split has been produced

42
Q

What is the purpose of a reverse current relay

A

To prevent current leaving from a battery and feeding the generator

43
Q

6.1 Identify typical aircraft applications for linear actuators

A

Trim systems, auxiliary door activation

44
Q

6.2 Describe the design features of electrical linear and rotary actuators

A

45
Q

6.3 Describe the construction features of electrical linear and rotary actuators

A

DC motor
Reduction Gear Train (Rotary gear box for rotary)
Ball in screw mechanism
Limit switches

46
Q

6.4 Identify typical aircraft applications for electrical rotary actuators

A

Used to control fuel flow, oil flow, pneumatic systems and environmental control systems

47
Q

What are three methods for starting a single phase induction motor

A

Split phase
Capacitor start
Shaded pole

48
Q

Which electricity type can be operated by an AC series motor

A

AC AND DC

49
Q

If you see a block diagram that looks dumb what is it

A

Regulated sine wave static inverter

50
Q

Describe phase rotation

A

Swapping the phase of a an AC motor to change the direction of rotation

51
Q

Induction AC Motor use a “” field in the stator

A

Rotating field

52
Q

How does an induction motor spin

A

The stator induces a current into the rotor with a magnetic field, creating a magnetic field in the rotor, which creates relative motion in the motor.

53
Q

How does a synchronous motor function

A

By applying DC current to a rotor winding, locking it into place with the multiphase rotating AC power source in the stator

54
Q

What is slip in an AC motor

A

Difference in speed of rotation between the magnetic field of the stator and the rotor

55
Q

What is the major advantage of a rotating field AC generator

A

Doesn’t require slip rings, which requires less maintenance

56
Q

How should the direction of rotation be changed in an AC motor

A

By reversing two of the leads to the motor

57
Q

What is the purpose of a constant speed drive

A

Regulates the frequency of AC power

58
Q

What is the advantage of a series DC motor

A

Can draw large amounts of torque on starting due to low resistance

59
Q

Memorise this

A

60
Q

Describe the construction of a split field series motor

A

Uses two field windings wound in opposite directions on the same pole.

ATV Electives (2 decks)

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