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AC machines > Handouts 1,2,3,5 > Flashcards

Handouts 1,2,3,5 Flashcards

1
Q

What happens to the speed of an AC universal motor as the load is decreased ?

A

Load goes down then the speed goes up

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2
Q

What is the primary difference between a start-type and run-type capacitor?

A
  • start electrolytic

- run oil filled

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3
Q

When creating a magnetic field, do the lines of flux flow from south to north across the air gap?

A

No, North to south

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4
Q

What is the rotational force produced by a motor called?

A

Torque

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5
Q

What type of AC machine coverts electrical input to mechanical output?

A

Motor

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6
Q

In an AC universal motor, are torque and speed directly or inversely proportional to each other?

A

Inversely

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7
Q

What approximately percentage of rated speed does a centrifugal switch open at?

A

75%

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8
Q

If the centrifugal switch fails to open as a capacitor-start induction-run motor accelerates to its rated speed, what could happen to the starting windings?

A

Overloads trip/ windings over heat

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9
Q

In reference to the left hand rule for conductors, what do the fingers and thumb represent?

A

Thumb- electron flow

Fingers- magnetic lines

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10
Q

In reference to the left hand rule for electromagnets, what do the fingers and thumb represent?

A

Thumb- north end

Fingers- electron flow

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11
Q

What is a measure of a materials ability to become magnetized called?

A

Permeability

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12
Q

What component of an AC machine supports the shaft and allows it to rotate freely?

A

Bearings

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13
Q

Does the stator of an AC machine produce a stationary magnetic field or an alternating magnetic field?

A

Alternating magnetic field

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14
Q

What are the terminal markings for start windings leads?

A

T5 and T8

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15
Q

In a capacitance start induction run split phase induction motor start field windings are wounded with ________ turns of __________ gauge wire relative to the run field windings

A

More, smaller

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16
Q

To reverse a 4 lead permanent slip capacitor motor, which wiring connections are interchanged?

A

T5 T8

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17
Q

List three types of power losses that occur in a split phase induction motor

A

Eddy currents
Hysteresis
Heat

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18
Q

Does the counter emf generated increase or decrease as the load is added to an ac series universal motor

A

CEMF goes up
LOAD goes up
(Increases) is the answer

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19
Q

What type of single phase AC motor has the highest starting torque characteristics?

A

Universal series motor

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20
Q

A rotating magnetic field is produced in an AC motor by “splitting” the phase through two separate field windings. What type of motor uses this principle?

A

Split phase induction motor

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21
Q

Why are pole pieces constructed of laminated sheets

A

To reduced eddy currents or to minimize losses

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22
Q

What are the brushes in an AC universal motor made of?

A

Carbon graphite

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23
Q

What is the minimum number of terminal leads require for connection of a dual voltage 115/230v resistance start induction run motor?

A

6 leads

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24
Q

In an AC universal motor when proper commutation is taking place, what colour is the commutator?

A

Dark chocolate

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25
Q

In a permanent magnet motor, where are magnetic flux lines most densely concentrated?

A

At the poles

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26
Q

What types of capacitor does a permanent split capacitor motor use?

A

Oil filled capacitor

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27
Q

What type of capacitor does a capacitor start induction run motor use?

A

Electrolytic

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28
Q

What are two factors that determine the amount of torque developed by a motor load?

A

Strength of magnetic field

Current

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29
Q

What is the portion of the stator pole piece is closest to the rotor assembly called?

A

Pole shoe

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30
Q

How is the capacitor in a capacitor start induction run split phase motor connected?

A

In series with the start windings

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31
Q

What solid state device can be used to disconnect the start windings in a resistance start induction run split phase motor

A

Thermistor

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32
Q

Does a current relay use normally open or normally closed contact is connected in series with the start windings?

A

Normally open

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33
Q

What type of motor has a short circuited time of heavy copper wire wounded around part of the stator pole?

A

Shaded pole induction motor

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34
Q

When an AC motor is first started, why is the inrush current so high?

A

Low CEMF

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35
Q

What are two advantages of a resistance start induction run motor

A

Good for frequent start condition

Constant fixed speed

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36
Q

What are two disadvantages of a resistance start induction run motor?

A

High starting surge current

Limited to 1/3 HP

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37
Q

What are two advantages of a capacitor start induction run motor?

A

Low in rush current on start up

High starting torque

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38
Q

What are two disadvantages of a capacitor start induction run motor

A

Can’t be started more than 8 times per hour

Prolonged current flow will damage capacitor

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39
Q

What are two advantages of a permanent split capacitor motor

A

Good starting torque

Good running torque

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40
Q

What are two disadvantages of a permanent split capacitor motor

A

Cap can over heat

Relies on cap

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41
Q

What are two advantages of a capacitor start capacitor run motor

A

Constant fixed speed

Good running torque

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42
Q

List five methods used in split phase motors to disconnect the start windings

A 
Centrifugal switch 
Hot wire windings 
Current relays 
Potential relays
Solid state starting relay
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43
Q

In a resistance start induction run split phase induction motor run field windings are winded with __________ turns of ___________ gauge wire relative to the start field windings

A

Less, larger

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44
Q

To reverse a 6 lead split phase induction motor which wiring connection are interchanged

A

T5 and T8

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45
Q

Is the starting torque characteristics of a capacitor start motor greater than or less than the starting torque characteristics of a resistance start motor

A

Greater

46
Q

Which type of disconnecting means for a split phase motor functions as both a starting relay and an overload relay

A

Hot wire relay

47
Q

Which split phase motor have their start windings disconnected after initial rotation is developed durn start up?

A

Resistance start induction run

Capacitor start induction run

48
Q

Which split phase motors have their start windings energized at all times

A

Permanent split capacitor

Capacitor start capacitor run

49
Q

What is the maximum phase displacement angle between the start and run windings of a capacitor start induction run split phase motor

A

90°

50
Q

What is the function of a centrifugal switch

A

Mounted inside a motor that serves as a disconnect the start windings

51
Q

What type of single phase motor would be best suited to be used for a residential refrigerator

A

Capacitor start induction run

52
Q

What is a thermistor

A

Device that exhibits a change of resistance with change of temperature

53
Q

Is the resistance of a start field windings higher or lower than the resistance of the run field windings in a capacitor start induction run split phase induction motor

A

Higher

54
Q

What are the minimum number of stator leads required for a single voltage, reversible split phase induction motor

A

4

55
Q

What are the minimum number of stator leads required for a dual voltage reversible split phase induction motor

A

6

56
Q

What are the minimum number of stator leads required for a single voltage non reversible split phase induction motor

A

2

57
Q

List three application of permanent split capacitor motors

A

Central air conditioners
Air handlers
Blowers

58
Q

List three applications of resistance start induction run motors

A

Washer machine
Dishwasher
Clothes dryer

59
Q

List three applications of capacitor start induction run motors

A

Fridges
Freezer
Wine cooler

60
Q

List two types of capacitors used in split phase induction motors

A

Oiled filled

Electrolytic capacitors

61
Q

When an AC motor is first started why is the in rush current so high?

A

The rotor current is only limited by the very low rotor circuit resistance

62
Q

What type of single phase motor does not use a squirrel cage rotor assembly

A

Universal series motor

63
Q

List two factors that determine the amount of torque developed by a motor

A

Strength of the main magnetic fields

Amount of current flow

64
Q

Why are pole pieces laminated

A

To minimizes the circulation of induced eddy currents within the core and hysteresis

65
Q

What type of single phase motor is typically not reversible

A

Shaded pole induction motor

66
Q

In an AC universal motor are torque and speed directly or inversely proportional to each other

A

RPM goes down
Torque goes up
So torque and speed are inversely

67
Q

If the number of poles in a shaded motor is double does the speed of the motor increase or decrease

A

Decreases

68
Q

What is the typical phase displacement angle in a shaded pole motor

A

10°

69
Q

What happens to the torque of an AC universal motor if the load is increased

A

If the load increases the torque will increase as well

70
Q

The amount of CEMF produced in a rotor assembly is proportional to what three factors

A

Amount of conductors
The magnetic field strength
The speed of rotation

71
Q

Is the shaded pole an induction motor

A

Yes

72
Q

Why are pole pieces constructed with silicon steel

A

To reduced hysteresis

73
Q

In universal motors, are the armature and field coils connected in series or parallel?

A

Series

74
Q

Which single phase motor is considered to be the most simple and least expensive?

A

Shaded pole induction motor

75
Q

What is the formula for synchronous speed

A

RPM=120xhz/# of poles

76
Q

What is the formula for rotor speed

A

RPM=120xhz/# of poles -%slip

77
Q

How should the direction of rotation of an AC universal motor be revered

A

Interchange armature leads A1 and A2

78
Q

Does a shaded pole induction motor rotate in the direction towards the shading coil potion of each pole piece or away from the shading coil portion of each pole
Piece

A

Towards

79
Q

Does the CEMF generated increase or decrease as load is added to an AC series universal motor

A

Load goes up
CEMF goes up
It increases

80
Q

List three applications of shaded pole motors

A

Small fans
Timers
Clocks

81
Q

List three applications of AC universal motor

A

Power tools
Sump pumps
Razors

82
Q

List three types of power losses that occur in AC machines

A

Mechanical
Electrical
Magnetic

83
Q

When creating a magnetic field, do the lines of flux flow from the north to the south across the air gap?

A

Yes

84
Q

What are the three factors that determine the strength of an electromagnet

A

Conductors
Current
Core

85
Q

Where are magnetic flux lines most densely concentrated

A

At the poles

86
Q

What is measure of a material ability to become magnetized called

A

Permeability

87
Q

What is resistance to magnetism called

A

Reluctance

88
Q

When an electromagnet reaches a point where strength increases only slightly with an increase in current, it is known as a point of ___________

A

Saturation

89
Q

What is the amount of magnetism left in a material after magnétisant force has stopped called

A

Residual magnetism

90
Q

In reference to the left hand rule for conductors, what do the fingers and thumbs represent

A

Thumb- current

Fingers- field

91
Q

In reference to the left hand rule for electromagnets what do the fingers and thumb represent

A

Thumb- north field

Finger- current

92
Q

Does an increase in current flow in a conductor result in an increase of magnetic field around the conductor

A

Yes

93
Q

What are two types of magnets

A

Permanent magnets

Electromagnets

94
Q

What is the rotational force produced by a motor called

A

Lorentz force

95
Q

When a conductor cuts through magnetic lines of flux a voltage is induced into the conductor. What is this principle called?

A

Electro magnetic induction

96
Q

In reference to the right hand rule motors what do the thumb, forefinger and middle finger represent

A

Thumb- thrust
Forefinger- field
Middle finger- current

97
Q

Does the stator of an AC motor produce a stationary magnetic field or a rotating magnetic field

A

Rotating magnetic field

98
Q

What is the purpose of a field winding in an AC machine

A

Create magnetic lines of flux

99
Q

Is a field winding in an AC motor considered an electrical load or an electrical source

A

Electrical load

100
Q

What are two types of bearings found in an AC machine

A

Sleeve and rolling

101
Q

Provide two reasons why the poles shoe of every pole piece is curved to conform to the surface of the rotor assembly

A

Wider and more even flux distribution

102
Q

What is the portion of the pole piece closest to the rotor called

A

Pole shoe

103
Q

What are the three components that comprise a rotor assembly

A

Shaft
Iron core
Rotor windings

104
Q

What components of an ac machine supports the shaft and allows it to rotate freely

A

Bearings

105
Q

List with electrical input requirements that are found on an AC machine name plate

A 
Manufacture name
Model number 
Serial number
Rated voltage 
Current (FLA)
kilowatts 
Horsepower
Speed
106
Q

How are eddy currents minimized in an AC machine

A

Thin coat of enamel within the core

107
Q

How are hysteresis minimized in an AC machine

A

Silicone steel alloys

108
Q

What components forms the axis for rotation of the rotor assembly in an AC machine

A

Shaft

109
Q

List 4 components of the magnetic circuit in an AC machine

A

Air gap
Pole shoes
Shaft
Frame

110
Q

List 4 components of the electric circuit in an AC machine

A

Brushes
Field windings
Lead
Series field windings

111
Q

List 4 mechanical components used in an AC machine

A

Frame
End plates
Bearings
Base

112
Q

What are the four types of enclosures for AC machines

A

Open type
Weather proof
Drip proof
Totally enclosed type

AC machines (1 decks)

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