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Level 2: DC Machines > Final Review > Flashcards

Final Review Flashcards

1
Q

What is the prime function of all DC motors?

A

To maintain starting current within safe limits

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2
Q

What type of protection does a three-point starter provide?

A

It provides low voltage protection

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3
Q

What type of compounding is used when constant voltage or speed is required?

A

Flat compounding

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4
Q

What type of manual starter provides a great ability to control speed

A

A four-point starter

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5
Q

What components ride against the commutator segments and connect the armature to the external circuit of a DC generator?

A

The carbon graphite brushes

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6
Q

What is the purpose of a field winding in a DC machine?

A

To create the main magnetic field

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7
Q

Once the DC motor is started and all the resistance is removed, what limits the current through the armature?

A

Counter EMF

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8
Q

What does a successful starting up a self-excited DC machine depend on?

A

Residual magnetism

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9
Q

How should the direction of rotation of a DC motor be reversed?

A

By changing the armature leads A1 and A2

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10
Q

What protective device connected in series with a shunt field do most large compound motors have?

A

A field loss relay

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11
Q

What is an advantage of a separately excited DC machine?

A

Constant field strength

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12
Q

If resistance is removed from the shunt field winding circuit, what will happen to the magnetic field?

A

It increases strength

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13
Q

If resistance is added to the shunt field winding circuit of a DC shunt motor, what will happened to the motor speed?

A

Less field strength equals less CEMF
More current through the armature equals more speed

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14
Q

What type of wound armature have their windings connected in parallel?

A

Lap wound

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15
Q

What is the distortion or bending of the main magnetic field of a DC machine caused by its interaction with a magnetic flux developed by the armature current called?

A

Armature reaction

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16
Q

What type of compounding occurs when a cumulative long-shunt compound motors full loaded speed is greater than no load speed?

A

Over compounding

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17
Q

What type of compounding occurs when differential short shunt compound generators full load voltage is less than it’s no load voltage?

A

Under compounding or differentially compounded

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18
Q

What is the function of the series field rheostat?

A

To divert current around the series field, thus controlling compounding

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19
Q

What is the commutator of a DC machine constructed of?

A

Each of the segments of the commentator are insulated from one another with a heat proof insulating material known as Mica

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20
Q

What is the position at which the armature windings are parallel to the lines of flux and there is no induced voltage called?

A

The neutral plane

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21
Q

What happens to the counter EMF generator as load is added to a series motor?

A

Speed decreases which causes counter EMF to decrease

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22
Q

What is the main disadvantage of a manual 3-point starter?

A

It has no speed control

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23
Q

What is the best way to slow or stop a DC motor under normal operation?

A

Dynamic braking

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24
Q

Will increasing the number of turns of wire in an armature coil of a DC generator cause an induced EMF to increase or decrease?

A

Increase

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25
Q

What is the function of the shunt field rheostat on a DC shunt motor?

A

To control the current through the shunt field

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26
Q

Are resistance and voltage directly or inversely proportional in a DC shunt generator?

A

Inversely

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27
Q

What two components are used to hold the brushes in place and maintain an even pressure?

A

Brush holders and springs

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28
Q

What component of a DC machine supports their shaft and allows it to rotate freely?

A

The bearings

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29
Q

What are the three factors that determine the strength of electromagnetic?

A

1: Turns
2: Core Strength
3: Current

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30
Q

What is the component of a DC generator that converts AC to DC called?

A

The commutator

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31
Q

What is the force that causes a motor to rotate known as?

A

Lorentz Force

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32
Q

What type of compound motor has its fields winding wound in such a matter that they aid each other in the production of magnetism?

A

Cumulative compound

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33
Q

Will increasing the number of turns of wire in an armature coil of a DC motor cause the CEMF to increase?

A

Increase

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34
Q

Name two industrial processes in which differential compound generator may be used?

A

Welding and electroplating

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35
Q

When starting a DC motor, what percentage of FLA shall the starting current be limited to?

A

150%

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36
Q

What type of DC motor is used when constant or adjustable speed is extremely important?

A

Separately excited shunt

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37
Q

In reference to the left hand rule for generators, what do the thumb forefinger and middle finger represent?

A

Thumb: Thrust
Forefinger: Main magnetic field
Middle finger: current through the armature

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38
Q

What are the windings embedded in slots or holes in the main pole face called?

A

Compensating windings

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39
Q

What are two types of magnets?

A

Electromagnets and permanent magnets

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40
Q

When a generator supplies current to a load, what is produced, which makes the armature assembly harder to turn?

A

Counter torque

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41
Q

What causes the shift of the neutral plane on a DC motor under load?

A

Current through the armature causing it to react with the main field

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42
Q

When a DC motor is first started, why is the armature current so high?

A

Not involving low armature resistance before counter EMF develops

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43
Q

Where are magnetic flux lines most densely concentrated?

A

At the pole face or shoe

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44
Q

What is the insulation separating the copper segments of the commentator constructed of?

A

Mica

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45
Q

What are the four components that comprise an armature assembly?

A

1: Shaft
2: Commutator
3: Armature Windings
4: Iron Core

46
Q

When electromagnetic reaches to a point where strength increases only slightly when an increase in current, it is known as a point of?

A

Saturation

47
Q

What are the three factors that determine the output of a generator?

A

1: Speed of the armature
2: strength of the main magnetic field
3: turns and configuration of the armature windings

48
Q

What are the three ways that armature reaction can be corrected?

A

1: Interpoles
2: Compensating windings
3: rotate the brushes to the neutral plane

49
Q

When proper communication is taking place, what color is a commutator?

A

Dark chocolate

50
Q

What happens to the torque of DC series motor as the load is increased?

A

It increases

51
Q

If resistance is added to the shunt field winding circuit of a DC generator, what will happen to the output voltage?

A

It decreases

52
Q

Is the resistance of a shunt field winding higher or lower than the resistance of the serious field winding?

53
Q

What are the windings wound around the interpoles called?

A

Commutating windings

54
Q

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

A

Residual magnetism

55
Q

What type of DC machine converts mechanical input into electrical output?

56
Q

What is the rotating assembly of a DC machine called?

A

Armature assembly

57
Q

What are the six components that comprise most DC machines?

A

1: enclosure
2: bearings
3: pole pieces
4: armature assembly
5: field windings
6: brushes
7: terminals

58
Q

What are the three basic types of armature? Windings?

A

1: lap wound
2: wave wound
3: frog leg wound

59
Q

In a series field winding in a DC machine considered a load or a source?

60
Q

What are two types of bearings found in a DC machines?

A

Sleeve and ball

61
Q

What is a DC generator that uses permanent magnetics as its field known as?

62
Q

What are the three types of field windings used in DC machines?

A

1: series
2: shunt
3: compound

63
Q

What is the mechanical force used to turn a generator called?

A

Prime mover

64
Q

Field windings are wound on to magnetic poles to form?

A

Electromagnets

65
Q

What is the proportion of the pole piece closest to the armature called?

66
Q

How can the ripple effect be smooth in the output of a DC generator?

A

More winding average output voltage is higher, less pulsation or slots

67
Q

What are the three types of DC machine field structures?

A

1: Permanent magnetic
2: separately excited
3: self-excited

68
Q

What type of armature winding provides modern voltage and modern current?

A

Frog leg wounds

69
Q

What type of wound armature have their windings connected in parallel?

70
Q

What type of armature windings provide high voltage and low current?

A

Wave wound

71
Q

Is the voltage induced into the armature windings of a DC generator AC or DC?

72
Q

How is the winding of an interpol connected in relation to the armature?

A

Commutating winding is connected in series

73
Q

Is a polarity of each interpol in a DC generator the same polarity or opposite in polarity of the main pole ahead of each interpole in the direction of rotation?

A

Same polarity

74
Q

What are the two main factors that affect the amount of torque developed in a DC motor?

A

Main magnetic field and armature magnetic flux

75
Q

Do series motors have an extremely low or extremely high starting torque?

A

Extremely high

76
Q

What happens to the torque of a DC series motor as a load is increased?

A

Torque increases

77
Q

What happens to the speed of a DC series motor as a load is increased?

A

Speed decreases

78
Q

Is a shunt generator considered a constant voltage generator?

A

Yes, because of its excellent voltage regulation characteristics

79
Q

What type of compound motor has its field windings wound in such a matter that they oppose each other in the production of magnetism?

A

Differential compound

80
Q

What type of DC machine converts electrical input to mechanical output?

81
Q

What type of wound armature have their windings connected in series?

A

Wave wound

82
Q

What type of armature winding provides low voltage and high current?

83
Q

Does the armature winding carry the same current as the shunt field windings?

84
Q

In a serious motor are torque and speed directly or inversely proportional to each other?

85
Q

What is an advantage of a separately excited DC machine?

A

Better control of output voltage generator and speed control motor

86
Q

What type of compound generator has its shunt field winding connected in parallel with both the armature and series field windings?

A

Long shunt

87
Q

Is the armature reaction proportional to the armature current?

88
Q

With a constant load, can armature reaction be corrected by shifting the brushes and therefore adjusting the neutral plane setting?

89
Q

What are the four types of enclosures for DC machines?

A

1: Open type
2: weatherproof
3: drip proof
4: totally enclosed type

90
Q

Is the commentator an electric or a mechanical switch?

A

Mechanical

91
Q

What type of DC motor is used when constant or adjustable speed is extremely important?

A

Shunt motor

92
Q

three factors for Right hand rule for motors

A

Thumb: is the direction of force
Forefinger: magnetic field by the field windings
Middle finger: current in armature conductor

93
Q

How is compounding controlled in a compound DC motor or generator?

A

By changing the strength of the series field via the series field diverter

94
Q

What type of compounding is used when constant voltage or speed is required?

A

Flat compound

95
Q

How is the output voltage of a DC shunt generator controlled?

A

A voltage regular changes the current to the shunt field

96
Q

What happens to the speed of a DC series motor as a load is increased?

A

Decreases speed

97
Q

What happens to the Counter EMF generated as load is added to a series motor?

A

Decrease counter EMF

98
Q

What is a function of the shunt field? Rheostat

A

To control current through the shunt field

99
Q

What is the function of the series field rheostat?

A

To divert current around the series field

100
Q

What type of armature winding provides high voltage and low current?

A

Wave wound

101
Q

What type of generator is considered a constant voltage generator?

A

Separately excited Shunt

102
Q

Are resistance of the shunt field rheostat and voltage output directly or inversely proportional and a DC shunt generator?

103
Q

Are resistance of the shunt field rheostat and speed directly or inversely proportional in a DC shunt motor?

104
Q

If resistance is added to the shunt field winding circuit of a DC shunt generator, what will happen to the output voltage?

A

It will decrease

105
Q

What are the two main factors that affect the amount of torque produced in a DC motor?

A

Maine field strength and armature field strength

106
Q

How is compounding controlled in a compound? DC motor or generator?

A

By changing the relationship of series and shunt fields through the series field diverter

107
Q

What are the three most common methods of automatically starting a DC motor?

A

1: counter EMF starter
2: current limit starter
3: time delay starter

108
Q

What type of wound armatures have their windings connected in series parallel?

A

Frog leg wound

109
Q

What is the main disadvantage of a manual 4 point starter?

A

It does not provide protection against field loss

110
Q

If resistance is removed to the shunt field winding circuit of a DC motor, what will happen to the motor speed?

A

It slows down

Level 2: DC Machines (1 decks)

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