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Electrician 3rd Year > Motors > Flashcards

Motors Flashcards

1
Q

Sync Speed of 2 pole motor?

A

3600RPM

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2
Q

Sync Speed of 4 pole motor?

A

1800

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3
Q

Sync Speed of 6 pole motor?

A

1200

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4
Q

Sync Speed of 8 pole motor?

A

900

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5
Q

Formula for sync speed?

A

Frequency x 120/ number of poles

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6
Q

A four pole motor is operating at 1655, what is the slip speed?

A

145

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7
Q

What are the six rotor parameters affected by slip?

A

Induced voltage, impedance of rotor, frequency of motor, current of rotor, reactance of rotor

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8
Q

What is rotor parameter is constant?

A

resistance

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9
Q

When is rotor voltage at a maximum?

A

When the rotor is stalled (blocked rotor)

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10
Q

What is the rotor frequency of a stalled motor?

A

60 hz

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11
Q

A rotor is found to have a pf of .7. A few moments later, the same rotor has a pf of .92. What does this mean?

A

The rotor has sped up

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12
Q

As load is added to a rotor, what will happen to the torque produced?

A

Increase

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13
Q

What is breakdown torque?

A

the max torque that a motor can produce. Any more and it would stall

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14
Q

What percent of sync speed to NEMA A and B motors produce breakdown torque?

A

70-80%

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15
Q

At what power factor does a rotor produce breakdown torque?

A

.707

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16
Q

What can be said about resistance and reactance at breakdown torque

A

they are equal

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17
Q

What is the inrush current in a typical NEMA A motor?

A

600% of full load current

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18
Q

A NEMA B rotor has ___ inductance than a NEMA A rotor

A

more

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19
Q

What type of NEMA motor is considered a double squirrel cage?

A

C

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20
Q

What rotor design has highest starting torque?

A

D

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21
Q

What rotor design has the highest full load speed?

A

A

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22
Q

What rotor design in the most efficient?

A

A

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23
Q

Which rotor design in the most common?

A

B

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24
Q

Which rotor design produces 275% of breakdown torque?

A

D

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25
Q

As a WRM is accelerated, the resistance of the rotor ___

A

decreases

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26
Q

What are two disadvantages of a wound rotor motor?

A

Expensive and hard to maintain

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27
Q

Can rotor speed ever be the same as sync speed?

A

No

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28
Q

Why can’t rotor speed be the same as sync speed?

A

Because then the magnetic fields would be in sync and no lines of force would be cut, therefore, no voltage would be induced

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29
Q

The speed difference between sync speed and rotor speed is known as ___

A

slip

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30
Q

The slip speed ___ as load is added

A

increases

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31
Q

A motor with low percent speed regulation is more efficient than one with high speed regulation. True or False?

A

True

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32
Q

What are three quantities that are DIRECTLY proportional to slip?

A

Induced voltage, frequency, and reactance

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33
Q

As a squirrel-cage motor accelerates from standstill to normal running speed, active rotor current:

A

increase then decreases

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34
Q

In North America, a motor running at 90% of sync speed has a rotor frequency of ____

A

6 hz

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35
Q

Mechanical power is the product of what two mechanical quantities?

A

Speed and torque

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36
Q

Is windage a mechanical or an electrical loss?

A

mechanical

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37
Q

What is the formula for output power of a motor?

A

Torque times speed divided by 9.55

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38
Q

Which rotor design produces the highest starting current?

A

A

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39
Q

Which motor has the highest breakdown torque?

A

A

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40
Q

Which design of motor has the lowest slip speed?

A

A

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41
Q

Which rotor design in the most common?

A

B

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42
Q

What is the starting torque of a type A motor?

A

150%

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43
Q

What is the breakdown torque of a type A motor?

A

200%

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44
Q

What is the starting current of a type A motor?

A

600%

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45
Q

Even though a type A motor is the most efficient, it isn’t the most common. Why?

A

Very high inrush current

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46
Q

How do we lower the inrush current in a type B motor compared to a Type A?

A

The rotor bars are embedded closer to the core, leading to a higher reactance (therefore, higher impedance and lower current)

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47
Q

What is the starting torque of a type B motor?

A

150%

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48
Q

What is the starting current of a type B motor?

A

500%

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49
Q

What is the breakdown torque of a type B motor?

A

200%

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50
Q

What is the starting current of a Type C motor?

A

500%

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51
Q

What is the starting torque of a Type C motor?

A

225%

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52
Q

When does a type C motor produce max torque?

A

at the moment of start

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53
Q

What is the starting current of a type D motor?

A

400%

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54
Q

What is the starting torque of a type D motor?

A

275%

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55
Q

When does a type D motor produce max torque?

A

at the instant of start

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56
Q

Which type of motor is the least efficient?

A

Type D

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57
Q

When is the speed control of a WRM most suitable?

A

from 0 RPM to Full load speed

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58
Q

Which motor is the best?

A

WRM

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59
Q

Why isn’t a WRM very common?

A

High cost and hard to maintain

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60
Q

The starting torque of a WRM can be adjusted by _____

A

by adjusting the resistance

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61
Q

How do we lower inrush current in a WRM?

A

connecting the resistors from the control circuit

62
Q

What is speed regulation?

A

Percentage change from no load to full load

63
Q

What is the formula for speed regulation?

A

no load - full load divided by full load x 100

64
Q

What is the formula for rotor voltage?

A

Ebr x slip

65
Q

What is the formula for rotor frequency?

A

Fbr x slip

66
Q

What is the formula for rotor current?

A

Ibr x slip

67
Q

What is the formula for active rotor current

A

Ir x pf

68
Q

What is the formula for rotor reactance?

A

Xbr x slip

69
Q

What is the formula for rotor impedance?

A

Pythagorean theorum

70
Q

What is the formula for rotor power factor?

A

R/Z

71
Q

When does breakdown torque occur in both words and as a number?

A

When reactance = resistance. .707 power factor

72
Q

Are type A and B rotors suitable for high inertia loads?

A

Fuck no

73
Q

Describe a type C motor

A

Double squirrel cage. The outer bars are small to cause higher resistance. The inner bars are large to cause high resistance

74
Q

What is the disadvantage of a type C motor?

A

doesn’t dissipate heat very well

75
Q

An ohmmeter indicates three groups of three. What kind of motor is this?

A

Delta

76
Q

An ohmmeter indicates one group of three. What kind of motor is this?

A

Wye

77
Q

An ohmmeter indicates three groups of two. What kind of motor is this?

A

Wye

78
Q

What is the first step in a lead ID for a delta motor?

A

Find three groups of three

79
Q

What is the second step in a lead ID for a delta motor?

A

Find centre of each group

80
Q

What is the third step in a lead Id for a delta motor?

A

Label T1 permanently

81
Q

What is the fourth step in a lead ID for a delta motor?

A

Flux shower

82
Q

What is the first step in a lead ID for a wye motor?

A

Find one group of three and three groups of two

83
Q

What is the second step in a lead ID for a wye motor?

A

Label centre points

84
Q

What is the third step in a lead ID for a wye motor?

A

Connect 15 volts across centre points to find our proper leads

85
Q

What is the fourth step in a lead ID for a wye motor?

A

Find polarities. Jumper our leads and then apply 15V across circuit. Measure from the centre to the end and if we get an additive polarity, it is correct. If we don’t, flip the leads.

86
Q

What is phase A on a IEC motor?

A

U

87
Q

What is phase B on an IEC motor?

A

V

88
Q

What is phase C on an IEC motor?

A

W

89
Q

What does TENV stand for?

A

totally enclosed non ventilated

90
Q

What is windage?

A

Energy lost due to air movement produced by motor

91
Q

Where do friction losses occur?

A

in the bearings

92
Q

What does a prony brake do?

A

Measures counter torque (and torque)

93
Q

What is a real life example of a prony brake?

A

The dial on a stationary bike

94
Q

How do we adjust the countertorque of a prony brake?

A

tighten or loosen the screw

95
Q

What are the three main parts of a motor?

A

frame, stator, rotor

96
Q

Torque is the product of what two quantities?

A

Force and radius

97
Q

What are two kinds of stator windings?

A

lap and concentric

98
Q

What are the main parts of a stator?

A

laminated slots, conductors, conductor insolation, protective sheets

99
Q

What are the main parts of a frame?

A

frame, end bells, bearings, junction box

100
Q

Are lap windings the same size or different?

A

same

101
Q

are concentric windings the same size or different?d

A

different

102
Q

Do lap or concentric windings have varying pitch?

A

concentric

103
Q

Slip speed is between ____ and _____ percent

A

2 and 5

104
Q

What are the two major components of a stator?

A

core and windings

105
Q

What is magnemotive force?

A

movement of charge caused by a magnetic flux

106
Q

When current is zero, flux is ___

A

zero

107
Q

Torque is called ____ force

A

Lorentz

108
Q

What finger points towards Lorentz force

A

Thumb (torque)

109
Q

Where is the fan likely located on a motor?

A

On the front

110
Q

If a conductor is forced down through a magnetic field, where is the most force on it?

A

on the bottom

111
Q

Current always flows from ___ to ____ outside a magnet

A

North to South

112
Q

Current always flows from ___ to ____ inside a magnet

A

South to North

113
Q

What is duty?

A

amount of time that a motor can run without a cooling period

114
Q

The drive end is called the ___ on a NEMA motor

A

back

115
Q

What are the four main classes of insulation?

A

A, B, C, D

116
Q

Which insulation class can be used for the hottest temperatures?

A

H

117
Q

What values are found on the nameplate?

A

The full load values

118
Q

Large motors are ALWAYS connected in ___

A

delta

119
Q

When is the speed control most practical for a WRM?

A

from half load to full load

120
Q

Should you hook up 208 volts to a 230 volt motor?

A

No

121
Q

As we add resistance to a WRM, speed ____

A

decreases

122
Q

When we hook up less than rated voltage to a motor, current _____

A

increase

123
Q

What does a motor do?

A

converts electrical power into mechanical power

124
Q

How does a motor work?

A

mutual induction

125
Q

What is the advantage of windings in slots of windings on poles?

A

more flexible manufacturing

126
Q

What does the frame do?

A

It holds the stator and its end brackets with their bearings

127
Q

What does the stator do?

A

It holds the stationary iron with its slots into which windings are inserted

128
Q

What do we have to make sure of when we replace a motor in an existing installation?

A

the same frame

129
Q

For NEMA motors, is the shaft on the front or the back?

A

back

130
Q

Looking down at a motor with the shaft pointing away from you, which side is the junction box on?

A

the right side

131
Q

The front end of a motor is referred to as what in IEC?

A

drive end

132
Q

1 hp = ____ W

A

746

133
Q

Is a motor where the name plate voltage is 230/460 suitable for connection to a 208 volt system?

A

fuck no

134
Q

What is the voltage variations?

A

10%

135
Q

What is the standard ambient temperature for motors?

A

40 degrees celsius

136
Q

What conditions have to be met for us to be able to multiply the power by the service factor?

A

Ambient temp of 40 or less, line voltages balanced, proper voltage and frequency applied

137
Q

Can we apply the service factor under non ideal conditions?

A

No

138
Q

Many three phase motors are dual voltage, true or false?

A

true

139
Q

What voltage are dual voltage motors usually designed for?

A

240/480

140
Q

What do terminal designations indicate?

A

polarity

141
Q

What do we connect T1 to?

A

L1

142
Q

How many windings do single voltage motors have?

A

Three

143
Q

How do we connect a dual voltage motor if we want to use the lower voltage?

A

in parallel

144
Q

How do we connect a dual voltage motor if we want to use the higher voltage?

A

In series

145
Q

How many leads do dual voltage motors have?

A

12, but only nine are brought out to the JB

146
Q

How can we change the direction of a motor?

A

swap any two leads

147
Q

How many windings do dual voltage motors have?

A

Three

148
Q

An ohmmeter reveals three groups of three. What kind of motor is this?

A

Delta

149
Q
A
150
Q
A

Electrician 3rd Year (6 decks)

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