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Period 2 - SAIT > Electrical Test > Flashcards

Electrical Test Flashcards

1
Q

Are single phase motors more efficient than three phase motors of comparable horsepowers?

A

No

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2
Q

Most single phase motors fall in to what horsepower range?

A

1/4hp to 20hp

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3
Q

Single phase split phase induction motors are classified by

A

the way the stator windings are used to starting and running

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4
Q

What are the main components of the resistance split-phase motor? (4)

A
  • frame, rotor, stator, end bells
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5
Q

What does a centrifugal switch disconnect?

A

the start windings

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6
Q

When does a centrifugal switch open?

A

at approximately 75% to 80% of the rated speed

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7
Q

In order for the motor to start, the current in the start start winding must be

A

out of phases with the current in the main winding

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8
Q

The two winding of an RSIR motor are electrically out of phases by

A

90 degrees for a two pole motor

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9
Q

The RSIR motor centrifugal switch is connected

A

in series with the start winding

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10
Q

The resistance split-phase induction motor has

A

low starting torque and high starting current

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11
Q

A resistance split phase motor is reversible if

A
  • the connections to the start winding are brought out of the connection box
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12
Q

A CSIR motor has a _________ capacitor in __________ with the ___________ winding

A

start; series; start

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13
Q

The starting torque of a capacitor-start motor compared to a resistance split-phase motor is

A

higher

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14
Q

In a motor, the run capacitor improves

A

power factor

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15
Q

In a motor, the start capacitor impoves

A

torque

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16
Q

The starting current of a CSIR motor compared to a resistance split-phase motor is

A

lower

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17
Q

How is the direction of rotation changed in a RSIR motor?

A

interchange the run winding leads OR interchange the the start winding leads but NOT BOTH

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18
Q

The capacitor of a CSIR motor is rated for

A

short time duty and is connected in series with the start winding

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19
Q

The phase displacement between the current of the start and main windings of a CSIR motor_______than that of a resistance split-phase motor

A

greater

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20
Q

On the low-voltage connection of a split-phase, single-phase motor, the main windings are connected in

A

parallel

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21
Q

A PSC motor utilizes a

A

low capacitance oil filled capacitor

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22
Q

Can permanent-split capacitor motor have more than one speed?

A

yes

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23
Q

A permanent-split capacitor motor

A

energizes the start and run winding when operating

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24
Q

What additional components does a two-value capacitor motor have that a permanent-split capacitor motor does not have?

A

a start capacitor and a centrifugal switch

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25
Q

What are common names for a two-value capacitor motor?

A

Capacitor Start Capacitor Run and Dual Value Capacitor Motor

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26
Q

Is a two-value capacitor motor reversible?

A

yes

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27
Q

The two-value capacitor motor has ________ starting torque

A

high

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28
Q

The centrifugal switch used in a two-value capacitor motor

A

Disconnects the start capacitor

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29
Q

A dual voltage motor connected for high voltage would have which terminals connected?

A

T2 and T3 connected together

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30
Q

A CSCR compressor requires a

A

potential relay

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31
Q

A current relay has

A

N.O. contacts

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32
Q

A potential relay includes

A

high impedance coil

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33
Q

A potential relay includes a

A

high capacitance coil

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34
Q

Resistance is determined by

A
  • material of device
  • size of the device
  • size of the wire
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35
Q

A resistive circuit phase angle and phase relationship is

A

0 degrees and peak at the same time

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36
Q

The SI unit for Torque is

A

Newton Meters

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37
Q

In a RSIR motor, the start winding is disconnected at

A

Approximately 75% of rated speed

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38
Q

A CSIR motor has________ capacitance than other motors

A

greater

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39
Q

A starting capacitor has greater capacitance than

A

the run capacitor

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40
Q

The horsepower rating of a motor is determined by

A

the speed and torque (HP=torque x speed divided by 7121)

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41
Q

In a PSC motor, the ________ is connected continuously

A

run capacitor

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42
Q

A shaded pole motor a _________ coil and ______ winding(s)

A

shading; 1

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43
Q

A capacitor is rated in

A

(micro) farads

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44
Q

The proper method to discharge a capacitor is to

A

connect a 20K ohm and 5 watt resistor across the terminals

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45
Q

To change the rotation direction in an RSIR motor

A

change only the run or the start terminals (NOT BOTH)

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46
Q

The run winding’s are mounted deep into the

A

stator slots

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47
Q

One benefit of skewered rotor bars is

A

quieter operation

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48
Q

The purpose of the end bells is to (3)

A
  • seal the motor
  • hold the bearings
  • support the shaft
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49
Q

The centrifugal switch has

A

N.C contacts and is mounted on the shaft

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50
Q

A dual voltage motor is connected for high voltage run winding connected

A
  • in series
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51
Q

A dual voltage motor is connected for low voltage run windings connected in

A

parallel

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52
Q

On a CSCR motor, the potential relay disconnects the

A

start capacitor and start windings

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53
Q

On a dual voltage RSIR motor connected for low voltage, the start winding would be connected

A

in parellel

54
Q

A current relay contains what type of contacts?

A

Normally Open contacts

55
Q

A potential relay contains what type of contacts?

A

Normally Closed contacts

56
Q

To change the state of the contacts, a current relay relies on

A

In rush current

57
Q

What is the definition of Power Factor?

A

the ratio of comparing true power in watts and the apparent power in VA

58
Q

The capacitance of a capacitor is determined by

A

the size of the conducting plates and the space between them

59
Q

A CSIR motor has a ___ capacitor connected temporarily and a _____ switch connected in ______ with the ______ winding

A

start; centrifugal; series; start

60
Q

A capacitor is connected in _____ with the ___ winding

A

series; start

61
Q

Dual voltage start winding terminals are labeled

A

T5 T6 T7 and T8

62
Q

What are the four types of split-phase motors

A
  • CSIR
    -RSIR
  • PSC
  • CSCR
63
Q

What are the two main components of the a split-phase motor?

A

stator and the rotor

64
Q

What are the three main components of a start or run capacitor?

A
  • two conductor plates
  • dielectric material
  • container to hold the plates and dielectric material
65
Q

What is the purpose of a shading coil in a shaded-pole motor?

A

delay the development of magnetic flux in the shaded part of the pole so that a rotating magnetic field is created

66
Q

What are the three switches that remove the start winding from the electrical circuit once a split-phases motor has started

A
  • centrifugal switch
  • potential relay
  • current relay
67
Q

What is the difference between an RSIR motor and a shaded-pole motor?

A
  • RSIS motor uses an electrical switch and shaded-pole has a shading coil on half of each pole
  • shaded pole has a lower starting torque than the RSIR
  • the shaded-pole motor uses and electrical switch to remove the start winding from the circuit once motor achieved its running speed
68
Q

What are the advantages of a PSC motor? (2)

A

good speed control and low running current

69
Q

What is the stator constructed of in all single-phase motors

A

quantity of stacked and laminated iron plates

70
Q

Which motor uses a potential relay?

A

CSCR motor

71
Q

Which motor uses a current relay?

A

RSIR and CSIR motors

72
Q

How long does the start capacitor stay in the electrical circuit when the motor is initially energized?

A

2 to 3 seconds

73
Q

Which motor has a rotor made of permanent magnets?

A

ECM rotor

74
Q

What is a microfarad?

A

Unit of measurement for capacitance

75
Q

What kind of a capacitor is typically rated at less than 50 microfarads?

A

the run capacitor

76
Q

Which motor circuit is constantly energized?

A

ECM motor circuit

77
Q

What type of current is applied to the control module of the ECM?

A

Alternating Current (AC)

78
Q

Are the windings of an ECM constructed as a three-phase winding? (T/F)

A

true

79
Q

What is the voltage rating of a potential relay coil?

A

the voltage rating is the peak of the measured cemf that is between the start and the common winding as the motor starts

80
Q

Name three components in the electrical circuit of an RSIR motor

A
  • start winding
  • run winding
  • centrifugal switch or current relay
81
Q

Name four components in the electrical circuit of a CSIR motor

A
  • start winding
  • run winding
  • start capacitor
  • centrifugal switch or current relay
82
Q

Name five components in the electrical circuit of a CSCR motor

A
  • start winding
  • run winding
  • start capacitor
  • run capacitor
  • potential relay
83
Q

Name three components in the electrical circuit of a PSC motor

A
  • start winding
  • run winding
  • run capacitor
84
Q

What are motor starters and compressor relays?

A

they are devices used to switch on and off electrical power necessary for the motor or compressor to operate

85
Q

What is a manual starter?

A

a switch that requires human power to open and close the electrical switch

86
Q

List the six components of a contractor?

A
  • core
  • coil or electromagnet
  • contact springs
  • contacts
  • armature
  • armature springs
87
Q

What does a relay use to change the position of the switch contacts?

A

an electromagnet to change the position of the switch contacts

88
Q

What happens to a magnetic coil when the coil voltage is too high?

A

the insulation on the coil wire breaks down because of the heat produced by the high current

89
Q

Explain what happens to a magnetic coil when the coil voltage is too low

A
  • the coil draws higher than rated current and can burn out
  • contact positions do not change
  • chattering of the contact can occur, cause arc damage to the contacts
90
Q

What are the four basic types of relays

A
  • plug in relays
  • industrial control relays
  • power relays
  • enclosed control relays
91
Q

What are the two basic components of a magnetic starter

A
  • contactor
  • overloads
92
Q

What do seal-in or holding contactors do?

A

keep the operating coil energized after the momentary contact start button is released

93
Q

What is a short circuit?

A

when the current of the circuit takes a path of lesser impedance than the circuit design

94
Q

What is an overload?

A

a current that is somewhat above the normal rated value for that circuit

95
Q

Name four types of overload protectors

A
  • solder pot
  • electronic overload
  • magnetic overload
  • bimetal (thermal) overloads
96
Q

What does the armature do in a contractor?

A
  • moveable metal component that is attracted to the magnetized core
  • it provides mechanical action that changes the position of the contacts attached to it
97
Q

Who approves electrical components in Canada?

A

Canadian Standards Association (CSA)

98
Q

What is the importance of the term “service factor” to a motor?

A

its a rating system that indicates the degree to which the motor can withstand periods of overload without damage

99
Q

Where is the internal thermal protection installed on a compressor

A
  • used on hermetic and semi-hermetic compressors to protect the motor from overheating
  • located and imbedded in or near the windings of the motor
100
Q

What are two types of thermal overload protectors?

A
  • solder pot/ melting alloy
  • bimetallic strip
101
Q

Are fuses overload protection devises?

A

no; they are over current protection devices

102
Q

What are two types of plug or cartridge fuses available?

A
  • instantaneous (non-time delay)
  • time delay
103
Q

Opposition to current flow

A

Resistance

104
Q

Resistance is determined by (3)

A
  • material of the device
  • size of the device (cross sectional area or diameter)
  • length of the wire
105
Q

What is the phase angle and phase relationship in a resistive circuit?

A

0 degrees; current and voltage are in phase

106
Q

What is the type of power converted in a resistive circuit?

A

true or real power

107
Q

What is the symbol and unit for true or real power

A

p; watts

108
Q

What is the power factor in a resistive circuit?

A

pf = 1

109
Q

What is the physical properties of an inductive circuit?

A

a coiled wire develops a new property called Inductance

110
Q

What is the symbol and unit for Inductance?

A

L; Henry (h)

111
Q

What is Inductance determined by? (3)

A
  • material of the core
  • size of the core
  • number of turns
112
Q

What are the 3 oppositions to current flow in an inductive circuit?

A
  • resistance
  • inductive reactance
  • impedance
113
Q

What is the symbol and unit for inductive reactance? What is inductive reactance determined by?

A

xL; ohms; xL = 2𝝅FL

114
Q

What is impedance, its symbol and unit?

A

impedance is total opposition to current flow; symbol is “z” and unit is ohms

115
Q

Impedance is a combination of

A

resistance and inductive reactance

116
Q

What is the phase angle and relationship for impedance?

A

1 to 89 degrees; current lags the voltage

117
Q

For impedance, what is the type of power converted, its symbol and unit?

A

True or real power; P; watts

118
Q

For impedance, what is the type of power not converted, its symbol and unit?

A

Reactive power (wasted power); qxL; var (volt reactive)

119
Q

For impedance, what is the total power, its symbol and unit?

A

Apparent power (total power consumed); S; volt amps

120
Q

What is the the power factor for Impedance?

A

true power ÷ apparent power (p÷s)

121
Q

Power triangle think Pythagoras

A

Apparent power (s) - hypotenuse side
true or real power (p) - horizontal side
reactive power (qxL) - vertical side

122
Q

Impedance triangle ***think Pythagoras)

A

Impedance (z) - hypotenuse side
Resistance (r) - horizontal side
Inductive reactance (xL) - vertical side

123
Q

How to find angle theta?

A

horizontal side ÷ hypotenuse + shift + COS Sign

124
Q

How is the phase angle and torque related

A

the lower the phase angle, the more torque a motor will have

125
Q

What is ohms law

A

Current is directly proportional to voltage and indirectly proportional to resistance

126
Q

What is kirchoff’s voltage law

A

voltage drop across a load must equal source voltage

127
Q

What is electron theory

A

Current flow through the load is negative to positive and through the source is positive to negative

128
Q

What is American WIre Gauge?

A

a sizing metric for copper wire; larger the # the smaller the diameter of the conductor

129
Q

What is voltage

A
  • electromotive force and is measured across two terminals
  • comparison of amount of electron flow between two terminals
  • voltage across a closed switch = 0volts
130
Q

What is Kirchoff’s Current Law

A

Current leaving a point must equal current entering that point

Period 2 - SAIT (3 decks)

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