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Motor controls > Motor controls review > Flashcards

Motor controls review Flashcards

1
Q

Two dissimilar metals bonded together have?

A

different expansion rates

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2
Q

If electrical contacts are permitted to open and close slowely

A

poor contacts are permitted to open

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3
Q

A metal that remans in liquid state at room temperature.

A

Mercury

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4
Q

An RTD is made out of

A

Platinum

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5
Q

A bellows type thermostat works on change in

A

pressure principle

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6
Q

A device that emplys the heating of two metals to produce a voltage is known as

A

thermocouple

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7
Q

Two or more thermocouples connected in series

A

thermopile

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8
Q

A device that works on principle of change in resistance with a change in heat is known as

A

Resistance temperature detector

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9
Q

A hall generator is constructed as a

A

Integrated Circuit

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10
Q

A hall sensor is used to sense the presense of a

A

Magnetic Field

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11
Q

If a disk with magnetic poles around its circumferance is attatched to a rotating shaft , and a hall sensor is mounted near the disk

A

An AC voltage is produced

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12
Q

Most proximity detectors will easily detect what type of metal?

A

IRON

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13
Q

A proximity detector that can detect the presence of non-metallic devices usually operates on a change in

A

capacitance

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14
Q

A photo conductive device changes

A

its resistance with light

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15
Q

Magnetic control systerm usually operates on

A

120 volts

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16
Q

A control transformer is often used to step

A

down 600v or 208v to 120v

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17
Q

ANOTC contact must be connected

A

on-delay relay if its to be time delayed when closing

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18
Q

Many electronic timers can be used as

A

DOE or DODE

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19
Q

Pulse timers

A

continually turn off and on at regular intervals

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20
Q

The most accurate way of plugging to stop a motor is with a

A

zero speed switch

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21
Q

3 Main methods of braking

A

Mechanical - Dynamic - Plugging

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22
Q

DOE stands for

A

delay on energization

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23
Q

Typically , SCIM and their locked rotor currents cary from

A

2 1/2 to 10 times the FLA

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24
Q

What kind of coupling is required for a Plugging switch

A

Direct Flexible

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25
Q

SCIM, 2 Pole @ 50 hz, ac scource will run at RPM

A

RPM = F x (120/ poles)

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26
Q

SCIM, 6 poles @ 60hz , ac source will run at

A

RPM = F x (120/ poles)

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27
Q

DOE Stands for

A

Delay on energization

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28
Q

the shaft of a plugging switch is most often

A

mechanically, connected to the shaft on the machine it controls

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29
Q

pluggin cotrol provides

A

rapid stop of motion

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30
Q

plugging switches are deigned to be added to control circuits

A

piolet device

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31
Q

Most machines in which plugging is done are driven by

A

SCIM

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32
Q

The rotating motion of a motor transmitted to plugging switch contacts either by a magnetic induction or by a

A

centrifugal mechanism

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33
Q

A plugging switch acts like a link between the motor and

A

reversing started

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34
Q

a starter used for a plugging switch will

A

interchange 2 of the 3 moter leads for a 3 phase motor
reverse direction of current through armature for a dc motor

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35
Q

when changing the direcion of motor rotation, the electrician should change connections at the scource of power or motor

A

scource of power or motor

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36
Q

squirrel cage induction motors are charcterized by

A

simplicity
reliabilty
ruggedness

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37
Q

With regard to SCM, the current

A

The current drops as motor speed increases

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38
Q

When a squirrel cage motor is connected directly to the plant distributionsystem at full voltage

A

either magnetic or manual

39
Q

With a SCM, when voltage is reduced to start the motor the

A

current is also reduced and so is the machines torque

40
Q

Which is the simplest of all starting methods

A

Across the line

41
Q

Most popular motor

A

3 phase SCIM

42
Q

initial inrush current is not comparable to

A

locked rotor current

43
Q

With a reactr or primary resistor type starters, reactors, or resistors are

A

connected in series with a motor

44
Q

It is desirable to limit the starting current of a motor if full voltage starting cause serious line disturbances on

A

lighting ccts
computer and electronics
fire alarm system

45
Q

Large inrush current during starting of large motors may cause

A

Utility line disturbances

46
Q

closed transition starting means the motos is

A

never disconnected from the line until the motor is operating at full voltage

47
Q

Conditions where it is not acceptable to start a motor across the line due to excessive

A

starting current or torque

48
Q

primary resistor starters consume

A

high energy and start with high power factor

49
Q

Split phase motors will disconnect the start winding from the power line using a

A

centrifugal switch

50
Q

If the motor is disconnected between the start and run stage, the starting method is refferd to as

A

open transition

51
Q

Most large HP motors are started at

A

65%

52
Q

some large motor circuits may use several starting because of

A

limitiations by the utility
torque limits of machine
length of acceleration time required

53
Q

Autotransformers starters are considered

A

inductive loads

54
Q

Some resistor and reacors starters use multiple steps of starting.
This is accomplished by tapping the resistor or reactor to provide different values of

A

resistanve and inductance reactance

55
Q

autotransformers are generally employed to start what type of motor

A

SCIM

56
Q

Motor started witha autotransformer reduced voltage starter

A

less current less torque

57
Q

When an autotransformer is used as a voltage starter

A

an adjustable timer controls when the motor recieves full voltage

58
Q

Another name for Star delta

A

wye-delta

59
Q

with a star delta, if the starter used has the required number of properly wired controls the motor can be

A

started in wye delta

60
Q

a star delta moto must be wound in such a manner that it iell run it

A

stator connected ran in delta

61
Q

autotransformer used as a reduced vltage starter must have a minimum of

A

3 taps

62
Q

with star delta motors

A

the full stator is used with no limiting devices

63
Q

star delta motors are used on loads having

A

high inertia, short acceleration periods

64
Q

the speed of a star delta depends on

A

frequency and number of poles

65
Q

care shouldbe taken when connecting the stator windings of a star delta motor the the load, contacts will otherwisw

A

reverse directions when the windings are changed from wye to delta

66
Q

the main reason to use a closed transtion starting method with a star-delta motor is to

A

Prevent line disturbances

67
Q

If a set of normally closed and normally open contacts share a common terminal the contact configuration is refered to ass

A

single pole double throw

68
Q

If a stator winding are connected in delta during the starting period , the starting current will be how many times greator than the current values if started in wye

A

3 times

69
Q

when selecting a relay for a particular application, one must determine

A

coil voltage
#of contacts
contact rating

70
Q

Most capacitive proximity detectors have a maximum sensing distance of

A

25 mm - 1inch

71
Q

capacitive proximity detectors can sense the presence of

A

wood copper or brass

72
Q

ultrasonic detectors emit a

A

high frequency sounds

73
Q

Photodetectors with both transmitter and reciever require protection when unts are mounted in same housing

A

use reflector for operation

74
Q

In canada, most 3 phase industrial motors operate on voltages ranging

A

208v or 600v

75
Q

common control systems operate on

A

120 volts

76
Q

conrol transformers are used to step down

A

600v or 208v down to 120v

77
Q

when using a 240v/480v to 120v control transformer on a 240v line (lower voltage)

A

Both primary windings are connected in parrallel

78
Q

when using a 240v/480v to 480v control transformer on a 240v line
(higher voltage)

A

Both primary windings are connected in series

79
Q

which is not a methof of interlocking

A

thermal interlocking

80
Q

A method by which starters are connected so that one cannot be started until the other is started is known as

A

sequence control

81
Q

To protect people, machines and production processes a

A

lockable disconnect

82
Q

which type of single phase induction motor cannot be used with a variable speed controller?

A

Motors with a centrifugal switch

83
Q

Variable frequency motor controllers must have some method of

A

reducing the applied voltage to the stator as frequency is reduced

84
Q

Most VFDs provide

A

low speeding torque
current limiting
automatic speed regulation

85
Q

A device could be installed to input accurate current draw data to a VFD?

A

Current transformers

86
Q

A device used to accuratley moniter the speed of a motor

A

Hall effect sensor

87
Q

Ramping refers to

A

accelereation and deeceleration to control motor

88
Q

In a VFD, the maximum speed of the motor is controlled by the

A

maximum hertz

89
Q

In a addition to their primary function of providing speed control for c motors , most variable frequency drivees can also provide

A

low speed torque control
current limiting
automatic speed regulation

90
Q

What device could be installed to input accurate current draw data to a vfd?

A

current transformers

91
Q

a device that should be used to acccurately moniter the speed is

A

hall effect sensor

92
Q

ramping refers to

A

acceleration and deacceleration control of a motor

93
Q

Many transistor- controlled VFD now employ a special type of a transistor called

A

insulated bipolar transistor

94
Q

Ina VFD, the ——– setiting controls the maximum speed of the motor

A

maximum hertz

Motor controls (8 decks)

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