Motor Controls

Question 1

An excellent choice for alternating current, all purpose, constant speed motor applications would be a

A) dc motor
B) squirrel cage motor
C) Stepping motor
D) None of the above

Answer 1

B) squirrel cage motor

Question 2

Squirrel cage induction motors are characterized by
A) simplicity C) Reliability
B) ruggedness D) All the above

Answer 2

D) All the above

Question 3

The part of the squirrel cage motor that rotates is called the
A) armature
B) rotor
C)Shaft
D)Stator

Answer 3

B) rotor

Question 4

The stator for a squirrel cage motor never has fewer than
A) 2 poles
B) 4 poles
C) 6 poles
D) 8 poles

Answer 4

A) 2 poles

Question 5

In a squirrel cage motor, the current induced has its largest value when the motor

A) is at a standstill
B) is just starting
C) has reached its highest torque
D) has reached its highest speed

Answer 5

A) is at a standstill

Question 6

With regard to a squirrel cage motors, which is not a design consideration?

A) internal resistance
B) internal capacitance
C) internal reactance
D) locked rotor current values

Answer 6

B) internal capacitance

Question 7

Typically for a squirrel cage motor, locked rotor currents vary from

A) 1-5 times FLA
B)2.5-5 times FLA
C)2.5-10 times FLA
D)2.5- 25 times FLA

Answer 7

C) 2.5-10 times FLA

Question 8

With regard to a squirrel cage motor, the current
A) remains constant as a motor speed increases

B)increases sharply as the motor approaches its full rated speed

C)drops sharply as the motor approaches its full rated speed

D)remains constant as the motor speed decreases

Answer 8

C) drops sharply as the motor approaches its full rated speed

Question 9

With a squirrel cage motor, current will not be induced in the rotor under a

A) load condition
B) no load condition
C)low torque condition
D) high torque condition

Answer 9

C) low torque condition

Question 10

The machine to which a squirrel cage motor is connected may be started only at

A) no load condition
B) normal load condition
C) an overload condition
D) all the above

Answer 10

D) all the above

Question 11

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

A) a Manuel starter may be used
B) a magnetic starter may be used
C) a or b above
D)neither a or b

Answer 11

C) A or B

Question 12

With regard to a squirrel cage motors, when the voltage is reduced to start the motor, the

A) current is increased, toque is reduced

B)current is reduced, toque is increased

C) current is increased, toque is increased

D) current is reduced, toque is reduced

Answer 12

D) current is reduced, torque is reduced

Question 13

Power utility voltage fluctuations may be caused by

A) sudden high surges of reactive current from large motors on starting

B)pulsations in current taken by electrical machinery driving reciprocating compressors and the like

C) the impulse demands of industrial x-ray equipment

D) all the above

Answer 13

D) all the above

Question 14

Which is not a method of starting polyphase squirrel cage motors

A) primary resistance starting
B)impedance starting
C) capacitive starting
D) part winding starting

Answer 14

C) capacitive starting

Question 15

What is the simplest of all starting methods?

Answer 15

Across the line

Question 16

The starting winding of a single phase motors is disconnected when the motor reaches about______ percentage of its rated speed?

Answer 16

75%

Question 17

The most popular motor used in north American industry is?

Answer 17

3 phase squirrel cage motor

Question 18

A thermistor protecting a motor exhibits_______ when temperature reaches a certain point

A) no change in resistance
B) a gradual change of resistance
C) a rapid change of capacitance
D) a rapid change of resistance

Answer 18

D) rapid change of resistance

Question 19

The initial in rush current of a motor is comparable to

A) the FLA
B) locked rotor current
C) no load amps
D) all the above

Answer 19

B) locked rotor current

Question 20

Another name for star delta motor starting is

A) triangle delta motor starting
B) diamond delta motor starting
C) tri-delta motor starting
D) wye - delta motor starting

Answer 20

D) wye delta motor starting

Question 21

With a wye delta motor, if the starter used has required number of properly wired contacts, the motor should be

A) started in wye and run in delta
B) started in delta run in wye
C) started in both wye and delta
D) run in both wye and delta

Answer 21

A) started in wye and run in delta

Question 22

A star delta motor must be wound in such a manner that it will run with its

A) rotor connected in wye
B) rotor connected in delta
C) stator connected in wye
D) stator connected in delta

Answer 22

D) stator connected in delta

Question 23

With wye delta motors,

A) half the stator winding is used with limiting device such as resistor or autotransformer

B) the full stator winding used with a limiting device such as a resistor or autotransformer

C)half the stator winding with no limiting device

D) full stator winding with no limiting device

Answer 23

D) full stator windings with no limiting device

Question 24

Wye delta motor are widely used on loads that require

A) low starting toque
B) high starting toque
C) reduced starting voltage
D) increased starting voltage

Answer 24

A) Low starting torque

Question 25

The speed of a wye delta motor depends on the A) frequency of the applied voltage and the number of stator poles B) frequency of the applied voltage and the number of rotors

Answer 25

A) frequency of the applied voltage and the number of stator poles

Question 26

Motors that are intended to operate on 2 voltages, such as 240 or 480, contain______ separate windings for each phase? A) 1 B) 2 C)3 D)4

Answer 26

B) 2

Question 27

Care should be taken when connecting the stator windings of a wye delta motor to the load contacts otherwise the motor might A) overheat B) reverse directions when the windings are changed from star to delta C) freeze up D) run at reduced speed

Answer 27

B) reverse directions when the windings are changed from star to delta

Question 28

With a reactor or primary resistor type starter, reactors or resisters are A) connected in parallel with the motor B)connected in series with the motor C) connected in parallel with the CR D) connected in series with a TR

Answer 28

B) connected in series with the motor

Question 29

In regards reactor or primary resistance starting, a start under load will result in A) longer acceleration time to full speed and longer initial inrush current period B) a shorter acceleration time to full speed and longer initial inrush current period

Answer 29

A) a longer acceleration time to full speed and longer initial inrush current period

Question 30

Large current inrush during the starting of large motors may cause A) the control circuit change B) utility line disturbances and damage to machines due to over torque C) excessive motor speeds D) all the above

Answer 30

B) utility line disturbances and damage to the machines due to over torque

Question 31

Closed transition starting means that the motor is A) connected to the line only when full voltage is applied B) never disconnected from the line from the moment it is first connected until the motor is operating at full voltage

Answer 31

B)

Question 32

There are conditions where it is not acceptable to start a motor across the line due to excessive A) starting current or torque B) size of equipment C) acceleration time D) cost of equipment

Answer 32

A) starting current or torque

Question 33

Primary resistor starters consume A) high energy and start with a high power factor B) high energy and start with a low power factor C) low energy and start with a high power factor D) low energy and start with a low power factor

Answer 33

A) high energy and start with high power factor

Question 34

The rate of rise of current in a circuit is ________ circuits. A) immediate in resistive B) always constant in AC C) at an exponential curve in induction D) both A and C above

Answer 34

D)

Question 35

If the motor is disconnected from the line between the start and run stage, the starting method is referred to as what?

Answer 35

An open transition

Question 36

Most motors are successfully started at A) 25% B)50% C) 65% D) 80%

Answer 36

B) 50%

Question 37

Both primary resistor and reactor starters are available for use on A) single phase reversing operation B) 3 phase reversing operations C) A and B D) neither A or B

Answer 37

C) A and B

Question 38

Some circuits may use several steps of starting because of A) limitations by the utility B) torque limits of a machine C) length of acceleration time desired D) all of the above

Answer 38

D)

Question 39

Starting transformers are considered A) resistive loads B) inductive loads C) capacitive loads D) all of the above

Answer 39

B) inductive loads

Question 40

Autotransformers used as reduced starter must have a minimum of A) 2 taps B) 3 taps C) 4 taps D) 6 taps

Answer 40

A) 2 taps

Question 41

Autotransformers starters are generally employed to start ______ type motors A) synchronous B) squirrel cage C) non-induction D) wound rotor

Answer 41

B) squirrel cage

Question 42

Some resistors and reactor starters use multiple steps of starting. This is accomplished by tapping the resistor or reactor to provide different values of A) resistance or capacitance B) frequency or resistance C) resistance or inductive reactance D) capacitance or inductive reactance

Answer 42

C) resistance or inductive reactance