Question 1

To reverse the direction of rotation of a three-phase motor, reverse _____.

Accepted Answer

A)   any one lead
B)   any two leads
C)   any three leads
D)   all leadsE) A) and D)
F) B) and C)

Question 2

Some motors are constructed so that they will operate on either of two voltages. When they are connected to operate on the lower of the two voltages, the windings are connected in _____.

Accepted Answer

A)   series
B)   parallelC) A) and B)
D) undefined

Question 3

Three lines supply power to a three-phase motor. If one of these lines should open, the motor will be connected to single-phase power. This condition is known as _____.

Accepted Answer

A)   double-phasing
B)   single-phasing
C)   triple-phasing
D)   free-runningE) B) and D)
F) A) and B)

Question 4

The wound-rotor induction motor is popular in industry because it has _____ starting torque and _____ starting current.

Accepted Answer

A)   low; low
B)   low; high
C)   high; low
D)   high; highE) B) and D)
F) B) and C)

Question 5

The set of squirrel-cage bars on the rotor of a synchronous motor is used to start the motor and is known as the _____.

Accepted Answer

A)   amortisseur winding
B)   starting bars
C)   synchronous starter
D)   rotor barsE) None of the above
F) C) and D)

Question 6

Some motors are constructed so that they will operate on either of two voltages. When they are connected to operate on the higher of the two voltages, the windings are connected in _____.

Accepted Answer

A)   series
B)   parallelC) A) and B)
D) undefined

Question 7

The differential selsyn has three stator windings connected in a wye and a rotor made of _____.

Accepted Answer

A)   three windings connected in a wye
B)   one windingC) A) and B)
D) undefined A

Question 8

For most squirrel-cage induction motors the typical percent slip is about _____ percent.

Accepted Answer

A)   zero to one
B)   two to five
C)   five to seven
D)   eight to tenE) A) and B)
F) None of the above

Question 9

In a three-phase motor, the speed of rotation of the magnetic field is called the _____ speed.

Accepted Answer

A)   magnetic
B)   slip
C)   synchronous
D)   rotorE) C) and D)
F) B) and D)

Question 10

The frequency of the current in a squirrel-cage rotor _____ as the rotor approaches synchronous speed.

Accepted Answer

A)   increases
B)   stays the same
C)   decreases
D)   is cut in halfE) C) and D)
F) None of the above

Question 11

The synchronous motor is an induction motor.

Accepted Answer

A) True 
 B)False

Question 12

In the consequent pole motor, if the number of poles is doubled, the motor speed will be _____.

Accepted Answer

A)   stay the same
B)   cut in half
C)   double
D)   go to zeroE) A) and B)
F) A) and C)

Question 13

If a piece of machinery needs a replacement motor and will be damaged if the new motor rotates the wrong way. The test equipment needed to test the rotation direction of the new motor is a _____.

Accepted Answer

A)   phase angle voltmeter
B)   MEGGER®
C)   digital multimeter
D)   phase rotation meterE) None of the above
F) C) and D) D

Question 14

A synchronous motor operated with no load and used for power factor correction is sometimes called a _____.

Accepted Answer

A)   synchronizer
B)   capacitor
C)   selsyn
D)   synchronous condenserE) A) and D)
F) A) and C)

Question 15

The squirrel-cage rotor is constructed of _____ and end _____ embedded in steel laminations.

Accepted Answer

A)   bars; bars
B)   rings; rings
C)   bars; rings
D)   rings; barsE) B) and D)
F) A) and B)

Question 16

The squirrel-cage rotor code letters indicate the shape (type)  of rotor bars. Different types of bars have a large effect on the _____ of a motor.

Accepted Answer

A)   operating voltage
B)   overload current
C)   starting torque
D)   synchronous speedE) B) and D)
F) B) and C)

Question 17

A squirrel-cage rotor induction motor has a synchronous speed of 3600 RPM and an actual rotor speed of 3450 RPM. What is the percent slip?

Accepted Answer

A)   4.17%
B)   4.35%
C)   24%
D)   23%E) B) and D)
F) B) and C)

Question 18

The torque of a squirrel-cage induction motor will be maximum when the phase angle between the stator and rotor fields is _____.

Accepted Answer

A)   0 °
B)   90 °
C)   180 °
D)   270 °E) B) and C)
F) A) and D)

Question 19

Selsyn motors operate on _____ voltage.

Accepted Answer

A)   two-phase
B)   single-phase
C)   three-phaseD) B) and C)
E) All of the above

Question 20

A motor is operating at 3450 RPM and is producing a torque of 32 lb-in. What is the output horsepower of the motor?

Accepted Answer

A)   1.75 hp
B)   2.13 hp
C)   4.57 hp
D)   6.93 hpE) A) and D)
F) A) and C) A

Exam 33: Three-Phase Motors

To reverse the direction of rotation of a three-phase motor, reverse _____.

Correct AnswerverifiedShow Answer

Some motors are constructed so that they will operate on either of two voltages. When they are connected to operate on the lower of the two voltages, the windings are connected in _____.

Correct AnswerverifiedShow Answer

Three lines supply power to a three-phase motor. If one of these lines should open, the motor will be connected to single-phase power. This condition is known as _____.

Correct AnswerverifiedShow Answer

The wound-rotor induction motor is popular in industry because it has _____ starting torque and _____ starting current.

Correct AnswerverifiedShow Answer

The set of squirrel-cage bars on the rotor of a synchronous motor is used to start the motor and is known as the _____.

Correct AnswerverifiedShow Answer

Some motors are constructed so that they will operate on either of two voltages. When they are connected to operate on the higher of the two voltages, the windings are connected in _____.

Correct AnswerverifiedShow Answer

The differential selsyn has three stator windings connected in a wye and a rotor made of _____.

Correct AnswerverifiedA

For most squirrel-cage induction motors the typical percent slip is about _____ percent.

Correct AnswerverifiedShow Answer

In a three-phase motor, the speed of rotation of the magnetic field is called the _____ speed.

Correct AnswerverifiedShow Answer

The frequency of the current in a squirrel-cage rotor _____ as the rotor approaches synchronous speed.

Correct AnswerverifiedShow Answer

The synchronous motor is an induction motor.

Correct AnswerverifiedShow Answer

In the consequent pole motor, if the number of poles is doubled, the motor speed will be _____.

Correct AnswerverifiedShow Answer

If a piece of machinery needs a replacement motor and will be damaged if the new motor rotates the wrong way. The test equipment needed to test the rotation direction of the new motor is a _____.

Correct AnswerverifiedD

A synchronous motor operated with no load and used for power factor correction is sometimes called a _____.

Correct AnswerverifiedShow Answer

The squirrel-cage rotor is constructed of _____ and end _____ embedded in steel laminations.

Correct AnswerverifiedShow Answer

The squirrel-cage rotor code letters indicate the shape (type) of rotor bars. Different types of bars have a large effect on the _____ of a motor.

Correct AnswerverifiedShow Answer

A squirrel-cage rotor induction motor has a synchronous speed of 3600 RPM and an actual rotor speed of 3450 RPM. What is the percent slip?

Correct AnswerverifiedShow Answer

The torque of a squirrel-cage induction motor will be maximum when the phase angle between the stator and rotor fields is _____.

Correct AnswerverifiedShow Answer

Selsyn motors operate on _____ voltage.

Correct AnswerverifiedShow Answer

A motor is operating at 3450 RPM and is producing a torque of 32 lb-in. What is the output horsepower of the motor?

Correct AnswerverifiedA

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The wound-rotor induction motor is popular in industry because it has _ starting torque and _ starting current.

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A

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D

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The squirrel-cage rotor is constructed of _ and end _ embedded in steel laminations.

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A