Deck 33: Three Phase Motors

Question 1

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

A) bars; bars
B) rings; rings
C) bars; rings
D) rings; bars

Answer 1

C

Question 2

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 _____.

A) double-phasing
B) single-phasing
C) triple-phasing
D) free-running

Answer 2

B

Question 3

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

A) magnetic
B) slip
C) synchronous
D) rotor

Answer 3

C

Question 4

Selsyn motors operate on _____ voltage.

A) two-phase
B) single-phase
C) three-phase

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 _____.

A) amortisseur winding
B) starting bars
C) synchronous starter
D) rotor bars

Question 6

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

A) increases
B) stays the same
C) decreases
D) is cut in half

Question 7

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 _____.

A) phase angle voltmeter
B) MEGGER
C) digital multimeter
D) phase rotation meter

Question 8

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

A) stay the same
B) cut in half
C) double
D) go to zero

Question 9

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

A) 1.75 hp
B) 2.13 hp
C) 4.57 hp
D) 6.93 hp

Question 10

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 _____.

A) series
B) parallel

Question 11

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

A) zero to one
B) two to five
C) five to seven
D) eight to ten

Question 12

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.

A) operating voltage
B) overload current
C) starting torque
D) synchronous speed

Question 13

When a squirrel-cage motor is first started, the value of the current draw is _____.

A) equal to the running current
B) smaller than the running current
C) twice the running current
D) several times the running current

Question 14

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

A) 0 °
B) 90 °
C) 180 °
D) 270 °

Question 15

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?

A) 4.17%
B) 4.35%
C) 24%
D) 23%

Question 16

The synchronous motor is an induction motor.

Question 17

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

A) synchronizer
B) capacitor
C) selsyn
D) synchronous condenser

Question 18

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 _____.

A) series
B) parallel

Question 19

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

A) low; low
B) low; high
C) high; low
D) high; high

Question 20

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

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

Question 21

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

A) three windings connected in a wye
B) one winding