Deck 18: Three-Phase Motors

Question 1

The squirrel-cage motor receives its name from the type of ____.

A) magnetic field used
B) phase winding used
C) stator used in the motor
D) rotor used in the motor

Answer 1

D

Question 2

The rotor of a wound-rotor motor is constructed by winding coils on the rotor ____ degrees apart.

A) 60
B) 90
C) 120
D) 180

Answer 2

C

Question 3

The phase windings of a delta-connected motor must be connected in parallel for use on low voltage.

Answer 3

True

Question 4

The speed performance of an induction motor is measured in percent ____.

A) induction
B) field
C) torque
D) slip

Question 5

If a motor is to be connected to high voltage, the phase windings will be connected in ____.

A) series
B) parallel
C) wye
D) delta

Question 6

The amount of ____ produced by the motor is calculated by finding the product of a constant, the stator flux, the rotor current, and the rotor power factor.

A) torque
B) induced voltage
C) current
D) power

Question 7

The starting torque of a squirrel-cage motor is high.

Question 8

What frequency should be applied to a six-pole motor to produce a synchronous speed of 400 RPM?

A) 10 Hz
B) 20 Hz
C) 40 Hz
D) 60 Hz

Question 9

It is possible to determine the direction of rotation of a motor before power is connected to it.

Question 10

The synchronous motor ____.

A) is an induction motor
B) must have DC excitation to operate
C) operate at a constantly changing speed
D) does not have the ability to correct its own power factor

Question 11

The stator winding of a motor is often referred to as the ____.

A) rotor
B) synchronizer
C) motor primary
D) motor secondary

Question 12

____ pole squirrel-cage motors permit the synchronous speed to be changed by changing the number of stator poles.

A) Consequent
B) Stator
C) Variable
D) Accelerated

Question 13

If the load on a synchronous motor becomes too great, the rotor will get out of sync with the rotating magnetic field. The amount of torque necessary to cause this condition is called the ____ torque.

A) pull-out
B) desynchronizing
C) imbalance
D) induction

Question 14

If it is intended that the motor maintain constant torque for both low and high speeds, the parallel wye connection will provide low speed and the series delta will provide high speed.

Question 15

The speed at which the magnetic field rotates is called the ____ speed.

A) rotor
B) motor
C) primary
D) synchronous

Question 16

Three lines supply power to a three-phase motor. If one of these lines should open, the condition is known as ____.

A) double phasing
B) single phasing
C) slippage
D) inductive slip

Question 17

The speed of a wound-rotor motor is uncontrollable.

Question 18

Maximum torque is developed when the stator and rotor flux are ____ with each other.

A) in phase
B) 90 degrees out of phase
C) 180 degrees out of phase
D) 270 degrees out of phase

Question 19

The rotor of a synchronous motor contains a set of squirrel-cage bars similar to those found in an A-type rotor. This set of squirrel-cage bars is used to start the motor and is known as the ____ winding.

A) stator
B) phase
C) amortisseur
D) pseudo-squirrel-cage

Question 20

The rotor frequency can be determined using the formula: ____.

A)
B)
C)
D)