Deck 4: Motor Types and Applications

Question 1

Which of the following motors is used for unity power factor ?

A)Hysteresis motor
B)Schrage motor
C)Universal motor
D)Reluctance motor

Answer 1

Schrage motor

Question 2

The motor used for the compressors is

A)d.c. series motor
B)shaded pole motor
C)capacitor-start capacitor-run motor
D)reluctance motor

Answer 2

capacitor-start capacitor-run motor

Question 3

Which of the following motors is used in a situation where load increases with speed ?

A)Induction motor
B)Three-phase series motor
C)Schrage motor
D)Hysteresis motor

Answer 3

Three-phase series motor

Question 4

In repulsion motor, zero torque is developed when

A)brush axis is 45° electrical to field axis
B)brush axis coincides with the field axis
C)brush axis is 90° electrical to field axis
D)both (b) and (c)

Question 5

Centrifugal switch disconnects the auxiliary winding of the motor at about ____ percent of synchronous speed

A)30 to 40
B)70 to 80
C)80 to 90
D)100

Question 6

Starting winding of a single phase motor of a refrigerator is disconnected from the circuit by means of a

A)magnetic relay
B)thermal relay
C)centrifugal switch
D)none of the above

Question 7

If a single phase induction motor runs slower than normal, the most likely defect is

A)worn bearings
B)short-circuit in the winding
C)open-circuit in the winding
D)none of the above

Question 8

Which of the following motors is used in tape-recorders ?

A)Hysteresis motor
B)Reluctance motor
C)Capacitor-run motor
D)Universal motor

Question 9

Which of the following statements regarding two value capacitor motor is incorrect ?

A)It is a reversing motor
B)It is preferred to permanent-split single-value capacitor motor where frequent reversals are required
C)It has low starting as well as rush¬ing currents
D)It has high starting torque

Question 10

Two-value capacitor motor finds increased application as compressor motor in small home air-conditioners because

A)it is comparatively cheaper
B)it has almost non-destructible capacitor
C)it has low starting as well as running currents at relatively high power factor
D)it is quiet in operation

Question 11

If the centrifugal switch of a two-value capacitor motor using two capacitors fails to open then

A)motor will not come upto speed
B)motor will not carry the load
C)current drawn by the motor will be excessively high
D)electrolytic capacitor will, in all probability, suffer break down

Question 12

In a universal motor, the most common cause of brush sparking is

A)open armature winding
B)shorted armature winding
C)shorted field winding"
D)all of the above

Question 13

If starting winding of a single-phase induction motor is left in the circuit, it will

A)run faster
B)spark at light loads
C)draw excessive current and overheat
D)run slower

Question 14

Most of the fractional horsepower motors have either

A)hard and annealed bearings
B)ball or roller bearings
C)soft and porous bearings
D)plain or sleeve bearings

Question 15

Which of the following statements regarding reluctance-start motor is incorrect ?

A)It is similar to reluctance motor
B)It is basically an induction motor and not a synchronous one
C)So far as its basic working principle is concerned, it is similar to shaded pole motor
D)the air-gap between rotor and salient poles is non- uniform

Question 16

To reverse the direction of rotation of acapacitor start motor while it is running we should

A)disconnect motor from the supply till it stops then reconnect it to supply with reversed connection of main or auxiliary winding
B)disconnect motor from supply and immediately reconnect it to supply with reversed connections of the main winding
C)reverse the direction of connection of the auxiliary winding and after motor comes to rest then connect auxiliary winding to the supply
D)reverse the direction of connections of the auxiliary winding and im-mediately connect it to supply

Question 17

In case of a reluctance motor, when the load is increased so that it cannot maintain synchronous speed the motor will

A)become unstable
B)draw excessive armature current and may burn out
C)fall out of synchronism and come to stand still
D)run as induction motor

Question 18

Which of the following motors has two separate windings on the motor ?

A)Repulsion motor
B)Repulsion induction motor
C)Repulsion start induction run motor
D)None of the above

Question 19

A shaded pole motor does not possess

A)centrifugal switch
B)capacitor
C)commutator
D)all of the above

Question 20

In a A.C. series motor armature coils are usually connected to commutator

A)through resistance
B)through reactances
C)through capacitors
D)solidly

Question 21

Which of the following statements regarding a reluctance motor is incorrect ?

A)It cannot be reversed, ordinarily
B)It requires no D.C. field excitation for its operation
C)It is nothing else but a single-phase, salient pole synchronous-induction motor
D)Its squirrel cage-rotor is of unsym-metrical magnetic construction in order to vary reluctance path bet¬ween stator and rotor

Question 22

A universal motor is one which

A)can be operated either on D.C. or A.C. supply at approximately the same speed and output
B)can be marketed internationally
C)runs at dangerously high speed on no-load
D)none of the above

Question 23

A repulsion motor is equipped with

A)slip rings
B)commutator
C)both (a) and (b)
D)none of the above

Question 24

The capacitors used in single-phase capacitor motors have no

A)voltage rating
B)dielectric medium
C)polarity marking
D)definite value

Question 25

If a D.C. series motor is operated on A.C. supply, it will

A)spark excessively
B)have poor efficiency
C)have poor power factor
D)all of the above