Practice Polyphase Induction Motors Multiple Choice Questions Quiz-4 - MCQGeeks.com

Q.1

A 3-phase 440 V, 50 Hz induction motor has 4% slip. The frequency of rotor e.m.f. will be

200 Hz
50 Hz
2 Hz
0.2 Hz

Q.2

When the equivalent circuit diagram of double squirrel-cage induction motor is constructed the two cages can be considered

In series
In parallel
In series-parallel
In parallel with stator

Q.3

Short-circuit test on an induction motor cannot be used to determine

Windage losses
Copper losses
Transformation ratio
Power scale of circle diagram

Q.4

The torque of a rotor in an induction motor under running condition is maximum

At the unit value of slip
At the zero value of slip
At the value of the slip which makes rotor reactance per phase equal to the resistance per phase
At the value of the slip which makes the rotor reactance half of the rotor

Q.5

What will happen if the relative speed between the rotating flux of stator and rotor of the induction motor is zero?

The slip of the motor will be 5%
The rotor will not run
The rotor will run at very high speed
The torque produced will be very large

Q.6

Which of the following methods is easily applicable to control the speed of the squirrel-cage induction motor?

By changing the number of stator poles
Rotor rheostat control
By operating two motors in cascade
By injecting e.m.f. in the rotor circuit

Q.7

In three-phase squirrel-cage induction motors

Rotor conductor ends are short-circuited through slip rings
Rotor conductors are short-circuited through end rings
Rotor conductors are kept open
Rotor conductors are connected to insulation

Q.8

In an induction motor if air-gap is increased

The power factor will be low
Windage losses will be more
Bearing friction will reduce
Copper loss will reduce in an induction motor

Q.9

In medium sized induction motors, the slip is generally around

0.04 %
0.4 %
4 %
14 %

Q.10

Blocked rotor test on induction motors is used to find out

Leakage reactance
Power factor on short circuit
Short-circuit current under rated voltage
All of the above

Q.11

Slip rings are usually made of

Copper
Carbon
Phosphor bronze
Aluminium

Q.12

The starting torque of a three phase induction motor can be increased by

Increasing slip
Increasing current
Both (A) and (B)
None of the above

Q.13

Rotor rheostat control method of speed control is used for

Squirrel-cage induction motors only
Slip ring induction motors only
Both (A) and (B)
None of the above

Q.14

If any two phases for an induction motor are interchanged

The motor will run in reverse direction
The motor will run at reduced speed
The motor will not run
The motor will burn

Q.15

Slip of an induction motor is negative when

Magnetic field and rotor rotate in opposite direction
Rotor speed is less than the synchronous speed of the field and are in the same direction
Rotor speed is more than the synchronous speed of the field and are in the same direction
None of the above

Q.16

The torque developed by a 3-phase induction motor least depends on

Rotor current
Rotor power factor
Rotor e.m.f.
Shaft diameter

Q.17

DOL starting of induction motors is usually restricted to

Low horsepower motors
Variable speed motors
High horsepower motors
High speed motors

Q.18

In induction motor, percentage slip depends on

Supply frequency
Supply voltage
Copper losses in motor
None of the above

Q.19

The complete circle diagram of induction motor can be drawn with the help of data found from

No-load test
Blocked rotor test
Stator resistance test
All of the above

Q.20

A 3-phase induction motor delta connected is carrying too heavy load and one of its fuses blows out. Then the motor

Will continue running burning its one phase
Will continue running burning its two phase
Will stop and carry heavy current causing permanent damage to its winding
Will continue running without any harm to the winding

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