Induction Motor MCQs Part 4

Multiple choice questions on Induction Motor Part 4 with brief explanatory answers.

The slip of three-phase induction motor at no-load is

The slip of three phase induction motor at no-load is:

1. Practically zero
2. 0.4
3. 0.525
4. 1

Correct answer: 1. Practically zero

The number of stator windings in a four-speed squirrel cage induction motor are

The number of stator windings in a four-speed squirrel cage induction motor are:

1. One
2. Two
3. Three
4. Four

Correct answer: 2. Two

The rotor core loss of 3 phase induction motor at no-load is

The rotor core loss of 3 phase induction motor at no-load is:

1. Practically zero
2. Small
3. Large
4. Half of the full load

Correct answer: 1. Practically zero

For a three-phase induction motor, the reactance of the rotor circuit is maximum at

For a three-phase induction motor the reactance of rotor circuit is maximum at:

1. No load
2. Half load
3. Full load
4. Starting

Correct answer: 4. Starting

Explanation:

Rotor reactance = s * Rotor reactance at standstill position

Under starting condition s = 1, Hence the rotor reactance will be maximum at starting

The stator of 3-phase induction motor produces magnetic field which by nature is

The stator of 3-phase induction motor produces magnetic field which by nature is

1. Steady in nature
2. Rotating
3. Alternating
4. None of above

Correct answer: 2. Rotating

What happens to the power factor of rotor circuit of 3 phase induction motor when its slip increases

What happens to the power factor of rotor circuit of 3 phase induction motor when its slip increases:

1. P.F increases
2. P.F decreases
3. P.F remains constant
4. P.F is independent of slip

Correct answer: 2. P.F decreases

Explanation:

Rotor P.F = Rotor Resistance/Rotor reactance

With an increase in slip the rotor reactance increases (due to increase in frequency) while the rotor resistance is constant. Thus with increase of slip, the P.F decreases.

A 3-phase induction motor whose stator is delta connected is carrying full load. If one of its fuses blows out then the motor

A 3-phase induction motor whose stator is delta connected is carrying full load. If one of its fuses blows out then the motor:

1. Will continue running burning its two phases
2. Will stop and carry heavy current causing permanent damage to its winding
3. Will continue running without any harm to the winding
4. Will continue running burning its one phase

Correct answer: 4. Will continue running burning its one phase

An induction motor is

An induction motor is:

1. Self-starting with low torque
2. Self-starting with zero torque
3. Not self-starting
4. Self-starting with high torque

Correct answer: 1. Self-starting with low torque

If air-gap is increased in an induction motor

If air-gap is increased in an induction motor:

1. Bearing friction will reduce
2. The power factor will be low
3. Copper loss will be reduced in an induction motor
4. Windage losses will be more

Correct answer: 2. The power factor will be low

In three-phase induction motor, the number of poles in the rotor winding is always

In three-phase induction motor, the number of poles in the rotor winding is always:

1. More than the number of poles in stator
2. Less than number of poles in stator
3. Equal to number of poles in stator
4. Zero

Correct answer: 3. Equal to number of poles in stator