Induction Motor MCQs Part 19

Induction Motor MCQs Part 19

At starting of double squirrel cage induction motor

At starting of double squirrel cage induction motor:

1. Low winding is more effective
2. Low cage winding has low reactance
3. Outer cage winding has good power factor
4. None of these

Correct answer: 3. Outer cage winding has good power factor

A 3 phase, 6 pole induction motor is connected to 25 Hz supply and at full-load, the rotor EMF makes 120 complete cycles in 2 minutes. The full load percentage slip is

A 3 phase, 6 pole induction motor is connected to 25 Hz supply and at full-load, the rotor EMF makes 120 complete cycles in 2 minutes. The full load percentage slip is:

1. 1%
2. 2%
3. 3%
4. 4%

Correct answer: 4. 4%

Explanation:

Frequency of rotor EMF (f’) = 120/(2 * 60) = 1 Hz

f’ = sf or s = f’/f = 1/25 = 0.04 = 4%

A 3-phase, 6-pole, 60 Hz induction motor delivers 3.8 kW @ 930 RPM. What is stator input if stator loss is 250 W

A 3-phase, 6-pole, 60 Hz induction motor delivers 3.8 kW @ 930 RPM. What is stator input if stator loss is 250 W

1. 5153 W
2. 9288 W
3. 10528 W
4. 26899 W

Correct answer: 1. 5153 W

Solution:

Ns = 120 f/P = 120 * 60/6 = 1200 RPM

N = 930 RPM

———————

Rotor output/Rotor input = N/Ns

Rotor input = Ns/N * Rotor output

Rotor input = 1200/930 * 3800 = 4903 W

———————

Rotor input = Stator output = 4903 W

Stator input = Stator output + Stator losses = 4903 + 250 = 5153 W

The slip in an induction motor depends on

The slip in an induction motor depends on:

1. Rotor input power
2. Supply frequency
3. Rotor copper losses
4. Rotor input power and rotor copper losses

Correct answer: 4. Rotor input power and rotor copper losses

Explanation: Slip (s) = Rotor Cu loss/Rotor input power

The shaft of an induction motor is made of

The shaft of an induction motor is made of

1. Aluminum
2. Carbon steel
3. Cast iron
4. Stainless steel

Correct answer: 2. Carbon steel