# Induction Motors MCQs

The induction motor (IM) is the most commonly used motor in modern electrical industries. Today Electrical Engineering XYZ shares MCQs on IM.

## An Induction motor is turning at 1200 rpm, the frequency is 60 Hz. The number of poles are

1. An Induction motor is turning at 1200 rpm, the frequency is 60 Hz. The number of poles are:

1. 2 poles
2. 4 poles
3. 6 poles
4. 8 poles

Explanation: From formula, P = 120 * f / Speed, P = 120 * 60 / 1200 = 6

## The correct statement about the induction motor (IM)

2. The correct statement about the induction motor (IM):

1. It requires no dc field current
2. It requires only one dc field current
3. It requires multiple dc field currents
4. None of them is correct

Correct answer: 1. It requires no dc field current

## Crawling is a phenomenon associated with squirrel cage design in which IM runs at a very slow speed, this phenomenon occurs due to

3. Crawling is a phenomenon associated with squirrel cage design in which IM runs at a very slow speed, this phenomenon occurs due to:

1. Low voltage
2. Heavy loads connected to rotor
3. Bad mechanical design of the machine
4. Harmonics

## Fractional slip can be expressed by the equation

4. Fractional slip can be expressed by the equation:

1. Rotor’s copper loss / Rotor’s input
2. Rotor’s copper loss / Rotor’s output
3. Stator’s copper loss / Stators input
4. Stator’s copper loss / Stators input

Correct answer: 1. Rotor’s copper loss / Rotor’s input

## A single phase motor is running slower than its original speed, the most obvious case which happened can be

5. A single phase motor is running slower than its original speed, the most obvious case which happened can be:

1. Winding is open
2. Winding is short
3. Bearings are warm
4. All are possible

Correct answer: 3. Bearings are warm

## The motor which has high starting torque

6. The motor which has high starting torque:

1. Squirrel cage induction motor
2. Slip ring induction motor

Correct answer: 2. Slip ring induction motor

## The synchronous speed of a 4 pole machine operated at 50 Hz is

7. The synchronous speed of a 4 pole machine operated at 50 Hz is:

1. 200 r/min
2. 1500 r/min
3. 10,000 r/min
4. 50 r/min

Synchronous speed = 120 *f/P = 120 * 50 / 4 = 1500 R/min

## Commonly, the power factor of a single phase induction motor is

8. Commonly, the power factor of a single phase induction motor is:

2. Lagging
3. Unity

## Which of the following Starting methods has the lowest starting torque associated with it

9. Which of the following method Starting methods has the lowest starting torque associated with it:

1. ATL
2. Auto-transformer
3. Wye-delta
4. All have equal

## The statement VFDs never use electronic components is

10. The statement VFDs never use electronic components is:

1. True
2. False