Induction Motor MCQs Part 7

Contents

- 1 The speed of the rotating flux of a 3-phase, 4 pole induction motor having 50 Hz supply will be
- 2 3-phase wound rotor motors are sometimes also referred as
- 3 A wound rotor motor is used in practical applications that require
- 4 The maximum voltage is induced in the rotor of a 3-phase induction motor for which of following condition
- 5 Under running conditions, the maximum torque of a 3-phase induction motor is
- 6 The approximate efficiency of a 3-phase induction motor running at slip s (in decimal) is given by
- 7 Design Engineers manufacture 3 phase induction motor is such a way that under running conditions the rotor should have
- 8 In a wound rotor motor, the rotor winding is wound for poles that are ________ that of stator winding
- 9 If a 3-phase, 4 pole, 50 Hz induction motor is at standstill position, what is value of rotor frequency
- 10 When an induction motor is running at full load, its rotor reactance is __________ rotor resistance

## The speed of the rotating flux of a 3-phase, 4 pole induction motor having 50 Hz supply will be

The speed of the rotating flux of a 3-phase, 4 pole induction motor having 50 Hz supply will be:

- 1500 RPM
- 1000 RPM
- 750 RPM
- 3000 RPM

Correct answer: 1. 1500 RPM

Solution: Rotating flux Speed = 120*f/P = 120*50/4 = 1500 RPM

## 3-phase wound rotor motors are sometimes also referred as

3-phase wound rotor motors are sometimes also referred as:

- Synchronous
- Series
- Commutator
- Slip ring

Correct answer: 4. Slip ring

## A wound rotor motor is used in practical applications that require

A wound rotor motor is used in practical applications that require:

- Less costly motor is not required
- High rotor resistance is required during
- High starting torque is required
- Speed control is required

Correct answer: 3. High starting torque is required

## The maximum voltage is induced in the rotor of a 3-phase induction motor for which of following condition

The maximum voltage is induced in the rotor of a 3-phase induction motor for which of following condition:

- When it is blocked
- When it runs at no load
- When it runs at full load
- None of the above

Correct answer: 1. When it is blocked

## Under running conditions, the maximum torque of a 3-phase induction motor is

Under running conditions, the maximum torque of a 3-phase induction motor is:

- Inversely proportional to supply voltage
- Directly proportional to rotor resistance
- Inversely proportional to rotor reactance at standstill
- None of the above

Correct answer: 3. Inversely proportional to rotor reactance at standstill

## The approximate efficiency of a 3-phase induction motor running at slip s (in decimal) is given by

The approximate efficiency of a 3-phase induction motor running at slip s (in decimal) is given by:

- 1-s
- 1+s
- s-1
- s^2

Correct answer: 1. 1-s

## Design Engineers manufacture 3 phase induction motor is such a way that under running conditions the rotor should have

Design Engineers manufacture 3 phase induction motor is such a way that under running conditions the rotor should have:

- High resistance
- High reactance
- Low resistance
- Large slip

Correct answer: 3. Low resistance

## In a wound rotor motor, the rotor winding is wound for poles that are ________ that of stator winding

In a wound rotor motor, the rotor winding is wound for poles that are ________ that of stator winding:

- Greater than
- Small than
- Equal to
- None of these

Correct answer: 3. Equal to

## If a 3-phase, 4 pole, 50 Hz induction motor is at standstill position, what is value of rotor frequency

If a 3-phase, 4 pole, 50 Hz induction motor is at standstill position, what is value of rotor frequency:

- Zero
- 25 Hz
- 50 Hz
- Anywhere between 10 and 50 Hz

Correct answer: 3. 50 Hz

Solution: Speed of magnetic field = 120*f/P = 120*50/4 = 1500 RPM

Slip Speed = Speed of magnetic field â Mechanical shaft speed = 1500 â 0 = 1500

Slip = Slip speed/Speed of magnetic fields *100% = 1500/1500*100 = 100% = 1

Rotor frequency (fâ) = sf = 1 * 50 Hz = 50 Hz

## When an induction motor is running at full load, its rotor reactance is __________ rotor resistance

When an induction motor is running at full load, its rotor reactance is __________ rotor resistance:

- Comparable to
- Very large as compared to
- Large compared to
- Very small

Correct answer: 1. Comparable to