Induction Motor MCQs part 5

Contents

- 1 For induction motor the relation among synchronous speed (Ns), rotor speed (N) and slip (s) is given by
- 2 The rotor output of an induction motor running at slip s is expressed mathematically in the form
- 3 The synchronous speed of a 3-phase induction motor having 10 poles and connected to a 50 Hz source AC source is
- 4 Compared to squirrel cage motors, the wound rotor motors are used less extensively because
- 5 The number of rotor bars in squirrel cage induction motor are generally
- 6 An induction motor is favored over a DC motor for the reason being
- 7 The operation of induction motor is based on which of the following machinery principles
- 8 The ratio of rotor copper losses to rotor input in an induction motor is given by
- 9 What is value of slip of three phase induction motor at no-load
- 10 The rotor of three-phase wound rotor induction motor is loaded with

## For induction motor the relation among synchronous speed (Ns), rotor speed (N) and slip (s) is given by

For induction motor the relation among synchronous speed (Ns), rotor speed (N) and slip (s) is given by:

- N = (s – I) Ns
- N = ( I +s) N
- N = sNs
- N = (l – s)Ns

Correct answer: 4. N = (l – s)Ns

## The rotor output of an induction motor running at slip s is expressed mathematically in the form

The rotor output of an induction motor running at slip s is expressed mathematically in the form:

- s * rotor input
- (1 – s) * rotor input
- (1 + s) * rotor input
- (1 – s) * (1 + s) * rotor input

Correct answer: 1. s * rotor input

## The synchronous speed of a 3-phase induction motor having 10 poles and connected to a 50 Hz source AC source is

The synchronous speed of a 3-phase induction motor having 10 poles and connected to a 50 Hz source AC source is:

- 300 RPM
- 600 RPM
- 1200 RPM
- 2400 RPM

Correct answer: 2. 600 RPM

Explanation: Speed = 120 * f/P = 120 * 50/10 = 600 RPM

## Compared to squirrel cage motors, the wound rotor motors are used less extensively because

Compared to squirrel cage motors, the wound rotor motors are used less extensively because:

- They always require slip rings on the rotor circuit
- Rotor windings are generally y-connected
- They are costly as well as they require greater maintenance
- None of the above

Correct answer: 3. They are costly as well as they require greater maintenance

## The number of rotor bars in squirrel cage induction motor are generally

The number of rotor bars in squirrel cage induction motor are generally:

- Equal to stator poles
- An even number
- A prime number
- None of these

Correct answer: 3. A prime number

## An induction motor is favored over a DC motor for the reason being

An induction motor is favored over a DC motor for the reason being:

- Provides fine speed control
- Provides high starting torque
- Is simple and rugged in construction
- None of these

Correct answer: 3. Is simple and rugged in construction

## The operation of induction motor is based on which of the following machinery principles

The operation of induction motor is based on which of the following machinery principles:

- Ampere’s law
- Lenz’s law
- Principle of self-induction
- Principle of mutual induction

Correct answer: 4. Principle of mutual induction

## The ratio of rotor copper losses to rotor input in an induction motor is given by

The ratio of rotor copper losses to rotor input in an induction motor is given by:

- 1/s
- s
- 1-s
- 1/(1-s)

Correct answer: 2. s

## What is value of slip of three phase induction motor at no-load

What is value of slip of three phase induction motor at no-load

- Practically zero
- 0.4
- 0.525
- 1

Correct answer: 1. Practically zero

## The rotor of three-phase wound rotor induction motor is loaded with

The rotor of three phase wound rotor induction motor is loaded with:

- Single phase winding
- Three phase winding
- Copper bars
- Squirrel cage induction rotor with bars tilted at 45 degrees

Correct answer: 2. Three phase winding