# Induction Motor MCQs with Answers Page-3

Induction Motor MCQs with answers:Following Multiple Choice Questions (MCQs) are based on “Three-Phase Induction Motor”. These are related with subject Electrical Machines or Basic Electrical Engineering.

Topics: torque-speed characteristics, speed control and braking of Induction motor.

This topic is mostly beneficial in the field of Electronics, Electrical and Mechanical Engineering.

These MCQs will be useful in various competitive examinations, entrance examinations, oral examination (Viva voce), certifications and interviews.

## MCQ on Induction Motor

##### Que.1 The power factor of squirrel cage induction motor is low at
1. heavy loads only
2. light loads only
3. rated loads only
4. light and heavy loads both

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#### Option 2: light loads only

##### Que.2 The starting torque of a 3-phase induction motor is __________ supply voltage.
1. inversely proportional to
2. directly proportional to square of
3. independent of
4. directly proportion to

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#### Option 2: directly proportional to square of

##### Que.3 The torque developed by a 3-phase induction motor depends on the following three factors
1. rotor emf, rotor current and rotor p.f.
2. voltage, current and frequency
3. synchronous speed, rotor speed and frequency
4. speed, current and stator poles

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#### Option 1: rotor emf, rotor current and rotor p.f.

Explanation:
Torque depends on
E2 = emf induced in rotor winding at standstill
s =per unit slip
f = supply frequency in Hz
X2 =standstill rotor reactance per phase
a = (R2 = rotor resistance per phase)
##### Que.4______ is the maximum torque that an AC motor develops with rated voltage applied at rated frequency without causingsudden drops in speed.
1. Breakdown torque
2. Pull-up torque
3. Locked rotor torque
4. Normal starting torque

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#### Option 1: Breakdown torque

##### Que.5 The starting torque of 3-phase induction motor can be increased by
1. Increasing slip
2. Increasing current
3. Both 1 and 2
4. None of the above

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#### Option 3: Both 1 and 2

##### Que.6 For regerative braking, the phase angle between stator phase voltage and the stator phase current should be _______
1. less than 90 degree.
2. greater than 90 degree.
3. equal to 90 degree.
4. equal to zero degree.

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#### Option 2: greater than 90 degree.

Explanation:
When the speed of the 3-phase induction motor is more than the synchronous speed, relative speed between the motor conductors and air gap rotating field reverses, as a result the phase angle because greater than 90o and the power flow reverse and thus regenerative braking takes place.
##### Que.7 ______ of induction motor is obtained when the motor is made to run on a single phase supply by disconnecting any one of the three phase from the source, and it is either left open or it is connected with another phase.
1. AC dynamic breaking
2. Self excited braking using capacitors
3. DC dynamic braking
4. Zero Sequence braking

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#### Option 1: AC dynamic breaking

##### Que.8 Identify the correct statement in case of braking of induction motor.
1. Plugging induction motor braking is done by reversing the phase sequence of the motor.
2. Plugging braking of induction motor is done by interchanging connections of any two phases of stator with respect of supply terminals.
3. Both above statements are correct.
4. Both statement 1 and 2 are incorrect.

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#### Option 3: Both above statements are correct.

##### Que.9 In _______ the capacitors are kept permanently connected across the source terminals of the induction motor.
1. AC dynamic breaking
2. Self excited braking
3. DC dynamic braking
4. Plugging

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#### Option 2: Self excited braking

##### Que.10 Identify the braking of induction motor from following diagram.
1. Plugging braking of induction motor
2. AC dynamic breaking
3. DC dynamic braking
4. Zero Sequence braking

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