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Polyphase Induction Motors

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1Electrical EngineeringMedium

A 3-phase induction motor delta connected is carrying too heavy load and one of its fuses blows out. Then the motor________?

Awill continue running without any harm to the winding

Bwill stop and carry heavy current causing permanent damage to its winding

Cwill continue running burning its one phase

Dwill continue running burning its two phase

Correct answer

B. will stop and carry heavy current causing permanent damage to its winding

Explanation

The correct answer is will stop and carry heavy current causing permanent damage to its winding.

2Electrical EngineeringMedium

A pump induction motor is switched on to a supply 30% lower than its rated voltage. The pump runs. What will eventually happen? It will________?

Aget heated and subsequently get damaged

Bstall immediately

Ccontinue to run at lower speed without damage

Dstall after sometime

Correct answer

A. get heated and subsequently get damaged

Explanation

The correct answer is get heated and subsequently get damaged.

3Electrical EngineeringMedium

The term ‘cogging’ is associated with________?

AD.C. series motors

Binduction motors

Ccompound generators

Dthree phase transformers

Correct answer

B. induction motors

Explanation

The correct answer is induction motors.

4Electrical EngineeringMedium

Less maintenance troubles are experienced in case of________?

Aboth A. and (b)

Bsquirrel cage induction motor

Cslip ring induction motor

Dnone of the above

Correct answer

B. squirrel cage induction motor

Explanation

The correct answer is squirrel cage induction motor.

5Electrical EngineeringMedium

Reduced voltage starter can be used with________?

Anone of the above

Bsquirrel cage as well as slip ring induction motor

Csquirrel cage induction motor only but not with slip ring motor

Dslip ring motor only but not with squirrel cage induction motor

Correct answer

B. squirrel cage as well as slip ring induction motor

Explanation

The correct answer is squirrel cage as well as slip ring induction motor.

6Electrical EngineeringMedium

The speed of a squirrel-cage induction motor can be controlled by all of the following except________?

Achanging supply frequency

Breducing supply voltage

Cchanging number of poles

Dchanging winding resistance

Correct answer

D. changing winding resistance

Explanation

The correct answer is changing winding resistance.

7Electrical EngineeringMedium

Short-circuit test on an induction motor cannot be used to determine________?

Awindage losses

Bpower scale of circle diagram

Ctransformation ratio

Dcopper losses

Correct answer

A. windage losses

Explanation

The correct answer is windage losses.

8Electrical EngineeringMedium

The power factor of an induction motor under no-load conditions will be closer to________?

A0.2 lagging

Bunity

C0.2 leading

D0.5 leading

Correct answer

A. 0.2 lagging

Explanation

The correct answer is 0.2 lagging.

9Electrical EngineeringMedium

Which of the following methods is easily applicable to control the speed of the squirrel-cage induction motor ________?

ABy changing the number of stator poles

BRotor rheostat control

CBy injecting e.m.f. in the rotor circuit

DBy operating two motors in cascade

Correct answer

A. By changing the number of stator poles

Explanation

The correct answer is By changing the number of stator poles.

10Electrical EngineeringMedium

A 3-phase induction motor stator delta connected, is carrying full load and one of its fuses blows out. Then the motor________?

Awill stop and carry heavy current causing permanent damage to its winding

Bwill continue running burning its two phases

Cwill continue running without any harm to the winding

Dwill continue running burning its one phase

Correct answer

D. will continue running burning its one phase

Explanation

The correct answer is will continue running burning its one phase.

A 3-phase induction motor delta connected is carrying too heavy load and one of its fuses blows out. Then the motor________?

Awill continue running without any harm to the winding

Bwill stop and carry heavy current causing permanent damage to its winding

Cwill continue running burning its one phase

Dwill continue running burning its two phase

Correct answer

B. will stop and carry heavy current causing permanent damage to its winding

Explanation

The correct answer is will stop and carry heavy current causing permanent damage to its winding.

Reduced voltage starter can be used with________?

Anone of the above

Bsquirrel cage as well as slip ring induction motor

Csquirrel cage induction motor only but not with slip ring motor

Dslip ring motor only but not with squirrel cage induction motor

Correct answer

B. squirrel cage as well as slip ring induction motor

Explanation

The correct answer is squirrel cage as well as slip ring induction motor.

A 3-phase induction motor stator delta connected, is carrying full load and one of its fuses blows out. Then the motor________?

Awill stop and carry heavy current causing permanent damage to its winding

Bwill continue running burning its two phases

Cwill continue running without any harm to the winding

Dwill continue running burning its one phase

Correct answer

D. will continue running burning its one phase

Explanation

The correct answer is will continue running burning its one phase.