Polyphase Induction Motors MCQs

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Correct options are highlighted when revealed.

1.What is the effect of adding resistance to the stator winding of an induction motor?

Raises the torque required by the loadReduces the motor's starting torqueEnhances the initial torque at startupHas no impact on motor performance

2.How can the starting torque of a three-phase induction motor be enhanced?

By increasing the slipBy raising the currentBy increasing both slip and currentNone of these

3.At what speed does the rotor of an induction motor operate?

At synchronous speedSlightly less than synchronous speedFaster than synchronous speedCan be any speed

4.In a star-delta starter used for an induction motor, what is the voltage applied to each stator phase relative to the line voltage?

A resistor is added in series with the stator windingThe stator receives a voltage lower than the rated valueA resistor is connected in the rotor circuitEach stator phase is supplied with 57.7% of the line voltageThe motor is started with full line voltage applied directly

5.In which situation is a slip ring motor favored over a squirrel cage induction motor?

When a high starting torque is necessaryWhen the load torque is substantialWhen a strong pull-out torque is neededIn all of the above cases

6.Which types of motors can utilize a reduced voltage starter?

Only slip ring motors, excluding squirrel cage induction motorsExclusively squirrel cage induction motors, not slip ring motorsBoth squirrel cage and slip ring induction motorsNone of the mentioned options

7.In which situation is a squirrel cage induction motor generally not chosen?

When minimizing the initial investment is the priorityWhen the goal is to reduce upkeep expensesWhen a high starting torque is critically requiredWhen all the above factors are important

8.Which type of induction motor generally requires the least maintenance?

Slip ring induction motorSquirrel cage induction motorBoth slip ring and squirrel cage motorsNeither of the above

9.In a squirrel cage induction motor, the induced electromotive force (e.m.f.) in the rotor is equal to which of the following?

It varies according to the mechanical load on the shaftIt depends on how many slots the rotor hasIt equals the slip multiplied by the rotor's standstill e.m.f.None of these options are correct

10.What is the main function of employing short-circuit gear in a motor?

To create a short circuit across the rotor via the slip ringsTo bypass the starting resistors within the starter circuitTo connect the stator windings in a star configuration by short-circuiting phasesNone of the above

11.How is the temperature of the stator winding in a three-phase induction motor measured?

Using the resistance increase techniqueBy employing a thermometerThrough embedded temperature sensorsBy utilizing all of the above methods

12.Which type of induction motor is most suitable for operating loads with high inertia?

Slip ring induction motorSquirrel cage induction motorEither slip ring or squirrel cage motorNeither slip ring nor squirrel cage motor

13.What happens to the rotor current in an induction motor when resistance is added to the rotor circuit while producing a specific torque?

14.What is the effect of adding reactance to the rotor circuit?

It lowers both the starting torque and the peak torque.It raises both the starting torque and the peak torque.It boosts starting torque, while the peak torque stays the same.It enhances starting torque, but the peak torque reduces.

15.Under what condition can an induction motor operate at synchronous speed?

When it is operating under loadWhen it runs in the opposite directionWhen supplied with voltage exceeding its rated valueWhen an electromotive force is applied to the rotor windingWhen the stator winding is disconnected

16.What causes the low power factor in an induction motor?

Leakage reactance in the rotorReactance present in the stator windingsLagging magnetizing current required to produce the magnetic fieldAll of the above factors

17.In an induction motor, the percentage slip is influenced by which of the following?

The frequency of the power supplyThe voltage supplied to the motorThe copper losses occurring within the motorNone of these

18.Given that R2 represents the rotor resistance, X2 is the rotor reactance at the supply frequency, and s denotes the slip, what is the condition for achieving maximum torque during operation?

s multiplied by R2 and X2 equals 1The product of slip and rotor resistance equals rotor reactanceRotor resistance is equal to slip times rotor reactanceRotor resistance equals slip squared multiplied by rotor reactanceNone of the above

19.In a double cage induction motor, what are the characteristics of the inner cage?

High inductance and low resistanceLow inductance combined with high resistanceLow inductance and low resistanceHigh inductance along with high resistanceNone of the above

20.What happens to the power factor of an induction motor when the air gap is increased?

The power factor decreasesWindage losses increaseBearing friction decreasesCopper losses decrease