Electrical machines top questions

1➤ Which of the following machines do NOT use equalizer rings?

4-pole simplex wave-wound DC machine6-pole simplex lap-wound DC machine4-pole simplex lap-wound DC machine4-pole duplex wave-wound DC machine

2➤ A transformer is said to be an isolation transformer, if its primary to secondary ratio is equal to ______.

0.511.50

3➤ In case of alternators with single-layer concentric windings, the number of slots is equal to _______ the number of coils

quadtwicehalfthrice

4➤ If the number of poles is 4 and number of slots is 24 , then the pole pitch will be- .

12 slots 4 slots 8 slots6 slots

5➤ In a 3-phase induction motor, the difference between stator output and rotor gross output is:

Rotor Cu lossesStator Cu lossesStator iron lossesWindage and friction losses

6➤ DC generators are designed to develop armature voltages not exceeding 650 V because of the limitations of ________

armature windingcommutatorfield windingstarters

7➤ .The parts of the armature electric circuit which take active part in emf generation are _______ .

the commutator segmentsThe overhangsThe coil sides inside the slots both the coil sides inside the slots and the overhangs

8➤ For which of the following DC motors, is the typical field of application mentioned?

Series motor : Belt driveCompound motor : Fly wheel driveSeries motor : Machine toolsShunt motor : Electric

9➤ The exciting coils of any DC machine are wound ________ .

in the armature slotsin the machinearound the poles separately

10➤ An electric motor may give noise due to

cooling airdefective bearingmagnetic effectall the above

11➤ What is the effect produced by the electric current in an electric motor ?

Magnetic effect only magnetic as well as heating effectheating as well as chemical effectheating effect only

12➤ If the applied voltage to a transformer primary is increased by keeping the V/f ratio fixed, then the magnetizing current and the core loss will, respectively

Increases and decreasesBoth remains the sameRemains the same and increasesDecreases and remains the same

13➤ If a sinusoidal voltage source is connected to a power transformer, its no-load current would be

Rich in third harmonics and its fundamental would lag the voltage by 90° Sinusoidal and lagging the voltage by 900 B. Sinusoidal and lagging the voltage by less than 90°Rich in third harmonics and its fundamental would lag the voltage by less than 90°None of these

14➤ EMF induced in a coil rotating in a uniform magnetic field will be maximum when the

Rate of change of flux linkage is maximumRate of cutting flux by the coil sides is minimumRate of change of flux linkage is minimumFlux linking with the coil is maximum

15➤ In a DC motor, the windage loss is proportional to

Supply voltageSquare of flux densitySquare of the armature speedSquare of the supply voltage

16➤ Generally the no-load losses of an electrical machine is represented in its equivalent circuit by a

Series resistance with a high valueParallel resistance with a high valueSeries resistance with a low valueParallel resistance with a low value

17➤ Compared to the salient-pole hydroelectric generators, the steam and the gas turbine generators have cylindrical rotors for

Accommodating larger number terms in the field windingProviding higher mechanical strength against the centrifugal stressReducing the eddy-current losses in the rotorBetter air-circulation in the machine

18➤ The aircraft alternators are designed to generate emf of high frequency of 400 Hz in order to

All of the aboveMake the system free from external disturbancesCompensate for high speedReduce the bulk

19➤ In cylindrical rotor, ______ portion of rotor is wound.

one-thirdone-halftwo-thirdwhole

20➤ The squirrel cage induction motor are provided with blades in order to.

Eliminate noiseFacilitate cooling of rotorNone of theseBalancing the rotor dynamics

21➤ The mmf produced by the rotor currents of a 3-phase induction motor

Is at standstill with respect to stator mmf Rotates at slip speed with respect to stator mmfRotates at synchronous speed with respect to rotorRotates at the speed of rotor in the air gap

22➤ In an induction motor if the air gap is increased

Its speed will reduce Its sped will increaseIts power factor will reduceNone of the above

23➤ In case of traveling cranes, the motor preferred for boom hoist is A. B. C. D.

Squirrel cage induction motorSlip ring induction motor Synchronous motorSingle phase motor

24➤ Electronic soft starters are used for motors to____:

Improve the loadingNone of theseAchieve variable speedProvide smooth start and stop

25➤ For an induction motor the torque is proportional to the product of: A. B. C. D.

flux and currentCurrent and impedance of the motorCurrent and power factor of the motorCurrent and power factor of the motor and flux

26➤ For slip ring induction motors:

Maximum torque is constant Maximum torque is not related to slip Maximum torque is inversely proportional to slipMaximum torque is proportional to slip

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