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MCQs 1: Slip of a induction motor will be zero,

At start When machine is rotating at its maximum speed When it is rotating at half of the maximum speed Cannot be zero
Answer Explanation

MCQs 2: A 4 pole, 3 phase, 50 Hz star connected induction motor has a full load slip of 5%. Then full load speed of the motor is

1500 1400 1405 1425
Answer Explanation

MCQs 3: A 50 Hz, 3 phase slip ring induction motor, has 6 poles on stator and 4 poles on rotor. Then the machine will run at

1000 rpm 1500 rpm 1400 rpm Machine will not run at all
Answer Explanation

MCQs 4: A 3 phase, 50 Hz squirrel cage induction motor, has 6 poles on stator and 4 poles on rotor. Then the machine will run at

1000 rpm 1500 rpm 1750 rpm Machine will not run
Answer Explanation

MCQs 5: The rotor frequency of a three phase induction motor is

Slip times the supply frequency 1 / slip times the supply frequency Equal to the supply frequency None of these
Answer Explanation

MCQs 6: The rotor resistance per phase on standstill and rotor reactance per phase on standstill of induction motor is

Slip times the rotor resistance at standstill and slip times rotor reactance at standstill Same as rotor resistance at standstill and slip times rotor reactance at standstill Same as rotor resistance at standstill and same as rotor reactance at standstill Slip times the rotor resistance at standstill and same as rotor reactance at standstill
Answer Explanation

MCQs 7: Nature of the rotor power factor in running condition is always

Leading Lagging Both (a) and (b) None of these
Answer Explanation

MCQs 8: If a voltmeter when connected to the rotor of an induction motor gives 150 oscillations per minute and stator frequency is 50 Hz. Then the slip of induction motor will be

3% 4.5% 5% 5.5%
Answer Explanation

MCQs 9: For a three phase induction motor, the two rotor frequencies are given by

sf, (1 - s) f sf, (2 - s) f (1 - s) f, (2 - s) f Sf , sf
Answer Explanation

MCQs 10: The torque produced in the induction motor depends on the following factors 1. The part of rotating magnetic field which reacts with rotor and is responsible for producing emf. 2. The magnitude of rotor current in running condition. 3. The power factor of the rotor circuit in running condition. Which of the above statement is true?

Only 1 1 & 2 2 & 3 1, 2 and 3
Answer Explanation

MCQs 11: The torque produced in a three phase induction motor is

Directly proportional to the square of the induced emf in rotor Directly proportional to the induced emf in rotor Inversely proportional to the square of the induced emf in rotor Inversely proportional to the induced emf in rotor
Answer Explanation

MCQs 12: For maximum torque, the only parameter which controls the torque is slip. The maximum torque is

directly proportional to the rotor resistance inversely proportional to the rotor resistance directly proportional to the slip times the rotor resistance independent of the rotor resistance
Answer Explanation

MCQs 13: When the torque produced by the induction motor is at its maximum, the slip is given by

X2 / R2 (R2 + X2) / X2 R2 / X2 R2 / (R2 + X2)
Answer Explanation

MCQs 14: A 400v, 4 pole, 3 phase, 50 Hz star connected induction motor has a rotor resistance and reactance per phase equal to 0.02 ohm and 0.2 ohm respectively. Then the slip at which maximum torque occurs and the corresponding maximum torque is (assuming stator to rotor turns ratio as 6)

10%, 159.08 N - m 20%, 318.16 N - m 11%, 159.08 N - m 10%, 318.16 N - m
Answer Explanation

MCQs 15: When an induction motor is loaded from no load to full load, its speed and slip

Increases, decreases Decreases, increases Both increases Both decreases
Answer Explanation

MCQs 16: An induction motor when loaded from no load to full load, its slip also varies from s = 1 to s = 0. Then the torques in the low slip region and in high slip region is

Both are directly proportional to the slip Both are inversely proportional to the slip Directly proportional to the slip, inversely proportional to the slip Independent of slip, proportional to the slip
Answer Explanation

MCQs 17: The curve obtained by plotting torque against slip from s = 1 to s = 0 is called torque slip characteristics. The nature of the graph in the low slip region and in the high slip region is

Rising exponential, decaying exponential Both will be straight line Straight line, rectangular parabola Straight line, decaying exponential
Answer Explanation

MCQs 18: If an induction motor is operating at a point in the high slip region, then the motor will be

Stable Unstable Either stable or unstable depending on the torque None of these
Answer Explanation

MCQs 19: The value of slip for motoring, generating and braking region respectively are

S > 1, 0 = s = 1, s < 0 S < 0, 0 = s = 1, s > 1 0 = s = 1, s > 1, s < 1 0 = s = 1, s < 0, s > 1
Answer Explanation

MCQs 20: When the slip of an induction machine is negative, it is running as a

Motor Generator Synchronous machine None of these
Answer Explanation

MCQs 21: A 16 pole, 50 Hz, star connected three phase induction motor has rotor resistance of 0.012 ohm per phase and rotor reactance of 0.220 ohm per phase at standstill. Its full load torque is at speed of 220 rpm. Ratio of its starting torque to maximum torque is

0.1208 0.1087 0.1102 0.1012
Answer Explanation

MCQs 22: If the rotor resistance of an induction motor is doubled, keeping the other parameters constant, then the maximum torque of the induction motor will become

Double Halved One fourth Remains same
Answer Explanation

MCQs 23: “By adding external resistance to rotor till it becomes equal to rotor reactance, the maximum torque can be achieved at start”. This statement holds for

Slip ring induction motor Squirrel cage induction motor Both a and b Neither a nor b
Answer Explanation

MCQs 24: A 4 pole, 50 Hz, wound rotor inductor is supplied at rated voltage and frequency with slip ring open circuited. If the rotor is driven by an external means at 1500 rpm opposite to the direction of stator field, the frequency of voltage across slip rings will be

50 Hz 80 Hz 100 Hz 0 Hz
Answer Explanation

MCQs 25: The approximate value of torque angle at which maximum pull out torque will occur under practical circumstances is

90 degree 75 degree 60 degree 30 degree
Answer Explanation

MCQs 26: For slip s of an induction motor, the ratio of rotor copper loss to the gross mechanical output is

1 / ( 1 - s) 1 / s ( 1 - s ) / s s / ( 1 - s )
Answer Explanation

MCQs 27: While delivering an useful power of 20 kW to the full load, a 3 phase, 50 Hz, 6 pole induction motor draws a line current of 50 A. it is connected to supply of 420 V and runs at a speed of 950 rpm. If mechanical losses are 1000 W, then its rotor copper losses and shaft torque are

1105.26 W, 201.03 N-m 1125.26 W, 201.03 N-m 1105.26 W, 208.09 N-m 1125.26 W, 208.09 N-m
Answer Explanation

MCQs 28: A 4 pole, 25 kW, three phase, 420 V, 50 Hz induction motor operates at an efficiency of 90% with a power factor of 0.8 lagging. The current drawn by the motor from the mains is

42.89 A 45.56 A 47.73 A None of these
Answer Explanation

MCQs 29: In a three phase induction motor, the mechanical load should be such that the equivalent load resistance referred to stator is equal to the

Total leakage reactance of the motor referred to stator Total leakage reactance of the motor referred to rotor Total leakage impedance of the motor referred to stator Total leakage impedance of the motor referred to rotor
Answer Explanation

MCQs 30: When an induction motor is working under loaded condition, its induced voltage will

Leads the magnetic flux by 90 degree Lags the magnetic flux by 90 degree Lags the magnetic flux by 30 degree In phase with the magnetic flux
Answer Explanation

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