300 Important Three Phase Induction Motor MCQ Question and Answer | PDF Free Download
1.At the instant of starting, the per unit slip of the 3-phase induction motor is
- A0.05
- B0.1
- C1.0
- D0.5
2.The mmf produced by the current of a 3-phase induction motor
- ARotates ate the speed of rotor in the air gap
- BIs standstill with respect to stator mmf
- CRotates at slip speed with respect to stator mmf
- DRotates at synchronous speed with respect to rotor
3.The mmf produced by the rotor currents of a 3-phase induction motor
- ARotates at the speed of rotor in the air gap
- BIs stand still with respect to stator mmf
- CRotates at slip speed with respect to stator mmf
- DRotates at synchronous speed with respect rotor
4.In an induction motor, the slip will be negative when
- AStator magnetic field and rotor rotate in opposite direction
- BRotor rotates at a speed less than synchronous speed and in the direction of rotation of stator field
- CRotor rotates at a speed more than synchronous speed and in the direction of rotation of stator field
- DNone of the above
5.A 3- phase induction motor is operating at slip s. If its two supply leads are interchanged then its slip at that instant will be
- A2-s
- B2+s
- C1+s
- DA-s
6.What is the frequency of rotor current of a 50 Hz induction motor operating at 2% Slip?
- A1Hz
- B100 Hz
- C2Hz
- D50 Hz
7. The frequency of rotor current at stand still is equal to
- AZero
- B2f
- Cf
- Dsf
8.In a slip ring induction motor, the frequency of rotor currents can be measured with a
- AGalvanometer
- BWattmeter
- CDC moving coil milli voltmeter
- DNone of the above
9.A 3- phase star connected induction motor is connected to 400V, 50 Hz ac supply. If the stator to rotor turn ratio is 2, the stand still rotor induced emf per phase is
- A115.5V
- B231 V
- C346.6 V
- D200 V
10.In a 3-phase 50 Hz induction motor the voltage between the slip rings at standstill is 50V At full load the slip is 0.04. The voltage between slip rings at full load is
- A50 V
- B2 V
- C20 V
- D5 V
11.The direction of rotor current produced in an induction motor can be determined by
- ALen?s law
- BInduction law
- CFleming?s right hand rule
- DFleming?s left-hand rule
12.In case of an induction motor the leakage, flux is more in comparison to that of a transformer. This is due to
- ARevolving rotor
- BAir gap between rotor and stator
- CHigher flux densities in induction motor
- DNone of the above
13.In an induction motor the phase reactance is _____in comparison to phase resistance.
- AQuite high
- BVery small
- CSlightly high
- DAlmost same
14.In a 3- phase induction motor reactance under running condition is less than as standstill value. This is due to reduction in
- ARotor inductance
- BStator magnetic flux
- CFrequency of rotor emf
- DMutual flux linking the stator and rotor
15.In an induction motor under running condition, the rotor reactance per phase is _______its standstill phase reactance.
- AS times
- Bequal to
- C1/s times
- D(1-s) times
16.Insertion of resistance in the rotor circuit of an induction motor to develop a given torque causes ____its rotor current.
- AAlmost no change
- BIncrease
- CDecease
- DNone of these
17.In an induction motor if the flux density is reduced to one half of its normal value then the torque will
- AReduce to one half
- BReduce to one fourth
- CRemain unchanged
- DIncrease for times
18.The starting torque of a squirrel cage induction motor is
- AVery large
- BVery low
- CSlightly more than full load torque
- DZero
19.For achieving high starting torque and high operation efficiency an induction motor should have _____rotor circuit resistance at starting and ____circuit resistance under operating conditions.
- AHigh, Low
- BLow, High
- CHigh, High
- DLow, Low
20.In a 3-phase slip ring induction motor, high stating torque is achieved by
- AIncreasing supply voltage V
- BIncreasing supply frequency f
- CConnecting a capacitor across the motor terminals
- DConnecting a star connected resistance across the slip ring terminals of the motor