300 Important Three Phase Induction Motor MCQ Question and Answer | PDF Free Download
1.When the applied voltage per phase is reduced to one half, the starting torque of a three-phase squirrel cage induction motor becomes
- A1/2 of the initial value
- B1/4 of the initial value
- CTwice of the initial value
- D4 times of the initial value
2.In a 3-phase induction motor the maximum torque
- AIs independent of rotor circuit resistance
- BVaries as rotor resistance
- CVaries as the square of rotor resistance
- DVaries inversely as rotor circuit resistance
3.For a slip ring induction motor, if the rotor resistance is increased then
- AStarting torque and efficiency increase
- BStarting torque decreases but efficiency increases
- CStarting torque increases but efficiency decreases
- DStarting torque and efficiency decrease
4.An induction motor has a rotor resistance of 0.002 ohm/ phase. If the resistance is increased to 0.004 ohm/phase then the maximum torque will
- AReduce to half
- BIncrease by 100%
- CIncrease by 200%
- DRemain unaltered
5.Breakdown torque of a 3-phase induction motor of negligible stator impedance is
- ADirectly proportional to the rotor resistance
- BInversely proportional to the rotor resistance
- CDirectly proportional to the reactance
- DInversely proportional to the rotor leakage reactance
6.A 4-pole, 50 Hz, 3-phase induction motor has blocked rotor reactance per phase which is four times the rotor resistance per phase. The speed at which maximum torque develops is
- A1,125 rpm
- B1,500 rpm
- C1,050 rpm
- D1,210 rpm
7.If the rotor circuit resistance is increased in an induction motor, the maximum torque will occur at
- ALower speed
- BHigh speed
- CThe same speed
- DNone of these
8.Beyond the point of maximum torque any further increase in loads will cause
- AIncrease in torque developed and so the motor will run at a high speed
- BNo change in the torque developed and so the motor will run at the same speed as before
- CDecease in torque developed and the motor will slow down
- DIncrease in current drawn from the supply mains resulting in damage to it
9.The torque-slip characteristic of a poly phase induction motor becomes almost linear at small values of slip, because in this range of slips
- AThe effective rotor circuit resistance is very large compared to the rotor reactance
- BThe rotor resistance is equal to the stator resistance
- CThe rotor resistance is equal to the rotor reactance
- DThe rotor resistance is equal to the stator reactance
10.The torque-slip characteristic of an induction motor is approximately a
- AStraight line
- BRectangular parabola
- CParabola
- DHyperbola
11.Stable operation of an induction motor is
- ABetween zero slip and unity slip
- BBetween 0.5 slip and 0.95 slip
- CBetween zero slip and slip corresponding to maximum torque
- DBetween slip corresponding to maximum torque and unity slip
12.With the increase in load on a squirrel cage induction motor
- AStator current increase
- BPower factor improves
- CSlip increase and The torque developed by the motor increases till it becomes equal to the load torque
- DAll of the above
13.Whenever poly phase induction motor is loaded
- AMotor speed decreases
- BStator flux cuts the rotor bars more rapidly
- CEmf induced in the rotor as well as its frequency increases and also Current in rotor bars increases
- DAll of the above
14.The losses that occur in an induction motor are
- AStator iron loss
- BRotor copper loss
- CWindage and friction losses
- DAll of the above
15.In a 3-phase induction motor iron loss mainly occurs in
- AStator and rotor
- BRotor core and rotor teeth
- CStator core and stator teeth
- DStator winding
16.Iron loss in the rotor of a 3-phhase induction motor is negligible. This is due to
- AVery low frequency of emf induced in the rotor
- BVery low emf induced in the rotor
- CVery low flux density in rotor parts
- DConstant magnitude of flux linking the rotor core
17.Rotor input of a three-phase induction motor is equal to
- AInput to motor - stator copper and iron losses
- BMechanical power developed - windage and friction losses
- CInput to motor ? windage and friction losses
- DInput to motor - stator iron losses - windage and friction losses
18.In an induction motor, what is the ratio of rotor copper loss and rotor input?
- A1/s
- BS
- C(1-s)
- Ds/(1-s)
19.The rotor power output of a 3-phase induction motor is 15 kW The rotor copper losses at a slip of 4% will be
- A600W
- B625W
- C650W
- D700W
20.The synchronous watt is
- AThe torque which under synchronous speed would develop a power of 1 watt or power of 1 watt or power input to rotor in watts
- BShaft output in watts
- CInput power to stator
- DThe unit of ratings of synchronous machines