300 Important Three Phase Induction Motor MCQ Question and Answer | PDF Free Download
1.The air gap flux density in an induction motor is usually kept low so as to
- AImprove efficiency
- BImprove power factor
- CReduce machine cost
- DNone of the above
2.A wound rotor induction motor can be distinguished from squirrel cage induction motor by
- APresence of slip rings
- BSize of frame
- CShaft diameter
- DAny of the above
3.For induction motors normally
- AThe stator winding is connected to ac supply and the rotor winding is short circuited
- BThe rotor winding is connected to ac supply and the stator winding is short circuited
- CBoth of the stator and rotor windings are connected to ac supply
- DStator winding is connected to ac supply and rotor winding to dc supply
4.A 3-phase, 4-squirrel cage induction motor has 36 stator and 28 rotor slots. The number of phases in the rotor is
- A3
- B9
- C7
- D8
5.The rotor slots are slightly skewed in squirrel cage induction motor to
- AIncrease the strength of rotor bars
- BReduce the magnetic hum and locking tendency of rotor
- CEconomize on the copper to be used
- DProvide case of fabrication
6.Skewing of the rotor in a three-phase squirrel cage induction motor reduces
- ANose parasitic torque, starting torque and pullout torque
- BNoise and parasitic toque, but increases starting torque and pull out torque
- CNoise and pullout torque, but increases parasitic torque ad starting torque
- DNoise, parasitic torque and starting torque, but increases
7.The principle of operation of a 3-phase induction motor is almost similar to a
- ASynchronous motor
- BRepulsion start induction motor
- CTransformer with a shorted secondary
- DCapacitor start induction motor
8.The rotor of a 3-phase induction motor rotates in the same direction as that of stator rotating field. This can be explained by
- AFaraday?s laws of electromagnetic induction
- BLens?s law
- CNewton?s law of motion
- DFleming?s right hand rule
9.Stator flux induces emf in the rotor bar
- ARotating at synchronous speed around stator
- BConstant in magnitude
- CMagnitude depending upon the load on the motor
- DNone of the above
10.The rotor circuit of an induction motor under operating condition is
- AAlways closed
- BAlways open
- CMay be open or closed depending upon the loading conditions
- DNone of the above
11.The 3-phase induction motor with rotor circuit open will
- ARun normally
- BGet overheated
- CNot run
- DMake noise
12.If any two leads from slip rings are interchanged in a 3-phase induction motor, then the motor will
- AContinue running in the same direction as before
- BRun in a direction opposite to previous one
- CNot run
- DGet damaged
13.Two of the supply terminals to a 3-phase induction motor get interchanged during reconnection after normal maintenance, when switched on to supply the motor will
- ARotate in the same direction as before maintenance
- BRotate in direction opposite to that before maintenance
- CNot start at all
- Dget heated and damaged
14.The direction of rotation of a 3-phase induction motor can be reversed by
- ATransposing any two leads from supply
- BTransposing any two leads from slip rings
- CTransposing all the three leads from the supply
- DDisconnecting any one phase
15.The rotor of an induction motor rotates in the direction of the rotation of stator field in order to
- AReduce the relative speed between the rotating stator field and the stationary rotor conductors
- BOppose the rotor current
- CIncrease the relative speed between the rotating stator field and stationary rotor conductors
- DNone of the above
16.The rotor of an induction motor never runs at synchronous speed because then the relative speed between the rotating flux and rotor will be
- AMaximum and hence, torque will be maximum
- BMaximum and hence, torque will be zero
- CZero and hence, torque will be maximum
- DZero and hence torque will be zero
17.The voltage actually used for setting of the useful flux in the air gap of 3-phase induction motor is
- AEqual to the applied voltage
- B> applied voltage
- C< applied voltage
- D= rotor induced emf
18.Synchronous speed is defined as the speed at which the
- AStator magnetic field rotates
- BRotor rotates on no load
- CRotor rotates on full load
- DNone of the above
19.The maximum possible speed of a 3-phase squirrel cage induction motor running at a slip of 4% is
- A2,880 rpm
- B3,000 rpm
- C1,440rpm
- D960rpm
20.A three phase 6 pole, 50 Hz, induction motor is running at 5% slip. What is the speed of the motor?
- A850 rpm
- B900 rpm
- C950 rpm
- D1000 rpm