Electrical interview:ROTOR ROTATION

                        When the three phase stator windings, are fed by a three supply a magnetic flux of constant magnitude is producing and rotate at synchronous speed in the air gap, these flux sweeps past the rotor surface and so cuts the rotor conductors.Due to the relative speed between stator and rotor conductors, an e.m.f is induced in the rotor conductors, according to faraday's law.Due to induced e.m.f current is produce and force is induced, according to lenz's law for opposing the relative speed the rotor rotate in the stator field flux direction.                                                                                                                                                                                     

Electrical Interview:3-PHASE INDUCTION MOTOR ACTS AS 2-PHASE

              When a three phase supply is applied to the induction motor,the 3-phase winding (120 degrees) produce three phase magnetic flux. Let the maximum value of flux due to any one of the three phases be 

and the total resultant flux in air gap is 1.5 times of maximum flux  .If one of the phase in 3-phase  suddenly damaged the induction motor acts as 2-phase motor. Because the motor produce 2 phase flux in air gap,the total resultant flux in this 2-phase case is only .Due to that the speed in 2-phase motor  is reduced as compared to the 3-phase induction motor.

                                       
                                                   3-phase motor resultant flux is = 1.5 times maximum flux.

                                                   2-phase motor resultant flux is = maximum flux.

                                                       

Electrical Interview: SKEWED SLOTS

                  When a 3-phase supply is given to the squirrel cage induction motor and there is a automatic pole formation is occurred. The formation of poles both on  rotor and stator are same, the magnetic locking(cogging)  is take place between the rotor and stator.for eliminating the magnetic locking between these we are must able to skewed the rotor slots up to desired level by doing this process also increase the starting torque of squirrel cage induction motor. In slip-ring motor we can not use skewed slots because the poles on the rotor and stator are not equal and also high starting torque. 

INDUCTION MOTOR POWERFACTOR

Slipring induction motor has the low power factor because the air gap between the stator and rotor is high.the slip ring motor draw large reactive power from mains due to large reactive power the power factor is reduced,but in squirrel cage motor has low air gap due to this reason the reactive power required is minimum the power factor is high as compared to slipring motor.

       ANSWER: slipring motor

Electrical Interview:D.C MOTOR

                         which motor has the high torqe
  1 series motor  2 shunt motor  3 induction motor  

answer is series motor because series motor torque is directly prportional to square of the electrical current flowing in the armature.practically series motors are used where highest starting torque required 

therefore series motors are used in hosting and cranes etc..

STARTER IN D.C MACHINES

         practically all d.c machines are started with the starter other wise d.c motor is burned because large current is flowing through armature. When ever a voltage is applied across the d.c motor with out a starter a large current is flowing through motor because at starting motor armature is standstill therefore back e.m.f is zero therefore it requires large current to start. For eliminate this situation we must insert a starter into the dc motor circuit then we control the starting current in the dc motor armature circuit.Starter is limit the starting current in the dc  motor armature circuit.