Performance Equations of Three Phase Induction Motor

When balanced 3-? voltages are applied to the  stator  winding  a rotating magnetic field  of constant amplitude is produced in the air gap. The speed of this rotating  field is given by .

The rotating flux  wave  cuts  the stationary rotor  conductors and  therefore  emf are induced  in the rotor  conductors. As  the  rotor  circuit is short  circuited these  induced emfs  give rise  to current  in the rotor  conductors. The interaction of these  rotor  currents  with  rotating  flux  wave produces torque in the rotor of a  3-? induction motor  and as a consequence rotor  begins to rotate. According  to len law the develop torque must oppose the cause by which  it is produce i flux  cutting  action. This is possible  only  if  the developed  torque forces the rotor  to  rotate  in the direction of rotating field. Due  to this  the relative speed  between rotating flux  and rotor  conductors  is reduced and therefore  the flux  cutting action also gets reduced. This  relative speed between  rotating flux  wave and rotor.