Induction Motor

Speed of Stator magnetic field = Ns

Speed of rotor = Nr

Slip, S = (Ns-Nr) / Nr

As the stator magnetic field rotates at Ns and the rotor rotates at Nr in the same direction the relative speed of magnetic field with respect to conductor is Ns-Nr

Fig. 1

In case of Induction motor the stator and rotor frequency are unequal so if s<1 rotor frequency is generally smaller as compare to stator frequency.

•Step 1:- 3-phase supply on stator    rotating magnetic rotates at Ns w.r.t stator (ground)

•Step 2:- rotor rotates at Nr

•Step 3:- frequency of V,I induced on rotor = sf

•Step 4:- Speed of rotor magnetic field w.r.t rotor

rotor = 120*s*f/p = sNs

•Step 5:- Speed of rotor magnetic field w.r.t stator or ground

                      sNs+Nr  = Ns-Nr+Nr = Ns                                   

Fig. 2

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