Fig. (1) shows the circuit of a 3-phase induction motor at any slip s. The rotor is assumed to be of wound type and star connected. Note that rotor e.m.f./phase and rotor reactance/phase are s E2 and sX2 respectively. The rotor resistance/phase is R2 and is independent of frequency and, therefore, does not depend upon slip. Likewise, stator winding values R1 and X1 do not depend upon slip.
Since the motor represents a balanced 3-phase load, we need consider one phase only; the conditions in the other two phases being similar.
At standstill. Fig. (2 (i)) shows one phase of the rotor circuit at standstill.
When running at slip s. Fig. (2 (ii)) shows one phase of the rotor circuit when the motor is running at slip s.