Starting torque of squirrel cage induction motor and slip ring induction motor.
Impedance traingle of rotor circuit of induction motor. Let E2 = rotar EMF per phase at stand still R2 = rotar resistance per phase X2 = rota reactance per per phase at stand still . Z2 = √( R2² + X2²) rotar impedance per phase at stand Still. I2 = E2 / √( R2² + X2²) = rotar current cos∅2 = R2 / √( R2² + X2²) = power factor T = K1 E₂ R2/( R2² + X2²) = rotor torque = K1 * E2 / √( R2² + X2²) * E2 * R2 / √( R2² + X2²) = K1 E₂² R2 /(R2² + X2²) if we increase the resistance of rotor circuit then we can improve the power factor. Torque in squirrel cage induction motor :- The resistance of squirrel cage rotor is fixed and small as compared to reactance. Reactance of rotor is high as frequency of a current is equals to supply frequency. Hance at starting power factor is poor. starting current is although very high but lags by very large angle behind E2. So the torque is only 1.5 times the full load torque but starting current is 5 to 7 times the full load current. Hence ...