Static Rotor Resistance Control Methods
This method is used only for slip ring induction motor in SRIM 3- phase variable resistor can be inserted in the rotor circuit and by varying this resistance in the rotor circuit and by varying this resistance the motor torque and hence speed of th motor can be controlled. This methods is used when speed drop is required for a short time.
It has some disadvantages if rotor resistances are not equal unbalances in voltages and currents occur at low speeds efficiency is reduced and with load variation speed is changed very quickly therefore chopper circuit is used.