Induction motors at light load run at low power factor and low efficiency. But if the stator supply voltage is reduced at light load condition, both the efficiency and power factor can be improved owing to reduction in magnetizing current and core loss. The proposed energy saver is a thyristorized phase control working in feed back mode. The motor has a unique characteristic of slip-efficiency as well as slip-power factor, which do not vary with supply voltage. Therefore, a method of stator voltage control based on operating power factor angle has been developed which will make the motor run at a slip that corresponds to maximum efficiency irrespective of the load condition. The change in load will be sensed as change in power factor and the supply voltage will be varied by controlling the thyristor firing angle. A three phase chopper control of the induction motor using a different algorithm of minimizing the input current is also in progress.
