Stator Voltage Control of three phase induction motor
By stator voltage control :
•Torque is directly proportional to stator voltage square.
•The torque is directly proportional to speed so if torque will decrease speed also decrease and if torque will increase speed also increase.
•So we can control speed of three phase induction motor by varying stator voltage.
•This method is suitable for application where load torque decreases with speed.
•This method is sometimes used for small motor fans.
•This method is very easy and cheap but still use rarely.
•Because by decreasing the voltage torque will reduce.
•But to maintain power (P=VI) this will increase current in motor which will heat the motor which is not good it causes losses.
•Also the torque is proportional to square of voltage so large voltage change is required for changing torque.