SOFT STARTER FOR THE THREE PHASE INDUCTION MOTOR

Three phase induction motor when directly started from 3-phase supply, the current requirement is very large i.e. 5 ? 7 times that of rated value. In order to mitigate the adverse effects of starting torque and high inrush currents, alternate method is adopted i.e. to use TRIAC based soft starter. Normally, soft starters are used for avoiding this problem and to achieve smooth starting of induction motor. Back to back TRIACs are connected and they are triggered by PWM technique. This is completely closed loop system and the speed of motor will be controlled automatically by use of feedback from motor. These strategies are implemented by the use of a microcontroller. Temperature sensing technique is being used so as to avoid any damage to the winding. The main advantage of this is reliable and efficient than any other starter. As current requirement is less so it plays a main role as energy saver too. It is used in industries to operate the motor at a desired speed.