Soft Starter for Induction Motor

Abstract

Induction motors, when direct switched take 5 to 7 times their full load current. This current will produce large line-voltage drop, which can affect other equipments connected to line. Further more, the resistance of the squirrel cage induction motor is fixed and small. The frequency of the motor currents equals to the supply frequency. Hence the starting current of the rotor is very large in magnitude. So, torque per ampere is very poor. It is roughly 1.5 times the full load torque.

Soft starters control the voltage applied to asynchronous motors during start up, reducing the starting current and torque to provide a smooth, steeples acceleration. The problem with conventional starters is frequent start/stop of the motor cause damage to the motor shaft. Start/stop by use of soft starter eliminates damage of the motor shaft. Smooth increase in operating voltage during start up eliminates transient torque associated with conventional starting methods thereby increasing the life of driving gears such as belts, chains, couplings, gears etc. It improves input power factor. Soft Starters solve the supply and load side problems associated with the conventional starters and in addition offer other benefits better control and monitoring. Here Atmega16L Micro controller is used for control. It has RISC architecture and Analog to Digital converter inbuilt.