Starting of Induction Motors:

At the time of beginning S = 1, the starting current may be as large as five to six times the full-load current. With such a big starting current, the motor must accelerate and reach normal speed quickly or else overheating can damage the motor. Thus, it is only small size motors that may be started direct on-line. Either a full voltage or reduced voltage is applied across the stator terminals to begin the induction motors. The decreased voltage limits the starting current but at the very same time it decreases the starting torque.