Star Delta Starter for 3 Phase Induction Motor:
Explanation: The stator winding of the motor which is designed for delta operation is connected in star during starting period. The arrangement is shown in the above figure; here six leads of the stator windings are connected to change over switch. At the instant of starting the switch is on the “Start” position which connects the stator winding in star connection so that each stator phase gets the VL/√3 volts, where VL is the line voltage. The application of reduction in voltage reduces the starting current and protects the motor. When motor pick up 75% of rated speed, the changeover switch is put to “Run” position which connects stator windings in delta connection. Now each stator phase gets full line voltage VL.