A star-delta starter is the most commonly used method for the starting of a 3 phase induction motor. In star-delta starting an induction motor is connected through a star connection throughout the starting period. Then once the motor reaches the required speed, the motor is connected through a delta connection.
A star-delta starter will start a motor with a star connected stator winding. When the motor reaches about 80% of its full load speed, it will begin to run in a delta connected stator winding.
A star-delta starter is a type of reduced voltage starter. We use it to reduce the starting current of the motor without using any external device or apparatus. This is a big advantage of a star-delta starter, as it typically has around 1/3 of the inrush current compared to a DOL starter.