It is a starting method that reduces the starting current and starting torque. The device normally consists of three contactors, an overload relay and a timer for setting the time in the star-position (starting position).
For the starting period (time set by the timer), the motor windings are connected in start (Y) and then the connection is changed to delta during normal run. Because of the star connection, the starting current is 1/3rd of the DOL (Direct-On-Line) starting; however the starting torque is also 1/3rd of the DOL starting torque. For this type of starting, the motor windings must have both ends (2 terminals for each phase, total 6 ends) terminated in the terminal.
OFF State: All Contactors are open
Star State: The Main and the Star contactors are closed and the delta contactor is open. The motor is connected in star and will produce one third of DOL torque at one third of DOL current.
Delta State: The Main and the Delta contactors are closed. The Star contactor is open. The motor is connected to full line voltage and full power and torque are available.