Why is star delta starter preferred with an induction motor?

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Why is star delta starter preferred with an induction motor?


The **star delta starter** is a preferred method for starting an **induction motor** due to several reasons¹²³.

When an induction motor is first connected in star, the phase voltage is reduced to 58% of the line voltage.

This reduction in voltage leads to a decrease in motor current, which improves the motor’s starting characteristics.

Consequently, the motor starts without any electrical and mechanical stress¹.During startup, an induction motor draws 6 to 7 times its rated current.

At this point, the rotor impedance is highly inductive, and the motor delivers very little torque. To limit the starting current and increase torque, the supply voltage needs to be reduced.

By connecting the stator winding in star configuration initially, the stator phase voltage is reduced by 42% of the supply voltage. After running the motor in star for a certain time, the timer switches on the delta contactor, connecting the motor winding in delta configuration.

This allows the full supply voltage to be impressed on the stator winding¹.While small-rated motors can be started directly on-line (DOL), as motor ratings increase, it becomes necessary to use a star delta starter¹.

The star delta starter reduces starting current by approximately 3-4 times compared to direct-on-line starting.

This reduction in current results in lower voltage drops and less power loss³.If you would like more information about star delta starters or induction motors, please let me know!

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