What is star- delta starter?

star delta starter is a control circuit used to start the motor in STAR connection so as to reduce the starting current drawn by the motor during starting so we don't have to use high capacity CB and cables consequently then when the motor take suitable running speed the circuit change the connection to Delta connection

The star delta starter is one of the most commonly used starter for the induction motors. This starter uses a TPDT switch.

The switch connects the starter winding in star initially thus reducing the phase voltage value by the factor of 1/root(3). And when the switch is thrown the windings get connected in delta so that it get its normal voltage value.

Usually this switching is made automatically by using relays.

I hope this explanation is useful to you.

Starters are used for reducing incoming line current ( in rush current) to acceptable or working levels of electrical equipment.

The current flow is reduced while using STAR connection. Formula is

When connecting in a Delta configuration then

Phase voltage = line voltage and Phase current =1/sq rt3 Line current. Or Line Voltage = phase voltage, Line current = sq rt3 x phase current.

When connected in a star configuration, then Phase voltage =1/sq rt3 Line voltage and Phase current = Line current. Or Line voltage = sq rt3 x phase voltage and Line current = Phase current