3 Phase Motor Star Delta Starter Circuit

In the star connection, the voltage across each winding is reduced by a factor of (1 divided by root three). This results in a starting current reduction to (1 divided by root three) of the DOL starting current and a starting torque reduction to one third of the DOL starting torque.

If a motor directly starts in delta then it can draw 5 times of its running current. This can cause nuisance trips of circuit breakers but it can also cause lights in a building to dim and other low voltage conditions. When a motor starts in star it draws far less current to the motor windings. In this way we can avoid nuisance trips of circuit breakers, lights blink, computer screen glitch etc.

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Posted in: Circuits, Starter Circuits