Semi-automatic star delta starter

In this post, working of semi-automatic star delta starter is given. It consists of 3 contactors – main contractor, star contactor and delta contact.

Semi-automatic star delta starter control circuit & working

Here the working of semi-automatic star delta starter is explained in steps.

Push on button.

The star contactor coil gets supply through phase R – OFF push button – ON push button – star contactor coil – D1 – phase Y. The star contactor becomes energized.
As soon as the star contactor ON, it is auxiliary contact S1becomes NC and S2 becomes NO.

Auxiliary contact S1: From NO to NC

Auxiliary contact S2: From NC to NO

The main contactor coil gets supply through phase R – OFF push button – ON push button – S1 – main contactor coil M – phase Y. The main contactor becomes energized.

Auxiliary contact M1: From NO to NC

As soon as the ON push button is released, the star contactor de – energized and its auxiliary contact change its position means NO to NC and vice versa (initial condition).

Auxiliary contact S1: From NC to NO

Auxiliary contact S2: From NO to NC

The coil of delta contactor gets supply through phase R – OFF push button – ON push button – M1 – S2 – delta coil – Y phase.
It should be remembered that ON push button is released only after the induction motor pick up its rated speed.

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