Electrical Revolution: Semi Automatic Star Delta Starter Control Circuit & Working

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.

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.

You may also like to read these posts

Energy conservation in industrial furnace