Control Circuit of Semi Automatic Star Delta Starter

Working of semi automatic star delta starter control circuit

• Press ON Push button
• The star contactor coil gets supply through phase R – OFF push button – ON push button – star contactor coil – D1 ( NC of delta ) – phase Y. 
• The star contactor becomes energized. 
• As soon as the star contactor ON, it’s auxiliary contact S1 becomes 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. The auxiliary contact M1 of main contact becomes NC.

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 ( NC of delta coil ) – delta coil – Y phase. 
• It should be remember that ON push button is released only after the induction motor pick up its rated speed. 

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