Control Circuit of Automatic Star Delta Starter

Working of 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 – T NC – star contactor coil – D1 ( NC of delta coil ) – phase Y. 
• The star contactor becomes energized and the timer coil gets supply at the same time. 
• As soon as the star contactor ON, its 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.
• As soon as the main contactor energized, its auxiliary contact M1 becomes NC from NO.

                     Auxiliary contact M1 : From NO to NC

• Now the main contactor gets supply through auxiliary contact M1.
• The contact of the timer becomes NO from NC condition as per its specific time setting.

                     Timer contact T : From NC to NO

• As soon as the contact of timer becomes NO, the star contactor de – energizes. Its all 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 –  M1 – S2 ( NC of star contactor ) – delta coil – Y phase. 
• The main contactor and delta contactor remain is in energized during running condition of the three phase induction motor.

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