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Close Transition Star Delta Sequence.


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i have a little bit confuse of sequence of start delta closed transition. what i understand is closed transition is to prevent the current spiked when the transition between star and delta are not connected. i just new , so i have study the old electrical schematic what i see in old project of my company first of all.


star contacter closed same time with closed transition contacter

then star contacter open and closed transition contacter remain closed

the delta contacter closed with the closed transition contacter.

and run continuously.


is it right?


from azham

Penang,Malaysia :)

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Hello Azham


There are two types of star delta starter.

The simplest and most common form is the open transition star delta starter and comprises three contactors, a main contactor, a star contactor and a delta contactor. In operation, the main contactor and the star contactor close together effectively connecting the motor to the supply in a star configuration. After a period of time, the star contactor opens, then after a small delay, the delta contactor closes.

for more information, see http://www.lmphotonics.com/star_delta.htm

The open transition causes high current and torque transients.


The second type of star delta starter is the closed transition star delta starter. This starter has four contactors. - there is an auxiliary delta contactor with one resistors in series with each pole, connected across the delta contactor. In operation, the main contactor and star contactor close together. After a period of time, the auxiliary delta contactor closes, then the star contactor opens, then the delta contactor closes.

The net result is that current flows through the motor windings at all times. There is no interruption of current flow.


Best regards,

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hi marke


thank you for your information, how about if i design sc (star contactor) , tc (closed transition contacter) ,

mc (main contacter), dc (delta contacter).



mc and sc closed together

after a time delay tc closed, once the tc closed,


at the same time, sc open by the n/c from tc

dc closed by the n/c from sc


is it still same?


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Hello Azham


I am not sure what you are referring to with your contactor names as in your first post you seemed to be calling the main contactor a closed transition contactor.

Without knowing what you are calling the main contactor, and the closed transition contactor, and how these are connected, it is impossible to comment.

I think that we need to have a sketch of the connections before commenting.


Best regards,

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