Star Delta Starter - 415v

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Your post is a little too vague (devoid of specifics) to elaborate on such a wide field. Here's some Wiki info you can read and then hopefully rephrase with some detail.

Thats great star delta delta star but be careful of wiki.

In some countries with weak power systems DOL starting was limited to 5HP. For above 5hp to about 30hp they used star-delta starters. Above 30hp they used slip ring type starters. In countries with strong grids there was no limit of 5hp for DOL.In star-delta starters during changeover from star to delta a current surge which is more severe than DOL may occur. So they developed the closed transition type star-delta starter. The limit depends on the load characteristics as the starting load in star-delta starting is low compared to DOL. They have other types too like auto transformer,VSD, VFD,soft start etc depending on the application.Changeover time fro star to delta too depends on load characteristics but normally 5secs is acceptable.

It depends upon the capacity of the upstream supply and whether or not a Peak Demand Tariff is being charged.