Use of Transformer

Hello Ranju

I assume what you spell as "trafo" means "transformer".

Almost every Electrical distribution system I can think of has transformer primaries connected in delta, secondary in star.

There is a simple reason for this: Long high-voltage transmissions do not require a Neutral conductor, (If one was installed, it would be of little use), so the cost of that is saved.

Mains supplies to factories/houses etc often requires 3 phase at a higher voltage, and single phase at a lower voltage, with a neutral wire for the single phase supply.

Example:

3 phase - 1 phase

• 380v - 220v
• 400v - 230v
• 415v - 240v

Because it is not generally desirable to have a neutral conductor run for hundreds of miles (lightning strikes and the like), the line and distribution network relays also normally require Delta Primaries, and star secondaries.

Those are the the simple reasons, there are other reasons, of increased complexity.

Kind Regards....

Generally in distribution system delta -star prtefered..But wht is the use of Star-star connection?

Hello Guest,

Although many Power Transformers I have worked on have the separate winding connections brought out to terminals (bushings and the like) and thus could be connected Primary star/Secondary star, in practice this is not done, except in the case of matching to an unusual supply Voltage, which to my knowledge has not been done.

Perhaps other Members may have found Power Transformers connected Star/Star, and wish to add the circumstances this type of connection has been done.

Read my earlier post please.

Kind Regards....

But in case of substation some cases star-star connewction use why?

Hello Guest,

Advise Country, Location, and Primary/Secondary Voltages of the substations you refer to.

Looking forward to your reply

Kind Regards....