Delta to Wye

You are talking apples and pears not apples and apples.

A delta system does not have a neutral. You may elect to ground one phase of the delta system, so that your system is grounded, or you may elect to leave the delta system not grounded. If you elect to leave it not grounded, you should install ground fault indication equipment. I would leave it ungrounded, because if it was grounded, a second phase to ground short would be a phase to phase fault at the full available system fault current. Or in simple english, a "big bang".

The distribution equipment is not "Wye" per say. It is either three wire or four wire. I would not use a 4 wire wiring system for a delta service, especially with so high of a system voltage.

If your secondary voltage at your sub station is 13.8 kV, what is the primary?

Thanks North really appreciate it, actually i havent get more information about it. Only partial info we got. Isolation Transformer 1:1 our best option. Only we considered maybe some option can be done without this. And i really appreciate your reply. Maybe you have some technical info or any option pleaseeeee let me know..thank you