In an Extra High Voltage transformer with HV side voltage of 132 KV and above, it is preferred to have the HV side as Star connection.
As voltage is reduced by √3 times in star connection. if we use star connection then Vph = VL /√3. As the insulation design is based on the voltage rating we can save the insulation cost by using Star connection, It will be a Non-Uniform Insulation (Graded Insulation).
But If we use Delta Connection then VL=Vph. so the Insulation Cost will be high, It Will be a Uniform Insulation (Non Graded Insulation)
No comment