EHV transformer dielectric specification improvements

EHV transformers have higher failure rates than lower voltage transformers. Many of these failures have been attributed to dielectric mechanisms. Therefore, the dielectric specification for these transformers has been enhanced by upgrading ratings, conducting comprehensive design reviews, performing voltage sensitivity analyses and proving the integrity of the transformer with improved dielectric tests. Most elements of the new specification have been applied to eight transformer designs, and the results are discussed. It is recommended that the industry further investigate insulation coordination and failure analysis of EHV transformers, and that standards be expanded to incorporate special requirements for these ratings