High temperature resins in class H dry type transformers

This paper presents a comparison of class H resins as applied to dry type distribution and power transformers of 220° C insulation class. The resins evaluated include silicones and a new family derived from diphenyl oxide. The distribution transformers include ratings through 5000 volt class and 500 KVA, and the power transformers include ratings through 15,000 volt class and 10,000 KVA. The applications utilize these resins as varnishes for impregnating coils and core-coil assemblies and as laminating resins for fabrication of insulating tubes. Comparisons are made which show the thermal, mechanical and dielectric advantages of the diphenyl oxide resins over the silicone.