Process for manufacture of high voltage transformers and the like

A process for making an encapsulated electrical insulation system such as a transformer which includes a porous fiber material filling. The system is vacuum baked at a temperature range of 100 DEG C. to 155 DEG C. for at least four hours, and is then vacuum impregnated with a mixture of a modified bisphenol A epoxy resin hardener comprising various acid anhydrides plus promoters. Pressure is then applied to the system of 1,000 psi. of nitrogen at 80 DEG C. for 2 to 12 hours. Thereafter, the temperature is increased to 110 DEG C. for 2 to 12 hours. The system is then cured at 135 DEG C. for approximately 12 to 24 hours. To minimize corona, shields are placed in selected portions of the transformer, the shields having edges formed into radii ends to avoid points at which corona would normally tend to concentrate. Also, the transformer is wound using ultra-clean components to obtain a transformer package that is free from impurities prior to impregnation.