Epoxy-Resin-Impregnated Paper Insulation System for Ultra-High-Voltage Applications

This paper is about the applications of an epoxy-impregnated paper insulation to ultra-high-voltage systems. An epoxy-impregnated paper insulation is a resin-rich void-free structure, and therefore has extremely superior voltage withstand characteristics. It also has outstanding resistances to thermal cycle and mechanical vibration. Consequently, such insulation systems can be applied easily to condenser bushings. From the standpoint of the production facilities, techniques, and economical considerations, in items with an overall length of more than 3 m, "prefab"-type condenser bushings, consisting of several condenser cores, are desirable. In cases when two-unit condenser cores are assembled leaving a simple conical-shaped gap between them, it is extremely effective to adopt a "potential-expanding"-type gap designed so that the equipotential surface in the gap will be in the vertical position to the cone surfaces as far as possible. The prefab-type condenser bushing of the 500-kV class was experimentally manufactured using this arrangement; it displayed all the desired properties. This paper also describes the other examples of applications of epoxy impregnated paper insulation: CT bushings and pulse transformers in the magnetic firing system for high-voltage dcconverters using thyristors, and draw-out-type condenser bushing for disconnecting devices used in the compact-type substation.