Latest advances in mica paper tapes for application to VPI´ed high voltage generators

Muscovite mica paper with narrow particle size distribution has been developed to improve properties of tapes to be used in the VPI process using epoxy resin. The small particle size, and narrow particle size distribution, results in uniform penetration of the bonding resin and accelerator into the mica paper in the process of tape manufacture. This particle size and distribution are also responsible for uniform penetration of the impregnating resin. The use of appropriate epoxy binder resins ensure compatibility with the impregnating resin. The accurate control of the combination of mica paper appropriate resin and accelerator are important contributors to the overall mechanical and electrical properties of the high voltage coils insulated with these new tapes. This paper presents the results of the dielectric performance when using these new tapes for vacuum-pressure-impregnated (VPI) groundwall insulation. The objectives are to develop a glass backed mica tape with higher dielectric properties than commercially available tapes. Custom tapes were developed; working with Cogebi. These tapes were used to make up insulated test bars which in turn were subject to electrical, chemical, and mechanical testing. This paper reviews the results of the tape improvement effort which leads to an improved groundwall system