Optimization Studies with Form-Wound Stator Groundwall Insulation

The effect of increasing the micabond resin content on the impregnation characteristics and electrical properties of a solventless epoxy resin impregnated groundwall insulation has been explored using small copper tube test samples. In this study, six different micabond materials, consisting of cycloaliphatic epoxy, bisphenol 'A' epoxy, epoxy-novolac, glycidyl-ester, and polybutadiene resins, were evaluated by increasing the bond resin content up to 24% in the mica wrapper. Impregnant retention and drainage data were obtained for each micabond material with the solventless epoxy resin. Retention efficiency (R/D) values were also computed and, with few exceptions, were found to drop sharply with increasing micabond resin content. The power factor data, obtained at 150°C and 1 kV, show that some of the micabond resins, e.g. cycloaliphatic epoxy, bisphenol 'A' epoxy and polybutadiene, exhibit lower power factors with increasing micabond contents, whereas others, such as epoxy-novolac micabond resins, show higher power factor values when bond resin content is increased. It is concluded that the best compromise of electrical compatibility and impregnation efficiency is obtained when the micabond resin content is in the range of 12 to 18% for most of these developmental resins.