A functional test comparison between mica over bare copper and double polyester glass over heavy polyester-amide imide insulation for high voltage multiturn coils

Many European and Asian manufacturers of high voltage multiturn coils have selected mica over bare copper as their preferred turn insulation rather than the double polyester glass over heavy polyester-amide imide film that is often used in the United States. A functional test program was developed to look at the process, performance and cost tradeoffs of both systems. A set of 6 test coils each were produced with both turn insulations. The manufacturing process was monitored and production observations are included in this report. All test coils were insulated with the same uncalcined muscovite mica ground wall tape and then impregnated with the same anhydride epoxy resin. The coils were then subjected to a series of surge tests, dissipation factor testing, voltage endurance and high voltage breakdown. A summary of the test results, conclusions and observations are included in this report.