Statistical Analysis on the Electrical Failure Properties of the Form-Wound Epoxy Micaceous Insulation Systems for Rotating Machines

FROM the test results obtained with various epoxy micaceous insulation systems used for form-wound coils of high voltage rotating machines, electrical failure properties such as breakdown voltage and voltage endurance time were analyzed statistically using a Weibull distribution. It has been determined both theoretically and experimentally, that these properties are governed by the size of a cable-like construction combining the four corner parts of the form-wound coils: the radius of the inner conductor edge, the insulation thickness, and length. Further, the dependence of the electrical failure properties on electrical, thermal and environmental stress, and on operating loads was determined. Finally, as a result of comparison between the failure properties of the model bar and the actual machine coils, equations were developed for estimating the failure properties of actual machine coils from small model bar coils. Additionally, the relationship between sample numbers and parameters of the Weibull distribution was considered, using random number data obtained from a computer.