Comparison of film capacitor designs for a high power density application

Three designs for an 8μF 3.1kV snubber capacitor were built and tested to compare the performance of different technologies for a high RMS current requirement. The designs were (1) extended foil , (2) metalized film, and (3) a hybrid containing both a metalized electrode and extended foil electrodes. All were impregnated with a vegetable oil and epoxy encapsulated in the same size case. The prototype of the hybrid design was only a 6μF capacitor due to machine limitations on winding dimensions that have since been resolved. A short-term, stepped-voltage test was performed on samples of each design until the units failed or to a maximum of 8.0kV, more than 2.5 times the rated voltage. Short-circuit discharge, AC partial discharge measurements, and AC stepped-stress tests were also performed and will be reported. The implications of these test data for the selection of specific capacitor technologies for power electronics applications will be discussed.