Differences in AC and DC Large-Area Breakdown Behavior of Polymer Thin Films

A large-area multiple breakdown measurement using self-healing gold sputtered electrodes was evaluated in determining the AC breakdown characteristics of insulating biaxially oriented polypropylene (BOPP) and BOPP-silica nanocomposite thin films. Results were compared with conventional small area measurements and it is shown that the large-area approach could be extended into AC measurements as long as good quality film-electrode interface in ensured. Special electrode arrangements are needed due to the absence of electrostatic force. AC small-area breakdown strength of pilot-scale films was ramp rate dependent but no such effect was clearly noticed for a commercial product. Conventional DC small-area breakdown measurements were also conducted and the results were compared to previously published large-area multiple breakdown data. The consistent results support the dependency between ramp rate and DC breakdown strength in the studied BOPP-silica nanocomposite.