Impact of surface discharge plasmas on performance of a metallized film capacitor

Surface breakdown discharges are one probable failure mechanism of metalliz ed polymeric film capacitors used in power systems, traction drives, and ot her technological applications. To assess whether surface breakdown dischar ges may undergo considerable elongation on the electrode surface to affect significantly capacitor performance, an equivalent electric circuit model i s developed for metallized polymer film capacitors under the thermal equili brium condition. With the aid of a surface field gradient mechanism, propag ation of surface plasmas is studied and the necessary condition for their p ossible elongation is obtained. Numerical examples of a metallized film cap acitor are used to demonstrate that surface breakdown plasmas and their elo ngation are unlikely to affect capacitor performance in a significant fashi on. Then the generic problem of plasma propagation is restudied under therm ally nonequilibrium conditions. Based on a heat conduction formulation in t he one-dimensional limit, a temperature gradient mechanism is proposed to e xplain the possible elongation of breakdown plasmas on an electrode surface . Numerical examples are again used to deduce that thermally nonequilibrium surface plasmas are unlikely to evolve into catastrophic flashover arcs to fail film capacitors. (C) 2001 American Institute of Physics.