Propagation modes of surface discharge plasma in a metallized polymer film capacitor

Surface breakdowns and their associated discharges are an important failure mechanism of metallized polymer film capacitors. To assess propagation of such discharges on the electrode coating surface and hence the impact on capacitor performance, we have recently developed a surface plasma model under non-equilibrium conditions. Through the identification of an electrical field mechanism and a temperature gradient mechanism, we have established a parametric range within which these surface plasmas are unlikely to elongate. Theoretical models of surface discharges are useful for a quantitative understanding of failure mechanisms in film capacitors. In this contribution, we extend our work further to study the dynamics of plasma propagation. Two propagation modes are identified, namely the elongation and extinction modes, and they are numerically explored over a very wide parametric range. Detailed features of plasma propagation provide important insights into their impact on capacitor performance. These results are also useful to aid optimization of capacitor designs through capacitor electrode architecture and insulation clearance.