Insulation resistance of metallized polypropylene film capacitors under different electric fields

In pulsed power systems, metallized polypropylene film capacitors (MPPFCs) facilitate the operation of the polypropylene film with a relatively small margin to its dc breakdown strength. The insulation resistance (IR) is one of the important factors that result in the reduction of the energy efficiency, as it represents a current leakage path through the dielectric. This paper concentrates on the leakage phenomenon in MPPFCs by the measurement and analysis of IR. Measurement of the IR under high electric fields is feasible due to the self-healing capability and a measuring system is established to measure IR under various electric fields. To sufficiently investigate IR changing with the electric fields, IR under low electric fields are also investigated. The results indicate that the time constant (called Equivalent IR) is extremely sensitive to the electric field and IR changes little under electric field lower than 10 V/μm. The assumption that influence of surface leakage in the margin on IR could be neglected is also validated by experiments. Finally, theoretical calculation of Equivalent IR based on the Poole-Frenkel (PF) effect is carried out.