Mechanism of insulation resistance in metalized polypropylene film capacitors

Metalized polypropylene film capacitors (MPPFCs) can work under high electric fields due to the self-healing characteristic. Leakage phenomenon caused by the insulation resistance (IR) in MPPFCs is one of the important factors resulting in the reduction of the energy efficiency. The IR is directly related to the DC electric conduction mechanism in polypropylene film. This paper mainly concentrates on the IR by investigating the electrical conduction mechanism of metalized films under high electric fields. Firstly the conduction mechanism of metallized films is discussed. Secondly IR is obtained under different electric fields based on an established measurement platform The Poole-Frenkel(PF) model presented in this paper includes the field-enhanced carrier density caused by the barrier height attenuation in directions both opposite and forward to the electric field, and the field-enhanced carrier mobility. The equation for electric conductivity based on this model gives not only the usual Ohm´s law at low fields but also at extremely high electric fields. And the IR calculations match well with the experimental results.