Electrical Treeing Breakdown and Measurement of Space Charge Fields in an LDPE Under a Needle-Plane Electrode System

In a previous report, we analyzed the characteristics of a space charge field formed in a low density polyethylene (LDPE) film under non-uniform electric fields, and also studied the electrical properties of the film by using thermally stimulated electrical measurement under a needle-plane electrode system. It was found that the electric field formed in an LDPE film near the needle electrode was relaxed by the space charge injected from the needle electrode into film. In a present paper, we firstly measured both the inception voltage of treeing and the length of the path generated in an LDPE film by the electrical treeing under a needle-plane electrode system. We then measured both thermally stimulated current (TSC) and thermally stimulated surface potential (TSSP) generated in an LDPE film. After that, we investigated the relationship between the electrical treeing and space charge formed in an LDPE film and the tip of needle electrode used in the present investigation was approximately as same as the length of the path generated by the electrical treeing. Finally, the mechanism of the electrical treeing was also investigated on the basis of our experiments.