DC Pre-breakdown Light in Hexane/low-density Polyethylene(LDPE) Insulation Composites using a long Image Guide Scope and a Streak Camera

Optical observations on pre-breakdown phenomena of hexane/low-density Polyethylene (LDPE) film insulation composites were carried out by using a system mainly consisted of a streak camera and a long image guide scope. The LDPE film was placed on a sphere of point-sphere electrode, which was filled with hexane. The parameters in this study were dc voltage polarity and voltage rises speed. In most cases, under positive polarity voltage regardless of the voltage rises speed, breakdown initiated in the bulk of hexane. While, in most of the case under negative polarity voltage regardless of the voltage rises speed, breakdown initiated at the tip of needle electrode. In most cases, from the obtained streak images, pre-breakdown light developed continuously at the same place where they initiated at least for 10ns. Breakdown voltage was higher under 0.1kV/s of voltage rises speed as compared to 1.0kV/s, regardless of the voltage polarity.