Use of image analysis in DC inclined plane tracking tests of nano and micro composites

Abstract

Leakage current magnitude is used as one of the failure criteria in the tracking and erosion test IEC 60587. The 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> harmonic is also often used to identify periods of arcing activity. This technique is not available for the equivalent dc test. This paper presents the use of a machine vision camera alongside measurements of leakage current to identify discharge activity during dc testing and so enable determination of arc intermittency. This simple image processing technique is shown to add significant value to the existing leakage current analysis techniques and can provide an understanding of the process of degradation and its dependence on voltage polarity. Tests are reported on a commercial silicone rubber compound, a micro-filled epoxy resin, and the same epoxy resin system with nano particle fillers at 5% by weight. It is shown that the technique is applicable to this wide range of materials. It is also shown that changes to the performance of the epoxy compound by the addition of nano filler is due to more than just improving discharge resistance, reported elsewhere. The wettability of the samples is seen to be important, controlling moisture flow during a test. For this reason, in the case of the top electrode being positive, the nano filled material failed the test earlier than the standard material, with reduced erosion but increased leakage current.