A New Approach to Treeing Inception Tests

The paper, stressing the importance of better understanding of physical phenomena leading to the inception of treeing in polymeric insulation, presents the quantitative and qualitative advantages of using needle electrodes for tree initiation tests with much sharper tips than those used in propagation studies. The experimental procedure of getting samples with embedded electrode tip radii of about 0.1 pm is presented. Samples of epoxy resin and polyethylene with different levels of crosslinking were investigated. For comparison tests, IEC needle electrodes were also used. Both electrical total charge and partial discharges and optical photoemission phenomena accompanying the initiation phase of treeing were recorded. The results show conclusively the proposed electrodes to give much less scatter in the results, to considerably shorten the test times, and to enable a much better differentiation between various materials with regard to their tree inception behavior than "classical" electrodes.