Non-uniform electric field partial discharge endurance and degradation of polymer insulation with and without additives

High voltage engineering has been dependent on material performance since the beginning of commercial electrical power. Higher electrical voltages, cost, and greater service life have been driving dielectric development since the late 1800's. To assist in the development of dielectrics, various tests have been devised to understand basic phenomena or to evaluate new materials. An investigation into whether blending of selected additives in polymers results in enhanced corona endurance and resistance to corona oxidation was made. Corona mechanisms are explained in terms of electric field and swarm parameters. Electrical degradation mechanisms are described. The investigation focused on two main classes of additives. The first additives are antioxidants. The antioxidants were melt blended into polyethylene. Antioxidants were selected due to the similarity of thermally induced oxidative degradation schemes and corona induced oxidative degradation schemes. Oxidative degradation is monitored by the use of X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and surface resistivity measurements. Corona current is observed by the use of a pulse train recorder. Corona endurance tests were done with a tester built to the American Society for Testing and Materials specification D2275. Results are reported of performance comparisons with a control polyethylene versus antioxidant loaded polyethylene. Antioxidant loaded polyethylene results suggest persistent performance gains in corona endurance over the control polyethylene. This is consistent with free radical and antioxidant theory.; The second additive was a polyhedral oligomeric silsesquioxane (POSS) with a chemical formula of [CH₃SiO_1.5]₈. This additive or filler is approximately one nanometer in diameter and is considered a nanomaterial. This filler was compounded with polypropylene, a polymer for which the filler has known compatibility. The filler with polypropylene comprises a multiphase system. The corona endurance testing of POSS-polypropylene is novel. Results are reported for the corona endurance performance in air of control polypropylene versus silsesquioxane loaded polypropylene. Polyhedral oligomeric silsesquioxane loaded polypropylene results suggest that performance gains in lifetime under ac partial discharge in air are realized compared to polypropylene without POSS, particularly for the most loaded composition of thirty percent.