AC conductivity effects of non-linear fillers in electrical insulation

This paper investigates the AC electrical characteristics of zinc oxide filled epoxy resin at high electrical fields. The AC conductivity of two filler concentrations, 10% and 20% was measured and compared with the conductivity of unfilled resin. In addition, zinc oxide powder was compressed into solid samples which were then impregnated with small amounts of epoxy resin used as a binder. The AC conductivity of these samples were also measured to give a comparison between high and low zinc oxide concentrations in epoxy resin. It has been observed that the AC conductivity of the 10% filled samples has similar characteristics and values to the unfilled samples, with current being purely capacitive. The 20% filled samples show evidence of AC non-linearity with a resistive peak forming at high fields, this peak increasing non-linearly with increased field. Similarly, the high concentration zinc oxide samples also show this non-linear resistive peak, although its formation occurs under much lower field conditions. The results from this study show that the inclusion of zinc oxide into polymer insulating materials can produce a non-linear AC conductivity when the volume fraction of filler is sufficient. Thus, the filled polymer composite material can offer surge arresting capabilities in addition to other benefits such as improved electrical tree resistance and space charge dissipation