Non-linear dc and ac conductivity in electrically insulating composites

The non-linear electrical behavior of zinc oxide, used to practical advantage in surge arresters on distribution power systems, has been replicated in epoxy resin, which has been filled with an appropriate volume fraction of this intrinsically semi-conducting material. Comparison has been made with epoxy resin containing a similar volume fraction of aluminum oxide in order to establish that the non-linearity observed in zinc oxide filled resin is a function of the zinc oxide itself and not simply an artifact resulting from the presence of any filler and the interfacial phenomena thereby arising. Previous work in this field, in both thermo-setting and thermo-plastic insulation has concentrated on dc voltage application. This work, in addition to extending the range of host materials to include epoxy resin using dc, has also explored the ac behavior. The results demonstrate that the inclusion of zinc oxide in epoxy resin is capable of producing non-linear conductivity when the filler volume fraction exceeds the percolation threshold (similar to15%).