On the Nature of Dielectric Loss in High-Voltage Insulation

Experimental observations have been made on resin samples containing one single cavity and on micaceous high voltage insulation. The results conflict with the generally accepted mechanism of voltage variation of the electrical characteristics of such samples, which mechanism is based on the influence of internal partial discharges. One different dissipative mechanism, namely the interfacial polarization or Maxwell-Wagner effect, is considered to fit these observations on a semi-quantitative basis. It takes into account the increase of the electrical conductivity of the surfaces struck by partial discharges, and the increase of the resistivity of the solid part of the insulation during its ageing under voltage. The relative contribution of these two mechanisms to the variation of the loss with applied voltage is influenced by voltage, temperature, frequency and of course, by the nature of the materials. According to the proposed model, the significance of some test specifications which consider the variation with applied voltage, of electrical properties of HV insulations, should be reconsidered.