Temperature Dependence of the Polarisation Characteristics of Epoxy Resin for Electrical Insulation

Abstract

Epoxy resin-based dielectric materials are widely used for electrical insulation. However, due to the application of electrical equipment in complex and diverse climatic environments, the characteristic variation of the material must be paid attention to. Besides, decoupling of the overall performance is necessary to trace the source of property variation. Thus, in this research, the polarisation characteristics over broad ranges of temperature and frequency of typical epoxy resin used for electrical insulation are investigated. Moreover, the Dissado–Hill model is adopted to quantitatively decouple the individual contribution of each microprocess. It indicates that the magnitudes of the polarisation processes below the glass transition temperature (T_g) are small, the influence of which on the overall polarisation characteristics is marginal. In comparison, the influence of α relaxation initiating above T_g on the magnitude of permittivity and the dielectric loss is prominent, which must be fully taken into consideration during insulation design. In addition, due to the long structure of repeating units in the backbone of epoxy, another polarisation process would appear at higher temperatures stemming from the internal relaxation of repeating units. Furthermore, the amplitude of conductance increases exponentially as temperature rises and would become the major component of loss at elevated temperatures. This research provides insights into the rational design of insulation structures and the development of novel epoxy materials.