Synergic Effects of Biaxial Mechanical Stress on Electrical Tree Growth of Epoxy Resin

Epoxy insulators are subjected to complicated mechanical stresses as well as strong electric field, resulting in frequent breakdown faults in gas-insulated transmission line (GIL). In this study, the synergic effects of biaxial stresses on electrical tree growth are investigated by pulling and compressing the epoxy samples in two perpendicular directions. Results show that tensile stress promotes the electrical tree growth, while compressive stress plays the role of suppressing first and then promoting as the stress value increases. That is, the relation between biaxial stresses is not only a competition but also a cooperation. The mathematical relations between the biaxial stresses and the tree growth rate are obtained by correlation analysis, and the energy model of brittle materials is proposed to explain the underlying mechanism, i.e., the tensile failure model for the competitive relation and the shear failure model for the cooperative relation. The energy model of epoxy resin is established quantitatively, and it is in good agreement with the experimental data. The outcomes of this study are hoped to provide references for the insulation design and material modification in UHV projects.