Epoxy resin is widely used in the support, insulation, and packaging components of electrical equipment owing to their excellent insulation, thermal, and mechanical properties. However, epoxy-resin insulation often suffers from thermal and mechanical stresses under extreme environmental conditions and a compact design, which can induce electrical tree degradation and insulation failure in electrical equipment. In this study, the photoelastic method is employed to investigate the thermal-mechanical coupling stress dependence of the electrical treeing behavior of epoxy resin. Typical electrical tree growth morphology and stress distribution were observed using the photoelastic method. The correlation between the tree length and overall accumulated damage with an increase in mechanical stress is determined. The results show that compressive stress retards the growth of electrical trees along the electric field, while tensile stress has accelerating effects. This proves that the presence of thermal stress can induce more severe accumulated damage.

Insulation failures of epoxy spacers applied in gas insulated transmission line/switchgear (GIL/GIS) often occur, primarily due to electric field distortion. In this paper, a field graded coating CaCu₃Ti₄O₁₂ (CCTO) is presented to enhance the flashover performance of a GIL/GIS spacer. First, CCTO layers of different thicknesses are deposited on the spacer surface using magnetron sputtering technology. Then, insulating properties of these sputtered spacers under alternating current, direct current, and polarity reversal (PR) voltages and with the existence of metal particles are researched by experimental and simulation methods. Results show the short-term (30 and 60 min) sputtering treatments have no obvious effect on improving insulating properties.