Simulation Analysis of Electrical-Thermal-Mechanical Coupling Property for Epoxy Resin-Impregnated Paper Bushings in Converter Transformer

Epoxy resin-impregnated paper (ERIP) DC bushings in converter transformers were subjected to long-term electrical, thermal, and mechanical overstress during operation. However, current research on degradation and failure issues of the ERIP composite insulation under multiphysics coupling remain limited. In this article, an electrical-thermal-mechanical multiphysics fields coupling model was constructed for ± 800 kV ERIP bushings. Based on the finite element method (FEM), the steady-state electric field, temperature field, and stress field distribution properties of the bushings under DC voltage are simulated. The simulation results showed that the temperature field, electric field, and stress field distribution of the bushings are extremely uneven. Particularly, at the interface between the ERIP composite insulation and the current-carrying conductor for the flange side region of the bushing, there were relatively high temperatures, strong electric fields, and stress concentrations. This region exhibits severe distortions in the electric and thermal fields, accompanied by pronounced stress concentration effects, which will greatly threaten the long-term insulation performance of the ERIP composite material and increase its risk of flashover and breakdown. Further analysis reveals that the interfacial stress distribution is mainly governed by mismatched thermal expansion among materials due to temperature rise, leading to thermally induced strain under multiphysics coupling. The research results of this study can provide a valuable insight for the subsequent insulation optimization design and fault analysis of converter transformer ERIP DC bushings.