Degradation behavior of resin-impregnated paper composites in DC bushings under extreme thermal cycling: From mechanisms to lifetime assessment

Abstract

Resin-impregnated paper (RIP) composites are widely used as high-performance insulating materials in DC bushings. However, in cold regions, these bushings are subjected to severe thermal stresses that irreversibly deteriorate their mechanical and electrical properties, thereby threatening the reliable operation of power systems. In this paper, accelerated thermal cycling tests are performed on RIP composite, followed by comprehensive characterization of surface morphology, physicochemical properties, mechanical strength, and electrical performance. Results show that microcracks primarily emerge at the early stages of thermal cycling, leading to mechanical and electrical degradation. In addition, moisture ingress and thermal aging elevate the ionic concentration, leading to higher trap density and dielectric losses, which further compromise insulation performance. Finite element simulation results indicate that degradation typically initiates at the interfaces between resin and paper. Furthermore, a mechanical failure lifetime model and an improved Havriliak-Negami dielectric response method are proposed for the prediction and assessment of the degradation state. By integrates experimental analysis, numerical modeling, and condition assessment, this study not only advances the fundamental understanding of thermal stress induced deterioration, but also provides practical guidance for the design of advanced insulating materials and the reliable operation of power equipment in extreme climates.