Tailored internal stress in dry cable termination by zirconium tungstate modified epoxy composite for low-temperature environments

Abstract Internal stress consisting of residual stress generated during the curing process of epoxy and thermal stress caused by temperature changes during operation will increase the insulation failure risk of epoxy-based power equipment. In this paper, the internal stress distribution inside a typical cable termination system under various temperatures is quantitatively evaluated, based on curing kinetics analysis and finite element simulation. It is indicated that the maximum internal stress appears at the interface between the metal insert and epoxy, reaching 83.2 MPa at −40 °C, due to thermal mismatch between different materials. The relationship between operational reliability of the termination, temperature and thermal expansion coefficient of the insulating material is established, considering the generated stress and intrinsic mechanical strength of epoxy. A modification method to reduce internal stress is proposed by introducing nanoparticles with negative thermal expansion characteristics into the epoxy. Results show that doping the 15% content of zirconium tungstate can reduce the thermal expansion coefficient and mitigate internal stress concentrations by 45.2% and 47.1%, respectively while maintaining electrical insulation and mechanical performance unaffected. As a result, the operating temperature of the cable termination could be extended below −40 °C. These results provide effective methods for assessing and improving the operational reliability of epoxy-based cable termination in low-temperature environments.