Wind power and photovoltaic power generation are far away from the power load center, which requires highvoltage DC cables for power transmission. However, the breakdown strength of the solid-solid interface composed of epoxy resin/silicon rubber (EP/SiR) in the cable accessories is low, which may easily lead to the failure of the cable. Therefore, it is urgent to study the influencing factors and improvement methods of the breakdown strength of the EP/SiR interface. A test system for measuring the breakdown characteristics of EP/SiR interface is established, and the breakdown characteristics of EP/SiR interface under different stresses are measured. The breakdown test found that the contact interface between EP and SiR is a weak area, and obvious ablation and carbonization traces can be observed. The breakdown strength of the EP/SiR interface increases with the increase of the applied stress perpendicular to the interface. The breakdown strengths of the interfaces formed by EP microcomposite/SiR and polyhedral oligomeric silsesquioxane modified EP microcomposite/SiR are higher than that of pure EP/SiR interface. From the perspective of changing the length of the interfacial air gap and suppressing the impact ionization in the air gap, the effect of stress on the breakdown strength is analyzed. The influence mechanism of doping modification on breakdown strength is analyzed from the viewpoint that polar materials easily form bound charges at the interface, thereby attracting carriers and hindering their movement. The research results provide experimental results and model support for material formulation optimization and breakdown strength improvement methods of plug-in cable joints.

bound charge and carrier interaction;impact ionization;interface breakdown;solid-solid interface;;plug-in DC cable accessory