Voltage Endurance Characteristics of Cross-Linked Polyethylene–Silicone Rubber Interface Subjected to DC and AC Voltages

When designing and inspecting power equipment, it is crucial to consider not only the distinctions between ac, dc, and ac–dc hybrid systems but also the voltage endurance characteristics. However, scientific design and research on the mechanism responsible for the breakdown of solid-solid interfaces (e.g., cable joints), which are weak points in electrical insulation, is lacking. Therefore, in this study, the insulating strength of the interface in relation to the electric field form and voltage endurance time is examined. Specifically, the increase in the insulation strength and the ablation of cross-linked polyethylene–silicone rubber (XLPE–SiR) interfaces are investigated based on the ramped breakdown and step-stress methods. The results illustrate that the dc breakdown strength surpasses the ac breakdown strength, while the ac field fails to reach the composite (ac–dc) electric field breakdown strength. Furthermore, the interfacial breakdown strength is influenced by both long-term and transient stresses. The interfacial breakdown process can be divided into three stages. The breakdown voltage increases in the short term with decreasing step-up rate. Step-stress tolerance experiments and simulations indicate that the highly distorted electric field at asperity contacts leads to cavity discharges and electrothermal losses, resulting in the ablation of the asperities on the rough surface. The electric field distortion decreases with decreasing interface roughness, leading to an increase in breakdown strength. Moreover, as the endurance time increases, the improvement of the ac breakdown strength is more significant than that of the composite electric field, while the dc breakdown strength shows the least improvement.