Performance Evolution of XLPE–EPDM Interface Insulation under Repetitive Impulse Discharges

Emerging power-electronic-based systems expose high-voltage equipment to frequent impulse stresses, posing challenges to the reliability of solid–solid insulation interfaces in components such as cable accessories. Although the breakdown characteristics of the interfaces have been widely studied, long-term degradation under such conditions remains insufficiently understood. This work investigates the performance evolution of the crosslinked polyethylene (XLPE)–ethylene propylene diene monomer (EPDM) interface under repetitive impulse discharges. An interfacial discharge platform under impulse voltage was constructed, and the corresponding discharge signals were recorded. The surface morphologies and chemical modifications of the post-discharge specimens were characterized. Results indicate that the discharge inception voltage (DIV) first increases and then decreases with the number of impulses. The rising stage is associated with the formation of a discharge-induced surface reformation zone (DSRZ), where localized asperities on the XLPE surface are oxidized and decomposed due to particle bombardment and thermal effects, leading to reduced surface roughness and improved interfacial contact. As the discharge progresses, carbonized byproducts begin to appear and gradually accumulate, counteracting the beneficial effects of the DSRZ and resulting in the turning point of the DIV. Eventually, the effect of carbonized byproducts dominates, causing a continuous decline in the DIV and a progressive deterioration of the interfacial condition. In addition to revealing the degradation mechanism, the stage-wise evolution of electrical signals provides valuable references for the monitoring and diagnosis of insulation conditions in high-voltage systems.