Surface Morphology Induced DC Breakdown Strength Reduction of XLPE Insulation for High Voltage Cables

With the increasing demand for high-voltage cable insulation reliability, the effect of surface morphology which is regulated by sandpaper grit size on the DC breakdown performance of cross-linked polyethylene (XLPE) is investigated in this study. Six kinds of XLPE samples with distinct surface morphology were prepared using different cutting tools and sandpapers, characterized by white light interferometry and scanning electron microscope, and tested for DC breakdown strength. The results indicate that reducing sandpaper grit gives rise to microstructures featuring high peak, wide spacing, and sharp edge, causing a gradual decline in DC breakdown strength of XLPE samples owing to heightened electrical field concentration and space charge accumulation. Notably, the conventional roughness parameter Sa fails to distinguish critical microstructural differences, as its statistical averaging nature masks local features like peak sharpness and crystalline defects. It is highlighted in the study that DC breakdown behavior is dominated by surface microgeometry rather than nominal thickness, and 3D morphology-based effective thickness correction in insulation performance evaluation is advocated. These findings provide a theoretical basis for optimizing high-voltage cable surface treatment processes.