Comparison of Radial Performance in Polypropylene‐Based Insulation for 100 kV DC Cables

ABSTRACT Polypropylene (PP) has emerged as a promising eco‐friendly alternative to cross‐linked polyethylene (XLPE) for high‐voltage direct current (HVDC) cables. This study systematically investigates radial differences in the insulation layer of blending‐modified PP cables. The insulation layer was stratified into three distinct radial regions: the conductor‐proximal inner layer, the intermediate middle layer, and the insulation shield‐adjacent outer layer. Radial variations in the polypropylene insulation layer, including melting and crystallization behavior, crystalline morphology, and electrical properties, were comprehensively characterized. The experimental results demonstrated negligible variation between melting temperature and crystallization temperature in different radial positions of the insulation layer. In terms of electrical properties, the outer layer exhibited significantly higher volume resistivity and DC breakdown strength at different temperatures, which were attributed to its elevated crystallinity and reduced crystallite dimensions. In contrast, the middle layer demonstrated lower crystallinity yet displayed larger crystallite sizes. Although the distinct crystalline structures give rise to slight differences in the electrical and mechanical properties of polypropylene insulation specimens at different radial positions, the specimens at different radial positions still exhibit sufficiently consistent characteristics. The results validate the feasibility of their application in HVDC cables.