Influence of Grafting Modification on High-Temperature Electrical Treeing Characteristics of Polypropylene Cable Insulation

Polypropylene (PP) is regarded as an environmentally friendly cable insulation material to replace cross-linked polyethylene (XLPE) owing to its thermoplastic nature, high-temperature resistance, and outstanding dielectric characteristics. Grafting modification was applied to satisfy the demand for a higher voltage power grid, and it was proved to be effective in enhancing the insulating performance of PP. The electrical tree is a common cause for cable insulation failure. This study examines the electrical tree initiation and growth characteristics of methyl methacrylate (MMA)-grafted PP under different temperatures. Our results indicate that high temperature can promote the electrical treeing process while grafting modification can hinder the process. The trap characteristics show that more deep traps are introduced in the grafted materials that can limit the motion of electrons and, thus, restrict the electrical tree initiation process. The crystallization morphology shows that the size of spherulites increases and the boundaries of the spherulites become blurry with higher MMA content. The compressed amorphous region and the tortuous boundaries of the crystalline can hinder the electrical treeing process. High temperature may improve charge carrier mobility and enhance the molecular chain relaxation, thus enlarging the free volume and finally accelerating the treeing process. The findings of this study would serve as a reference for designing grafted PP insulation for power cables.