Effect of Functional Grafting Modification on Dielectric Properties of Polypropylene Insulation Part II: Space Charge and DC Breakdown

This paper investigates the effect of antioxidant grafting on the electrical properties of polypropylene (PP) insulation for HVDC cables. The DC conductivity, space charge distribution, and breakdown characteristics of grafted modified PP are tested, and the results are compared with the neat PP. The experimental results indicate that grafted PP with antioxidants containing functional groups can effectively reduce high-temperature conductivity and inhibit the injection of space charges. Compared with the neat PP, DC breakdown strength of the grafted PP samples has significantly improved from 70 to 90°C and can still maintain a high breakdown strength after heteropolar DC pre-stressing. The electrostatic potential and molecular orbitals of grafted PP are calculated, revealing that antioxidants containing functional groups can introduce deeper localized state traps, effectively trapping charge carriers, reducing carrier damage to the molecular chain, and improving breakdown strength. In conclusion, antioxidant grafting can significantly enhance the space charge and breakdown characteristics of PP and thus is expected to be applied in PP-insulated cables.