Space Charge Characteristics and Breakdown Properties of Nanostructured SiO₂/PP Composites

Polypropylene (PP) has gained attention in the industry as an environmentally friendly material. However, its electrical properties are compromised due to space charge accumulation during operation, limiting its application in high-voltage DC cable insulation. This study investigates the effect and mechanism of SiO₂ with a DDS surface hydrophobic treatment on space charge suppression and the electrical properties of PP composites. The PP matrix was doped with SiO₂ nanostructures, both with a DDS surface hydrophobic treatment and untreated as a control group. The functional group structure and dispersion of nanostructured SiO₂ in the matrix were characterized. The findings reveal that the incorporation of SiO₂ nanostructures effectively mitigates charge accumulation in PP composites. However, a high concentration of unsurfaced nanostructures tends to agglomerate, resulting in inadequate space charge suppression and a diminished DC breakdown field strength. Nonetheless, surface treatment improves the dispersion of SiO₂ within the matrix. Notably, the composite containing 1.0 wt% of surface hydrophobic SiO₂ exhibits the least space charge accumulation. Compared to the base material PP, the average charge density is reduced by 83.9% after the 1800 s short-circuit discharges. Moreover, its DC breakdown field strength reaches 3.45 × 10⁸ V/m, surpassing pure PP by 19.4% and untreated SiO₂/PP composites of the same proportion by 24.0%.