Effect of nanoparticle surface modification on breakdown and space charge behavior of XLPE/SiO2 nanocomposites

This paper focuses on the effect of nanoparticle surface modification on the DC breakdown and space charge behavior under DC endurance test of XLPE/SiO₂ nanocomposites. A titanate (TC) and a vinylsilane (VI) coupling agents, both of which contain non-polar functional groups, were used as surface modifiers for SiO₂ nanoparticles. FESEM results clearly show that TC and VI coupling agents improved nanoparticle dispersion within XLPE matrix compared with unmodified nanocomposites, where occurred severe agglomerations larger than 1 μm in size. The improvement of nanoparticle dispersion was due to the increase of surface hydrophobicity of SiO₂ nanoparticles. In addition, it was found that surface modification improved DC breakdown strength under different temperatures compared to XLPE or unmodified XLPE/SiO₂ nanocomposites. XLPE/VISiO₂ nanocomposites possessed the highest DC breakdown strength and relatively low dispersibility. The results of space charge measurements under DC endurance test reveal that the introduction of SiO₂ nanoparticles could not effectively suppress the injection and movement of space charge until organic surface modification, which was believed to contribute to the formation of more and deeper trap sites considering the better dispersion of SiO₂ nanoparticles within XLPE matrix. The space charge results also show that breakdown during DC endurance test usually occurred after the largest electric field passed, which is believed to be the degradation of dielectrics caused by the formation, movement, accumulation, and dissipation of space charge. Finally, the lower electric field distortion of modified XLPE/SiO₂ nanocomposites was considered to decrease the degradation of XLPE/SiO₂ nanocomposites.