Electrical surface breakdown characteristics of micro- and nano-Al2O3 particle co-doped epoxy composites

Epoxy microcomposites are basic materials for gas-insulated switchgear (GIS) spacers that are subjected to huge electrical stress. Previous works have indicated that nanoparticles are beneficial to dielectric performance. However, surface electrical breakdown, a typical fault in GIS of co-doped micro- and nanoparticles in epoxy composites, is seldom studied. In this work, numerous concentrations of micro- and nano-Al2O3 are co-doped into an epoxy matrix; the surface traps, surface charging, and surface breakdown voltages (V-sb) of the co-doped composites are studied, and the influence of micro- and nano-Al2O3 on the electrical surface breakdown is clarified. The results show that V-sb first decreases and then increases with the microparticles, and V-sb decreases from 25.34 kV to 19.52 kV. As the number of nanoparticles increases, V-sb increases and then decreases when the microparticle loading is low, but decreases and then increases when the microparticle loading exceeds 40 wt%. Micro-Al2O3 particles introduce surface shallow traps into epoxy composites, while small amounts of nano-Al2O3 introduce deep traps. Two different mechanisms dominate the surface charging and V-sb of epoxy micro-nanocomposites. When the surface conductivity is lower than 7 x 10(-14) S, the surface charges are reduced by the suppression of electrode injection as the trap depth increases, and V-sb increases. When the surface conductivity exceeds 7 x 10(-14) S, the surface charge dissipation rate increases with the surface conductivity and V-sb increases as the surface conductivity increases. Our work indicates that co-doped micro- and nano-particles should keep the surface conductivity away from the specic value (7 x 10(-14) S) to safeguard insulation properties for GIS spacers.