Surface trap effects on flashover voltages of epoxy/Al2O3 nanocomposites for high voltage insulation

In this paper, surface trap distribution and the affected surface charge transport properties in epoxy/Al2O3 nanocomposites were studied to provide theoretical and experimental basis for improving surface flashover performance in vacuum. Four different contents of nano-Al2O3 particles were doped into epoxy and different trap distribution of samples was calculated from the surface potential decay method. Surface charge injection was identified by a direct current integrated charge [DCIC-Q(t)] method. Secondary electron emission (SEE) coefficient were obtained combing testing and fitting method. Results showed improved charge injection resistance, reduced charge mobility and SEE coefficient at a slight concentration of 0.5 wt% and 1 wt% by introducing deep traps. Continuing to increase nanoparticles in matrix was proved to reduce trap depth and have adverse effects. The surface flashover voltages reached the highest at 1 wt% nano-doping, which was in accordance with the percolate threshold loading content for trap depth, charge injection field and SEE coefficient. Surface charge injection caused the local field enhancement at the counter electrode and increased the possibility of surface flashover. Deep traps over 1 eV contributed to carrier capture, reduced charge injection and had a positive effect on increasing surface flashover voltage.