An experimental device is designed for surface flashover test along gas-solid interface

where the finger electrodes or flat electrodes are alternatively installed

and the stainless steel finger type electrodes with 10 mm curvature radius are selected. The peak output voltage of pulse power reaches to 135 kV with 20 ns rise time and 5 μs full width at half maximum. The experimental properties of pure epoxy and epoxy composite samples are discussed under nanosecond pulse in air and SF

6

. The breakdown properties of air and SF

6

under different pressure are investigated by using finger electrodes. Moreover

the surface flashover properties of pure epoxy samples under different air and SF

6

gas pressure and the flashover properties of epoxy/Al

2

O

3

·3H

2

O composites filled with different filler concentration in 0.4 MPa are also analyzed. The experimental results show that the dispersion of surface flashover voltage of epoxy in SF

6

gets higher than that in air

and the surface flashover voltage of the composite approaches the lowest while the filler concentration reaches to 20%.