Insulation characteristics of GIS spacer for very fast transient overvoltage

V-t characteristics of spacer surfaces for VFT were investigated under particle contaminated conditions. V-t characteristics for VFT were measured with the particle length, oscillation frequency, amplitude, and damping factor of VFT waveform as parameters. Differences in V-t characteristics for VFT due to variation of oscillation frequency, amplitude, and damping factor were small. Further, they were compared with V-t characteristics for lightning impulse. The dielectric strength of spacer surfaces for VFT was found to be at least equivalent to the dielectric strength for lightning impulse.