Assessment of breakdown voltage of SF6/N2 gas mixtures under non-uniform field

The dielectric breakdown of SF₆/N₂ gas mixture insulating system is believed to be sensitive to local irregularity of the electric field which may result from the presence of defects such as contaminants adhering to the electrode surface and surface roughness. Normally the surface roughness is produced from machine finishing and due to the aging of the system. This paper models the insulation breakdown mechanism of SF₆ gas mixture in the presence of surface roughness for non- uniform field gaps. The electric field inside the gap is computed by using the charge simulation method taking into consideration the perturbations of the field in the presence surface roughness. The breakdown voltage is assessed by applying the criterion of slightly and highly divergent field and using the experimental results of figure-of-merit which is a measure of quantifying of the sensitivity of the gas to the effects of the electrode surface roughness.