The influence of surface roughness and dielectric coating on AC and DC Breakdown Voltage in SF6

The surface roughness of SF6 insulated systems has a significant influence on the breakdown voltage especially at high gas pressures. Small surface irregularities can reduce the breakdown voltage. A thin dielectric coating could be a possible remedy. To evaluate the influence of rough surfaces with and without dielectric coating the distribution function of the breakdown voltage is of interest. Low probability quantiles and the influence of the first breakdown are relevant for designing GIS systems. The cumulative frequency functions of the breakdown voltage for positive and negative DC-voltage and AC-Voltage for electrodes with different technical surface roughness and coating thickness were determined. A hemisphere-plane electrode at a SF6 pressure of 0,4 and 0,5 MPa was investigated The hemisphere was covered with a thin epoxy resin coating. The plane electrode is polished and uncoated. For AC voltage an estimation of the normal distribution of a certain breakdown number (1st, 2nd, …) has been done.     «

The surface roughness of SF6 insulated systems has a significant influence on the breakdown voltage especially at high gas pressures. Small surface irregularities can reduce the breakdown voltage. A thin dielectric coating could be a possible remedy. To evaluate the influence of rough surfaces with and without dielectric coating the distribution function of the breakdown voltage is of interest. Low probability quantiles and the influence of the first breakdown are relevant for designing...     »