PD measurements in N2-SF6 gas mixtures with the UHF method

Highly stressed gas insulated systems are very sensitive to small defects like particles or sharp protrusions. For the detection of such defects in gas insulated substations (GIS) with pure SF₆ insulation several PD measuring methods, the conventional method according to IEC 60270, the acoustical or the UHF method are in use. Especially the UHF method proved to be very sensitive. For N₂-SF₆ mixtures, it still has to be proved that the UHF method is applicable for sensitive PD measurements. Therefore PD measurements were carried out on different mixtures to examine whether the UHF method can be used for diagnostics in gas-insulated transmission lines (GIL). In addition, measurements of the PD currents in the time domain also were made to gain comprehensive results