Comparison of GIS UHF partial discharge measurements in clean air and SF6

Gas-insulated switchgears (GIS) as junctions of transmission and distribution networks have increased significance for the assurance of a high quality of the electrical power supply. Considering the increasing cost pressure to the network provider and system erector the reliability and quality of the electrical equipment needs to be assured. Therefore, suitable diagnostic technologies are commonly used to monitor electrical equipment and to potentially extend their service life. For GIS insulation monitoring the UHF partial discharge (PD) monitoring have become the industry standard. More than 40 years' experience exist for such PD measurements in SF₆ GIS. Due to the significant Global Warming Potential (GWP) of SF₆ alternative insulation gases are introduced in last years. The most promising approach in compliance with expected regulations of F-Gas restrictions including PFAS (poly- and perfluoroalkyl substances) is using Clean Air under increased pressure as insulation [1]. Clean Air is a mixture of 80 % Nitrogen and 20 % Oxygen and has a GWP of zero. To understand the impact of the alternative gas on the UHF PD Monitoring approach detailed comparisons of UHF PD measurements in SF₆ and Clean Air are presented in this paper. Investigated are the amplitudes and frequency ranges in which PD signals can be measured. And the PRPD patterns that can be observed for typical PD defects are shown for Clean Air and SF₆. Standard monitoring equipment with a frequency range of 300 to 1500 MHz is used. The conclusion of the detailed investigation is that the standard UHF PD monitoring systems can be used for Clean Air GIS as well as for SF₆ and PRPD patterns look quite similar with some minor deviations.