Partial Discharge Behavior of Natural Origin Gases Depending on Gas Pressure and Electric Field Homogeneity

Gas-insulated switchgear (GIS) offers multiple advantages compared to air-insulated switchgear (AIS); primarily, due to its more compact design and reduced maintenance requirements. In recent years, environmentally friendly replacement gases for SF6 have become an important research topic, not least because EU regulation will ban the use of SF6 in new equipment for its member states in the coming years. For detecting defects inside equipment, partial discharge (PD) measurements are an important and well-established method, including in acceptance tests (FAT and SAT) and online monitoring. An important question is whether the PD behavior of various defects analyzed in SF6 differs in potential replacement gases. In this work, standard geometries in form of needle plane arrangements were used to analyze the PD inception behavior of natural origin gases (synthetic air, CO2 and N2,) in comparison to SF6 at various application relevant pressures. PD was measured both by the conventional (IEC 60270 conform) and UHF technique, recording the phase resolved partial discharge patterns (PRPDs), as well as emitted UHF-pulses. The tip radius and the protrusion length of the needle electrode were varied in order to investigate the influence of the electric field distribution on the PD inception behavior. Results show positive pressure dependence, but also deviations from the linear growth of PDIV, intermittent discharge behavior in synthetic air for some conditions and high-current discharges in the N2 in the setup used.