Characteristics of SF6 Alternative Gas for GIS Application in KEPCO

SF6 is one of the most serious greenhouse gas with global warming potential of 23900, and mainly used as the insulation gas inside GIS(Gas Insulated switchgear). So KEPCO is trying to adapt alternative eco-friendly gases instead of SF6. Among alternative gases, the gad mixture of C4F7N and CO2 is focused for GIS uses because of its good insulation property, adequate boiling point and moderate GWP and toxicity. Firs we constructed the measurement process of mixing ratio using GC and standard mixing gas with uncertainty of 0.006%. Next, for the purpose of the GIS diagnosis, the partial discharge pattern from various defects is obtained and compared that of SF6 or CO2. We also studied the decomposition propertied after the thermal and arc aging. CO is found out as major by-product. So we decided to check out the gas aging through the CO concentration. Finally the breakdown voltage according to the moisture concentration is measured to determine the limitation of moisture concentration inside GIS. We have plan to use properties of gas mixture for maintain eco-friendly GIS.