Very low SF6 insulation gases for medium voltage switchgear

Due to Global Warming concerns, switchgear with lower Global Warming Potential (GWP) may become desirable. This work investigates using very low (<10%) levels of Sulfur Hexafluoride (SF(6)) along with common gases for insulating Switchgear. Design of Experiments (DOE) is used to isolate significant factors and to generate a model, an empirical equation for predictive use. For calculating GWP of gas mixtures, a weighted average calculation is made. Results show that mixtures of 0-5% SF(6) and Carbon Dioxide (CO(2)) may be sufficient for 15 kV class equipment, and 3-8.5 % SF(6) with CO(2) may be sufficient for 25 kV. In this work, CO(2) was more effective than Nitrogen. Using the weighted average calculation for GWP, these blends compare favorably with the automotive air conditioner refrigerant (R-134a, GWP = 1,300) in common use today. R-134a is approved by international agreement for automotive use to 2030(l). The resulting DOE model proved to have excellent predictive power.