g3—the alternative to SF6 for high-voltage equipment

Abstract

Since the 1970s, transmission and distribution network relies on SF6 technology because of its remarkable arc quenching properties and dielectric insulation. However, with its high GWP of 23,500 and an atmospheric lifetime of 3200 years, the SF6 insulating gas has significant environmental impacts if it leaks into the atmosphere. In a first part, the paper draws up a status of the regulatory and financial constraints on SF6 in the world. In a second part, the paper develops how Grid Solutions, a joint venture between GE and Alstom, has addressed this environmental issue, by developing, together with the 3M Company, a SF6-free solution. The result is a gas mixture named g3 (green gas for grid), based on 3M NovecTM 4710 and CO2. This new gas mixture reduces the global warming potential by 98% compared to SF6 with only minor design modifications by respect to typical SF6 design. It is a technically and economically viable alternative to SF6, which let foresee a major revolution in the high-voltage technology. Finally, the paper describes the first applications of this g3 mixture to 420 kV Gas-Insulated Lines (GIL). Indeed, at this voltage level, GIL represents on average 50% of the SF6 installed mass in a global high voltage substation. SF6-free GIL can thus bring a quick and massive reduction of SF6 mass installed by utilities. The environmental benefits of this new technology is provided though the results of a complete Life Cycle Assessment (LCA) that has been carried out to compare SF6 and g3 technology. This LCA shows that the use of g3 in the 420 kV GIL allows to considerably reduce environmental impact on Global Warming but also on all other environmental indicators (ozone depletion, acidification, metal depletion, etc.), compared to the SF6 technology.