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 Novec^TM 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.