To reduce the CO2 emission of electricity generation and transmission, SF6 gas needs to be replaced by more environmentally friendly gas. A solution to replace SF6 in high voltage equipment is the mixture of Fluoronitrile CF3CN with CO2 and O2. In this paper, a choice of insulating gas based on theoretical analysis is mentioned including intrinsic gas properties and also CO2 footprint analysis. Experiments were then realized to verify the thermal and dielectric characteristics of gas mixture in the equipment. Finally, investigation tests were conducted with the actual SF6 design of GIS but filled with the mixture and showed very good performance. The results confirm the feasibility of using CF3CN-CO2-O2 mixture as insulating gas in HVDC GIS.

Sulphur hexafluoride (SF6) is one of the six types of greenhouse gas covered by the Kyoto Protocol. Its global warming potential (GWP) is 23,500 times greater than carbon dioxide, making it potentially the most potent greenhouse gas on earth. It also has a lifetime in the atmosphere of up to 3,200 years, compared with around 100 years for carbon dioxide. However, SF6 gas is an excellent dielectric insulator that has been used since 1965 for electrical insulation because of its very high electrical rigidity. Worldwide, 80% of the SF6 produced is used in high-voltage AIS circuit breakers and GIS. High-voltage electrical equipment is not sealed and leaks by design. A normative leakage rate has been defined for GIS (1% until 2003, then 0.5% until 2022). By 2022, the leakage rate has been reduced to 0.1%/year for equipment using SF6 and 0.5%/year for equipment using alternative gases. For AIS circuit breakers, the leakage rate of 0.5%/year was incorporated in 2010. By the end of 2022, RTE’s installed base represented a mass of around 580 tons of SF6, with average annual emissions of 5.2 tons over [2017-2021], falling steadily over the period, and 3.82 tons in 2022, year of COLIBRI’s industrialization. Beyond environmental aspects, appearance of leaks necessarily entails maintenance operations ranging from refilling to maintain electrical insulation, to switching off equipment in order to change seals. These operations are costly (labor/supplies) and also require electrical interlocking, which increases the complexity of maintenance planning. To limit SF6 emissions and fight against global warming, while at the same time limiting the impact on operating and maintenance resources, RTE has developed a process for sealing GIS by injecting a fluid into the flange connections between the compartments during operation: the COLIBRI process.

245 kV and 420 kV substations represent more than 65% of the installed SF6 gas [1] on the grid in Europe. A large plan in Europe and in the United Kingdom consists in refurbishing existing substations and installing a large number of new assets to support the integration of renewable energy. A successful elimination of SF6 can only be done by applying SF6 alternatives at these voltage levels. Following the successful completion of the LIFEGRID project aiming at the development of a 420 kV 63 kA Circuit breaker, the demonstrated ratings of the circuit-breaker and corresponding performance will be described. An outlook on the bay and circuit-breaker architecture will be introduced to underline the benefit and robustness of the design. An update on the type tests and performance available with the bay elements will also be exposed. Disconnector bus transfer and bus charging current switching characteristics will be detailed with a comparison between the existing SF6 and the g3 (CF4-based gas mixture) versions. Then, the available performances of the fast-earthing switch for induced current switching beyond IEC standard requirements will be detailed. Finally, an outlook of the progress of the first installation of the complete 420 kV GIS substation installation will be shown. The 420 kV GIS g3 Bay and Circuit-Breaker developments are now completed and type-tested. This opens the way to an eco-friendly, complete, economical, viable and immediate SF6 abandon.