On Sept. 30, 2020, the EU released a detailed report (1) outlining alternatives to sulphur hexafluoride (SF6) for use in switchgear and related equipment. The report also extensively covers market impact and cost issues. This is the latest in a series of indications that the pressure is on to phase out SF6, as part of the EU’s mission (2) to cut harmful greenhouse gas (GHG) emissions by two-thirds between 2014 and 2030. Replacing SF6 would be a significant contribution by the energy distribution industry as it the biggest GHG contributor for this sector.
For decades, SF6 has been used in switchgear as an insulation material and current-breaking medium, providing excellent electrical properties and chemical stability that help prevent short circuits and accidents. It is widely used across transmission and distribution, high voltage (HV) and medium voltage (MV), from large power stations to wind turbines and substations.
The ban on SF6 in the energy sector lags behind other industries. Historically, that was partly due to a lack of viable alternatives, but that has changed, with several switchgear manufacturers making significant investments in SF6-free solutions across MV and HV, some of which are already successfully deployed.
The September 2020 EU report forms part of the EU’s review of the F-Gas Regulation, which is in a public consultation (3) period until the end of December 2020, and EU Commission adoption is planned for the fourth quarter of 2021. Tighter regulation around SF6 in the energy industry is one of the expected outcomes. Even before the September 2020 report, the spotlight was already on SF6, for instance it is listed in the Kyoto Protocol (4). With a global warming potential (GWP) of 23,500, SF6 is considered the most potent of greenhouse gases. A recent study by the University of Antwerp (5) also suggests that reported SF6 emissions are underestimated and provides a projection of potential CO2 equivalent savings for a SF6 phase out, using the example of 145kV gas insulation switchgear (GIS).
Given that evaluating and implementing alternatives will take several years for an energy provider, there is no time to lose. The biggest challenge is to find a solution that lives up to SF6’s performance legacy, as well as meeting environmental requirements. The good news is that through the collective R&D of experienced switchgear manufacturers and other experts, today power utilities have several alternatives to SF6.
There are three main alternative approaches to SF6 replacements in play today: based on 3M Novec 5110 Insulating Gas which is a C5-Fluoroketone; based on 3M Novec 4710 which is a C4-Fluoronitrile; and dry air based in combination with a vacuum interrupter. These are all outlined in the EU report, as well as another report published in February 2020, by T&D Europe (6), the European association of the electricity transmission and distribution equipment and services industry.
Milestones in Practice
Nor are these alternatives just theory: there are numerous installations that have been reported across the European region. For instance, Novec 5110 mixtures with dry air have been in service in primary MV since 2016 and are now available up to 40.5kV. Other SF6-free solutions based on filtered air (12 – 24kV) or natural origin gases (12kV) have just been piloted in 2020 In secondary ring main units (RMUs), Novec 5110/air mixtures have been in service in 24kV RMUs since 2016. Filtered air RMUs for 12kV and 24kV have been piloted during 2020, while 12kV RMUs with natural origin gases have been in service since 2019.
In HV, a 170kV gas insulated switchgear (GIS) based Novec 5110 mixture with CO2 and O2 was the first SF6 alternative installed in a HV GIS, located in Zurich in 2015. GIS using a Novec 4710, CO2 and O2 mixture was first installed in a 145kV GIS in 2017, and is now used at 15 sites with a total of 100 bays. 72.5kV and 145kV GIS using synthetic air as insulating media together with vacuum interrupter for circuit-breaking have been available since 2016.
Switchgear Manufacturers Pushing the Boundaries
Switchgear manufacturers behind these alternatives continue to push the boundaries of what is possible and nearly all of them have also responded to the EU roadmap for the F-gas revision (7) with detailed proposals for an SF6 phase out.
In addition, some manufacturers have also published their development roadmap or objectives to extend their SF6-free portfolio.
GE Grid Solutions is using a gas mixture based on 3M Novec 4710 Insulating Gas in its g3 (pronounced “g cubed”) technology. GE has announced a g3 roadmap (8) until 2025 to extend its SF6-free portfolio up to 420kV which also includes an EU Life (9) funded project.
AirPlus is a gas mixture using Novec 5110 Insulating Gas from 3M and is used by ABB in MV equipment, and by Hitachi ABB Power Grids in HV equipment. ABB (10) has also announced its objective that up to 90% of its GIS portfolio variants will be SF6 free. Hitachi ABB Power Grids (11) has an ongoing project with German utility TransnetBW (12) to upgrade a 380kV substation with its eco-efficient, SF6 free technology.
Additional switchgear manufacturers, such as Siemens Energy (13) and Schneider Electric (14), have made similar announcements expanding their SF6 -free portfolios.
These are just some of the milestones achieved in replacing SF6 to date. It is important to bear in mind that what might work for one application may not be the best fit for another. The T&D report also provided a comparison of some key criteria to consider, including dielectric strength, available voltage, minimum operating temperature, heat dissipation and the gas insulation switchgear footprint.
Regardless of the chosen approach to replacing SF6, the EU report estimates that — depending on the voltage class — a full commercialization of alternative solutions is already realistic after a transition period of two to five years, for example for MV, and for HV GIS up to 145kV. The report also evaluates potential cost increases and concludes that “in general, where the SF6-free alternatives are more costly than switchgear containing SF6, policy intervention is likely to be needed to trigger a transition.”
In the meantime, switchgear manufacturers will continue to develop SF6 replacements beyond current voltage levels, and as the clock is ticking, now is the time for utility companies to start planning for an SF6-free future. After all, rather than wait to be forced to act, it is better to have sufficient time to evaluate alternatives and phase-out strategies, in the interests of utility firms and the planet alike.