Since the mid-twentieth century, sulfur hexafluoride (SF6) has been widely used as a replacement for oil as an insulator in electrical equipment, with one of its largest uses today being in electrical switchgear. SF6has proven to be reliable and highly effective in applications where arcing can be expected and its use has enabled smaller, cleaner designs and greater equipment durability over time.
By almost all accounts, SF6has been a strong performer in electrical equipment.
The global warming concern
However, SF6is also a “greenhouse gas” (GHG). As one of the group of compounds known as fluorinated gases, SF6turns out to be the most potent GHG in terms of its global warming potential (GWP).
With this realization have come strict measures to help limit the release of SF6into the atmosphere. These include careful accounting of the production and distribution of SF6as well as limits on its use.
In the United States, the EPA began investigating SF6in 1997. In 2012 it mandated reporting for equipment with nameplate capacities of 17,820 lb or more. This has resulted in a marked decrease in emissions. Many states – most notably California, but also including Washington, Oregon, Massachusetts, and New Jersey – have followed suit by instituting SF6reporting regulations and lowering permissible emissions.
As early as mid-2000, the European Climate Change Programme (ECCP) identified SF6reduction as a key component in its GH reduction initiatives to meet the Kyoto Protocol commitments made by the EU. Plans included the eventual banning of some F-gases in specific applications as well as strengthening the operational controls of systems that use these gases and limiting their production and import/export activities. These efforts have continued under the Paris Climate Agreement of 2015. With the next UN Climate Change Conference scheduled for November 2020, many participating countries are now drafting updates to their climate plans, or Nationally Determined Contributions (NDCs). Environmentalists anticipate that 2020 may mark a turning point in GHG reductions, ushering in even more rapidly tightening regulations.
F-gases, including SF6, are increasingly subject to local and regional regulations that aim at limiting their use in a bid to meet the applicable sustainability and environmental targets.
Logging successes, but challenges remain
Great advances have been made in GH reduction in applications such as aerosol propellants and air conditioning. For example, the automotive industry and HVAC manufacturers in general have over a number of years phased out the use of HFC-based refrigerants. Some uses of SF6, such as in magnesium production, have also been drastically curtailed. However, its use continues in several applications.
85% of the SF6produced today is used in high-voltage and medium-voltage electrical switchgear along with other gas-insulated electrical equipment. The record keeping for these closed systems reflects very low loss rates of 2% or less industrywide. Other uses of SF6where the gas is not in a closed system include medical and metallurgical applications. Although these applications account for a smaller portion of SF6usage, they contribute most of the SF6that is released into the atmosphere.
Where are the rules today and where are they going?
In the EU
The EU has set the goal of reducing its F-gas emissions bytwo-thirds by 2030. Although much of this will come from using less of the gases covered by the Montreal Protocol, SF6is an integral part of the mix. Specific measures being implemented include limiting the total amount of F-gases that can be sold in the EU; banning the use of F-gases in many new types of equipment; and preventing F-gas emissions through monitoring, servicing, and end-of-life (EoL) gas recovery.
SF6recovery is especially important. The most climate-damaging driver of SF6 impacts involves the potential equipment EoL emissions. This process for a unit of MV switchgear encompasses the final journey of SF6from its extraction from the switchgear to transport to recycling or destruction. European regulations for SF6handling and recovering exist, but implementation of these rules is uncertain.
The Fraunhofer Institute for Energy Economicsestimatesthat different users exhibit a range of quality in their behavior at SF6EoL – from good SF6handling to negligence – depending on whether the switchgear owner is a large electric utility or a member of the more fractured private market. Fraunhofer estimates the following SF6leakages during that lifecycle stage:
large utility best practice 1.5%
actual leakages best guess 10%
worst case 40%
Only stronger regulation of the decommissioning of SF6equipment, and/or enforcement of the existing policy can solve this problem.
In the US
In California, these types of regulations are promulgated through the state’s Air Resources Board (ARB). Although a phase-out schedule is currently in place, including increasingly stringent limits on allowable SF6emissions rates, which in 2020 bottomed out at just 1%. Current plans include a staged phasing out of SF6use, beginning with equipment rated at 72 kV or less at the end of 2024. Its use in higher voltage equipment will occur at the end of 2026 and 2028, with the equipment with the highest rated voltage (550 kV) no longer being allowed to use SF6as of December 31, 2030.
Future limits on SF6production
Most regulations that ultimately will affect the use of SF6address the chemically similar family of fluorinated gases commonly referred to as ‘F-gases.’ This includes hydrofluorocarbons (HFCs), which are relatively short-lived, and perfluorocarbons (PFCs), which can remain in the atmosphere for many years. Both HFCs and PFCs have been largely replaced by more environmentally friendly alternatives. Thus, as F-gas regulations grow more stringent, they will increasingly affect SF6.
Alternative technologies change the game
Regulatory activities concerning SF6use have continued to grow in recent years, centered primarily in California and the European Union (EU). These regulations have mostly granted exemptions for the continued use of SF6in high- and medium-voltage switchgear for the reason that alternative technologies did not exist. But manufacturers who are thinking long-term have been working to develop more sustainable alternatives to SF6-based technology and several now offer creative new approaches to switchgear design, operation, and maintenance. As these new technologies have been proven in field trials, both the EU and California are showing an increased willingness to move toward further reducing the production and use of SF6. For example, regarding SF6in medium voltage switchgear applications, the European Commission is currently assessing the feasibility of SF6alternative technologies that enable the replacement of this GHG.
The new technologies differ from one manufacturer to another, with some choosing to focus on reducing GWP with the help of alternative gases. Certain equipment manufacturers, including Schneider Electric, have elected to avoid the uncertainties surrounding new and unproven alternative gases and instead use pure air for this green transition. In addition to being safe for people and the planet, this air-based approach reduces future regulatory risk. The new green and digital switchgear range, SM AirSeT, has alreadywon the Industrial Efficiency Award at the 2020 Hannover Messeand received the prestigious iF Design Award earlier this year.
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Originally posted onSE Blog & Authored byFrederic Godemel
About the author:
Mr. Godemel’s career at Schneider Electric, which he joined in 1990, has developed mostly around the power business in both low & medium voltage, in operational functions in France and more recently in China. He holds a degree in engineering from Centale and an MBA from Essec. He was named to his current position in January 2019, having held earlier positions as Executive Vice President for Global Field Services being based in Dubai, UAE.