Gas leaks

Paul Reeve considers the compelling arguments for and against banning sulphur hexafluoride

It's understood that more renewable energy and a decarbonised electricity grid will play a vital role in tackling carbon emissions. These 'low to no-carbon' energy solutions, however, may rely on a man-made substance with an environmental sting in the tail.

Sulphur hexafluoride (SF6) is a colourless, odourless, non-toxic and non-flammable gas, five times denser than air. It is believed to be the world's most potent greenhouse gas, with a global warming potential 23,500 times greater than CO2, molecule per molecule. So why is it so vital to the development of a decarbonised electrical industry?

SF6 is an excellent electrical insulator, great at preventing short circuits in medium and high-voltage electrical installations. SF6 has been deployed in circuit breakers and switchgear in power stations, wind turbines and electrical sub-stations, to quench arcs and stop short circuits. Often, it replaces oil-filled circuit breakers that contained harmful polychlorinated biphenyls.

“SF6 can still be deployed in switchgear to ensure electrical safety“

Pressurised high-density SF6 enables compact gas-insulated switchgear, ideal for space-constrained applications. It also has a reliable track record, and maintenance requirements are low – handy if your equipment is, for example, part of a wind turbine in the North Sea.

SF6 is a fluorinated gas, or F-gas. The EU has prohibited many F-gases, and SF6 is already banned from many applications. Even so, it can still be deployed in switchgear to ensure electrical safety and reliability. Despite its massive global warming potential, the airborne concentration of SF6 is only a tiny fraction of atmospheric CO2, currently only contributing 0.2% to overall global warming. However, there has been a near doubling of the atmospheric concentration of SF6 during the past two decades.

The Environment Agency oversees UK rules on recovery of the gas, which is necessary when switchgear fails or degrades – but leaks and accidental releases do occur. As the gas does not break down easily, the lost SF6, along with other operational losses around the world, could exert a greenhouse effect well into the next millennium.

All this means that the European Commission is set to revisit the situation during the first half of 2020 and investigate whether suitable alternatives could enable further restrictions on SF6 in electrical switchgear. Various companies have stepped up with cost-effective alternatives for use in medium voltage (MV) equipment, notably using vacuum or solid insulation technology – but proven alternatives for high voltage (HV) switchgear may take longer to deploy.

While it's impossible to predict what the Commission will do in 2020, it might, for example, ban new usage of SF6 in MV switchgear, while examining alternatives for HV. Even then, it may have to allow time for market and operational adaptation. There also seems little sense in removing SF6 from existing switchgear – certainly not at speed. Instead, it's vital that ongoing electrical equipment operation and decommissioning does not let the gas escape.

While the days of SF6 in global electrical switchgear are not over, 2020 may be the year when those days become numbered – at least in Europe.

Paul Reeve, CEnv FIEMA is a Fellow of the Royal Society of Chemistry and director of CSR at electrical trade body ECA.

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