Replacing SF6 for switchgear with fresh air

For years, SF6 has provided an efficient and non-toxic means of insulating medium and high-voltage switchgear. But its potency as a greenhouse gas means it’s on the way out. Martin Sweeney of Lucy Electric explains more.

Sulphur hexafluoride is widely used in medium and high-voltage switchgear for good reason.

Its high dielectric strength makes it possible to create smaller ring mains units. It enabled the replacement of carcinogenic compounds like the polychlorinated biphenyls used in oil-filled circuit breakers. And SF6 can interrupt large current loads, making it great for high-voltage applications.

Unfortunately, SF6 is also a potent greenhouse gas.

Just how potent? Some 22,800 times more potent than carbon dioxide over a 100-year period. That’s as measured by Global Warming Potential (GWP), which ranks gases according to their ability to trap heat in the atmosphere.

Sulphur hexafluoride is a high GWP gas because for a given mass, it traps substantially more heat than CO2. It also lasts much longer in the atmosphere than some major greenhouse gases (methane, for example has a lifetime of 12 years, versus 3,200 years for SF6).

Although volumes of SF6 in the atmosphere are tiny compared to CO2 (three parts per trillion versus 421 parts per million for carbon dioxide in 2022), they have been rising since the 1980s. That means pressure is on to phase out SF6, with a warming potential exceeding that of some problematic hydrofluorocarbons and other gases like tetrafluoromethane and hexafluoroethane.

Europe is leading the way. The EU will ban medium-voltage switchgear using SF6 from 2026. In Britain, we’re expecting similar measures to eventually be adopted by the government.

Introducing the Sabre EcoTec

That means it’s time for ring main units that employ technology other than SF6. So at Lucy Electric, we’ve decided to use nothing more harmful than air itself, in fact synthetic air, which guarantees the purity of the insulating gas for our Sabre EcoTec medium-voltage switchgear design – in a footprint that’s compatible with our existing Sabre ring mains units.

The Sabre EcoTec represents four years’ careful engineering work and is now in a number of small-scale trials with DNOs. We’ve employed load break technology in our overhead lines and adapted it to our existing Sabre ring mains unit.

Thanks to clever design, we’ve been able to keep the benefits of the Sabre family in terms of size, cost, application, and options – but with zero global warming potential. In fact, as we are using bottled air, the dielectric material in the Sabre EcoTec is cleaner than the air we breathe.

The physical footprint is key to the viability of the design. We don’t want customers to have to redesign switch rooms and substations or pour more concrete to accommodate it. If another two feet of concrete plinth is required for installation, that has a knock-on effect in terms of a customer’s carbon emissions, which defeats the object.

So, we’ve been careful to design the Sabre EcoTec clinically to guarantee minimum physical impact – so much so that it’s possible to bolt the new switchgear to an existing Sabre plinth without redrilling. We also want to minimise maintenance, which is why we have resisted the temptation to increase air pressure and instead employed shunt vacuum interrupter technology from our equipment for overhead lines.

Much of the engineering design has involved making that vacuum-bottle technology work at a compact size.

SF6: A small piece of the sustainability jigsaw

We don’t use a lot of SF6, we don’t leak a lot of SF6, and technically it’s easier for us to replace SF6 and dispose of it responsibly. But the entire electricity industry including our supply chain is determined to reduce its impact on the environment, and we expect not only the UK but also many countries around the world to follow the EU’s lead in banning SF6 from switchgear. In fact, some of our customers in the developing world are among the early adopters of SF6-free technology.

But the Sabre EcoTec is just one part of a much wider sustainability strategy at Lucy Electric that has seen us reduce the carbon intensity of our operations, a key metric that assesses the efficiency of our emissions in relation to our economic activities. In 2023, the carbon intensity of our operations decreased by 13.6% from the previous year, which is why we can say with confidence we’re heading in the right direction when it comes to combating global warming.

For example, we are using solar power to generate electricity at our sites and taking measures to improve energy consumption and reduce emissions from freight. We are also increasing our reporting of Scope 3 greenhouse gas emissions. Phasing out of SF6 is just part of a wider picture: one that acknowledges that older ways of doing things are no longer viable if we are to protect the planet and its people.

The next EcoTec ranges will be to develop similar solutions for 24kV and 36kV. Currently, there is no 36kV solution on the market, and it may require a different type of physical infrastructure. Either way, we will be developing a system that uses nothing more harmful than fresh air as the dielectric material – and that helps avoid the fugitive emissions of one of the most powerful greenhouse gases.

Want to learn how to eliminate SF6 from your medium-voltage switchgear? We’ve got you covered here.