Utility Week

34 | SEPTEMBER 2022 | UTILITY WEEK Achieving net zero requires 'bold steps' away from SF6 Comment A s a highly e cient electrical insulator, SF6 (sul- phur hexa uoride) has been a vital component of switchgear design since the 1950s. It is stable, non- ammable, non-toxic, inert, and exceptional at arc quenching. However, SF6 is also a very harmful greenhouse gas, with a global warming potential 24,000 times greater than carbon dioxide. Leakages of SF6 may occur during the manufactur- ing, shipping, storage, decommissioning, disposal, or recycling of gas-insulated switchgear. When the gas escapes, it lingers in the atmosphere for 3,000 years. Consequently, the potential climate impact of SF6 has prompted the industry to develop environmentally friendly alternatives. The EU's current regulation requires an overall reduction in emission of uorinated gases, or F-gases – including SF6 – by two-thirds by 2030 versus 2014 levels. Fortunately, advances in science and engineering now o' er competitive SF6-free alternatives. Dry air – air with zero moisture content – is one e' ective alternative to SF6 as an insulating medium. It is particularly e' ective in networks rated at up to 12kV. Above this, higher dielectric strength is required. This can be achieved by increasing pressure. Dry air, for example, needs to operate at a pressure of several bars to perform as an insulating medium for 36kV switchgear. This requires mechanical design changes to the switchgear such as developing tanks with thicker walls and potentially cylindrical geometry like that used on high-voltage switchgear. This drives costs upwards and creates operational challenges, with any loss of pressure immediately impacting performance and requiring a DNO to take said unit out of service immediately. Addi- tionally, operators would likely want to deploy pressure sensors to monitor its eet for pressure loss – and this would require signi˜ cant investment. It's possible to avoid these limitations by implement- ing a low-pressure design that uses an eco-e cient gas instead of dry air or SF6 for switchgear rated higher than™12kV. For example, a gas mix based on a small percentage – less than 20% – of uoroketone molecules added to dry air. This has almost the same insulating performance as SF6 but with a 99.9% lower global warming potential. As a result, switchgear ˜ lled with this gas mix operates only slightly above atmospheric pressure. Therefore, careful choice of insulating gas inside switchgear can design out the cost and risk of using high-pressure systems. Furthermore, the uoroketone molecules only linger for up to 16 days before breaking down, making them much more eco-friendly than SF6. Fortunately, most operating procedures involving SF6-free alternatives don't di' er much from those using the gas. The switchgear for both relies on gas in a sealed container. Access to the tank in both instances demands a trained technician or contractor to handle the gas. The same applies to the switchgear's end of life when the gas must be removed for the materials to be recycled. However, operators using SF6-free gases are exempt from regulatory reporting on their gas inventory. SF6- free gases remain safe during operation and at the end of the switchgear's lifetime. Yet the biggest challenge in switching, in most cases, is that operators cannot simply replace the gas in switchgear designed for SF6 with an eco-friendly alternative because the new type of gas may react with some materials in existing switchgear tanks. However, some modern switchgear designs have been developed to be compatible with both SF6 and the uoroketone mix, so switching will gradually become easier. These dual-compatible gas insulated switchgear designs are on the market already. The acceptance of eco-e cient switchgear has been promising as global utilities strive to cut emissions related to SF6 leakages. A good example is Northern Powergrid. The util- ity adopted two switchgear variants at substations in County Durham, both of which use alternatives to SF6 gas to reduce environmental impact. According to a senior executive at Northern Powergrid, the utility has already reduced SF6 leaks by 23%, and the pilot project will play an important role as the utility aims to reduce this by a further 15% by 2028. Ultimately, achieving net-zero targets requires bold steps to transform our energy infrastructure – all the way down to technical details like switchgear insulating gas. It may seem a small detail, but it can have a major impact on availability and operational expenditure. This uoroketone gas mix is a technology with potential to help electrical distribution networks combat climate change and phase out the use of SF6 gas. Modern gas mixes, such as those developed by ABB and 3M, were developed commercially, but are now available under open patent. As a result, other switchgear manu- facturers now have the opportunity to develop their own new-generation SF6-free switchgear. The ˜ rst steps taken to remove SF6 from the grid, such as those by UK Power Networks and Northern Pow- ergrid, are important. But only once we've seen these new technologies applied at scale, in the real world, will operators actually gain the necessary understanding and familiarity for them to adjust their strategies long-term. Stephen Gibbs, product marketing director for distribution solutions, ABB UK For Stephen Gibbs' comment piece in full, go to https://utilityweek.co.uk/ achieving-net-zero-requires- bold-steps-away-from-sf6/

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