SF6 and the Shift Toward Greener Alternatives

They say one of AI’s strongest characteristics is its ability to find patterns in unstructured data. I wonder what patterns it would find in my unstructured inbox. Most of my emails are about the power grid and it’s technologies, but for the most part the subject matter is scattered all over the place. A few days ago, however, I had several emails discussing the options to sulfur hexafluoride (SF6) gas-insulated switchgear. I hadn’t seen emails about SF6 or its issues for a long time.

It's one of those subjects that doesn’t readily jump to mind when we’re talking about extreme weather or decarbonization, but it should be. SF6 has one of the highest global warming potentials (GWP) of all greenhouse gases. Its GWP is 24,300 higher than carbon dioxide and can last thousands of years in the atmosphere if leaked from equipment. As I started reading these press releases, it brought back memories of my first encounter with SF6.

I had taken the position of senior substation engineer at a southwestern utility and was assigned the task of adding shunt capacitor banks to ten substations. Each station would have two large parallel 115kV banks installed on its bus. Back in those days, the interruption device of choice was the oil circuit breaker (OCB), but there were problems. Shunt capacitor banks produce high inrush currents and high transient recovery voltages, all of which were beyond OCB technologies.

The Pros & Cons

The solution was a new adaptation of SF6 circuit breaker technology. One that was designed for capacitor bank switching at the 115kV voltage level. SF6 was seen as an amazing medium. Its voltage insulation, current interruption, and arc quenching properties were superior to oil. Also, SF6 circuit breakers required much less maintenance, and it didn’t have the limitations of OCB devices.

To be fair, in those days, there wasn’t much talk about global warming or greenhouse gas emissions either. That happened later, but as SF6 became more commonplace some concerns popped up. My first warnings about SF6 gas came at my yearly hazmat recertification classes. The byproducts of SF6 arc quenching were at the top of the hazard list that year. An electric arc inside the SF6 filled breaker tank produces toxic byproducts that are extremely dangerous. So much so, it was recommended that anyone likely to be exposed should wear personal protection equipment.

It wasn’t long after that, the topic of SF6 gas’s GWP started hitting the tradeshows and conferences. From that point on, when SF6 was mentioned the discussion shifted to eliminating SF6 from all transmission and distribution equipment. It took a while, but manufacturers and suppliers accepted the challenging of replacing SF6. It started at the lower end of the voltage and current spectrum, but those have steadily expanded covering a wider range, which is why those emails caught my attention.

What's the Alternative?

The first one came from a colleague at Siemens Energy. They are expanding the voltage levels of their F-gas-free gas-insulated switchgear (GIS) to the 420kV level with a pilot project in partnership with Elia, Belgian’s transmission system operator. In addition, the European Union (EU) is co-funding the project. The EU has a goal for eliminating F-gases (i.e., specifically gases that contain hydrofluorocarbons) by 2050. The Siemens Energy “clean-air” alternative is mixture of nitrogen and oxygen. The F-gas-free switchgear utilized by this pilot system will replace an existing switchgear in one of Elia’s substations.

Another email was from a colleague at Hitachi Energy. They sent me an announcement about Hitachi Energy delivering the world’s first 550kV SF6-free GIS to the Central China branch of the State Grid Corporation of China (SGCC) soon. This 550 SF6-free GIS is part of their EconiQ product portfolio using a mixture of CO2 and oxygen and C4-fluoronitrile gases. SGCC said this project “will contribute to effectively reduce the consumption and emissions of greenhouse gases.” Hitachi Energy has been providing SGCC with 145kV EconiQ GIS and live tank circuit breaker products since 2022.

These emails represent two different alternatives for SF6 replacements from two manufacturers. There are other manufacturers and there are other technologies gaining traction in the quest to replace SF6. So far clean-air, synthetic air, vacuum, and fluoronitrile gas mixtures are the leading contenders. Research is taking place in solid state technologies too. The takeaway here is the fact that options are available and they’re moving into higher voltage and current levels. It’s definitely a trending topic to watch!