Clean Air Instead of SF6
 Das spezifische globale Erwärmungspotential von SF6 ist etwa 23.500 höher als das von CO2.

written by Marcel Knobloch on Friday, July 23, 2021

The insulating gas SF6 is harmful: About half a percent of man-made global warming is probably due to this greenhouse gas.

Protective gas for switchgear

Sulfur hexafluoride (SF6) is the most powerful greenhouse gas known to date and is mainly used in electrical engineering. SF6 is used as a protective gas in switchgear, at voltage levels of up to 1,200 kV.

The global-warming potential of SF6 is 23,500 times greater than that of CO2. One kilogram of SF6 in the atmosphere is therefore equivalent to 23.5 tonnes of carbon dioxide.

The EU released about 300 tonnes of SF6 into the air in 2017, equivalent to 1.3 million extra cars on the road. A single kilo of SF6 heats up the earth as much as 24 people flying from London to New York and back. The gas remains in the atmosphere for up to 3,200 years before it breaks down. CO2 lasts there for about 1,000 years.

The synthetic gas SF6 has been used since the 1960s and is employed in gas-insulated switchgear in the power grid. It is used as an insulating gas for the electrical conductors. SF6 does not degrade naturally, or only very slowly at best . About half a percent of man-made global warming is probably due to this insulating gas – too much to simply ignore. Experts estimate that around 7,000 tonnes escape into the atmosphere every year. Gas escapes occur even during the production of SF6, but it is also released due to mistakes in the handling of high-voltage equipment. Better handling and optimized production – this would save some of the emissions.

Since 1995, a steady increase in the atmospheric concentration of SF6 has been observed. The atmospheric lifetime of SF6 is difficult to calculate accurately but is about 3,200 years.

Shifting the problem to other countries

Emissions of SF6 are showing a downward trend in European countries as well as in the USA and Japan. In contrast, total SF6 emissions from electrical equipment in Turkey have been rising sharply since 1995, when Turkey became a party to the UNFCCC. One reason could be the production capacities that European manufacturers have relocated to Turkey.

Environmental factors of SF6 gas

CO2 as a substitute gas?

In the high voltage field, there are still no established solutions today. Here the search is for alternative gases or gas mixtures. One of these alternative gases is CO2. High-voltage switchgear is already offered with it. But CO2 is not used for pure insulation applications, because its insulation properties are significantly poorer than those of SF6, and the equipment would have to be made substantially larger.

EU Directive on SF6 gas is in progress

If the gas is a poorer insulator, the distances between the high-voltage components must be increased to prevent flashover. To prevent this, special gases, usually containing fluorine, are added to the CO2 – these improve the electrical insulation properties. The problem: they all have their advantages but also their disadvantages. Unfortunately, the search still continues for the perfect alternative, and it is not yet possible to remove SF6 from the old systems, refill them one-for-one with something new and continue to run them. Depending on the application, various gas mixtures will have to be used – one gas mixture at cool temperatures and a different one at higher temperatures, for example.

For industry, this is somewhat inconvenient: in future, instead of the all-rounder SF6, it would have to use different gas mixtures for different fields of application. Despite these problems, industry – in Europe, at least – has committed itself to gradually reducing emissions. Concrete policy requirements could accelerate this process in the long term. A new European Directive on the handling of SF6 is currently being drafted. It is hoped that it might contain the first steps towards a statutory regulation of emissions.

The search for alternative gases

Today, sulfur hexafluoride is used in all high-voltage engineering – in large power stations, wind turbines and substations. As an insulating gas in electronic switchgear, its purpose is to prevent short circuits and fires. SF6 is one of the fluorinated gases that are used as propellants, refrigerants and extinguishing agents. Despite intensive scientific research, there is as yet no physically-electrically equivalent gas that can directly replace SF6.

Research projects are currently underway in many countries, including at the Swiss Federal Institute of Technology (ETH) in Zurich. Bucher Hydraulics supports ETH Zurich's research project to find alternatives to the harmful greenhouse gas SF6.

It's unrealistic to say that it all has to be gone in three years. That won't work. But let's say you take the reductions you've made in the past, extrapolate them into the future, and make them mandatory. That would be something that policymakers could do a good job of setting out, and then work with industry to find solutions on how to make it happen.

– Christian Frank, Professor High Voltage Engineering at the Swiss Federal Institute of Technology (ETH)

Learn more about the ETH Zurich research project and the collaboration with Bucher Hydraulics here: Sustainable Development - Alternatives to Sulfur Hexafluoride

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