Replacing SF6

Jun 20, 2023

A decade ago, there were no viable alternatives to using SF6 as insulation gas in high-voltage switchgear, even though this fluorinated gas is considered to have the highest global warming potential. Today, alternatives are available and the F-gas era appears to be ending, writes Dr Mark Kuschel of Siemens Energy.

It truly is a sight to behold: an offshore wind farm with over 100 giant turbines covering an area of 300km2. With a capacity of 714MW, the East Anglia One wind farm off England's Suffolk coasts produces enough renewable energy to power the equivalent of more than 630,000 homes.

To watch the power-generating field amidst the relentless waves of the southern North Sea is extremely impressive. Yet there's a hidden feature that also makes the wind farm notable. On each wind turbine, the field uses the greenest insulation possible for its high-voltage switchgear: clean air instead of SF6 (sulphur hexafluoride), which used to be the standard.

The answer is indeed blowin’ in the wind, and the times they are a-changin’.

This article is part of the ‘Future Energy Perspectives’ series, in which experts from Siemens Energy share their insights into how we can move towards a decarbonised energy system.

SF6, a man-made and odourless gas, belongs to the family of F-gases (fluorinated gasses). As the most harmful and long-lasting greenhouse gas emitted by human activity, it's 25,200 times more potent than CO2 and has an atmospheric lifetime of up to 3,200 years.

According to the US Environmental Protection Agency, around 80% are used worldwide in the switchgear industry. Therefore, it's clear that tackling this segment is paramount.That's why East Anglia One should lead the way for effective efforts towards protecting the environment.

It doesn't just generate renewable energy, but it also sets new standards in decarbonizing the power transmission part of the project.The wind farm has been in operation for almost three years, being one of the first using switchgear with a global warming potential (GWP) of zero.

Today, the continued use of SF6 and other fluorinated gases in high-voltage insulation are pressing concerns when it comes to clean power transmission, especially, as the demand for insulated switchgear has risen sharply.

This is due to decentralised renewable energy production, the global rise in electricity consumption and increased urbanisation which also increases the demand for small substations, and hence, for compact environmentally friendly switchgear.

Regulators have taken note and are increasingly pushing away from fluorinated gases. For instance, the high GWP of SF6 led the EU to prohibit SF6 in 2014 for most applications, except for the power sector due to a lack of alternatives at the time.

In April 2022, the European Commission proposed a revision of this key legislation calling for more restrictions on using F-gases in grid technologies.

It would reduce F-gases by 90% by 2050, and ban using F-gases in switchgear with a GWP of more than 10 by 2026 to 2031 (high-voltage), depending on the voltage of the switchgear.

It also allows for flexibility in niche situations where F-gas-free alternatives might not be available.

In California, regulation is already in place to remove F-gases from gas-insulated switchgear. And unsurprisingly, at the recent COP27 in Egypt, F-gases were central topics of panel discussions aimed at exploring F-gas-free alternatives globally.

Read the latest on F-gas regulation in Europe:EU parliamentarians double down on fluorinated gas emission reductions

What made SF6 such a popular gas for switchgear in the first place?

For obvious reasons, it's a highly effective arc-quenching and insulating medium with long-term stability, and with precautions, relatively safe to handle. Until the 1960s, oil was used as an arc-quenching media for high-voltage circuit breakers in substations around the world.

However, it had a variety of disadvantages, such as fire risk and maintenance intensity. When SF6 was first implemented, it was seen as an excellent alternative for improving the performance and safety of high-voltage applications.

Currently, SF6 is still the standard gas used in switchgear worldwide today. Thousands of tons of SF6 are installed in switchgear globally every year, with an expected lifespan of 40-60 years.

For sure, manufacturers aren't taking risks posed by SF6 lightly. Current state-of-the-art technology allows for keeping the leakage rate of SF6 below 0.1% per year.

At the same time, system engineers are all sensitized to and trained in the careful handling of switchgear components containing SF6.

Yet, given the net-zero target that's been embraced worldwide to minimize climate change, SF6 will need to be completely phased out for switchgear equipment.

The main contenders for replacing SF6 are based on gases of natural origin, such as CO2, O2, and N2, and gas mixtures, including other man-made fluorinated gases having a fraction of the climate impact of SF6.

Though fluorinated gas mixtures have less global warming potential than SF6, the GWP is still some hundreds above 1. In addition, these gas mixtures lose their effectiveness at very low temperatures.

There is also a risk that switchgear components wear out more quickly, which in turn, reduces switching performance and results in higher maintenance costs.

In addition, gas handling is much more complex than with natural-origin gases, and service and storage requirements are correspondingly higher. In this case, the tightness of the switchgear is above SF6 and results in higher maintenance costs. As these F-gases belong to the ‘forever chemical’ PFAS (per- and polyfluoro-alkyl) group, they can involve further risks.

As PFAS chemicals are connected to environmental pollution and health risks, there's a global trend towards PFAS phase-out and regulatory restrictions for these substances, where alternative solutions are available.

To actively ensure sustainability, one of the biggest market players, 3M, announced at the end of 2022, that it would exit (PFAS) manufacturing and work towards discontinuing its use of PFAS across its product portfolio by the end of 2025.

The other alternative to SF6 are F-gas-free products that use natural-origin gases as an insulation medium. This gas technology poses zero harm to the environment, climate and human health. But how realistic is it to move away from SF6 -insulated switchgear to natural-origin gases as insulation?

Today, more and more switchgear manufacturers, transmission and distribution operators as well as regulators favour F-gas-free-options with GWP of zero, or < 1, with no contamination risk of the atmosphere, water, or soil.

That also means there's no need for careful handling, recycling, and reporting as required by law when using SF6 and other F-gases in some parts of the world.

Finally, looking at the proposed different transition timelines for phasing out SF6, it's clear that today's F-gas-free technology can meet that challenge.

Download your copy of ‘Replacing F-gases in switchgear: a revolution in the making’

It's already happening: and not just offshore. In 2018, Siemens Energy supplied a substation of Norwegian network operator BKK Nett in Bergen with a clean air switchgear from its ‘Blue Portfolio’.

Clean air consists of purely 80% nitrogen and 20% oxygen and has a GWP of zero. Worldwide, the company currently has more than 1,000 switchgear units with clean air in operation.

From 2030 onwards, Siemens Energy aims to sell only F-gas-free products globally. Also, other manufacturers are very active: companies from Europe, Japan, South Korea and China are able to offer natural-origin gases-based switchgears, e.g. offering also circuit breakers based on CO2/O2 gas mixture with a GWP < 1.

And some of these companies have formed an alliance called "Switching gears for net zero" calling for zero F-gases in switchgear.

Natural origin gases with GWP < 1 means no new emissions, easy and safe handling, no health risks to workers or environmental harm. The CO2 footprint of natural origin gas equipment is significantly lower than that of SF6 and offers the only solution to have zero direct emissions and is able to achieve zero carbon footprint when coupled with a fully decarbonized supply chain.

Using natural origin gas solutions reduces life cycle costs of the equipment significantly. The equipment can be used at very low temperatures of up to -50°C without any countermeasures.

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Though the path ahead may seem clear, during this transitional phase switchgear manufacturers, as well as transmission operators, still have their work cut out for them.

That's particularly the case with wind farms. While there are first projects equipped with F-gas-free switchgear in wind turbines, the switchgear combining the power infeed with voltages above 145 kV still uses SF6-insulated switchgear (albeit only kilograms, not tonnes as in many substations).

Why? Alternative products with clean air or other harmless gas mixtures are not available yet for this kV-range.

But it's no secret that they’re in the works. At Siemens Energy, for instance, validations for switchgear with 400kV are in progress, while switchgear with no circuit breaker function like instrument transformers and gas-insulated busducts are already available for up to 420kV.

Other manufacturers are also pushing forward. So, F-gas-free alternatives should also be available for these higher voltage-ranges soon.

ABOUT THE AUTHOR

Dr Mark Kuschel is Head of International Standardization at Siemens Energy, steering standardization and regulation topics for the company's Grid Technologies business. For more than 20 years he has held various positions in the Transmission and Distribution business, where he was also one of the initiators of sustainable, F-gas-free products.