Ever since the “net zero” philosophy has gained currency, there has been a rethink in the entire energy value chain. Right from power generation to last-mile power distribution, experts are working overtime in devising a culture that could significantly reduce carbon emissions, as a precursor to the cherished net-zero ambition.
Speaking of electrical equipment, there has been much debate about the ubiquitous sulphur hexafluoride (SF6) gas that is extensively used in switchgear. SF6 technology and its usage is so well entrenched in the switchgear industry that it can be quite disconcerting to imagine a world that seeks to be free of SF6.
As an insulating gas that has been in use for over 50 years, SF6 does a wonderful job. For one, it has drastically cut down the geographical footprint of air-insulated switchgear (AIS). Compared to conventional AIS substations, GIS substations occupy just one-third, or sometimes even less, of land used by AIS substations. In fact, in countries like India, where land-related difficulties are so commonplace, there could not have been a better boon than GIS substations.
Why is then SF6 being blacklisted? The reason is very simple. SF6 has now been recognized as a greenhouse gas. The presence of SF6 in electrical equipment can ultimately militate against the net-zero philosophy. A colourless and odourless gas, SF6 is at least 20,000 times more ecologically damaging than carbon dioxide. Besides, once SF6 gets into the atmosphere, it stays there for over 2,000 years, which is known as “atmospheric residence time”. On the other hand, carbon dioxide has a much lower atmospheric residence time, and its extent is also naturally controlled by the carbon dioxide cycle.
In developed countries, even though SF6 is used, there generally prevails a culture to regularly monitor the gas whilst in the equipment. In very advanced cases, there is online monitoring that immediately detects any SF6 leakages, on almost real-time basis. In general, SF6 handling and monitoring is an area where India still needs to progress, many experts feel.
At the moment, there is a very large base of switchgear containing SF6 and therefore technology for handling and monitoring this greenhouse gas becomes crucial. Even as we aspire to move towards an SF6-free world, the journey would take at least 20 years, experts feel. Besides, while the developed countries would lead SF6-free technology, it would take longer for it to be imbibed in the developing world. India therefore has indeed a long way to go given that today, even SF6 handling has huge scope for improvement.
There are several alternatives that are being considered for SF6. These include the use of clean air, hydrogen, nitrogen, etc. Some companies like Eaton have even developed “solid” switchgear technology where there no insulating gas, and it is believed that there is no compromise on the size of the switchgear, as compared to GIS.
Weaning away from SF6 will be done in phases – starting from medium voltage (MV) and gradually moving towards higher voltages. European nations are expected to take the lead in banning the use of SF6 in MV applications. In fact, way back in April 2018, Siemens introduced its first SF6-free MV switchgear that uses natural constituents of ambient air as the insulating material, as an alternative to SF6. Siemens has been developing what is called its “Blue Portfolio” where the company would develop technologies that do not use any fluorine gases (F-gases), not just SF6. In fact, Siemens has been actively deploying vacuum interruption technology for its MV switchgear for over 40 years. In 2018 itself, Siemens announced that it extended vacuum breaker technology to switchgear of 145kV rating.
A pertinent question remains: Whenever the world goes SF6-free, how does one tackle the huge amount of SF6 that is already present in the existing base of electrical equipment worldwide?
The opinion on this is divided. According to Derk Jan Koetje, Senior Consultant IIoT, WIKA, it would be generally difficult to replace SF6 with alternatives, in existing equipment. However, SF6 present in decommissioned equipment could be safely removed and stored. If regulations still permit, this SF6 gas could be redeployed. On a technical note, Koetje explained that it is important to check for the quality of SF6 gas. Oftentimes, SF6 lying in the equipment deteriorates in quality, in that it becomes humid. One needs to dehumidify the gas and lower what is called as the “dew point” of the gas. This improves the physical parameters of SF6 and therefore its technical efficiency.
Speaking of replacing SF6 from existing equipment, there appears to be breakthrough. In December 2021, National Grid, a prominent grid operator in UK and USA, announced its partnership with Hitachi Energy in a pilot project to replace SF6 with a greener alternative, in its existing fleet of HV switchgear. According to information available, the alternative being considered is a fluorinitrile-based gas mixture that would be less harmful than SF6 but strictly, would still be in the realm of F-gases. Incidentally, National Grid has pledged to become completely SF6-free by 2050.
It appears that the aforementioned mixture of fluorinitrile-based gases would move towards being a viable alternative to SF6. In April 2021, GE Grid Solutions and Hitachi Energy (then known as Hitachi ABB Power Grids) entered into a landmark agreement that provides for both companies to share complementary intellectual property related to their respective SF6-free solutions. This will help accelerate the use of fluorinitrile-based eco-efficient insulation and switching gas in high-voltage equipment as an alternative to SF6. Earlier in 2021, an EU Commission report concluded that fluorinitrile-based gas mixtures may be the only insulating and switching gas alternative to SF6 when space is a constraint.
Even though various alternatives to SF6 are being looked into, this process is currently fragmented. Technology leaders like Siemens, GE, Hitachi and Eaton are working rather independently on SF6 alternatives and technologies.
However, experts feel that there should be push towards uniform material and technology. This could help in bringing economies of scale to switchgear manufacturers, worldwide. According to Ripunjay Parikh, Director – Sales, Electrical Sector, Eaton Power Quality Pvt Ltd, “Eaton will definitely contribute to the SF6-free ecosystem on a common platform. If everyone works on a different technology, the economies of scale might not be viable. Industry is expected to come to a common standard and definitely, we will find solutions to SF6.”
When SF6 is mentioned, one mainly thinks of GIS. However, there is another dimension that generally has not come under wide discussion —the use of SF6 in wind turbines. The switchgear associated with wind turbines can contain anywhere between 3 kg to 5 kg of SF6. This is apart from the SF6 used in the substations associated with the power transmission systems of wind farms. India currently has over 40 GW of wind power installed capacity, and has targeted to reach 140 GW by 2030. Handling and monitoring of SF6 in wind turbines is therefore going to assume critical importance in the years to come.
Migrating to SF6 alternatives will be the priority of the developed world, in the medium term. India does not have to worry too much about SF6 at the moment. It can align its policies depending on the stance that the developed nations adopt. All the same, it is important to acknowledge that India is aggressively augmenting its power transmission infrastructure, of which GIS substations form a critical component. India’s usage of SF6 is clearly growing. Even as the world works towards alternatives to SF6, which can gradually be imbibed by India, improving SF6 monitoring and handling practices is a responsibility that India should fully honour.
Note: The author is Editor, T&D India, and may be reached at venugopal.pillai@tndindia.com. The author has interacted with personalities quoted in this story during Elecrama 2023. Companies like Siemens are working on producing switchgear without the use of SF6 under what is called as its “Blue Portfolio”. Featured image shows one product under Siemens’ Blue Portfolio.