Eliminating SF6: an agreement between rivals7 July 2021
A landmark cross-licensing agreement between Hitachi ABB Power Grids and GE points the way towards a new global standard for SF6-free HV technology, employing fluoronitrile gas mixtures, its signatories believe. James Varley reports
Image: EconiQ 145 kV SF6-free switchgear (Courtesy: Hitachi ABB Power Grids)
“We are paving the way for a new global industry standard”, said Dr Markus Heimbach, MD, HV products, Hitachi ABB Power Grids, commenting on the recently announced landmark cross-licensing agreement between Hitachi ABB Power Grids and GE relating to the use of fluoronitrile based gas mixtures as an alternative to SF6 in high voltage equipment. “And the new agreement has the potential – and I firmly believe this will happen – to greatly accelerate the adoption of SF6-free high voltage equipment across the industry”, thanks to the benefits arising from standardisation, not least of which is simplification of service, maintenance and operator requirements.
Up to now, Hitachi ABB Power Grids has used gas mixtures employing fluoroketones (typically in combination with CO2 and O2) as an alternative to SF6 in HV applications. But henceforward it will focus on fluoronitrile and is developing a new SF6-free HV portfolio called EconiQ, which includes equipment employing a fluoronitrile/ CO2/O2 gas mixture. This supersedes AirPlus, which was a name solely for gas mixtures mainly using fluoroketone/CO2/O2.
With EconiQ “we will offer only one fluoronitrile/CO2/O2 mixture for gas insulated switchgear, dead tank breakers and hybrid switchgear”, says Dr Heimbach, including for both indoor and outdoor applications, with outdoor applications meaning down to -30°C. “We could offer a ‘stronger’ mixture for use indoors, ie, with better technical specifications, because it doesn’t go below zero, but we are using a single mixture because we want to have a platform approach and we want our customers only to have to take care of one mixture.”
SF6 gas, which has been the norm in the T&D business for almost half a century due to its unique physical properties, is pretty much the “perfect gas for insulation and even more so for switching”, says Dr Heimbach.
The downside is its huge global warming potential (if leaked), which is about 22 800 times that of CO2. It is a very potent greenhouse gas and has an estimated life span of about 3200 years in the earth’s atmosphere.
The fluoroketone mixture has very low global warming potential, less than CO2, and significantly less than the fluoronitrile mixture. But its performance (in terms of arc quenching and insulation) is not as good as fluoronitrile based mixtures, necessitating larger high voltage equipment sizes. This was a deciding factor for Hitachi ABB Power Grids. It’s all about “striking a balance between switching performance, insulation properties and global warming potential”, says Dr Heimbach.
A recent EU Commission report has concluded that fluoronitrile-based gas mixtures may indeed be the only insulating and switching gas alternative to SF6 in high voltage applications when space is a constraint.
Also, as Dr Heimbach points out, in terms of global warming potential, while fluoronitrile mixtures may be at a disadvantage relative to fluoroketones, they are about 100 times better than SF6.
Alstom’s T&D business (now part of GE) was the first to use fluoronitrile-based gas mixtures (called “g3”) for its SF6-free product range and these “feature the same compactness and performance as traditional SF6 equipment”, according to Heiner Markhoff, CEO of GE’s Grid Solutions.
Under the new cross licensing agreement, Hitachi ABB Power Grids and GE will share complementary intellectual property related to their respective SF6-free solutions but will keep the product development, manufacturing, sales, marketing and service activities of their gas solutions fully independent and “each company will continue to independently grant and set terms of licenses to its respective intellectual property, hence preserving supplier base diversity for the industry and fair competition.”
The agreement is described as “non-exclusive”, so other players in the HV business could join at some stage in the future.
Siemens Energy has adopted a different approach to SF6 elimination in HV equipment – a combination of “technical air” (ie, an 80%/20% mixture of pure nitrogen and oxygen, aka “clean air”) for the gas insulation plus vacuum breakers for switching.
Dr Heimbach believes vacuum technology is “a good solution below 145 kV”, but at higher voltages it “becomes difficult and is certainly not economic.” He speaks from experience having once had responsibility for vacuum breaker R&D within ABB.
Technical air/vacuum technology, with avoidance of fluorinated gases, eliminates any global warming potential, of course, but “you have to build bigger and you encounter increased losses, so when you look at environmental lifecycle assessment it is inferior to fluoronitrile based mixtures...The need to build large by far offsets the advantages of employing gas with lower global warming potential.”
As already mentioned, fluoronitrile/CO2/O2 mixtures are included in Hitachi ABB Power Grids’ new EconiQ portfolio of SF6-free equipment, but for some applications, eg, live tank breakers, a CO2/O2 mixture is the optimum choice.
A recent example is the EconiQ live tank breaker for 72.5 kV and 145 kV to be installed by Hitachi ABB Power Grids in Spain for Iberdrola as part of a refurbishment project at its Alhama de Murcia substation.
This is the first installation of EconiQ SF6-free high voltage outdoor live tank breakers in Spain.
The EconiQ equipment (pictured) is based on well-proven gas circuit breaker design, with minimal footprint and high reliability, says Hitachi ABB Power Grids.