Secure migration to SF6-free switchgear
Published by Leah Jones,
The achievement of electricity grids with net-zero emissions is a popular topic and is aligned with the significant efforts being made in electricity generation, as outlined in the European Green Deal. Currently, over 95% of carbon dioxide equivalent (CO2-e) emissions produced by transmission and distribution networks are due to transmission losses.
Although the energy generation mix will eventually lead to a zero-carbon footprint, the remaining CO2-e emissions will be due to the presence of SF6 gas stored in T&D equipment. It is now widely acknowledged that SF6 is the most potent man-made greenhouse gas, with a CO2-e (Global Warming Potential [GWP]) of 25 200, a new higher value estimated in the 6th IPCC Assessment Report.
KEMA Labs is geared up to support the industry with the development such SF6-free switchgear irrespective of the chosen technology. Specially developed measurement techniques required for deeper examination of the interrupting capabilities can be made available as well. The global emission rate of SF6 is approximately 9000 ± 400 tpy, contributing several tenths of a percent to the worldwide CO2-e emission. This amount is equivalent to approximately 100 million gasoline automobiles' exhaust. Moreover, SF6 has an atmospheric lifetime of 3200 years, which is much longer than that of CO2 (300 – 1000 years). Hence, reducing SF6 emissions is even more effective than compensating for them by reducing CO2 emissions elsewhere. The industry is investing heavily in developing SF6-free equipment, and even competitors are collaborating and sharing patents to achieve this goal in a shorter period than it took to achieve the technical maturity of their SF6 predecessors.
SF6 alternatives can be either based on interruption in vacuum combined with insulation using natural-origin gases (GWP <1) or consist of a mixture of CO2, oxygen, and a small fraction of fluoronitriles (C4-FN) or fluoroketones (C5-FK) for interruption and insulation. C4-FN mixtures have GWP in the range of 300 – 750 and are mostly used in transmission equipment, whereas C5-FK mixtures have GWP <1 and are primarily used in distribution. SF6 alternatives serve two functions, namely electric insulation and switching and electric insulation with a pressurised gas.
At present, SF6-free equipment can be found in a voltage range of 10 – 170 kV and is applied in all switchgear: circuit breakers, load break-, (high-speed) earthing- and disconnecting switches. However, compared to SF6, the key parameters of the alternative mixtures are very different, and redesign of all SF6-free equipment is necessary to deal with the higher stresses compared to SF6. The availability of alternative fluorinated gases is now transferred to most existing manufacturers and is not the exclusive ownership of the product launching manufacturers. Newcomers and start-ups come with innovative prototypes, but only rigorous independent testing can qualify these as solutions.
The multitude of new products can be confusing to system operators, and many have yet to decide on a technology, as indicated by a poll at the CIGRE conference 2021. Although 80% of respondents plan to install SF6-free GIS within five years, 72% have not yet decided on the technology. This hesitation is partly due to insufficient experience and knowledge of the state of technology. However, the willingness to phase out SF6 is clear, but the road towards it seems not clear yet.
Uncertainty is also created by (future) regulations. The European Commission has proposed a regulation that prohibits the installation and replacement of fluorinated greenhouse gases in switchgear in stages by voltage rating until a total prohibition by 1 January 2031. An even stricter SF6 phasing-out scheme has been legally adopted in California, with a GWP of ≤1 ending 1 January 2033. The industry is taking the reduction of SF6 very seriously, and the recent publication of ambitious roadmaps towards SF6-free switchgear demonstrates it. In this respect, KEMA Labs has already achieved an extensive test experience in our High-Power Laboratories, which includes:
- Switchgear from 15 different manufacturing sites.
- Up to 145/170 kV at 50 kA three-phase synthetic.
- Mostly R&D tests, no type-test certificate issued.
- Short-circuit (all duties), capacitive, shunt reactor, bus transfer, MV internal arc.
Read the article online at: https://www.energyglobal.com/special-reports/19052023/secure-migration-to-sf6-free-switchgear/
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