SF6 free switching equipment for the future
In 2018, Cigré created the Working Group (WG) A3.41 ‘Interrupting and switching performance with SF6 free switching equipment’. The WG now has 42 members from all over the world and we had our kick-off meeting early this year in Arnhem. In this blog, as convener of this Working Group, I want to inform you more about the background, the scope and what we want to achieve. This WG interacts with other Cigré working groups investigating the application of non-SF6 gases or gas-mixtures in medium- and high-voltage switchgear (B3.45) and the dielectric performance of eco-friendly gas-insulated systems (D1.67).
Modern switching equipment for the transmission level voltages is based on SF6 gas technology, because of the excellent arc quenching and dielectric insulation properties of the gas. However, the global warming potential of SF6 is 23,500 times higher than CO2. It is one of the six gases designated in the Kyoto Protocol in 1997.
Several efforts have been conducted to develop different SF6 free switching equipment with considerably lower global warming potential factor such as gas mixtures and the development of vacuum switchgear and circuit breakers at transmission voltages up to 145 kV. First pilot projects have already been started in the transmission and distribution networks.
The WG will collect information focusing on the interrupting and switching performance with SF6-free switching equipment and investigate these capabilities during the expected lifetime under typical switching conditions. In addition, the feasibility of extra high-voltage circuit breakers (EHV CBs) will be briefly addressed by considering cost and economic aspects.
The WG will collect available interrupting and switching performance data with different SF6 free alternatives and field experiences from the pilot projects along with expectations and opinions from the pilot utilities. The WG reviews the advantages and disadvantages of all SF6 free solutions in comparison with today’s state-of-the-art SF6 technology. We will evaluate the interrupting and switching performance during the expected lifetime, have a look at long term stability and the impact on maintenance works related to switching.
The work will also comprise the evaluation of a possible feasibility study on EHV vacuum circuit breakers.
Many of the relevant international standards for testing of GIS focus on SF6 and may not be directly transferable to green alternatives. At present, we face the issue that there is no standardization for mixtures of gases as they differ in composition and are more difficult to handle than single-molecule gases such as SF6. Therefore, the WG will provide guidelines for utilities. For example, to reveal which factors have to be kept in mind when they use alternative gases as a solution for switching. Consequently, the WG provides possible feedback or recommendation for the standards and testing procedures. This is highly relevant, since at KEMA Laboratories we see already plenty of development testing of HV switchgear with all the relevant SF6 alternative gases proposed by the industry.
The deliverables will be published as a Technical Brochure and report in Electra and it will be presented at conferences. I will keep you informed about our progress!