Global Warming Potential Considerations for Gaseous Sf₆ Alternatives Along the Switchgear Lifetime

Abstract

Next-generation environmentally friendly switchgear will not use SF6. Currently, all of the main manufacturers in the world are developing products using alternatives based on CO2 as a background gas. The use of FluoroNitriles, 3M™ Novec™ 4710, C4F7N (C4FN) is addressed by different producers under different trademark names. In most cases, Oxygen is added for health and/or functional reasons. In terms of potential climate impact, considering only the GWP of the single gas mixture components is insufficient. In order to better evaluate and understand the advantages the different alternatives offer in comparison to SF6, the GWP calculations of the gas mixtures over a defined timeframe are much more complete. Additionally, not only the GWP of the gas mixtures in new condition is to be considered, but also their evolution through the switchgear lifetime. Arcing, created in all switching and interrupting test duties of HVCB will cause reversible and irreversible chemical reactions that produce new compounds with different dielectric, arc quenching, and environmental properties as the original molecule. Based on thermodynamic calculations, CFD simulations, and gas analysis of samples of alternatives that have been subjected to arcing, this work studies the effect the byproducts of the different mixtures have in terms of climate impact, dielectrics, and arc quenching. This paper offers different scenarios of electrical and gas degradation, from very uncommon events e.g., T100s to very common ones e.g., switching of nominal and/or capacitive currents. The influence of the always evolving gas mixtures along the lifetime of the equipment is evaluated and compared in terms of performance and the climate impact.