Byproducts in the Insulating Gaseous Matrix of a Gis

Abstract

Sulfur hexaflouride (SF₆) is a man-made gas, offering excellent electrical, thermal, and acoustical insulation properties, and as such, it has been extensively employed for a variety of applications, i.e. power distribution (mainly), semiconductor foundries, metallurgy, tracer gas, sound sealing (double glazing, torpedo noise silencer), thermal sealing, diving equipment, aeronautical, wind tunnels, telecommunications, relays, antennas, medical (ultrasounds, ophthalmology) etc1 . However, SF₆ has been identified to be one of the strongest greenhouse gases, having a global warming potential 25000 greater, compared to that of CO₂, and an exceptionally long lifetime (estimated between 1800 and 3200 years). SF₆ is primarily employed worldwide (approximately 80% of its total production) as a gaseous insulator for high-voltage systems (GIS) including switchgear, gas insulated transmission lines, and power transformers. The current trend is to reduce SF₆ quantities within electrical equipment by mixing it with natural gases. As a result, the interest for possible SF₆/gas mixtures for power applications has been reignited. Most of the research work is now focused on SF₆/N₂ gas mixtures2, as it appears to be suitable for industrial non uniform electric field applications, combining environmental compatibility with comparable dielectric performance of pressurized SF₆ and overall cost effectiveness. Other possible mixtures of SF₆ that have been recently proposed are the SF₆/CO₂/N₂ instead of the SF₆/CO₂ mixtures for transformer applications, and also, SF₆ with dielectric mixtures of CHF₃ and CF₄ diluted at 50% to 75% with N₂ for possible applications at lower temperature environments, thus combining environmental compatibility with reduced gas decomposition rates3.