Environmental Effects of Electrically-Stressed Sulfur Hexafluoride

School of Electrical and Computer Eng., National Technical University of Athens, Greece

Abstract

High Voltage (HV) equipment such as power switches, current or voltage transformers, and flexible HV transmission lines insulated by pressurized SF₆ (or SF₆/N₂ mixtures) offer component compactness, high reliability and low maintenance demands compared to all conventionally insulating components (i.e. air, organic solid insulants, and mineral oils). Though SF₆ insulation for HV applications was initially proposed during late ‘60s, it was spread worldwide rapidly due to offered significant economic advantages, and now SF₆ GIS substations dominate the share in electrical networks in densely populated districts. However, it was in mid ‘90s when the first ecological concerns were brought about the SF₆ gas use. These mainly stream out by either of the following facts: (i) SF₆ is a strong green-house gas with a global warming potential of almost 25,000 greater than that of CO₂ and its molecules exhibit an exceptionally high lifetime in earth atmosphere estimated to vary between 750 and 2500 years, and (ii) when electrically stressed (independent of temperature i.e. either high-power arcs developing at 20,000K during the switching actions, or corona discharges developing at 300K due to high electric field effects) toxic byproducts may be formed, some having high cyto-toxicities i.e. S₂F₁₀, oxyfluorides, H₂S and HF.