Environmental Effects of Electrically-stressed Sulfur Hexafluoride

High Voltage (HV) equipment such as power switches, current or voltage transformers, and flexible HV transmission lines insulated by pressurized SF 6 (or SF 6 /N 2 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 SF 6 insulation for HV applications was initially proposed during late ‘60s, it was spread worldwide rapidly due to offered significant economic advantages, and now SF 6 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 SF 6 gas use. These mainly stream out by either of the following facts: (i) SF 6 is a strong green-house gas with a global warming potential of almost 25,000 greater than that of CO 2 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. S 2 F 10 , oxyfluorides, H 2 S and HF.