SF6 Gas Analysis for GI Switchgear

SF6 Gas Analysis introduction

SF6 gas analysis introduction – for more than 50 years, Sulphur Hexafluoride (SF6) which is a man made gas has been used successfully in various industries. It is extremely chemically stable, non-flammable and highly electronegative, with an excellent dielectric property of approximately 2.5 times more than air.

The most important application of SF6 is it’s use in gas insulated switchgear (GIS) in electricity transmission and distribution systems. SF6 acts as an extremely efficient insulation medium and a very effective arc suppression element during the switching process.

SF6 is chemically inert and stable, its reactivity is among the lowest of all substances, pure SF6 is not toxic and does not cause corrosion, though some of its decomposition products are and do.

Greenhouse gas

However SF6 is a potent greenhouse gas. Its GWP (Global Warming Potential) is 22’800 (CO2 = 1), but its contribution to the man-made greenhouse effect is only 0.06%. SF6 was listed, along with five other gases, in the Kyoto Protocol. The environmental critical properties of SF6 generated the need for improved measurement techniques with minimised gas loss. It is therefore important to keep check on the quality of this insulator through SF6 gas analysis using an instrument such as the MBW 973-SF6.

Gas Insulated Switchgear

For SF6 filled gas compartments, SF6 in accordance with either IEC 60376 or IEC 60480 is used. In order to prevent condensation, the maximum allowable water content is defined by a dew-point no higher than – 5 °C.  Gas compartment fill specifications typically define much lower dew points (manufacturer dependent). This provides benefits to system reliability by reducing the amount of Hydrogen and Oxygen available for reaction with Sulphur and Fluorine.

Gas quality measurements are performed during production, installation and maintenance.  MBW 973-SF6 gas analysers have been used for this application for almost 50 years and the 973-SF6 was the first instrument to include gas recovery as part of the measurement procedure.  They continue to be the instrument of choice for the major switchgear manufacturers for SF6 gas analysis thanks to their precision, reliability and low maintenance cost.