Gas Density

Sulphur hexafluoride (SF6) is used in gas insulated switchgear because of its outstanding insulation and spark extinguishing (arc-quenching) properties. It thus makes it possible to set-up complex and safe ­power distribution systems even in large cities. The insulation strength depends basically on the gas density.
The safety of the facility is guaranteed when the correct level of gas density is maintained within the enclosed systems. The tightness of the installation has to be checked and controlled constantly as a leakage would result in a decrease in the insulation properties. Because SF6 is a strong greenhouse gas, strict regulations regarding the SF6 consumption have to be met by the switchgear operators in an increasing number of countries. These regulations stipulate a permanent monitoring of gas leakage which is done with gas density monitors or gas sensors. Gas density is often indirectly determined by the gas pressure using manometers or pressure sensors. As the pressure in the hermetically closed volume varies enormously with temperature, such devices need temperature compensation, which are a source of errors.