Application of a multi-parameter sensor system for monitoring dielectric insulation of gas mixtures

The high global warming potential of SF6 motivates the search for eco-friendly dielectric insulation gases. Perfluorinated ketones (FKs) diluted in a carrier gas were recently found to have dielectric properties acceptable for application in high and medium voltage gas-insulated switchgear (GIS). Pilot installations equipped with FK-based insulation gas mixtures are already in operation as this new type of SF6 alternative is approaching maturity for market introduction. SF6 alternatives are generally based on mixtures of gases. An accurate monitoring system for measuring the concentration of FK is desirable because the insulation performance is a function of its composition. We identified a robust and low-cost method for deriving the concentration in a binary gas mixture employing simultaneous measurement of pressure, temperature and density. We have tested two embodiments of this scheme using commercially available sensors. For both, a relative accuracy of better than 4% of the FK content was achieved. A long-term campaign in which an operating outdoor GIS filled with FK-based insulation gas was tracked showed that the measurement is suitable for field environments. The universality of the method and its easy realization with off-the-shelf equipment is of value for any application requiring concentration tracking of binary gas mixtures.