Determination of gas leakage rate of gis-test systems by measurement of pressure and temperature

Potential leakage of SF₆ gas in encapsulated switchgear can lead to larger outages of substations. Therefore effective SF₆ monitoring is necessary in to guarantee a certain level of reliability and to address growing environmental awareness. In order to analyze the switchgear condition, the detection of very small leakage rates is required. As broadly published, the measurement of gas density in SF₆ switchgear is superimposed by substantial fluctuation over the time. The fluctuation originates from non uniform and time-varying temperature distribution. In order to reduce the level of fluctuation in the measured signal, a two level model has been introduced and published in the past. The model is based on a thermal network which calculates the temperature distribution along the surface of the vessel. In a second step this model calculates either the gas pressure by means of an averaging algorithm or the gas density distribution by computational fluid dynamics (CFD). The combination of both models allows the prediction of pressure or density fluctuation at a certain position in the gas. The current paper shows recent development of a measurement system with special emphasis on practical applications. First practical experiences and results are carried out.