Monitoring the SF6 pressure level in metal-enclosed switchgear to detect gas leakages

Recently, electric utilities decide to permanently monitor the SF₆ gas level in gas insulated switchgear. This is mainly because of two reasons: The optimization of their maintenance strategy and environmental awareness associated with greenhouse gas emissions. The detection of small gas leakages is not an easy task. The authors propose a model which allows using pressure sensors. The problem of high pressure fluctuations is solved by means of a model-based filter which reduces the fluctuations significantly. The core of the model consists of an approximation by which the mean temperature of the gas can be estimated. The expected pressure level can be approximated by information about the mean gas temperature. This allows to filter the output signal from the pressure sensor. The model was successfully tested on a gas insulated bus-bar. The filtered pressure value is well suited to detect leakages already at an early state.