Photoacoustic Detection of SF6 Decomposition By-products with Broadband Infrared Source

By virtue of stable performance and less occupied area, SF6 (sulfur hexafluoride) gas-insulated power apparatuses are widely used in the high-voltage and extra-high-voltage substations. These SF6 gas-insulated power apparatuses play a vital role in power systems, and their operating state is closely related to the stability of power systems. Due to the destructiveness of the insulation faults in the SF6 gas-insulated power apparatuses, insulation faults attract more attention. SF6 decomposition by-products analysis is recognized as a powerful monitoring technique for the detection of developing insulation faults within SF6 gas-insulated power apparatuses. Nowadays, on-line SF6 gaseous decomposition by-products analysis has become increasingly relevant for timely insulation fault detection, especially in the context of the ageing worldwide SF6 gas-insulated power apparatuses. Photoacoustic technology has proven to be one of the best analytical techniques for detection trace constituents in gas mixtures, and has been successfully applied to on-line dissolved gas analysis (DGA) for detecting faults within transformer main tanks and associated oil filled equipment. In this paper, a highly selective and sensitive photoacoustic system has been designed and developed for SF6 gaseous decomposition by-products analysis. This photoacoustic system comprises of a photoacoustic cell, a broadband infrared source as an excitation source and a sensitive electret microphone as a photoacoustic signal detector. The detection of four components of SF6 decomposition, that is SO2F2, SO2, CF4, and CO2, has been carried out. In our photoacoustic system, the sensitivity of the four gas components in SF6, SO2F2, SO2, CF4 and CO2, are 0.831 mu V/ppm, 1.888 mu V/ppm, 2.213 mu V/ppm, and 5.695 mu V/ppm, respectively. The minimum detection limits of the four gas components, SO2F2, SO2, CF4 and CO2 in SF6, for a signal to noise ratio of 1, are 0.45ppm, 0.26 ppm, 0.245 ppm, and 0.10 ppm, respectively. To validate the performance of our photoacoustic system, GCMS (Gas Chromatography Mass Spectrometer) is used as the reference system to compare the concentration of several pseudo-unknown samples. Based on the results, it is shown that this photoacoustic system can be applied for SF6 gaseous decomposition by-products analysis very well.