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 μν/ppm, 1.888 �- BC;ν/ppm, 2.213 μν/ppm, and 5.695 μν/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.