Abstract:If faults such as overheating, partial discharge, or arc interruption occur during the operation of gas insulated switchgear (GIS) equipment, SF6 gas will react with other substances or decompose. The concentration of SO2 generated by different discharge faults decomposition is common between 0~1 000 μL/L. Therefore, it is feasible to use SO2 as a detection gas and judge the status or defects or faults of SF6 equipment based on the concentration of SO2. However, commercial SO2 sensors with different sensing principles can not take into account the detection accuracy, manufacturing cost, equipment volume and other aspects. In order to solve the above problems, this paper designs a portable SO2 detection system with short response time, high sensitivity, detection limit width, low cross sensitivity, and temperature compensation, which can detect SO2 gas in the SF6 background inside GIS. This article first explores the temperature drift correction method under air background, measures the peak to peak output voltage of the detector at concentrations of 0~1 000 μL/L and temperatures of 0~40℃, proposes the concept of correction coefficient at different temperatures, and establishes a relationship model between the correction coefficient, detector output peak to peak, and SO2 concentration. The average prediction error of the model in the air background is 1.2%, and compared with before temperature drift correction, the corrected sensor detection error can be reduced by 92.1%. Due to the high cost of conducting long-term SO2 temperature drift compensation experiments under the SF6 background, and the fact that the greenhouse effect of SF6 is 23 500 times that of CO2 gas, it severely limits the practical application and promotion of this technology in terms of economy and environmental protection. Therefore, the next consideration is to migrate the temperature compensation method under the air background to the SF6 background for detection. In the experiment, it was found that even if the absorption spectra of SF6 and SO2 overlap, the pyroelectric sensor can still generate further response and be used for SO2 concentration calibration due to the saturation of high-purity SF6 absorption. The average error of the SO2 concentration calibration formula is only 2.82% when the compensation coefficient is transferred from the air background to the SF6 background. Compared with before temperature correction, the corrected sensor detection error is reduced by 71.0%, and the temperature drift correction effect is significant. In addition, H2S and CO are important components specified in the maintenance regulations for switchgear, in order to ensure that the SO2 detection device will not be affected by the above gases, cross sensitivity experiments were conducted on the three gases: H2S, CO, and SO2. The average response error of SO2 before and after mixing a single interfering gas was 4.5%, and the average response error of SO2 before and after mixing two interfering gases was 5.1%. Finally, on-site discharge experiments were simulated, Set a breakdown discharge voltage of 15 kV for GIS equipment, collect gas samples from 20, 40, 60, and 80 discharges, and use non-dispersive infrared (NDIR) sensors and gas chromatographs to detect the measured gas separately. The NDIR sensor produces a significant step response, and the response result is inverted into the concentration of SO2. Compared with the detection result of the gas chromatograph, the average error of the two is only ±3.8 μL/L.
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