Design Of SF₆ Decomposition Products Detection Device

With requirements of substation reliability and compactness continue to increase, gas-insulated substation (GIS) with advantages of high reliability, high security, low maintenance and small size has been widely used. However, due to various latent insulation defects, gas-insulated substation will lead to electrical failure, which may lead to a large area of power paralysis and bring a huge disaster to the society. Studies have shown that the most common features of substation electrical fault is partial discharge before breakdown completely. Therefore, monitoring of substation electrical failure can be achieved by partial discharge detection.Researchers according to the physical and chemical phenomena associated with partial discharge proposed a variety of methods to determine the partial discharge. Analysis of SF6 decomposition products generated by partial discharge is a very valuable method. SF6 decomposition components generated by partial discharge are plentiful but the practice has shown that by measuring the decomposition products of SO₂ and H2S can achieve the goal of monitoring the discharge condition and determining the cause of discharge within gas-insulated substation. This study is to design SO₂ and H2S gas concentration measurement devices. H2S as a highly toxic gas is danragous to do the experiment in laboratory, this dissertation only study on the measurement of SO₂ concentration.This dissertation, based on electrochemical sensor method, designed SO₂ electrochemical sensor's signal conditioning circuit and corresponding microprocessor measurement system. In software system, the moving average algorithm was used for digital filtering to eliminate noise interference, and an accurate and stable output was acquired.As concentration measurement device based on SO₂ electrochemical gas sensor can not realize the on-line measurement, this dissertation further designed a SO₂ gas concentration measurement device based on infrared absorption spectrμm analysis. In the progress of realization, first designed the direct absorption optical system. Then according to the characteristics of photodetector's output signal, signal conditioning circuit based on the ICL7650 chopper-stabilized amplifier was designed, which effectively realized the weak concentration signal amplification. Finally, the signal was collected by A/D and sent to microprocessor. In the software system, combining of arithmetic mean and moving average digital filtering method was used to remove the interference factors in the light path, to redue detection error generated by the instability of light source and detector and to increase the output stability.Finally, the gas configuration device was designed. This device was used for calibration of the two devices designed. Calibration data was obtained and then processored using least squares fitting method, through which the input and output characteristics straight lines of the two devices were obtained. Experimental verification was done for the calibrated devices. Experimental results show that the resolution of SO₂ electrochemical sensor concentration measuring device has higher resolution and stability; the sensitivity of SO₂ concentration measuring device based on mid-infrared absorption spectrum has relatively low sensitivity and poor stability.