Research On Detection Method Of Sulfur Hexafluoride And Its Decomposition Products Based On FAIMS

Sulfur hexafluoride（SF₆）is a highly electronegative gas with outstanding arc extinguishing and insulation capabilities,which is widely used as an insulating gas in electrical equipment.The leakage and decomposition of sulfur hexafluoride will reduce the insulation performance and affect the safety performance of the equipment.Sulfur hexafluoride is also a gas with a strong greenhouse effect.Currently,80%of sulfur hexafluoride emissions in the atmosphere come from leaks in electrical equipment.With the rise of new energy sources such as solar and wind energy,the widespread use of distributed power transformation and distribution systems has greatly increased the risk of leakage.Therefore,leakage detection and decomposition product detection of sulfur hexafluoride in electrical equipment is not only a basic guarantee for the safe and stable operation of electrical equipment,but also a major demand for the rapid development of new energy power systems in the dual-carbon context.FAIMS is an analytical technology used to separate and characterize trace gases.It has the advantages of fast detection speed,high sensitivity,and can be combined with MEMS technology to achieve miniaturization.It has great application potential in the fields of environmental pollution detection,explosives detection,chemical poison detection,and other fields.However,the gas components in the on-site detection environment are complex and the concentrations of different gas components vary greatly,which will affect the detection sensitivity and accuracy of FAIMS.Because of the problems and deficiencies existing in the on-site detection environment,this thesis designs and optimizes the ionization source and the structures of migration tubes based on traditional FAIMS,and uses them for the detection of sulfur hexafluoride leakage and its decomposition products.The specific research contents of this thesis are as follows:（1）A stable and reliable FAIMS experimental platform has been built.Dopant-assisted Atmospheric Pressure Photo-Ionization（DAPPI）is used to achieve high-abundance ionization of gas-phase ions,and a high-precision and highly integrated FAIMS migration tube is designed to achieve efficient separation of gas-phase ions.A multi-layer shielding structure is used to reduce system noise interference.Sulfur hexafluoride and its decomposition products are used as sample gas to verify the qualitative and quantitative detection capabilities of the experimental platform,and the detection limit of gas components can reach the ppm level.（2）Because of the strong electronegativity of sulfur hexafluoride,this thesis proposes a new method combining the DAPPI source and FAIMS for detecting trace amounts of sulfur hexafluoride.Acetone is used as a dopant to achieve high-sensitivity detection of sulfur hexafluoride,and sulfur hexafluoride is detected in negative ion mode to improve the selectivity of the proposed method.This thesis studies the effects of dopant concentration and relative humidity on detection sensitivity,and selects ammonia,benzene,and hydrogen sulfide as interferences to verify the selectivity of the proposed method.Finally,this thesis studies the linear relationship between the concentration of sulfur hexafluoride and the signal intensity of the characteristic ion peak,and determines the detection limit of sulfur hexafluoride.Experimental results show that the use of a DAPPI source can effectively improve the ionization efficiency of sulfur hexafluoride.The linear coefficient of fitting the dopant concentration and the signal intensity of the characteristic ion peak of sulfur hexafluoride is96.1%.The detection sensitivity of sulfur hexafluoride is inversely proportional to the relative humidity.The use of Nafion tubes can effectively control the relative humidity of the gas.Sulfur hexafluoride has a characteristic fingerprint that differs from air background and typical interfering substances,so sulfur hexafluoride can be distinguished in mixtures from interfering substances such as ammonia,benzene,and hydrogen sulfide.There is a good linear relationship between the sulfur hexafluoride concentration and the signal intensity of the characteristic ion peak.The linear coefficient is 99.8%.The detection limit of sulfur hexafluoride is 0.02 ppm.（3）Aiming at the problems of complex gas components and large differences in concentration of different gas components in on-site detection environments,this thesis designs a new analyzer structure called Tandem-FAIMS and proposes a method to separate target ions from complex gas components,and applies the method to the task of detecting sulfur hexafluoride decomposition products.This thesis uses benzene,styrene,and their mixtures as samples to verify the effectiveness of the proposed method,and selects hydrogen sulfide and sulfur dioxide as sample gases to verify the application potential of Tandem-FAIMS in the task of detecting sulfur hexafluoride decomposition products.Experimental results show that under the condition of low dispersion voltage（DV=480 V,550 V）,the proposed method can effectively separate overlapping ion peaks and obtain the characteristic ion peak information of the two substances at a concentration ratio of 10:1,the error is within±0.5 V.There is a good linear relationship between the concentration of hydrogen sulfide and sulfur dioxide and the signal intensity of the characteristic ion peak,and the detection limit can reach 0.1 ppm.The research work of this thesis can provide theoretical support for sulfur hexafluoride leakage detection and decomposition product detection,and is expected to provide core sensor device support for detection solutions for large-area distributed electrical systems.