Influence Of Spark Energy And Metal Materials On The Decomposition Characteristics Of Sparked SF₆

SF6 gas insulation equipment has become an important part of the power grid,the safety and reliability of its operations are closely related to the healthy development of the social economy and the stability of the people’s livelihood.With the continuous development of partial discharge caused by various insulation defects inside SF6 gas insulated equipment,partial discharge will evolve into spark discharge failure which is more serious.Spark discharge failure has serious deterioration effects on high-pressure guide rods,contacts and pot insulators.At the same time,the process of SF6 gas discharge decomposition is greatly aggravated,and a vicious circle is formed.Therefore,it is necessary to monitor the occurrence of spark discharge in the equipment and eliminate fault sources in time to avoid more serious damage to the equipment.Existing research results show that:in the spark discharge process,SF6 will undergo a series of complex chemical reactions with trace amounts of water,oxygen,and other impurities in the equipment,producing numerous sulfur-and carbon-containing gas decomposition products.The formation characteristics of these gaseous decomposition products are affected by many factors such as spark discharge energy,metal electrode materials,trace moisture,trace oxygen,and solid insulating materials.At the same time,the spark discharge process is accompanied by local ultra-high temperatures and violent collisions between gas molecules and metal and non-metallic components,which will lead to the occurrence of deteriorative corrosion of metal components or solid insulating materials near the fault point of the sparks.And powdered solid products are generated.Therefore,the gas-chromatography-mass spectrometer was used to analyze the decomposition products of SF6 spark discharge qualitatively and quantitatively,and the X-ray photoelectron spectroscopy analysis was used to analyze the content of each element in the solid products.The SF6 spark discharge decomposition characteristics under the influence of different discharge energy,solid insulation materials,and different metal electrode materials were acquired.The main work and conclusions obtained in this paper are as follows:1.A SF6 spark discharge decomposition system with controllable discharge frequency and energy is constructed.The high-voltage relay is used to precisely control the on-off state of the charge-discharge circuit,so that the energy stored in the energy storage capacitor is periodically released between the spark gaps to generate a spark discharge with stable frequency and energy.The real-time measurement of the spark discharge energy is realized,and the GC/MS analysis method suitable for quantitative detection of the SF6 spark discharge decomposition characteristic products is debugged.2.The correlation between discharge energy and SF6 spark discharge decomposition was obtained.SF6 spark discharge characteristic decomposition gases are CF4,SO2F2,SOF4,SOF2,and SO2.Under the same spark discharge energy,the generation of CF4,SOF2 and SOF4 showed a‘linear’upward trend with the increase of the number of spark discharges,SO2F2 and SO2 show an‘exponential’upward trend.With the same number of spark discharges,the amount of CF4 and SOF2 increase with the increase of spark discharge energy,and tends to be saturated,SO2F2 continues to decline and tends to be saturated.The differences of the energy required for the cleavage of SF6 molecules into SF5,SF4 and SF2,and the rate of SOF4 and SF4hydrolysis both result in the inverse correlation between the generation of SOF2 and SO2F2 and the spark discharge energy.Since the key factor affecting the rate of SO2production is the H2O content,the amount of SO2 produced remains constant after the spark energy reaches a certain level.3.The characteristic quantity of the spark discharge energy in the device is constructed.7 kinds of component characteristic quantities are constructed,including the total decomposition amount of CT,the decomposition amount of sulfur products CS,the ratio of the component characteristic c（SOF2）/c（SO2F2+SOF4）and the effective gas producing rate Rr（CF4）,Rr（SOF2）,Rr（SO2F2）,etc.4.With the increase of spark discharge energy,the relative contents of the atoms of F,S,Fe,W in the solid product are increased to different extents,the relative content ratios of nonmetal to metal atoms,F/Fe,F/W,S/Fe,and S/W,showed a decreasing trend,indicating that the increase of spark discharge energy increased the extent of metal materials participating in the spark discharge process.The main forms of Fe in solid products are FeS,FeF3,Fe2O3 and Fe.The relative contents of FeS and Fe are increased with the increase of spark energy,it shows that under high-energy spark discharge,the ability of SF6 molecules to generate free S atoms is enhanced.5.Obtained the impact characteristics of organic solid insulation materials on the spark discharge decomposition of SF6.When the discharge involves organic solid insulating materials,due to the large amount of C,H,O elements contained in the organic solid insulating materials,extremely favorable conditions are created for the formation of characteristic decomposition products such as CF4,SO2,SO2F2,and SOF2.The combination of richer active C atoms and free F atoms increased CF4 production by a factor of four,at the same time,the OH group in the solid insulating materials is easily cleavable from the C atom,and combines with the H atom to generate H2O,which accelerates the hydrolysis rate of intermediate products such as SF4 and SOF4,that makes the concentration of SO2F2 and SOF2 increase slightly,and increases the concentration of SO2 by 4 times,however,the speed of SOF4 hydrolysis eventually inhibited the production of SOF4.In addition,the component characteristic quantity c（CF4）/Cs that characterizes whether the solid insulating materials involved in the spark discharge region of the SF6 gas insulated device is also constructed.6.The mechanism of the impact of metal materials on the SF6 spark discharge decomposition process is revealed.Under different metal materials,the production of CF₄,SOF₂ and SOF₄ showed a“linear”upward trend with the increase of the number of spark discharges,the production of SO₂F₂ and SO₂ showed an“exponential”upward trend,indicating that the evolution of each characteristic decomposition gas of SF6 spark discharge with the number of spark discharges was not influenced by metal materials.The highest content of C atoms in stainless steel is the main reason for the formation of CF4 below the Fe electrode.The formation of sulfur-containing gas decomposition products and the rate of gas production both have the regular pattern of Al>Cu>Fe,and this can be reasonably explained by four aspects of boiling point of metal,the fluorination reaction exothermic energy,metal work function,and metal oxide film.The content characteristic ratio c（CF₄）/Cs shows a“decrease-saturation”trend with the increase of the number of spark discharges,and under the influence of three metal materials,the stable value of the characteristic ratio exists,so it can be used as an important feature to determine the type of metal material components involved in spark discharge faults in SF6 gas insulated equipment.7.In the solid product,the content of non-C and non-O elements under the Al electrode is the highest,and the ratio of Al/W atoms is greater than Fe/W and Cu/W,it shows that when metallic materials participate in the SF6 spark discharge process,Al and SF6 react the most.Through XPS analysis of the solid products under three kinds of metal materials,we know that,Fe is present in the form of FeF3,Fe2O3,FeS,and Fe.The Fe atoms in FeF3 account for 80%of the total number of atoms;Al is mainly based on AlF3 and Al2O3,Cu exists mainly in the form of CuF2 and CuO.