Impact Of Pressure On SF₆ Partial Over-thermal Decomposition Characteristics

SF6 gas insulation equipment has the advantages of high dielectric strength,small footprint,and is widely used in modern power transmission and transformation systems.However,the device often induces abnormal heating of the device due to the increase in contact resistance,and further causes Partial Over-thermal Fault(POF).Under the action of POF,SF6 insulation gas will be decomposed to generate various decomposition components such as SOF2,SO2F2,SO2,CO2,H2S,CS2,etc.,and its decomposition characteristics are closely related to the internal fault properties of the equipment,which can pass SF6 partial Over-thermal decomposition characteristics to diagnose equipment internal faults.However,the pressure of the SF6 gas filled in the gas insulated devices of different voltage levels is different,and the pressure of the SF6 gas directly affects the local superheat decomposition.Therefore,studying the influence of atmospheric pressure on local superheat decomposition of SF6 and its mechanism is one of the foundations for the establishment of SF6 decomposition component analysis(DCA)fault diagnosis method.To this end,this paper focuses on the influence of atmospheric pressure on the local overheating decomposition of SF6 gas insulation and its mechanism of action.The work carried out and the innovative conclusions obtained are as follows:(1)The influence of air pressure on the distribution of temperature field inside a closed air chamber is obtained through numerical calculation of multiple physical fields.With the increase of air pressure,the temperature of the air outside the wall has increased.When the air pressure is 0.5 MPa,the temperature of the highest point of the outer wall reaches 304.59 K;the shape of the high temperature of the air room(temperature ?300?)follows the pressure.The change from the "concave" shape to the "sword" shape extends upwards,and the area of the high-temperature zone increases with the increase of air pressure.(2)The influence of pressure on the overheating decomposition of SF6 was obtained experimentally.With the increase of air pressure,the molar concentration of all the characteristic components has an increasing trend;the pressure also affects the appearance time of H2S gas.With the increase of air pressure,the time of H2S shortens;with the increase of air pressure,SO2 The percentage of SOF2 in the total product decreased,and the percentage of SO2F2 increased most significantly.In the effective gas production rate,the effective gas production rates of CO2 and SO2 tended to fluctuate with the pressure change.There was no saturation trend;c(SO2F2)/c(SO2+SOF2)and c(SO2F2)/c(SOF2)had the strongest correlation with air pressure and a linear positive correlation with air pressure.(3)Molecular dynamics simulations were used to preliminarily clarify the mechanism of atmospheric pressure on the thermal decomposition of SF6.The increase of pressure will promote the local superheat decomposition of SF6 to produce SF5,SF4,SF3 and SF2,and SF5 and SF4 are the main low-fluorine sulfides;the number of molecules of SFs,SF4,SF3 and SF2 changes with time under different pressures.The trend showed a trend of "stacking" and then decreasing,and the accumulation time shortened with the increase of air pressure;the proportion of SF5 and SF4 decreased with the increase of air pressure,while the proportion of SF3 and SF2 increased relatively.The percentage of the decomposition products SO2 and SOF2 in the total product decreased as the pressure increased.