Study On Surface Flashover Characteristics Of Insulators In SF₆?CF₄ And N₂ Mixed Mixture

SF₆ is widely used in gas insulated transmission line?GIL?due to its good insulation.But SF₆ has strong greenhouse effect,and its liquefaction temperature is high.Therefore,the study on SF₆ gas alternatives has become a hot topic.The use of SF₆/CF₄ and SF₆/N₂ mixture,can not only reduce the use of SF₆ in electrical power equipment,reduce its impact on the environment,but also can meet the use of power equipment in extremely cold areas.Gas-solid interface is the weak link of insulation in high voltage power equipment.At present,there is little research on the surface flashover of insulators in SF₆/CF₄ and SF₆/N₂ mixed gases under DC voltage.Therefore,the study on the surface flashover characteristics of insulators in SF₆,CF₄ and N₂mixed gases has important theoretical value and practical significance.In this paper,according to the actual application environment of insulators in high voltage electrical equipment,the finger electrode system and needle plate electrode system was designed to simulate slightly uneven electric field and extremely uneven electric field.The finite element software was used to simulate the electric field distribution of the two-electrode system,and the uneven coefficient of the electric field under the two electrodes in the electrode spacing of 5mm was calculated.and set up an insulator surface flashover test platform in the mixed gases under DC voltage,conducting the surface flashover test of insulator in SF₆/CF₄ and SF₆/N₂ mixed gas under DC,The flashover voltage value of PTFE insulators were measured under the condition of pressure range of 0.1⁰.4 MPa,different electrode spacing,different mixing ratio of SF₆/CF₄,SF₆/N₂ mixed gas,The influence of gas pressure,electrode spacing,SF₆ mixing ratio and voltage polarity on flashover characteristic was analyzed.The results show that the DC flashover voltage of insulators in SF₆/CF₄ and SF₆/N₂mixtures increases with the increase of mixture pressure within the range of 0.1⁰.4MPa under the same conditions.In the two mixed gases,the different polarity DC flashover voltage increased with the increase of SF₆ ratio in the mixed gases under finger electrode.The flashover voltages of different polarities vary with the increase of SF₆ content in the two mixed gases are different under the needle plate electrode.In SF₆/N₂ mixed gas,with the increase of pressure,when pressure reaches a critical value,The flashover voltage in 40%SF₆/60%N₂ mixed gas will be higher than it in 60%SF₆/40%N₂ mixture,and the positive and negative polarity DC flashover voltage curve will be under a certain critical pressure,with the increase of SF₆ content show the tendency of growth slow or even falling phenomenon,namely,the"hump"effect of flashover voltage under needle plate electrode;In the two mixed gases,with the increase of electrode spacing,the surface flashover voltage increases while the flashover field intensity decreases.When the electrode spacing is small,the flashover field intensity decreases slightly.The flashover voltage of the two mixed gases both has polarity effect,and the polarity effect reversal phenomenon of the DC flashover voltage of the SF₆/CF₄ mixed gases is analyzed emphatically.The mathematical processing method of weibull distribution is introduced to analyze the flashover voltage under different conditions.