Analysis Of Breakdown Triggered By Particles Of Different Dimension In DC GIL Filled With SF₆/N₂

Gas insulated transmission line(GIL)has been widely used in the field of high voltage transmission system due to its high reliability,compactness,and capacity of high transmission.However,In the GIS/GIL's fabrication,assembly and operation process,the generation of metal particles is unavoidable,such as the metal chips that are not cleaned internally during the fabrication process,the debris generated during the handling process,the mechanical abrasion caused by contact insertion in operation and the metal dust generated by spark discharge.Metal particles are an important factor to restrict the insulation endurance capacity of GIL.Under the action of electric field force,the free metal particles in the GIL can move towards the vicinity of the high-voltage electrode or the insulator,causing gas-gap breakdown,which poses a great threat to the insulation performance of GIL.When the metal particles are under the action of a DC electric field force,they become more active and cause greater damage.Therefore,to tackle these metal particle problems associated with DC GIL,this research work has been carried out in various steps.In view of the problem of conductive particle pollution in DC GIL,its effect on the surface charge accumulation of insulators was studied.Within this research work,the multi-physics simulation software COMSOL was used to establish a microscopic model of charge accumulation on the surface of the insulator,which included the effects of particle pollution and generation,recombination,migration,and diffusion of gas-side space ions.The influence of particle attachment position on charge accumulation was analyzed in depth.On the other hand,in order to verify the correctness of the simulation analysis,a rotating charge measurement experimental platform considering the influence of metal particles was established.The simulation analysis and experimental results show that the conductive particles adhering to the insulator surface can cause a sharp increase in surface charge accumulation.The increase in charge density caused by particles attached to the middle part is more significant,and the electrical charge accumulated at the two ends of the particles is opposite in polarity.The particle-triggered breakdown experiment is carried out under the stress of DC voltage.Results show that the gas insulation strength is highly reduced with the interference of metal particle either spherical or linear wire metal particle.Therefore,a coaxial and ball bowl electrode system is used to conduct experiment on SF6/N2 gas mixture using DC voltage.An experimental work is conducted in account to the influential factors on breakdown of SF6/N2 gas mixture with the influence of linear/spherical metal particle such as voltage polarity,SF6/N2 gas pressure and different concentration,particle length,radius and number of metal particles,based on an experimental analysis.Additionally,an experimental study on coaxial electrode system is conducted to analyze the influence of two linear wire particles distance on DC breakdown voltage.Based on the finite element method,the electric field distribution characteristics of the electrode model used in the experiment are analyzed and a one-dimensional discharge model that can simulate the electric field of concentric ball electrodes is built and the boundary of the model to consider the actual discharge process plasma chemical reactions that occur in discharge process is set,which are mainly considered 13 Plasma Chemical Reactions.Further,considering the influence of parameters such as air pressure and the mixing ratio of SF6 and N2,the simulation is performed at 100 kPa,200 kPa 300 kPa,20%SF6/80%N2,10%SF6/90%N2,50%SF6/50%N2 proportion of discharge,and found that this simulation method can effectively obtain different VI curves.After analyzing experimental and simulation results for the breakdown voltage of SF6/N2 gases mixture using Ball Bowl Electrode under DC stress,the following observations have been made.DC positive breakdown voltage of SF6/N2 gas mixture increases with increase in the amount of SF6 percentage,at high pressure the breakdown voltage tends to get saturated.DC positive breakdown voltage of SF6/N2 gas mixture difference decreases as the percentage of SF6 gas concentration increases at the same pressure.DC positive breakdown voltage of SF6/N2 gas mixture results from simulation is higher than experimental results due to some discharges and environmental effects at same pressure and concentration of SF6/N2 gas mixture.The conclusions of this thesis are helpful to deepen the understanding of the mechanism of flashover faults and breakdown in gaseous dielectrics caused by metal particles in DC GIL and provide some theoretical guidance for the insulator structure design and the harmless measures of metal particulate pollutants in DC GIL.