Study On Partial Discharge Characteristics Of Typical Defects In GIS

GIS（gas insulated switch gear）for short has many advantages,such as small floor area,high reliability and so on.It is widely used in power system.Because GIS is a fully enclosed combined power equipment,its internal structure is complex and precise,transportation bumps,improper operation and other reasons can easily lead to insulation defects in the equipment and lead to partial discharge.The operation experience at home and abroad in recent years shows that the internal partial discharge of GIS seriously affects the reliability of GIS,which further affects the stable operation of the whole power system.Therefore,studying the discharge characteristics of GIS internal defects is of great significance to ensure the safe and reliable operation of GIS.The main research contents of this paper are as follows:Firstly,based on the discharge experiment,the discharge behavior of typical defect model of126k V GIS equipment is studied,and the electrostatic field analysis model is established according to the experimental platform.The relationship between the critical corona starting voltage of defects and the gap distance is analyzed,and the defect field strength is solved in the electrostatic field by finite element simulation.For the tip defect,the criterion of critical corona field strength is proposed to judge whether the discharge is carried out,and the correctness of this criterion is verified by experiments.By calculating the electric field non-uniformity coefficient,the discharge research is extended from special to general,and the discharge behavior of defects with different sizes and spacing is analyzed.The discharge properties of various defects are also discussed to pave the way for plasma analysis.Then,in order to further study the micro mechanism of discharge,this paper studies the SF₆gas discharge theory,establishes a set of reaction formulas to study the complex gas discharge behavior,simplifies the simulation model and retains the secondary electron emission behavior.Considering the influence of photoionization generated in the discharge process on the discharge process,referring to the discharge experiment on the basis of"disk ionization"studied by predecessors,the ionization influence term is added to make the simulation more suitable for the actual discharge,paving the way for the following simulation analysis.Finally,using the plasma module discharge model in COMSOL finite element simulation software,a corona discharge model in line with the experimental platform is established.The changes of the number of micro particles in time and space during SF₆ discharge are simulated,and the correctness of the simulation model is verified by measuring the discharge voltage.The following conclusions are obtained through simulation:the generation process of discharge from scratch is very rapid.When the applied voltage is close to the critical corona starting voltage,the particle number density has changed.When the discharge is complete,the particle number density can reach more than 10~5 times of the initial density.The discharge behavior is mainly concentrated in the arc with large curvature and the tip head.The generation of corona discharge depends on the field strength,and the field strength far away from the electrode area can not reach the critical corona field strength,so the discharge is only generated around the defect.Considering the polarity effect,this paper also simulates the influence of different polarity on the discharge process,combined with experiments to verify the correctness of the simulation,and theoretically analyzes the micro reasons for the different positive and negative corona starting voltages.