Research On Surface Charge Dissipation Mechanism Of DC GIL Insulator

After long-term operation of DC gas insulated transmission line（GIL）,a large amount of charge will accumulate on the insulator surface,this will have the flashover voltage of the insulator surface reduced.The research on the dissipation of surface charge is helpful to break through the restriction of insulator surface charge accumulation on the further application of DC GIL.Under the background that UHV construction is incorporated into the new infrastructure construction in China,it is of great significance to study the dissipation of surface charge of DC GIL insulator.Based on the self-designed DC GIL platform and surface charge measurement device,this paper carries out experimental research on the dissipation of surface charge in terms of surface charge accumulation,surface charge accumulation location,insulator surface conductivity and air humidity.The results show that with the increase of surface charge accumulation,the dissipation rate of surface charge is faster;with the distance between the surface charge accumulation position and the grounding center guide rod,the dissipation rate of surface charge is slower;with the increase of surface conductivity,the dissipation rate of surface charge is faster;increasing air humidity can promote the dissipation of surface charge.In order to study the dissipation of insulator surface charge which is more close to the actual operation of DC GIL,the three-dimensional modeling of the experimental platform is carried out in COMSOL simulation software,module selection,governing equations,physical model,boundary conditions and mesh generation are introduced in detail,and the typical results of the simulation model are displayed.In order to further study the dissipation mechanism of surface charge,based on DC GIL three-dimensional model,the effects of surface conductivity,ion pair formation rate and volume conductivity on surface charge dissipation were studied.The results show that:（1）in the stage of 0-30s charge accumulation caused by external action,with the increase of surface conductivity,the surface charge accumulation slows down;the ion pair formation rate is in the order of magnitude,and its enhancement effect on the charge accumulation process is not obvious With the increase of ion pair formation rate,the charge accumulation process is gradually accelerated;with the increase of ion pair formation rate,the charge accumulation process is significantly enhanced at the order of magnitude or above;the bulk conductivity has no effect on the charge accumulation process.（2）In the 30-630s stage of surface charge dissipation,the bulk conductivity is less than 10^-14 order of magnitude,the ion pair formation rate is less than 10³ order of magnitude,and the charge dissipation process is mainly carried out through the surface conductivity;when the ion pair formation rate is less than 10³ order of magnitude,and the bulk conductivity exceeds 10^-14 order of magnitude,the charge dissipation is mainly carried out through the surface conductivity and bulk conductivity;when the bulk conductivity is 10^-14 order of magnitude,the charge dissipation process is mainly carried out through the surface conductivity and bulk conductivity Below that,the ion pair formation rate reaches 10³ order of magnitude or more,and the charge dissipation is mainly through surface conductance and neutralization with ions in the gas.