| HVDC transmission is the key to solving the problem of uneven energy distribution in China.DC bushing is one of the key components that connecting the converter station and the AC/DC equipment.DC bushing plays a vital role in the entire transmission system,and its stability is the guarantee of safe and stable operation of the power grid.In the recently DC bushing failures,there were many micron free metal particles founded,which had a great influence on the insulation properties.However,the motion and discharge characteristics of free metal particles in the bushing were not clear at present.In this paper,the motion and discharge characteristics of free metal particles in DC bushing were studied by means of model construction,simulation analysis and experimental research.The research result could be used as structural optimization and design of DC bushings.In order to study the charge and motion characteristics of particles under different distribution conditions,a motion model of the particle was established.Starting from a single particle present on the electrode,motion models of single particle,linear array of particles,single layer of particles,and multilayer particles were constructed.In order to study the clustering distribution of small-sized particles,a model of particle clusters was built.Charge and model were analyzed for the particles attached to the surface of epoxy capacitor core or insulator.And an equivalent model of particles on epoxy surface was proposed under certain conditions.In this way,the force,charge,and:initial motion field strength of different distribution forms of particles were obtained.Statistics and analysis of particles were done for cause of production,shape,distribution and movement trend of particles in operating DC bushing.Two typical bushing structures were simulated in COMSOL using the finite element method.And the conclusion was carried out that the capacitor core surface,the current-carrying conductor connection,and the support insulator were the positions of the most concentrated electric field and easiest particle attachment.Force situation were analyzed according to the operating state and the installation angle of the bushing.Motion model was applied to the operating state of DC bushing to analyze the charge capacity,force state and motion characteristics.A experiment platform was built for motion and discharge characteristics of free mental particle.In the case where the particles were distributed on the surface of the electrode and the epoxy,experiments on the effects of particle size,width,thickness,and other factors were done on particle motion and discharge characteristics.By comparing with theoretical model result,the conclusions were obtained that with the diameter decreasing and width and thickness increasing,the particles were more likely to move in the electric field due to the effect of the electric field force,and the flashover voltage between the electrodes was lower. |
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