Research On Corona Discharge Suppression Of HVDC Transmission Lines Based On The Dielectric Barrier

The high voltage direct current(HVDC)has the advantages of flexible control mode,large transmission capacity and interconnection of different frequency alternating current systems,which has been widely used at home and abroad in recent years.However,considering the overall economy,the HVDC transmission lines generally operates in the corona discharge state,which results in a large number of charged particles around the lines,and electromagnetic environment problems such as corona loss,radio interference and audible noise.In addition,in a long time scale,charged suspended particles in the air are constantly adsorbed and accumulated on DC transmission lines and converter station equipment,which seriously endangers the safety of operating equipment and greatly increases the cost of operation and maintenance.At present,the research on the corona effect of HVDC transmission lines has become more and more mature,while the methods to suppress the corona discharge of HVDC transmission lines are few and the theoretical analysis is not deep enough.In this paper,the effect of inner diameter,film thickness and film material of conductor covered with film on corona discharge of HVDC line under single and double polarity is studied from two aspects of composite field strength and ion current density by using a wire to plate experimental device,and compared with the corresponding bare conductor.In addition,the differences of the inner diameter,film thickness and film material in corona discharge suppression are explored,and the mechanism of charge accumulation and dissipation is studied.The specific results are as follows:The experimental results of the comparison between conductors covered with film and bare conductors show that the conductor covered with film mainly relies on the gas conduction mode to accumulate the heteropolar charge produced by the discharge.After the corona discharge,the dielectric barrier effect of the conductors covered with film has an excellent ability of suppressing corona discharge.In terms of composite field strength,the ground level field strength of conductor covered film with is far lower than that of bare conductor,and the ground level field strength of conductor covered film is lower than the nominal field strength,while the ground level field strength of bare conductor is significantly higher than the nominal field strength.In terms of the ion current density,the ground level ion current density of the conductor covered film is nA/m~2 level,while the ground level ion current density of the bare conductor is?A/m~2 level.Compared with the bare conductor,the conductor covered film has almost no ion current.In addition,both the bare conductor and the conductor covered film have obvious polarity effect.The ground level composite field strength and the ion current density in the negative region are higher than those in the positive region,so the positive corona discharge is more easily suppressed.The results of the influence of conductor parameters on corona discharge suppression show that the ability of conductor covered with film to suppress corona discharge is related to the surface field strength,voltage polarity and film material.When the dielectric thickness of conductor covered with film is fixed,the smaller the inner diameter of conductor,the stronger the ability of suppressing the corona discharge;When the inner diameter of conductor covered with film is fixed,the corona threshold voltage can be increased by increasing the film thickness,but the ability of suppressing corona discharge is weakened.Under the negative polarity,more charges can be accumulated on the surface of the conductor,but the suppression effect of corona discharge is weaker than that of the positive polarity.In addition,due to the difference of microstructure of different film materials,compared with conductor covered with PVC film,the conductor covered with XLPE film has stronger charge accumulation ability and can better suppress corona discharge.The influence of conductor parameters on the surface charge dissipation shows that the rate of charge dissipation is related to the surface field strength,film material and the charge polarity after the voltage disappears.The higher the surface field strength,the more charges can be accumulated,but the rate of charge dissipation is also relatively faster.Compared with conductor covered with PVC film,the charge dissipation rate of conductor covered with XLPE film is slower,and the charge dissipation process of conductor covered with XLPE film is mainly air neutralization dissipation,while the charge dissipation process of conductor covered with PVC film includes volume dissipation and air neutralization dissipation.In addition,compared with the results of positive polarity,the film conductor has a faster charge decay rate under negative polarity.