Calculation And Research Of Electromagnetic Environment In UHVDC Transmission Lines

With the increasingly rapid growth of economic and the growing demand for the largedistance and large capacity power transmission, UHV transmission technology is beingdeveloped rapidly in our country. With very-long distance, ultra-large capacity, low losspower ability, UHV dc transmission should be developed vigorously.When UHV dc transmission lines is operating normally, the electric field intensity on thesurface of the conductor which exceed a certain critical value will occur corona discharge,more than the interspaces will be full of formed the synthetic electric field and ion currentdensity from charged ions. And the same time, corona discharge cause radio interference andaudible noise. In order to meet the requirements of environmental protections, theelectromagnetic environment parameters need be controlled to the reasonable scope in thedesign of transmission line. This article has studied the electric field effect, ion current density,audible noise and radio interference of the UHV dc transmission lines.First of all, this paper analyzes the corona mechanism and distribution characteristics ofelectric field on the surface of the conductor, studies the calculation methods of electric fieldintensity on the surface of bundled conductor, and compares the advantages anddisadvantages of the several computing methods which are the Markt-Mengele method,successive image method, simulation charge method. And the surface electric field intensityaffected from the lines structure parameters is studied, which draws the conclusion: changingthe number of bundled conductor, conductor radius and bundled spacing could effectivelyreduce the biggest electric field intensity on the surface of the conductor.Secondly, the synthesis electric field and ion current density of UHV dc transmission linesare analyzed and calculated in this paper. Based on the finite element method, this paper usesthe meshless method to calculate the synthesis electric field, use iterative method to calculatethe space charge density and spatial electric potential, through numerical difference methodsfor the study of space potential, and finally calculate and obtain the synthetic field intensityand ion current density. The calculation results are analyzed and verified, it turns out that theproposed method in this paper has good accuracy.Finally, this paper calculates and analyzes the radio interference and audible noise,definite the radio interference and audible noise limits, and detailed analysis the influence thatthe circuit structure parameters have made on the radio interference and audible noise, theanalysis results show that the UHV dc transmission lines use the6x LGJ-720/50type wire, wire to ground height is not less than18meters, in this design scheme calculated radiointerference and audible noise all meet the national limit standard. And through changing thecross-section of conductor, wire to ground height, conductor bundled spacing, and the numberof bundled conductor could reasonably reduce the radio interference and audible noise level,and the influence of the number of bundled conductor is the most obvious.