Study On Corona Onset Electric Field And Total Electric Field Under UHVDC Transmission Lines

It is of necessity to develop the UHVDC transmission system which is with alarger transmission capacity, longer transmission distance and other bettercharacteristics in our national needs. But the change of electromagnetic environmentunder transmission lines, radio interference, audible noise and other issues caused byUHVDC corona effect can not be avoided. The present researches on corona onsetcharacteristic of DC transmission lines mainly concentrated in two aspects includingcorona electric field and corona onset voltage, and the calculation on corona onsetcharacteristic of DC transmission lines generally ignores the difference of positive andnegative corona onset mechanisms. The level of total electric field is an importantindicator of electromagnetic environment under DC transmission lines, while theresearches on total electric field under transmission lines mostly focus on the effects oftransmission lines parameters to total electric field. With the rapid development ofUHVDC transmission project construction, we are prompted to consider the situation ofthe total electric field distribution with building or human body nearby under DCtransmission lines.This paper starts with the different positive and negative corona onset mechanisms,has emphasis on the typical UHVDC transmission lines corona onset electric field andthe total electric field distribution with building or human body nearby. The followingworks are mainly discussed in this paper.Firstly, the positive and negative corona self-sustaining criterions and the totalelectric field formation mechanisms are described, and calculation process of spaceelectric field on the surface of conductors and nominal electric field under transmissionlines is derived by the using of charge simulation method. Then the total electric fieldcalculated model is worked up based on Deutsch synthetic. The foundation to studycorona onset voltage and total electric field under transmission lines has beenestablished.Secondly, the conditions of positive and negative self-sustaining developing areproposed separately, the positive and negative corona onset calculated models areestablished according to photoelectric effect electron radiation mechanism. The effectsof sub-conductor radius, wire-to-ground height, split spacing, pole spacing andparameters of stranded structure to corona onset voltages and corona onset electric fields around each sub-conductors of typical bipolar transmission lines are discussedand analysis. Then the ways to reduce the transmission lines corona effects fromengineering are put forward. The conclusion that the transmission lines corona degree of-+/-+arrangement is lowest has been obtained by comparing corona onset electric fieldof different double-circuit arrangements on the same tower transmission lines.Thirdly, two different house models are taken as examples to establish the2-Dcalculated model of total electric field under UHVDC transmission lines with buildingnearby.3-D calculated model of total electric field under UHVDC transmission lineswith building nearby is developed. And the difference of2-D and3-D calculated resulthas been compared. Then, the influences of housing structure, housing height, distancefrom the center line to house and other factors to adjacent total electric distribution arediscussed. And the results of total electric field under different double-circuitarrangements on the same tower transmission lines with building nearby are calculatedto compare. The height restriction of building under transmission lines and theavoidance distance from building to center of transmission lines are both proposed.Finally, the issue of total electric field distribution with human body located underUHVDC bipolar transmission lines has been investigated. The parameters of areasonable simplified human body model are selected, then the contour maps withhuman body located separately on positive and negative polar side in the condition thathuman body model connected directly to ground are drawn to describe adjacent totalelectric field distribution. And the influences of different human body station styles,different human body heights, different distances from human body to transmissionlines center and other factors to distortion of total electric field with human nearby arediscussed.