| High voltage corridor occupies a large area of land,it has profoundly affected the landscape and environment,then how to minimize the effects of power transmission on the environment is what China is facing.Trees are lossy media,and with the polarization effect in the electric field,it can give rise to electric field shielding effect.The polarization mechanism of trees and its effect on electric field are not known to us at present.This paper,with the four species of poplar,larch,Manchurian ash and lilac as the experimental objects,studies the measurement of the electromagnetic parameters.Based on the data statistical analysis,the tree species in the Mao'ershan Experimental Forest Farm of Northeast Forestry University are selected,measured and calculated and the mathematical model for calculating the electric field of trees is set up.This paper puts forward that the Green function should be used to implement the calculation of the two dimensional electric field of trees while the finite element method should be used to implement three-dimensional analysis of the electric field and thus we can make a scientific prediction towards the electric field shielding effect of trees and by planting trees reduce the impact of transmission line electric field on the environment and the transmission corridor area.The major findings are as follows:(1)With direct measurement of electrical conductivity in the living trees and the sample analysis of dielectric constant to obtain the electromagnetic parameters of poplar,larch,Manchurian ash and lilac,it studies the influences of frequency and moisture content on the electromagnetic parameters.With regard to the thousands-times-higher-than-usual dielectric constant values in trees with low frequency and high moisture content,it analyzes the polarization mechanisms of trees,finds out what interferences in dielectric constant measurement through the theoretical formula,designs the fixtures suitable for the measurement of trees with high moisture content;through the measurement of the labeled dielectrics,it testifies the effectiveness of interference elimination scheme and with data statistical analysis,it sets up a mathematical model for calculating the electric field of trees.(2)With regard to the fact that the emulation charge method is difficult to be implemented in the calculation of the two dimensional electric field of trees,this paper presents the method of using the Green function to improve the emulation charge method,the charge is set on the wire and inside the tree,the boundary condition of the horizontal earth is further considered and the image charges are set on all charges.The result shows that when the observation plane is 0?1.5m above the ground,there is no obvious change in the electric field;when the transmission lines cross the forest or when there is uneven ground,there will be more obvious changes in power frequency electric field,audible noise and radio interference.(3)With regard to the fact that in three-dimensional analysis of the electric field,the huge difference between the diameter of the wire and the size of the spatial solution leads to an excessively higher density of element mesh,this paper puts forward the finite element method.This paper takes Xilingol League-Shandong 1000kV UHV Alternating Current Lines as an example and concludes that trees can greatly shield the electric field of high voltage transmission line,the width of power transmission corridor can be reduced by 49.70%,and the maximum electric field can be reduced by up to 96.22%.Dielectric constants of tree canopy and trunk,tree height,and tree density greatly affect the electric field shielding effect while the electrical conductivity of trees and seasonal factors have little effect on the electric field.Through the comparison of the experimental results,it is better to reduce the electric field of the transmission line by planting trees than the widely used method of erecting the shielding lines.High voltage transmission line is the carrier of power delivery and the basis of power grid.The studies on the electromagnetic parameters of trees set up a mathematical model for calculating the electric field of trees.By planting trees reduce the impact of transmission line electric field on the environment and the transmission corridor area.The calculation of the influence of the trees on the power frequency electric field have great significances in solving high voltage corridor environment and its land requisition. |
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