Research On The Geoelectric Fields Induced By The Magnetic Storms In Complex Conductivity Structures

The geoelectric structure affects magnitude and distribution of geoelectric field induced by the magnetic storm,and then influences magnitude and distribution of geomagnetic induced current(GIC)in power grids.It is of great significance to know the influence of geoelectric structure on induced geoelectric field for calculating accurately and mitigating GIC in power grid.Compared with the countries in high magnetic latitudes,the east-west and north-south components of the geoelectric field in mid-to-low latitudes are both very large.So the calculation of geoelectric field requires more accurate data of geoelectric structure.Considering the fact that there is complex geoelectric structure and large-scale power grid in China and power grids in mid-to-low latitudes requires accurately calculated GIC,the influence of geoelectric structure on geoelectric field distribution is studied in the thesis.Based on the model and calculation method with the finite data of geoelectric structure,this thesis reveals the influence characteristics of geoelectric structure on the geoelectric field distribution.The main research contents and results are as follows:1)The influence of conductivity variations on the geoelectric field distribution is studied.A three-dimensional model of the Earth conductivity is established to calculate the induced geoelectric field distribution.A simplified two-dimensional finite element method is then provided to analyze the E-polarization and H-polarization geoelectric field respectively.The model and method are verified by comparing the calculation results of typical models between finite element method and analytical method.And the influence of different conductivity structures on geoelectric field is calculated by using finite element method.It is found that the geoelectric field distortion is affected by frequency,conductivity difference between adjacent areas,interface shape,distance from interface and sea water depth.2)Based on the theory of distributed source transmission line(DSTL),the method used to calculate geoelectric field is put forward.The DSTL models including uniform conductivity and coast effect are established respectively.The nodal admittance network composed of equivalent-pi type circuit is deduced.The geoelectric field distribution for a typical model is calculated.Compared with the finite element method,the DSTL method is verified.On this basis,the transmission sheet model of the Earth conductivity is proposed,which is used to calculate the geoelectric field distribution in the complex geoelectric structure.3)A GIC calculation model suitable for E and H polarization is proposed.The influence of lateral conductivity variation on GIC in power grid is systematically analyzed and quantified.Taking the geomagnetic storm event on November 9,2004 as an example,the GIC through the neutral point of the transformer in the Ling'ao Nuclear Power Station is calculated with one-dimensional,two-dimensional and three-dimensional Earth conductivity models.The comparison between the calculated values and the measured data verifies and explains the application value and significance of the method in this thesis.These research results will provide reference for the Earth modeling and calculation of geoelectric field,which is greatly significant to evaluate the risk of magnetic storm disaster in power grid and develop reasonable defense strategies.