Research On Distribution Characteristics Of Earth Potential Near UHVDC Grounding Electrode

In recent years,the rated current of ±800 kV.8 000 MW and 10 000 MW converter station grounding electrode constructed is 5000 A and 6250 A respectively in China.Due to the large current into the ground of DC grounding electrode,On the one hand,the influence of ground electrode potential(ESP)on the underground pipe network is larger:On the other hand,the distribution of the earth potential near the DC earth electrode is more complex because of the large influence area and the difference of the earth's electricity and structure.In this paper,according to the geophysical conditions of deep geoelectricity and its structural differences,the distribution characteristics of the ground potential near the UHVDC grounding electrode are studied,including the model and algorithm for calculating the earth potential near the UHVDC grounding electrode,so as to provide a scientific method basis and evaluation model and algorithm for controlling the impact of the UHVDC grounding electrode on the pipeline network.The main research work and achieved results of the paper are as follows:1)Based on the data of magnetotelluric sounding.the idea of studying the earth electrode potential is put forward,Using the data of shallow and deep magnetotelluric sounding,The distribution of ESP and the shallow geoelectricity and its structure are studied,And the relationship between deep geoelectricity and its structure and its influence on ESP,Through the study of the relationship between ESP and shallow and deep earth resistivity,The idea of calculating ESP Based on Geodetic sounding data is put forward.2)Considering the influence of shallow and deep geoelectricity and its structure on ESP,as well as the influence of horizontal and vertical mutation on ESP distribution.It is analyzed that the problems existing in the calculation of DC grounding electrode ESP by equivalent resistance and layered resistance earth model,Based on the three-dimensional earth resistivity model and the finite element method,the ESP and its distribution of the grounding electrode are calculated.The validity of the model algorithm is proved by the measured data of the Jinsi grounding electrode in the west of Zhejiang,Province.3)Using the electromagnetic sounding data and data of national geodetic exploration projects such as the national deep exploration plan,Three dimensional earth resistivity models of Zhalute and Gaoqing DC grounding electrodes of Zhaqing UHVDC project and Zhushuangcun DC grounding electrodes of Shangshan UHVDC project are established,The modeling depth of the three models is 310 km and the modeling area is about 200 000 km2.And through the theoretical calculation of the grounding electrode sites and the near area ESP in Zhalute,Gaoqing and Zhushuangcun.The characteristics of ESP mutation caused by different geological faults and the sudden change of coastal seawater electricity are revealed.The research work and results show that,Due to the different electric properties and structures of the earth electrodes,as well as the influence of coastal effect and other factors,The ESP equipotential distribution curve caused by the grounding current into the grounding electrode is no longer a concentric circle distribution centered on the DC grounding electrode,no matter in the inland area or in the coastal area.The ESP distribution of the grounding electrode is obviously different in all directions.Therefore,it is necessary to establish a three-dimensional geodetic model as deep as hundreds of kilometers to deal with the influence of UHVDC earth potential on the pipeline network.