Research on Earth Resistivity Measuring and Modeling of HVDC Deep-well Grounding Electrode Sites

HVDC Deep-well grounding electrode covers a small area, which effectively alleviates the problem of difficulty in selecting the site of grounding electrode. Due to the small number of electrodes, each sub-electrode has to bear tens of times the current of conventional electrodes. In order to reduce the current density on the electrode, it is usually necessary to use long vertical electrodes to extend into low resistivity layers’ hundreds of meters underground. Because it involves a wide range of underground depths, it is particularly important to accurately evaluate the distribution of resistivity at the electrode site for calculating the electrical parameters of deep-well grounding electrodes. In this paper, four-point method (FP), controllable source audio magnetotelluric method (CSAMT) and magnetotelluric method (MT) are proposed to analyze the conductivity structure of the shallow layer, deep layer and the vicinity of the electrode, and the earth resistivity model of deep-well grounding electrode is obtained. By comparing the on-site grounding resistance measurements of practical engineering application, it is found that the absolute error of the earth resistivity model obtained in this paper is $0.064\Omega $ when calculating the grounding resistance of the deep-well grounding electrode. Engineering examples show that the exploration method in this paper has strong adaptability to the site, and the earth resistivity modeling method has good reliability.