Effect of Lateral Earth Resistivity Changes on Earth Surface Potential Around Dc Grounding Electrodes

Abstract

In the trial stage of Xiluodu-Zhexi ± 800 kV HVDC project, grounding current trough DC electrode incurred severe DC bias in substation transformers near the Jinsi electrode, indicating further research on the factors influencing such DC bias problem and since vertical and lateral change of soli resistivity could be one of the main factors, their mechanisms should be studied. Besides a normal layered earth resistivity model, a complex model was established to simulate forms of lateral resistivity changes according to measured soil resistivity data at the site of Jinsi electrode. Then ESP was calculated with finite element method and the effect of lateral change on ESP and its characteristics was analyzed. Later, an assumed case example demonstrated the error of DC bias estimation caused by such ESP distortion. The results suggest the distance from DC electrode to the lateral change interface influences ESP distortion the most, and a high resistivity region in shallow layers at 5 km from DC electrode could incur a relative error of 25.9% in DC bias estimation. The grounding location and impact assessment has indicated that the measurement range of the earth resistivity should be investigated.