Calculation Of Dc Earth Surface Potential Distribution And Its Influence On Power System DC Bias

The unbalanced distribution of DC surface potential(DCESP)is the key to the DC bias of power system transformers.The unbalanced operation,unipolar operation of the HVDC transmission system,and the return flow of rail transit rails will all generate current into the ground,which will affect the distribution of DCESP [1-2].The ground current of the subway is affected by the rail-to-ground transition resistance,the traction return system,the train load and the electrical structure of the earth,and the resulting ESP gradient distribution is always dynamic [3-4].The topography between the two existing substations is complex,especially in cities,which are affected by factors such as highways and buildings.The number of locations for measuring ground potential data is limited and discontinuous.The method of restoring the DC surface potential distribution based on the data measured at discontinuous locations is studied.Build a CDEGS subway simulation model to obtain the DC surface potential distribution data around the subway,and intercept the data of several discontinuous sections as simulated measurement sections.With the help of neural network algorithm,the ESP of the measurement segment is used as a known quantity to train the built neural network model,and finally the remaining test data is substituted into the trained neural network for model evaluation,and its reduction effect and influencing factors are analyzed.The study of the DC distribution algorithm in the DC transmission project mainly includes the derivation of the Green’s function caused by the point current source to determine the distribution of DC current and the influence of different ground electrode shapes,pole site soil structure,marine geology,etc.on the DC current distribution [4-5].This topic is based on the principle of field-circuit coupling to calculate the effect of DC ground potential on the bias current,and calculates the interference effect of DC bias on the three-phase current system with the help of MATLAB/simulink.And based on electromagnetic theory and solid mechanics theory,with the help of COMSOL finite element calculation of multi-physics transformer DC bias effect.This project relies on the Kunliulong DC and Lugaozhao DC projects to model the grounding electrode,the converter station grounding grid,the grounding electrode line and the tower grounding device.Analyze the distribution of the ground surface potential when the shared grounding electrode is used for one DC unit and the other DC for grounding electrode circuit maintenance work,and evaluate the safety risks of maintenance personnel.The calculation results show that when the temporary grounding wire is manually dismantled or hung,the line near the grounding electrode has a relatively large contact voltage,which poses a safety risk to the maintenance personnel.It is necessary to take corresponding safety measures to ensure the personal safety of the maintenance personnel.The research results of this paper provide a new idea for DC surface potential measurement,which can promote the development of DC bias research field.