Research On The Modeling Method For Earth Electric Field Around ±800kV DC Electrode

With a higher voltage level, the ±800kV UHVDC projects have longer transmission distance and larger power transmission capacity. While in the single-polar operation phase, the current that flows into the earth through the DC electrode will cause distortion in earth surface potential (ESP). Larger grounding current in the ±800kV HVDC project, with a magnitude of thousands of ampere, will subsequently induce ESP distortion in a larger area around the DC electrode, causing severe DC bias problems in substations nearby. The calculation for ESP around DC electrode is subject to the current magnitude, parameters of the DC electrode and the distribution of soil resistivity distribution, among which the soil resistivity has the most complex influence on the ESP. The thesis investigated the modeling method for the soil electric field in search of a modeling method that properly considers all the influence factors, so as to improve the accuracy of DC bias estimation.The thesis proposed a finite element calculation method for ESP with soil resistivity and DC electrode model. Starting with a uniform earth resistivity model, the thesis first discusses the penetration depth of the grounding current and then, upgraded from the classic soil resistivity models, it is proposed that the grid soil resistivity be used for ESP calculation. With the calculation for a typical ESP distribution, the influence on ESP from different parameters is analyzed. A mirror image method is also used to validate the modeling and calculation method proposed. Eventually, measured soil resistivity data is used to validate the compatibility of the soil resistivity model proposed, and influence on ESP from soil resistivity lateral changes is analyzed, revealing the possible aggravation of DC bias current in AC substations.Results of the thesis improved the accuracy of ESP model, providing modeling method for DC electrode and soil resistivity, showing influence of parameters on the ESP, revealing the influence of soil resistivity lateral change on ESP and DC bias distribution. This thesis provides a more practical modeling method for the grounding electric field and DC bias estimation.