Modeling Calculation And Analysis Of The DC Circulating Network Of The Current Field Generated From DC Electrode

With the wide-range use of HVDC, in influence of current transmit electricity system on the AC system has been increasing, especially that the current transmit electricity system operates under single pole-earth operating way, which causes part of the transformer of the grid to vibrate more strongly with increased noise and reduced safety of the equipment. Recent researches mainly focus on the impact of DC bias on transformers and relevant methods of analysis, leaving the studies of the distribution of HVDC current in AC system almost a blank.In order to study the diffusing of direct current in AC system, calculations must be made on grounding resistance of ground electrode. This thesis resorts to the resemblance of fields mentioned in franklinism analogue method, calculates current field by means of calculating static field first. Also does the thesis explain the calculation methods of grounding resistance of grounding grids inhomogeneous and multi-layer medium, with relevant computer programs to support.Accepting the theory that the direct current grounding electrodes and AC grounding electrodes have a coupling of some degree, this thesis proposes a concept of coupling resistance, which numerically analyses the coupling when huge DC current diffusing to earth, and brings forward two methods to calculate coupling resistance. One is to compare grounding grids to hemispherical conductors, and deduce a resolution formula of coupling resistance. The second uses emulation charge method to calculate coupling resistance by means of numerical analysis Both methods are based on the franklinism analogue method mentioned in Chapter 2, calculating coupling resistance by relative mutual capacitance between both poles.Based on calculations of grounding resistance and coupling resistance, and with a concept of the power system layout and the operation of power system , this thesis builds up a model of resistance network caused by direct current grounding electrodes、grounding grids、current transmission lines-resistance of transformer, abstracting a complex current field to a simple circuit, transforming the interaction of electric field、circuit into pure circuit, greatly simplifying the analysis. With sufficient proof of actual cases, the method of pure resistance network could be utilized to analyze the impact of DC diffusing in AC system, according to which future locations of direct current grounding electrodes could be selected.