Study On Heavy Current Experiments And Simulation On The Impulse Characteristics Of Actual Tower Grounding Electrodes

Lightning is the main reason for the trip fault of transmission line.With China entering the era of rapid development of UHV,it is necessary to protect the transmission line against lightning,reducing the tower grounding resistance is one of the most effective measures to improve the lightning withstand level.The impulse characteristics of grounding electrode are different from the power frequency characteristics,it is instructive to study the impulse characteristics of the grounding electrodes to reduce the impulse grounding resistance of the tower.The research on the heavy current experiment of impulse characteristics of actual grounding electrode is few,the simulation results based on CDEGS often do not take into account the influence of soil nonlinear ionization,and the research on impulse current dispersing of complex grounding electrodes and optimized design based on current dispersing is not enough.Therefore,this paper study for solving the problems mentioned above.Firstly,the heavy current field experiment with grounding electrodes of 110~500kV transmission line tower were conducted based on the large-scale impulse current generator.The different amplitude impulse current is applied to the grounding electrodes of tower,and the maximum current amplitude is 23.5kA,and the impulse current waveform and the voltage waveform at the current injection point are measured.The impulse grounding resistance and impulse coefficient of each grounding electrode are calculated,and the influence of different factors on the impulse grounding resistance and impulse coefficient is summarized.Secondly,this paper analyzes the soil ionization process around the grounding electrode under the impulse current,and establishes the simulation model considering the effect of soil nonlinear ionization.Using CDEGS as the simulation platform,and establishing the grounding electrode simulation model in CDEGS,the calculation method of impulse characteristics by iterative calculation is proposed.The correctness of the simulation model,simulation method and field experiment method are verified by the simulation analysis of the experimental examples.Based on the above simulation model,the influence of the factors such as grounding materials,grounding resistance reduction agent,lightning current waveform,current injection point and quantity and grounding depth on impulse grounding resistance of the actual size grounding electrode are analyzed by the simulation analysis.The impulse current dispersing of the grounding electrodes in field experiment and its extension are also analyzed,and the influence of impulse current amplitudeand waveform,soil resistivity and grounding depth on the impulse current dispersing is studied with horizontal radiation grounding.Finally,based on the law of the impulse current dispersing of the grounding electrodes,the method is proposed to optimize the grounding electrodes structure by adding short conductor in the conductor section with weak current dispersing capacity and the end of the grounding electrodes,and summed up the reasonable way to add short conductors.In this paper,two kinds of improved grounding electrodes are proposed,and the impulse grounding performance of the improved grounding electrodes and the typical grounding electrode is compared by simulation analysis.The results show that the improved type can effectively reduce the grounding resistance of the grounding electrodes.In this paper,the impulse characteristics of the actual grounding electrodes are studied by field experiment and simulation method based on electromagnetic field,and the method of grounding electrodes structure optimization is proposed.The experimental and simulation methods and the conclusions can provide guidance for practical engineering design.