Research On Grounding Characteristics Of Poles And Towers Based On Expanded Graphite Composite Grounding Material

Power system mainly adopts steel,copper and some plating alloy of metal ground material.Metal grounding materials are faced with corrosion problems in practical operation for a long time and the service life of grounding network is limited.In addition,metal grounding materials are also faced with such problems as difficult transportation and construction under complicated terrain conditions,poor compatibility between grounding electrode and soil,frequent theft and man-made damage accidents,and use of resistance reducer to accelerate metal corrosion,etc.Nonmetallic material graphite composite grounding electrode can greatly alleviate the above problems,in view of the existing solid graphite composite grounding materials,considering the practical situation of lightning current and short-circuit current is given priority to with high frequency wave,high frequency under the condition of the skin effect of grounding electrode is increasingly obvious,so the structure is optimized to improve,preparation of expanding graphite composite grounding electrode,in optimizing the grounding characteristics,improve material utilization,enhance the security and stability of power grounding system is of great significance.In this paper,the main research contents of the ground dispersion characteristics of the expanded graphite composite grounding electrode and its distortion similarity simulation test are as follows:(1)Using the CDEGS ground simulation software,the influence law of the grounding material resistivity,permeability and diameter on the grounding electrode dispersion under the impact condition is obtained.Research shows that the material permeability has little effect on self-inductance,so the increase of permeability will not greatly aggravate the inductance effect.Under the premise that the inductance effect basically determines the non-uniform distribution of the current at high frequency,the material permeability and resistivity further change the distribution of the impulse current by affecting the resistance of the grounding electrode under the skin effect.CDEGS software was used to simulate the dispersion characteristics of copper,steel,solid graphite composite grounding materials and expanded graphite grounding materials.(2)Using finite element method,COMSOL software was used to compare and analyze the influence of the resistivity and magnetic permeability of copper,steel and graphite composite grounding materials on the skin effect of grounding electrode from the perspective of field analysis.On this basis,the structure of solid graphite composite grounding electrode was optimized to prepare expanded graphite composite grounding electrode.The results show that the dispersion characteristic of graphite grounding materials is more prominent than that of traditional metal grounding materials,and the expanded graphite composite grounding materials is better than the solid graphite composite grounding materials under the condition of high frequency and high resistance.When the diameter expansion rate of graphite composite grounding electrode is 30%?40%,the skin effect of grounding can be effectively reduced under the condition of considering other properties.(3)Considering the problem that some test parameters cannot be scaled down according to the similar conditions in the simulation test of the expanded graphite composite grounding electrode,an extrapolation method for the simulation test of power frequency and impact grounding,which is applicable to the simulation test of the inside and outside radius and resistivity of the grounding with incomplete similarity,is proposed by using the incomplete similarity theory.The sensitivity of grounding electrode to each distortion under different soil and similar ratio conditions was analyzed by simulation.The results show that when only the soil resistivity distortion exists,the prediction error varies greatly,and when the soil resistivity is large,the prediction error is relatively small.Item is only equivalent diameter distortion,low soil resistivity,the prediction error is about 30%,when the soil resistivity is higher than 500 ?·m,the prediction error basically stable at about 25%.Although the increase of soil resistivity can reduce the prediction error,the effect is not significant.Under the condition of the same distortion coefficient,the diameter distortion plays a decisive role in the prediction error.(4)A prediction coefficient correction method is proposed to improve the accuracy of the prediction results of the distorted similarity model.The results show that the prediction accuracy of the model is very high,and it is suitable for the grounding test of power frequency and impact ground,and the accuracy of the prediction value under the power frequency condition is higher than that under the impact condition,the smaller the similarity ratio is,the higher the prediction accuracy is.