Study And Experimental Research On The Influence Of Corrosion Layer On The Grounding Performance Of Grounding Electrodes

Tower grounding electrode is an important infrastructure to dissipate the fault current of transmission lines.The quality of its grounding performance is the prerequisite for ensuring the safety and stability of power system.Affected by soil and leakage current,corrosion is common phenomenon in the carbon steel grounding electrodes that have been in operation for many years.The surface of corroded grounding electrode is wrapped with corrosion product,which affects the normal current dissipation process and weakens the grounding performance.The accurate analysis of the grounding performance with corrosion layer can promptly detect the grounding fault of the electrode,which is of great significance to the safety the power system.In the current research on the corroded grounding electrode,most of them only consider the effect of the effective diameter reduction and ignore the influence of the corrosion layer,which can cause inaccurate results in the corrosion diagnosis of the grounding electrode.In order to solve the above problem and improve the research of the corroded grounding electrode,a method for calculating the grounding parameters of the grounding electrode with corrosion layer is proposed in this paper.And based on this method,the effects of the corrosion layer on the leakage current,grounding resistance,grounding potential rise(GPR)and the step voltage are analyzed in detail.This work systematically reflects the influence of corrosion layer on the grounding performance and provide a solid theoretical basis for furthering studying on the corrosion process and the corrosion diagnosis of the grounding electrode.The main research contents of this paper are as follows:(1)Based on the basic principle of electrochemical corrosion,the leakage current corrosion mechanism of the grounding electrode is analyzed.The influence of the leakage current on the corrosion process of the electrode is studied,and the dissolution law of the grounding electrode surface is obtained.Based on the XRD analysis,the chemical composition and proportion of the corrosion products are studied,and the volume expansion coefficient of the corrosion products is obtained.Finally,according to the corrosion dissolution and deposition characteristics of the electrode,the grounding electrode model with corrosion layer is constructed.(2)The influence of the high resistivity corrosion layer on the grounding performance is analyzed by the effect of the equivalent surface charge distribution.Combining the point matching method and the boundary element method,a numerical method is proposed to calculate the grounding parameters of the corroded grounding electrode.By dividing the grounding electrode and the interface between the corrosion layer and the soil,the leakage current of the grounding conductor and the surface charge of each element can be calculated,therefore the grounding resistance and GPR distribution influenced by the corrosion layer can be determined.Finally,the effectiveness of the method in this paper is verified by the grounding calculation software CDEGS.(3)Based on the grounding calculation method of corroded grounding electrode proposed in this paper,the grounding parameters of three typical electrodes,including the horizontal grounding electrode,the vertical grounding electrode and the square-ray grounding electrode in the uniform soil and multi-layer soil are studied.The effect of the decrease of the radius and the corrosion layer on the leakage current density,ground resistance,GPR and the step voltage are analyzed.(4)Field experiments are carried out on 5-base tower grounding electrodes in Quzhou area.The accuracy and applicability of the method to calculate the grounding parameters of the corroded grounding electrode are proved.In addition,samples of ground electrodes in different corrosion condition are selected for outdoor simulation experiments.By comparing the test results of the grounding resistance and the GPR distribution,the grounding performance of corroded ground electrodes are further analyzed.