Study On The Effect Of Grounding Current Discharge On The Corrosion Process Of Carbon Steel Grounding Electrode

The grounding electrode is the main component of the grounding device.It is generally buried in the soil for the flowing of grounding current such as power system towers,communication towers,and electrical equipment to ensure safe operation of the power grid and power equipment.At present,most of the grounding materials used in China are carbon steel.The main chemical component is iron,which is prone to corrosion in soil.The grounding electrode is a metal conductor that grounding current flows into the soil.When the current is discharged,a discharge current is formed on the surface of the grounding electrode,so that the grounding electrode is in the electromagnetic environment generated by the grounding current.The generation of discharge current will directly affect the natural corrosion process of the grounding electrode and cause its electrochemical corrosion behavior to change.Under the influence of natural corrosion and grounding current,the structure and material of the contact surface between the grounding electrode and soil are changed,and the deposition layer of the corrosion product gradually covers the surface of the grounding electrode.When the corrosion is serious,the current flowing into the earth is not smooth,in the event of short-circuit or lightning strike,grounding faults can easily occur,often causing an increase in power accidents.However,due to the complexity of the soil and the corrosion characteristics of the soil corrosion and the coexistence of the grounding current,it is very difficult to comprehensively describe the grounding corrosion behavior.At present,there is no carbon steel grounding corrosion model that considers both the natural corrosion and the influence of the grounding current.There is a lack of research on the influence law of the grounding current on the grounding corrosion behavior,which brings many difficulties to grounding corrosion prediction,evaluation and corrosion protection.Therefore,a carbon steel grounding natural corrosion model was established to study the influence of grounding current on grounding corrosion behavior,to test the physical and chemical properties of corrosion deposits,and to analyze the microstructure of corrosion product deposits,in order to understand the evolution law of grounding corrosion process.It is of great significance to predict grounding corrosion and metal corrosion protection.In this paper,systematic work is carried out around the natural corrosion behavior of carbon steel grounding electrode and the effect of grounding current on the corrosion process.Firstly,the natural corrosion model of carbon steel grounding electrode is established.The influence mechanisms of DC current and AC current on the corrosion process are analyzed.The natural corrosion,DC corrosion and AC corrosion process of grounding electrode are simulated.The simulation calculation results and experimental measurement results were compared and analyzed,and the influence law of the grounding current on the grounding electrode corrosion process was obtained.Combined with Xray scanning test and electron microscope scanning experiment,the influence of grounding current on the physical and chemical properties of grounding corrosion products and the structure of the sedimentary layer was analyzed.The influence of grounding current on important parameters such as corrosion potential,corrosion current density,and corrosion rate was obtained by simulation and experimental tests.The main research work is as follows:(1)Comprehensively consider the process of electrochemical corrosion of cathode and anode of carbon steel,diffusion of substances,equilibrium reaction of particles,multistage hydrolysis of ferrous ions,deposition process of corrosion products and corrosion deformation of the surface of the grounding electrode,a natural grounding corrosion model is established.On the basis of the corrosion model,the natural corrosion process of a straight round steel wire with a buried wire laid horizontally was simulated.The change law of the important parameters such as grounding corrosion potential,corrosion current density is analyzed.(2)Analyzed the microscopic mechanism of grounding corrosion under the action of DC grounding current.Based on the natural corrosion model,combined with DC current discharge characteristics of grounding electrode,the mathematical relationship between grounding current and corrosion variable was established.In view of the corrosion problem of the DC grounding electrode in the DC transmission system,the DC corrosion process of the horizontal straight carbon steel grounding electrode with a ground lead was simulated and the influence of the DC current on the grounding corrosion process was analyzed.(3)Analyzed the microscopic mechanism of the AC corrosion of carbon steel and the AC corrosion characteristics of the grounding electrode.Based on the study of the laws of natural corrosion and DC corrosion,combined with the AC current discharge characteristics of the grounding electrode,simulating grounding electrode corrosion process,established an experimental platform for experimental measurement,and obtained the influence law of AC grounding current on grounding corrosion process.(4)An experimental platform was set up,and the DC corrosion behavior and AC corrosion behavior of the grounding electrode were measured experimentally,and the simulation calculation results and experimental measurement results were compared and analyzed.The chemical composition of the corrosion products and the microstructure scanning images of the deposited layer of the corrosion product were obtained by XRD composition test and electron microscope scanning experiments,and the effects of AC on the properties and microstructure of the corrosion products were analyzed.