Research On The Electromagnetic Influence Of Ground Current From DC Earth Electrode On The Buried Metal Pipeline

With the construction and development of HVDC projects and oil & gas pipelines projects in our country,the DC grounding electrode is adjacent to the oil & gas pipelines from time to time.When the DC grounding electrode is operated by monopole ground loop-line operation,too thousands of ampere current may cause electromagnetic interference to nearby buried metal pipeline,therefore,the study of the electromagnetic interference of DC grounding electrode has important significance for grounding electrode location selection and pipeline design.In this paper,by establishing model and simulating analyzsis,the influence of DC grounding electrode on pipeline under different conditions is analyzed.First,in this paper,introducing the structure of HVDC system,the layout of the grounding electrode and the current and potential distribution of DC current in the earth,analyzing the electromagnetic interference principle of grounding electrode to pipeline,and classifying the interference degree of the grounding electrode of the pipeline,the limit values stipulated by different fields at home and abroad are summarized.Then,based on the CDEGS software,builting the grounding electrode and the pipeline model,and analyzing the distribution rules of the pipeline potential,pipeline current,pipe ground potential and leakage current density along the infinite long pipeline under the influence of the DC grounding electrode,using pipe ground potential as an indicator to measuring the interference,the influence of soil resistivity and pipeline length on the pipe ground potential is studied.Taking the finite length pipe as the research object,analyzing the pipe ground potential distribution with a certain length of pipe,which is influenced by the operation mode of the grounding electrode and the relative position of the electrode;Considering the operation characteristics of the DC grounding electrode,the electro-corrosion depth of the metal tube wall is calculated;puting forward the concept of critical length based on the interference rule of grounding electrode to different length pipelines,and analyzing the factors that affecting the critical length,it is concluded that,the critical length is not affected by the DC grounding current,increases linearly with the distance of the grounding electrode,increases exponentially with the soil resistivity,and decreases exponentially with the resistivity of the coating.Finally,the effect of interference suppression is studied,by installating insulated joint and forced drainage devices.By comparison with the non-installed protective devices,installating insulated joints can not reduce the overall pipe ground potential,which is only effective for a section of pipeline,increasing the working current of the drainage device can effectively reduce the pipe ground potential along the pipeline,this protection can effectively suppress the interference for the pipeline which buried in high soil resistivity.