Research On The Interference Law Of Ground Current From HVDC Ground Electrode On The Buried Pipelines

With the rapid development of HVDC transmission projects,the dc interference phenomenon caused by the stray current from the earthing pole to the ground is becoming more and more common.Under the operation condition of grounding pole single pole earth circuit of HVDC transmission,the stray current into the ground flows in or out along the leakage point of the insulation layer of the pipeline nearby,causing corrosion of the pipeline body and hydrogen embrittement,reducing the service life of the pipeline.When dc interference is serious,it will also cause the risk of ground discharge of auxiliary equipment of the pipeline,abnormal operation of instruments and valve actuators,etc.Therefore,it is of great scientific significance to study the interference law of the grounding pole of HVDC transmission to the buried pipeline nearby,to protect the pipe body and ancillary equipment of the pipeline,to improve the reliability of equipment operation,and to ensure the safe operation of the pipeline.In this thesis,the coupling interference mechanism of the incoming current to the pipeline under the single pole operation mode of the HVDC grounding electrode is studied,the distribution of the constant current field and the pipeline potential near the grounding electrode is calculated,and a simple calculation method of the corrosion rate is proposed;the mechanism of the solenoid valve misoperation caused by the DC stray current is studied,and the pipe ground potential difference is proposed as a measure of the DC interference of the solenoid valve.Based on the CDEGS software,the simulation model of the coupling interference of the HVDC ground electrode to buried metal pipeline by the stray current entering the ground is established by using the field ground electrode,pipeline and soil parameters.The reliability of the model is verified by the physical rationality and grid independence.The distribution of the current field near the ground pole of HVDC transmission is calculated and the variation rule of ground potential gradient is analyzed.The distribution of pipeline potential difference,leakage current density per unit area and axial current in different seasons were studied.Taking the potential difference between pipe and ground as the research object,the influence law of the change of surface and deep soil resistivity under horizontal stratification on the pipe interference is studied,and the conclusion is drawn that the potential difference between pipe and ground decreases with the increase of surface soil resistivity in the presence of low resistance layer.The change rule of the relative position between the pipe and the ground pole is studied.The protective measures of adding insulation joint to the pipeline are put forward,and the results show that it can obviously reduce the amplitude of interference voltage,block the axial current of the pipeline,and reliably prevent the wrong operation of the solenoid valve.A potential acquisition system with the functions of automatic collection of tube ground potential difference data and remote communication is set up to monitor the degree of direct current interference on line through automatic collection of tube ground potential difference data.This paper introduces the hardware structure of automatic potential acquisition system,studies the de-drying and frequency division of discrete digital signal,and realizes the high-precision signal acquisition.The accuracy of the system was tested in the laboratory,and the results showed that the accuracy of the system reached the expected requirements.The potential data collected from the field were compared with the simulation results to verify the correctness of the interference rules obtained.