Study On Calculation Method Of Coupling Voltage Of Buried Steel Pipelines Due To Nearby Overhead AC Transmission Line

With the increase of urban development and energy demand,the situation that overhead alternating current(AC)transmission lines and buried steel pipelines exist in the same corridor becomes more common.As the transmission line approaches,AC voltage will be coupled to the pipeline to accelerate metal corrosion and threaten the safety of the pipeline structure.Traditionally,the coupling voltage calculation methods mainly include electromagnetic field simulation and calculation using earth loop equivalent model,which are complicated and time-consuming to reach the result of the coupled voltage on the pipeline.Therefore,the study aimed at a fast and reliable method for calculating the coupled voltage on pipelines nearby the overhead transmission lines is of great significance for evaluating pipeline interference and ensuring the safety of pipeline operation.This paper researches the calculation methods of voltage distribution on the pipeline when nearby transmission line is in steady-state,as well as the maximum coupling voltage of the pipeline when short-time large current flows into the ground.The main research contents and conclusions are as follows:(1)As for the inductive coupling voltage on the pipeline during normal operation of the line,its influence factors are analyzed.Based on the calculation results of the coupling voltage under different factor values,a calculation model for the unit-length pipeline coupling voltage is established,and neural networks are used to deal with nonindependent nonlinear factors.In addition,the distribution pattern of pipeline coupling voltages under different geographical relationships is studied,and the influence when insulation connection and coating damage exist on pipeline is discussed.The formulas of number and location of the lowest voltage of pipeline coupling voltage are given.Finally,a pipeline coupling voltage calculation method based on the inductive unitlength voltage increment and the its distribution pattern is proposed.(2)The method of calculating the maximum value of the resistive coupling voltage of the pipeline under the short-time high-current grounding condition is studied.A resistive voltage analysis model of the pipeline near the high current grounding is established,and the parameters affecting the coupling voltage are discussed.According to the calculation results using different parameter values,the calculation formula of the withstand voltage of the power frequency current to the pipe body and the anticorrosion layer is obtained.The typical spectral distribution of the lightning current is analyzed,and the formula of the resistive coupling voltage at different frequencies is obtained.A timefrequency conversion method is proposed to calculate the time-domain response of the resistive coupling voltage of the pipeline when the lightning current enters the ground.This method is used to analyze the influencing factors of the time domain response of bearing voltage of the pipeline coating under a specific lightning current waveform.(3)The correctness of the calculation method described in this paper is verified by comparing the calculation value and the field test value of coupling voltage in the actual case in the literature,with evaluation method of pipeline risk shown.An example is given to analyze the interference sources and voltage distribution of AC-coupled voltages in the pipelines near the electric network of the railway.In additional,using the survey results,a method for evaluating the voltage of pipeline coupling when parameters are missing is illustrated.