Induced voltage levels on buried pipelines collocated with overhead electric power transmission lines are usually mitigated by means of grounding the pipeline. Maximum effectiveness is obtained when grounds are placed at discrete locations along the pipeline where the peak induced voltages occur. The degree of mitigation achieved is dependent upon the local soil resistivity at these locations. On occasion it may be necessary to employ an extensive distributed grounding system, for example, a parallel buried wire connected to the pipe at periodic intervals. In this situation the a priori calculation of mitigated voltage levels is sometimes made assuming an average value for the soil resistivity. Over long distances, however, the soil resistivity generally varies as a log-normally distributed random variable. The effect of this variability upon the predicted mitigated voltage levels is examined. It is found that the predicted levels exhibit a statistical variability which precludes a precise determination of the mitigated voltage levels. Thus, post commissioning testing of the emplaced mitigation system is advisable.
Keywords: ac induction, induced ac voltages, induced voltage mitigation, pipeline grounding, soiltivity measurements, resistivity measurements