A previous paper1 has addressed the question of estimating mitigation requirements for pipelines installed in high voltage AC corridors, such as to maintain induced voltages at acceptable levels during normal operating conditions on the power system. This paper addresses the more difficult problem of estimating what mitigation is required to maintain pipeline coating stress voltages within acceptable limits during fault conditions on the power system. The difficulty of this undertaking arises primarily from the fact that AC interference during fault conditions includes not only induction, but also voltages transferred through earth to the pipeline location from power line poles or towers near which the fault has occurred: as a result, the analysis is more complex and the mitigation requirements are influenced by a greater number of factors. Furthermore, since the goal is to minimize the voltage difference between the earth and the pipeline steel, the interaction between the earth and bare mitigation wire buried next to the pipeline and connected thereto must be considered. This paper shows how factors such as soil resistivity, soil layering, length of parallelism, proximity of pipeline to transmission line, fault current levels, transmission line static wire type, transmission line structure grounding and coating resistance determine mitigation requirements.
Keywords: AC mitigation, induced voltages, grounding pipelines, coating stress voltages, power line fault conditions, computer modeling, cost estimates