Challenging AC Interference Mitigation: a Case Study of Mitigation beyond the Pipeline Corridor

Abstract This case study examines a unique installation of AC mitigation for a high-pressure natural gas pipeline system affected by a newly constructed 500 kV overhead powerline. The pipeline system was equipped with corrosion rate probe remote monitoring units (RMUs) shortly after the powerline was energized and before the parallel counterpoise AC mitigation system was installed. Before and after the initial AC mitigation installation, pipeline AC current densities were excessively high and significantly greater than predicted by initial computer modeling. Various field analyses and computer simulations were conducted to determine the cause of the unexpected conditions, refine the computer models, and develop an appropriate solution. The final mitigation involved an uncommon approach, including the installation of 4,500 feet of buried mitigation conductor along the powerline corridor, outside the pipeline right-of-way, to counterbalance the induced voltage on the pipeline. Real-time monitoring of pipeline conditions showed the installed mitigation extension has been effective in reducing AC current densities below the maximum tolerable limit. This project underscores the importance of collaboration between the pipeline and powerline companies and their respective AC interference experts during the design, installation, and ongoing monitoring of AC mitigation systems.