Level Reduction of Induced AC Interferences on a Gas Pipeline by Permutation of «phases» of the HVAC Power Line

High Voltages (HV) power lines can generate an induced alternating voltage (AC) on nearby gas pipelines. In the ongoing operation of HV power lines, consideration must be given to the risk to the safety of persons and the risk of corrosion that may affect the integrity of the pipeline. It is necessary to carry out studies of reduction of these interferences. When a risk of AC interference on a pipeline has been identified by the proximity of an HV power line, the installation of earthing systems is often the solution. In the documentation, permutation phase is one of the most effective techniques to reduce the level of AC interferences. In this article, we will discuss the case of an energy corridor in France where three natural gas transmission pipelines are subject to strong AC electrical interferences due to the proximity of HV power lines. Without a reduction system, AC voltage levels close to 200 V were simulated in the steady state condition. The usual solution chosen was to set up several earthing systems (nine) after studying the electrical configuration of the structures in the field and by simulation via the CRINOLINE tool. Despite these arrangements, it was found that the alternative voltage had been reduced, but insufficiently in view of the design standards. Therefore, it was decided to try a solution that had rarely been implemented. This solution consists in studying the impact of the spatial layout of the electrical conductors of the HV lines which then led to a phase swap on the HV powerline. Alternative voltage measurements carried out in the field because of this work confirmed the significant level of mitigation.