Electromagnetic Coupling of Overhead High Voltage Transmission Lines to Pipelines in Multilayer Soil: Parametric Analysis

Abstract

Metallic pipelines and power transmission lines often share common corridors. As result of their electromagnetic coupling, lightning and power system faults may give rise to excessive transient pipeline-to-soil voltages that may endanger people and disrupt pipeline system safety and reliability. Therefore, safety analysis require accurate modelling of the electromagnetic interactions between such complex systems [1]. Due to the adopted approximations, the accuracy and capability of the existing numerical models is often limited to low-frequency analysis in uniform soil [2]. Such models are well established and provide fast and decent assessment of the induced voltages due to coupling to insulated pipelines with homogeneous structure, for normal operating conditions and faults at power frequencies. However, they are not well optimized for dealing with the conductive coupling in case of using protective grounding on the pipeline; estimating the coating stress voltages in case of lightning current discharge in nearby grounding systems and the treatment of the soil stratification. In this paper, we perform parametric analysis of the electromagnetic coupling of overhead high voltage transmission lines and tower grounding to buried pipelines. Different scenarios are considered: a) inductive coupling in normal operation of power system, b) inductive and conductive coupling in case of single-phase ground fault in power system, and c) coating stress voltages in case of lightning current discharge through nearby transmission line tower grounding. The parametric analysis should provide insight on the influence of layered earth on the induced voltages due to different mechanisms of coupling and help to identify which scenarios of electromagnetic coupling are most critical for the safety of the pipeline system. We also analyse the effectiveness of different mitigation techniques in reducing the induced voltages in the different scenarios. Analysis are performed by full-wave electromagnetic model, based on the method of moments, that accurately accounts for the electromagnetic coupling in presence of multilayer soil [3]. Due to the size and complexity of the systems, the numerical model requires some optimizations that are also discussed in this paper.