Stefan Obradović

The aim of this paper is to analyze the conductive coupling between the earthing grid of the 220/66/11 kV substation and the nearby underground pipeline, under fault conditions. It evaluates the potential risks to personnel safety, pipeline integrity, and outlines necessary mitigation measures. The pipeline passes approximately 40 m from the substation, which is within the proximity threshold of 150 m specified by the EN 50443 standard for considering conductive coupling. The study is focused on analyzing the effects of a single-phase-to-earth fault at the substation and its impact on the pipeline. Under fault conditions, high voltages can appear between the pipeline and surrounding soil, which can lead to coating stress voltages and touch voltages. To evaluate conductive interference, the primary concern is the voltage to earth of the pipeline. For personnel protection, the interference voltage shall not exceed the values stated in EN 50443 and IEEE 80. The latter specifies a stricter limit of 235 V for a fault duration of 0.35 s. For pipeline protection, the interference voltage shall not exceed 2000 V, both for the pipeline system relative to earth and across insulating joints. Coating stress voltages were calculated along the pipeline, with results showing that the voltage in the vicinity of the substation is just below the 2000 V limit as defined by EN 50443. The calculated voltages across the insulating joints are below the 2000 V threshold, as specified by EN 50443. Touch voltages, which can pose a significant safety risk to personnel, were calculated along the pipeline. In the vicinity of the substation, touch voltage values exceed the IEEE 80 limit of 235 V. The study identified a zone where touch voltages exceed this threshold, with a maximum of 2006 V. This zone corresponds to the locations of above-ground appurtenances where the risk of electric shock is highest. To address the risk posed by touch voltages, the study recommends insulation of the operation location with sufficient insulating material. A surface layer of at least 80 mm of insulating material with a specific electrical resistivity of 10,000 Ωm is required to mitigate the risks effectively. This insulation shall ensure that the appurtenances can only be touched by standing on the insulating layer, thus reducing the risk of electric shock. After applying the recommended surface layer, touch voltages were recalculated, and the results showed that they fall below the 235 V threshold, ensuring personnel safety. The results underline the need for regular monitoring and implementation of safety measures to protect both personnel and pipeline infrastructure from the hazardous effects of fault-induced conductive interference.

Keywords: conductive coupling, interference, substation, pipeline, earth fault, touch voltage