Nikola Tesla Institute
Dr. Maja Grbić
Analysis of the conductive coupling between 220/66/11 kV substation and nearby pipeline during earth fault / Methodology for the assessment of exposure of workers to electric and magnetic fields during maintenance work in the vicinity of high voltage on double-circuit overhead power lines / Analysis of Electromagnetic Field Levels in the Vicinity of the Mixed Transmission Power Line Tower at the Location of Transition from Overhead to Cable Section
ABSTRACT: Analysis of the conductive coupling between 220/66/11 kV substation and nearby pipeline during earth fault
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
ABSTRACT: Methodology for the assessment of exposure of workers to electric and magnetic fields during maintenance work in the vicinity of high voltage on double-circuit overhead power lines
Current practice for conducting works on maintenance of transmission double-circuit overhead power lines in the Republic of Serbia requires that, although the work is done on one line only, during work both lines have to be de-energized. This current practice in the Serbian transmission system is being changed in order to enable the possibility for de-energizing only the power line on which the work is done (passive system), so that the other power line on the same towers can stay in operation (active system). Before the approval for such a working practice is given, it is necessary to analyze all the potential risks to which the workers can be exposed and, if necessary, provide adequate protection measures. Such a practice includes a certain risk related to exposure of workers to electric and magnetic fields, which requires further analysis. While the work is being done on the passive system workers are exposed to electrоmagnetic field emitted by the active system. Thе paper presents a detailed analysis of the risk concerning the exposure of workers to electromagnetic field on the example of a typical double-circuit overhead power line. The analysis is based on results obtained by measurements and calculations of electric field strength and magnetic flux density. By measurements of electric field strength and magnetic flux density the field values corresponding to the time period of measurements are obtained. Since the power line voltages do not change significantly, results of electric field strength obtained by measurements can be directly used for the assessment of the workers’ exposure. On the other hand, since the power line load currents are variable, the results of magnetic flux density obtained by measurements have to be analyzed taking into account the active system load currents in the period of measurements, in order to come to the more general conclusion which has to take into consideration the most unfavorable working regime, leading to the highest exposure levels. For that reason, the field calculations based on power line modeling are conducted. When analyzing the impact of electric and magnetic fields on workers it is assumed that the worker stays inside the working area defined by the procedure for conducting work on double-circuit power lines. The working area is defined as the space around passive system conductors up to the power line vertical axis. The work can be done from the tower directly or from the elevated platform, while the maximum distance between the tower and the working point is 30 m. Measurements of electric field strength and magnetic flux density are carried out at the measurement points located inside defined working area. In order to carry out measurements inside the working area the new measurement method was developed. The values of electric field strength and magnetic flux density obtained by measurements and calculations are compared to the action levels prescribed by current national regulations and Directive 2013/35/EU, based on which the conclusion on compliance of the obtained results with the aforementioned regulations is given.
Keywords: Electric field strength, magnetic flux density, Directive 2013/35/EU, exposure of workers, double-circuit overhead power line
ABSTRACT: Analysis of Electromagnetic Field Levels in the Vicinity of the Mixed Transmission Power Line Tower at the Location of Transition from Overhead to Cable Section
The paper analyzes the levels of electromagnetic field in the vicinity of a 110 kV mixed transmission line tower, at the transition point between the overhead and underground sections. The aim of the research is to quantify the electromagnetic field levels near this tower and to compare them with the field levels on the overhead and underground cable sections of the line. The research encompasses two complementary approaches – field measurements and numerical modeling. The measurements of electromagnetic field were conducted under real conditions in the vicinity of the aforementioned tower, using appropriate measuring equipment. In addition to measurements, electromagnetic field calculations are performed using specialized software. The model includes all relevant parameters of the transmission line, including conductor geometry and heights above the ground and electrical characteristics of the line. Simulations will provide a detailed insight into the spatial distribution of the electromagnetic field and enable comparisons with experimentally obtained results. The obtained results will provide an understanding of the differences in electromagnetic field levels around the tower compared to the levels in the overhead and underground cable sections of the transmission line. These results will be analyzed in the context of current regulations regarding the protection of the general public from non-ionizing radiation. Besides analyzing electromagnetic field levels, the paper also proposes measures to reduce the field levels around such towers and emphasizes the importance of proper planning and design of transmission lines to minimize the negative impacts of the electromagnetic field on the environment. The conclusions of the paper provide specific information on the characteristics of the electromagnetic field in the particular conditions of transition from an overhead to an underground cable transmission line. They contribute to further research and the development of methods for reducing electromagnetic radiation near power transmission lines.
Keywords: electromagnetic field, non-ionizing radiation, electric field strength, magnetic flux density, mixed transmission line, power transmission line
Biography of the presenter
Dr. Maja Grbić was born in Belgrade in 1985. She received a BSc, MSc and a PhD degree in 2010, 2012 and 2021, respectively, from School of Electrical Engineering, University of Belgrade. Since 2010 she has been employed at the Nikola Tesla Institute of Electrical Engineering, at the Power Facilities Department. Her primary field of interest has been research in the area of electromagnetic fields. She has participated in over 50 major projects and studies, 65 expert evaluation studies regarding influence of electromagnetic field sources on the environment, as well as in the preparation of over 1200 testing reports. In 2018 she has been appointed head of the accredited Laboratory for electromagnetic field testing. She has published 88 papers in national and international journals and conference proceedings, 62 of which as the main author. She was awarded for the best papers presented at CIRED Serbia (2012 and 2022) and CIGRE Serbia conferences (2019, 2021 and 2023). She was awarded by the Belgrade Chamber of Commerce for the best master’s dissertation and by the Serbian Chamber of Commerce for the best doctoral dissertation. She is a member of CIGRE and IEEE as well as Serbian national CIGRE and CIRED Committees.
