Nikola Tesla Institute
Dr. Maja Grbić
Impact of mobile telephony base stations on the general public from the aspect of electromagnetic fields and proposed protection measures / Analysis of Safety of Workers Due to Electromagnetic Induction During Maintenance on Parallel Transmission Lines
Abstract: IMPACT OF MOBILE TELEPHONY BASE STATIONS ON THE GENERAL PUBLIC FROM THE ASPECT OF ELECTROMAGNETIC FIELDS AND PROPOSED PROTECTION MEASURES
The paper presents an analysis of the results of high-frequency electromagnetic field measurements performed in the living environment near base stations located at multiple sites. Measurement locations were selected based on the position of the antenna mast, at points where the highest levels of electromagnetic fields were expected. In addition to the results obtained by broadband measurements, which provide the value of total electromagnetic field within a specific frequency range, the paper also presents the results obtained by frequency-selective measurements. This type of measurement enables a more detailed analysis of individual electromagnetic field sources, i.e., identification of the contribution of individual mobile telephony systems to the overall electromagnetic field level across different frequency bands. The paper shows the maximum electric field values obtained by extrapolation, which could occur under conditions of maximum telecommunication traffic. This approach allows comparison of the measured values with the expected maximum values, thereby contributing to an objective assessment of exposure. Special attention in the paper is given to the analysis of the influence of various factors that can significantly affect the distribution and intensity of the electromagnetic field in the vicinity of base stations. Primarily, the impact of the height difference between the base station and the ground, as well as the distance of the base station from surrounding buildings and areas where people spend time, was considered. These parameters play an important role in determining electric field levels at specific locations, since changes in antenna mounting height, antenna tilt, or distance from the measurement point can significantly alter the distribution of electromagnetic field. Analysis of these factors makes it possible to better understand the propagation of electromagnetic waves and their interaction with the environment, as well as to assess the potential impact on the general public. The main objective of the conducted analysis is to determine the level of exposure of the general public to high-frequency electric fields in buildings where people spend extended periods of time. The results obtained in increased sensitivity areas were used to evaluate compliance with the limit values defined by the Regulation on Limits of Exposure to Electromagnetic Fields. In order to prevent excessive exposure of the general public to high-frequency electromagnetic field emitted by mobile telephony base stations, certain measures are implemented from the design and construction phase through the commissioning phase and continuously during operation. Regular measurements of electromagnetic field levels at defined intervals is a legal obligation of the owner of the electromagnetic field source. The paper provides recommendations and measures that are based on and confirmed by practical examples. Measures to reduce exposure primarily include proper selection of base station locations, correct antenna orientation, determination of safety zones with restricted access, as well as regular and proper maintenance of the installed equipment.
Keywords: electromagnetic field, electric field, exposure of the general public, rulebook, mobile telephony base station
Abstract: Analysis of Safety of Workers Due to Electromagnetic Induction During Maintenance on Parallel Transmission Lines
The paper presents a detailed analysis of safety of workers during maintenance works on the 110 kV overhead line SS “Lastva” – SS “Tivat”. The research focuses on the risk analysis arising from the inductive influence of adjacent 110 kV and 400 kV overhead lines, which run parallel to the observed line along certain sections. In situations where the adjacent lines remain in operation while maintenance is performed on the subject line, induced electromotive forces occur, which can generate dangerous potentials on the phase conductors and surrounding structures. Therefore, it is necessary to analyze the safety of the linemen performing the work. The calculation methodology is based on the complex mathematical modeling of each individual transmission line span using the π-model in the EMTP-RV software tool. Since each span possesses specific geometric parameters, every span between two towers is modeled separately to achieve maximum precision when calculating electrical quantities along the entire route. Special attention is paid to the geometric arrangement of conductors, taking into account line deviation angles and variations in horizontal and vertical phase clearances. Touch and step voltage calculations in the vicinity of the towers were performed in the XGSLab software package, with precise modeling of three different types of applied tower grounding systems consisting of various configurations of horizontal and vertical contours. Soil resistivity is defined according to real values measured on individual sections of the route, thereby ensuring high reliability of the results. The analysis includes calculations in the normal operating regime under maximum line load conditions, as well as in scenarios involving a single-phase line-to-ground fault on the adjacent, active lines. The paper analyzes different grounding methods for the line under maintenance: the case when the line is grounded at both ends, when it is grounded at one end only, and when it is ungrounded at both ends. The obtained results are compared with the permissible touch and step voltage values prescribed by the valid regulations. In the normal operating regime, where a continuous influence exists, the permissible touch and step voltage value is 65 V. In the fault regime (single-phase line-to-ground fault), a fault clearance time of 0.4 s was adopted based on actual relay protection settings, which corresponds to a permissible touch and step voltage value of 187.5 V. Based on the conducted simulation, the most critical points along the route were identified and the conditions under which induced potentials can exceed the prescribed limits were defined. The paper defines mandatory protective measures, the application of which will ensure the safe operation of linemen even under the most unfavorable operating conditions.
Keywords: induced electromotive force, overhead transmission line, single-phase ground fault, touch voltage, step voltage, EMTP-RV, XGSLab
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, 80 expert evaluation studies regarding influence of electromagnetic field sources on the environment, as well as in the preparation of over 1400 testing reports. In 2018 she has been appointed head of the accredited Laboratory for electromagnetic field testing. She has published over 100 papers in national and international journals and conference proceedings, over 70 of which as the main author. She was awarded for the best papers presented at CIRED Serbia (2012, 2022) and CIGRE Serbia conferences (2019, 2021, 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.