Levels of electromagnetic fields in the vicinity of transmission power lines and facilities and mitigation techniques

Protection of the general public from the exposure to electromagnetic fields is a very important area, which has been the subject of intensive research during the last few decades. As a result of the aforementioned research, international recommendations and standards were adopted, and in a large number of countries national regulations were adopted as well, which, among other things, determine the prescribed limits of exposure of the general public to electromagnetic fields. This topic has become particularly important in the Republic of Serbia during the last 15 years, bearing in mind the fact that in 2009 national regulations in the field of general public protection from non-ionizing radiation in the environment were adopted. The regulations, among other things, prescribe the exposure levels of the general public in increased sensitivity areas, as well as the methods and testing frequentness. Since transmission lines and facilities are the subject of consideration, a presentation and an analysis of the most important provisions of national regulations related to power frequency (50 Hz) electromagnetic field are given. In practice, testings are carried out by measurements, and in certain cases also by calculations. By measuring, the results of the electric and magnetic fields at a given moment are obtained, which depend on the conditions on the field at the time of measurements. These conditions include the current geometry of the field source, its load current, voltages, as well as the existence of objects near the measurement points that can lead to electric field perturbation. When evaluating compliance with the prescribed exposure limits, it is necessary to take into account the operating conditions of the source, which are the most unfavorable from the aspect of the field levels that occur in its surroundings. Therefore, in order to estimate the highest possible levels of electric and magnetic fields, in certain cases it is necessary to perform field calculations, whereby it is necessary to model the most unfavorable case in terms of human exposure. Due to their length and distribution, as well as their proximity to increased sensitivity areas, overhead lines are very important sources of low-frequency electromagnetic fields in the environment. In the case of existing lines and transformer stations, the first and, if necessary, periodic testings are carried out once every four years. In the case of the construction of new overhead transmission lines and transformer stations or the reconstruction of the existing ones, current national regulations require that an expert evaluation study referring to the influence of electromagnetic fields on the environment should be carried out. Expert evaluation study includes measurements of electric and magnetic fields, which takes into account the current state, i.e. the impact of existing electromagnetic field sources if they exist at a given location, as well as the electromagnetic field calculations for the future state, which takes into account the contribution of the source that is being built or reconstructed. If during the first or periodic testing in the increased sensitivity area the values of the electric or magnetic field that exceed the reference level are measured, it is necessary to apply measures to reduce the field value. The aforementioned measures can be applied at the field source or at the protected area, and they differ depending on whether it is necessary to reduce the level of electric, magnetic or both fields. Based on a large number of testings carried out in the previous period, the field levels that occur in the vicinity of transmission overhead power lines and transformer stations are shown and an analysis of the obtained results is given. Based on the experiences from the previous period, it was concluded that in practice the cases in which the measured values of the electric or magnetic field exceed the prescribed limits are rare. Real examples in which the reference levels were exceeded during previous testings were also presented, as well as the methods that were applied to reduce the field values below the prescribed reference levels.