tailieunhanh - CIRED 2003 - Round Table on Magnetic Field Mitigation Techniques

In this contribution several topics concerning magnetic fields and overhead medium voltage power lines are reviewed: simple formulation to assess the magnetic field (MF) level; characterization of magnetic fields generated by typical three-phase and one-phase primary distribution lines, with balanced and unbalanced current; and main mitigation techniques, analysed in relation with typical reduction level obtained. Additional data concerning cost and performance of different solutions are also provided | For some planned new distribution double-system 110 kV high-voltage overhead lines and power cable lines the possibilities to reduce EMF emissions in the environment were analyzed to be taken into account as an input guideline for the design phase. Within the existing technologies and set starting-points the reduction measures such as optimal phase configuration, reduction of the distance between phases, selection of advantageous geometrical disposition of the conductors, increase of the distance to the conductors (vertical or horizontal) were defined and checked regarding its feasibility. In our contribution case analysis for the two planned high-voltage overhead lines from Slovenian practice are shown (namely 2 x 110 kV Polje – Vič and 2 x 110 kV Grosuplje – Trebnje), taking into account the foreseen two three-phase system underground cable on a segment of densely populated area. Comparisons of the field diagrams show the efficiency of the mentioned field reduction measures. The field diagrams were aimed to be used in the design phase of the transmission line route for the predictive determination of the clearances (ground clearances, distances from the conductors to objects) that assure the legally imposed permissive emission values. These estimated clearances are smaller when the reduction measures such as optimal phase configuration are applied, which consequently results in easier and less expensive design solutions and environmental siting of the line.