Modelagem computacional de blindagens para campos magnéticos de baixa frequência considerando fator de redução e impacto térmico

Abstract

The growing demand for electrical energy means that the population is increasingly subjected to low frequency electromagnetic fields. This reality contributes to the definition of more restrictive laws and norms on the population's exposure limits to these fields. The use of shields is necessary for the mitigation of the low frequency magnetic field, mainly in the vicinity of the main sources of field, such as: overhead lines, underground cables and substations. The present work aimed to develop a computational study on the low frequency magnetic field mitigation techniques. Initially, a bibliographic review was made regarding the main shielding methods and the applicability of using each technique in the main field sources. Among the mitigation techniques studied, the following stand out: conductor rearrangement, compensation loops and shielding with metallic materials (conductive or ferromagnetic). From the theoretical review, the use of COMSOL Multiphysics® software was defined for the design of different types of shielding systems. The evaluation of the shielding performance was made based on the attenuation of the magnetic field and the thermal impact caused. In most of the works found in the literature, the design of the shielding is done by modeling the problem in two dimensions (2D), not representing the terminations of the shielding and, consequently, the variation in performance along the length. This work presents simulations in two and three dimensions, in order to evaluate the performance of the mitigation techniques and advantages of the improvement of the computational model for three dimensions (3D). The analysis of the results showed the importance of 3D modeling in the calculation of the shielding effectiveness along the length of metallic shields. In addition to representing the effects of the plate terminations, 3D modeling allows to simulate field sources that have variations in the positions of the conductors along the length. At the end of the present work, a junction zone of a typical 138 kV line arrangement was modeled. For the case study, it is proposed to use a flat aluminum plate that reduces the magnetic field, with the 3D simulation demonstrating the shielding performance throughout the region of interest and the field attenuation up to the established limit.