Determinação dos níveis de campo elétrico e da elevação de temperatura no interior de transformadores de potência considerando diferentes combinações do meio isolante por análise fluidodinâmica

Abstract

Power transformers are the equipment with the highest added value for the transmission and distribution of electricity. The capacity of the transformer is related to its thermal performance, so that the operating temperature of the windings becomes important parameters to determine the nominal conditions of the equipment and its load limit. The life span of a transformer is directly connected to its thermal profile and its internal insulation, a fact that makes them important parameters for carrying out transformer projects. With the temperature rise, there are variations in the dielectric properties of the materials used in the construction of the equipment and these variations reflect in the electrical support of the transformer and generate areas with greater susceptibility to suffer partial discharges inside the equipment. Thus, this work aims to evaluate the insulation system of a Itaipu power transformer using the losses in full load in the windings as a heat source. The chosen approach is the realization of three-dimensional geometric modeling and numerical simulation by Computational Dynamic Fluid (CDF) and the Finite Element Method (FEM), to consider the internal physical conditions of the transformer. With the results of the simulations, the values of the oil flow velocities, the temperature profiles in the active part and the electric field distributions inside the equipment are obtained. With the knowlegde of these quantities, the impacts generated in the substitution of mineral oil for vegetable oil as the main source of cooling and insulation in the design of this equipment were evaluated and although globally the vegetable oil presents benefits in reducing temperature and the electric field, it was found that is inefficient in reducing the point of higher temperature in this model of power transformer.