Navegando por Autor "FONSECA, Wellington da Silva"

Agora exibindo 1 - 2 de 2

Acesso aberto (Open Access)
Análise de esforços eletromagneto-mecânicos nos enrolamentos de um transformador sob condições de correntes de inrush
(Universidade Federal do Pará, 2016-04-27) FONSECA, Wellington da Silva; SOEIRO, Newton Sure; http://lattes.cnpq.br/7303174583088137; NUNES, Marcus Vinícius Alves; http://lattes.cnpq.br/9533143193581447
This thesis presents an analysis of the effect of electromagnetic origin forces on structural deformation, stress and safety factor in power transformers when they are subjected to inrush currents. The methodology adopted is based on a magneto-mechanical assessment of the transformer using the finite element method (FEM). In this sense, the operating condition of its transformer energization is considered to accurately estimate the magnetic field density in the ferromagnetic structure and to find the values of mechanical stresses or forces in the axial and radial directions on the windings. These components are distributed over energized the high-voltage windings for observing the mechanical loading, which are more susceptible to such current actions. With this goal, it is implemented two- dimensional (2D) and threedimensional (3D) modeling of the discretized transformer structures in consolidated software, which are based on the Finite Elements Method, intended so to obtain more precise results in calculating the variables described. Comparisons between the results from the numerical method with those obtained by analytical methods are made, demonstrating that the FEM provides more precise distribution of stresses along the windings of the transformers when subjected to operating limits conditions as under currents inrush. It is also presented the magnetic flux distribution in the transformer, with high currents circulating in concentric winding of this. It modifies the flux path, causing in a significant increase in the leakage field and consequently on radial and axial forces. The results obtained for the structural behavior of the windings during inrush currents were also seen that the ends of the windings, where the spacers are located, producing high structural weakness due to the axial electromagnetic forces. This also implies a reduction in the safety factor at the ends windings ends and should be considered on the design of power transformers.
Acesso aberto (Open Access)
Modelagem de transformadores de núcleo amorfo usando método de elementos finitos
(Universidade Federal do Pará, 2010-05-21) FONSECA, Wellington da Silva; NUNES, Marcus Vinícius Alves; http://lattes.cnpq.br/9533143193581447
The amorphous materials are becoming broadly used in transformers industry, due to the low losses in its core, since they have a hysteresis loop narrower compared to the traditionals cores of silicon steel. However, its cost of these materials is a great factor against its use in electric power systems. Study the cost / benefit in terms of technical performance and robustness must be considered when we want to design transformers which use this material type. The main contribution of this work is the performance analysis of the transformer in short-circuits, since the equipment failures cause a reduction in revenue, not only for expenses maintenance, but also because the concessionaire does not sell its product, electric energy, and it could be submitted to penalties by regulatory agency in the electricity sector. Under short-circuit conditions, the windings of transformers are submitted to mechanical efforts produced by Lorentz forces, these forces arise as a flux result produced by conductors in parallel that carry current in the same direction. In this case, study the electromagnetic behavior of the transformer is essential for obtaining such forces. To develop this work, the software Finite Element Method Magnetics (FEMM) was used. This tool is based on the finite element method in the calculations of the electromechanical magnitudes and, consequently, the calculation of forces acting in the spires, which allow the calculations of the strain. Finally, this paper deals with the application of the FEMM tool to calculate the mechanical effort and the simulation of the electromagnetic behavior of a distribution transformer.