Estudo de transitórios de manobra e ferrorressonância em transformadores de fornos elétricos a arco

Abstract

In this work, a computational model was presented to evaluate the nonlinear behavior of transformers used in Electric Arc Furnaces (EAF) and Ladle Furnaces (LF), considering their response to low-frequency transients and slow-front waveforms up to 20 kHz. The main objective was to use this model to identify and quantify the equipment's performance under such operational conditions. Potential improvements were addressed through proposed design modifications aimed at mitigating failures caused by transients. To achieve this, the model parameters were determined using three approaches: analytical calculations based on design data, two-dimensional finite element simulations, and experimental measurements. The modeling incorporated the magnetization curve of the steel in the high saturation range, above 2.0 T. The model was validated through 3D finite element simulations and experimental measurements. Based on this, simulations were carried out in MATLAB/Simulink to evaluate the current and voltage waveforms at the high-voltage terminals. A current was applied to the 2D transformer model developed in finite element software to analyze the radial and axial mechanical stresses on the windings and the saturation of the magnetic flux. The main results indicate that, unlike power transformers, furnace transformers operate under saturation conditions during recurrent transient events. Furthermore, the simulations indicated increased mechanical stresses during these disturbances. The occurrence of ferroresonance under asymmetric switching conditions was also confirmed, with sustained voltages and currents until protection systems were triggered. Therefore, to reduce overvoltage and overcurrent peaks, an increase in the magnetizing inductance was proposed through changes in the transformer design. This can be achieved by replacing the silicon steel core with a material of higher relative permeability, increasing the cross-sectional area of the core, or increasing the number of turns.