A thermal analysis of a 5 kVA dry-type transformer under linear and non-linear loads conditions is studied in this paper. The main goal here is to calculate the hottest-spot transformer temperature under free convection through the resolution of the heat conduction equation in three dimensions (3D) using COMSOL Multiphysics®. The proposed technique was validated through experimental data obtained in laboratory. The temperature inside the cores was measured under the influence of free convection. The radiation emission was also measured through a thermal camera. The heat transfer coefficient for both conditions was obtained from empirical correlations. The hottest-spot temperatures were determined from the analysis in the commercial software which was used for the numerical simulations of the transformer heating and cooling under some loading conditions. The temperature residuals, that is, the experimental temperature values subtracted by the numerical temperature values, were below 10%. The numerical analysis found that the hottest-spot temperatures in the core reached 20 °C above the transformer insulation limit. The location of the hottest-spot as well as the obtained temperatures can be used to improve more resistant dry-type transformers.
Optimal filter design considering the system uncertain behavior has been a topic of research for a long time. Due to the lower cost, passive filters are still considered the most common solution for harmonic distortion problems. This paper presents a heuristic methodology for the placement and sizing of passive filters through ranking solutions based on the standard quality index THD (Total Harmonic Distortion). The developed method was implemented and applied to a simplified test system. The results showed that it is possible to mitigate harmonic distortion using a distributed approach during the filter selection. Additionally, since the method is mainly based in a heurist approach, it avoids the complexity associated with of use of advanced mathematical tools and artificial intelligence techniques. The analyses contemplate the condition with background distortion.Index Terms--Passive filters, optimal placement, filter design.I.
This paper aims at investigating electrical and mechanical performance of three-phase salient pole synchronous generator with unbalanced and non-linear loading. The time domain technique is employed to represent the three-phase synchronous generator. By studying the generator operation with nonideal AC load conditions, the machine electrical and mechanical impacts caused by unbalances and harmonics are evaluated and discussed. Besides theoretical studies, experimental results obtained from a 2kVA three-phase prototype were derived so as to validate the computational approach and conclusions. Finally, by using a real size generator of 25MVA, more realistic results are computationally achieved and discussed.I.
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