Abstract The lack of data is a hindrance to the experimental determination of magnetic cores characteristics. This work presents a non-invasive and field-applicable methodology for electromagnetic devices characterization. Based on fundamental equations of electromagnetism and routine tests, the methodology was applied to obtain, at low frequency: the core loss separation, the hysteresis loop and its BH curve of a three-phase dry core-type transformer. The required equipment and the procedures to do the characterization are presented and discussed. The results were compared with experimental data obtained from tests that were carried out on the same material using a Single Sheet Tester device. The results show a difference in losses of 4.9% for hysteresis, 1.5% for dynamic, and 3.3% for total losses. In the no-load test comparison there was a difference of 4% for dynamics and 1.8% in total losses. The proposed methodology can be applied to different magnetic core types as well as to single-phase transformers and reactors.

Abstract In this work we propose a new method to separate iron losses by removing low frequency tests and reducing the number of experiments. The article deals with methodologies that use numerical methods to find the mathematical model coefficients of magnetic loss separation in hysteresis loss (Wh), eddy current loss (Wed) and excess loss (Wex). Three methodologies are presented and depend on experimental tests such as (i) varying magnetic induction Bm and constant supply frequency (f) of 50 Hz, (ii) constant magnetic induction around 1 T and varying frequency. The first methodology is based on Newton’s method to solve the numerical system generated with experimental data from two laboratory experiments. These data were reported in past references. Another two methodologies are based on genetic algorithms (GA). One of them depends on experimental data from both experiments and the another depends on experimental data only from experiment (i). Results indicate that genetic algorithms method presents excellent solutions in comparison with other ones. The GA method with two tests allows a better representation of the experimental behavior of the sample with maximum errors varying from 1.10% to 0.20%. In GA method with one test, minimization varied from 6.924 × 10−05 to 3.186 × 10−05.

Abstract The Jiles-Atherton scalar hysteresis model presents five parameters used to represent the material tested and used to calculate the magnetic losses. This article presents a comparative analysis of the performance of two methods of identifying these parameters. In the first method, the equations of Jiles-Atherton were assembled into a single non-linear ordinary differential equation as a function of the variables of interest. An algebraic system of five equations with five unknowns is obtained by evaluating the non-linear ordinary differential equation in five points belonging to the branch of the experimental hysteresis loop. The parameters are obtained by solving this system of equations using the method of Non-Linear Least Squares (NLLS). In the second method, the inverse model of Jiles-Atherton is used to calculate the magnetic field H from the experimental values of magnetic induction B. Using the method of genetic algorithms (MGA), the objective function given by the sum of the relative error of calculated magnetic field and experimental magnetic field along the hysteresis loop is minimized. To validate methods the experimental curves were compared with calculated ones. When applying the methods, it was verified that NLLS besides providing more accurate results, it is faster when compared to MGA. In the MGA the convergence of the calculated magnitudes to the experimental magnitudes improves when one of the chromosomes of the initial population is the solution obtained applying NLLS.

Abstract An accurate modeling of materials is essential to obtain reliable results in fields calculation. The Jiles-Atherton approach is widely used for modeling the magnetic hysteresis and depends on its set of five parameters to properly represent material. In this article is proposed an original methodology for obtaining this set of parameters avoiding the derivatives rough calculation and using the calculation of integrals. From the model equations, a new methodology with two nonlinear algebraic systems of five equations in five unknowns is obtained. The initial magnetization curve, the anhysteretic curve and filtering data are not necessary. The proposed methodology also does not restrict the search space of parameters. The parameters assume values in the interval (0,∞). Calculated data were compared with experimental data to validate the methodology. The simulations showed that the proposed method can obtain an accurate set of parameters from a single experimental hysteresis loop and with low computational effort.

Este estudo se refere a caracterização, medição e análise das perdas no ferro. Apresenta-se uma metodologia de caracterização dos materiais magnéticos em função da variação da indução no material, procurando apontar, na medida do possível, algumas questões que existem nestes ensaios e explorar as perdas no ferro sob regimes de fluxo magnético nas formas senoidal e não-senoidal, em função da variação da freqüência de operação.

The iron losses are evaluated, measured and analyzed. The Si-Fe sheets are magnetically characterized under a sinusoidal induction waveform and at one frequency. In this study, the iron losses are predicted with the magnetic core working in a non-sinusoidal regime and other frequencies and we present a novel magnetic material characterization methodology in function of the flux density variation in the material, trying to denote some problems in the characterization analysis and to explore the iron losses under magnetic flux regimes with sinusoidal and non-sinusoidal waveforms.

Os autores documentam a cardiopatia difusa fibrosante, com todos os sintomas clínicos e dados de autópsia pertinentes à insuficiência cardíaca congestiva, em um dos 21 cães infectados com a cepa Colombiana (cinco morreram na fase aguda e quatro continuam vivos) e cinco, dos 13 infectados com a cepa Berenice-78 (oito morreram na fase aguda), num período de oito anos de observação. Em vista destes resultados, os autores sugerem que o cão possa vir a ser um modelo experimental, adequado para o estudo da história natural da doença de Chagas, preenchendo os requisitos estabelecidos pelo Comitê Assessor de Doença de Chagas do Programa Especial de Pesquisa e Treinamento em Doenças Tropicais da Organização Mundial de Saúde.

The authors found the fibrosing chronic chagasic cardiopathy with congestive heartfailure in one out of the 21 dogs infected with the Colombian strain (five died in acutephase andfour are alive)five out of the 13 animais infected with the Berenice-78 strain eight died in acute phase) were observed until eight years of infection with T. cruzi. In view of these results, the author suggest that the dog could be a suitable experimental model for the study of the natural history of Chagas' disease. The dog conforms with the requisites of the World Health Organization (WHO) Steering Committee of Chagas' disease of the Programmefor Research Training in Tropical Diseases.