Application study of Fe78b13Si9 amorphous alloy in low power transformer cores.

Esta tese apresenta um estudo sobre as aplicações da liga FeygB13Si9 amorfa em núcleos de transformadores, focalizando sobretudo a operação em vazio destes equipamentos, em comparação com transformadores comerciais que empregam em seus núcleos de materiais ferromagnéticos cristalinos. Para efeito de analise, partiu-se de um modelo equivalente do transformador, para discutir as perdas no núcleo, em vazio e em carga, destacando o efeito do material magnético sobre tais perdas e sobre a corrente de excitação do equipamento. Em termos práticos, um pre-protótipo de transformador monofásico de 100 VA, 220 V/ 110 V, 60 Hz, foi projetado e construído, para servir de base para a realização de um protótipo de transformador de 1,0 kVA, 220 V/ 110 V, 60 Hz, utilizando como material magnético para os respectivos núcleos a liga Fe78B13Si9 amorfa. Os núcleos destes transformadores foram submetidos a um tratamento térmico, sob a ação de um campo magnético, numa atmosfera de argônio. A realização e a avaliação deste tratamento magnetotérmico, são apresentadas, incluindo o cálculo das induções magnéticas, empregando o método das diferenças finitas. Os resultados obtidos, com este tratamento, que teve por objetivo relaxar as tensões introduzidas durante o processo de confecção dos núcleos, confirmaram a melhoria nas propriedades magnéticas do material da liga amorfa. Esta relaxação estrutural foi confirmada pela realização de ensaios de Calorimetria Diferencial de Varredura, simulando as condições do tratamento magnetotérmico sobre os núcleos, analisando amostras do material amorfo como recebido do fabricante e apos o tratamento ter sido realizado. Os ensaios comparativos diretos, de curto-circuito e de circuito aberto, mostraram que os transformadores projetados e construídos com núcleos de liga Fe78B13Si9 amorfa são mais eficientes que os transformadores com núcleo de FeSi.The object of this thesis is to evaluate the performance of transformer cores designed and built from the amorphous alloy FeygB^Siq. A simple transformer equivalent circuit is used to carry out these investigations. The main focus is on the effect of the magnetic material on the total loss on the excitation current. A finite difference method is used to help the design of two single-phase transformer prototypes, with the following rated values: 100 VA and 1,0 kVA, 220V/T10V, 60 Hz. The as-cast material structure were examined using X-ray diffractometer. These amorphous cores are annealed in an argon atmosphere, under a DC magnetic field applied along the ribbon length for inducing uniaxial anisotropy. The crystallization behaviour was examined by differential scanning calorimetry (DSC) and no one crystallization was observed. The achieved results are compared with test data obtained on two commercial silicon-steel transformers with the same rated values. It is shown amorphous cores are more efficient than silicon-steel cores

Current transformers with nanocrystalline alloy toroidal core: analytical, computational and experimental studies

In this paper are presented theoretical analysis and experimental results concerning the performance of toroidal cores used in current transformers. For most problems concerning transformers design, analytical methods are useful, but numerical methods provide a better understanding of the transformers electromagnetic behaviour. Numerical field solutions may be used to determine the electrical equivalent circuit parameters of toroidal core current transformers. Since the exciting current of current transformers alters the ratio and phase angle of primary and secondary currents, it is made as small as possible though the use of high permeability and low loss magnetic material in the construction of the core. According to experimental results presented in this work, in comparison with others soft magnetic materials, nanocrystalline alloys appear as the best material to be used in toroidal core for current transformers

Performance of single wire earth return transformers with amorphous alloy core in a rural electric energy distribution system

In this paper are presented some considerations about the performance of single wire earth return amorphous alloy core transformers in comparison with conventional silicon steel sheets cores transformers used in rural electric energy distribution network. It has been recognized that amorphous metal core transformers improve electrical power distribution efficiency by reducing transformer core losses. This reduction is due to some electromagnetic properties of the amorphous alloys such as: high magnetic permeability, high resistivity, and low coercivity. Experimental results obtained with some single-phase, 60 Hz, 5 kVA amorphous core transformers installed in a rural area electric distribution system in Northern Brazil have been confirming their superior performance in comparison to identical nominal rated transformers built with conventional silicon steel cores, particularly with regard to the excitation power and to the no-load losses

Histopatology of the reproductive tract of Nellore pubertal heifers with genital ureaplasmosis

<div><p>ABSTRACT In order to study and characterize the lesions in the reproductive tract of Nellore heifers naturally infected with Ureaplasma diversum and presenting granular vulvovaginitis syndrome (GVS), fragments of uterine tube, uterus, cervix, vagina and vulva of 20 animals were evaluated. The macroscopic lesions of the vulvovaginal mucosa were classified in scores of “1” mild, until “4”, severe inflammation and pustular or necrotic lesions. The histopathological evaluation was performed using scores of “1” to “4”, according to the inflammatory alterations. The fragments with severe microscopic lesions (3 and 4) were from the uterine tubes and uterus, which showed leukocytes infiltration and destruction and/or necrosis of epithelium. Alterations in the lower reproductive tract fragments were mild, but characteristics of acute inflammatory processes. The histopathological findings of the reproductive tract of females naturally infected with Ureaplasma diversum are consistent with injuries that compromise the environment from the local where spermatozoa acquires ability to fertilize an oocyte until those where the oocyte is fertilized. Therefore, animals with GVS should be identified early in the herd, because, besides the reduction in the fertility rates caused by tissue damages, they can contribute to disseminate the microorganism. Key words: bovine, tissue evaluation, reproduction, Ureaplasma diversum.</p></div

Nanocrystalline material in toroidal cores for current transformer: analytical study and computational simulations

Based on electrical and magnetic properties, such as saturation magnetization, initial permeability, and coercivity, in this work are presented some considerations about the possibilities of applications of nanocrystalline alloys in toroidal cores for current transformers. It is discussed how the magnetic characteristics of the core material affect the performance of the current transformer. From the magnetic characterization and the computational simulations, using the finite element method (FEM), it has been verified that, at the typical CT operation value of flux density, the nanocrystalline alloys properties reinforce the hypothesis that the use of these materials in measurement CT cores can reduce the ratio and phase errors and can also improve its accuracy class