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Abstract(s)
A necessidade de instalar transformadores de potência nas proximidades de populações leva a que haja necessidade de garantir que o nível de ruído emitido pelos mesmos seja o menor possível. A geração de ruído em transformadores e máquinas elétricas é um tema muito complexo e, por isso, as diversas fontes de ruído em transformadores têm sido alvo de inúmeros estudos, sendo a magnetostrição do núcleo tipicamente a principal. Neste trabalho foi feito um levantamento de informação relativo ao magnetismo e materiais magnéticos, bem como relativamente a aspetos construtivos e processos de fabrico de transformadores. Foram reunidos resultados de estudos de vários autores sobre a influência dos processos de corte da chapa magnética e do seu impacto na magnetostrição. Também foram analisados dispositivos para análise do comportamento magnético da chapa e os Tipos de instrumentação existentes que podem ser utilizados para medição de magnetostrição. Como não havia informação relativamente à estrutura metalográfica específica dos tipos de chapa frequentemente utilizados pela EFACEC, foi feita uma análise metalográfica para averiguar o tamanho e a orientação do grão e se era detetável deformação e alteração significativa do grão na zona do corte. Foram identificados o tamanho e a forma do grão, mas não se detetaram deformações e alterações significativas provocadas pelo corte. A caracterização experimental da magnetostrição é muito controversa. Não há normas que definam claramente os processos de medição, instrumentos de medição e procedimentos. Neste trabalho foi utilizado um sistema composto por uma ponte de Epstein e um extensómetro colado numa chapa de teste. Com este sistema foi possível medir a magnetostrição ainda que com muito ruído elétrico, que teve de ser eliminado por um conjunto de filtros digitais. Foram testadas diversas quantidades de chapas e registados valores para várias gamas de indução, concluindo-se que os ensaios com menos chapas permitiam obter resultados mais representativos.
The need to install power transformers near populations has led to an increasing interest in the reduction of their noise level. The generation of noise in transformers and electric machines is a very complex subject and that is why a diversity of noise sources in transformers have been the object of numerous studies, where the magnetostriction of the core is typically the main one. In this work, information was collected regarding magnetism and magnetic materials, as well as regarding construcTIon and manufacturing aspects of transformers. Results of studies by several authors on the influence of the cuƫng processes of the electric steel sheet and its impact on the magnetostriction were analysed. Devices for the analysis of the magnetic behaviour of electric steel sheets and the types of instrumentation that can be used for magnetostriction measurement were also studied. As there was no information regarding the metallographic structure of the specific types of steel sheets used by EFACEC, a metallographic analysis was carried out to ascertain the size and orientation of the grain and detect deformation and grain modification in the cuƫng zone. The size and shape of the grain were identified but no significant deformation caused by the cutting process was detected. The experimental characterization of magnetostriction is very controversial. There are no standards clearly defining measuring instruments and procedures. In this work, a system composed of an Epstein bridge and a strain gauge was used in one of the steel sheet test plates. With this system, it was possible to identify magnetostriction even from noisy measurements, where noise had to be eliminated by a set of digital filters. Several amounts of steel sheets were tested, and values were recorded for various induction ranges, being concluded that the tests with less plates allow to obtain more representative results.
The need to install power transformers near populations has led to an increasing interest in the reduction of their noise level. The generation of noise in transformers and electric machines is a very complex subject and that is why a diversity of noise sources in transformers have been the object of numerous studies, where the magnetostriction of the core is typically the main one. In this work, information was collected regarding magnetism and magnetic materials, as well as regarding construcTIon and manufacturing aspects of transformers. Results of studies by several authors on the influence of the cuƫng processes of the electric steel sheet and its impact on the magnetostriction were analysed. Devices for the analysis of the magnetic behaviour of electric steel sheets and the types of instrumentation that can be used for magnetostriction measurement were also studied. As there was no information regarding the metallographic structure of the specific types of steel sheets used by EFACEC, a metallographic analysis was carried out to ascertain the size and orientation of the grain and detect deformation and grain modification in the cuƫng zone. The size and shape of the grain were identified but no significant deformation caused by the cutting process was detected. The experimental characterization of magnetostriction is very controversial. There are no standards clearly defining measuring instruments and procedures. In this work, a system composed of an Epstein bridge and a strain gauge was used in one of the steel sheet test plates. With this system, it was possible to identify magnetostriction even from noisy measurements, where noise had to be eliminated by a set of digital filters. Several amounts of steel sheets were tested, and values were recorded for various induction ranges, being concluded that the tests with less plates allow to obtain more representative results.
Description
Keywords
Aço elétrico Chapa magnética LabVIEW Magnetostrição Ponte de Epstein Ruído Transformador de potência Vibrações Electrical steel sheet Epstein frame Magnetostriction Power transformers Noise Vibrations