Loss and Noise Analysis of Transformer ComprisingGrooved Grain-Oriented Silicon Steel

For the reduction of transformer noise and efficient use of energy, we developed a domain-refined highly grain-oriented silicon steel with a linearly grooved surface by an electrolytic etching method. The steel showed very low iron loss even after a high-temperature annealing process, such as stress relief annealing, while magnetic flux density at 800 A/m, which is one of the very fundamental evaluation criteria for grain-oriented silicon steel, was lower than that without grooves. In light of our previous study, steels with a low flux density are disadvantageous for lowering transformer noise, but there have been no reports on the detailed noise property of this grooved grain-oriented silicon steel. In this paper, we investigated transformer noise as well as the transformer loss for the first time by fabricating three model transformers, each of which comprised one of the following grain-oriented electrical steels: grooved grain-oriented silicon steel having flux density of 1.90 T at 800 A/m, non-grooved grain-oriented silicon steel having flux density of 1.93 T at 800 A/m, and non-grooved grain-oriented silicon steel having flux density of 1.90 T at 800 A/m. As a result, transformer loss exhibited a tendency similar to the loss of a single sheet, and the grooved grain-oriented silicon steel showed the lowest loss. As for noise, even with the lower flux density, the grooved grain-oriented silicon steel showed a very low noise level equivalent to that of the non-grooved grain-oriented silicon steel with the high flux density, while the non-grooved grain-oriented silicon steel with the low flux density showed the largest noise level. From the results of magnetostriction measurements and dynamic domain observation by a newly developed method, it was found that the grooves had little influence on the generation of magnetic domains, which increased magnetostriction and transformer noise. Thus, we confirmed that low noise and low loss properties of the transformer were both realized by the application of the grooved silicon steel.