Electromagneto-mechanical numerical analysis and experiment of transformer influenced by DC bias considering core magnetostriction

Abnormal vibration may cause the internal failure of transformers. In particular, the nonlinear saturation vibration of the iron core under direct current (DC) magnetic bias will lead to serious structural damage. In this paper, the dynamic process of transformer deformation under magnetic bias is completed by studying the magnetostrictive effect of ferromagnetic materials and analyzing the strain of the iron core. First, the silicon steel magnetostriction model is proposed and the computing processing is analyzed which explains the directivity characteristics of oriented silicon steel. Next, a coupled transformer model of the electromagnetic field and mechanical strain are built based on the piezomagnetic effect. Then, a dry transformer is performed in finite element (FE) application and after that, the displacements of test points are calculated by using measured magnetostriction curves and the FE model. Finally, vibration test is done to analyze the DC bias characteristics. The result of both calculation and measurements reveal that the magnetostriction of silicon material is the key factor of core vibration. It leads to the DC bias of transformer core remarkably and the magnetostriction of core material must be considered for transformer design and its applications.