Study On The Vibration Of Transformer Core Based On The Magnetostrictive Intrinsic Model Of Grain-Oriented Electrical Steel Sheet

Vibration of high voltage, large capacity power transformer generated at run time will not only affect the normal operation and service life of equipment, reduce equipment reliability, but also noise generated by vibration will have a negative impact on people’s work and life.Transformer noise comes from the vibration of ontology and cooling device, in which core’s vibration caused by magnetostriction is the main reason. Studies on the vibration and noise of transformer are mostly based on the magnetostrictive phenomenon. Generally, studies are divided into two steps. First step of these studies focus on establish mathematical model of magnetostriction, so that magnetostrictive strain can be obtained when magnetic field distribution is known. Second step, the obtained magnetostrictive strain will be equivalent to magnetostrictive force, then apply the force to transformer core model so that vibration and deformation cansed by magnetostriction can be obtained.Existing magnetostriction models mainly focus on the complex relationship between magnetostriction strain and magnetic field, without considering the influence of other factors especially external stress, furthermore these models are derived from experimental data fitting, do not have physical meanings, and meanwhile the limitation of experimental data also limits the scope of these models. While grain-oriented electrical steel sheets used in transformer cores are ferromagnetic materials, and it is known that magnetostriction of ferromagnetic materials comes from domain wall displacement and domain rotation. For the difference of manufacturing process, domain structure of grain-oriented electrical steel sheets is not the same with common ferromagnetic materials, so that the corresponding magnetostriction. This paper introduces the magnetic domain structure of grain-oriented silicon steel sheets, and analyzes the effect of magnetic field and prestress on magnetic domain structural changing, then the inner relationship of microscopic magnetic domain structure change and the macroscopic magnetostriction is derived. Finally on this basis, from the macroscopic thermodynamics, a new intrinsic model for magnetostriction is presented by expanding the Gibbs free energy density for polynomial form. This model can overcome the shortcomings of existing models and is versatile.Based on the magnetostrictive intrinsic model, the research on vibration of transformer core is carried out. The research mainly includes the establishment of mathematical vibration model and simulation model of transformer core. The measured results of power transformer in operation showed that magnetostriction will not only cause vibration parallel to plane but also cause vibration perpendicular to plane. Therefore, in the mathematical vibration model of transformer core, the magnetostriction effect is equal to magnetostrictive force both in plane and in normal directions, and the forces are obtained by the elastic mechanics theory and the principle of conservation of energy respectively. The simulation model is constructed by finite element software ANSYS, so that the coupling between electric field and magnetic field and the coupling between magnetic field and structure field can be easily realized, and can be used to analyze the magnetic field distribution and structural deformation. Analysis result shows that the magnetostrictive intrinsic model and equivalent magnetostrictive force model built in this paper can well predict core vibration. It means that the work of this paper has laid a good foundation for subsequent establishment of three dimensional transformer model and analysis of transformer noise.