Research On Magnetostriction Of Silicon-steel Sheet And Vibration And Noise Of Transformer Under DC Bias

This dissertation focuses on the vibration and noise problem of transformer resulted from the DC magnetic bias, which is supported by programs of the National Natural Science Fund and the TBEA Co., Ltd. In the transformer, the vibration by DC bias not only causes the ambient noise, but also may damage transformer, which can threaten the safety of power grid. Therefore, there is important theoretic and practical significance to investigate the magnetostriction characteristic of the silicon steel sheet under the DC bias condition. The main works are listed as follows:Based on one laser magnetostriction measurement system, the magnetostriction characteristics of non-oriented and oriented silicon steel sheets are studied in detail. From measurement, a great deal of significant data are obtained such as B-H curve, the butterfly curve of magnetostriction, the relation between peak-to-peak value and magnetic field, and noise characteristic of magnetostriction. Furthermore, the anisotropy of magnetostriction is also discussed through altering the angle between the specimen and the rolling direction, which supplies accurate magnetostriction data for numerical analysis of vibration and noise in the electrical devices such as motor and transformer.For the deviation of magnetostriction caused by DC bias, during the measurement in this dissertation, firstly the DC bias magnetic field is superposed to the excitation field. Then the effect of DC bias on magnetostriction is researched and discussed. This dissertation analyses the primary reason causing variation of both time-domain signal and frequency components, and also their fundamental law.The assembling process of transformer core may result in some strain to affect the magnetic property of silicon steel sheet and magnetostriction. By applying tensile stress and compression press along the direction of magnetic field, this paper studies the corresponding influence from different directions and magnitudes. The variation law of peak-to-peak magnetostriction and A-weighted magnetostriction velocity level resulted from tensile stress and compression press is summarized. In addition, it proposes a scheme of applying different stresses to reduce the magnetostriction property.In the finite element analysis, the parametric curve is required. Therefore, based on the measured butterfly curves of magnetostriction, the corresponding parametric curves of magnetostriction with respect to magnetic flux density and magnetic field intensity, respectively are obtained by using the interpolating method. And then one orthotropic mathematic model of modeling the magnetostriction is proposed. It is validated by using one 2D example. Moreover, the multi-physic analysis of transformer( coupling the electromagnetic field, structure field, and acoustic field) is carried out by using the COMSOL. Its effectiveness is validated by applying it to one 160 kVA transformer.Finally, in order to check the proposed multi-physic method of calculating vibration and noise, taking two 160 kVA transformers as examples, the experiment of no-load vibration noise under DC bias is carried out. The vibration displacement and speed at the sampling points are measured. The noise of one transformer is measured by applying one noise enclosure to the other one Under different no-load voltages, this dissertation also discusses the variation trend of noise and the influence law of DC bias on core vibration signal and its frequency spectrum. It supplies one method of using the vibration noise to check whether the DC bias occurs. Also this paper gives some suggestions to decrease the vibration noise of transformer iron core.