Research Of Mul-physics Coupling In Transformer’s Vibration And Noise Under DC Bias Conditions

With the development of technology and continuous improvement of people’s lifequality, the urban consumption of electricity has increased year by year. In recent years, therapid development of HVDC transmission technology made the electrical transmissionquicker and more convenient. However, the frequency of DC bias which caused by the DCtransmission systems with monopolar ground loop mode and bipolar unbalanced runninghas become higher. The DC bias can cause lots of damage to power transformers which isan important equipment in the grid, such as loss and temperature increased, insulationdamage, as well as noise and vibration intensified which is the most intuitive performance.Meanwhile, as a lot of electricity substations build in the urban areas and transformersinstalled in the residential area, the environment problems has become increasinglyprominent. Therefore, the noise performance is important technical parameters oftransformer as well as mechanical and electrical properties. This thesis focus on thetransformer’s vibration and noise problems under DC bias, carrying out the theoreticalanalysis and experiment study.The vibration of the transformer core mainly caused by two reasons: First, siliconsteel sheet in an alternating magnetic field induced by the magnetostrictive; Second,electromagnetic attraction generated by magnetism leakage existed between joint ofsilicone steel slice and folded sheet. According to the basic theory of electromagnetic field,electromagnetic problem of transformer was simulated in this thesis under DC bias withfield circuit coupled method in the three-dimensional transient field. And electric field,magnetic field, structural stress field and acoustic field were conducted by COMSOLMultiphysics software, calculated the vibration and noise distribution of transformer underDC bias with the three-dimensional transient solver. Free modal analysis of transformercore is conducted based on modal analysis theory, calculated the first ten naturalfrequencies and mode shapes, and decide the resonance frequency. In the experiment, the transformer with DC bias was simulated by dual Epstein framewiring schematic. Vibration and noise measurement instrument were applied to measuretransformer’s noise and vibration. Regularity conclusions were proposed by noise andvibration data acquisition and post-processing analysis. The reasonableness of thesimulated method was verified by the comparison between the experimental results and thesimulated results. Finally, specific control methods of transformer’s noise and vibrationwere obtained.