DC bias is one of the main reasons for the increase of vibration and noise of large-scale transformer. It is essential to fully understand the vibration and noise characteristics of large-scale transformers under DC bias for the evaluation of the operating state of transformers and the reduction of noise and vibration. This paper mainly studies a 406 MVA EHV large-scale transformer’s vibration and noise characteristics under DC bias. Firstly, based on the field-circuit coupling finite element method, the no-load operation characteristics under different DC bias currents are simulated and analyzed, and the law of excitation current under different DC biases is analyzed. Secondly, a multi-physics coupling model of circuit-magnetic field-solid mechanics-pressure acoustics is established, and considering the influence of magnetostriction, the effective value of vibration displacement and the time-frequency characteristics of noise signal at different measuring points of the transformer under DC bias are obtained. Thirdly, the sound level is measured at different measuring points around the transformer, and the simulated value is compared with the actual measured value to verify the effectiveness of the proposed transformer vibration and noise calculation method. Finally, the Hilbert-Huang transform (HHT) method is used to extract the vibration and noise characteristic quantities of a large transformer under DC bias, and a transformer vibration characteristic based on the energy ratio of the noise signal intrinsic mode function (IMF) is proposed. This method can effectively identify the severity of the DC bias of the transformer, which can provide a certain theoretical basis for the transformer noise reduction design, and it can accurately grasp the operating status of the transformer and provide a theoretical basis for the timely application of measures to suppress the DC bias.

 

DC bias; vibration; noise; multi-physics coupling; transformer; intrinsic mode function（IMF）