Research On Vibration And Noise In Transformer Core With DC Magnetic Bias

As the development of social economy and the improvement of people’s livingstandard, the demand for electricity of daily life is getting huger. Because the electricpower distribution of our country is not uniform, the development of HVDC with largecapacity and long transfer distance is becoming inevitable. But when the transformer run inthe double pole unbalanced operation mode or monopole earth loop operation mode, thedirect current will flow over the winding, and then causes DC magnetic bias phenomenon,which leads to half wave saturation of core flux, as well as increases the excitation current,harmonic, reactive loss, temperature, core vibration and noise of transformer. As a result,the safe operation of transformer and power grid is damaged. The further study wasdeveloped on the problem of vibration and noise of transformer core with DC magneticbias in this thesis.Modal analysis of calculation and modal analysis of experiment were done by thefinite element analysis software of ANSYS and Workbench and the four-channel vibrationtest and modal analyzer of BVM-300-4M in this thesis. Through the modal analysis of asmall core model and a160kVA transformer, the ranges of elasticity modulus wereconfirmed which are Suitable for them. And the influence of the elastic modulus, Poisson’sratio and density on the natural frequencies and mode shapes were analyzed and the lawwas summed up. Then on the basis of the results of modal of the small core model and160kVA transformer, modal analysis of the160kVA transformer under bottom constraintcondition and a product-level transformer under free constraint condition was done, andthe methods which can guide the modal analysis of large-scale transformer had beenacquired and were provided to change the natural frequencies of transformer in the designstage for enterprises.According to the actual conditions of the laboratory, a reasonable experimental planwas made, and the experimental phenomena of DC magnetic bias of transformer wasachieved. Through the transformer vibration test of different points with DC magnetic bias,the weak link of the transformer structure was found in the process of vibration. And through the vibration and noise test with different DC magnetic bias, the influence laws ofDC magnetic bias phenomenon to the transformer vibration as well as its noise wereanalyzed, and which have an important guiding significance on the future experimentalstudy of transformer vibration and noise with DC magnetic bias.