Research On Vibration And Noise In Transformer Core Under DC Bias

With 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 bias phenomenon, whichleads 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. Because more and moretransformers are installed in people’s living surrounding, the noise pollution of transformeris also harmful to people’s physical and mental health. The emphatically analyzes andfurther study were developed on the problem of vibration and noise in transformer coreunder DC bias in this thesis.Modal analysis is base of the study of mechanical vibration and noise, by whichmodal shapes and natural frequencies can be obtained to analyze the possibility ofresonance of the structure, and then guide the design of machinery structure, in order toavoid resonance. Modal analysis was done on the core structure of a SCB2-160transformer based on ANSYS in this thesis, and a reasonable calculation method oflaminated core and material properties were confirmed. The influence of structurecomponent on the natural frequencies of core was analyzed, and reasonable suggestions ofavoiding resonance were obtained, with the modal that easy resonance was founded. Whatis more, modal analysis was also done on the cavity structure of transformer in this thesis,and the modal shapes and natural frequencies of both axial and radial were obtained. Theresult analysis shows that this transformer was not easy to resonance in normal operation.In this thesis, the experimental research on the problem of transformer vibration andnoise was done. A reasonable experimental plan was made, that made the laboratorysimulation of DC bias phenomenon come true. By the transformer vibration test of different points under DC bias, the weak link of the transformer structure was found in theprocess of vibration. And by the vibration test of different DC bias, the influence laws ofDC bias phenomenon to transformer vibration as well as its frequency spectrumcharacteristics were analyzed.By the measurement of transformer noise, the general rules of noise affected by DCbias were obtained, and the noise spectrum characteristics under DC bias or not wereanalyzed, then the general conclusions were obtained, which is an important guidingsignificance on the future experimental study of transformer noise under DC bias.