DC Bias Current Calculation And Vibration And Noise Characteristics Of Transformer

With the gradual completion of the AC-DC hybrid UHV power grid in China,the DC bias of transformer caused by the operation mode of single gigantic circuit in the HVDC transmission project is becoming more and more serious.Because of the influence of DC grounding pole on the surface potential and the characteristics of low resistance of AC system,transformers grounded at neutral point are vulnerable to DC bias.DC bias not only endangers the safety and reliability of transformer operation,but also causes vibration and noise problems,which have a negative impact on the environment of operators and residents.For this reason,this paper focuses on the vibration and noise of transformer under DC bias,studies the calculation method of DC bias current and DC current suppression measures,and analyses the influencing factors and distribution law of DC bias current.Based on the calculation results,the typical DC range of the transformer is proposed.On this basis,the vibration and noise characteristics of the transformer under DC current are studied.Firstly,the generation mechanism of neutral point DC of transformer around UHVDC single gigantic circuit operation is analyzed,and the modeling and simulation calculation are carried out according to the actual load-intensive AC network.The influence and law of DC grounding current,substation location,isolation device,substation grounding resistance and line type on DC of transformer neutral point are analyzed,and the typical range of DC current of transformer neutral point under worst condition is determined,which provides an excitation reference for the following research on vibration and noise characteristics of power transformer under DC bias.Secondly,the source of transformer vibration is analyzed.Based on the coupling of electromagnetic field and structural force field,a simplified vibration simulation model of 1000 k V single-phase four-column UHV oil-immersed autotransformer is established.The model is solved by finite element method,and the amplitude and frequency spectrum of transformer core vibration under normal operation and different DC bias are calculated.The influence of DC current on the vibration characteristics of transformer is analyzed.Finally,based on the method of structural force-field coupling sound field,the noise distribution of transformer is calculated by finite element method.The noise sound voltage level of transformer under normal operation and different DC currents is analyzed,and the influence of DC current on the noise characteristics of transformer is analyzed,which provides a reference for the DC current limit of extra-high voltage transformer.This paper compares and analyses the advantages and disadvantages of the existing DC bias current suppression measures,and studies the possible problems of the existing DC bias current suppression measures under some special conditions,and puts forward a feasible new scheme,which can economically and effectively solve the problem of DC bias of power transformers.