Analysis Of The Influence Of Neutral-Point Low DC Input On The Noise Of Low Noise Transformer

As a special running case of power transformer,DC magnetic bias will cause a series of problems in power transformers,and have some impacts on the power system.Among them,the transformer operating noise change is the most easily recognized and found one.In recent years,low noise transformer has become more and more welcomed by the market,because of its low operating noise,less effects on the surrounding residents' normal living environment,less restricts for the substation selection,especially suitable for the use of urban areas.With the increasing number of low-noise transformers' put into operation,the impact of DC intrusion on low-noise transformers has also been paid more and more attention.In this paper,through a case that in a domestic 220kV substation,two same-type low-noise environmental transformers in operation,noise of the neutral ground transformer suddenly became large,if disconnect the ground,connect another transformer's neutral point to ground,then the new neutral ground transformer's noise increased,analyze this case,starting from the field noise test data and spectrum characteristics,comparing the original factory test data,combing the test data of substation under a variety of operating conditions,we can find out that the two transformer neutral points have small DC current inputs.The paper demonstrates the possibility that the two transformers have a small DC input at neutral point,and analyzes and determines the source of DC.Firstly,on the basis of discussing the various core structure forms,the theoretical basis of the no-load performance and the engineering calculation process,this paper analyzes the possibility of abnormal performance of no-load performance such as transformer noise,and the material,structure and technology of the transformer manufacturing process,and confirms the low noise performance of the transformer.Then,the paper explores the possibility that DC input of neutral point causes noise of the low noise environmental protection power transformer,from physical properties and selection of transformer core material.And explores the noise change of transformers with different performance under the same conditions,and further confirms that transformers with lower design flux density and excellent materials are more sensitive to DC.Finally,the paper lists other harms of DC intrusion on transformer and grid,puts forward the proposal about operation and maintenance of the transformer in two stages in accordance with whether to eliminate the fault.First,during the DC short-term existence period,the transformer continues to hang the maintenance and repair measures;second,to eliminate the DC source or take isolation measures within one year after the transformer monitoring,maintenance and repair measures.According to this case,the paper makes some suggestions about the type choice,material choice,design structure,technology control during manufacture to realize low noise.