Study On The Vibration And Noise Of High Impedance Transformer Under DC Bias

As the necessary electrical equipment for power grid construction,the safety and reliability of the transformer becomes one of the hot issues in the field of engineering.With the increasing capacity of the power system,the short circuit current becomes larger and larger.In order to reduce the harm caused by the short circuit current to the transformer and other power equipment,the high impedance transformer with the ability of resisting short circuit is widely used at home and abroad.Meanwhile,with the rapid development of amorphous magnetic materials,the amorphous alloy transformer with the advantages of low loss has become the most popular transformer product.However,the phenomenon of abnormal vibration and noise is often occurred in the operation of the transformer.According to the study,DC bias is one of the important reasons for this phenomenon.This is a new research direction for the research of high impedance transformer with amorphous alloy as the core under DC bias.Therefore,this paper focuses on the analysis of the vibration and noise of high impedance transformer under DC bias.The main research work is as follows:(1)Based on a 220 kV three-phase three winding on load voltage regulating oil immersed transformer,three design schemes are presented to improve the short-circuit impedance of the middle and low voltage winding.The design of three kinds of high impedance transformer with different winding structure is realized.The correctness of the proposed scheme is verified by calculating the short-circuit impedance of transformer using the two methods of analytical method and finite element method.The eddy current loss and loss density distribution of the fuel tank and clamp caused by different schemes are calculated.The research of the influence on the loss of structure parts in the manufacturing process of high impedance transformer provides the basis for the design of the high impedance transformer in the future.(2)The factors that affect the vibration and noise of the transformer are analyzed,based on the principle of DC bias and the basic principle of vibration and noise.It is concluded that Magnetostriction is an important reason for the vibration of transformer core.The ability of three kinds of typical three-phase transformer to withstand DC bias is analyzed.Meanwhile,based on the multi physics field coupling software COMSOL,the coupling calculation method of the electromagnetic field,the structural force field and the sound field is proposed to solve the problem of vibration and noise of high impedance transformer under DC bias.The variation of magnetic flux density,no-load excitation current and harmonic before and after DC magnetic biasing is analyzed in detail.The analytical method is used to calculate the magnetic flux density of the core.It is concluded that the error of magnetic flux density calculated by finite element method is less than that calculated by analytical method.On the basis of the analysis,the influence of the bias current on the vibration and noise of the transformer core is analyzed,and the general conclusion is obtained.At the same time,according to the theory of modal analysis,the modal analysis of the transformer core is made to determine the resonant frequency which may lead to the resonance of the core.This chapter makes the foundation for the study the influence of DC bias on the vibration and noise of transformer.(3)The vibration of the body and the core of a three-phase amorphous alloy transformer under no-load condition of high voltage side is measured by using the vibration acceleration sensor,and the regularity of the vibration of the transformer is obtained by analyzing and processing the vibration data.Meanwhile,the effectiveness of the multi physics field coupling method is verified by comparing the experimental results with the simulation results,by which the vibration and noise of high impedance transformer under DC bias is calculated.It lays the foundation for the experimental research of the transformer vibration and noise.