| With the advancement of urbanization,the increasing strictness of laws and regulations,and the enhancement of residents’ awareness of environmental protection,the noise problem of substations has become one of the focal issues of substation complaints.Through on-site measurement and analysis of the acoustic environment of the substation indicate that its noise characteristics are mainly reflected in the power frequency and low frequency,and the spectral characteristics show that the noise peaks are concentrated in 50Hz,100Hz,200Hz and 400Hz.However,due to the limitation of the law of quality,it is difficult for traditional noise reduction materials or structures to effectively control low-frequency noise and cannot meet the noise reduction requirements of substations.Therefore,it is necessary to develop a new type of noise reduction material with excellent acoustic performance for the spectral characteristics of substations.The emergence of subwavelength phononic crystals and acoustic metamaterials has opened up new ideas and directions for low-frequency noise control in substations,and has made it possible to solve the stubborn problems that have plagued the power system for many years.Aiming at the current difficulties in low-frequency noise control of substations,this paper carries out research on the establishment of sound source models of transformer equipment based on finite element method and the mechanism and application of phononic crystals and acoustic metamaterials on the regulation and application of low-frequency noise in substations from the aspects of noise prediction and control.In terms of noise prediction,this article compares and analyzes three different measurement methods of substation noise including sound pressure measurement,sound intensity measurement and vibration measurement,and summarizes their respective advantages and disadvantages as well as applicable conditions.The near-field distribution method and attenuation distribution method of substation noise measurement are used to measure and analyze the substation noise.Based on the measured data and the finite element-boundary element theory,the equivalent sound source model of the main equipment of the substation is established,and the noise prediction research of the transformer and reactor is carried out based on the built sound source model.The study found that the sound source model established based on the theory of finite element-boundary element coupling can make the interference effect of sound waves be well reflected.By comparing with the measured data,the average error between the simulated value and the measured noise value is basically controlled within 3dB,which can accurately predict the noise propagation and attenuation of transformer equipment.In terms of noise control,this paper proposes to use phononic crystals and acoustic metamaterials as materials for low-frequency noise control in substations,and introduces a cavity structure to increase the sound transmission loss(STL)in the passband of the phononic crystal plate.The results show that the average STL of the phononic crystal cavity plate is increased by more than 30dB compared with the ordinary phononic crystal plate,and its peak value can be as high as 100dB.In order to clarify the noise reduction mechanism of phononic crystals and acoustic metamaterials,this paper analyzes the phononic crystals and phononic crystals from various perspectives such as dynamic vibration reduction mechanism,dynamic mass density,modal participation factor,mode displacement analysis,and equivalent mass-spring model.The noise reduction mechanism of acoustic metamaterials is analyzed and researched,the similarities and differences,advantages and disadvantages of the mechanism analysis from different angles are summarized,and the mechanism research and analysis paradigm is proposed based on the plate and membrane phononic crystals.Based on the analysis and research on the noise reduction mechanism of phononic crystals,a hybrid acousto-elastic metamaterial is proposed,which combines the modal and mode displacement to study its band gap,STL and vibration transmission loss(VTL)characteristics,based on The equivalent mass-spring model analyzes the mechanism of hybrid acousto-elastic metamaterials,and studies and analyzes the influencing factors of STL and VTL respectively.The results show that the xy mode representing the in-plane wave(S wave)after the energy band decoupling corresponds to the VTL,and the z-mode out-of-plane wave(P wave)corresponds to the STL.It is confirmed that although the periodicity of metamaterials is only reflected in the xy direction,the spatial freedom of band calculation is three-dimensional.Through the modal analysis of the decoupled energy bands,it that the starting point of the xy mode band gap is the translational tensile mode of the scatterer-cladding layer in the x and y directions,and the end point is the translational tensile mode of the matrix-cladding layer in the x and y directions.The starting point of the z-mode band gap is the translational shear mode of the scatterer-cladding layer in the z-direction,and the end point is the translational shear mode of the matrix-scatterer in the z-direction.The average error between the equivalent mass-spring model calculation frequency and the transmission loss peak frequency is less than 3 Hz.Among the influencing factors,the opening angle of the sector ring silicone rubber has the greatest impact on VTL and STL.In order to break through the bottleneck of acoustic metamaterials in the field of low-frequency noise control,a pre-radial membrane acoustic metamaterial is proposed,which combines modal and mode displacement to study its band gap and STL characteristics.The mechanism of membrane and plate is analyzed based on dynamic mass density and equivalent mass spring model,and the influencing factors of STL are analyzed.The results show that the pre-radial membrane acoustic metamaterial has low-frequency broadband acoustic characteristics.There are three frequency bands with sound transmission loss greater than 30dB in the range of 0-100Hz,which are 8-33Hz,48-52Hz and 54-100Hz,respectively.The total bandwidth is 75 Hz,and the acoustic properties are far superior to conventional acoustic metamaterials.Through the comprehensive analysis of the mode shape and sound intensity streamline,it is found that the noise reduction mechanism of the novel metamaterial is the(0,0),(2,0)and(0,2)modes of the film within 0-100Hz.And the z-direction scatterer-cladding layer resonance of the board and the bridging coupling between the two first-order resonance frequencies.Among the structural factors,film thickness and plate thickness have the greatest impact on STL.The thinner the film thickness and the thicker the plate thickness,the better the low-frequency and broadband acoustic properties of the metamaterial.Finally,the engineering application of phononic crystals is explored and researched,and a universal process for engineering applications of phononic crystals is proposed according to the characteristics of phononic crystals.According to the noise spectrum characteristics of substations and relevant regulations and standards,a lightweight design method for local resonance phononic crystal panels is proposed.Based on this method,a lightweight supercell phononic crystal panel for substation noise spectrum characteristics is designed,and its STL characteristics are numerically calculated.At the same time,its noise reduction mechanism is analyzed and researched through the composite sound intensity streamline diagram of vibration mode displacement and sound pressure level.This paper aims to improve the accuracy of noise prediction of the sound source model of transformer equipment in substations.The low-frequency noise control mechanism of phononic crystals and acoustic metamaterials from multiple angles is studied,and the phononic crystals and acoustic metamaterials suitable for low-frequency noise control is designed based on the noise reduction mechanism,in order to realize the application of phononic crystals and acoustic metamaterials in low-frequency noise fields such as substations.The research conclusions can provide theoretical basis and method guidance for the prediction and control of substation noise,low-frequency vibration and noise control of phononic crystals and acoustic metamaterials.This provides technical support for reducing the harm to humans caused by noise from newly built or in operation substations,and increasing the economic and environmental benefits of power grid construction and operation,which is conducive to the sustainable development of green and environmentally friendly power grids. |
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