| In power system,transformer plays an important role in power conversion.To ensure the reliable and stable operation of transformer is to ensure the stability of power supply and distribution.However,due to the complex operation environment of power system,transformer windings are likely to have winding displacement fault under the impact of shortcircuit current,which seriously threatens the power supply reliability of power system.Frequency response method is widely used in winding fault detection because of its simple test and positive repeatability.However,due to the high cost of actual transformer,it is unable to carry out winding fault simulation,explore the frequency response variation law under fault,and establish a reliable and accurate winding frequency response simulation model,which is of great significance for winding fault identification.In this paper,the mathematical model of the state space equation of the winding is established by considering the frequency variation characteristics of the electrical parameters of the winding,which can effectively improve the simulation accuracy of the frequency response.At the same time,the mathematical model of the oscillation wave of the winding is established,and the correctness of the model is verified by comparing the simulation and the measured oscillation wave curves.1)In this paper,the frequency variation characteristics of electrical parameters of windings are analyzed.In the finite element eddy current field,a two-dimensional model of winding is established to analyze the current density distribution affected by skin effect and proximity effect at high frequency,and the winding resistance at different frequencies is calculated.Based on the finite element eddy current field,the demagnetization characteristics of silicon steel sheet at high frequency are analyzed,and the homogenization model of laminated core is established.The frequency variation characteristics of core permeability are calculated by using classical formula Based on the correlation between frequency permeability inductance,the frequency variation characteristics of winding inductance parameters are calculated in the finite element static magnetic field;the capacitance parameters of winding are calculated by combining the finite element method with the formula method,and the capacitance parameters are basically unchanged when the frequency is greater than 1k Hz.2)Then,based on the lumped parameter circuit model,the state space equation model of the winding considering the frequency variation characteristics is established by using the frequency variation characteristics of the electrical parameters of the winding.The frequency response curve of the winding is obtained by simulation,and the correctness and accuracy of the proposed model are verified by experiments and comparative analysis with the traditional model.Based on the state space equation of the winding,the oscillation wave time space equation is established.Then,the correctness of the model is verified by comparing the similarity between the simulation waveform and the measured waveform in the time domain and frequency domain.3)Finally,based on the finite element simulation,the change law of electrical parameters of the winding under axial displacement is obtained;combined with the state space equation model of the winding considering the frequency variation characteristics,the frequency response curve under axial displacement is obtained by simulation,and the fault identification characteristics of the winding under axial displacement are obtained by analyzing the change law of the characteristic resonance points of the frequency response curve;at the same time,the vibration wave time domain simulation model is used to obtain the fault identification characteristics The variation law of oscillation wave under axial displacement is obtained,and the variation law of characteristic wave crest and wave trough is summarized to provide reference for winding fault identification. |
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