Study On Nonlinear Frequency Domain Dielectric Response Of Transformer Oil-Paper Insulation

As an important equipment in power grid,the safe and stable operation of power transformer is related to the normal life of people and the operation of society.Oil-paper insulation is an important part of oil-immersed transformer.In the long-term operation process,it will be affected by a variety of aging factors,such as electricity,heat and vibration,and its aging state determines the service life of transformer.Therefore,in recent years,a large number of scholars have conducted research on the aging state evaluation of oil-paper insulation.However,according to the research findings,the frequency domain dielectric spectrum of oil paper insulation is subject to different test excitation,and there is a nonlinear phenomenon,which will lead to the test results are not consistent with the actual electrical performance of oil paper insulation,and affect the evaluation results.In order to study the nonlinear frequency-domain dielectric response of oil-paper insulation and eliminate the influence of nonlinear phenomena on the test,this thesis studied the influence of aging degree and moisture on nonlinear phenomena respectively,so as to provide accurate dielectric properties parameters for the evaluation of oil-paper insulation aging.In order to study the effect of aging of insulated board on the nonlinear dielectric response of oil-paper insulation in the frequency domain,a thermal aging test was carried out at 130℃ for up to 120 days,and a frequency-domain dielectric response test platform was built to test the variable temperature FDS of oil-paper insulation under different excitation under different aging degrees.The equivalent circuit model was established by adding the conductivity loss correction Davidson-Cole model and combining with the transfer function.The modified model parameters calculated by the oil-impregnated board with different aging degrees were different,and the modified model parameters directly affected the impedance parameters of the equivalent circuit model.Therefore,the nonlinear frequency domain dielectric response relationship between the aging degree and the oil-paper insulation was obtained.In order to study the influence of moisture on the nonlinear frequency domain dielectric response of oil-paper insulation,this thesis carried out a moisture absorption test,and carried out a temperature variable FDS test of oil-paper insulation with different moisture content under different excitation.Based on Garton theory,an ion motion oscillation model was proposed,and the influence of ion motion on conductivity was analyzed.The main curve of AC conductivity was calculated by frequency temperature translation and conductivity translation.Considering that water molecules exist in the form of water groups,the mobility of water groups is calculated through the conductivity to achieve the quantitative calculation of the loss factor difference of oil-immersed board caused by nonlinear phenomenon under different water content.According to the insulation test results between transformer windings,it is found that the dielectric response curves in the frequency domain tested under different test excitation do have nonlinearity.Based on IDAX,this thesis analyzes the dielectric response test wiring in the frequency domain between transformer windings and analyzes the dielectric response phenomenon in the nonlinear frequency domain between transformer windings through simulation calculation.Under the premise of correct connection,the existence of nonlinear phenomenon is verified by field frequency-domain dielectric response test of transformer,which proves that nonlinear phenomenon has an impact on the subsequent evaluation of transformer insulation state.