Research On Fractional Model And Its Application Of Oil-paper Composite Insulation Structure

Oil-paper composite insulation is an key part of transformer equipments insulation. It is important for the depth study of the characteristics of a composite structure of oil-paper to establish its exact circuit model. Low frequency fractional model of dielectric has been deduced from universal relaxation law in time domain and frequency domain. Capacitance spectroscopys of oil-paper composite insulation under different temperatures were curve-fitted by total least squares. It showed that fitting results were quite precise at low frequency, especially under 1Hz. Besides, the influence of temperature for fractional exponent of fractance was researched through fitting spectrum of the same oil-paper under different temperature. So improved Maxwell-Wagner model which was based on the proposed low frequency fractional model was applied to describe characteristics of oil-paper composite insulation under 1min polarity reversal voltage. Fractional linear differential equations with constant coefficients has been established. The test data was fitted through combining genetic algorithms and numerical solution of fractional linear differential equations. It has been verified to be feasible by accurate fitting results. On the other hand, broadband fractional model of oil-paper insulation composite structures has been proposed in this paper by combining dielectric theory and fractional calculus from the Cole-Cole model with double relaxation mechanism proposed by existing literature. The correctness of model has been verified by way of fitting the experimental data using broadband fractional model. The model parameters of dry insulating paper and oil- immersed insulating paper were also acquired at the same time via fitting dielectric response data using total least squares. Then capacitance spectroscopys of TIV oil- immersed paperboard was fitted respectively by broadband fractional model,extended Debye model and Maxwell-Wagner model. Fit residuals of broadband fractional model was minimal, which reflected superiority of its. Besides, macro model of oil-paper insulation system of transformer was build. The influence of parameter changes for capacitance spectroscopys of oil-paper insulation system has been simulated in MATLAB. Simulation results were consistent with test results in other literatures. It confirmed the truth of that broadband fractional model could be applied to assess aging characteristics of oil-paper insulation system of transformer.