| Transformer is the most critical equipment in the process of power grid safe operation. The serious accidents caused by transformer will not only lead to the damage of transformer itself, but also interrupt the power supply. The oil-paper insulation-induced transformer faults accounted for an important part of transformer accidents. So far, no single ideal diagnostic method existed can directly guide the resolution of practical engineering problems. Therefore, the research for obtaining the new features of oil-paper insulation aging volume, and thus to provide accurate and valuable reference for the assessment of the transformer oil-paper insulation aging state, is no doubt of great significance.The Frequency Domain Spectroscopy (FDS) based on the method of frequency domain media response is an non-destructive testing methods which diagnose the power transformer insulating state. In this paper, the author first measured the polarization current in real transformers, analyzed the aging mechanism of insulating oil and insulating paper. Moreover, the author processed the equivalent circuit simulation of oil-paper insulation system in laboratory by extending the Debye model, and analyze the effect of the changing parameters of extended Debye model on the related parameters of spectrum. Through the accelerated thermal aging tests for oil-paper insulation products in laboratory, the author analyzed the variation rule of FDS parameters under different conditions.The author did a preliminary study on the frequency domain response characteristic of transformer oil-paper insulation system by combining the means of simulation and test, and analyzed the test results under the guidance of dielectric polarization theory and provided technology accumulation for the actual use of frequency domain spectroscopy (FDS) in non-destructive diagnosis of actual transformer oil-paper insulation aging state. Major findings are listed below:①the simulation results of the equivalent circuit model in transformer oil-paper insulation system show that, different branches of the circuit parameters on the FDS there is influence: the changes of insulation resistance and geometric capacitance in oil-paper insulation system would only affect the imaginary part of FDS curve complex permittivity and the real part of complex capacitance respectively; the changes of largest time constant branch circuit parameters mainly affect the low frequency of complex permittivity; the intermediate time constant branch circuit parameters affect a little on the low frequency segment of the real part of complex capacitance curves and the intermediate frequency segment of the imaginary part of complex capacitance curves; the minimum time constant branch circuit parameters mainly affect the affect the intermediate frequency segment of the imaginary part of complex capacitance curves.②The first tanδobtained in the characteristic frequencies of low frequency part follows the exponential function well with the aging time. And we can use the low-frequency variation of FDS to evaluate oil-paper insulation aging information.③the measuring temperature affect the oil paper insulation aging status diagnosed by FDS significantly, the use of frequent temperature shift factor can put FDS curve under any measuring temperature to the same reference degree, which could unleash the impact of measuring temperature on the FDS measurement results. The FDS curve of oil-paper insulation sample expand with the increasing of test samples moisture content significantly, preliminary results show that it can be used to assess the transformer oil-paper insulation moisture.④the thickness-altering of insulating paper layers exert a greater impact on the complex capacitance, thus may reflect the winding deformation or burning state of transformer. Different types of insulation paper will affect the measurement results of FDS, hence the using of FDS to diagnose insulating paper transformer of different types should apply relevant data for evaluation.
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