The Equivalent Circuit Modeling And Aging Diagnosis Of Transformer Oil-paper Insulation Based On The Polarizations Spectrum Method

This thesis is based on the National Natural Science Fund Project method in the aging diagnosis of oil paper insulation based on the circuit analysis method and the recovery voltage response.(Number:61174117). As a key equipment in the power system, the reliability of the oil paper insulation transformer’s operation affects the security of the whole power grid. The return voltage method is a nondestructive electric method that used for the diagnosis of transformer insulation. It can provide a lot of insulation aging information. The transformer insulation structure, humidity, temperature will have an impact on the results when diagnosis the insulation state of transformer in the use of recovery voltage method. In order to study the relationship among the polarization spectrum and return voltage characteristic parameters and the insulation condition of transformer, a simulation experimental platform is built in the laboratory and the equivalent circuit of extended debye model is designed. Then diagnosis the aging condition of transformer oil paper insulation through the simulation of the experiment. The main work of this thesis is:1.Based on the debye dielectric response model, Put forward an analytic method of an equivalent circuit parameters identification of single polarization branch and the two branch of the polarization, and verify its correctness. Proposed a new method for equivalent circuit parameter identification of transformer oil paper insulation and strictly knocked down the calculation formula of return voltage method. Validated the feasibility of judging the oil paper insulation aging characteristics using the polarization spectrum. The simulation results reflect the research on polarization spectrum analysis of oil paper insulation’s relaxation process can be very good. Then provides a new way for analysis of the influence of transformer insulation aging factors.2. Simulate the transformer insulation condition change by changing the parameters of the equivalent circuit. Analyses the change in polarization circuit time constant in case of equivalent circuit parameters of transformer insulation aging state of the system and research the pre insulated electric parameters. Changes in the time constant of the mainly reflects the aging condition of solid insulation, small time constant branch reflect the aging condition of transformer oil insulation. In one transformer, the return voltage peak is small, the initial slope smaller. That reflect the insulation performance is better. Introduced two pre insulated electric parameters of polarization index and absorption ratio to the judgment. And get another method of transformer insulation condition.3.Build an experiment platform in the laboratory. Through the analysis of the polarization/depolarization current curve, the expression method by fitting the depolarization current curve to identify the equivalent parameters and the depolarization current curve is used for fitting the curve is proposed. Through the parameters calculation and Matlab/simulink simulation analysis, verify the correctness of by fitting the depolarization current curve to identify equivalent model parameters. By changing the extended debye model equivalent circuit parameters, study the relationship between the equivalent circuit parameters and the polarization/depolarization current. Verified the feasibility of polarization/ depolarization current curve for the diagnosis of transformer insulation aging. Also provides a new method for insulation aging when discuss the transformer oil paper through the polarization/depolarization current curve.