The Time Domain Dielectric Spectroscopy Diagnosis Technology Research Of Oil-paper Insulation Of Transformer

The statistics show that most of the blackout accidents caused by electrical equipment failure are due to transformer oil-paper insulation damage.Therefore,in order to ensure that power grid can operate safely and reliably,it must be ensured that the operating power transformer oil paper insulation should be in good condition.The subject derives from the sub-project of National Natural Science Foundation of China project 'the diagnostic method of oil-paper insulation aging based on circuit analysis and return voltage response(Grant No.61174117)'.Taking oil-paper insulation system of power equipment as the research object,establishing a hybrid circuit model which fits better to actual relaxation response process according to the measured data of time domain dielectric spectroscopy,analyzing the influence law of oil-paper insulation aging state on the characteristic quantity of the time domain dielectric spectroscopy,this thesis puts forward a comprehensive diagnostic method of oil-paper insulation aging that contains integration of improved AHP and gray correlation method.The main work of this paper is as following:(1)According to the time domain dielectric response theory and oil-paper insulation dielectric relaxation response,this thesis expounds the principles,advantages and disadvantages of existing dielectric response equivalent circuit model,and puts forward a new circuit model which fits better to the actual relaxation response process of oil-paper insulation system-hybrid circuit model,deduces the mathematical mode of each circuit model parameters identification,and uses the coincidence degree method and improved interval particle swarm algorithm to accurately calculate each parameter value.Finally,the correctness,reliability and superiority of the hybrid electric circuit model are proved by the examples.(2)Starting from the return voltage method,taking the measured characteristic quantity of the return voltage method and hybrid circuit model characteristics as the research object,it verifies the influence law of oil-paper insulation aging state on each characteristic quantity through theoretical analysis and cases,and it obtains the criterion for each characteristic quantity to diagnose the aging degree of power transformer oil-paper insulation system.Among them,the main features measured are:the initial slope of the peak,the peak voltage and the main time constant,and the characteristic of the hybrid circuit model is the insulation resistance,the geometric capacitance,the polarization branch number and the average relaxation time constant.(3)Starting from the polarization and depolarization current method,firstly,it analyzes the characteristics widely recognized now-depolarization electric quantity,finding that the characteristic quantity is not universal to transformers of different aging degree.Therefore,this paper puts forward a method of averaging depolarization electric quantity to make up for the deficiency of the depolarization electric quantity.Secondly,because the insulation status information is difficult to be reflected by depolarization current curve,this paper proposes a new spectral line-depolarization energy spectrum and extract the peak energy and peak time constants of the spectrum.Finally,it is verified through theory and cases that these two new features can effectively evaluate the insulation aging state.(4)This thesis integrates the time domain dielectric spectrum characteristics,introduces and improves the analytic hierarchy process,construct the evaluation analytic hierarchy system of oil-paper insulation aging,and distributes the contribution degree of each feature quantity on the result of oil-paper insulation aging diagnosis-the weight.Finally,a comprehensive evaluation method of oil-paper insulation aging state that improves the gray correlation method is proposed,filling the blank of a diagnostic method of oil-paper insulation aging using each time domain dielectric spectrum characteristics comprehensively,solving the problem that it is difficult to directly determine the power transformer oil-paper insulation aging status when several characteristic values compete.