Oil-Paper Insulation Diagnosis Technique Of Transformer By Using Relaxation Response Character

Power transformer is the core equipment in the power grid.The safe and reliable operation of oil-paper insulation transformer is related to the stability of the whole power grid.A lot of researches show that insulation deterioration is the main reason for the fault of transformer.Therefore,it is of great significance to assess the status of oil-paper insulation accurately and timely for the reliable operation of the whole power grid.This research supported by the National Natural Science Foundation of China(project name:Aging Assessment of Oil-paper Insulation Based on Circuit Diagnosis Method and Recovery Voltage Response,Fund No.61174117)is aimed at the accurately and effectively diagnosing the insulation status of oil-paper.The object of this research is the insulation status of oil-paper insulation transformer.And in accordance with the test result of relaxation response,both the mathematical model of the relaxation response of oil-paper insulation and the equivalent circuit model of relaxation response are established in this research;the relationship between the relaxation response characteristic value and the aging status of oil-paper insulation is deeply analyzed;the method based on fuzzy rough set theory to diagnose the insulation status is put forward.The main work of this research is as follows:(1)Based on the theory of relaxation response and relaxation response character of oil-paper insulation,the process of the relaxation response of the oil-paper insulation is analyzed in this research;the feature and principle of relaxation equivalent circuit are expounded and the circuit model of relaxation equivalent circuit is built.And based on the circuit model of relaxation equivalent circuit,the effect the test parameters of relaxation response and the parameters of equivalent circuit bring to the result of relaxation response is studied respectively.(2)In order to figure out the number of the relaxation branches and decompose the depolarizing current accurately,starting from the function spectral line of the depolarizing current,this thesis decomposes different relaxation processes in the depolarizing current with quadratic time domain differential method,deduces the the number of the relaxation branches in accordance with the peak points of quadratic differential spectral line and put forward the spectrum analysis method of depolarizing current based on quadratic time domain differential.(3)Through the mathematical analysis of relaxation character of relaxation response function,the calculation model of the relaxation time is obtained;and on the basic of the calculation model of the relaxation time,a new method to identify equivalent circuit parameter of oil-paper insulation is introduced in this thesis.Then through simulation of instance,the method is proved to be feasible and accurate.From the viewpoint of relaxation time,the relationship between relaxation time and the aging status of oil-paper insulation is analyzed,which brings in a new idea for the diagnosis of aging status of oil-paper insulation.(4)Two new characteristic values relaxation loss and depolarization relaxation energy are brought in through the deep study of relaxation response process.And how these two characteristic values change with the change of the deterioration of oil-paper insulation of the transformer is researched in accordance with the analysis of the instance.In addiction,the relationship between the relaxation response characteristic values(insulation resistance,geometric capacitance,the peak value of the initial slope of the recovery voltage,the main time constant of polarization spectrum,peak voltage and so on)and the aging status of the insulation system is also studied in the thesis.Then the relaxation response characteristic values are using to diagnose the aging status of the insulation of transformer.(5)In order to solve the problem that each characteristic value deduces different diagnosis results in the process of integrated evaluation,to delve the correlation between each evaluation index and diagnosis result,and to make up for the shortage of the study of the redundant characteristic values,by analyzing the theory and instance of relaxation response characteristic value,this thesis proposes the integrated evaluation index of oil-paper insulation aging,presents an integrated evaluation method which is based on the theory of fuzzy rough sets which provides a new method for the integrated evaluation of the status of oil-paper insulation.