Research On Diagnosis Of Oil-paper Insulation Condition In Transformer Based On Return Voltage Characteristic Quantities

Return voltage method based on dielectric response theory is still a newnon-intrusive diagnosis method for insulation condition of transformer. Thispaper takes oil-paper insulation condition of transformer as the research object,further researches the characteristics and change law of parameters of returnvoltage, and aims at diagnosing oil-paper insulation condition of transformerscientifically, improving its reliable operation and prolonging its service life. So,the research has not only the important theoretical value, but also a goodextensive practical application prospect.Main contributions of this thesis are listed as following:1．This paper reviews methods for modeling dielectric response equivalentcircuit of insulation systems, and analyses the superiority and inferiority ofthese methods. Based on this analysis, the paper establishes a mathematicalmodel with the data of initial slope of return voltage for solving parameter ofdielectric response equivalent circuit. The model of parameters identification isnot limited by sampled experimental data of return voltage, which can easilyidentify equivalent circuit parameters of dielectric response only through normalreturn voltage measurement.2．To identify equivalent circuit parameters of dielectric response accurately,this paper adopts the Particle Swarm Optimization (PSO) to extract theoptimization problem, and basic PSO algorithm is improved. The chaos search isintroduced into PSO, and bio-disaster theory can be used to evaluate theproblem of premature convergence. The improved hybrid PSO is used to solveequivalent circuit parameters, the obtained results show that the local searchability is improved, and the probability of finding the global optimal value byhybrid PSO is better than that by using modified genetic algorithm.3．The calculation formula of return voltage from the equivalent circuitmodel was deduced. And polarization spectrums of two transformers areobtained according to the formula. By comparing measured and simulatedpolarization spectrum, the results show that the established mathematical modeland obtained circuit parameters are feasible and effective.4．According to identified parameters and calculation formula of returnvoltage, connecting with the practical variation situation of parameters with insulation condition, this paper simulates and analyzes change law ofpolarization spectrum with variation of parameters, which can provide a newidea and characteristic quantity for diagnosis of insulation condition.5．Experimental study is performed on the influences of poling voltage andthe ratio of charging time and discharging time on polarization spectrum. Then,the relationship between relaxation time and dominant time constant isderived. The function relation between moisture in solid insulation anddominant time constant under20℃is established, which can provide evidencefor quantity analysis of insulation condition.6． The correlation between initial slope, dominant time constant andinsulation condition were experimentally studied. On the basis of simulationanalysis and experiments, a synthetic diagnosis method for insulation conditionof transformer with standard polarization spectrum is put forward. This methodcombines dominant time constant and initial slope to determine the synthesizedcondition. A diagnosis example indicates the synthetic method is effective.7．The influences of field test environment on polarization spectrum wereexperimentally studied, and precautions and measures of avoiding interferenceware presented. The generation mechanism of non-standard polarizationspectrum was revealed by dielectric response equivalent circuit, which isclassified by the influence factors. A diagnosis method for insulation conditionof transformer with non-standard polarization spectrum is also proposed. Adiagnosis example testifies the efficiency of the method.