Study On Diagnosis Of Oil-paper Insulation Aging Based On Relaxation Response Equivalent Circuit Method

This thesis is a sub topic of the National Natural Science Foundation of China(No.61174117)《Aging Diagnosis Method of Oil-Paper Insulation Condition Based on Recovery Voltage Response and Circuit Analytical》.Taking oil-paper insulation system of power transform as the main research object,It deeply analyses the influences of parameter variation of relaxation response equivalent circuit on recovery voltage polarization spectrum,characteristic quantity,micro water content and furfural content based on extended Debye equivalent circuit model,presents a new method of using the equivalent circuit parameters to diagnose insulation aging status of transformer for reducing the failure rate of transformer’s insulation and improving the reliability of power system security and stability.Therefore,diagnosing oil-paper insulation state of transformer by using relaxation response equivalent circuit parameters has the huge economic efficiency and engineering application value.Main research work of this thesis are listed as following:(1)This thesis systematically describes the modeling process of relaxation response equivalent circuit of oil-paper insulation transformer,analyses the equivalent circuit model by recovery voltage method,deduces the recovery voltage of the equivalent circuit model and the calculation formula of all parameters;It presents a new method of adopting chaos particle swarm optimization(CPSO)to identify the equivalent circuit parameters based on the particle swarm optimization and the chaos theory.it lays a foundation for subsequent judgment of oil-paper insulation aging condition based on the equivalent circuit parameters,and the validity of the method is approved by a practical example.(2)This thesis deeply analyses the expression of recovery voltage and deduces the internal relations between the expression of recovery voltage and the number of equivalent circuit’s polarization branch,first presents a method of decomposing return voltage curve by using differential decomposition method of return voltage curve,and determines the number of equivalent circuit’s polarization branch by using the number of recovery voltage’s sub curve,provides a reliable method to establish an equivalent circuit which can accurately reflect aging condition of oil-paper insulation transformer,thereby lays an important foundation for accurately diagnosing insulation aging of transformer.(3)Based on the relaxation response equivalent circuit parameters of oil-paper insulation transformer,this thesis detailedly analyses the influences of parameter variation in equivalent circuit on recovery voltage polarization spectrum,characteristic quantity of recovery voltage and aging of insulating medium,reveals that the small time constant branches of the equivalent circuit reflect the aging state of insulation oil,the large time constant branches of the equivalent circuit reflect the aging state of insulation paper and the middle time constant branches of the equivalent circuit reflect the interfacial polarization state of insulating medium.it provides important criterion to accurately diagnose aging status of transformer insulating medium in the future by using the equivalent circuit parameters.(4)According to aging information of multiple oil-paper insulation transformers and parameters of relaxation response equivalent circuit,this thesis deeply analyses the influences of variation of moisture content in insulation paper and furfural content in oil on the equivalent circuit parameters,and presents the function relation between moisture content in insulation paper,furfural content in oil and the time constant of equivalent circuit’s large time constant branch,provides a new method for the determination of moisture content in insulation paper and furfural content in oil,and their reliability are verified by checking validity.At the same time,this thesis presents time constant diagnosis method of the relaxation response equivalent circuit and aging evaluation method of equivalent relaxation polarization strength to analyze the aging condition of oil-paper insulation transformer.