Study On Multi-factor Aging Properties And Characteristic Parameters Extraction Method Of Transformer Oil-paper Insulation

In order to further explore the quantitative relationship between the parameters of the dielectric response model and the actual aging state of transformer,and improve the accuracy of the status assessment and life prediction of transformer insulation,this paper mainly base on the principle of dielectric response,simultaneously,the classical Davidson-Cole model is used to extract the dielectric properties of oil-paper insulation and to evaluate the aging state under different aging conditions,such as single heat,electro-thermal,electro-thermal-vibration,etc.Meanwhile,in order to eliminate the impact of the insulation structure on the extraction of parameters,the dielectric loss factor tan? which is associated with the real and imaginary parts of the dielectric constant is chosen as the fitting data.Then the nonlinear least squares fitting method is used to extract the shape parameters,relaxation time,relaxation dielectric constant of Davidson-Cole model,and the relationship between the characteristic parameters of the aging model and the aging state of the transformer oil-paper will be established.In this paper,an electro-thermal-vibration combined aging test platform is set up,and the basic aging temperature is 130°C.The accelerated aging of oil-paper insulation samples will be carried out for 40 days by comparing single thermal aging,electrothermal aging and electrothermal vibration combined aging.During the aging process,the aging samples are tested for FDS frequency domain spectrum,conductivity,water content,polymerization degree,etc.,and then the test data will beanalyzed.Finally,based on the modified Davidson-Cole model,the characteristic parameters are extracted,and the quantitative function relationship between different characteristic parameters and aggregation is established.The results show that the three model parameters extracted from the experimental data are all related to the degree of polymerization of the oil-paper insulating aging.With the extension of aging time,the value of the shape parameter and the degree of cardboard polymerization shows an exponentially reduced relationship,and as the aging conditions changes,the curve appears to reverse.When the degree of polymerization is greater than 600,the value of shape parameters will increase with the increase of aging stress conditions.On the contrary,the degree of polymerization is less than 500,and the shape parameters value will drop with complexity of stress conditions with aging.The relaxation time parameter shows a significant trend of linear descent with the reduction of the degree of polymerization.During the whole aging process,the slope of the curve about the relationship between relaxation time and DP will gradually increases with the increase of the severity of aging stress conditions.Besides,the relaxation dielectric constant will increase with the decrease of the degree of polymerization.Under different stress conditions,the relaxation dielectric constant exhibits the collection characteristics of the data.