The Dielectric Spectrum Characteristics And Quantitative Assessment Of Transformer Oil-paper Insulation Aging

The main insulation system of power transformer is the oil-paper insulation system.The insulation of the insulation system plays an important role in the service life of the transformer.Therefore,the insulation test becomes an important basis to ensure the safety and stability of the power system.FDS owns an excellent noise-filtering performance,and can directly distinguish the influence of insulating oil,insulating paper and oil-paper structure from different parts of the spectrum,which makes FDS have an important advantage in researching low dielectric loss material.Domestic and foreign scholars have accumulated some experience in diagnosing the insulation state by using the frequency-domain dielectric spectroscopy technique,but there are still some problems.At present,there are few studies on the quantitative analysis of the aging characteristics of the frequency domain parameters.Therefore,based on dielectric constant of frequency domain on transformer oil-paper insulation,Davidson-Cole model is established in this dissertation,and its characteristic parameters are analyzed to find out the characteristics of insulation degradation of oil-paper.In this dissertation,transformer oil-paper insulation system was accelerated aging at 90 ?,110 ?,130 ? for 60 days,and the FDS test,the degree of polymerization test,moisture content test were done.The relationship between degree of polymerization,water content and aging time were analyzed.At the same time,the FDS test was done at different test temperatures.In this dissertation,based on the measured dielectric spectroscopy data,the method with Davidson-Cole model was proposed to assess the condition of insulation aging quantitatively.The extraction method of Davidson-Cole model parameter was studied by simulation.Nonlinear fitting method was used to extract Davidson-Cole model parameters in frequency-domain dielectric spectra on different aging degree and different test temperatures.The quantitative relationship between dielectric parameters and degree of polymerization,moisture content and test temperatures were analyzed.In this dissertation,the relationship between degree of polymerization,moisture content and aging time on different aging degrees were studied.The results show that the degree of polymerization decreases with the aging time,and the higher the aging temperature,the faster the polymerization degree decreases.The moisture content increases with the aging time,and the higher the aging temperature,the faster the water content increases.The moisture content increases with the aging time,and the higher the aging temperature,the faster the water content increases.The results show that the parameters of Davidson-Cole model(??????)are directly related to the aging degree and the test temperatures.As the aging time increases,? which is the shape characterization parameters of Davidson-Cole model,gradually decreases,and ?? which is the short of the steady-state dielectric constant and the optical-frequency dielectric constant,is also increases.The relaxation time decreases with the deline of the degree of polymerization.It can be seen that ? decreases with the increase of the test temperature,showing a negative exponential relationship;?? increases with the increase of temperature,showing a positive exponential relationship;? decreases with increasing temperature,showing a negative exponential relationship.The content of this dissertation is to provide some references to judge the aging degree of transformers accurately.