Research On Quantitative Evaluation Of The Aging Degree Of Transformer Oil-paper Insulation Based On FDS

Power transformers are important equipment in the power system.It is the focus of power system to accurately evaluate the aging state of transformer oil paper insulation by appropriate technical to ensure the safe and reliable operation of equipment.Frequency-domain dielectric response technology has been widely used by scholars at home and abroad in the field of evaluation of oil-paper insulation by its rich characterization of insulation information and strong antiinterference ability.In order to deeply explore the quantitative relationship between the parameters of the oil-paper insulation frequency domain dielectric model and the actual aging degree of the transformer and improve the accuracy of evaluating the aging state of the oil-paper insulation of the transformer,this paper is mainly based on the frequency domain dielectric response principle and in-depth study of the dielectric relaxation theory,the traditional Cole-Cole model is modified by introducing conductance loss.Since the real part and the imaginary part of the complex permittivity contain similar information,nonlinear least square method is used to fit the test data of the imaginary part of the complex permittivity to extract the relaxation time constant、shape parameters and static dielectric constant in the modified Cole-Cole model and establish the function relation between the characteristic parameter and the aging state of the transformer oil-paper insulation.In this paper,a thermal aging experiment platform was built and the aging temperature was set at 130°C.The single-layer oil-immersed paperboard and transformer oil samples were subjected to 45-days accelerated thermal aging experiments.The oil impregnated paperboard and transformer oil in the aging process were sampled regularly to test FDS,conductivity,polymerization degree and transformer acid value and analyzed the above test data under different aging conditions.In this paper,combined with the frequency-temperature shift theory,the average relaxation activation energy of oil-paper insulation models with different aging days is calculated.The results show that as the degree of aging deepens,the average relaxation activation energy of oil-paper insulation decreases exponentially.The activation energy does not change with temperature.The characteristics of the frequency domain dielectric spectrum measured at different temperatures are reduced to 30℃ and eliminate the influence of temperature on the frequency domain dielectric response test curve.The test results show that as the aging days of the oil-paper insulation increase,the degree of polymerization of the insulation paperboard decreases significantly,the acid value in the oil increases significantly.In order to be able to quantitatively characterize the aging state of oil-paper insulation,characteristic parameters are extracted from the frequency domain dielectric parameter relationship and fitted to the functional relationship between the degree of aging of the oil-paper insulation and the degree of polymerization of the paperboard and the acid value in the oil.The results show that the characteristic quantity shape parameters,relaxation time constant and static dielectric constant change significantly under different aging states of oil-paper insulation,which can effectively characterize the aging degree of oil-immersed paperboard and transformer oil.There is a positive exponential relationship between the degree of cardboard polymerization and the shape parameters,relaxation time.The static dielectric constant increases exponentially with the decrease of the degree of cardboard polymerization.The shape parameter decreases linearly with the increase of the acid value in the oil.The relaxation time parameter value and the acid value in the oil shows a negative exponential relationship.The static dielectric constant increases exponentially with the increase of the acid value in the transformer oil.At the same time,as the aging of oil-impregnated paperboard deepens,the imaginary part of the complex permittivity increases in the middle and low frequency range.As the age of insulating oil increases,the imaginary part of the complex permittivity increases in the full frequency range.