Study On Aging Characteristics Of Oil-immersed Paperboard For 1000kV AC Transformer

With the continuous construction of the national UHV project,how to evaluate the insulation aging of HV,UHV and UHV transformers has become an urgent problem to be solved in the power industry.At present,more and more scholars at home and abroad use dielectric response theory to evaluate the operation of oil-immersed transformers,but only limited to the study of dielectric response parameters of oil-paper insulation system.Therefore,this paper studies the influence of environmental factors on polarization depolarization current,and explores the influence of polarization depolarization current on transformer insulation aging based on step temperature and insulation aging degree.The main research contents of this paper are as follows: An electrical-thermal aging test platform for oil-paper insulation is designed and implemented independently,a polarization depolarization current(nA level)measurement system is developed,and the upper computer software development based on Lavbiew is completed.On this basis,a series of electricalthermal aging tests of oil-immersed insulated cardboard were carried out.Polymerization degree test was carried out for different aging degree test samples,and oil-immersed insulated cardboard samples with different aging degree were prepared.The polarization depolarization current(PDC)at step temperature was studied,and the family of PDC curves was obtained.The experimental results were analyzed to explore the influence of step temperature and aging degree on the PDC characteristic curve of oil-immersed insulated cardboard.The influence of step temperature and aging degree on the characteristic curve of polarization depolarization(PDC)was verified by simulating the edge electric field of oil-immersed insulated cardboard under bivariate conditions.This paper draws the following conclusions: under the combined action of step temperature and aging degree,the polarization depolarization current curves of oil-immersed insulated cardboard specimens shift obviously to the upper left,and the time when the curve reaches the stable value moves forward.The polarization depolarization current accelerates to shift to the upper left when the temperature is above 50 C,which indicates that the number of carriers and the thermal motion of ions in the insulation increase when the temperature is above 50 C.The calculation of electrical conductivity and the simulation of electric field at the edge of insulating material further verify that 50 is the inflection point of the polarization depolarization characteristic curve of this experiment.It provides a new idea for evaluating insulation aging state of transformer by polarization depolarization current method.