Evaluation Method Of Aging Status Of Oil-Immersed Insulating Paper Within Transformer Based On FDS

The insulation system of large-scale oil immersed transformer will gradually age under the combined action of various stresses(such as electricity,heat,machinery,etc.),and eventually fail,even lead to electrical failure in serious cases.On the one hand,the service life of some transformers in China's power grid has been nearly 30 years,which is near the end of their insulation life.If these transformers are replaced at one time,not only a lot of manpower and material resources are needed,but also a huge waste will be caused.On the other hand,if the transformer has insulation fault,it is difficult and time-consuming to repair.Therefore,if the aging state of the current insulation system can be determined by appropriate monitoring and evaluation methods during the operation of power transformer,it will be of great significance to improve the operation reliability of the equipment and avoid the occurrence of electrical accidents.Firstly,this paper analyzes the factors that affect the aging of oil impregnated insulating paper of transformer,and probes into the influence of mechanical vibration which has been often ignored on the aging of oil impregnated insulating paper,and discusses the aging judgment methods with the degradation products of cellulose,physical quantity and electrical quantity as the characteristic quantity;Secondly,the paper machine thermal aging test platform was designed and built.A series of accelerated machine thermal aging tests were carried out on the insulating paper at different frequencies,amplitudes and aging times at different temperatures.The frequency domain dielectric spectrum(FDS)characteristics,tensile strength(TS)and polymerization degree(DP)of the samples with different aging times in the range of10-3-103 Hz were measured.The change rule of FDS curve was studied and the tan?-f curve characteristic of the sample was analyzed.It was found that the low frequency band could be used as the characteristic frequency band to characterize the aging degree of the sample.In this paper,the exponential relationship between dielectric loss factor and corresponding tensile strength of samples with different aging time under characteristic frequency is explored,and the correctness of this relationship is proved by experimental data.Based on this,nondestructive testing of mechanical strength of insulating paper and effective evaluation of aging state can be realized.Furthermore,the resistance-capacitance parameters of each branch of the extendedDebye model(EDM)of the prototype are obtained by using an optimal fitting algorithm,and the relationship between the identification parameters of the extended Debye model and the aging state of the oil-immersed insulating paper is preliminary investigated.The further study of the parameters of EDM model parameters and its correlation with insulation aging provides a basis.The work done in this paper can provide reference for the operation and monitoring of the insulation system of the converter transformer.