Study On Aging Evaluation Method Of Silicone Oil-immersed Insulating Paper Of On-board Transformer Of Electric Multiple Unit

With the vigorous development of high-speed railway,the safe and stable operation of high-speed railway has attracted more and more attention.The on-board transformer of electric multiple unit(EMU)is the key equipment to realize voltage conversion,locomotive traction and braking,it is of great significance to ensure its safe and stable operation.The insulation structure design of on-board transformer is more compact than that of ordinary power transformer,the internal electric field and thermal field of transformer are more concentrated,and the operation environment are worse.The insulation materials inside the transformer will gradually and irreversibly age under the influence of electricity,heat,moisture,acid and other factors,among which thermal aging is the most important factor leading to the aging of oil paper insulation.Therefore,it is of great engineering significance to deeply study the thermal aging mechanism and evaluation method of on-board transformer oil paper insulation.Firstly,dimethyl silicone oil and cellulose insulating paper are selected for the thermal aging experiment of oil paper insulation.the frequency domain dielectric spectroscopy(FDS)and degree of polymerization(DP)experiment of the silicone oil-immersed insulating paper aged 0～49 days are carried out,and the relevant aging parameters are obtained.Secondly,according to the existing theory of activation energy and the calculation method of thermal aging activation energy based on FDS method,a calculation method of average activation energy of silicone oil-immersed insulating paper is proposed.The average activation energy calculated is substituted into the zero order aging kinetic model and applied to the measured data to prove the effectiveness of the average activation energy data.Thirdly,through the analysis and derivation of the related theory of dielectric response,based on Havriliak-Negami(HN)dielectric response model and grey wolf optimizer(GWO),a separation method of conductivity loss and polarization loss in the process of dielectric response is proposed,and the FDS data sub process of silicone oil-immersed insulating paper is analysed.Finally,through the study of the mechanism of oil paper aging process and dielectric response process,it is found that the aging products will not only catalyze the thermal aging process,but also the polar products will participate in the dielectric response process of oilimmersed paper.the concepts of aging correction translation coefficient and time-varying pre exponential factor are proposed to describe the aging process and dielectric response process of oil paper respectively.Through the separation method of conductivity loss and polarization loss in the dielectric response process,the dielectric response process and frequency division curve translation of FDS data of different aging samples are realized,and the mapping relationship between aging correction translation coefficient and aging time is found.Based on the calculated average activation energy,a modified aging kinetic model is proposed.By applying the model to the measured DP and time relationship data,it is found that the modified aging model has better fitting effect on the DP data.Finally,an aging evaluation method of silicone oil-immersed insulating paper is proposed,and the effectiveness of the method is verified by experiments.