Effect Of Moisture On Thermal Aging Characteristics Of Nomex Insulation Paper In Vehicle Traction Transformer

At present,the insulation material of the key parts of the domestic vehicle traction transformer is Nomex insulation paper,which is in a relatively harsh working condition and is likely to be wet during the operation of the transformer.Temperature and moisture are the main factors causing the aging of oil-paper insulation.When the moisture content and operating temperature of oil-paper insulation are too high,it will greatly accelerate the aging of insulation materials,shorten the service life of transformers and easily cause electrical accidents.In order to better study the thermal aging characteristics of the internal insulation of the traction transformer in the vehicle after damp,this paper designs the Nomex oil-paper insulation samples with different initial moisture content based on the Nomex insulation paper and the conventional insulating oil in the operating conditions of the vehicle traction transformer.The aging parameters of Nomex insulating paper and insulating oil were tested by multi-cycle heat aging test at 180 C.The moisture content,tensile strength,microstructure and FDS parameters of Nomex oil-paper insulating oil with different moisture content were studied with aging time.The law of change.Finally,the modified Cole-Cole model was used to fit the frequency spectrum of Nomex oil-paper insulation in different moisture content and different aging conditions,and the characteristic parameters which can characterize the moisture content and the aging degree of the insulation paper were extracted.The insulating oil gradually turns yellow with the aging process,and the moisture in the oil also shows a rising trend.The tensile strength of Nomex insulating paper also decreases with the increase of aging time.In particular,when the initial moisture content of the oil-paper insulation increases,the tensile strength decreases rapidly during the first three aging cycles,and the surface color of the Nomex insulation paper also changes with aging,and the initial moisture content of the oil-paper insulation is higher.The color change is more obvious.The results of the micromorphology of Nomex insulation paper are as follows:With the increase of the initial moisture content of the oil-paper insulation,the chopped fibers are disordered,thinned,bent or even broken,and the pulp distribution is loose even in the same aging cycle.The extent of obvious defects increases.As the moisture content increases,the FDS curve of Nomex insulating paper also shows an upward trend,and the larger area is mainly the low frequency band.Finally,the use of the correction amount Cole-Cole model fitting parameters obtained shows that,with a high quantity of oil-paper insulation Nomex sensitivity to moisture,is sensitive to parameters Nomex insulating paper aging condition.When moisture is present,the heat aging of Nomex insulation paper is mainly carried out by hydrolysis.The increase of moisture content in Nomex oil-paper insulation increases the rate of aging,and water molecules and aging products affect the polarization of Nomex oil-paper insulation.process.Finally,the relationship between the parameters obtained by fitting the Cole-Cole model and the moisture content and the degree of aging is analyzed.It can provide reference for the evaluation of the insulation state of the traction transformer in the vehicle by using non-destructive testing technology.