Influence Of Thermal Aging On Partial Discharge Of Nomex Paper Used In Traction Transformer Study

The stability and safety of the insulation system is one of the necessary conditions to ensure the normal operation of the transformer.Different from the general oil-immersed transformer,the on-board Traction transformer uses the mixed oil-paper insulation system,the lower part of the temperature rise uses the conventional fiber insulation paper,and the higher part uses Nomex insulation paper.With the increase of service life,due to the on-board transformer having short-term negative operation characteristics and being affected by environmental factors such as high temperature and humidity in different operation sections,Nomex insulating paper and other insulating materials will deteriorate correspondingly,which will lead to partial discharge and affect the service life of the insulation system.According to a large number of actual fault,it known to that thermal aging is one of the main reasons that Nomex paper appear damage,therefore in combination with Nomex paper partial discharge researsh in thermal aging and thermal aging on the influence law of partial discharge,it's having important theoretical value and engineering significance to study Nomex paper the running state of the vehicle variable pressure and prevention of failure.This paper first carried out the Nomex paper aging test and prepared Nomex paper samples with different degrees of aging.On this basis,a partial discharge test was carried out to explore the partial discharge parameters and physical phenomena of Nomex paper with different degrees of aging.The results showed that Nomex paper discharge processes with different degrees of aging could be divided into three stages: pre-discharge,middle discharge and late discharge.Nomex paper discharge initially occurs at pulp and then develops along the interface between pulp and pre-cut fiber,while aging exacerbates the interface roughness and promotes discharge development.The effect of aging on Nomex paper discharge parameters is small in the early stage of discharge.However,with the development of discharge,the effect of aging on discharge parameters becomes more and more significant.According to the microstructure of the sample,the change of discharge parameters is related to the black spot formed by the sample.The black spot is the result of the combined action of methyl polar compound and naphthalene with carbon chain structure,which affects the change of discharge parameters.In order to better understand the effect of thermal aging on discharge,Nomex paper discharge tests were carried out at different oil temperatures,which explore the rule of different oil temperatures on the development of Nomex paper discharge.It was found that the oil temperature would affect the discharge process.With the increase of oil temperature,the initial voltage and breakdown voltage both showed a downward trend,and the breakdown voltage was more sensitive to temperature.In the initial stage of discharge,the temperature has little influence on Nomex paper discharge parameters.However,as the discharge progresses into the middle stage and the late stage,the temperature influence gradually increases.Through analysis,it is concluded that the higher the temperature,the faster the development of Nomex paper surface creepage trace by changing the conductivity and dielectric constant of Nomex paper.Finally,combined with the oil temperature and aging test,it was found that under the same temperature condition,with the deepening of the aging degree,the Nomex paper with different aging cycles showed greater differences in the discharge parameters.Under the same aging cycle,the higher the temperature,the greater the difference of Nomex paper discharge parameters.High temperature and aging simultaneously promote the Nomex paper's discharge development process and affect the Nomex paper insulation life.