Study On Insulation Performance And Life Assessment Of Fastener In Urban Rail Transit

With the increase of the operating time of the urban rail transit system,rail fasteners are affected by factors such as environment and stress damage,the insulation performance of the fastener is damaged,and part of the current leaks into the ground to form stray currents.Stray currents will cause electrochemical corrosion to public facilities such as steel bars of subway tunnel structure and metal pipelines along the tunnel,and bring great hidden danger to subway operation.Therefore,it is of great significance to study the insulation performance of fasteners,evaluate the aging life of insulation,and explore the influence law of environmental pollution factors on the insulation performance of fasteners for the protection of stray current.Introducing the composition and structure of traction reflux system of urban rail transit,a rail-drain network-earth equivalent resistance network model was established,an distribution formula for stray currents was obtained based on Kirchhoff’s law,and the influence degree of each factor on the stray current is analyzed through MATLAB simulation,the importance of fasteners in stray current protection was revealed.Establishing finite element model of fastener system based on the elastic III fasteners,the influence law of insulation components to the overall resistance fasteners was analyzed through ANSYS simulation,and the equivalent circuit model of fastener was proposed.The impact of humid environment on the resistance of each insulation component of the fastener was explored,according to the protection regulations,the insulation failure state of the fastener is analyzed,and the wet equivalent circuit model of the fastener system is proposed.The results show that the aging of the insulation components and the surface current leakage are the main reasons for the insulation failure of the fastener system.The surface current leakage has a greater impact on the insulation performance of the fastener,which can cause insulation failure in a relatively short time.According to the actual environment of the tunnel,different densities of salt pollution and metal pollution are configured to build a test platform to explore the influence of surface pollution on the insulation performance of fasteners in humid and oily environments.From the experimental results: the type and concentration of surface contamination have little effect on the insulation performance of fasteners in dry and oily environments;salt contamination is more likely to form surface leakage paths and cause stray current leakage in humid environments.Experiments show that,the simultaneous effect of surface pollution and moist air is the main reason for the surface current leakage of fasteners during subway operation.The aging life of the fastener system and its insulation components is evaluated based on the above research,the characteristic parameters of the insulation performance of the fastener are selected,the measurement method of the characteristic parameters is proposed,and the accelerated aging test plan is formulated.With the passage of aging time,the change law of the insulation performance of each insulating component under different aging temperatures is analyzed,DC resistivity is selected as the characteristic quantity for life evaluation based on the Arrhenius model,and the life evaluation equation of the fastener system and each insulating component under the action of thermal stress is derived.There are 54 figures,10 tables,and 75 references in this thesis.