Study On Insulation Performance Of Rail Insulated Fastener In Urban Rail Transit

Urban rail transit adopts DC power supply mode,and rail is the main path of traction return current.The rail has a certain resistance,moreover,rail and ground cannot be completely insulated,so the stray current flowing into the ground will be produced.The stray current will corrode metallic facilities such as underground metal pipelines and structural steel.At present,a fastener is installed between rail and sleeper in design of subway to ensure a high insulation resistance between rail and ground.The installation design of fastener only takes into account the physical contact insulation,and does not consider the effects of material aging,environmental pollution,moisture and other factors on the insulation performance.Therefore,in actual operation of subway,the insulation performance of fastener can not meet the requirements.It is imperative to study the influence factors and improvement measures of the insulation property of fastener.This paper first introduces the structure of fastener,the components and the electrical characteristics of parts.In this paper,the finite element simulation software ANSYS is used to establish the whole pollution model of fastener,and the flow path of leakage current,the composition mode and value of surface resistance and body resistance under different pollution conditions are studied.The results show that:Surface resistance has a great influence on insulation property of fastener,and the surface resistance of the fastener is far less than the body resistance under general contamination.The surface resistance of the fastener is related to surface conductivity,thickness of pollution and leakage distance of surface current.When the contamination conductivity is 10^-5S·m^-11 body resistance of gauge block and rail pad is all above 10⁶M?,but the surface resistance of fastener on different surface is only 10¹00M?.At same time,this paper set up the artificial pollution test platform of fasteners,use the solid layer method in fastener surface smear,and simulate the environment with different relative humidity,temperature and salt fog.The influence of different climatic factors on the resistance R₁ between rail and rail pad and the resistance R₂between rail pad and sleeper,respectively,is measured in this paper,and study the weakness of the insulation.The results show that:Relative humidity and wetting time have obvious influence on the insulation performance of fasteners.Because water vapor in the air condenses on surface of fastener,it can increase surface conductivity of fastener and form a conductive path on the surface of insulated devices.Due to the small leakage distance,iron cushion plate is easily affected by the moisture in air.When humidity reaches 90%,the value of R₂ is less than 2M?.In salt fog environment,salt in fog will attach to surface of fastener and lead to decrease of surface resistance.The effect of temperature rise on insulation property of fastener is mainly reflected in the inhibition of condensation of water vapor on surface of fastener.Finally,according to results of finite element simulation and artificial contamination test,measures to enhance insulation performance of fastener are studied.It can be obtained from two aspects of increasing the leakage distance and improving the ability to resist water and filthy.The results show that:Surface resistance increases and two part of insulation resistance increases by about 50%after10mm's extension on the side of rail pad and iron cushion plate.The under rail pad increases along the direction of rail and iron pad,and the value of R₁ is increased by50%⁷0%.Replacing iron cushion plate with composite materials with excellent mechanical strength and insulation properties.The liquid contact angle of insulating material is increased so that moisture in the air is difficult to moisten the surface of fastener.