Research On Dynamic Stray Current Distribution And Suppression Schemes In Typical Section Of Tianjin Rail Transit

With the development of urban rail transit,the problem of stray current is becoming more and more serious.The electrochemical corrosion of stray current on structural reinforcement and metal pipeline in tunnel cannot be ignored.The fundamental reason of stray current is that the running rail as return rail cannot be completely insulated from the ground.In this thesis,the stray current distribution characteristics of the typical sections of Tianjin Rail Transit are studied,and the stray current suppression scheme is proposed,which is of great significance for stray current control.Firstly,this thesis establishes the subway tunnel structure model based on CDEGS.The CDEGS modeling process is described in detail,and the electrical and geometric parameters needed for modeling are listed.The CDEGS model is compared and verified with the traditional resistance network model,highlighting the modeling characteristics of CDEGS model close to reality.The potential and current distribution of the return conductor in the tunnel DC traction power supply system are calculated.Secondly,the actual measurement schemes for the typical section parameters of Tianjin Rail Transit are proposed,and the typical section model of Tianjin Rail Transit is built based on the measured data and line data.The influence of rail-to-ground transition resistance,train running position,train running condition and soil resistivity on stray current are analyzed.The influence degree of stray current on the station grounding grid is studied.The distribution of the electric potential and electric field in the soil between the tunnels under the condition of crossing and overlapping tunnels are studied.The results show that the rail-to-ground transition resistance is the decisive factor affecting the stray current.When the train is located at the middle point of the power supply section or when the train is accelerating or regenerative braking,the stray current is large.The soil will affect the stray current by affecting the concrete resistivity.It is found that the increase in the contact voltage amplitude and current amplitude of the station grounding grid is concentrated in the vicinity of the tunnel.It is found that corresponding measures should be taken to prevent stray current corrosion of metal pipelines between crossing and overlapping tunnels.Finally,according to the typical section model of Tianjin Rail Transit,the stray current suppression schemes are proposed.The stray current collection efficiency of uniform distribution and centralized distribution of longitudinal steel bars of Stray Current Collection Grid is compared,and the optimal layout scheme of Stray Current Collection Grid with longitudinal steel bars spacing of 0.3m is obtained.Although the cross-sectional area of the centralized Stray Current Collection Grid with longitudinal steel bars spacing of 0.3m is smaller when using 14 longitudinal steel bars with radius of 0.008 m in double layer than when using 7 longitudinal steel bars with radius of0.012 m in single layer,the stray current collection efficiency is higher,reaching 70.14%.The influence law of concrete resistivity on stray current is obtained,and the scheme of water cement ratio and admixture ratio to improve concrete resistivity is optimized.The scheme reduces the influence of soil on concrete resistivity and the harm of stray current to reinforced concrete structure.