Research On Distribution Characteristics And Detection Of Stray Current In Transit System

In urban rail transit,the rail not only acts as the running line,but also as a conductor for traction current flowing back to the traction substation.However,it is difficult for rail to be completely insulated from the earth.At the same time,the existence of rail resistance causes a part of current flow into the earth without returning to the substation through the rail,and the leak of current will seriously affect the normal operation of the train and accelerate the corrosion of buried metal structure,it can even threaten personal safety.Therefore,it is great significance to study the distribution characteristics of stray current and the detection of stray current corrosion.In this paper,the traction characteristics of the metro vehicle are introduced into the DC traction system,and the dynamic distribution model between the stray current and the running characteristics of the metro vehicle was established.The distribution of stray current under traction characteristics is analyzed,and the influence of the slope,tunnel and curve radius on the distribution of stray current and rail voltage is considered.The results show that the influence of traction characteristics and traction path on the stray current is worthy to attention.In view of the present study of stray current distribution models are based on the train under static condition,and the evaluation of buried metal corrosion mainly based on the calculation of the stray current as an indirect indicator of the degree of corrosion of the buried metal.Based on the data of Guangzhou metro line 2,the finite element model of dynamic train was established,the dynamic distribution characteristics of stray current and pipeline potential were analyzed.According to the multiple physical field calculation,the corrosion quantity of the buried pipeline is calculated in different soil resistivity and different pipeline buried depth.The results show that the corrosion degree of buried pipeline can be directly reflected by calculating the corrosion quantity of pipeline through coupled multiple physical field calculation.And then combined with the actual situation of multiple buried pipeline was established,the distribution of stray currents at different relative positions between the cathodic protection pipeline and the unprotected interference pipeline was analyzed,the results show that the cathodic protection current,the height,the relative angle and thehorizontal distance between the protection pipeline and the interference pipeline can affect the stray current distribution of the interference pipeline.Compared with the actual field test,the experimental device for simulating the stray current corrosion of metro can better analyze the stray current corrosion.In the experiment,corrosion tests of different soil conductivity and buried depths was carried out.The experimental samples were tested by electromagnetic acoustic resonance detection technology.The average frequency difference of the resonant spectrum of the specimens under different experimental conditions was compared and the thickness difference of the specimens before and after corrosion was calculated.The results show that the calculation error is less than 5%by comparing with the actual measurement data of the corrosion specimen thickness,so the electromagnetic acoustic resonance can better detect the corrosion of stray current.