Research On Stray Current Protection And Monitoring Of Urban Rail Transit

Stray current corrosion is an important problem in DC traction power supply return system.Take the stray current drainage system and strengthen the monitoring system is the principle of stray current protection design.It is important to increase the research on stary current collecting and monitoring for stray current corrosion protection.A DC traction power supply and return system model about the influence of the stray current collection system on the distribution of stray current is established.The rectifier unit is equivalent to a voltage source series resistance,and the train is equivalent to a power source.The reflux system is expressed by distributed parameters and centralized parameters.The model also considers the characteristics of the drainage device.Then,a power flow calculation model under concentrated parameters is established by dividing the catenary,rails,stray current collection network and the ground into different layers,and dividing the traction station and the train into many planes.Since only the current results of the train and the traction station are concerned,the catenary node and the train node are equivalent to the traction network node,and the power flow calculation model is simplified.Combing with the power flow calculation results and the boundary conditions of the distributed parameter model,the rail potential distribution of the multiple sections of the line is obtained.The distribution of stray currents and the efficiency of collecting stray currents is calculated.Based on a Qingdao subway project,the influence of many parameters on the stray current distribution is evaluated.The result shows that the rail longitudinal resistance,rail to stray current collection network(SCCN)resistance,and the state of drainage device will affect the primary stray current.The longitudinal resistance of rail,state of drainage device,SCCN to earth resistance,and longitudinal resistance of SCCN will affect the efficiency of SCCN.The experiment of drainage device work or not is carried out when a train runs in Chengdu Metro.Based on the traction power supply and return system model,the SCCN to earth resistance is calculated,and the distribution of rail potential and stray current is obtained.The results show that the efficiency of SCCN is low,and the average efficiency is less than12.73%.When the drainage device works,the primary stray current is increased by more than5 times,and the efficiency of SCCN is reduced to about 4%.A rail insulation defect diagnosis method based on spatiotemporal correlation of rail potential is proposed.This method combines with the characteristics of rail potential data in stray current monitoring system,which views the continuous rail potential as monitoring object.K-means is used to classify the monitoring data to reduces the scale of data processing.Then the improved Minkowski distance formula is used to measure the similarity to detect the insulation defects.This method can diagnose the local insulation defects,and provide an effective method for stray current monitoring system.