Analysis On The Variation Law And Influencing Factors Of Ground Potential Near Subway

Subway in China has developed rapidly in the past 50 years and has become an important means of transportation for citizens.At present,the rail can not be completely insulated from the ground.With the continuous increase of subway operating lines and the increase of operating years,the insulation performance of the rail to the ground is gradually aging,which leads to the increase of the leakage of subway backflow current,and then the stray current problem is increasingly prominent.Stray current will not only cause electrochemical corrosion of buried metal and structural steel bar near the line,but also cause DC bias magnetic phenomenon in urban power grid.The stray current can not be effectively monitored when it flows in the soil,but the ground potential can effectively represent the variation rule of stray current in the process of propagation.Based on this,this paper reflects the variation characteristics of stray current by studying ground potential distribution law and influencing factors,which is of great significance for buried metal protection and stray current assessment.According to the composition structure of subway power supply and backflow system.Taking into account the actual information of subway depot,parking lot and ground grid of urban substation,a ground potential simulation model of contact track-rail-drain networkground network-earth was built based on CDEGS platform.The rationality of the model is verified by using the lumped parameter method.The validity of the model is verified by the measured data of subway,which lays a foundation for the study of the law of ground potential variation and its influencing factors.Based on the above ground potential simulation model,the static characteristics of ground potential distribution are studied.Based on the structural parameter variables of urban rail transit,the static distribution characteristics of ground potential under different parameters of subway are studied.The influence of different working conditions of single guide device on ground potential distribution in depot was studied.By changing soil resistivity to simulate different geological structures,the influence of different soil resistivity on ground potential distribution is analyzed.The ground potential distribution characteristics were studied under different distances between the buried metal and the normal line,different depths of the buried metal,different resistance values and whether the metal is broken or not.Considering the ground grid structure of urban substation,the variation of ground potential before and after setting the ground grid is analyzed.The results show that the variation of the metro parameters has a great influence on the ground potential,and the longitudinal resistance of the rail has the greatest influence.There is a direct relationship between the working state of the single guide device in the depot and the ground potential distribution nearby.When the soil resistivity is low,the influence range of stray current on the ground potential is larger.Buried metal can change the potential trend and magnitude of the nearby surface.The closer the distance between the metal and the normal line and the shallower the buried depth,the greater the potential amplitude of the nearby ground and the denser the distribution of the isopotential line.The increase of longitudinal resistance of buried metal and metal damage will increase the ground potential nearby.The dynamic distribution characteristics of ground potential were studied based on station position and departure interval.Considering the distribution of urban underground pipe network,the underground pipe network model is added to the above simulation model.According to the line information,the train position-traction current curve under the fastest traction strategy was plotted,and the position-traction current curve data were input into the model to complete the dynamic simulation of ground potential.Then,the variation of ground potential near a metro line in Shenzhen was studied.The results show that the dynamic distribution of ground potential along the whole line is closely related to the running state of the train,and the areas with serious ground potential distortion are mostly concentrated near the depot.Therefore,more attention should be paid to the insulation protection of the metro depot while the insulation protection of the whole line is done well.The single buried metal near the main line has a large current and a great influence on the ground potential when the train is running dynamically.The urban underground pipe network will absorb the stray current and change the ground potential.