Study On Stray Current Of DC Traction Power Supply System For Urban Rail Transit

Urban rail transit is an important part of modern urban transportation,which has achieved rapid development in recent years.It plays a very important role in effectively alleviating urban traffic pressure and solving urban congestion.Urban rail transit not only brings convenience to people's lives,but also brings many problems.Its power supply mode uses DC traction power supply.At the same time,the running rail not only plays the role of bearing and guiding the locomotive,but also return is the flow path for the traction current to return to the negative electrode of the traction substation.However,it is impossible to achieve complete insulation between the running rail and the ground,which causes part of the traction current to leak to the ground during the return flow through the running rail to form stray currents.The stray current does not flow according to the expected path,so it will cause electrochemical corrosion to the buried metal,affect the normal operation of signal equipment and endanger the safety of maintenance personnel.Firstly this paper introduces the research status of stray currents in urban rail transit at home and abroad,the composition of traction power supply system,the formation process of stray current,the mechanism and harm of electrochemical corrosion,and the collection and monitoring system of stray current.In order to further clarify the distribution law of stray current to reduce its harm to the safe operation of urban rail transit,this paper uses CDEGS professional simulation software to conduct simulation research.The HIFREQ module in the software is used to establish a three-dimensional conductor network topological structure model in which the track is placed on the ground and the tracks are discretely distributed between the track and the ground.At the same time,an experimental test platform is established in the laboratory.The rationality and correctness of the simulation model for the study of stray current are verified by comparing the experimental test data with the software simulation data.Based on the above model,the effects of different locomotive running conditions and different power supply methods on the distribution characteristics of stray current in the rail-ground structure are analyzed;in the rail-row-ground model,the effects of the negative electrode of traction substation directly grounded and floating grounded on the reinforcement current of the aisle bed,stray current of the running rail leakage,rail-ground voltage,and collection efficiency of the drainage network are studied;in the rail-row-buried metal model,the effect of different soil models on the stray current through buried metal and the proportion of leakage stray current in buried metal,drainage network and ground are analyzed.Aiming at some factors affecting stray current,the simulation analysis of stray current by changing model parameters and spatial conductor layout.The results show that the rail-ground transition resistance is the main factor affecting the stray current leakage.When the rail-ground transition resistance is infinite,the leakage current is almost zero;the effect of soil resistivity on stray current mainly depends on the size of the rail-ground transition resistance;When the length of the running rail is longer than the distance between the locomotive and the traction substation,the stray current will increase the reasonable installation of a unidirectional conduction device on the running rail can effectively reduce the generation of stray current.