Research On Stray Current And Rail-to-earth Resistance In Urban Rail Transit

At present,urban rail transit which uses DC traction power supply system using rail track as reflux track requirements rail insulation installation to earth,minimizing rail resistance,shortening the distance of substations to control rail potential and stray current.The stray current will not only cause damage to the reinforced concrete structure,but also damage the buried pipeline,and bring harm to the depot and parking lot directly.The most effective way to control the stray current is to control the rail-to-earth resistance of main line and the rail potential of stations.Firstly,this paper focuses on the stray current Domestic and international standards to comb and analysis.The current national standard CJJ49 about stray current and rail-to-earth resistance is relatively backward and is urgently needs to improve.The current research status of stray current,rail potential and rail-to-earth resistance is analyzed,and the distribution regular of stray current is studied by establishing a system model of bilateral power supply system and changing reflux system parameters in this paper.The methods of accurately measuring the electrical parameters of the reflux system is summarized.Based on LabVIEW,a set of high-precision multi-channel test device is developed to accurately measure the parameters of the reflux system.The measured longitudinal resistance of the stray current collecting network is larger than the initial design value,and the concrete casting can increase the resistance value by 2.33%~5.63%.Rail-to-earth resistance measurements had been lack of actual cases,this paper puts forward in the field of rail transition resistance measurement method and analysis the key factors influencing the resistance.These are significant to power supply design,operation and maintenance.Secondly,this paper studies the influence of stray current generated by main line on the depot and parking lot.The total amount of stray current in the parking lot is as high as 610.20 A,and in the depot is as high as 302.40 A.Stray current is more than just metal pipeline corrosion harm,and main stray current flows from the earth through several kilometers and returns to the main line from the parking lot and depot,causing the damage of equipment and the burning of temporary ground wire in the parking lot and depot.In order to prevent the traction current of the main line and protect the safety of staff and equipment,the depot and the parking lot of the metro are usually set up the unidirectional conduction device paralleling the insulated rail joint.However,the aging of the rail joint and the present unidirectional conduction device not only become the circulation path of the stray current which is leakage from the main line rail and is collected by the rail in the depot and parking lot.Calculation model of urban rail reflux system is established in this paper.Through the real working condition of line and real train traction current data,the influence of unidirectional conduction device and the rail overvoltage protect device(OVPD)on the rail potential of stations is analyzed.Through the simulation and verification of this paper,the equivalent grounding of the parking lot and the depot makes the rail potential of the main line rise by 27.20 V.At the same time,the operation group closes OVPDs permanently in some stations to reduce the local rail potential,but it leads a rise of 51.09 V in other stations.Finally,in view of the problems exposed by the simulation and test,this paper proposes a novel rail reflux device which is used in the depot and parking lot,and it can effectively solve the problem of stray current in the depot and parking lot and control the influence on the rail potential of main line.