| The metro plays a momentous role in promoting the development of the city and the progress of the modern society.With the continuous improvement of the metro lines,the stray current caused by DC traction power supply system has become increasingly severe.Stray current will not only cause electrochemical corrosion damage to metal conductors along the tunnel but also cause DC bias of main transformers in urban power grids.Grasping the dynamic distribution of stray current is of great significance to the daily operation and maintenance of the metro.Based on CDEGS software,a 3D network model is established to study stray current in this paper.In order to construct the multi-locomotive model under the multi-interval condition,this paper proposes a ground traction power supply model in the existing three-tier spatial structure model(air,concrete,soil)and three-tier metal conductor structure model(rail,current drainage net(CDN),structural metal).Then,the traditional analytical method is used to verify the rationality and practicality of this model.Secondly,this paper compares the static simulation results between the single-interval condition and multi-interval condition.Combined with the power supply technology used in the actual project,it also proves the necessity of using multi-interval power supply model to study stray current distribution.Based on multi-interval power supply model,the static distribution characteristics of stray current are studied.Firstly,by adjusting the structural parameters,the effects of different line conditions and fault types on the distribution of stray current are studied.Secondly,the simulation models for multi-locomotive in the same interval or in different intervals are established to research the stray current variation when the running state of each locomotive changes.The simulation results show that the increase of the longitudinal resistivity of the rail and the decrease of the resistivity of the insulation layer have vital influence on stray current;the effect of partial insulation failure is limited.Local fracture of CDN will lead to the distortion of longitudinal current in the conductors under the ground,but less effect on the rail.Multiple locomotives in an accelerating state in the same interval will obviously raise the railto-earth potential in this interval.For another condition,if the locomotives in the accelerated state and the braking state are separated on both sides of the line,this can lead to some negative effects such as increased rail-to-earth potential and the rise of stray current in the soil.Based on the actual operation lines,the study of dynamic distribution characteristics of stray current is carried out.According to Shijiazhuang Metro Line 3,combined with locomotive traction current simulation curves under target-speed-running-strategy(TSRS)and fastest-speed-running-strategy(FSRS),we create a simulation schedule to realise the dynamic simulation of stray current.Secondly,from the perspective of dynamic distribution,the necessity of analyzing the stray current distribution using multi-interval condition is proved.Finally,we study the variation of stray current under double track condition through simulating the uplink and downlink dual-channel tunnel.The results show that this line satisfies the basic working condition;the rail-to-earth potential and polarization potential positive offset average value of CDN meet the specification requirements.The rail-to-earth potential in dual-channel tunnel has a significant derease,which leads to the decrease of CDN-to-earth potential and stray current formed by single channel.The dual-channel model with cross bonds has basically the same distribution of each parameter in uplink and downlink.Based on Faraday's law,the distribution curves of metal conductors along the metro are plotted under dynamic conditions,so that we can further study the impact of different power supply conditions on the calculation of conductor corrosion.This paper analyzes the distribution characteristics of conductor corrosion when locomotives in different operation states under multi-interval condition.In addition,this paper also researches the changes in the amount of conductor corrosion under dual-channel tunnel condition.The results show that under actual operating conditions,the distribution of corrosion amount of the rail and CDN has a certain regularity,and it is related to the station location and station type.The corrosion hazard caused by the selection of FSRS is more serious than TSRS.In the dual-channel model,the variation of the maximum corrosion of the rail and the CDN is inconsistent,and there is a big difference in the total amount of corrosion of each conductor.Analysis shows that the CDN is more sensitive to cross stray current between uplink and downlink than the rail.Based on the multi-interval,multi-locomotive and 3D simulation model,this paper provides a new solution to research the stray current.The simulation results are more in line with the actual operation of the metro and can guide the staff to take effective protective measures to control stray current. |
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