| Nowadays,the rail is widely used as return rail of DC traction power supply system for the metro.Due to the resistive rail cannot be completely insulated from the ground,the problem of stray current caused by operation of metro is becoming more and more obvious as the insulation performance of rail is gradually aging,resulting in electrolytic corrosion of underground metal components such as pipelines and building structural steel bars,and even the DC bias of power transformers in urban power grid.In this context,considering the complexity of metro power supply network and the traction return underground network,calculating the distribution and analyzing the characteristics of metro stray current are of great significance for the evaluation and mitigation of stray current.According to the structures of metro power supply network and the traction return underground network,considering the interaction of locomotives and the characteristics of the multiple return path of stray current of the underground network structure,the power flow calculation model of metro power supply network and stray current calculation model in multiple metro power supply sections are established.The AC/DC power flow calculation is realized by combining the forward and backward substitution method and the loop current method.Then,based on the Kirchhoff’s law,the electric equations of the traction return underground network structure are written and solved by the boundary condition of the principle of the electric parameter balance.Thus,the distribution of stray current in multiple metro power supply sections is solved,which lays a foundation for the calculation and characteristic analysis of the metro stray current.According to the above calculation model and calculation method,the distribution characteristic of stray current in multiple metro power supply sections is analyzed.The control variable method is used to calculate and analyze the influence of the position and the driving power of locomotives running on the metro line on the rail-to-ground voltage and stray current distribution.For the same power supply section and different power supply sections of the metro line,the distribution of rail-to-ground voltage and stray current under the different number of locomotives running on line and their combined locomotive operation scenarios is analyzed respectively.Meanwhile,the sensitivity analysis of the influence of main factors such as rail conductivity and rail-to-ground insulation performance on stray current distribution are carried out.The result shows that the rail-to-ground voltage at the position of the running locomotives and the traction power substations has an inflection point,and the current of current drainage net accounts for the specific gravity of stray current is not the same as that at the different positions along the metro line.Compared with the locomotives running in different power supply sections,when the number and the traction power of locomotives in the same operating condition increases in the same power supply section,the amplitudes of rail-to-ground voltage and stray current increase significantly.The decrease of the rail conductivity results in a significant increase in the amplitudes of the rail-to-ground voltage and the stray current,while the aging of rail-to-ground insulation performance has a relatively obvious effect on the increase of the amplitude of stray current.Based on the penetration characteristics of traction return underground network,the influence of metro line conditions on the distributions of rail-to-ground voltage and stray current is analyzed.The calculation method of stray current under the condition of uneven distribution of electrical parameters such as rail conductivity and rail-to-ground insulation is studied.By dividing the line segments according to the condition,the calculation method of stray current in multiple power supply sections based on micro-element analysis method is improved.Based on the metro operating plan,the time-space distribution characteristics of the rail-to-ground voltage and stray current in the metro operation cycle and the time-varying law of the platform rail-to-ground voltage are also analyzed.The result shows that the calculation model and method can solve the metro stray current distribution of the uneven electrical parameters of the underground structure effectively,and it has better adaptability for the metro line operated in stages and the metro line with different corrosion aging degree of the regional underground network structure.It is possible to grape the time-varying distribution law of railto-ground voltage and stray current along the line according to the operating plan.It can provide a reference for the protection of rail overvoltage and the suppression of stray current.According to the electrical topological structure of the double-track metro power supply network and the electrical coupling characteristic of the traction return underground network structure,considering the influence of the metro track-to-track cross bond,the stray current calculation model of the underground network structure in multiple double-track metro power supply sections is established,and the distribution of stray current of double-track metro is calculated and analyzed.The result shows that the model and method consider the influence of power flow distribution of metro power supply network on power supply current of traction substations and the flow of the locomotives running on the upline and downline,and take into account the electrical coupling relationship between the upline and downline traction return underground network structure.Therefore,the calculated results of the distribution of rail-toground voltage and stray current are different from those of the single-track metro line model.In addition,the track-to-track cross bond can effectively average the rail-to-ground voltage amplitude of the upline and downline,reduce the risk of rail over-voltage at the stations,and it has an inhibitory effect on stray current under different locomotive operations of the upline and downline in the same power supply section.Based on power flow calculation of the power supply network and stray current calculation of traction return underground network structure,the calculation method and distribution characteristic of stray current are analyzed.The paper improves the calculation method of metro stray current in multiple power supply sections according to the metro line condition and the double-track metro structure.The calculation method provides a solution for analyzing the rail-to-ground voltage and stray current distribution in multiple power supply sections,and it has great significance to the protection and mitigation of rail-to-ground voltage and stray current of metro line. |
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