| As an important part of urban rail transit,the rapid development of metro brings huge benefits to the development of the city,and at the same time,it brings more adverse effects to the Power Grid.The metro adopts DC power supply,and the running track of the metro locomotive is also used as the return path of locomotive DC load current.Because of the DC resistance of the rail,DC current will generate voltage drop on the rail.The rail of the metro cannot be completely insulated from the earth,and part of the current is leaked to the earth.The distribution field of the Earth Surface Potential(ESP)is formed near the metro.The potential difference between different grounding devices near the metro will form a grounding circuit,causing DC current to flow into the AC Power Grid.The DC current in the grounding circuit will cause the DC bias for the grounding transformer,increase the harmonic content,and cause a variety of harm to the Power Grid equipment.In this paper,the calculation model of earth potential distribution along the metro is established,and the experimental platform of earth potential is built.Combined with theory and simulation analysis,the action mechanism and influencing factors of the metro to the grounding circuit of the Power Grid are studied.The main contents of the paper are as follows:(1)The structural differences between different types of urban rail transit are analyzed,and the more significant reasons for the influence of the metro to the Power Grid are more significant than that of other urban rail transit methods.Based on the equivalent complex image method,the Green's function expression of earth potential is solved.The calculation model of earth potential distribution along the metro is established,and the equivalent parameters of the metro system in the model are quantified.The distribution of ESP is analyzed by theory.(2)The distribution characteristics of ESP along the metro with the single and bilateral power supply are studied by programming the earth potential distribution program in MATLAB and CDEGS.The factors that affect the distribution of ESP,such as Metro locomotive current,location,length of power supply section,transition resistance,soil resistivity,metro line intersection and parallelism,are simulated and analyzed.(3)A network field-circuit coupled model of DC distribution network is established,and the difference between the calculation method of current distribution in the grounding circuit of the metro station during the steady and transient process is analyzed.The simulation of grounding loop network in CDEGS is carried out.The influence of the number of grid loops,the area of the grounding grid and conductor distribution density on the amplitude and distribution of the DC current in the earthing loop of the Power Grid is studied.(4)The simulation experimental platform for the earth potential distribution and the grounding circuit current along the subway is built,and the experimental simulation of the earth potential of various different experimental parameters is carried out through several experiments to improve the experimental scheme of the earth potential simulation.The grounding loop current under different circuit resistance is simulated to verify the correctness of theory and simulation.Based on the research contents,this paper put forward relevant preventive measures. |
PDF Full Text Request