Distribution Characteristics And Suppression Methods Of Metro Stray Current In Urban Area Power Grid

With the rapid development of urban rail transit,the leakage of metro stray current is becoming more and more serious.Up to now,the problem of DC bias of transformer has occurred in many cities with metro.More and more attention has been paid to the influence of metro stray current on urban area power grid.As the distribution characteristic of metro stray current in urban area power grid is not clear,the optimization of suppression methods for DC bias of transformer caused by metro stray currents is rarely involved,and the overall management ideas and suppression effect of DC bias based on urban area power grid need to achieve further breakthrough,this paper establishes a simulation model of the distribution in the urban area power grid of metro stray current and analyzes the measured data to study the distribution law and characteristics of the metro stray current in the urban area power grid.Finally,the optimal suppression method of DC bias of transformer caused by metro stray current is studied according to the conclusions.In order to clarify the distribution of metro stray current in urban area power grid,the simulation model of the distribution of metro stray current in urban area power grid is built based on PSCAD/EMTDC.This paper puts forward the equivalent modeling method of substation with 220 kV and above voltage level,the equivalent of power grid with 110 kV and lower voltage level,the calculation method of equivalent load,the equivalent simulation of geographical location distribution of each substation,the equivalent construction of the transmission line and its lightning protection line,the equivalent method of the metro stray current intruding into the power grid,and so on.Finally,the correctness and feasibility of the model are verified and analyzed according to the measured data of DC at the neutral point of each transformer.The conclusion shows that the model can be used to study the distribution and influencing factors of metro stray current in urban area power grid.According to the simulation model of metro stray current distribution in urban area power grid,the distribution characteristics of metro stray current are studied.Based on the measured data of DC at neutral point of transformer,the correlation between metro stray current and metro operation is analyzed,and the influence of closed loop network operation mode on the distribution of metro stray current is studied.The simulation results show that metro stray current exists in the transmission line,the lightning protection line and the ground,and the DC at the neutral point of the transformer increases when the leakage reactance of the transformer or the nearby earth resistivity decreases.The change of the nominal area of the lightning protection line and the voltage fluctuation have little influence on the metro stray current distribution,but the voltage fluctuation makes the DC bias of the transformer more serious.The research on the suppression of DC bias in urban area power grid with autotransformer needs to be considered as a whole.The analysis of the measured data shows that the amplitude of the metro stray current in the urban area power grid is highly related to the density of the passenger flow,and its amplitude fluctuation and its frequency spectrum are related to the departure interval period.the operation mode of closed loop network makes the invasion of metro stray current into urban area power grid more serious.To realize the optimal suppression of DC bias caused by metro stray current,according to the distribution and characteristics of metro stray current in urban area power grid,the optimal configuration of capacitor blocking device is obtained by the effective establishment of objective function.The scheme takes into account the probability of the distribution of metro stray current affected by capacitor blocking device.The analysis of the calculation example shows that the scheme has a good effect on the suppression of the DC bias and effectively saves the cost of suppression.The effectiveness and rationality of the algorithm is further verified by the optimization of the suppression scheme under different limit values of DC at the neutral point of transformer.The comparison and analysis with the traditional suppression scheme show that this method can further improve the suppression efficiency of the DC bias caused by metro stray current.