Research On Electromagnetic Coupling Relationship Between Subway And Power Grid

Due to the good speed regulation performance of the DC motor,the DC power supply system is widely used in the subway,causing the subway to cause the DC bias fault of the grounding transformer in the surrounding AC power grid,thereby affecting the normal operation of the AC power grid.Current research believes that the stray current of the subway will cause uneven ground potential distribution on the adjacent ground.There is a potential difference between the grounding grids of the two substations,which will cause DC current to invade the AC grid and cause the DC bias fault of the grounding transformer.This paper studies the feasibility of generating magnetic bias current through electromagnetic coupling between the space electromagnetic field and nearby transmission lines while the traction power supply system provides energy for the subway.Through the analysis of the source of the DC bias of the power grid,it is of great practical significance to the construction of the subway,to control the DC bias of the power grid,and to ensure the normal operation of the power grid.This article focuses on the following parts:Analyzed the rail transit structure and power supply system,established the electromagnetic coupling model between the overhead catenary of the subway and the nearby transmission lines,and deduced the static induced voltage of the catenary on the transmission line under different spatial position relationships between the transmission line and the catenary.The dynamic induced voltage on the line by the moving magnetic field generated by the movement of the car body.CDEGS simulation software was used to establish a transmission line-catenary simulation model,and the influence of the parallel length of the grid,the relative displacement difference,the lines of different heights in the grid system,and the current of the catenary and return rail on the induced voltage of the grid was obtained.The study found that the induced voltage increases linearly with the increase of the parallel distance;decreases with the increase of the relative displacement,and the magnitude of the decrease is first large and then small;it increases with the height of the transmission line;it increases proportionally with the increase of the catenary current.It is found that the induced voltage changes with the dynamic position of the car body.The dynamic induced voltage first increases and then decreases with the increase of the parallel length of the subway and the transmission line,and decreases with the increase of the distance between the train and the transmission line.The small ones are getting faster and faster.Field measurements were carried out on multiple subway lines in Guangzhou,realtime monitoring of the induced voltage signals caused by the subway,restoration of the catenary current and the induced voltage signals of the moving car body on the transmission line,and found that the subway traction power supply system has a strong impact on the AC power grid.The coupling effect.The induced voltage of the viaduct is about 15% higher than the induced voltage of the tunnel.The preliminary judgment is the shielding effect of the tunnel steel bar and soil on the magnetic field.After preliminary calculation and actual measurement,the static induced voltage of 1km transmission line can reach 1.5V,and the dynamic induced voltage accounts for about20%-50% of the static induced voltage.Based on the actual parameters of the transmission line network,a DC model including the transmission line,grounding transformer,grounding grid,pole tower,and overhead line ground loop near the subway was established.Taking the 1.5V induced voltage of a 1km transmission line as an example,the DC resistance of transformer windings,Research on the distribution of magnetic bias current by substation grounding resistance and transmission line DC resistance has found that the substation grounding resistance is the main factor affecting the bias current,followed by transmission lines,and transformer windings have the least impact.When the train starts,the peak value of the bias current caused by the static induced voltage of the 6km transmission line can reach about 10 A,and the bias current caused by the dynamic voltage generated by the train movement can reach 5A.It is found that the spatial electromagnetic coupling between the subway and the power grid is an important factor that can not be ignored in the DC bias of the transformer.