The Influence Analysis of the Power Grid Topology on the Stray Current Invading Transformers

During the operational process of the metro lines, the traction current discharged from the working grounding wheels flows back to the terrestrial traction substations through the steel rail, as the DC stray current may be generated due to the poor insulating condition between the rail and the ground. The characteristics of the DC stray current invading the transformer settled at the terrestrial substation is affected by a series elements including the train's operational condition, the ‘rail -ground’ transition resistance, the soil structure and power grid topology. Exploring the influence factors of the stray current lays the foundations for further preventing the negative impact brought from stray current. In order to analyze the influence of the power grid topology on the stray current invading transformers, a coupling model involving the up and down metro lines with the power grid is built, based on the finite element method (FEM). Based on this FEM model, the variation of stray current invading the transformer is analyzed along with the relative position between the power grid single circuit and the metro line varying, meanwhile the variation of the power grid's topology is also considered. It is found that with the complexity of the power grid topology, the total amount of stray current invading the power grid increases, whereas the stray current flowing through the majority of the transmission lines decreases. In addition, no matter the two transformers constituting the power grid circuit are on the same side or on the opposite side of the metro line, the stray current invading the grid tends to increase with the reduction of the angle between the metro line and the power grid circuit.