2001 IEEE/ASME JOINT RAIL CONFERENCE TORONTO, ONTARIO, CANADA April 17-19,2001 ANALYSIS OF STRAY CURRENT, TRACK-TO-EARTH POTENTIALS &SUBSTATION NEGATIVE GROUNDING IN DC TRACTION ELECTRIFICATION SYSTEM

In the first part of the paper, we will look at a stray current model under the ideal conditions with uniformly distributed track-to-earth resistances and develop the track-to-earth potentials and stray current relationships within a segment of track. We then will expand the model to include buried metallic structures in the vicinity of the track using field theory to calculate the potential gradients generated due to flow of rail current and show that a potential difference experienced by a crossing or paralleling underground structure that traverses these gradients could cause stray current corrosion. We will discuss the limitations of these models with the actual conditions such as non-uniform track-to-earth resistances, non-uniform soil resistivities. In the second part, we will look at the stray current model when there are inadvertent breakdowns in the track insulation. The points of rail insulation breakdown may be approximated using the spherical ground electrode model and equipotential lines to illustrate the flow of stray current. Common grounding of the substation negative bus, substation ac ground mat and electric utility