Analysis of the earth potential problems of the electrified railway

Abstract

The traction return circuit of the electrified railway is usually that the overhead contact line system (OHL) transmits current to the electric locomotives, then the current returns to the traction substations by the rails and earth. That is, it belongs to the unbalanced power-supply system that uses the rails and earth as return conductor. Near the point of earth that current enters into the rails, it causes the earth potential to rise, and it cause dangerous impact or interference impact on the earthed telecommunication equipment and lines by the way of earth resistance coupling. Earth is assumed to be a homogeneous medium with an infinite plane in the existing theoretical calculation of earth potential. However, most of geology in nature where railway passes belongs to irregular nonhomogeneous medium. It raises a problem for theoretically calculating the earth potential. Furthermore, during the processes of survey and design of the electrified railway in the past, many technicians cited the earth resistivity that can be used for calculating mutual inductance coefficient to the formulas of earth potential. This method is wrong for calculating the earth potential in the nonhomogeneous medium. It may cause multiple error for calculating the earth potential and slip in adopting the protective measures for the earth potential. In view of the above-mentioned circumstances, this paper analyzes the characteristics of the interference sources and impact ways, and presents a new method for solving the problem of calculating the earth potential in the nonhomogeneous medium.