Simulation model for drainage protection of earth-return circuits laid in stray currents area

Abstract Proper design of drainage protection against stray currents requires the knowledge of current and potential distribution along the rails of the d.c. railway system and the installation to be protected (cable, pipeline, etc.). Usually, a calculation model is used in which these earth-return circuits are treated as separate. In reality, the protected structure and the rail can be placed close together and conductive coupling between them exists, resulting in different current and potential distributions along both structures when comparing with the case of the separate structure. In this paper, a calculation model is presented in which an interchange of currents flowing along both structures – equivalent rail and protected structure – is taken into account. The formulae in closed forms are derived for calculation of such parameters as longitudinal current, potential to the remote earth, and potential to the adjacent earth. An attempt to incorporate electrode kinetics into the model is also made. In the simulation model, the polarization phenomenon is modeled by an iteratively calculated non-linear resistance. Example calculations are carried out in which the influence of the resistance of the drainage connection and the drainage current on the protection efficiency are examined. The relations presented may be useful at the design stage of protection systems containing electric drainages.