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Running rails are used as the return path for the train current in most DC electrified rail transit systems. The resultant rail voltage causes stray current to return to the DC supply source via other paths, such as nearby metallic infrastructure. Stray current is the main cause of corrosion in metallic parts located in the railway proximity. This study reviews various earthing schemes including thyristor earthed, diode earthed, floating and solidly earthed and corrosion phenomenon in DC railway traction systems. Then, based on simulations, a comparative study of safety and corrosive effects of the stray current, produced by various earthing schemes is presented. The study is part of the concept designed to control the stray current at Tehran Metro Line 3. Results of the study have been validated by simulation studies using a multi-train simulation software tool and the system data from Tehran Metro Line 3. The study shows some interesting findings such as corrosion damage increases near traction substations.

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This article presents a state-space model with time-delay to map the relationship between known input-output data for discrete systems. For the given input-output data, a model identification algorithm combining parameter estimation and state estimation is proposed in line with the causality constraints. Consequently, this article proposes a least squares parameter estimation algorithm, and analyzes its convergence for the studied systems to prove that the parameter estimation errors converge to zero under the persistent excitation conditions. In control system design, the U-model based control is introduced to provide a unilateral platform to improve the design efficiency and generality.A simulation portfolio from modeling to control is provided with computational experiments to validate the derived results.

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The neutral wire in most existing power flow and fault analysis software is usually merged into phase wires using Kron's reduction method. In some applications such as fault analysis, fault location, power quality studies, safety analysis, loss analysis, etc., knowledge of the neutral wire and ground currents and voltages could be of particular interest. In this paper, a general short circuit analysis algorithm for three-phase four-wire distribution networks, based on the hybrid compensation method, is presented. In this novel use of the technique, the neutral wire and assumed ground conductor are explicitly represented. A generalized fault analysis method is applied on the distribution network for conditions with and without embedded generation. Results obtained from several case studies on medium and low voltage test networks, with unbalanced loads, for isolated and multi-grounded neutral scenarios, are presented and discussed. Simulation results show the effects of neutrals and system grounding on the operation of the distribution feeders.

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