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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In this paper, we propose the enhancement of existing power system stability analysis techniques through the use of a proposed set of potential energy indices, applied for observing the separation of generators into critical sets during transient events. This proposed potential-energy-based description of system transient stability behavior permits the formation of a critical generator cutset, which is then used in a quantitative single machine equivalent (SIME) energy-function analysis of system stability. The derivation of the method will show that the proposed potential energy indices do not rely on a detailed representation of the network model, making the indices suitable for use in a variety of applications. This method enhances the current capabilities of SIME analysis for pre-fault offline stability studies, but may also be useful for near-real-time stability analysis, owing to the lack of dependence of the proposed potential energy indices on the network parameters. The ability to utilize the proposed indices without the need for network parameters or fault location information, typically obtained from updated SCADA data, potentially allows the proposed method to be applied for real-time stability analysis utilizing only PMU input data.

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