DC-electrified traction systems are a potential source of stray current that may corrode internal and external structures and installations. The stray current intensity depends on several factors (traction current, rail insulation, concrete mat and piers resistance), that are accounted for in the proposed model. The case of a viaduct and a victim-buried pipeline is considered in detail, and the estimated impressed voltage on the pipe is compared successfully with experimental results.

A comprehensive analysis of published experimental data and formulae for the determination of the electrical parameters of railway traction lines is performed. Several results from different authors are presented with particular attention to different assumptions and environmental conditions. Additional measurements were performed over the 5 Hz-200 kHz frequency range on a line section purposely prepared at La Spezia Railway Station (Italian State Railways). Theoretical formulae are considered and their validity is checked against experimental data. There is general accordance within common variations of the most critical parameters; calculations and measurements agree over the entire frequency range and are very accurate in the frequency range 50 Hz-50 kHz, where significant conducted disturbance lies.

The problem of the determination of the real distribution of the return current in electric railway traction systems is considered. One or more conductors (depending on the specific supply system) are purposely set up to carry the traction return current flowing from the rolling stock axles back to the supply (i.e., substation); yet, part of the return current flows through signalling conductors (disturbing current) and through the earth, depending on the value of the electric parameters of the system, on the circuit arrangement, and on the relative position of the supply, the rolling stock, and signalling devices. The amplitude (as a percentage of the total return current) of the disturbing current may be high enough to cause interference to signalling. This work investigates the behavior of the return current in AC and DC electric railway systems, on the basis of a reference system for the variation of the most important electrical parameters. The definition of the transfer function between the return current and the signalling circuit variables is an important element for the compatibility analysis between train detection systems, rolling stock and infrastructure, to promote the cross-acceptance of rolling stock in Europe and abroad.

Leakage currents from a dc-electrified railway requires careful consideration throughout the life time of the railway. The design objective is to minimize the current leakage from the railway return path (the running rails for a dc-electrified railway, with possibly additional conductors in parallel for ac-electrified systems). For this objective to be met, the design needs to account for foreseeable misuse during the construction phase (i.e., the lack of independence between the earthing system and the stray current collection system, due to space and construction exigencies in a viaduct) and degradation of insulation due to ageing and poor maintenance. Perhaps, more importantly, other influences, such as the train characteristics, time tabling, headway, multiple train movement, etc., need consideration to determine the worst case leakage current and, thus, the ability to define appropriate mitigations with respect to stray current management. In this paper, we describe the implementation of an integrated model for the assessment of stray current for a dc-electrified railway, in which these factors are considered. We provide an analysis of the stray current magnitude under worst case train operating conditions (i.e., multiple trains with a 90-s headway accelerating) and highlight factors that determine the efficiency of the stray current collection system. The integrated model presented enables a detailed assessment of all factors impacting the stray current magnitude, as well as an assessment of the overall performance of the stray current collection system.

An electric traction system supplied at 2 /spl times/ 25 kV with autotransformers (ATs) is considered. The conductors' arrangement is that of the new European High Speed Railway Line (HSRL) under construction: The overhead supply conductors in contact with the train pantograph are connected to a symmetrical circuit (the feeder) with the purpose of current balancing; the traction return current flows from the rolling stock axles back to the supply (i.e., substation) through the traction rails and additional return conductors. The test campaign carried on the Rome-Naples HSRL allowed the validation of the multiconductor transmission line model used for system analysis. Measurements were performed in normal system configuration (2 /spl times/ 25-kV supply) and degraded configuration (1 /spl times/ 25 kV with AT and feeder not operating). Metrological issues (accuracy and consistency) are detailed for the presented results.

The problem of determination of the accurate distribution of the return current in AT (autotransformer) electric traction systems (supplied at 2/spl times/25 kV) for High Speed Railways is considered. The path of the traction return current flowing from the rolling stock axles back to the supply (i.e., substation) is composed of the traction rails and additional earth potential conductors. The overhead supply conductors in contact with the train pantograph are connected to a symmetrical circuit (the feeder) with the purpose of current balancing. This arrangement and its influence on current to earth are considered: the return current divides among rails (as signalling disturbing current) and earth, depending on the value of the electric parameters of the system and the earth and on the circuit arrangement and on the relative position of system devices. The amplitude (as a percentage of the total return current) of the disturbing current may be high enough to cause interference to signalling. This work investigates the behavior of the return current in AT electric railway systems, on the basis of a reference system for the variation of the most important electrical parameters.