Abstract
Electrified transportation systems (ETSs) are affected by stray current problems impacting within and outside the right of way on reinforcement, buried metal structures and foundations. Stray current protection systems have recently been integrated in the track structure. Track electrical quantities are, thus, usually measured to assess track insulation and protection efficiency but should be backed up by additional measurements at the affected structures and installations, in order to assess their exposure and risk of corrosion. Ideally, a stray current monitoring system proceeds from the measurement of these quantities, to data collection and archival, to data presentation, analysis and prediction. Feasible sensors and probes, the impact of environmental conditions and uncertainty are considered for the measurement at the physical level. Data analysis is critically reviewed considering the variability of operating conditions and the effectiveness of each quantity as indicator of track insulation and protection efficiency. Given the normal spread of values, for data presentation and interpretation, suitable techniques are considered based on averaging, curve similarity and feature extraction, and also for the task of assessing compliance to limits or reference values and establishing a trend that may drive informed maintenance decision.
Highlights
Corrosion induced by stray current (SC) is a significant problem of electrified transportation systems (ETSs) and has attracted a lot of attention, especially for systems operated at dc, such as light railways, metros and rapid transit in general: general system analysis [1,2,3,4,5,6,7] including design optimization and defects [8,9], impact on buried conductive pipes [10,11], with both deterministic and stochastic approaches [12,13]
Provided that the train return current is known with sufficient accuracy, the stray current protection (SCP) efficiency can be measured in real time by the stray current monitoring system (SCMS), if the SCP currents are included among the SCMS quantities to measure
An opposite requisite is economizing on the number of measurement channels and probes and, as a consequence, installation and maintenance. Another element that influences the implementation is that the lack of standardized requirements and technical references makes the contractual specifications vague and weak, reduced to a simple “there must be a stray current monitoring system to check stray current protection”; there is no quantitative specification for the relevant aspects discussed in the Introduction and there are no benchmarks and no acceptance criteria
Summary
Corrosion induced by stray current (SC) is a significant problem of electrified transportation systems (ETSs) and has attracted a lot of attention, especially for systems operated at dc, such as light railways, metros and rapid transit in general: general system analysis [1,2,3,4,5,6,7] including design optimization and defects [8,9], impact on buried conductive pipes [10,11], with both deterministic and stochastic approaches [12,13]. Extrapolation that accounts for system ageing, adverse environmental conditions and maintenance procedures is not possible unless periodic monitoring is established This may be implemented as track insulation and impressed potential measurements routinely carried out by a specialized team (accessing the track during night engineering hours) or continuously by a stray current monitoring system (SCMS), operating 24/7. The SCMS features automatic logging, can remove human error (e.g., during measurements and when collecting data, especially if short time is available) and is economically more efficient (if the initial cost and savings in man-hours during system life are included) It can give indications for preventive maintenance and corrective actions. Methods to verify the accuracy and effectiveness of an existing SMCS are proposed using simulated current leakage scenarios
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