Stray Current Control of Direct Current-Powered Rail Transit Systems: A Guidebook (2020) / Chapter Skim
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Pages 34-46
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34 Stray Current Control Design, Mitigation, and Testing of DC Rail Transit Systems Stray current leakage and the corrosion caused by this leaked current in DC traction power systems have combined to be an ongoing issue especially in slab or embedded tracks. These tracks typically run through urban traffic areas, city centers, tunnels, and between utility lines.
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Stray Current Control Design, Mitigation, and Testing of DC Rail Transit Systems 35 that they were not aware of any stray current corrosion issues at their system. The rest did not respond to this query.
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36 Stray Current Control of Direct Current-Powered Rail Transit Systems: A Guidebook Out of the 35%, some of the agencies completed the questionnaire with a request for anonymity. Appendix C presents the long questionnaire.
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Stray Current Control Design, Mitigation, and Testing of DC Rail Transit Systems 37 The feedback from general consultants indicated the need for experienced consultants for stray current testing and control or for focusing on getting the transit agency staff more trained and comfortable with carrying out stray current measurements. The consultants also unanimously agreed that there is a dire need for a guideline to address the design, testing, and maintenance of the stray current control process.
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38 Stray Current Control of Direct Current-Powered Rail Transit Systems: A Guidebook The track is mostly embedded (95%) with an approximately 1-mile-long direct fixation track and a small section of ballasted track.
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Stray Current Control Design, Mitigation, and Testing of DC Rail Transit Systems 39 both LRT and bus rapid transit systems and a dedicated chapter on corrosion control comprising stray current corrosion. The transit agency carries out systemwide stray current testing such as track-to-earth resistance, track slab stray current flow, and audio frequency tracing measurements, if needed.
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40 Stray Current Control of Direct Current-Powered Rail Transit Systems: A Guidebook Conclusion When asked what the key issues are, the Transit Agency 1 staff indicated that they would rather not construct an embedded track within the urban area due to high traffic volume and regular maintenance issues. In a situation where there is no other alternate route, they would like to ensure that the rail is completely isolated (use of modified rail boot)
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Stray Current Control Design, Mitigation, and Testing of DC Rail Transit Systems 41 60% of the track miles are underground, with more than 470 station locations. The systems design represents three distinct styles, with the primary difference being the platform lengths.
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42 Stray Current Control of Direct Current-Powered Rail Transit Systems: A Guidebook Findings from Testing and Corresponding Corrosion Issues Because this system is older, issues are inevitable and they have been fixed in the past. However, the recent upgrades to the tracks and the overall system have rendered the previous corrosion records obsolete.
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Stray Current Control Design, Mitigation, and Testing of DC Rail Transit Systems 43 systems. The substation spacing varies from 0.5 miles to 2 miles for both the LRT and HRT systems.
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44 Stray Current Control of Direct Current-Powered Rail Transit Systems: A Guidebook • Areas of low track-to-earth resistance along the lines. • Possibility of a substation being grounded, which results in stray current leakage.
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Stray Current Control Design, Mitigation, and Testing of DC Rail Transit Systems 45 • Track slab electrical continuity and current flow, and • Cell-to-cell potential gradient measurements. This testing occurs every 5 years based on the track performance and current leaks.
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46 Stray Current Control of Direct Current-Powered Rail Transit Systems: A Guidebook help transit agencies in keeping the stray current leakage to a minimum but will also help in implementing QC measures. The implementation of recommendations and best management practices in these guidelines, coupled with a preplanned maintenance regime, comes with an initial cost; however, such proactive measures will help reduce the unpredictable and repetitive cost of repair and breakdown down the line.
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