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Suggested Citation:"Chapter 5 - Conclusions." National Academies of Sciences, Engineering, and Medicine. 2020. Stray Current Control of Direct Current-Powered Rail Transit Systems: A Guidebook. Washington, DC: The National Academies Press. doi: 10.17226/25768.
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Page 65
Page 66
Suggested Citation:"Chapter 5 - Conclusions." National Academies of Sciences, Engineering, and Medicine. 2020. Stray Current Control of Direct Current-Powered Rail Transit Systems: A Guidebook. Washington, DC: The National Academies Press. doi: 10.17226/25768.
×
Page 66
Page 67
Suggested Citation:"Chapter 5 - Conclusions." National Academies of Sciences, Engineering, and Medicine. 2020. Stray Current Control of Direct Current-Powered Rail Transit Systems: A Guidebook. Washington, DC: The National Academies Press. doi: 10.17226/25768.
×
Page 67

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

65 Conclusions Chapter 5 summarizes the work done in the preparation of this guidebook, presents the main conclusions, and offers some suggestions for potential future work. 5.1 Literature Review Chapter 2 presents a literature review of existing work. The chapter includes a review and study of international and domestic standards discussing different practices available to the transit agencies and explains previous work on the control and mitigation of stray current corrosion. This literature review compiles the data, research, and criteria from a wide range of sources on stray current. The study and investigation encompass the review of theoretical, practical, and experimental approaches to address stray current leakage and corrosion issues in DC-powered transit systems. Although many transit agencies have their own standard criteria, the rationale behind their initial limiting voltage and current values is unknown. Besides investigating the historical development of stray current corrosion mitigation tech- niques, the literature review includes the study of existing stray current testing techniques and their use within a transit system. The study team looked at design criteria manuals for various agencies around the world to help perform a comparative analysis of different norms adopted by transit agencies. 5.2 Transit Agency Data Assembly, Studies, and Field Testing Chapter 3 compiles data assembled by sending questionnaires to real world, DC-powered rail transit systems inquiring about their process of SCC or their collection system. Based on the findings of the initial questionnaire, a longer questionnaire was sent to a select few agencies followed by a series of one-on-one interviews with transit agencies and corrosion consultants. The chapter also includes the findings of different SCC criteria and testing methods adopted by a diverse cross section of U.S. and international DC-powered transit agencies. The chapter elaborates on various stray current mitigation and testing procedures and their results for a real-life transit agency and for an actual startup transit system. Reviewing and compiling the results of these questionnaires and interviews highlights that in most instances the use of the limiting values for the SCC (including the limiting values set forth for slab current testing and track-to-earth testing) are drawn from industry experience rather than from actual testing and design parameters. It is also evident that most of the agencies had not conducted pre-revenue testing and did not have a regular testing and maintenance plan. The data also indicated that transit agencies are not maintaining a log of the stray current corrosion issues C H A P T E R 5

66 Stray Current Control of Direct Current-Powered Rail Transit Systems: A Guidebook nor are they tracking the expenditure to mitigate those corrosion problems. Furthermore, most of the transit agencies interviewed relied on outside consultants to conduct their stray current corrosion testing due to limited knowledge and understanding of the issue, coupled with the absence of guidelines. Corrosion staff from all the agencies interviewed mentioned that they would like to have proper guidelines and standards and a preferred management plan for stray current mitigation. The questionnaire and findings have been presented in a matrix format in the appendices and throughout Chapter 3. Stray current corrosion issues for three U.S. transit agencies are illustrated in the chapter. This compilation of a range of real world data informs a unique, holistic perspective that the track-to-earth resistance for the track largely depends on isolation methods and techniques incorporated at the time of design and construction and then onward during the maintenance of tracks. The data in this chapter also highlight that testing methods and frequency of testing should be adapted based on the age of the transit system, location of the tracks, type of the track bed, type of the structure under investigation, and the source of leakage. Chapter 3 strengthens the argument for performing baseline surveys and pre-revenue testing for a startup line. 5.3 Recommendations and Guidelines Chapter 4 uses the data collected from the literature review and stray current testing observa- tions, coupled with the information gathered from the questionnaire and corrosion consultant interviews, to develop a stepwise process for achieving a uniform stray current isolation and QC for an embedded track. This chapter highlights that it is relatively easier to implement stray current isolation, mitigation, and collection options on a newer transit system with proper foresight and planning by following the logical sequence of the design process than to maintain a stringent maintenance and testing regime on an older system. A significant part of the work described in this guidebook addresses the design of SCC methods, sustainability of SCC, and the control of rail-to-earth voltages for DC-powered rail transit systems for North American transit agencies. The guidebook is to be used by tran- sit agencies, design, and maintenance practitioners and to influence new system construction, extensions, and maintenance and operation of existing systems. The guidebook includes, for the first time under one cover, the design and sustainability of SCC for DC-powered rail transit systems, with a primer that explains all significant issues in readily understandable terms for a non-technical audience. It is the first compilation of data that identifies the domestic and international body of knowledge pertaining to principles, procedures, methods, and criteria for achieving and documenting acceptable levels of stray current and rail-to-earth potential. 5.4 The Potential for Future Work This synthesis report or guidebook includes recommended procedures for achieving stray current isolation and mitigation techniques. Areas were identified that may need further development. These include, but are not limited to, the following: • Simulation modeling to calculate and design for stray current leakage: Use of software modeling to conduct a thorough analysis of leakage currents and their proposed mitigation techniques. The use of a stray current simulation model, along with traction power design analysis, at the

Conclusions 67 inception of DC transit system track design would prove to be an invaluable proactive step in achieving the desired SCC. • Material lost and cost impact: The research scope reveals the potential corrosion impact on the structure for different scenarios and the total stray current leakage. However, key data missing are the potential costs of the SCC. This cost can be broken down into the cost to carry out the isolation to avoid the stray current corrosion design and the cost to perform potential mitigation measures once the problem is identified on an existing system. A means to ascertain these costs could help transit owners in making key decisions for providing the corrosion mitigation measures at the time of initial construction versus during the transit service or revenue phase. The authors also identified the following areas as potential knowledge gaps during the research. The areas are touch potentials and their correlation with SCC and mitigation, equip- ment grounding and system grounding, optimum maintenance cycles and essentials, and methods for anonymously sharing costs and experiences across the various transit agencies.

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Stray current and stray current–induced corrosion remain concerns among transit agencies, electrolysis committees, utility owners, providers, and electric railway carriers across the globe. It is easier to implement stray current isolation, mitigation, and collection options on a newer transit system with proper foresight and planning by following the logical sequence of the design process than to maintain a stringent maintenance and testing regime on an older system.

The TRB Transit Cooperative Research Program's TCRP Research Report 212: Stray Current Control of Direct Current-Powered Rail Transit Systems: A Guidebook allows transit agencies, design, and maintenance practitioners to influence new system construction, extensions, and maintenance and operation of existing systems.

Improving the Safety and Sustainability of Stray Current Control of DC-Powered Rail Transit Systems (PowerPoint slide deck) highlights the research review and guidebook development.

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