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1 This guidebook documents best practices for those seeking guidance on design, main- tenance, and testing of stray current control for direct current (DC)-powered rail transit systems. The guidebook includes the study of both national and international transit agencies and is formatted as a reference guide for finding the information and resources needed to implement and evaluate not only stray current control (SSC) and mitigation measures but also the testing and maintenance strategies for transit operators. The overall objective of the Transit Cooperative Research Programâs Project D-16 was to develop a guidebook on design and sustainability of SCC and control of railcar-to-earth and rail-to-earth voltages for DC-powered rail transit systems. The guidebook includes (a) a primer that explains all significant issues in readily understandable terms for non technical people, (b) guidelines addressed to design and maintenance practitioners, (c) historical performance data (based on agency interviews) of third rail and overhead contact, and (d) recommendations for further research. Besides achieving the preceding objectives, the guidebook also addresses the following fundamental questions: ⢠What is stray current? ⢠How do I know I have it? ⢠What do I do to mitigate it? ⢠What levels of stray current are acceptable? ⢠What levels of rail-to-earth potential are acceptable? ⢠What levels of track-to-earth and rail-to-rail resistance are required? ⢠What maintenance testing is required and how is the testing to be conducted? This guidebook is the recent effort undertaken by the Transit Cooperative Research Program (TCRP) to provide a user-friendly framework of consolidated guidelines and recommendations that will help in mitigating or potentially eliminating stray current leakage from DC-operated rail tracks by using the data collected from transit agency and corrosion consultant interviews, stray current corrosion survey questionnaires, and field testing. The guidebook presents a progression from initial considerations of establish- ing a baseline survey for investigating the potential stray current risk to recommending mitigation and collection methods during construction and operation. The guidebook also recommends potential testing and maintenance strategies to control or minimize the leakage of stray current. There are five chapters plus five appendices: Chapter 1 defines the methodology of the research done in the preparation of the guide- book and explains the various terms used in the subsequent sections of this guidebook. S U M M A R Y Stray Current Control of Direct Current-Powered Rail Transit Systems: A Guidebook
2 Stray Current Control of Direct Current-Powered Rail Transit Systems: A Guidebook Chapter 2, which is the literature review section, gives a brief outline of the process of corrosion and the different traction power alternatives available to the transit agencies. This chapter documents and explains previous work on the control and mitigation of stray current corrosion, including the review and study of national and international design criteria and standards. The study and investigation encompass the review of theoretical and practical approaches, as well as experimental approaches, to address the stray current leakage and stray current corrosion issue in DC-powered transit systems. Some of the literature studied includes calculations for limiting stray current leakage by using various mitigation methods; this aids in justifying the potential enforcement of the recommended limiting values and testing requirements. Chapter 3 discusses the process of SCC or collection system at different real-world DC-powered rail transit agencies, including their design criteria, operation modes, physical environment, track construction type, and testing methods. The data for this discussion were assembled by communicating with the respective transit agency representatives by using custom-made questionnaires (questionnaires along with the responses are pro- vided in the appendices). In-person interviews of stray current corrosion consultants and conducting face-to-face interviews and testing of selected transit agencies supplemented the data. Additionally, information on a select few transit systems was acquired through study of the transit agency performance, testing procedures, maintenance standards, and actual stray current testing. The chapter elaborates on the various stray current testing procedures and their results for existing transit systems, including a startup transit system in the United States and an international transit operator. Chapter 4 provides a synopsis of the stray current issue and the best way to foresee its effects, thereby developing a plan of control and mitigation. A stepwise process is devel- oped for achieving uniform stray current isolation and quality control for all forms of tracks using the data collected from the literature research, U.S. and international transit agency interviews, meetings with corrosion consultants, and stray current testing observations. Chapter 5 summarizes the review of work done, presents conclusions drawn and objec- tives achieved, and describes potential future work. Appendices A through E present a short survey, responses from transit agencies, a long questionnaire, responses from transit agencies, and a decision matrix.
