BACKGROUND
Direct current (DC)-powered transit systems have been faced with major repairs and modifications to signal and traction power systems because of ineffective negative return rail isolation. An indication of the magnitude of the financial costs is cited in a comprehensive research report published by the IEEE in the 1990s, where it was estimated that a major portion of the estimated $500 million per year from stray current corrosion losses was borne by DC-powered transit properties and the surrounding infrastructure assets. This figure does not take into account the costs associated with signal problems and repairs.
The cost to DC-powered transit systems has been increasing steadily due to stray current issues. 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? How large is the transit corridor for protection? What levels of track-to-earth and rail-to-rail resistance are required? What maintenance testing is required? What costs and safety issues are related to signal system failure? How is maintenance testing conducted? The need for specific criteria for these areas is required for the transit community to make appropriate decisions concerning the costs and implementation of control measures.
Research is needed to develop a Guidebook on design and sustainability of stray current control and control of railcar-to-earth and rail-to-earth voltages for DC-powered rail transit systems, including (a) a primer that explains all significant issues in readily understandable terms for non-technical people, (b) guidelines addressed to design and maintenance practitioners (e.g., recommended hazard analysis and safety certification checklist items), (c) case studies (third rail and overhead contact), and (d) recommendations for further research.
Implementation of results from this research may significantly reduce start-up and ongoing problems in new and existing DC-powered rail transit systems, including signal failures; controlling railcar-to-earth and rail-to-earth voltages; and the loss of public metallic assets over time, owned by transit agencies, municipalities, public utilities, and others. System safety and stability may be significantly improved, while maintenance costs and train delays may be substantially reduced. This research could potentially influence new system construction, extensions, and maintenance and operation of existing systems.
OBJECTIVE
The objective of this research is to develop a Guidebook on design and sustainability of stray current control and control of railcar-to-earth and rail-to-earth voltages for DC-powered rail transit systems. The Guidebook shall include (a) a primer that explains all significant issues in readily understandable terms by non-technical people, (b) guidelines addressed to design and maintenance practitioners (e.g., recommended hazard analysis and safety certification checklist items), (c) case studies (third rail and overhead contact), and (d) recommendations for further research.
TASKS
Task descriptions are intended to provide a framework for conducting the research. The TCRP is seeking the insights of proposers on how best to achieve the research objective. Proposers are expected to describe research plans that can realistically be accomplished within the constraints of available funds and contract time. Proposals must present the proposers' current thinking in sufficient detail to demonstrate their understanding of the issues and the soundness of their approach to meeting the research objective.
Phase I
Task 1. Identify the domestic and international body of knowledge that pertains to principles, procedures, methods, and criteria for achieving and documenting acceptable levels of stray current and rail-to-earth potential. Include, at a minimum, existing and proposed standards (and the background used to develop those standards), methods of measurement, implementation, and compliance. Review the results of relevant research on stray current, including practices, performance data, research findings, lessons learned, emerging technologies, and other related information. Review relevant literature for rail-to-earth potential effects on people and animals, as well as stray current effects on tracks, signals and communications, utilities, structures, and equipment.
Task 2. Survey DC-powered rail transit systems to collect pertinent information on design criteria; technical/performance specifications; hazard analysis; safety certification; constructability issues; monitoring and maintenance of stray current controls; and agency criteria for rail-to-earth potentials.
Task 3. Identify a representative sample of at least 6 DC-powered rail transit systems for case studies that illustrate effective practices for stray current control and control of railcar-to-earth and rail-to-earth voltages for DC-powered rail transit systems. This sample should include a mix of old and new third rail and overhead contact systems. Explain why the chosen systems were selected. Explain what information is to be gathered in the case studies, such as decision trees and standard procedures.
Task 4. Based on Tasks 1 through 3, identify the key decision metrics associated with implementing and maintaining stray current control and safety control of rail-to-earth potentials. For each of the case studies, identify how their stray current control systems were selected, their standards or regulatory frameworks, and any oversight agency involvement. Identify guidelines that are available in citable versions and those which will require further development. Prepare a detailed outline for the draft Guidebook and a prioritized list of identified guidelines recommended for further development. Prepare an updated Phase II work plan for developing guidelines.
Task 5. Prepare an interim report documenting the results of Tasks 1 through 4.
Phase II
Task 6. Develop guidelines per the approved Phase II work plan.
Task 7. Prepare a Guidebook of recommended practices and design and maintenance criteria associated with stray current controls and prevention of excessive rail-to-earth potentials using both passive and active techniques. The Guidebook shall include (a) a primer, (b) guidelines, (c) case studies, and (d) additional research needs. The primer in the Guidebook should include topics such as earthing strategies and their cost-effectiveness; leakage prevention; electrical continuity of concrete reinforcement; stray current test stations; track-to-earth resistance; rail-to-rail resistance; impedance bonding; power system modeling; and galvanic and impressed current cathodic protection.
Task 8. Submit a final report documenting the entire research effort. Include, as separate deliverables for use by transit agencies, an updated PowerPoint presentation, an executive summary of the project, and a Guidebook that provides a recommended decision-making process and guidelines for selecting appropriate stray current control design and maintenance practices. The guidelines on stray current control must be in a format suitable for use by practicing engineers for design and maintenance.
