Transit Traction Power Cables: Replacement Guidelines (2024)
Chapter: Summary
SUMMARY
Transit Traction Power Cables: Replacement Guidelines
The transit industry in the United States uses insulated cables for traction power supply and negative return cables between traction power substations, tie switches, and points of delivery to transit vehicles, whether a third (contact) rail or an overhead contact system (OCS). Insulated cables are also used for power feeds from utilities at medium voltages such as 15 kV. In addition, third-rail systems use jumper cables to provide continuity of power around third-rail gaps and expansion joints. The conductor insulation system is used for traction power cables, lower-voltage power distribution, and signal/communication systems. The entire system is typically designed for 30 years of operation. Many of the transit systems in the United States have been in operation for 30 years or more with the original cables still in service.
Many cables in transit tunnels have failed because of water penetrating the cable insulation, damaging the insulation and corroding the copper conductors. In some subway tunnels, the conduits themselves have degraded to the point where they cannot be cleaned out and used for their original purpose. Transit systems in the United States have experienced cable fires and system-wide closures due to the degradation of traction in power cable insulation. In recent years, storms in United States have inundated transit tunnels and exacerbated cable life-cycle concerns.
The main objective of this research was to develop guidelines to determine when to replace transit system cables. The research includes a study of current practices for (1) assessing insulation aging, and (2) replacement of cables before failure, including (a) approaches used in transit systems for which there are no monitoring programs or testing systems, (b) factors affecting the life of cables, and (c) effective practices of transit agencies.
This guide presents research on the replacement of transit traction power cables. A survey of transit agencies, practitioners, and suppliers was carried out for the research. After reviewing the survey results, 10 case studies were developed. As part of the case study investigation, selected agencies were examined in detail. Their problems and solutions were analyzed to gather information about typical scenarios, and extended participation of their personnel contributed to the research.
The guide presents practical solutions to the challenges faced by transit agencies by covering the agencies’ experiences and practices. Practitioners are provided answers to some critical questions along with detailed investigations, survey results, and case studies. In addition, an optimization procedure for cable replacement and life evaluation was developed. Finite element analysis results are also presented. In the case studies, best practices from various states are shared, while opportunities and challenges are addressed. Since the conditions and types of systems may affect the decision-making process and asset management strategy, agencies have developed unique approaches to the problems they have experienced. While presenting these unique approaches, the guide provides resources for practitioners to use in their decision-making processes and in responding to the issues they face.
