Developing a Guide for Transit Traction Power Cables (2024)
Chapter: 7 Conclusions
Chapter 7. Conclusions
The guide was prepared as part of the TCRP C-24 Project. Through this research, several significant results were obtained regarding the traction power cables. As part of the research, a guide was produced for “Replacement of Transit Traction Power Cables” by reviewing the current practices such as ongoing maintenance and cost-effective strategies in the industry, which will help industry personnel in their practices with power cables. A survey was administered to transit agencies, practitioners, and suppliers to answer these questions. Agencies’ responses provided data on current practices. Selected case studies of different locations provided information about their practices. In this research, a practical investigation was introduced, an optimization procedure was also developed for the guide, and finite element analyses were run to define the cable behavior.
The research project answers the key questions to obtain information to establish repair and replacement procedures. Failure detection and locating methods to repair promptly have been explained in the guide. While the failure detection test may be more accessible, the repair or even replacement process is complicated. This is demonstrated by various findings from cable failure analysis, condition monitoring and diagnosis, life assessment methods, fault location, maintenance, and replacement strategies. Those methods also show that partial failures can occur due to faulty repairs and manufacturing defects, poor workmanship, and other external factors.
This research illustrated all the parameters involved in the installation process and in the testing phase to determine the deterioration and aging of the cables. The research investigated the transit systems’ varying size, age, and location. Parameters like jacketing, method of insulation, operating voltage, and the effects of weathering on lifespan of power cables. Some factors like water, electrical treeing, corrosion, overheating, and aging cause defects and cable failure in these systems were investigated. The other factors that cause defects and cable failure such as water, electrical treeing, corrosion, overheating, and aging are explored.
The survey results indicated that there are many types and applications of transit power cables, and there are some types of cables that tend to be used commonly. The average lifetime for transit power cables, which helps to establish a repair and replacement timelines and assists with the cost and benefits analysis of repair work. The survey results have demonstrated that the manufacturer-specified lifespan for the cable is per the expected and observed lifespan of the cables in service. Evaluating the costs/benefits of replacing a cable section instead of repairing is essential for decision-making processes. To evaluate survey results, statistical analyses were carried out. Then, content analysis was run to detect the most used words in the responses to the survey questions.
After the survey section, the case study section details ten case studies that were investigated in detail to understand their maintenance practices. They covered a wide range of systems from small to large and from old to new. The degree of degradation assessment is approached differently in each of the case studies. Some agencies have no cable monitoring systems in use. They generally
disconnect and deactivate the system for weeks in case of any failure. The process to replace cables is only initiated once a cable failure occurs.
Some of the parameters affecting the smart replacement strategy of the agencies are identified according to research. Some cable deteriorating factors have been verified as well. These factors need to be observed and controlled if possible, depending on the environment and usage of the cables. The degree of degradation assessment approaches has been explained. Early detection of cable faults by periodic physical inspections aid in preventive maintenance and in making cost effective replacement decisions. A high percentage of stations do not have any cable monitoring systems to detect aging or damage. This is called a “run to fail” process. This approach is found to be increasing the demand for timely maintenance plans in the agencies. Decisions on replacement mostly depend on budget availability or operation detection.
Based on the responses to the survey questions, the estimated lifetime of power cables is around 35 to 40 years. On-site, various tests can be conducted to study the cable faults and a list of cable inspection methods has been identified. It is easier to test and repair overhead wirings, but more equipment needs to be deployed to detect faults in underground cables.
To investigate cable life span, some techniques were outlined. There is a large variety of cable testing taking place. Therefore, there is an increasing demand for a standardized testing procedure to make more accurate decisions regarding repairs and replace. The smart and other replacement strategies are not commonly utilized in most cases.
The research discussed some of the expected challenges and proposed solutions for the cables failure rate modeling along with the modeling bases, formula, and procedure. In addition, an optimal replacement period process and model considering minimizing the average cost has been developed as a part of the guide. A simplified methodology for determining the optimal cable replacement period for various conditions has been proposed as a part of the optimization process in Chapter 5. In the same chapter, finite element analysis of cables was also provided to present the cable behavior under various loading conditions such as tension, torsion, thermal, and water effect. As a result of the finite element analysis, stress values for cables were determined.
As a conclusion, the guide presents practical solutions for the problems faced by the agencies. Problems and solutions created by the agencies are shared in the guide to share the best practices. Sections are designed to help practitioners to get an organized and systematic guide for the traction power cables.
