Chapter 4. Case Studies

4.1. Case Study Structure

Based on the survey results, ten case studies were developed. Case studies were developed to demonstrate maintenance practices from a variety of systems (small, large, old, and new) by engaging industry subject matter experts experienced in the design, construction, maintenance, and operation of traction power systems. Interviews were carried out in the selected locations for the case studies. The case studies were carried out in Greater Cleveland (1), New Orleans (2), California Bay Area (3), New York (4-5), Oregon (6), Utah (7), Maryland (8), Washington (9), and Minneapolis-St.Paul (10). The selected case study states are given in Figure 4.1 and the Tables as listed below.

Case Study 1: Greater Cleveland Regional Transit Authority given at Table 4.1.

Case Study 2: New Orleans Regional Transit Authority given at Table 4.3.

Case Study 3: California Bay Area Rapid Transit given at Table 4.5.

Case Study 4: New York City Transit given at Table 4.15.

Case Study 5: New York Amtrak’s Replacement Case given at Table 4.16.

Case Study 6: Oregon Tri-County Metropolitan Transportation District, given at Table 4.18.

Case Study 7: Utah Transit System given at Table 4.25.

Case Study 8: Maryland given at Table 4.26.

Case Study 9: Washington Metropolitan Area Transit Authority given at Table 4.27.

Case Study 10: Minneapolis-St.Paul Transit System given at Table 4.28.

4.2. Case Study 1: Greater Cleveland Regional Transit Authority

Table 4.1. Greater Cleveland Regional Transit Authority

4.3. Case Study 2: New Orleans Regional Transit Authority

Table 4.2. New Orleans Regional Transit Authority

4.4. Case Study 3: California Bay Area Rapid Transit

Table 4.3. California Bay Area Rapid Transit

4.5. Case Study 4: New York City Transit

Table 4.4. New York City Transit

4.6. Case Study 5: New York Amtrak Replacement Case

Table 4.5. Replacement of New York Amtrak’s 12kV PILC Traction Power Cables

Another case study was created based on Levi (2018) for replacement of Amtrak’s 12kV PILC traction power cables, a PILCs are considered to have the highest dielectric strength, lowest dissipation factor and lowest dielectric loss compared to both XLPE and EPR. XLPE performs better than EPR. PILC does not suffer from thermal expansion like EPR and XLPE, EPR has better overload tolerance than XLPE. Lead leakage from PILC cables is the main concern. PILC Lead Sheath is completely impermeable, Moisture ingress can occur at a rapid rate if the PILC sheath is damaged, EPR has better moisture resistance properties compared to XLPE. Figure 4.2 illustrates the Amtrak 12kV distribution for this case study.

PILC cables have been used since the late 1800s. They are resilient. Amtrak PILC cables have been used for nearly 90 years. The concerns are mainly a lack of splicer skills, and difficult to maintain. Underground cable design has evolved. Aging increases the probability of failure. PILC cable life is 44 years typically. The oldest installations are 70-90 years old; (mean age is 80 years). Current design life of EPR cables is predicted as 40 years (per study by EPRI). In Figure 4.3, a sample PILC cable failure is seen. Thermal failure, primarily due to moisture ingress, tends to increase insulation conductivity, which is approximately 40% of failure incidences. The electrical phenomenon is partial discharge, which is approximately 60% of failure incidences.

4.7. Case Study 6: Oregon Tri-County Metropolitan Transportation District of Oregon

Table 4.6. Oregon Tri-County Metropolitan Transportation District of Oregon

4.8. Case Study 7: Utah Transit System

Table 4.7. Utah Transit System

4.9. Case Study 8: Maryland Transit System

Table 4.8. Maryland Transit System

4.10. Case Study 9: Washington Metropolitan Area Transit Authority

Table 4.9. Washington Metropolitan Area Transit Authority Findings and Required Actions per Special Directive No. 17-1, Notice No. 1 (December 9, 2016)
https://www.transit.dot.gov/sites/fta.dot.gov/files/2022-06/Special-Directive-17-1-TractionPower.pdf: In accordance with 49 U.S.C. § 5329, 49 CFR § 670.27, and the authority delegated to the FTA Administrator by the Secretary of Transportation, 49 C.F.R. § 1.91, the FTA directs WMATA to take the following actions [excerpts]:

4.11. Case Study 10: Minneapolis-St.Paul Metro Area Transit System

Table 4.10. Minneapolis-St.Paul Metro Area Transit System

Metro Transit is the primary public transportation operator in the Minneapolis–Saint Paul area of the U.S. state of Minnesota and the largest operator in the state. The system is a division of the Metropolitan Council, the region’s metropolitan planning organization (MPO).
Metro (styled as METRO) is a high-capacity rapid transit network serving the Minneapolis–Saint Paul metropolitan area. Its transit operations are shown in Figure 4.4. As of 2020, the system consists of two light rail lines (Blue and Green Lines) and three bus rapid transit lines (Red Line, A and C Lines) operated by Metro Transit. The five lines connect downtown Minneapolis and St. Paul with Bloomington, Minneapolis-St. Paul International Airport, Roseville, and Brooklyn Center, with several new lines and extensions in the planning stages.
Minnesota Public Utilities	The Minnesota Public Utilities Commission (PUC) is the consumer protection agency charged with regulating public utilities such as electric and telephone services.
Integrated Distribution Plan	Minnesota Public Utilities Commission has started a project to file an annual Integrated Distribution Plan (IDP), published in 2019. The plan includes reviewing and evaluating the current system and planning to meet future needs. When traction power cables are concentrated, they are most often installed underground in groups of banks of pipes encased in concrete that are commonly called “duct banks.”

4.12. Conclusions

The ten case study agencies were interviewed to understand their maintenance practices. They covered systems from small to large and from old to new. The degree of degradation assessment is approached differently in 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. Others do routine maintenance, and in most cases, agencies do periodic physical checks and inspections where they look for signs of weathering, fire or heat damage, and cuts/tears in the jackets. Some agencies perform tests like insulation resistance tests at reduced voltage. They add additional jacketing in areas known to have excessive wear the aerial structures where the cables must have expansion and rub the side of the concrete structure. Some agencies have insufficient resources to support the testing, inspection, and maintenance. Agencies have a maintenance schedule to inspect the feeder cable in a timely manner to observe any potential issues and damage to the existing cable. Some diagnostic indicators such as heat increase in the substation are observed by the maintenance crew,. Agencies perform visual inspections in maintenance holes and taps, and run hi-pot, meggering and thumb tests. Insulation resistance and hi-potential test are often run by the agencies. According to the case studies, some run no tests and take a "run to fail" mode.

In the investigation process, several factors need to be observed and controlled if possible, depending on the environment and usage of the cables in each case. The effecting factors include temperatures that have the most effective and are most common between all cases. Temperature plays a more significant role on bare copper conductors than feeder cables. Treeing, water damage, degradation in insulation level, and aging increase the probability of failure. The life cycle of the cables is relatively long, and one case has a 10-year test plan with an asset health cable replacement program focusing on replacing underground cable systems that have had multiple failures. Thermal failure, moisture ingress, partial discharge, splices and taps subjected to seasonal water immersion in underground vaults, ultraviolet rays, birds, rodents, below water level, toxic manufacturing areas such as foundries, chemical plants, coating plants with acid baths, salt spray from freeway bridges are the main concerns for the agencies. Smart replacement systems are not common yet in the agencies studied. Only one agency had a smart new monitoring system and replacement strategy all over the case studies. Most agencies studied did not have a cable replacement program. Cables have only been replaced as part of substation renewal projects, when capital development allocates funds for cable renewal in the budget, or if cable failures have a major impact on the operations. In some cases, agencies created techniques to enhance cable lifespan. These techniques included cable jacketing specially designed taps, and PVC sealed cages. Cables are repaired mainly by being spliced with a new cable. However, replacing the whole section would be a choice in some cases, if the system needs to be replaced, if it is economically possible, or a better option. Repair and replacement of cables are the options for the agencies, and it is a decision-making process for them.

A scheduled maintenance can be a good time to determine the needs for the cables and start this decision-making process. In general, agencies attempt to work during non-revenue hours or in combination with other work outages. A Summary Chart for Case Studies is given in Table 4.11.

Table 4.11. A Summary Chart for Case Studies