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12 Survey 3.1 Surveyed Transit Agencies Many transit systems worldwide use third rails. The studied third rails in the current research include the following eight transit agencies: Chicago Transit Authority, Long Island Rail Road, Washington Metropolitan Area Transit Authority, Massachusetts Bay Transportation Authority, Southeastern Pennsylvania Transportation Authority, Metropolitan Atlanta Rapid Transit Authority, Los Angeles County Metropolitan Transportation Authority, and Baltimore Metro Subway. 3.2 Survey Development A multi-section survey was developed that included (1) respondent information, (2) agency information and size, (3) general information about third rail insulators, (4) cost of insulator failure, and (5) causes of insulator failure. The participant invitation email and survey are accessible in Appendices A and B. 3.3 Survey Results The results of the survey are presented category by category (five categories) in this section and are discussed and visualized, when applicable. 3.3.1 Agency Information and Size Basic information about the geographical location and size of the transit system was collected in this section of the survey. Results indicated that 50% of the surveyed transit systems made 100 million to 150 million passenger trips/year; and the least transited passenger trips/ year was approximately 50 million. 3.3.2 General Information About Third Rail Insulators Respondents were asked to provide information about the insulators in their system, including the number and types of insulators, the number of failures, and the amount of clearance space around them. The surveyed transit agencies estimated that they have an average of 10 insulator failures per year, but three out of eight of them have less than five failures per year. Each surveyed transit agency considers its own clearance space because of several different limitations such as safety considerations. The highest reported clearance space was 20 inches. C H A P T E R 3
Survey 13 Five out of eight surveyed transit agencies experience less than 10 hours of delays annually, and the maximum estimated delay is approximately 40 hours. On average, 1,000 passenger hours are lost annually because of insulator failures in each surveyed transit system. The average cost of maintenance per insulator (excluding the cost of the insulator) among the surveyed agencies was estimated to be US$281. All the surveyed third rail systems implement top contact; however, one of them uses bottom contact in some sections of their system. 3.3.3 Cost of Insulator Failure According to the surveyed transit agencies, porcelain insulators are the most expensive, with an average cost of US$256, and epoxy insulators are the least expensive, with an average cost of US$108. Five out of eight of the agencies declared that they do not track current leakage. 3.3.4 Causes of Insulator Failure As shown in Figure 3, dirt buildup, cracks/fractures, and flashovers/arcing are the top three causes of insulator failure, with failure rates of 14.9%, 11.3%, and 10.4%, respectively. Salt- water penetration, vandalism, and lightning are the least frequent causes, with 0.6%, 1.4%, and 1.4% rates of occurrence, respectively. The responses collected from the surveyed agencies indicated that humidity, hot water, and cold water equally lead to insulator failures. Of the different potential safety failure events, smoke events caused by arcing are the most observed, while damaged electrical equipment is the least observed. Figure 4 depicts the five particle types with different originations that are present in the surveyed transit agencies. It shows that carbon dust (27%) and dirt (23%) are the most common particles, and grime and rust particles (15%) are the least common particles in these transit systems. Figure 3. Average rate of occurrence of each cause of insulator failure in surveyed agencies.
14 Third Rail Insulator Failures: Current State of the Practice 3.3.5 Preventive Strategies for Insulator Failure Seven preventive strategies are used by all the surveyed agencies to predict and diagnose failure. Visual inspection is the most frequently used by all the agencies, and mechanical inspections, heat testing, thermal imaging, predictive models, periodical voltage measurement, and infrared inspections are also used. The rate of failure in renewed segments decreased in all the agencies except one that reported the same number of failures for both renewed and not-renewed segments. While one of the surveyed transit agencies performs cleaning every month, two of the surveyed transit agencies do it every 24 months, which is the least frequency reported. Two of the surveyed transit agencies perform the cleaning once a year, one of them does it every 6 months, and two of them do not clean at all. Figure 4. Percentage of each type of particle that leads to insulator failures in all the surveyed agencies.
