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22 Conclusions and Future Research The results of the survey of eight transit agencies showed an average of 10 insulator failures annually. Five of the transit agencies experience less than 10 hours of delays per year. The results also showed that an average of 1,000 passenger hours are lost annually in each transit system as a result of insulator failures. Porcelain insulators are the most expensive, at an average cost of US$256, and epoxy insulators are the least expensive, at US$108. Dirt buildup is the most frequent cause of insulator failure among the surveyed agencies and saltwater penetration is the least frequent. More key findings from the survey include the following (see Appendix E for detailed survey results): ⢠Four of the eight surveyed transit agencies perform 100 million to 150 million passenger trips/year; the least number of passenger trips/year is approximately 50 million. ⢠While five of the investigated agencies declared that they do not track current leakage, two of them specified the corresponding cost as less than US$5,000 per year. ⢠Dirt buildup, cracks/fractures, and flashovers/arcing are the top three causes of insulator failures. ⢠Saltwater penetration, vandalism, and lightning are the three least frequent causes of insu- lator failure. ⢠Smoke events resulting from arcing are the most frequently encountered safety failures in the studied agencies, while damaged electrical equipment is the least. ⢠Visual inspection is the most frequently used insulator-failure diagnosis method, and mechanical inspection is the second-most frequently used method. ⢠The failure rate in renewed segments reduced in all the surveyed agencies, while in one of the agencies, the same number of failures was reported for the renewed and not-renewed segments. The results of the five case studies showed that the materials used for insulators are porcelain, fiberglass, wood, and epoxy; porcelain is used the most. Dirt buildup is the most frequent cause of failure in four of the case studies. The main undesirable impacts of insulator failures on the operation of third rail transit systems are the waste of labor, increased material costs, loss of ridership, and loss of the passengersâ trust. In addition, some agencies have discovered that the resin-fiberglass ratio is important for containing insulator breakdowns. As such, future research could investigate different materials and/or the ratio of different components that could be used to improve insulators. Analysis of the different insulator design could also be conducted. C H A P T E R 5
