Resolution No. 4814 - Laserfiche WebLink

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repair crew (2 or 3 people with necessary equipment) can restore power to a distribution circuit with common types of damage in 1 or 2 hours after ardvin9 at the damage site. Electric transmission lines (110 kV and higher) are less vulnerable to winter storm damage because of more robust design specifications. Also, such lines are usually higher above the ground and much less prone to tree branches falling on lines. Furthermore, because of the higher voltage (compared to distribution lines), power utilities must diligently pursue tree trimming programs to avoid flashovers from lines being too close to trees. Nevertheless, transmission lines do sometimes fai~ due to large tree falls, rapid growth of trees near lines, unusually high winds or heavy ice loads. The Eugene/Springfield Metro Area is subject to outages of electric power primarily due to line failures. One possible failure mode would be the transmission lines that feed the Eugene/Springfield Metro Area from the north and south. More common failure modes would be failures of the trunk distribution lines within the Eugene/ Springfield Metro Area and failures of distribution circuits or service drops from distribution lines to individual buildings. All of these ~ailures are most likely due to tree falls during wind storm events. Mitigation projects to reduce the frequency and duration of electric power systems include: augmenting tree trimming programs and hardening lines and poles in locations where ice loading or wind effects result in repeated outages. In some cases, adding connections to improve redundancy of power feed paths and adding disconnect switches to minimize areas affected by any given failure are also worthwhile. In addition to such "hard" mitigation possibilities, there are also "soft" or planning mitigation projects. For example, enhancing mutual aid agreements with nearby utilities can reduce the duration of major outages by increasing the number of crews and equipment for making repairs. Other planning/logistics measures such as ensuring that adequate supplies of parts and equipment are available may also reduce the duration of future outages. For the Eugene/Springfield Metro Area, augmenting tree trimming programs, especially for the transmission lines and the trunk distribution lines is probably the most effective mitigation measure, in selected locations upgrading lines and poles to better withstand loads from trees, wind and ice may also be appropriate. If there are key links in the systems that are highly prone to repetitive failures, undergroundin9 of limited portions of such links may also be appropriate. 13,8 Potentia~ Impacts on the Eugene/Springfield Metro Area The potential impacts of closures, disruptions, and outages of transportation systems and utilities are summarized below in Table 13.2. Public Review Draft: August 6, 2004 13-9