Resolution No. 4814 - Laserfiche WebLink

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is moved back and forth between California, the Pacific Northwest and western Canada. The transmission system is a network of high voltage lines (500 kV and 230 kY) and substations which transmit power between generation plants and the local distribution system. The distribution system is a network of lower voltage lines and substations which carries power from transmission system substations to neighborhoods and eventually to individual customers. Power outages in Lane County are most likely to result from disruption of the transmission lines carrying power from outside Lane County or within Lane County, or damage to the local distribution lines within the Eugene/Springfield Metro Area. The generating plant system has sufficient redundancy so that failures of one or more plants do not usually lead to significant power outages. However, because of the limited generation capacity within Lane County, major disruptions in the transmission system would result in substantial curtailment of available power. A major ice storm in the Columbia River area could conceivably fail all of the 500 kV transmission lines feeding Lane County from the north. However, the transmission system has enough redundancy that the power needs of Lane County would likely be met by a combination of local generating capacity and transmission of power from California. However, a severe ice storm with 2 to 4" of ice over much of Lane County could result in failure of all north-south 500 kV and 230 kV transmission lines within Lane County. Such a failure, which is unlikely, but certainly not impossible, would probably entail widespread power outages for 2 to 5 days. The most frequent power outages, however, are due to failure of the local subtransmission or distribution system lines. Winter storms are the most frequent cause of significant electric power outages, with wind being the primary culprit. Electric distribution lines, the Iow voltage lines that deliver power to neighborhoods, are the most vulnerable electric system component in winter storms. Failures most commonly result from tree falls or from "burn downs" when wind-swayed cables touch or get too close to each other and short circuit. Distribution system failures may also be due to utility pole failures. Distribution lines may also fail due to ice loading in excess of design specifications or from landslides or debris flows or flooding which knock out utility poles. Failures of distribution system lines are thus the most common failure mode for electric power systems. Power system outages are more common and of longer duration in rural areas compared to urban or suburban areas. Rural areas are more prone to electric outages because they have a higher percentage of above-ground lines and are more likely to have hilly areas with high concentrations of trees and higher wind speeds than in flatter terrain. In rural areas, with lower population density, there is also a higher ratio of length of distribution lines per customer. With a longer length of exposed line, the probability of an outage is higher for a rural customer than for an urban customer. Once a portion of a power distribution circuit fails, all customers in that part of the circuit lose power. The duration of the power outage depends on the number of outages and the number of repair crews available for repairs. A typical power utility Public Review Draft: August 6, 2004 13-8