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"Transmission Line Reliability, Climate Change and Extreme Weather"

Gibson Peters, Tony DiGioia Jr., P.E.,Chris Hendrickson, and Jay Apt

Transmission lines in service today in the US have been designed using a multitude of design approaches and structural loading criteria. The principal cause of structural failures is associated with weather events that produce loads that exceed the structural loading design criteria. In some cases, failures have been the result of inadequate design, construction and/or maintenance practices, airplane or vehicle accidents and criminal activities.
The cost of storm-caused transmission outages is significant, costing utilities and users on the order of $270 million per year and $2.5 billion per year (2003 $ís) respectively. The cost of storm damages may be under-appreciated by utilities and regulators since standard industry reliability indices (SAIDI & SAIFI) omit the costs of large storm related outages.
Currently available data suggest that the frequency and severity of hurricanes and ice storms will increase in the future. There has been a doubling of Category 4 and 5 Atlantic hurricanes from 1970 to 2004 which is the same time period during which ocean temperatures have increased. If this trend continues, it will have a significant impact on utility and user costs due to structural failures. Studies have shown that increases in CO2 levels in the atmosphere could increase hurricane wind velocities by about 10%, resulting in an increase in wind loading of about 20%.
Under current policy, there is a lack of financial incentives for transmission line owners to upgrade/uprate, refurbish and/or build new lines. For example transmission line owners in restricted jurisdictions do not incur penalties associated with user costs caused by storm outages.
Based on the above observations and conclusions, recommendations are made concerning the collection and scope of SAIDI & SAIFI data, the adoption of a Survivability Design Concept, the adoption of transmission line investment incentives and the revision of structural loading design criteria manuals to include survivability design concepts and the impacts of climate change.

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