icfi.com 1 Framework for Determining Separation Distances Between Transmission lines in Wyoming icfi.com © 2008 ICF International. All rights reserved. Presented to Planning Coordination Committee Spokane, WA September 30 – October 02, 2009

icfi.com 2 Need for the Study Multiple EHV transmission lines and varying line separation distances – up to 5 miles – have been proposed in Wyoming.

icfi.com 3 Goals of the Study Develop a framework for determining minimum separation distances between EHV transmission lines to mitigate simultaneous multiple line outages Apply the framework to Wyoming and determine a minimum range of line separation distances based on consideration of reliability issues

icfi.com 4 Range of Variation for Optimal Separation Distance Installation & Maintenance Cost and Time Environmental Permitting Delays Future need for new transmission lines Line de-rating risk Ease of adherence to environmental regulations and land-use constraints Public opposition Visual impact concern Optimal Range for Line Separation Distance

icfi.com 5 Framework to Determine Separation Distance

icfi.com 6 Components of Separation Distance AB-MIN –Depends on industry codes – NESC, OSHA rules –Considers transmission tower height and sag length CASE-MIN –Project specific –Can be positive or negative –Example: Project passes through a narrow valley that may force separation distance to be less than AB-MIN REG-MIN –Based on regionally varying factors such as weather –Can be positive or negative –May require detailed analysis to determine separation distance

icfi.com 7 SD A-MIN = AB-MIN SD ACR-MIN = AB-MIN + CASE-MIN + REG-MIN Determine CASE-MIN Determine REG-MIN SD = [SD A-MIN, SD ACR-MIN ] Determine AB-MIN Determining Range of Separation Distance from Framework Components START END

icfi.com 8 Application to Wyoming 1 Based on available data on wind speeds in Wyoming; also assumed to comply with NESC extreme wind and ice loading scenarios. 2 More details on assumptions regarding specific characteristics of tornadoes can be found in the report. START AB-MIN ~= 260 feet CASE-MIN = 0 feet (To be determined as needed on a case-by-case basis) Mitigate risk of outage of multiple lines due to fire by installing fire-breaks and/or early detection system and operations guidance. Mitigate risk of outage of multiple lines due to high winds and tornadoes by designing transmission lines to withstand 101 mph wind speeds 1 and at least F0 class tornadoes. 2 Mitigate risk of outage of multiple lines due to lightning-related outages by installing shield wires or transmission line arresters. REG-MIN ~= 1,240 feet Separation Distance, SD = [SD A-MIN, SD ACR-MIN ] SD A-MIN = AB-MIN ~= 260 feet SD ACR-MIN = AB-MIN + CASE-MIN + REG-MIN ~= ,240 = 1,500 feet SD ~= [260, 1,500] END

icfi.com 9 Minimum Separation Distance (in feet) 260, 1,500 AB-MIN = 260 REG-MIN = 1,240 CASE-MIN = 0 Minimum Range of Separation Distance in Wyoming

icfi.com 10 The Study Includes … Robust, universally applicable framework that can be used to determine separation distances between transmission lines and that consider WECC reliability criteria for multiple line outages 1 Application of the framework to the state of Wyoming using mathematical formulations to derive outage probabilities due to regional factors affecting reliability 1 The framework is not intended as a substitute for WECC approval

icfi.com 11 The Study Does Not … Replace or intend to replace the WECC path rating process, reliability analyses or any other analyses required by WECC Address the environmental and land use impacts related to line separation distances

icfi.com 12 Conclusions and Recommendations No universal one size fits all line separation distance exists Separation distance involves the competing issues of power system reliability, environmental and land use impacts, and costs To be applicable on a large scale, a framework for determining minimum line separation distance should consider all competing issues

icfi.com 13 T H A N K Y O U ! Presented by: Robert J. Henke, ICF International, Ken Collison, ICF International,