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Framework for Determining Separation Distances Between Transmission lines in Wyoming

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Presented to

Planning Coordination Committee

Spokane, WA September 30 – October 02, 2009

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Need for the Study

Multiple EHV transmission lines and varying line separation distances – up to 5 miles – have been proposed in Wyoming.

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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

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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 oppositionVisual impact concern

Optimal Range for Line Separation Distance

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Framework to Determine Separation Distance

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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

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SDA-MIN = AB-MINSDACR-MIN = AB-MIN + CASE-MIN + REG-MIN

Determine CASE-MIN

Determine REG-MIN

SD = [SDA-MIN, SDACR-MIN]

Determine AB-MIN

Determining Range of Separation Distance from Framework Components

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END

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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.

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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 speeds1 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 = [SDA-MIN, SDACR-MIN]

SDA-MIN = AB-MIN ~= 260 feet

SDACR-MIN = AB-MIN + CASE-MIN + REG-MIN

~= 260 + 0 + 1,240 = 1,500 feet

SD ~= [260, 1,500]

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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

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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 outages1

• Application of the framework to the state of Wyoming using mathematical formulations to derive outage probabilities due to regional factors affecting reliability

1The framework is not intended as a substitute for WECC approval

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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

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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

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T H A N K Y O U !

Presented by:Robert J. Henke, ICF International, rhenke@icfi.com; 303-792-7810Ken Collison, ICF International, kcollison@icfi.com; 703-934-3806