Reaching a Balance between Land Use and Reliability Factors

1. Reaching a Balance between Land Use and Reliability Factors WECC-0071 Drafting Team May 26,2010

2. TWE Project Summary 3,000 MW capacity 600 kV HVDC About 725 miles total in four states 3-year construction 2015 in-service date Capable of delivering renewable energy from various Wyoming wind projects

3. Land Use Objectives Maximize use of West-wide Energy Corridors and federal agency-designated utility corridors Route parallel to other linear facilities such as existing transmission lines, pipelines, highways Minimize the distance between the TWE Project and parallel transmission lines Land Use concerns drive lines closer together

4. Transmission Reliability Objectives Maximize Reliability of Bulk Power System Risk of adverse initiating events increase as transmission lines are placed closer together Structure failure impacting adjacent line Conductor failure impacting adjacent line Localized environmental event – fire, storm, etc. The more severe the initiating event the more risk of system failure in the form of regional (cascading) blackouts System Reliability concerns drive lines further apart

5. Applicable Line Siting Reliability Standards NERC Category C.5 Initiating Event: ‘Any two circuits of a multiple circuit tower line’, Extended by WECC to Include: Adjacent Circuits within a Common Corridor System Limits or Impacts: Planned/Controlled Loss of Demand and/or Curtailed Generation allowed, no cascading outages allowed NERC Category D.7 Initiating Event: ‘All transmission lines on common right-of-way’ System Limits or Impacts: Evaluate for risks and consequences.

6. Illustration NERC/WECC Initiating Events and Categories |- WECC Common Corridor-| X – indicates failed circuit, - indicates operating circuit • * Category D.7 requires analysis of ‘all transmission lines on a common right-of-way’ • ** Approximate generator tripping needed to prevent system instability

7. An Important Observation Category C.5 events can usually be managed or mitigated by generator tripping or other RAS without loss of load Category D.7 events may be too large to be managed or mitigated by generator tripping or other RAS without widespread loss of load

8. Category D.7 Issues • Impact on obtaining a path rating • What does “evaluate for risks and consequences” mean in the path rating process? • Potential for derating • WRS5. For any event that has actually resulted in cascading, action must be taken so that future occurrences of the event will not result in cascading, or it must demonstrate that the …. MTBF is greater than 300 years …. and approved by PCC.

9. Impact on Path Rating – Possible Solutions Clarify that mitigation is not required for Category D.7 events to obtain a path rating Create a “safe harbor” so that contingencies involving lines not in a WECC Common Corridor are not considered to be Category D.7 events Create a “safe harbor” so that mitigation is not required for Category D.7 events for contingencies involving lines not in a WECC Common Corridor

10. Potential for Derating – Possible Solutions Require a demonstration during path rating process that line separation is sufficient to meet the 300-year MTBF standard. This determination would not be subject to review under WRS5. Create a “safe harbor” so that line separation for contingencies involving lines not in a WECC Common Corridor would be deemed sufficient to meet the 300-year MTBF standard under WRS5.

11. Closing Thoughts Clarity is needed on Category D.7 events to facilitate siting and financing of new transmission lines. Current requirement to “evaluate for risk and consequences” causes uncertainty and confusion for project developers, permitting authorities and investors. The WECC-0071 Drafting Team should expand its scope to consider Category D.7 events