Biennial Transmission Plan Studies Update - DRAFT April 6, 2011

NTTG Planning Committee 2 John Leland - Chair, Northwestern Energy Dave Angell - Vice Chair, Idaho Power Chris F. Collins - NextEra Energy Resources, Inc. Brian DeKiep - Montana Public Service Commission Erik Egge - Black Hills Power Marshall Empey - UAMPS Darrell Gerrard - PacifiCorp Bill Hosie - TransCanada Rhett Hurless - Grasslands Renewable Energy Don Johnson - Portland General Electric Kim Johnson - Riverbank Power Corp. Paul Kjellander – Idaho Office of Energy Resources Rodney L. Lenfest - Sea Breeze Pacific Matthew Stoltz - Basin Electric Jim Tucker - Deseret Power Electric Cooperative David Walker – Wyoming Public Service Commission Ted Williams - Gaelectric, LLC NTTG Planning Purpose Provide a forum where all interested parties are encouraged to participate in the planning, coordination, and implementation of a robust transmission system that is capable of supporting an efficient west-wide electricity market while meeting WECC and NERC reliability standards.

Study Steps  Null Case – Current network with 2020 NTTG Loads  System cannot serve loads reliably  Core Case – Current network with infrastructure upgrades and ‘Foundation List’ projects  Based on WECC 2020 Heavy Summer Base Case  Dispatched within PROMOD over 8784 hours of2020 as modeled by TEPPC in PC0 Base Case  Five hours of stress in NTTG’s footprint exported for power flow analysis  Cases were solved and passed N-1 contingency analysis within study criteria 3

Study Steps (cont.)  Scenario Cases – Four Levels of Resource Addition  3,000 megawatts in Montana  3,000 megawatts in Wyoming  3,000 MW in Montana, 3,000 MW in Wyoming  6,000 MW in Wyoming  Studied for the same five hours as for Core Case  Scenario resources added; offset by generation reductions  Removed generic California & Arizona ‘RPS’ resources added by TEPPC, remaining reductions at nuclear plants  Looked for limited transmission additions that would allow all five hours to pass an N-1 contingency study 4

Selecting the Hours Studied  Congestion most likely during  Peak load  High transfers  Studied to identify hours with maximum flows and paths at limits  Remote development of renewable resources may lead to high flows to load areas  2 Peak load hours  Winter: July 27, Hour Ending 16:00  Summer: December 22, Hour Ending 18:00  3 High transfer hours  March 2, Hour Ending 21:00 (highest spring exports)  October 4, Hour Ending 21:00 (highest fall exports)  August 10, Hour Ending 13:00 (highest annual import) 5

Peak Load Hour Selection 6 Hours of coincidental peak load for the NTTG footprint were selected.

High Transfer Hours Selection 7 Mar 02, H21 Aug 10, H13 Oct 04, H21 Red markers show hours exceeding 96% of maximum or minimum

The Resource Scenarios 8 CaseAdded Wind Generation Location NullExisting Gen CoreNone Scen 3 3,000Montana Scen 4 3,000Wyoming Scen 23,000 Montana Wyoming Scen 1 6,000Wyoming

Resources Displaced/Reduced 9 Reduce generic resources added by TEPPC to meet RPS, planning reserve targets in California and Arizona Different dispatches in each of the five hours means different generators were reduced Reduce output of San Onofre, Diablo Canyon, Palo Verde to get required megawatts Ratio of two California MW for each in Arizona Alberta and Oregon generators had been added by TEPPC to meet California RPS needs

Contingency Analysis  Performed using PowerWorld program  N-0: Test the network with all elements in service  N-1: Test the network with removal of single elements  Contingency lists contained elements in the Northern Tier footprint at or above 230 kV  Report significant changes at or above 230 kV  Elements in the Northern Tier footprint were monitored  Increase in flows by more than 2% in elements above 100% of rating  Voltage changes of more than 1%, outside 90%-110% range 10

Midpoint Aeolus Clover Crystal Robinson Results of Scenario 4 Analysis 11 Scenario 4 – 3,000 MW in Wyoming –Significant problems occurred on the high export hours (March noted here) –Problems with paths TOT2A, COI Generic Solution: Add Transfer Capability 1)1,500 MW capacity from Clover (Central UT) to Crystal (Southern NV) Still 900 MW over COI limit 2)1) + 1,500 MW capacity Midpoint-Robinson COI less than 100 MW over, 200 violations 3)1) + 1,500 MW capacity Aeolus-Crystal COI 104 MW over limit, 132 violations 3) appears adequate, violations can can be resolved by local controls Other hours studied have fewer issues

Results of Scenario 3 Analysis Scenario 3 – 3,000 MW in Montana –Significant problems again occurred on the high export hours –Problems with Montana to Northwest, COI paths Generic Solution: Add Transfer Capability 1)Added 1,500 MW from Townsend (Central MT) to Midpoint (Central ID) Montana-Northwest over by 400 MW Still 1,700 MW over on COI 2)Tested 3,000 MW transfer capability from Townsend via Midpoint and Robinson to Harry Allen Fixed problems on Montana-Northwest COI just 325 MW over limit 77 violations 2) appears adequate, violations can be resolved with local controls –Other hours studied again have fewer issues 12 Townsend Midpoint Harry Allen Robinson

Results of Scenario 2 Analysis Scenario 2 – 3,000 MW in Montana, 3,000 in Wyoming –Adding Townsend-Midpoint and Clover-Crystal was inadequate 1,700 MW over limit on COI, 1,600 MW over Montana-Northwest limit –Tested combined Scenario 3 and Scenario 4 transmission additions 3,000 MW capability from Townsend via Midpoint and Robinson to Harry Allen plus 1,500 MW from Aeolus to Crystal plus 1,500 MW from Clover to Crystal 29% over limit on Victorville-Lugo 350 MW over COI limit of 4,800 MW 98 criteria violations –Appears adequate, violations can be resolved with local controls –Other hours have not been tested, given previous dominance of March hour 13 Townsend Midpoint Aeolus Clover Crystal Robinson

Results of Scenario 1 Analysis Scenario 1 – 6,000 Megawatts in Wyoming –Adding 3,000 MW transfer capability Clover-Crystal line was inadequate 2,100 MW over limit on COI, 433 criteria violations –Also adding 3,000 MW transfer capability Aeolus-Crystal still left problems COI was 760 MW over its limit 147 criteria violations –Further addition of 1,500 MW transfer capability Midpoint-Robinson left fewer problems COI still 200 MW over limit 119 remaining criteria violations –Addition of phase shifting transformers or substituting two kV DC lines would likely further reduce problems 14 Midpoint Aeolus Clover Crystal Robinson

Initial Conclusions  Adding 3,000 MW of generation in either Montana or Wyoming appears to require 3,000 MW of additional transfer capability through a partial 500 kV double-circuit AC or single-circuit DC solution to deliver via Southern Nevada to Arizona and California  Delivery via Northwest would require upgrades MT-NW and to COI  Adding 3,000 MW in both Montana and Wyoming works relatively well with double-circuit 500 kV AC from Townsend to Harry Allen via Midpoint and Robinson, a 500 kV line from Aeolus to Crystal and another from Clover to Crystal. DC tie lines of comparable capacity should work as well  With 6,000 MW in Wyoming, double-circuit from Aeolus to Crystal plus double-circuit from Clover to Crystal still needs Midpoint- Robinson to get reasonable results. Again DC tie lines should be adequate as well 15

Next Steps NTTG Biennial Planning Cycle 16

QUESTIONS? 17