TransCanyon Cross-Tie Transmission Project

Transcription

1 TransCanyon Cross-Tie Transmission Project Cross-Tie Phase I Progress Report Supplemental Simultaneous Analysis Final Report Revision 1.1 August 2017

2 Table of Contents 2 Page Executive Summary Introduction and Project Description Study Overview Power Flow Case Description Power Flow Case Modifications PacifiCorp Generation Queue PacificCorp Generation Queue Dynamics Data Simultaneous Analysis for Selected WECC Paths Contingency Lists Study Methodology and Assumptions Simultaneous Path Study Results Path 37 (Tot 4A) Aeolus South (Aeolus-Clover) Summary of Path Flows for the Aeolus South Analysis Summary of Case Data for the Aeolus South Analysis Contingency List for the Aeolus South Analysis Diverged Cases for the Aeolus South Analysis Thermal Overloads for the Aeolus South Analysis Voltage Violations for the Aeolus South Analysis Transient Stability Results for the Aeolus South Analysis Aeolus Area Generation Tripping Timing Reactive Margin Results for the Aeolus South Analysis Conclusions for the Aeolus South Analysis Aeolus West (Aeolus-Anticline) Path 66 (COI) Summary of Path Flows for the Path 66 Analysis Summary of Case Data for the Path 66 Analysis Contingency List for the Path 66 Analysis Diverged Cases for the Path 66 Analysis Thermal Overloads for the Path 66 Analysis Voltage Violations for the Path 66 Analysis Transient Stability Results for the Path 66 Analysis Reactive Margin Results for the Path 66 Analysis Conclusions for the Path 66 Analysis Path 78 (Tot 2B1) Summary of Path Flows for the Path 78 Analysis Summary of Case Data for the Path 78 Analysis Contingency List for the Path 78 Analysis Diverged Cases for the Path 78 Analysis Thermal Overloads for the Path 78 Analysis Voltage Violations for the Path 78 Analysis Transient Stability Results for the Path 78 Analysis Reactive Margin Results for the Path 78 Analysis Cross-Tie Curtailments Associated with Simultaneous Path 78 Loading

3 Mitigation Analysis for Path Conclusions for the Path 78 Analysis Path 35 (Tot 2C) Summary of Path Flows for the Path 35 Analysis Summary of Case Data for the Path 35 Analysis Contingency List for the Path 35 Analysis Diverged Cases for the Path 35 Analysis Thermal Overloads for the Path 35 Analysis Voltage Violations for the Path 35 Analysis Transient Stability Results for the Path 35 Analysis Reactive Margin Results for the Path 35 Analysis Cross-Tie Curtailments Associated with Simultaneous Path 35 Loading Mitigation Analysis for Path Conclusions for the Path 35 Analysis Path 29 (Intermountain-Gonder) Summary of Path Flows for the Path 29 Analysis Summary of Case Data for the Path 29 Analysis Contingency List for the Path 29 Analysis Diverged Cases for the Path 29 Analysis Thermal Overloads for the Path 29 Analysis Voltage Violations for the Path 29 Analysis Transient Stability Results for the Path 29 Analysis Reactive Margin Results for the Path 29 Analysis Cross-Tie Curtailments Associated with Simultaneous Path 29 Loading Mitigation Analysis for Path Conclusions for the Path 29 Analysis Appendix 1 Stability Plots for the Aeolus South Path Appendix 2 Stability Plots for Path 66 Appendix 3 Stability Plots for Path 78 Appendix 4 Stability Plots for Path 35 Appendix 5 Stability Plots for Path 29 3

4 Executive Summary The Cross-Tie Transmission Project (Cross-Tie) is an EHV transmission intertie that is proposed to be constructed between the future Clover 500 kv substation (PacifiCorp) near Mona, UT and the Robinson Summit 500 kv substation (NV Energy) near Ely, NV. The anticipated in-service date for Cross-Tie is the fourth quarter of Cross-Tie is comprised of the following major transmission elements: a 213 mile, ACSR conductor, 500 kv transmission line, 50% total series compensation on the 500 kv line, and 2x90 MVAr shunt reactors at each end of the line. This supplemental report investigated simultaneous flows for several WECC Rated Paths that are anticipated to be impacted by the Cross-Tie Project. This study examined two potential scenarios that represent different transmission system configurations in the Aeolus area during the build out of the Gateway West and Gateway South Projects. These scenarios are described below. Scenario I This scenario includes Gateway South (Aeolus South) and the Aeolus- Populus 500 kv section of Gateway West (Aeolus West). All 500 kv sections of the Gateway West Project west of Populus Substation were removed from the case and the system model was changed to reflect the existing transmission system along this path. Scenario II This scenario includes Gateway South (Aeolus South), the Aeolus 500/230 kv transformer, and the Aeolus area 230 kv upgrades. All 500 kv sections of the Gateway West Project are removed from the case and the system model was changed to reflect the existing transmission system along this path. The Scenario I case is slightly different from the cases used for the non-simultaneous analysis in the Phase I report. The difference is that the Anticline-Populus 500 kv line section was removed in the Phase I studies to replicate the Gateway West model consistent with the latest Pacificorp IRP (April 4, 2017) and to be consistent with the Gateway West model currently being used by CAISO to study the benefits of the submitted Interregional Transmission Projects (ITPs) in enabling imports of Wyoming renewable generation into California. Several WECC Rated Paths were identified as candidates where simultaneous limitations with the Cross-Tie Project could potentially occur. A screening level analysis was performed on each of these Rated Paths. The objective of this screening level analysis was to identify constraints, determine how these constraints impact the proposed Cross-Tie rating, and identify potential mitigation that could be implemented to achieve the desired simultaneous Cross-Tie rating. This initial analysis is supplemental to the WECC Path Rating Process Phase 1 Study Report (a.k.a., a Comprehensive Progress Report) to give advanced notice of the impacts that the Cross-Tie Project may have on other WECC Rated Paths. These studies are listed in Table ES-1. 4

5 Table ES-1 Selected WECC Rated Paths WECC Path Interaction Simultaneous Condition Path Rating Other WECC Rated Path Interactions Scenario I Gateway South and Gateway West to Populus Included Cross-Tie at 1,500 MW Scenario II Only Gateway South Cross-Tie at 1,500 MW Path 37 (TOT 4A) 2175 MW N-S X X Aeolus South 1,700 MW N-S X N/A Aeolus West 2,160 MW N-S Includes Bridger-Anticline West, Borah West and Midpoint West Paths at maximum flow E-W X N/A Path 66 (COI) 4,800 MW N-S PDCI at 3100 MW N-S X X Path 78 (TOT 2B1) 600 MW N-S IPP net import at 1,200 MW, Path 27 (IPP DC) at 2,400 MW N-S. Include nomogram limit with Path 79 (TOT 2B2) X X Path 35 (TOT 2C) 600 MW N-S IPP net import at 1,200 MW, Path 27 (IPP DC) at 2,400 MW N-S. Include nomogram limit with Path 79 (TOT 2B2) Path 29 (Intermountain-Gonder) 200 MW E-W X X X X This screening level analysis utilized the WECC Path Rating Catalog to select a few limiting contingencies to be studied for each selected Path. In addition, engineering judgement was utilized to select other contingencies that might impact the rating of the Cross-Tie Project. Three to ten contingencies were selected based on the Path that was studied. Several variations of the most severe or limiting contingency were also evaluated as part of this analysis. Conclusions The Cross-Tie Project will require an Accepted Rating. The Phase I studies indicated that the Cross-Tie Project can meet the requirements of the NERC Reliability Standards/WECC Criteria and that the proposed 1,500 MW rating for the Cross-Tie Project is achievable. However, this supplemental analysis indicated that there are simultaneous interactions with other WECC Rated Paths that may cause curtailments when there are high simultaneous flows on both paths. The more severe issues found in this analysis are related to both the SWIP South and Cross-Tie Projects. The issue of rating SWIP South was previously studied with SWIP North modeled rather than with the Cross-Tie Project. The current cases do not include SWIP North and it is anticipated that mitigating actions for SWIP and its ratings and for Cross-Tie and its ratings will be required respectively as they qualify in the WECC rating process. There appear to be mitigation options available that, if feasible, resolve these interactions and allow the full 1,500 MW capability of Cross-Tie to be achieved simultaneously with the rated flows on the other Paths. A new set of rating studies for SWIP South would likely be required to determine a new rating and resolve issues if the Cross-Tie Project replaces SWIP North. A summary of the initial simultaneous analysis conclusions is provided below. Aeolus South - The Cross-Tie Project has no adverse impact on the Aeolus South Path. Aeolus South is primarily used to load the Cross-Tie Project. It is possible that generation 5

6 tripping required for the Aeolus-Clover and Aeolus-Anticline 500 kv lines could potentially be used to mitigate issues that the Cross-Tie Project exacerbates on other WECC Rated Paths. Path 66 - The studies indicate that Cross-Tie has no adverse impact on Path 66. Path 78 - The Cross-Tie Project impacts the simultaneous operation of Path 78. The Cross-Tie Project could be limited to as low as 950 MW in cases where Path 78 is scheduled above 500 MW. The loss of SWIP South is the most severe contingency. Mitigation that may allow the Cross-Tie Project to achieve the full 1500 MW rating simultaneously with Path 78 is as follows: Generation tripping in the Aeolus area, and Bypassing of the Aeolus-Clover or Huntington-Pinto series capacitors. There may also be a need to install shunt capacitors on the lower voltage system in the Pinto area to mitigate some identified voltage concerns. Path 35 - The Cross-Tie Project impacts the simultaneous operation of Path 35. The Cross-Tie Project could be limited to as low as 500 MW in cases where Path 35 is scheduled above 350 MW. The loss of SWIP South is the most severe contingency. Mitigation that may allow the Cross-Tie Project to achieve the full 1500 MW rating simultaneously with Path 78 is as follows: Generation tripping in the Aeolus area, Bypassing of the Red Butte-Sigurd and Three Peak-Sigurd 345 kv series capacitors, Bypassing of the series capacitors in the Aeolus South 500 kv line, and Insert the series capacitors in the Huntington-Pinto 345 kv line. Path 29 - The Cross-Tie Project impacts the simultaneous operation of Path 29. The Cross-Tie Project could be limited to as low as 1050 MW in cases where Path 29 is scheduled above 150 MW. The loss of the Cross-Tie 500 kv line is the most severe contingency for overloads on the underlying 230 kv system in parallel with the Cross-Tie Project. The loss of the SWIP South transmission line is the most severe contingency for impacts on the Summit Intertie (Path 24). Mitigation that may allow the Cross-Tie Project to achieve the full 1500 MW rating simultaneously with Path 29 is as follows: Generation tripping in the Aeolus area, and Bypassing of the series capacitors in the Aeolus South 500 kv line. There are also some possible impacts to the Summit Intertie revealed by this sensitivity analysis. These Summit Intertie impacts should be investigated further in a future analysis (e.g., the Phase 2 study). Path 37 and Aeolus West An analysis of these Paths became too complicated for a simple screening study and it was decided to leave this issue to Phase 2 of the WECC 6

7 Path Rating Process where input from a WECC Project Review Group will be provided to help resolve the issues identified in the initial analysis done for this report (see Sections 3.1 and 3.3). Based on the analysis that has been done to date, it is likely that the Cross-Tie Project would have minimal impact on these two Paths. 7

8 1. Introduction and Project Description The Cross-Tie Transmission Project is an EHV transmission intertie that would be constructed between the future PacifiCorp-East (PACE) Clover 500 kv bus and NV Energy s Robinson Summit 500 kv substation. The anticipated in-service date for Cross- Tie is the fourth quarter of Figure 1-1 (following pages) provides a conceptual single line diagram of the Cross-Tie Transmission Project. Figure 1-2 is a map indicating the proposed route of the Project. Figure 1-3 is a map showing high voltage Transmission lines, adjacent Balancing Authority boundaries, and some of the WECC Rated Paths near the Cross-Tie Project. Cross-Tie is comprised of following transmission elements: A 500 kv line (213 miles, ACSR conductor) between the Clover and Robinson Summit substations, 50% total series compensation on the 500 kv line (29 ohms at each end), and 2x90 MVAr shunt reactors at each end of the line. It is anticipated that the maximum loading capability of Cross-Tie would be 1,500 MW. This value is dependent upon the complete build-out of the Robinson Summit-Harry Allen 500 kv Transmission Project (One Nevada Line). Commonly referred as SWIP- South, the complete build-out includes the following electric transmission facilities: Two phase-shifting transformers (345/345 kv, +/-48, 600MVA each) at NV Energy s Robinson Summit 345 kv bus: one connected to the Falcon-Robinson Summit 345 kv line, and one connected to the Gonder-Robinson Summit 345 kv line. 70% series compensation added to the Robinson Summit-Harry Allen 500 kv Line (35%/45 Ohms at each end of the line). The Harry Allen-Eldorado 500 kv Line (HAE, alternately known as the Southern Nevada Intertie Project or SNIP) will also need to be in-service. The HAE 500 kv Line is expected to be about 60 miles long, with one segment of 70% series-compensation at Harry Allen. The objective of this analysis is to determine a path rating for the Cross-Tie Project and identify any possible associated transmission constraints and/or impacts on selected WECC Paths. The Cross-Tie Project will be stressed simultaneously with other WECC Paths and a determination of any limitations will be evaluated. Limiting contingencies identified in the WECC Path Rating Catalog will be evaluated as well as several other contingencies related to or impacted by the Cross-Tie Project. 8

9 Figure 1-1: Cross-Tie Transmission Project Single Line Diagram 9

10 Figure 1-2: Proposed Cross-Tie Transmission Project Route 10

11 Figure 1-3: Cross-Tie Transmission Project High Voltage Transmission Lines Near the Cross-Tie Project Anticline Substation 11

12 2. Study Overview This section of the report describes the data sets and assumptions that were utilized in this analysis. All power flow and transient stability work was performed to be in compliance with NERC Reliability Standards and WECC Criteria. The General Electric Positive Sequence Load Flow (GEPSLF) program (version 19.0_02) was used for the analysis. 2.1 Power Flow Case Description Three recently approved WECC base cases were selected for this analysis. The cases used are listed as follows: 2026 Heavy Summer (26hs1a.sav) - approved Heavy Winter (26HW1a.sav) - approved Light Spring (26LSP1Sa.sav) - approved The 2026 Heavy Summer case is a general 10-year case with typical flows throughout the WECC system. The case models expected peak load for the months of June-August. The case has median/high hydro conditions in the Pacific Northwest and a high thermal generation output in Southern California, Arizona, New Mexico, and Southern Nevada. Some of the significant path flows in this case are C0I 4525 MW, PDCI 2240 MW, IPP DC 620 MW, West of River 6415 MW, and East of River 2621 MW. The 2026 Heavy Winter case is a general 10-year case with typical flows throughout the WECC system. The case models expected peak load for winter conditions. The case has high hydro conditions in the Pacific Northwest and a high thermal generation output in the Pacific Northwest, Idaho, Montana, Colorado, and Wyoming. It has a medium level of thermal generation output in California, Arizona, New Mexico, and Southern Nevada. Some of the significant path flows in this are C0I 1620 MW, PDCI 1185 MW, IPP DC 590 MW, West of River 6825 MW, and East of River 3690 MW. The 2026 Light Spring case is a 10-year case with high wind generation dispatch. The case models expected minimum load for the months of March-May. The case has 30% wind output represented in all areas. Some of the significant path flows in this case are C0I 2800 MW, PDCI 2145 MW, IPP DC 320 MW, West of River 6035 MW, and East of River 3365 MW. Each of these power flow cases was modified to include the Cross-Tie Project and necessary adjustments were made to stress the Project and other critical Paths. 12

13 2.2 Power Flow Case Modifications The WECC power flow cases selected for this analysis modeled the Gateway West and Gateway South Projects which include the transmission lines required to accommodate the addition of over 5,000 MW of renewable generation in southeastern Wyoming. The cases were modified to include the Cross-Tie 500 kv Transmission Project, the 345 kv, 600 MVA Phase shifting transformers at Robinson Summit, the appropriate series compensation for the SWIP South 500 kv Project, and the Harry Allen-Eldorado 500 kv transmission line. In addition, it was desired to study potential scenarios that represent two different transmission system configurations at Aeolus during the build out of the Gateway West and Gateway South Projects. These scenarios are described as follows: Scenario I This scenario includes Gateway South (Aeolus South) and the Aeolus-Populus 500 kv section of Gateway West (Aeolus West). All 500 kv sections of the Gateway West Project west of Populus Substation 1 were removed from the case and the system model was changed to reflect the existing transmission system along this path. Scenario II This scenario includes Gateway South (Aeolus South), the Aeolus 500/230 kv transformer, and the Aeolus area 230 kv upgrades. All 500 kv sections of the Gateway West Project are removed from the case and the system model was changed to reflect the existing transmission system along this path. It is anticipated that the Cross-Tie Project would primarily be loaded by the generation in the Aeolus area. These two scenarios will have an impact on how much Aeolus generation will be required to load up the Cross-Tie Project. The WECC base case generation changes required to load up the Cross-Tie Project are described in the next section. 2.3 PacifiCorp Generation Queue The original WECC base cases that were selected for the analysis included 1,440 MW of generation in the area near Aeolus Substation. An additional 4,340 MW of generation was added to the power flow case and is off-line. This generation is brought on-line as necessary to stress the Gateway West (Aeolus West) and Gateway South (Aeolus South) Paths. Tables and show the PacifiCorp queue generation that is modeled in the Wyoming area. 1 Note that the Scenario I case is somewhat different from the case developed for the non-simultaneous analysis. The non-simultaneous cases also eliminate the Anticline-Populus 500 kv line section. 13

14 Table shows about 1,000 MW of queue generation that has been suspended or deactivated. Some of this generation was included in previous studies that determined the 230 kv reinforcements required as part of the Gateway West Project. Table shows about 5,500 MW of queue generation that was added to the Utah area. This generation was only used in cases where Cross-Tie and the other applicable WECC Paths could not be stressed simultaneously by the Aeolus area generation. This situation occurred for the cases where IPP, Intermountain-Mona, Path 35 or Path78, and Path 79 were stressed simultaneously. In these scenario s, Aeolus South was also heavily stressed. The Wyoming generation in the Aeolus area was primarily used to stress the Cross-Tie project. The generation added in the Utah area was used if there was not sufficient Aeolus area generation to stress all the desired Paths or if increasing the Aeolus area generation caused other problems in the system. 14

15 Table Wyoming Area Queue Generation Modeled in the Original WECC Base Cases Q# Request Date Request Status Company Name Service Type Application Rules MW County ST Region Point of Interconnection Type 7 3/7/2001 In Service Rock River I, LLC ER LGI 50.0 Carbon WY PACE Foote Creek substation, 34.5 kv circuit Wind 8 3/8/2001 In Service Exxon Mobil Production Company NR LGI Lincoln WY PACE Monument Switching Station Natural Gas 12 8/27/2001 In Service FPL Energy Wyoming, LLC ER LGI Uinta WY PACE Longhollow Switching Station Wind 90 6/22/2006 In Service Mountain Wind Power, LLC NR LGI 60.0 Uinta WY PACE Muddy Creek substation Wind 96 10/9/2006 In Service Mountain Wind Power II, LLC NR LGI 79.5 Uinta WY PACE Muddy Creek substation Wind 117 1/18/2007 In Service PacifiCorp Commercial & Trading ER LGI 99.0 Carbon WY PACE Freezeout substation Wind 118 1/18/2007 In Service PacifiCorp Commercial & Trading ER LGI 19.5 Carbon WY PACE Freezeout substation Wind 126 3/5/2007 In Service PacifiCorp Commercial & Trading ER LGI Converse WY PACE Windstar substation near Dave Johnston Plant Wind 153 8/8/2007 In Service Top of the World Wind Energy, LLC ER LGI Converse WY PACE Dave Johnston-Yellowcake Line Wind /8/2007 In Service Chevron Global Generation NR SGI 19.5 Natrona WY PACE Sand Hills Line between Casper & Platte Junction Wind 119-A 1/29/2007 In Service PacifiCorp Commercial & Trading ER LGI Carbon WY PACE Foote Creek substation Wind 203 2/26/2008 In Service PacifiCorp Commercial & Trading ER LGI Carbon WY PACE Shirley-Basin substation on the Miners - Difficulty Line Wind 220 5/12/2008 In Service Three Buttes Windpower ER LGI 99.0 Converse WY PACE Latigo substation between Casper and Windstar line Wind 335 6/1/2010 In Service Pioneer Wind Park I, LLC NR LGI 40.0 Converse WY PACE Amassa substation, (DJ - Difficulty) Wind 306-A 12/3/2009 In Service Pioneer Wind Park I, LLC NR LGI 40.0 Converse WY PACE Amassa substation, (DJ - Difficulty) Wind Total

16 Table New Wyoming Area Queue Generation Added to the Base Cases Q# Request Date Request Status Company Name Service Type Application Rules MW County ST Region Point of Interconnection Type 272 5/14/2009 In Service PacifiCorp Commercial & Trading ER LGI Carbon WY PACE Proposed new substation on the Miners-Difficulty Line Wind 375 3/4/2011 In Progress Eurus Dry Creek Wind LLC ER LGI Carbon WY PACE Proposed Heward substation Wind 706 9/4/2015 In Progress N/A NR/ER LGI Carbon WY PACE Freezeout substation Wind 707 9/4/2015 In Progress N/A NR/ER LGI Carbon WY PACE Shirley Basin-Freezeout transmission line Wind 708 9/4/2015 In Progress N/A NR/ER LGI Carbon WY PACE Shirley Basin substation Wind /9/2015 In Progress N/A NR/ER LGI Converse WY PACE Windstar substation Wind /12/2015 In Progress N/A NR/ER LGI Converse WY PACE Yellowcake Antelope Mine transmission line Wind /29/2015 In Progress N/A NR/ER LGI Uinta WY PACE Canyon Compression-Railroad transmission line Wind /11/2015 In Progress N/A NR/ER LGI Albany WY PACE Freezeout substation Wind /13/2015 In Progress N/A NR LGI 80.0 Sweetwater WY PACE Raven substation Solar 783 8/3/2016 In Progress N/A NR/ER LGI 30.0 Natrona WY PACE Bar Nunn substation or Casper substation Solar 784 8/4/2016 In Progress N/A NR/ER LGI 80.0 Natrona WY PACE Casper substation Solar 785 8/4/2016 In Progress N/A NR/ER LGI Natrona WY PACE Casper substation Wind 789 8/8/2016 In Progress N/A NR LGI 74.9 Fremont WY PACE Thermopolis-Riverton transmission line Solar 801 9/20/2016 In Progress N/A NR LGI 80.0 Natrona WY PACE Bar Nunn substation Solar 802 9/20/2016 In Progress N/A NR/ER LGI 80.0 Natrona WY PACE Bar Nunn substation Solar 807 9/30/2016 In Progress N/A NR LGI 75.9 Carbon WY PACE Standpipe substation Wind /20/2016 In Progress N/A NR/ER LGI Uinta WY PACE Canyon Compression-Railroad transmission line Wind /5/2016 In Progress NR/ER LGI Carbon WY PACE High Plains - Foote Creek transmission line OR Foote Creek substation Wind /5/2016 In Progress NR/ER LGI Carbon WY PACE Aeolus substation Wind 409-A 1/26/2012 In Progress Intermountain Wind, LLC NR LGI 80.0 Albany WY PACE Freezeout substation Wind 409-B 1/26/2012 In Progress N/A NR LGI 80.0 Albany WY PACE Freezeout substation Wind 409-C 1/26/2012 In Progress N/A NR LGI 80.0 Albany WY PACE Freezeout substation Wind 409-D 1/26/2012 In Progress N/A NR LGI 80.0 Albany WY PACE Freezeout substation Wind Total

17 Table Wyoming Area Queue Generation that has Been Suspended or Deactivated Q# Request Date Request Status Company Name Service Type Application Rules MW County ST Region Point of Interconnection Type 199 2/20/2008 Suspended Simpson Ridge Wind Farm, LLC ER LGI 200 Carbon WY PACE Miners-Freezeout transmission line Wind 200 2/20/2008 Suspended Simpson Ridge Wind Farm, LLC ER LGI 100 Carbon WY PACE Miners-Freezeout transmission line Wind 201 2/20/2008 Suspended Simpson Ridge Wind Farm, LLC ER LGI 100 Carbon WY PACE Miners-Freezeout transmission line Wind 290-A 9/22/2009 Suspended Sweeney Park Wind Farm ER LGI Sweetwater WY PACE Rock Springs-Point of Rocks transmission line Wind 290-B 9/22/2009 Suspended Sweeney Park Wind Farm ER LGI Sweetwater WY PACE Rock Springs-Point of Rocks transmission line Wind 290-C 9/22/2009 Suspended Sweeney Park Wind Farm ER LGI 50.4 Sweetwater WY PACE Rock Springs-Point of Rocks transmission line Wind 306-B 12/3/2009 Deactivated N/A NR LGI 50.4 Converse WY PACE Amassa substation, (DJ - Difficulty) Wind 306-C 12/3/2009 Deactivated N/A NR LGI Converse WY PACE Amassa substation, (DJ - Difficulty) Wind Total Table.3-4 New Utah Area Queue Generation Added to the Base Case Q# Request Date Request Status Company Name Service Type Application Rules MW County ST Region Point of Interconnection Type 3 1/23/2001 In Service Utah Municipal Power Agency ER LGI 200 Salt Lake UT PACE West Valley substation, 138 kv Natural Gas 20 4/30/2003 In Service PacifiCorp Commercial & Trading ER LGI 280 Juab UT PACE Mona substation Natural Gas 21 4/30/2003 In Service PacifiCorp Commercial & Trading ER LGI 245 Juab UT PACE Mona substation Natural Gas 44 6/3/2004 In Service PacifiCorp Commercial & Trading ER LGI 535 Utah UT PACE Timp - Tri-City Line Natural Gas /27/2009 In Service PacifiCorp Energy ER LGI 625 Utah UT PACE New Steel Mill substation Natural Gas /25/2011 In Progress Sevier Power Company, LLC ER LGI 525 Sevier UT PACE Sigurd substation Natural Gas 710 9/17/2015 In Progress N/A NR/ER LGI 204 Kane UT PACE Sigurd-Glen Canyon Solar 763 6/22/2016 In Progress N/A NR/ER LGI 200 Iron UT PACE Three Peaks substation Solar 771 7/11/2016 In Progress N/A NR/ER LGI 525 Iron UT PACE Sigurd-Three Peaks transmission line Solar 774 7/11/2016 In Progress N/A NR/ER LGI Iron UT PACE Hickory Red Butte (Sigurd #2) transmission line Solar 777 7/13/2016 In Progress N/A NR/ER LGI 200 Emery UT PACE Emery substation Solar 787 8/8/2016 In Progress N/A NR/ER LGI 200 Emery UT PACE Emery-Sigurd #2 345 kv line OR Huntington-Sigurd 345 kv line Solar 788 8/8/2016 In Progress N/A NR/ER LGI 200 Emery UT PACE Emery-Sigurd #2 345 kv line OR Huntington-Sigurd 345 kv line Solar 805 9/30/2016 In Progress N/A NR LGI 136 Kane UT PACE Sigurd-Glen Canyon transmission line Solar /11/2016 In Progress N/A NR LGI 240 San Juan UT PACE Pinto substation Solar /8/2016 In Progress NR/ER LGI 525 Tooele UT PACE Clover-Oquirrh transmission line Solar /8/2016 In Progress NR/ER LGI 525 Utah UT PACE Camp Wiilliams-Mona Transmission Line Solar Total

18 2.4 PacificCorp Generation Queue Dynamics Data The WECC dynamics data associated with each of the WECC power flow cases was used as a starting point for this analysis. Type 3 generic wind turbine models and the newer generator/converter models for solar plants were used to represent the PacificCorp Queue generation additions in Wyoming and Utah. The same basic models were used for each plant with the MVA values changed to reflect the size of the plant modeled. Both wind and solar generation plants were assumed to have an MVA rating equal to MVA for each 2 MW of plant output. Figure shows the generic dynamic data used for wind generation. Figure shows the generic dynamic data used for solar generation. 18

19 Figure Generic Dynamic Data Assumptions for the Aeolus Area Wind Generation # # No repc_a model is included because the response of the plant controller is such that no response will be visible during the transient time frame. # Change mva=xxxx to a integer multiple of MVA. Each individual wind turbine has an MVA base of MVA. # regc_a "GNRIC WND G1" "1 " : #9 mva=xxxx "lvplsw" 1.0 "rrpwr" 0.65 "brkpt" 0.9 "zerox" 0.4 "lvpl1" 1.22 / "vtmax" 1.2 "lvpnt1" 0.2 "lvpnt0" 0.1 "qmin" -1.3 "accel" 0.5 "tg" "tfltr" 1 "iqrmax" 49.0 "iqrmin" "xe" 0 reec_a "GNRIC WND G1" "1 ": #9 "mvab" 0.0 "vdip" 0.9 "vup" 1.25 "trv" 0.02 "dbd1" "dbd2" 0.12 "kqv" 2.4 / "iqh1" 1.0 "iql1" -1.0 "vref0" 1.05 "iqfrz" 0.15 "thld" 0.0 "thld2" 0.0 "tp" 0.05 "qmax" "qmin" "vmax" 1.1 "vmin" 0.9 / "kqp" 5.0 "kqi" 5.0 "kvp" 5.0 "kvi" 5.0 "vref1" 0.0 "tiq" 0.01 "dpmax" 99.0 "dpmin" "pmax" "pmin" 0.0 "imax" 1.2 / "tpord" 0.01 "pfflag" 0 "vflag" 0 "qflag" 1 "pflag" 0 "pqflag" 0 "vq1" 0.0 "iq1" 0.0 "vq2" 0.20 "iq2" 1.0 "vq3" 0.50 "iq3" 1.0 / "vq4" "iq4" 1.0 "vp1" 0.0 "ip1" 0.0 "vp2" 0.20 "ip2" 0.50 "vp3" "ip3" 0.50 "vp4" "ip4" wtgq_a "GNRIC WND G1" "1 " : #9 "mvab" 0.0 "kip" 0.5 "kpp" 2.5 "tp" 0.4 "twref" 60.0 "temax" 1.1 "temin" 0 / "p1" 0.2 "spd1" 0.58 "p2" 0.4 "spd2" 0.72 "p3" 0.6 "spd3" 0.86 "P4" 0.8 "spd4" 1.0 "tflag" 0 wtgt_a "GNRIC WND G1" "1 " : #9 "mvab" 0.0 "ht" 6.7 "hg" 5.7 "dshaft" 1.5 "kshaft" 0.2 "wo" 1 wtga_a "GNRIC WND G1" "1 " : #9 "mvab" 0.0 "Ka" "Theta0" 0 wtgp_a "GNRIC WND G1" "1 " : #9 "mvab" 0.0 "kiw" 25.0 "kpw" "kic" 10 "kpc" 1 "kcc" 0.7 "tpi" 0.3 / "pimax" 27.0 "pimin" 0 "piratmx" 10.0 "piratmn"

20 Figure Generic Dynamic Data Assumptions for Solar Generation # # No repc_a model is included because the response of the plant controller is such that no response will be visible during the transient time frame. # Change mvab=xxxx to an integer multiple of MVA. Each individual solar inverter has an MVA base of MVA. The qmax, qmin, # pmax, and pmin variables of the reec_b model were changed to reflect PU output characteristics in respect to mvab of the regc_a model. # regc_a " GNRIC SLR G1" 0.48 "1 " : #9 mvab=xxxx "lvplsw" 1. "rrpwr" 10.0 "brkpt" 0.9 "zerox" 0.4 "lvpl1" 1.22 / "vtmax" 1.2 "lvpnt1" 0.8 "lvpnt0" 0.4 "qmin" -1.3 "accel" 0.7 "tg" 0.02 "tfltr" 0.02 "iqrmax" 999. "iqrmin" "xe" 0. reec_b " GNRIC SLR G1" 0.48 "1 " : #9 "mvab" 0. "vdip" -99. "vup" 99. "trv" 0.02 "dbd1" -0.5 "dbd2" 0.5 "kqv" 0. / "iqh1" 1.5 "iql1" -1.5 "vref0" 0. "tp" 0.5 "qmax" XXXX "qmin" XXXX "vmax" 1.1 "vmin" 0.9 "kqp" 0.0 "kqi" 0.1 "kvp" 0.1 / "kvi" 40. "tiq" 0.2 "dpmax" 999. "dpmin" "pmax" XXXX "pmin" 0. "imax" 1.3 "tpord" 0.4 "pfflag" 1. "vflag" 1. "qflag" 0. / "pqflag" 1. 20

21 2.5 Simultaneous Analysis for Selected WECC Paths Several WECC Rated Paths were identified as candidates where simultaneous limitations with the Cross-Tie Project could occur. The purpose of this analysis was to identify these constraints, determine how these constraints impact the proposed Cross-Tie rating, and identify potential mitigation that could be implemented to achieve the desired Cross-Tie rating under simultaneous flow conditions. This initial screening analysis is supplemental to the WECC Phase 1 Rating Report (or Comprehensive Progress Report) 2. The selected WECC Rated Paths to be stressed simultaneously with Cross-Tie for these studies are listed in Table Table Selected WECC Rated Paths WECC Path Interaction Simultaneous Condition Path Rating Other WECC Rated Path Interactions Scenario I Gateway South and Gateway West to Populus Included Cross-Tie at 1,500 MW Scenario II Only Gateway South Cross-Tie at 1,500 MW Path 37 (TOT 4A) 2175 MW N-S X X Aeolus South 1,700 MW N-S X N/A Aeolus West 2,160 MW N-S Includes Bridger-Anticline West, Borah West and Midpoint West Paths at maximum flow E-W X N/A Path 66 (COI) 4,800 MW N-S PDCI at 3100 MW N-S X X Path 78 (TOT 2B1) 600 MW N-S IPP net import at 1,200 MW, Path 27 (IPP DC) at 2,400 MW N-S. Include nomogram limit with Path 79 (TOT 2B2) X X Path 35 (TOT 2C) 600 MW N-S IPP net import at 1,200 MW, Path 27 (IPP DC) at 2,400 MW N-S. Include nomogram limit with Path 79 (TOT 2B2) Path 29 (Intermountain-Gonder) 200 MW E-W X X X X 2.6 Contingency Lists This screening level analysis utilized the WECC Path Rating Catalog to select the limiting contingencies to be studied for each Path. In addition, engineering judgement was utilized to select any other contingencies that may impact the rating of the Cross-Tie Project. Three to ten contingencies were selected based on the Path that was studied. Several variations of the most severe or limiting contingency were also evaluated for mitigation purposes. A list of the contingencies studied for each Path is provided in the appropriate Simultaneous Path Study Results Sections of the Report. 2 Additional simultaneous studies on these Paths will be performed during Phase 2 of the WECC Path Rating Process. 21

22 2.7 Study Methodology and Assumptions Power flow analysis was used to evaluate thermal and voltage performance of the transmission system under NERC Category P0 (normal conditions with all elements inservice), and selected NERC Category P1 (emergency conditions with one element out of service), and selected NERC Category P2 (emergency conditions with multiple elements out of service). Contingencies were selected based on the limiting contingencies listed in the WECC Path Rating Catalog or by using engineering judgment. Normal thermal loading was typically reported when a transmission component was loaded above 95% of the appropriate Amp/MVA rating. Emergency thermal loading was typically reported when a transmission component was loaded over 95% of its appropriate emergency Amp/MVA rating and if there is a change in flow greater than 0.5% from the pre-contingency flow. For brevity, the report tables show data that exceed 99% of the applicable rating. In addition, selected transmission lines were monitored for every base and contingency case regardless of flow. Monitored normal voltage violations were limited to the conditions where per unit (PU) voltages were less than 0.95 or greater than Monitored emergency voltage violations were limited to the conditions where per unit voltages were less than 0.90 or greater than Voltage deviations less than -8% between the pre- and postcontingency states were listed in the report tables. The latest WECC Regional Criterion defined in TPL-001-WECC-CRT3 was used in evaluating the system performance for the dynamics analysis results. The elements of this criterion are: Dynamics results shall be stable and damped. Following fault clearing, the voltage shall recover to 80% of the pre-contingency voltage within 20 seconds of the initiating event for all P1 through P7 events, for each applicable BES bus serving load. Following fault clearing and voltage recovery above 80%, voltage at each applicable BES bus serving load shall neither dip below 70% of precontingency voltage for more than 30 cycles nor remain below 80% of pre-contingency voltage for more than two seconds, for all P1 through P7 events. For Contingencies without a fault (P2.1 category event), voltage dips at each applicable BES bus serving load shall neither dip below 70% of pre-contingency voltage for more than 30 cycles nor remain below 80% of pre-contingency voltage for more than two seconds. All power flow and dynamics analysis was conducted with version 19.0_02 of General Electric s PSLF/PSDS/SCSC software. 22

23 3. Simultaneous Path Study Results The objective of this study is to perform a screening level analysis of the WECC Rated Paths that may be impacted the most from the addition of the Cross-Tie Project. Only a few contingencies that were deemed to be the most critical for each Path were selected. This section discusses the study results for the interactions of the WECC Rated Paths selected to be stressed simultaneously with the Cross-Tie 500 kv Project. 3.1 Path 37 (Tot 4A) Path 37 is also known Tot 4A and currently has a non-simultaneous rating of 1,025 MW in the northeast to southwest direction. The Path currently consists of three 230 kv lines and is also dependent on the Path 38 (Tot 4B) flow. The real-time rating can range between MW with the later value based on the winter ratings of the lines. A typical real-time rating centers around 650 MW. The critical disturbances and limiting elements vary based on the conditions and remedial actions are required to achieve the rated transfer capability. The critical contingencies and remedial actions are not specifically listed in the WECC Path Rating Catalog. Path 37 will be upgraded to 2,175 MW with the implementation of the Gateway West Project. The WECC Path Rating Catalog identifies the critical disturbance as the Aeolus- Anticline 500 kv line. However, it also mentions that remedial actions are required for other N-1 and N-2 contingencies, but the Path Rating Catalog does not list the contingencies or remedial actions 3. It is also currently unknown if the new rating will be non-simultaneous and/or impacted by real-time conditions as is true with the current rating. The Path 37 limits are dependent on Path 38 (Tot 4B) which has a non-simultaneous rating of 880 MW. The real-time rating for Path 38 is MW and typically centers around 475 MW. The critical disturbances and limiting elements vary based on the study conditions and are not listed in the WECC Path Rating Catalog. It is also unknown if or how the Path 37 upgrades will impact the Path 38 rating. The flow on Path 38 could also potentially impact the amount of generation tripping in the Aeolus area for the Aeolus South and Aeolus West contingencies. 3 The 2017 WECC Path Rating catalog states the following for the Post-Gateway Path 37: Remedial actions are required to achieve the rated transfer capability. For certain N-1 & N-2 outages, the Dave Johnston 230/115 kv transformer needs to be tripped. RAS schemes applicable to the West and South of Aeolus Path ratings. The Path Rating Catalog also states the following in the Pre-Gateway Path 37 description: Remedial actions are required to achieve the rated transfer capability. Following an outage, all overloaded lines and transformers must have their loading reduced to continuous ratings with 15 minutes. This is accomplished by reducing schedules and adjusting generation. The specifics of the remedial actions required for contingencies in this area and how to apply seasonal and emergency ratings is not documented in the Path Rating Catalog. 23

24 In addition, about 4,340 MW of new generation was added to the Aeolus area in the power flow cases based on the PacifiCorp generation queue. There was about 1,440 MW of queue generation already present in the cases and it appears that about 1,000 MW of queue generation has been suspended or deactivated. The 230 kv system upgrades associated with the Gateway West project were based on some of the generation that has been suspended and it is unknown how the other queue additions will impact the transmission system and the WECC Rated Paths in this area. Analysis of this area indicated that the loss of the Cross-Tie 500 kv line only had about a 6% impact on the Path 37 flow and that it tended to reduce this flow. The loss of the Aeolus South and Aeolus West lines had much larger impacts on this area. The Path 37 issues must be addressed and resolved for these other Projects to be implemented. For the reasons described in this section, it was determined that the Path 37 analysis should be postponed until the Phase II studies. It was determined that there are too many variables and unknowns in this area to conduct an accurate and meaningful simple screening analysis of Path 37 without input by the Project Review Group (PRG). 3.2 Aeolus South (Aeolus-Clover) Aeolus South is also known as the Gateway South Transmission Project and consists of a new 500 kv transmission line that runs from Aeolus Substation in eastern Wyoming to Clover Substation in central Utah. Clover is also the termination point for the Cross-Tie Project. Aeolus South has a north to south rating of 1,700 MW Summary of Path Flows for the Aeolus South Analysis Table thru shows the Path flows that exceed 90% for the each of the power flow cases that were developed for the Aeolus South analysis. The Cross-Tie Project, Path 66, Path 65, and Path 27 are loaded to their rated values for every seasonal and scenario case evaluated in this analysis. Table Aeolus South - Path Flows for the 2026 Heavy Summer Case Scenario I 2026 Heavy Summer Scenario II Path No Path Name Rating 1 Rating 2 MW Flow % Rating MW Flow % Rating 18 MONTANA - IDAHO BRIDGER WEST IPP DC LINE PACIFIC DC INTERTIE (PDCI) COI Cross Tie Aeolus South Harry Allen-Eldorado (SNIP)

25 Table Aeolus South - Path Flows for the 2026 Heavy Winter Case 2026 Heavy Winter Scenario I Scenario II Path No Path Name Rating 1 Rating 2 MW Flow % Rating MW Flow % Rating 18 MONTANA - IDAHO BRIDGER WEST IPP DC LINE PACIFIC DC INTERTIE (PDCI) COI Cross Tie Aeolus South Harry Allen-Eldorado (SNIP) Table Aeolus South - Path Flows for the 2026 Light Spring Case Scenario I 2026 Light Spring Scenario II Path No Path Name Rating 1 Rating 2 MW Flow % Rating MW Flow % Rating 18 MONTANA - IDAHO BRIDGER WEST IPP DC LINE PACIFIC DC INTERTIE (PDCI) COI Cross Tie Aeolus South Harry Allen-Eldorado (SNIP) Summary of Case Data for the Aeolus South Analysis Tables thru show the case area data for each of the scenario and seasonal case flows evaluated. The original plan for this analysis was to stress the Cross-Tie Project by increasing generation in the Aeolus area and decreasing generation in Southern California. However, the selected WECC base cases were moderately/lightly loaded on some Paths into California that were desired to be stressed during the studies. Adjustments made to stress these Paths resulted in low generation levels in Southern California 4. Since generation levels were high in Arizona, Cross-Tie was stressed to 1,500 MW by increasing Aeolus area generation in Southeastern Wyoming (Area 65 PACE) and decreasing generation in the Arizona area (while maintaining COI flow). 4 COI (Path 66) and PDCI (Path 65) were stressed primarily by increasing generation in the Northwest (Area 40) and decreasing Southern California (Areas 22, 24, 26) generation. The IPP DC (Path 27) was stressed primarily by increasing generation at Intermountain or in the Utah area (PACE), and decreasing generation in the immediate LADWP area. 25

26 Table Aeolus South Area Data for the 2026 Heavy Summer Case 2026 Heavy Summer Scenario I Scenario II AREA AREA NAME P Gen P Load P Loss P Intchg P Gen P Load P Loss P Intchg 10 NEW MEXICO 3,433 3, ,434 3, EL PASO 1,576 2, ,576 2, ARIZONA 24,423 23, ,851 23, , NEVADA 6,541 6, ,540 6, MEXICO-CFE 3,295 3, ,293 3, IID 2,484 1, ,029 2,484 1, , SANDIEGO 4,867 5, ,869 5, SOCALIF 17,953 23, ,770 18,291 23, , LADWP 5,832 7, ,352 6,298 7, , PG AND E 25,855 28, ,380 25,857 28, , NORTHWEST 34,250 27,674 1,288 5,288 34,725 27,674 1,377 5, B.C.HYDRO 11,993 8, ,948 11,994 8, , FORTISBC ALBERTA 14,447 14, ,448 14, IDAHO 2,346 4, ,125 2,347 4, , MONTANA 3,134 2, ,131 2, WAPA U.M SIERRA 2,552 2, ,552 2, PACE 15,127 9, ,562 13,458 9, , PSCOLORADO 8,701 8, ,695 8, WAPA R.M. 6,868 6, ,850 6, Table Aeolus South Area Data for the 2026 Heavy Winter Case Scenario I 2026 Heavy Winter AREA AREA NAME P Gen P Load P Loss P Intchg P Gen P Load P Loss P Intchg 10 NEW MEXICO 3,143 2, ,141 2, EL PASO 1,004 1, ,004 1, ARIZONA 23,048 16, ,872 23,356 16, , NEVADA 3,425 3, ,425 3, MEXICO-CFE 1,917 1, ,917 1, IMPERIALCA 1, , SANDIEGO 2,106 3, ,450 2,108 3, , SOCALIF 5,601 16, ,958 5,399 16, , LADWP 4,175 4, ,314 4,178 4, , PG AND E 17,764 19, ,886 17,765 19, , NORTHWEST 41,480 32,733 1,498 7,329 41,929 32,733 1,538 7, B.C.HYDRO 13,113 11, ,113 11, FORTISBC 762 1, , ALBERTA 15,479 15, ,479 15, IDAHO 1,837 2, ,171 1,844 2, , MONTANA 3,109 2, ,110 2, WAPA U.M SIERRA 1,924 2, ,925 2, PACE 12,345 8, ,845 11,758 8, , PSCOLORADO 6,633 6, ,627 6, WAPA R.M. 6,334 5, ,309 5, Scenario II

27 Table Aeolus South Area Data for the 2026 Light Spring Case 2026 Light Spring Scenario I Scenario II AREA AREA NAME P Gen P Load P Loss P Intchg P Gen P Load P Loss P Intchg 10 NEW MEXICO 2,225 2, ,222 2, EL PASO 849 1, , ARIZONA 12,093 10, ,707 12,456 10, , NEVADA 1,511 2, ,511 2, MEXICO-CFE 1,289 1, ,289 1, IMPERIALCA SANDIEGO 2,084 2, ,085 2, SOCALIF 3,180 11, ,886 2,857 11, , LADWP 2,603 2, ,604 2, PG AND E 12,154 13, ,920 12,155 13, , NORTHWEST 24,266 17, ,418 24,611 17, , B.C.HYDRO 6,528 6, ,529 6, FORTISBC ALBERTA 8,598 7, ,595 7, IDAHO 1,105 1, ,112 1, MONTANA 3,313 1, ,982 3,323 1, , WAPA U.M SIERRA 1,432 1, ,431 1, PACE 11,078 7, ,096 10,649 7, , PSCOLORADO 3,880 4, ,876 4, WAPA R.M. 4,322 3, ,018 4,298 3, , Contingency List for the Aeolus South Analysis Normal and emergency conditions are evaluated to determine any impacts that may occur with the simultaneous loading of Cross-Tie and Aeolus South. The WECC Path Rating Catalog identifies a few critical contingencies that determine the 1,700 MW north to south limit for Aeolus South. The loss of Cross-Tie was also selected to be studied. These contingencies are listed in Table Variations of generation tripping for these contingencies were also investigated to mitigate any potential issues that occurred. The shaded regions of the table indicate the limiting contingencies that are defined in the WECC Path Rating Catalog. The WECC Path Rating Catalog identifies that 600 MW of generation tripping may be required for the two critical contingencies. Because of the Scenario II case where Aeolus West is eliminated, and the fact that this analysis utilized more queue generation in the Aeolus area than what was likely used to determine the 600 MW generation tripping number, other generation tripping sensitivities were also evaluated. In addition, the WECC Path Rating Catalog does not identify any 230 kv contingencies in the Aeolus area as related to the Aeolus South Path. However, it does state that several contingencies in the area can impact the Path 37 and Path 38 limits for both the existing and post-gateway systems. Because of the unknowns associated with which queue generation will be constructed, the unknown contingencies that limit the Path 37 and 38 27

28 simultaneous analysis, and the use of winter ratings in the existing Path nomograms, the critical local area contingencies were not studied in this analysis. It is assumed that the appropriate 230 kv transmission will be constructed to accommodate the queue generation additions. Therefore, any 230 kv overloads in the Aeolus area were ignored for this analysis. The location of the installed queue generation, and the status of the Aeolus West Project could also significantly impact the amount and location of generation used in the generation tripping schemes related to Aeolus South. The amount of generation tripping used in this analysis may need to be changed significantly depending on the final configuration of the generation and 230 kv transmission in this area. Table Selected Contingencies for the Aeolus South Analysis NERC No Contingency Description P0 0 Base Case - Normal Conditions P Trip Cross-Tie 500 kv Transmission Line 10.1 Trip Cross-Tie 500 kv Transmission Line (600 MW Gen Tripping RAS) 10.2 Trip Cross-Tie 500 kv Transmission Line (1200 MW Gen Tripping RAS) 60 Trip Aeolus South 500 kv Transmission Line (No RAS) 60.1 Trip Aeolus South 500 kv Transmission Line (600 MW Gen Tripping) 60.2 Trip Aeolus South 500 kv Transmission Line (1200 MW Gen Tripping) 80 Trip Aeolus-Anticline #1 500 kv Transmission Line (No RAS) 80.1 Trip Aeolus-Anticline #1 500 kv Transmission Line (600 MW Gen Tripping RAS) 80.2 Trip Aeolus-Anticline #1 500 kv Transmission Line (1200 MW Gen Tripping RAS) Diverged Cases for the Aeolus South Analysis Several cases had numerical divergence issues for this analysis. These cases consisted of the Aeolus South or Aeolus West contingency with no generation tripping RAS. Tables thru indicate the diverged cases for each of the scenarios and seasons studied. Table Aeolus South Heavy Summer - Summary of Diverged Cases 2026 Heavy Summer NERC No Contingency Description Scenario I Scenario II P Trip Aeolus South 500 kv Transmission Line (No RAS) Diverged Diverged 80 Trip Aeolus-Anticline #1 500 kv Transmission Line (No RAS) Diverged Solved Table Aeolus South Heavy Winter - Summary of Diverged Cases 2026 Heavy Winter NERC No Contingency Description Scenario I Scenario II P Trip Aeolus South 500 kv Transmission Line (No RAS) Diverged Diverged 28

29 Table Aeolus South Light Spring - Summary of Diverged Cases 2026 Light Spring NERC No Contingency Description Scenario I Scenario II P Trip Aeolus South 500 kv Transmission Line (No RAS) Solved Diverged Thermal Overloads for the Aeolus South Analysis Tables thru indicate the thermal overload issues for the contingencies selected to analyze Aeolus South. Initially, there were very severe normal overloads indicated on the Aeolus-Freeze Out 230 kv line due to about 770 MW of generation added at Freeze Out. This generation was subsequently moved to Aeolus to eliminate the severe normal overloads. There were very severe overloads in the Aeolus area for the Aeolus South contingency and several of the power flow cases diverge when generation tripping is not implemented. Generation tripping sensitivities of 600 MW, 900 MW, 1,200 MW, 1,500 MW, and 1,600 MW were investigated to eliminate overload issues. All generation tripping is assumed to be near Aeolus or Windstar substations. The Scenario I cases, where Gateway West is present, have no overload violations with 600 MW of generation tripping. The Scenario II cases, with only Gateway South modeled, can require up to 1,600 MW of generation tripping to eliminate the overloads. These overload issues are associated with the Gateway West and Gateway South Projects rather than the Cross-Tie Project. The generation tripping required for the Aeolus South contingency can be a function of the location of the generation selected to be tripped and any transmission projects implemented to accommodate the large concentration of generation in the area 5. Generation tripping could also be a function of flows on other WECC rated Paths. There is currently an operating nomogram for Path 37 (Tot 4A) and Path 38 (Tot 4B). With a large injection of generation into the Aeolus area, flows on Path 37 are typically from north-to-south. The flow on Path 38 would tend to be in the south-to-north direction. If Path 38 flows in the south-to-north direction are reduced (via Montana phase shifters), the generation tripping requirements to eliminate overloads may increase for the Aeolus South contingency. It is unknown if the Path 37/38 nomogram will be updated when Path 37 is upgraded. However, the overloads seem to indicate that this would be a requirement and that the amount of Aeolus area generation tripping required could vary based on this operating nomogram. The amount of generation tripping required can vary significantly from case to case due to various factors. The Scenario I cases, where Gateway West is present, have no 5 The transmission reinforcements currently defined in the Aeolus 230 kv system as part of the Gateway West Project are based on a certain level of PacifiCorp queue generation in the Aeolus area. About 1,000 MW of this generation has been deactivated or suspended. Another 4,300 MW of generation in this area was added to the case. This may change the transmission reinforcements that are needed in the Aeolus area and impact the amount of generation tripping required. 29

30 overload violations with 600 MW of generation tripping. The Scenario II cases, with only Gateway South, can require about 1,600 MW of generation tripping to mitigate overloads on the Platte-Standpipe 230 kv line. The level of generation tripping is not a function of the Cross-Tie Project, but the Cross- Tie Project may be able to use this generation tripping as a form of mitigation for issues with the simultaneous loading of other Paths. In addition, it appears that generation tripping can vary based on the operating conditions in the Aeolus area. For these reasons, the generation tripping was set to a slightly more conservative level of 1,500 MW for the simultaneous analysis in later sections. 30

31 Table Aeolus South Heavy Summer - Summary of Thermal Overloads 2026 Heavy Summer MVA Scenario I Scenario II NERC No Contingency Description Monitored Branch Section Rating P Dir Area % Rating % Rating P Trip Aeolus South 500 kv Transmission Line (600 MW Gen Tripping) BAR-X BITR CRK Ckt # ) BAR-X ECHOSPRG Ckt # ( DAVEJOHN AMASA Ckt # (-- * DIFICULT AMASA Ckt # ) * DIFICULT SHIRLYBS Ckt # (-- * LATHAM ECHOSPRG Ckt # ) MARYLKSB /MARYLKSB Bank # ) PLATTE LATHAM Ckt # ) PLATTE STNDPIPE Ckt # ( PT ROCKS BITR CRK Ckt # ( QUARTZ /QUARTZ Bank # ) Trip Aeolus South 500 kv Transmission Line (900 MW Gen Tripping) BAR-X BITR CRK Ckt # ) BAR-X ECHOSPRG Ckt # ( LATHAM ECHOSPRG Ckt # ) MARYLKSB /MARYLKSB Bank # ) PLATTE LATHAM Ckt # ) PLATTE STNDPIPE Ckt # ( PT ROCKS BITR CRK Ckt # ( Trip Aeolus South 500 kv Transmission Line (1200 MW Gen Tripping) MARYLKSB /MARYLKSB Bank # ) PLATTE STNDPIPE Ckt # ( Trip Aeolus South 500 kv Transmission Line (1500 MW Gen Tripping) PLATTE STNDPIPE Ckt # ( Trip Aeolus South 500 kv Transmission Line (1600 MW Gen Tripping) PLATTE STNDPIPE Ckt # (

32 Table Aeolus South Heavy Winter - Summary of Thermal Overloads 2026 Heavy Winter MVA Scenario I Scenario II NERC No Contingency Description Monitored Branch Section Rating P Dir Area % Rating % Rating 60.1 Trip Aeolus South 500 kv Transmission Line (600 MW Gen Tripping) BAR-X BITR CRK Ckt # ) PLATTE STNDPIPE Ckt # ( PT ROCKS BITR CRK Ckt # ( Trip Aeolus South 500 kv Transmission Line (900 MW Gen Tripping) BAR-X BITR CRK Ckt # ) PLATTE STNDPIPE Ckt # ( PT ROCKS BITR CRK Ckt # ( Trip Aeolus South 500 kv Transmission Line (1200 MW Gen Tripping) BAR-X BITR CRK Ckt # ) PLATTE STNDPIPE Ckt # ( PT ROCKS BITR CRK Ckt # ( Trip Aeolus South 500 kv Transmission Line (1500 MW Gen Tripping) BAR-X BITR CRK Ckt # ) PLATTE STNDPIPE Ckt # ( PT ROCKS BITR CRK Ckt # ( Table Aeolus South Light Spring - Summary of Thermal Overloads Light Spring MVA Scenario I Scenario II NERC No Contingency Description Monitored Branch Section Rating P Dir Area % Rating % Rating P Trip Aeolus South 500 kv Transmission Line (600 MW Gen Tripping) AMASA DAVEJOHN Ckt # ) * BAR-X BITR CRK Ckt # ) BAR-X ECHOSPRG Ckt #1 505 ( LATHAM ECHOSPRG Ckt # ) PLATTE LATHAM Ckt # ) PLATTE STNDPIPE Ckt #1 501 ( PT ROCKS BITR CRK Ckt #1 478 ( Trip Aeolus South 500 kv Transmission Line (900 MW Gen Tripping) BAR-X BITR CRK Ckt # ) PLATTE STNDPIPE Ckt #1 501 ( PT ROCKS BITR CRK Ckt #1 478 ( Trip Aeolus South 500 kv Transmission Line (1200 MW Gen Tripping) BAR-X BITR CRK Ckt # ) PLATTE STNDPIPE Ckt #1 501 ( PT ROCKS BITR CRK Ckt #1 478 ( Trip Aeolus South 500 kv Transmission Line (1500 MW Gen Tripping) BAR-X BITR CRK Ckt # ) PLATTE STNDPIPE Ckt #1 501 ( PT ROCKS BITR CRK Ckt #1 478 (

33 3.2.6 Voltage Violations for the Aeolus South Analysis Tables thru indicate the voltage violation issues for the contingencies selected to analyze simultaneous flows on Aeolus South and the Cross-Tie Project. These tables show all the voltage deviation issues for buses with a base voltage greater than 35 kv. The tables indicate that the loss of Aeolus South can result in very low voltages in the Aeolus area and diverged cases in some instances. The cases diverge when no generation tripping is implemented. Generation tripping sensitivities of 600 MW, 900 MW, 1,200 MW, and 1,500 MW were investigated to eliminate voltage deviation issues. All generation tripping is assumed to be near Aeolus or Windstar substations. The Scenario I cases, where Gateway West is present, have no voltage violations with 600 MW of generation tripping. The Scenario II cases, with only Gateway South, can require up to 1500 MW of generation tripping to keep the voltage deviation greater that -8%. A more precise evaluation of generation tripping will be required once the amount and location of the installed queue generation is known and any associated transmission projects are determined. 33

34 Table Aeolus South Heavy Summer - Summary of Voltage Violations 2026 Heavy Summer Scenario I Scenario II NERC No Contingency Description Bus Name Area Base VPU Cont VPU % Dev Base VPU Cont VPU % Dev P Trip Aeolus South 500 kv Transmission Line (600 MW Gen Tripping) OREBASIN BAR-X MUSTANG LATHAM ECHOSPRG ATLANTIC BADWATER BAIROIL MANSFACE GREATDIV MUSTANG OREBASIN PLATTE PLATTE TROWBRDG PT ROCKS SPENCE WHISKEYP WYOPO HILLTP KIRBY CR COL GEN BITR CRK BADWATER WYOPO BASIN BOYSEN CARTERMT COPPERMT HDOME JIMREADY PILOT BU THERMOPL WINDRIVR HARRSBRG BUFBASIN HDOME CMTDUM BUFFALO HEAD Trip Aeolus South 500 kv Transmission Line (900 MW Gen Tripping) BAR-X LATHAM ECHOSPRG PLATTE PLATTE TROWBRDG BITR CRK Trip Aeolus South 500 kv Transmission Line (1200 MW Gen Tripping) LATHAM ECHOSPRG PLATTE TROWBRDG BITR CRK Trip Aeolus South 500 kv Transmission Line (1500 MW Gen Tripping) BAR-X LATHAM ECHOSPRG PLATTE PLATTE TROWBRDG

35 Table Aeolus South Heavy Winter - Summary of Voltage Violations 2026 Heavy Winter Scenario I Scenario II NERC No Contingency Description Bus Name Area Base VPU Cont VPU % Dev Base VPU Cont VPU % Dev P Trip Aeolus South 500 kv Transmission Line (600 MW Gen Tripping) BAR-X MUSTANG LATHAM ECHOSPRG ATLANTIC BADWATER BAIROIL MANSFACE GREATDIV MUSTANG PLATTE PLATTE TROWBRDG PT ROCKS RIVERTON SPENCE WHISKEYP WYOPO HILLTP KIRBY CR COL GEN BITR CRK BADWATER WYOPO BOYSEN COPPERMT HDOME JIMREADY PILOT BU THERMOPL WINDRIVR HARRSBRG BUFBASIN HDOME CMTDUM BUFFALO HEAD Trip Aeolus South 500 kv Transmission Line (900 MW Gen Tripping) BAR-X LATHAM ECHOSPRG BAIROIL PLATTE PLATTE TROWBRDG WHISKEYP BITR CRK Trip Aeolus South 500 kv Transmission Line (1200 MW Gen Tripping) LATHAM ECHOSPRG PLATTE TROWBRDG BITR CRK Trip Aeolus South 500 kv Transmission Line (1500 MW Gen Tripping) LATHAM ECHOSPRG PLATTE PLATTE

36 Table Aeolus South Light Spring - Summary of Voltage Violations 2026 Light Spring Scenario I Scenario II NERC No Contingency Description Bus Name Area Base VPU Cont VPU % Dev Base VPU Cont VPU % Dev P Trip Aeolus South 500 kv Transmission Line (600 MW Gen Tripping) VANBUREN AMISTAD CLAPHAM CLAPHAM CLAYTON ROSEBUD LATHAM ECHOSPRG BAIROIL PLATTE PLATTE TROWBRDG WHISKEYP BITR CRK Trip Aeolus South 500 kv Transmission Line (900 MW Gen Tripping) ECHOSPRG PLATTE TROWBRDG BITR CRK Trip Aeolus South 500 kv Transmission Line (1200 MW Gen Tripping) ECHOSPRG Trip Aeolus South 500 kv Transmission Line (1500 MW Gen Tripping) LATHAM ECHOSPRG PLATTE PLATTE

37 3.2.7 Transient Stability Results for the Aeolus South Analysis Dynamics analysis was performed for a few selected contingencies. The selected contingencies include the loss of the Cross-Tie Project and contingencies identified in the WECC Path Rating Catalog. These contingencies are listed in Table Table Dynamics Contingencies Evaluated for the Aeolus South Path NO CONTINGENCY DESCRIPTION 10 Clover 3PH Fault - Trip Cross-Tie 500 kv Transmission Line (Flash Capacitors) 60 Aeolus 3 PH Fault - Trip Aeolus South 500 kv Transmission Line (No RAS) 60.1 Aeolus 3 PH Fault - Trip Aeolus South 500 kv Line (650 MW Gen cycles) 60.2 Aeolus 3 PH Fault - Trip Aeolus South 500 kv Line (1550 MW Gen cycles) 70 Robinson Summit 3PH Fault - Trip SWIP South 500 kv Transmission Line 80 Aeolus 3 PH Fault - Trip Aeolus-Anticline 500 kv Transmission Line 80.1 Aeolus 3 PH Fault - Trip Aeolus-Anticline 500 kv Line(650 MW Gen cycles) Stability plots are included in Appendix 1. The analysis concluded that the system was stable and that there were no voltage deviation or frequency violations or out-of-step units for cases with sufficient generation tripping RAS applicable to the appropriate Scenario cases. This analysis ignores the first few cycles after the fault is cleared. In this time frame, there were simulated voltage and frequency spikes that may cause the protection relays to trip generation in the Aeolus area. For this reason, these relay models were deactivated for this analysis. This issue is specifically related to disturbances in the Aeolus area and does not impact the Cross-Tie Project. Note that the generation tripping RAS is slightly different for the dynamics and power flow cases (600 vs 650 for Scenario I and 1500 vs 1550 for Scenario II) 6. This was done to ensure consistency in the selection of tripped units between all the dynamics cases that were evaluated. In addition, the generation tripping RAS was implemented in 20 cycles for this analysis. An evaluation of the generation tripping RAS timing was also performed and is described in the next section Aeolus Area Generation Tripping Timing An investigation of the generation tripping timing was also performed for the Aeolus South contingency. For this analysis, a 4-cycle fault is applied at the Aeolus 500 kv bus. This investigation was performed for the Heavy Summer Scenario I and Scenario II 6 The Scenario I case includes the Gateway South and parts of the Gateway West Project. The Scenario II case only includes the Gateway South Project. 37

38 cases. The frequency protection on the Aeolus area generation was disabled for this analysis. The voltage profile in the Aeolus area was high for the Scenario cases utilized in the analysis. Adjustments to reduce the overall 230 kv system voltage could improve the response due to the loss of the Aeolus 500 kv lines. This type of sensitivity analysis was not performed for these studies. There is also a synchronous condenser modeled on the Aeolus 230 kv bus. For this analysis, it was assumed that this device would provide near 0 MVAR during normal conditions. In addition, it was found that tripping the capacitors at the Aeolus 500 kv bus with the Aeolus South 500 kv line contingency could also potentially improve the initial high voltage spike. For the Scenario I case with the voltage protection relays active, approximately 1,980 MW of generation (10 units) were tripped due to a high voltage spike at about 0.5 to 1.75 cycles after the fault is cleared. The 230 kv voltages in the area were high in the initial case and maintaining a lower voltage profile or adding reactors and providing dynamic reactive support in certain locations may help further. The voltage spike in this case is more severe because Gateway West is present. For the Scenario II case with the voltage protection relays active, approximately 1,310 MW of generation (6 units) was tripped due to a high voltage spike at about 0.75 cycles after the fault is cleared. The issues described in the preceding paragraphs are a function of the Aeolus South and Aeolus West Projects and should be resolved during the analysis phases of those projects. The addition of the Cross-Tie Project should have a minor impact on these issues. However, the power flow analysis for other Paths indicated that the loss of Cross- Tie or the SWIP South contingency may also require generation tripping in the Aeolus area. Because of this issue, a determination of an allowable time delay used to trip the Aeolus area generation for these more remote contingencies was evaluated. This analysis was conducted with the voltage protection disabled. Plots and are voltage plots for Scenario I and Scenario II respectively. These plots show the voltage spike that could trip these units during the disturbance and roughly the point in time where the system is unstable. Both plots indicate that generation tripping RAS should be implemented by at most about 30 cycles after the fault is initiated. Plots and are the same voltage plots with 650 MW and 1550 MW of generation tripping at 30 cycles after the fault is initiated. These plots indicate that stability is achieved if generation tripping is implemented up to 30 cycles after the fault is initiated. 38

39 Figure Scenario I Voltage Plot for Freeze Out Queue Generator Figure Scenario II Voltage Plot for Freeze Out Queue Generator 39

40 Figure Scenario I Voltage Plot for Freeze Out Generator (650 MW gen trip) Figure Scenario II Voltage Plot for Freeze Out Generator (1550 MW trip) 40