Gateway South Transmission Project

Transcription

1 Phase 1 Comprehensive Progress Report Volume 1 - Technical Report Report Prepared by PacifiCorp Transmission Planning Department November 21, 2008 WECC1-V4

2 Phase 1 Comprehensive Progress Report Executive Summary Introduction The Gateway South project was announced by PacifiCorp in May 2007 to provide increased transmission capacity between Wyoming, Utah and southern Nevada. PacifiCorp initiated the Western Electricity Coordinating Council (WECC) Regional Planning Project Review process for Gateway South and the related Gateway West projects on June 25, The Gateway South Regional Planning Report was issued on May 28, The purpose of this Phase 1 comprehensive progress report is to demonstrate that sufficient technical studies have been conducted for the Gateway South Transmission Project (GS Project) to define the non-simultaneous planned rating(s) for the project and to describe the project preliminary plan-of-service. The Phase 1 studies that are outlined as part of the Study Plan (see Appendix A) focused on the non-simultaneous rating of the GS project, with some limited interactions with other paths and limited simultaneous analysis with the Gateway Projects. These limited simultaneous path interactions include the following: Gateway South (Aeolus Mona) and West of Aeolus and/or Bridger West transmission paths. Mona South and TOT 2C transmission paths (series paths) TOT 2B and TOT 2C transmission paths (exiting nomogram) Due to the scope and nature of the GS project, the Phase 1 portion of this study plan is intended to establish non-simultaneous ratings for the proposed transmission paths listed in Table 1. Table 1. Proposed Gateway South Transmission Lines Line Description 1 Aeolus Mona 500 kv, double circuit line 2 Mona South 500 kv, single circuit 500 kv line and single circuit 345 kv line 3 Red Butte Crystal 500 kv, single circuit line Transmission Path New New TOT 2C Path Rating Direction N S Bidirectional Bidirectional Due to the simultaneous interactions between the Gateway South and Gateway West projects, additional analysis was performed to evaluate the Gateway West project, east of Bridger (Bridger Aeolus Windstar). Because of this overlap between the two projects, WECC1-V4

3 Page ii of vii portions of this analysis will be included in both the Gateway South and Gateway West comprehensive progress reports. In an effort to assure that the proposed Energy Gateway Project (Gateway West, South and Central) were not dependant on other proposed projects to achieve their proposed ratings, sensitivity studies were performed to evaluate system performance with and with out the other project. Project Plan-of-Service An overview of the Gateway South transmission system modifications are summarized below and are illustrated in Figure 1. (A complete plan-of-service summary for the Project is included in the report Introduction Section I.) The Gateway South plan-ofservice calls for new 500 kv transmission facilities that will link Wyoming with the Utah Wasatch Front and continue to southern Utah/Nevada. Aeolus Mona 500 kv #1 & #2 (400 miles) Mona 500/345 kv #1 and #2 autotransformer (1500 MVA) Mona Sigurd 500 kv #1 (75 miles) Sigurd 500/345 kv #1 autotransformer (1500 MVA) Sigurd Red Butte 500 kv #1 (160 miles) Sigurd Red Butte 345 kv #2 (160 Miles) Red Butte 500/345 kv #1 autotransformer (1500 MVA) Red Butte 345 kv, Static VAr Controller (SVC) for voltage control Red Butte - Crystal 500 kv #1 (95 miles) Crystal 500 kv #1 thru #4 Phase Shifting Transformers (450 MVA, ±50 Degrees) Planned Operating Date The Gateway South schedule currently identifies the following in-service dates for key portions of the transmission project: Red Butte 345 kv SVC October 2011 Sigurd Red Butte 345 kv #2 December 2012 Red Butte Harry Allen (600 MW) Upgrade December 2012 Aeolus Mona 500 kv December 2016 Mona Sigurd Red Butte 500 kv December 2016 Red Butte Crystal 500 kv December 2016 Summary and Conclusions The following conclusions were drawn from the Phase 1 studies: Gateway West Analysis (included due to interactions with Gateway South) 1. TOT 4A Path Studies Based on technical findings of this report, the facilities proposed between Aeolus and Windstar will support increasing the nonsimultaneous TOT 4A path rating from 820 MW to 3435 MW. The limiting outage on this ii

4 Page iii of vii path is the N-1 of the Aeolus Windstar 500 kv line. Interactions between the TOT 4A path and other transmission paths will be evaluated during the Phase 2 (simultaneous) technical study review. To withstand a single circuit 500 kv outage, the Dave Johnston Difficulty Aeolus 230 kv line must be rebuilt to ACSR conductor/phase. Additionally, the Aeolus Windstar 230 kv #1 and #2 line must be constructed with ACSR conductor/phase. Interactions between the TOT 4A path and other transmission paths will be evaluated during the Phase 2 (simultaneous) technical study review. 2. West of Aeolus Path Studies Based on technical findings of this report, the facilities proposed between Jim Bridger and Aeolus will support a path rating of 2050 MW (simultaneous with South of Aeolus rating of 3000 MW). The West of Aeolus path rating is limited by the double line outage (N-2) outage of the Aeolus Bridger 500 kv line and the Aeolus Creston 230 kv or the Creston Bridger 230 kv lines and how much generation at Aeolus and Windstar that can be tripped for a specific system conditions. While the requirement for generator tripping at Jim Bridger (for outages west of Bridger), Aeolus or Windstar has been identified within the report, specific levels of Wyoming generator tripping vs. path flow levels and resource mix/location will need to be addressed in follow-on analysis. If the 230 kv line west of Aeolus (constructed 500 kv, energized 230 kv) was converted to 500 kv operation, transfers on the West of Aeolus path could be increased and generator tripping levels could be greatly reduced. Interactions between the West of Aeolus path and other transmission paths will be evaluated during the Phase 2 (simultaneous) technical study review. Gateway South 1. South of Aeolus (Aeolus Mona) Path Studies Based on technical findings of this report, the facilities proposed between Aeolus and Mona will support a path rating of 3000 MW (simultaneous with West of Aeolus flows of 2050 MW and Bridger West flows of 5200 MW). The Gateway South (South of Aeolus) path rating is limited by the double line outage (N-2) outage of the Aeolus Mona 500 kv #1 and #2 lines and how much generation at Aeolus and Windstar that can be tripped for a specific system condition. While the requirement for generator tripping at Jim Bridger (for outages west of Bridger), Aeolus or Windstar has been identified within the report, specific levels of Wyoming generator tripping vs. path flow levels and resource mix/location will need to be addressed in follow-on analysis. iii

5 Page iv of vii If the 230 kv line west of Aeolus (constructed 500 kv, energized 230 kv) was converted to 500 kv operation, generator tripping levels could be greatly reduced. Interactions between the Gateway South path and other transmission paths will be evaluated during the Phase 2 (simultaneous) technical study review 2. Mona South Path Studies Based on technical findings of this report, the facilities proposed South of Mona Path (Mona Sigurd Red Butte) will support a path rating (simultaneous with the TOT 2B paths) of at least 2400 MW north to south and 790 MW south to north. The Mona South path rating is limited by (1) load levels in southern Utah and (2) rating of the TOT 2C transmission path. Further Interactions between the Mona South path and other transmission paths will be evaluated during the Phase 2 (simultaneous) technical study review. 3. TOT 2C Path Studies Based on technical findings of this report, the facilities proposed to be added to the TOT 2C Path (Red Butte Harry Allen/Crystal) will support a path rating (simultaneous with the TOT 2B paths) of at least 2100 MW north to south and 1700 MW south to north. The TOT 2C path rating is limited by the outage of the Red Butte Crystal 500 kv line, and subsequent (proposed) tripping of a portion of the series capacitor bank at Harry Allen. Further Interactions between the TOT 2C path and other transmission paths will be evaluated during the Phase 2 (simultaneous) technical study review. Voltage Stability Analysis Voltage stability analysis was performed on the Case 1a, 1b and 1c base case for each of the paths noted above. Per the WECC reactive margin requirements, the 5% case showed acceptable reactive margins for the n-1 outages while the 2.5% case showed acceptable reactive margin for the n-2 outages. Sensitivity Studies Sensitivity study technical results have demonstrated that the Energy Gateway Projects can achieve their rating with or without the Great Basin North 500 kv line being constructed. The technical findings of this report demonstrate that sufficient technical studies have been conducted for the Gateway South Transmission Project (GS Project) to define the non-simultaneous planned rating(s) for the project and to describe the project preliminary plan-of-service. iv

6 Page v of vii FIGURE 1 Gateway South Single-line Gateway West Aeolus 230 kv to Windstar 500 kv to Windstar 230 kv to Creston/Bridger SVC 230 kv MVA 500 kv to Bridger Middle kv Gateway Central 500 kv to Limber Middle miles 3 - Athabaska/TW Mona #1 #2 500 kv MVA Sigurd 500 kv 345 kv 75 miles 3 - Athabaska/TW MVA 345 kv Red Butte #2 160 miles 3 - Athabaska/TW Crystal 500 kv 1500 MVA 345 kv 160 miles 2 Cardinal 954 ACSR 95 miles 3 - Athabaska/TW New 500 kv NPC Bus 500 kv MVA +50 PST 500 kv 345 kv 230 kv v

7 TABLE OF CONTENTS Gateway South Transmission Project Page vi of vii I. Introduction...1 General Project Plan-of-Service Planned Operating Date II. Objectives...4 A. Satisfy Reliability Criteria B. Define Plan-of-Service C. Acquire a Non-Simultaneous Rating III. IV. Approach...6 Conclusions...8 V. Summary of Study Results...11 VI. Discussion of Technical Results...23 VII. Sensitivity Studies...35 VIII. Phase 1 Technical Findings...44 vi

8 Page vii of vii APPENDICES APPENDIX A APPENDIX B APPENDIX C APPENDIX D APPENDIX E APPENDIX F APPENDIX G Study Plan Energy Gateway Project Plan of Service Base Case Summaries Power Flow - tables, flow diagrams Post Transient Outages - tables, flow diagrams Sensitivity Studies - tables, flow diagrams Voltage Stability - reactive margin tables Dynamic Stability Performance Tables Dynamic Stability Plots vii

9 Phase 1 - Comprehensive Progress Report I. Introduction General The Gateway South project was announced by PacifiCorp in May 2007 to provide increased transmission capacity between Wyoming, Utah and southern Nevada. This project is designed to meet the needs of PacifiCorp s network transmission customers by delivering network resource to network loads, supporting retail customer load growth, and improve reliability. PacifiCorp initiated the Western Electricity Coordinating Council (WECC) Regional Planning Project Review process for Gateway South and the related Gateway West projects on June 25, This process was completed on May 28, 2008 with the issuance of the Gateway South Regional Planning Report. The purpose of this Phase 1 comprehensive progress report is to demonstrate that sufficient technical studies have been conducted for the Gateway South Transmission Project (GS Project) to define the non-simultaneous planned rating(s) for the project and to describe the project preliminary plan-of-service. This report summarizes the results of technical studies conducted in concert with Gateway West Transmission Project to evaluate the planned ratings of the Energy Gateway Projects. These technical studies include power flow, transient stability, and post-transient power flow and voltage stability analysis. Appendix A contains the detailed study plan that was followed to complete these studies. Project Plan-of-Service The Gateway South Project proposed plan-of-service system additions/ modifications are summarized below: Aeolus Mona 500 kv #1 & #2 (400 miles, 3- Athabaska/TW ) Mona 500/345 kv #1 and #2 autotransformer (1500 MVA) Mona Sigurd 500 kv #1 (75 miles, 3- Athabaska/TW ) Sigurd 500/345 kv #1 autotransformer (1500 MVA) Sigurd Red Butte 500 kv #1 (160 miles, 3- Athabaska/TW ) Sigurd Red Butte 345 kv #2 (160 Miles, 2-Cardnal 954 ACSR) Red Butte 500/345 kv #1 autotransformer (1500 MVA) Red Butte 345 kv, -100 MVAR/+250 MVAR SVC, plus three MVAR MSC capacitors (nominally, the output should be held to -20 MVAR/+50 MVAR during steady-state conditions) Red Butte - Crystal 500 kv #1 (95 miles, 3-Athabaska/TW ) Crystal 500 kv #1 thru #4 PST (450 MVA, ±50 Degrees) The proposed plan-of-service single-line diagram for the Gateway South Project is illustrated in Figure 2. The complete plan-of-service for the Gateway South Transmission Project is provided in Appendix B. The transmission system changes

10 Page 2 of 51 defined above will support nonsimultaneous path flows up the levels defined in this report. Planned Operating Date The Gateway South schedule currently identifies the following in-service dates for key portions of the transmission project: Red Butte 345 kv SVC October 2011 Sigurd Red Butte 345 kv #2 December 2012 Red Butte Harry Allen (600 MW) Upgrade December 2012 Aeolus Mona 500 kv December 2016 Mona Sigurd Red Butte 500 kv December 2016 Red Butte Crystal 500 kv December 2016

11 Page 3 of 51 FIGURE 2 Gateway South Single-line Gateway West Aeolus 230 kv to Windstar 500 kv to Windstar 230 kv to Creston/Bridger SVC 230 kv MVA 500 kv to Bridger Middle kv Gateway Central 500 kv to Limber Middle miles 3 - Athabaska/TW Mona #1 #2 500 kv MVA Sigurd 500 kv 345 kv 75 miles 3 - Athabaska/TW MVA 345 kv Red Butte #2 160 miles 3 - Athabaska/TW Crystal 500 kv 1500 MVA 345 kv 160 miles 2 Cardinal 954 ACSR 95 miles 3 - Athabaska/TW New 500 kv NPC Bus 500 kv MVA +50 PST 500 kv 345 kv 230 kv

12 II. Objectives Gateway South Transmission Project Page 4 of 51 The objectives of this study are summarized below: A. Satisfy Reliability Criteria The study results will comply with the PacifiCorp, Idaho Power, NV Energy (Nevada Power/Sierra Pacific) and NERC/WECC planning standards. B. Define Plan-of-Service 1. Provide an opportunity for WECC members to review and comment on the Project proposed plan-of-service. 2. Establish a consensus that the plan-of-service supports the project nonsimultaneous rating. C. Acquire a Non-Simultaneous Rating 1. Establish a non-simultaneous rating for the following transmission paths: o Gateway South (Aeolus Mona) o Mona South (Mona Sigurd Red Butte) o TOT 2C (Red Butte Harry Allen 345 kv and Red Butte Crystal 500 kv) Due to the simultaneous interactions between the Gateway South and Gateway West projects, additional analysis was performed to evaluate the Gateway West project, east of Bridger (Bridger Aeolus Windstar). Because of this overlap between the two projects, portions of this analysis will be included in both the Gateway South and Gateway West comprehensive progress reports 2. The sensitivity analysis was performed as a preliminary assessment of interactions between GS and projects that are planned to be developed in the same time frame as GS. Additionally, one other project was analyzed in parallel with GS which could have an impact on the performance of the existing transmission system. This project, Gateway West (GW) will be constructed at least one year before GS. The following projects and uncertainties were evaluated as sensitivity cases: a. A single 500 kv line generic version of a northern Nevada project will be modeled to include either the Ely Energy Center & 500 kv Line, or the Great Basin South 500 kv lines. The Great Basin North 500 kv line (Robinson Summit Cedar Hill 500 kv) was modeled both inservice and out-of-service as a sensitivity. (See Case 1A-S configuration.) b. Southern portion GS: Mona Sigurd Red Butte, bi-directional rating (For this analysis, the southern Utah flows in Case 1c was compared with Case 1a.)

13 Page 5 of 51 c. TOT 2C: Add a second Red Butte Harry Allen/Crystal line, bidirectional rating d. Different resource mix in Wyoming was evaluated to determine the impact of higher concentrations of wind generation. 3. Provide a Comprehensive Progress Report for submittal to the WECC Planning Coordination Committee (PCC) for entry into Phase 2 of the WECC Path Rating Process for the Gateway South Transmission Project.

14 Page 6 of 51 III. Approach Due to the complexity of the Gateway South Transmission Project, a variety of technical studies were required to establish a non-simultaneous rating for project segments that traversed the Wyoming, Utah, Idaho and southern Nevada transmission systems. Appendix A contains the detailed study plan that was followed to complete these studies. The following technical studies are documented in this Report: A. Gateway West Because of simultaneous interactions between Gateway West and Gateway South, there will be some overlap in technical findings between the two reports. Specific technical analysis included: 1. TOT 4A Path Studies These studies evaluated the impacts of adding two-230 kv lines and one-500 kv line to the TOT 4A path. Interactions between this path and other paths (TOT 4B, etc.) will be addressed during Phase 2 studies. 2. West of Aeolus Path Studies Due to interactions between this path and the South of Aeolus (Aeolus-Mona) transmission path, both paths will be heavily loaded during the analysis. These studies evaluated in interaction of new transmission lines constructed on the West of Aeolus path. Due to the significant transmission system that would be constructed to support transfers west of Aeolus to Bridger, the West of Aeolus path has been defined. This path will include the following transmission lines: o Aeolus Bridger 500 kv, measured at Aeolus o Aeolus Creston 230 kv, measured at Aeolus o Platte Latham (Echo Springs) 230 kv, measured at Platte o Mustang Bridger 230 kv, measured at Mustang o Mustang Wind River 230 kv, measured at Mustang Please refer to the Gateway West Comprehensive Progress Report for the technical analysis that support the non-simultaneous planned rating(s) for the Gateway West Project and a description of the project preliminary plan-ofservice. B. South of Aeolus (Aeolus Mona) Studies These studies evaluated the impacts of adding the two Aeolus Mona 500 kv lines on the transmission system. Due to interactions between this path and the Gateway West paths (West of Aeolus and Bridger West), both paths will be heavily loaded during the analysis. C. Mona South (Mona Sigurd Red Butte) Studies These studies evaluated the impact of adding the Mona Sigurd Red Butte 500 kv lines in parallel with existing 345 kv facilities to form the Mona South path. Due to

15 Page 7 of 51 heavy transfers through southern Utah, a second Sigurd Red Butte 345 kv line has been identified as part of the Gateway South project. D. TOT 2C (Red Butte Harry Allen/Crystal) Studies These studies evaluated the impact of adding the Red Butte Crystal 500 kv line on the TOT 2C path. Interaction between the TOT 2C and 2B (Glen Canyon Sigurd 230 kv and Pinto Four Corners 345 kv) were also evaluated. E. Sensitivity Studies Various sensitivity studies were performed (see Appendix A study plan) to evaluate the impact of the Gateway South under varying system configurations and conditions.

16 IV. Conclusions Gateway South Transmission Project Page 8 of 51 As substantiated by the technical analysis documented in this report, the following conclusions can be drawn: A. Gateway West - TOT 4A Path and West of Aeolus Path Studies 1. TOT 4A Path Studies Based on technical findings of this report, the facilities proposed between Aeolus and Windstar will support increasing the nonsimultaneous TOT 4A path rating from 820 MW to 3435 MW. The limiting outage on this path is the N-1 of the Aeolus Windstar 500 kv line. Interactions between the TOT 4A path and other transmission paths will be evaluated during the Phase 2 (simultaneous) technical study review. To withstand a single circuit 500 kv outage, between Aeolus and Windstar, the Dave Johnston Difficulty Aeolus 230 kv line must be rebuilt to ACSR conductor/phase. Additionally, the Aeolus Windstar 230 kv #1 and #2 line must be constructed with ACSR conductor/phase. Voltage stability analysis was performed on the Case 1a, 1b and 1c base case for the TOT 4A path. Per the WECC reactive margin requirements, the 5% case showed acceptable reactive margins for the n-1 outages while the 2.5% case showed acceptable reactive margin for the n-2 outages. 2. West of Aeolus Path Studies Based on technical findings of this report, the facilities proposed between Jim Bridger and Aeolus will support a path rating of 2050 MW (simultaneous with South of Aeolus rating of 3000 MW). The West of Aeolus path rating is limited by the double line outage (N-2) outage of the Aeolus Bridger 500 kv line and the Aeolus Creston 230 kv or the Creston Bridger 230 kv lines and how much generation at Aeolus and Windstar that can be tripped for a specific system conditions. While the requirement for generator tripping at Jim Bridger (for outages west of Bridger), Aeolus or Windstar has been identified within the report, specific levels of Wyoming generator tripping vs. path flow levels and resource mix/location will need to be addressed in follow-on analysis. If the 230 kv line west of Aeolus (constructed 500 kv, energized 230 kv) was converted to 500 kv operation, transfers on the West of Aeolus path could be increased and generator tripping levels could be greatly reduced. Voltage stability analysis was performed on the Case 1a, 1b and 1c base case for the West of Aeolus path. Per the WECC reactive margin requirements, the 5% case showed acceptable reactive margins for the n-1 outages while the 2.5% case showed acceptable reactive margin for the n-2 outages. Interactions between the West of Aeolus path and other transmission paths will be evaluated during the Phase 2 (simultaneous) technical study review.

17 Page 9 of 51 B. South of Aeolus (Aeolus Mona) Path Studies Based on technical findings of this report, the facilities proposed between Aeolus and Mona will support a path rating of 3000 MW (simultaneous with West of Aeolus flows of 2050 MW and Bridger West flows of 5200 MW). The Gateway South (South of Aeolus) path rating is limited by the double line outage (N-2) outage of the Aeolus Mona 500 kv #1 and #2 lines and how much generation at Aeolus and Windstar that can be tripped for a specific system condition. While the requirement for generator tripping at Jim Bridger (for outages west of Bridger), Aeolus or Windstar has been identified within the report, specific levels of Wyoming generator tripping vs. path flow levels and resource mix/location will need to be addressed in follow-on analysis. If the 230 kv line west of Aeolus (constructed 500 kv, energized 230 kv) was converted to 500 kv operation, generator tripping levels could be greatly reduced. Voltage stability analysis was performed on the Case 1a, 1b and 1c base case for the South of Aeolus path. All reactive margins evaluated met WECC requirements. Interactions between the Gateway South path and other transmission paths will be evaluated during the Phase 2 (simultaneous) technical study review. C. Mona South Path Studies Based on technical findings of this report, the facilities proposed South of Mona Path (Mona Sigurd Red Butte) will support a path rating (simultaneous with the TOT 2B paths) of at least 2400 MW north to south and 790 MW south to north. The Mona South path rating is limited by (1) load levels in southern Utah and (2) rating of the TOT 2C transmission path. Voltage stability analysis was performed on the Case 1a, 1b and 1c base case for the Mona South path. Per the WECC reactive margin requirements, the 5% case showed acceptable reactive margins for the n-1 outages while the 2.5% case showed acceptable reactive margin for the n-2 outages. Further Interactions between the Mona South path and other transmission paths will be evaluated during the Phase 2 (simultaneous) technical study review. D. TOT 2C Path Studies Based on technical findings of this report, the facilities proposed to be added to the TOT 2C Path (Red Butte Harry Allen/Crystal) will support a path rating (simultaneous with the TOT 2B paths) of at least 2100 MW north to south and 1700 MW south to north. The TOT 2C path rating is limited by the outage of the Red Butte Crystal 500 kv line, and subsequent (proposed) tripping of a portion of the series capacitor bank at Harry Allen. Voltage stability analysis was performed on the Case 1a, 1b and 1c base case for the TOT 2C path. Per the WECC reactive margin requirements, the 5% case showed acceptable reactive margins for the n-1 outages while the 2.5% case showed acceptable reactive margin for the n-2 outages.

18 Page 10 of 51 Further Interactions between the TOT 2C path and other transmission paths will be evaluated during the Phase 2 (simultaneous) technical study review. E. Sensitivity Studies Sensitivity study technical results have demonstrated that the Energy Gateway Projects can achieve their rating with or without the Great Basin North 500 kv line being constructed. The technical findings of this report demonstrate that sufficient technical studies have been conducted for the Gateway South Transmission Project (GS Project) to define the non-simultaneous planned rating(s) for the project and to describe the project preliminary plan-of-service.

19 Page 11 of 51 V. Summary of Study Results A brief summary of the power flow, stability, post-transient, voltage stability and sensitivity studies completed to evaluate the performance of the Gateway Project are presented in this section. Appendix D, E and F contain technical study findings, flow diagrams and performance tables which are discussed in this section and discussed in detail in Section VI and VII. Study assumptions, guidelines, criteria and methodology, and system representations are described in the Study Plan provided in Appendix A. In addition, the plan-of-service for the entire Energy Gateway Project is summarized in Appendix B. A. Gateway West (TOT 4A Path and West of Aeolus Path) Studies After the preliminary Gateway Project plan-of-service was developed, three base cases representing a wide range of resource mix and flow conditions for the 2015 Heavy Summer operating conditions were used to evaluate the Gateway West Project (Bridger Aeolus Windstar) facility additions under a wide range of flows conditions. 1. TOT 4A Path a. Power Flow Analysis Power flow study results for all three base cases indicate: 1) For all base cases conditions, there were no steady-state (N-0) bus voltage or line flow violations within the study area. 2) For all single contingency (N-1) disturbances, there were no bus voltage or line loading violations. 3) line loading violations were evident for this portion of the system in the base cases. b. Stability Analysis Stability study results indicate: 1) All disturbances simulated were stable and system performance was well within the NERC/WECC and PacifiCorp Planning Standards tolerances. 2) The rating of this path is limited during high transfer conditions (Case 1a) by the single line (N-1) outage of the Aeolus Windstar 500 kv line causing the dynamic voltage dip at Difficulty 230 kv dipping by 26.5% to.753 pu (below 20% voltage deviation for 26.5 cycles). Upon replacing the Dave Johnston Difficulty Aeolus 230 kv proposed line conductor ( ACCC) with ACSR conductor and repeating the disturbance, the dynamic voltage dip at Difficulty 230 kv dipping by 22.8% to.792 pu (below 20%

20 Page 12 of 51 voltage deviation for 15 cycles). This performance meets the NERC/WECC transient voltage criteria. Conclusion: The Dave Johnston Difficulty Aeolus 230 kv line must be rebuilt to ACSR conductor/phase. Additionally, the Aeolus Windstar 230 kv #1 and #2 line must be constructed with ACSR conductor/phase. 3) In reviewed the Case 1b (N-1 and N-2) dynamic stability study findings vs. Case 1a, the following results were noted: o It is evident from the voltage swings that reducing thermal generation at Bridger and Windstar while increasing wind generation at Aeolus and on the 230 kv system in Wyoming will reduce the system impacts of the Aeolus - Windstar 500 kv outage. (Change in voltage swing on 230 kv system south of DJ reduced.) c. Post-Transient Analysis Post-transient study results within this portion of the three base cases indicate: 1) For all single contingency (N-1) disturbances, there were no bus voltage or line loading violations. 2) line loading violations were evident for this portion of the system in the base cases. d. Voltage Stability Analysis Voltage stability analysis was performed on the Case 1a, 1b and 1c base case for the TOT 4A path. Appendix F contains all the Tables associated with the reactive margin (Q/V) study results. Per the WECC reactive margin requirements, the 5% case showed acceptable reactive margins for the n-1 outages while the 2.5% case showed acceptable reactive margin for the n-2 outages. Study Conclusion: Based on technical findings of this report, the facilities proposed between Aeolus and Windstar will support increasing the nonsimultaneous TOT 4A path rating from 820 MW to 3435 MW. The limiting outage on this path is the N-1 of the Aeolus Windstar 500 kv line. Interactions between the TOT 4A path and other transmission paths will be evaluated during the Phase 2 (simultaneous) technical study review. 2. West of Aeolus Path a. Power Flow Analysis Power flow study results for all three base cases indicate:

21 Page 13 of 51 1) For all base cases conditions, there were no steady-state (N-0) bus voltage or line flow violations within the study area. 2) For all single contingency (N-1) disturbances, there were no bus voltage or line loading violations. 3) Under heavy transfer conditions west and south of Aeolus (Case 1a and 1b), Jim Bridger generator tripping will be required (see posttransient results) for the double line (N-2) outage of the Jim Bridger Populus 500 kv #1 and #2 lines to alleviate (1) overload conditions on Three Mile Knoll 345 kv series capacitor and (2) overloads on the Hunter #2 345/24 kv GSU transformer. (This overload condition can also be relieved by adjusting the Hunter GWU transformer taps.) 4) Under light transfer conditions (Case 1c) west and south of Aeolus generator tripping will not be required for this double contingency (N- 2) outages. b. Stability Analysis Stability study results indicate: 1) All disturbances simulated were stable and system performance was well within the NERC/WECC and PacifiCorp Planning Standards tolerances. 2) In reviewed the Case 1b (N-1 and N-2) dynamic stability study findings vs. Case 1a, the following results were noted: It is evident from the voltage swings that reducing thermal generation at Bridger and Windstar while increasing wind generation at Aeolus and on the 230 kv system in Wyoming will: o Increased the system impacts of the Aeolus - Bridger 500 kv (N-1 and N-2) disturbances. (Change in voltage swings in southern Wyoming) o Reduce the system impacts of the Bridger - Populus 500 kv (N-1 and N-2) disturbances. (Change in voltage swings at Caribou and other locations significantly reduced.) c. Post-Transient Analysis Post-transient study results within this portion of the three base cases indicate: 1) For all single contingency (N-1) disturbances, there were no bus voltage or line loading violations. 2) For the double line (N-2) outage of the Aeolus Bridger 500 kv line and the Aeolus Creston 230 kv line or the Creston Bridger 230 kv line: o Under light or moderate flow conditions (Case 1a and 1c) on the West of Aeolus Path (<1300 MW), for this N-2

22 Page 14 of 51 contingency, there were no bus voltage or line loading violations. o However, under high flow conditions (Case 1b) on the West of Aeolus path (>2050 MW), for this N-2 contingency, 1100 MW of generator tripping will be required at Aeolus to prevent voltage collapse (none converged solution). After generator tripping, the case solved and there were no bus voltage or line loading violations. 3) For the double line (N-2) outage of the Bridger Populus 500 kv #1 and #2 lines: o Under light flow conditions (Case 1c) on the West of Aeolus path (<975 MW) and Bridger West path (<3345 MW), for this N-2 contingency, there were no bus voltage or line loading violations. o Under moderate flow conditions (Case 1a) on the West of Aeolus path (<1300 MW) and high flow condition on Bridger West Path (5200 MW), for this N-2 contingency, generator tripping will be required at Bridger (750 MW) to prevent voltage collapse (none converged solution). After generator tripping, the case solved and there were no bus voltage or line loading violations. o However, under high flow conditions (Case 1b) on the West of Aeolus path (>2050 MW) and maximum flow condition on Bridger West path (5200 MW), for this N-2 contingency, generator tripping will be required at Aeolus (1100 MW) to prevent voltage collapse (none converged solution). After generator tripping, the case solved and there were no bus voltage or line loading violations. e. Voltage Stability Analysis Voltage stability analysis was performed on the Case 1a, 1b and 1c base case for the West of Aeolus path. Appendix F contains all the Tables associated with the reactive margin (Q/V) study results. Per the WECC reactive margin requirements, the 5% case showed acceptable reactive margins for the n-1 outages while the 2.5% case showed acceptable reactive margin for the n-2 outages. Study Conclusion: Based on technical findings of this report, the facilities proposed between Jim Bridger and Aeolus will support a path rating of 2050 MW (simultaneous with South of Aeolus flows of 3000 MW). The West of Aeolus path rating is limited by the double line outage (N-2) outage of the Aeolus Bridger 500 kv line and the Aeolus Creston 230 kv or the Creston Bridger 230 kv lines and how

23 Page 15 of 51 much generation at Aeolus and Windstar that can be tripped for specific system conditions. While the requirement for generator tripping at Jim Bridger (for outages west of Bridger), Aeolus or Windstar has been identified within the report, specific levels of Wyoming generator tripping vs. path flow levels and resource mix/location will need to be addressed in follow-on analysis. If the 230 kv line west of Aeolus (constructed 500 kv, energized 230 kv) was converted to 500 kv operation, transfers on the West of Aeolus path could be increased and generator tripping levels could be greatly reduced. Interactions between the West of Aeolus path and other transmission paths will be evaluated during the Phase 2 (simultaneous) technical study review. B. South of Aeolus (Aeolus - Mona) Path Studies After the preliminary Gateway Project plan-of-service was developed, three base cases representing a wide range of resource mix and flow conditions for the 2015 Heavy Summer operating conditions were used to evaluate the South of Aeolus Path (Aeolus Mona) facility additions under a wide range of flows conditions. 1. Power Analysis Power flow study results for all three base cases indicate: a. For all base cases conditions, there were no steady-state (N-0) bus voltage or line flow violations within the study area. b. For all single contingency (N-1) disturbances, there were no bus voltage or line loading violations. c. Under heavy transfer conditions west and south of Aeolus (Case 1a and 1b), Windstar generator tripping will be required (see post-transient results) for the double line (N-2) outage of the Aeolus Mona 500 kv #1 and #2 lines, to prevent system voltage collapse (none converged solution). Upon tripping generation, there were no bus voltage or line load violations. d. Under light transfer conditions west and south of Aeolus (Case 1c) generator tripping will not be required for this double contingency (N-2) outages. 2. Stability Analysis Stability study results indicate: a. All disturbances simulated were stable and system performance was well within the NERC/WECC and PacifiCorp Planning Standards tolerances. b. For the double line (N-2) outage of the Aeolus Mona 500 kv #1 and #2 lines:

24 Page 16 of 51 o Under light flow conditions (Case 1c) on both the West of Aeolus path (<1300 MW) and the South of Aeolus path (514 MW), for this N-2 contingency, no generator tripping will be required and system performance meets the NERC/WECC transient voltage criteria. o Under moderate flow conditions (Case 1a) on the West of Aeolus path (<1300 MW) and maximum flow conditions on the South of Aeolus path (3000 MW), for this N-2 contingency, generator tripping will be required at Windstar (680 MW) to achieve voltage stability. After generator tripping, the case solved and system performance meets the NERC/WECC transient voltage criteria. o Under high flow conditions (Case 1b) on the West of Aeolus Path (>2050 MW) and maximum flow conditions on the South of Aeolus path (3000 MW), for this N-2 contingency, generator tripping will be required at Aeolus (1100 MW) and Windstar (600 MW) to achieve voltage stability. After generator tripping, the case solved and system performance meets the NERC/WECC transient voltage criteria. c. In reviewed the Case 1b (N-1 and N-2) dynamic stability study findings vs. Case 1a, the following results were noted: o It is evident from the voltage swings that reducing thermal generation at Bridger and Windstar while increasing wind generation at Aeolus and on the 230 kv system in Wyoming will increased the system impacts of the Aeolus - Mona 500 kv (N-1 and N-2) disturbances. (Change in voltage swings in southern Wyoming and the Cache Valley of Northern Utah). o A change in Wyoming generation (type and location) appears to have only minor impacts on Western Interconnection system performance outside of Wyoming. (E.g. Southern Utah/Nevada disturbances, N-2 PV generation, and IPP DC Line bi-pole outage.) 3. Post-Transient Analysis Post-transient study results within this portion of the three base cases indicate: a. For all single contingency (N-1) disturbances, there were no bus voltage or line loading violations. b. For the double line (N-2) outage of the Aeolus Mona 500 kv #1 and #2 lines: o Under light flow conditions (Case 1c) on both the West of Aeolus path (<1300 MW) and the South of Aeolus path (514

25 Page 17 of 51 MW), for this N-2 contingency, there were no bus voltage or line loading violations. o Under moderate flow conditions (Case 1a) on the West of Aeolus path (<1300 MW) and maximum flow conditions on the South of Aeolus path (3000 MW), for this N-2 contingency, generator tripping will be required at Aeolus (1100 MW) to prevent voltage collapse (none converged solution). Additionally, a 100 MVAr shunt capacitor (proposed) will be required at Bonanza 345 kv to meet the WECC post-transient voltage deviation criteria. Following generator tripping the case solved. Upon switching a capacitor at Bonanza, there were no bus voltage or line loading violations. o Under high flow conditions (Case 1b) on the West of Aeolus Path (>2050 MW) and maximum flow conditions on the South of Aeolus path (3000 MW), for this N-2 contingency, generator tripping will be required at Aeolus (1100 MW) and Windstar (600 MW) to prevent voltage collapse (none converged solution). After generator tripping, the case solved and there were no bus voltage or line loading violations. Study Conclusion: Based on technical findings of this report, the facilities proposed between Aeolus and Mona will support a path rating of 3000 MW (simultaneous with flows on West of Aeolus of 2050 MW and Bridger West of 5200 MW). The South of Aeolus (Aeolus - Mona) path rating is limited by the double line outage (N-2) outage of the Aeolus Mona 500 kv #1 and #2 lines and how much generation at Aeolus and Windstar that can be tripped for specific system conditions. While the requirement for generator tripping at Jim Bridger (for outages west of Bridger), Aeolus or Windstar has been identified within the report, specific levels of Wyoming generator tripping vs. path flow levels and resource mix/location will need to be addressed in follow-on analysis. If the 230 kv line west of Aeolus (constructed 500 kv, energized 230 kv) was converted to 500 kv operation, generator tripping levels could be greatly reduced. Interactions between the South of Aeolus path and other transmission paths will be evaluated during the Phase 2 (simultaneous) technical study review.

26 Page 18 of Voltage Stability Analysis Voltage stability analysis was performed on the Case 1a, 1b and 1c base case for the South of Aeolus path. Appendix F contains all the Tables associated with the reactive margin (Q/V) study results. Per the WECC reactive margin requirements, the 5% case showed acceptable reactive margins for the n-1 outages while the 2.5% case showed acceptable reactive margin for the n-2 outages. C. Mona South Path Studies After the preliminary Gateway Project plan-of-service was developed, three base cases representing a wide range of resource mix and flow conditions for the 2015 Heavy Summer operating conditions were used to evaluate the Mona South Path (Mona Sigurd Red Butte) facility additions under a wide range of flows conditions. 1. Power Flow Analysis Power flow study results for all three base cases indicate: a. For all base cases conditions, there were no steady-state (N-0) bus voltage or line flow violations within the study area. NOTE: Under maximum TOT 2B path flow conditions in the Case 1a base case, depressed steady-state voltages were noted near the Pinto and Sigurd PST transformers. Voltages were well within the design specification for the substation equipment. b. For all single contingency (N-1) disturbances (evaluated under heavy north to south and south to north flow conditions), there were no bus voltage or line loading violations. c. line loading violations were evident for this portion of the system in the base cases. NOTE: In the Gateway West (West of Aeolus study results above), under heavy transfer conditions west and south of Aeolus, Jim Bridger generator tripping will be required (see post-transient results) for the double line (N-2) outage of the Jim Bridger Populus 500 kv #1 and #2 lines to alleviate (1) overload conditions on Three Mile Knoll 345 kv series capacitor and (2) overloads on the Hunter #2 345/24 kv GSU transformer. (This overload condition can also be relieved by adjusting the Hunter GWU transformer taps.) 2. Dynamic Stability Analysis Stability study results indicate: a. All disturbances simulated were stable and system performance was well within the NERC/WECC and PacifiCorp Planning Standards tolerances.

27 Page 19 of Post-Transient Analysis Post-transient study results within this portion of the three base cases indicate: a. For all single contingency (N-1) disturbances, there were no bus voltage or line loading violations. b. line loading violations were evident for this portion of the system in the base cases. 4. Voltage Stability Analysis Voltage stability analysis was performed on the Case 1a, 1b and 1c base case for the Mona South path. Appendix E contains all the Tables associated with the reactive margin (Q/V) study results. Per the WECC reactive margin requirements, the 5% case showed acceptable reactive margins for the n-1 outages while the 2.5% case showed acceptable reactive margin for the n-2 outages. Study Conclusion: Based on technical findings of this report, the facilities proposed South of Mona Path (Mona Sigurd Red Butte) will support a path rating (simultaneous with the TOT 2B paths) of at least 2400 MW north to south and 790 MW south to north. The Mona South path rating is limited by (1) load levels in southern Utah and (2) rating of the TOT 2C transmission path. Further Interactions between the Mona South path and other transmission paths will be evaluated during the Phase 2 (simultaneous) technical study review. D. TOT 2C Path After the preliminary Gateway Project plan-of-service was developed, three base cases representing a wide range of resource mix and flow conditions for the 2015 Heavy Summer operating conditions were used to evaluate the Mona South Path (Mona Sigurd Red Butte) and the TOT 2C Path (Red Butte Harry Allen/Crystal) facility additions under a wide range of flows conditions. 1. Power Flow Analysis Power flow study results for all three base cases indicate: 1) For all base cases conditions, there were no steady-state (N-0) bus voltage or line flow violations within the study area. 2) For maximum north to south flow conditions on the TOT 2C path (Case 1a and 1b), the (N-1) outage of the Red Butte Crystal 500 kv line will result flows on the Harry Allen 345 kv #1, #2 and #3 phase shifting transformers exceeded the emergency rating. This overload condition can be relieved by bypassing the Red Butte 345 kv series capacitor.

28 Page 20 of 51 NOTE: Additionally, under N-1 outages of the RB-CR 500 kv line in the Case 1a base case, depressed steady-state voltages were noted near the Pinto and Sigurd PST transformers. Voltages were well within the design specification for the substation equipment. 3) For heavy south to north flow conditions on the TOT 2C path (Case 1c), for all single contingency (N-1) disturbances, there were no bus voltage or line loading violations. 4) line loading violations were evident for this portion of the system in the base cases. 2. Dynamic Stability Analysis Stability study results indicate: a. All disturbances simulated were stable and system performance was well within the NERC/WECC and PacifiCorp Planning Standards tolerances. 3. Post-Transient Analysis Post-transient study results within this portion of the three base cases indicate: 1. For maximum north to south flow conditions on the TOT 2C path (Case 1a and 1b), the single line (N-1) outage of the Red Butte Crystal 500 kv line will result flows on the Harry Allen 345 kv #1, #2 and #3 phase shifting transformers exceeded the emergency (104%). This overload condition was relieved by bypassing 50% of the Harry Allen 345 kv series capacitor. At this point in the simulation, flows on the Sigurd 230 kv PST were 99% of the emergency rating, flows on the Pinto PST were 90% of the emergency rating and flows on the HA 345 kv PST were 94% of the emergency rating. 2. For heavy south to north flow conditions on the TOT 2C path (Case 1c), for all single contingency (N-1) disturbances, there were no bus voltage or line loading violations. However, following the single line (N-1) outage of the Red Butte Crystal 500 kv, flows on the Pinto PST were 91% of the emergency rating, flows on the Sigurd 230 kv PST were 92% of the emergency rating, and flows on the HA 345 kv PST were 86% of the emergency rating. 3. There were no double contingency (N-2) bus voltage or line loading violations that were evident for this portion of the system in the base cases.

29 Page 21 of Voltage Stability Analysis Voltage stability analysis was performed on the Case 1a, 1b and 1c base case for the TOT 2C path. Appendix E contains all the Tables associated with the reactive margin (Q/V) study results. Per the WECC reactive margin requirements, the 5% case showed acceptable reactive margins for the n-1 outages while the 2.5% case showed acceptable reactive margin for the n-2 outages. Study Conclusion: Based on technical findings of this report, the facilities proposed to be added to the TOT 2C Path (Red Butte Harry Allen/Crystal) will support a path rating (simultaneous with the TOT 2B paths) of at least 2100 MW north to south and 1700 MW south to north. The TOT 2C path rating is limited by the outage of the Red Butte Crystal 500 kv line, and subsequent (proposed) tripping of a portion of the series capacitor bank at Harry Allen. Further Interactions between the TOT 2C path and other transmission paths will be evaluated during the Phase 2 (simultaneous) technical study review. E. Sensitivity Studies Due to the judicious selection of resources and path flows modeled in the Case 1a, 1b and 1c base cases, the following sensitivities have previously been addressed in the study findings above: 1. Different resource mix in Wyoming to evaluate higher concentrations of wind generation. (For this analysis, Case 1b will be used to evaluate higher concentrations of wind vs. Case 1a.) 2. Southern portion GS: Mona Sigurd Red Butte, bi-directional rating (For this analysis, the southern Utah flows in Case 1c will be compared with Case 1a.) 3. TOT 2C: Add a second Red Butte Harry Allen/Crystal line, bi-directional rating Each of these base cases assumed that the Great Basin North 500 kv line (Robinson Summit Cedar Hill 500 kv) would be in-service prior to the completion of both the Gateway West and Gateway South projects. As the Great Basin North 500 kv line may potentially have an impact on the Energy Gateway Project, sensitivity analysis was performed with the Case 1a base case to ascertain any changes in system performance if the Great Basin North 500 kv line is out-of-service. This sensitivity analysis was also performed to demonstrate that the Energy Gateway Projects can achieve their rating with or without the Great Basin North 500 kv line being constructed. Detailed technical findings of the sensitivity studies are provided in Section VII. A summary of the sensitivity study findings is summarized below:

30 Page 22 of 51 Removal of the Great Basin North 500 kv line (Robin Summit Cedar Hill 500 kv) will: 1. Based on power flow steady-state and contingency analysis results modeled in the study area, no significant difference was seen in study results. 2. From a transient stability perspective: o Voltage dips in key locations following N-2 of the Aeolus Mona 500 kv line (w/generator tripping) will be 4-5% deeper (duration below 20% will increase 19.6 cycles). o Voltage dips in key locations following N-2 of the Bridger -Populus 500 kv line (w/generator tripping) will be 1.5% deeper (duration below 20% will increase 6.2 cycles). o Voltage dips for key locations following N-2 of the Aeolus Windstar 500 kv line will be 1.3% deeper All transient stability simulations modeled met the NERC/WECC dynamic voltage dip criteria. 3. From a post-transient power flow perspective, only minor differences were seen in the study results. Study Conclusion: Sensitivity study technical results have demonstrated that the Energy Gateway Projects can achieve their rating with or without the Great Basin North 500 kv line being constructed.

31 Page 23 of 51 VI. Discussion of Technical Results Technical study results noted below assume system changes noted in Section VIII were implemented in the Energy Gateway configuration. While the analysis covered a large geographical area, technical results will be documented below by specific path or geographical area. Technical results in this section are documented in Appendix D (power flow, flow diagrams, post-transient), F (Dynamic Stability Performance Tables) and E (voltage stability). The tables inserted in subsections below were developed based on a review of the study results in these appendices. During the course of evaluating the three Gateway base cases (1a, 1b, and 1c), concerns surfaced relating to the high voltage that was evident on the line side of series capacitors at Three Mile Knoll 345 kv, Populus 345 kv, Three Peaks 345 kv, Pinto 345 kv and Red Butte 345 kv, during steady state and contingency conditions. As this issue was so prevalent in the various tables developed to summarize the technical study findings, it was decided that rather than repeat the same finding in multiple locations in Sections A, B and C below, it will be addressed at the start of this section. Series Capacitor Over Voltage Concerns Issue: Under steady-state (N-0), single-contingency (N-1) and doublecontingency (N-2) conditions, high bus voltages ( to pu) were noted on the line-side of the series capacitors at Three Mile Knoll 345 kv (existing), Pinto 345 kv (parameters being specified), Three Peaks 345 kv (being procured), Red Butte 345 kv (planned), and Populus 345 kv (being procured). Resolution: B&V has indicated that per Appendix D, the maximum voltage on the line side of the series capacitor would be about 125%. This value was observed on the Bridger Populus 345 kv circuit series capacitors for the loss of both Bridger Populus 500 kv circuits. As per IEEE Std , capacitors may be operated above rated voltage under emergency and infrequent conditions. The magnitude of the over voltages that may be tolerated without loss of life is dependent upon the duration of each over voltage, the number of applications and

32 Page 24 of 51 the temperature of the capacitor. The capacitor short time power-frequency capabilities given in IEEE Std is shown on the previous page, which is only a representative curve. Similar characteristics need to be specified for the new series capacitors, based on this report s finding. PacifiCorp provides the following feedback: Three Mile Knoll 345 kv: The following capability (excerpt from the equipment specification) is provided: The following series capacitor banks, which are in the procurement stage (draft specifications provided) meet this high voltage requirement: o Populus 345 kv: o Three Peaks 345 kv: o Pinto 345 kv: Recommendation: As future series capacitor banks are specified, high voltage concerns need to be addressed. A. Gateway West (TOT 4A Path and West of Aeolus Path) Studies 1. TOT 4A Path After the preliminary Gateway Project plan-of-service was developed, three base cases representing the 2015 Heavy Summer operating conditions were used to evaluate the modified TOT4A transmission path under a wide range of flows conditions. The technical results that are based on analysis performed for this path are summarized below: a. Power Flow Analysis The results of power flow analysis results for this path are summarized below: 1) Steady-State Conditions Case 1a (High Thermal) Case 1b (High Wind) Case 1c (High So. Utah S-N) No steady-state (N-0) bus voltage or line No steady-state (N-0) bus voltage or line No steady-state (N-0) bus voltage or line loading violations were evident for this portion loading violations were evident for this portion loading violations were evident for this portion of the base case. of the base case. of the base case. base case. 2) Contingency Conditions Case 1a (High Thermal) Case 1b (High Wind) Case 1c (High So. Utah S-N) base case.