TransWest Express AC and DC Project Comprehensive Progress Report (CPR) 3,000 MW DC and 1,500 MW AC WECC Phase 1 Analysis

Transcription

1 TransWest Express AC and DC Project Comprehensive Progress Report (CPR) 3,000 MW DC and 1,500 MW AC WECC Phase 1 Analysis July 25, 2018

2 Table of Contents 1. Introduction Project Description and System Topology Plan of Service Planned Operating Date Study Methods Base Case Development Post Transient Power Analysis Post-Transient Voltage Stability Transient Stability Affected Path Stress Test (10% Test) Path Independence Test Generation Drop via Remedial Action Schemes (RAS) Non-Simultaneous Analysis Results Non-Simultaneous Analysis Commercial Operation Buildout Base Case Development Post-Transient Power Analysis Post-Transient Voltage Stability Transient Stability Analysis Non-Simultaneous Analysis Full Buildout Base Case Development Post-Transient Power Analysis Post-Transient Voltage Stability Transient Stability Analysis Affected Path Stress Test Results Commercial Operation Buildout Full Buildout, SWIP-N Included Sensitivity, Full Buildout, Cross-Tie Project Included Path Independence Test Results Test 1: Schedule a Fixed Amount of Power on Project Test 2: Do Not Schedule Power on Project Sensitivity Studies Non-Simultaneous Analysis Full Buildout, Cross-Tie Project Base Case Development Post-Transient Power Analysis Post-Transient Voltage Stability Transient Stability Analysis Study Findings and Conclusions / Recommendations Appendix A Post-Transient and Transient Stability Contingency Lists Appendix B Post-transient Power Study Results Appendix C Voltage Stability Study Results Appendix D Transient Stability Study Results Appendix E Power Plots Appendix F Transient Stability Plots Appendix I Plan of Service Appendix J Schedule/Milestones Appendix K Project Review Group (PRG) Roster Appendix L Approved Study Plan

3 Executive Summary TransWest Express LLC (TransWest) is developing the TransWest Express Transmission Project (TWE Project), a 3,000 MW, transmission project in the western U.S. The TWE Project recently completed Phase 2 of the WECC Path process as a 730-mile, 1,500 MW Stage 1, 600 kv high voltage direct current (HVDC) system between south central Wyoming and southeastern Nevada. The proposed project is now in Phase 3 of the WECC path rating process and the path rating becomes effective upon implementation of the project. An alternative Plan of Service for the TWE Project that would include AC and DC segments (the TWE AC and DC Project) could potentially better meet the project objectives to provide the needed transmission capacity between the Wyoming wind resource areas in the Rocky Mountain region and the existing transmission systems that serve California, Nevada and Arizona. The TWE AC and DC Project includes a 406-mile, 3,000 MW HVDC system terminating at a bus adjacent to the Intermountain substation and a 324-mile, 1, kv AC system from the adjacent Intermountain substation to a Southern terminal in the Eldorado Valley. As shown in Figure 1, the TWE HVDC portion of the Project will extend from south central Wyoming to the Intermountain 345kV substation in Utah. The AC potion of the Project will extend from a new Intermountain 500 kv substation in Utah to southeastern Nevada. The primary use for the TWE Project is to deliver wind generated electricity from Wyoming to markets in the desert southwest. In addition, the TWE AC and DC Project will provide needed transmission capacity between balancing areas in multiple regions including CAISO, WestConnect and NTTG. Figure 1 TWE HVDC Transmission Project 3

4 This report describes the system studies that have been performed to demonstrate a Proposed for 3,000 MW (north-to-south) on the TWE DC Project and a Proposed of 1,500 MW (north-to-south) on the TWE AC Project. Additional WECC Phase 2 studies will be needed to achieve an Accepted of 3,000 MW and 1,500 MW, respectively. Major Findings The results of the system studies described in this report demonstrate that the TWE AC and DC Project does interact with existing WECC path ratings as identified in Section 4 of this report. Therefore, it is recommended that the TransWest Express Project be accepted into Phase 2A of the WECC Path process with the Plan of Service described in Appendix I. Following are key findings of the Comprehensive Progress Report. Both the TWE AC and DC components of the Project will be new WECC Paths since they are independent of all other paths. Study results were positive and did not yield significant planning criteria violations. The Affected Path Stress Test (10% test) results indicate that there are a number of existing WECC paths that will require simultaneous analysis in the WECC Phase 2 studies. Some of the paths indicate that the TWE AC and DC project have a very strong correlation. Loss of the Aeolus TWE-Wyoming No.1 and No.2 500kV lines results in the underlying 230kV system to yield a line that exceeds its thermal limit. A solution for this double line contingency would be to trip the TWE Wyoming 230kV bus from the Platte Latham 230kV line. This opens the path to mitigate the high flow during this contingency. Further discussions with PRG members will be helpful in assessing if there are any issues in coordinating operation of both the IPPDC and TWE DC lines. Furthermore, scheduling and generation tripping at the Intermountain substation should be further explored to determine trip amounts for various levels of flow scheduled to the Intermountain substation. 4

5 1. Introduction This report describes the results of system studies that have been performed to demonstrate a Proposed of 3,000 MW (north to south) for the TWE AC and DC Project Project Description and System Topology The TWE AC and DC Project includes the elements listed in Section 1.2, Plan of Service. The TWE AC and DC Project will initially be interconnected in 2022 to the existing Wyoming 230 kv transmission facilities and the planned 500 kv Gateway West transmission line. In the future, the TWE Project will be interconnected to the Gateway South transmission line. Both Gateway 500 kv transmission lines are planned to be routed immediately adjacent to the TWE Project s Northern Terminal, which have completed Phase 2 of the WECC Project Review Process and have received Accepted s 1. Because the TWE Project may be in service prior to completion of WECC Projects that are pursuing a WECC Phase 2 status, two levels of Project development, referred to as Buildouts, will be considered in this study plan: 1. TWE Project Commercial Operation Buildout: Represents system conditions when the TWE AC and DC Project is planned to be placed into commercial operation prior to other projects. This scenario will assume that the following transmission projects have been placed into commercial operation: a. TWE AC and DC Project b. Gateway West Segment D.2. c. Eldorado Harry Allen 500 kv line d. Delaney-Colorado River 500 kv line 2. TWE Project with Full Buildout: Represents system conditions for the Full buildout. This scenario will assume that the following transmission projects have been placed into commercial operation: a. TWE AC and DC Project b. Gateway West c. Eldorado Harry Allen 500 kv line d. Delaney-Colorado River 500 kv line e. Gateway South (addition to item 1 above) f. North Gila-Imperial Valley #2 Project (addition to item 1 above) g. Southwest Intertie Project North (SWIP-N) consisting of Midpoint to Robinson Summit, 70% series compensated. (addition to item 1 above) A system map and a one-line diagram showing the TWE AC and DC Project Commercial Operation Buildout are provided in Figures 2 and 3. 1 The Gateway West and Gateway South sponsors originally planned to develop the Gateway Projects as double circuit 500 kv lines in two stages. However, the sponsors have elected to remove Stage 2 of these projects from the Project Review Process. Therefore Accepted s will not be sought for Stage 2 of these projects at this time. 5

6 Generation: The system that was studied included 3,280 MW of wind generation connected to the TWE Project Northern Terminal in Wyoming. This generation was dispatched to achieve a flow of 3,000 MW 2 at the TWE Project Northern AC Terminal and 1,500 MW at the TWE Project Southern Terminal. Figure 2 TWE AC and DC Project System Map 2 This assumes 280 MW of losses on the DC line project. 6

7 Figure 3 TWE AC and DC Project System One Line 7

8 1.2. Plan of Service The TransWest Express AC and DC project consists of the following system additions: 1. TWE Northern DC Terminal a. New substation with 500 kv and 230 kv busses 3 located south of Rawlins, Wyoming. approximately 60 miles west of the planned (PacifiCorp) Aeolus substation b. Connected to the Wyoming grid by looping the following lines in and out. (Because the Northern Terminal s proposed location is immediately adjacent to the proposed Gateway South and Gateway West routes, no additional line length was assumed for these loops. A 230 kv switching station will be added to the Platte-Latham 230 kv line with a two mile line connected to the Northern Terminal.) i. An existing 230 kv line between Platte and Latham substations ii. A planned Gateway West project 500 kv (series compensated) line between Aeolus and Anticline substations once this line has been constructed 4 iii. A planned Gateway South project 500 kv (series compensated) line between Aeolus and Clover substations once this line has been constructed 5 c. Two (2) 500/230 kv transformers with an aggregated capacity of approximately 1,000 MW depending on final configuration and studies 6 d. Thyristor-based HVDC converter rated for 3,225 MW at the converter station e. Number of synchronous condensers rated at +300/-150 MVAr needed for each buildout: Commercial Buildout Full Buildout 3000 MW 230/500kV Northern Terminal 3000 MW, 230/500kV Northern Terminal 7 5 f. Approximately +/-150 MVAr STATCOM on the 230 kv bus g. Approximately 1500 MVAr [ MVAr] shunt capacitors and filter banks on the 230 kv bus 2. TWE HVDC Transmission Line a. 406 miles of ±500 kv, 3000 MW bi-pole, HVDC transmission line consisting of 3 conductors of kcmil Athabaska/TW conductor per pole 3. TWE Southern DC Terminal at Intermountain Substation a. Connected to the Intermountain 345 kv bus via two (2) short transmission lines. b. Thyristor-based HVDC converter rated 3,000 MW at the converter station c. Approximately 2400 MVAr [ MVAr] shunt caps and filter banks on 500 kv bus d. Approximately +/-150 MVAr SVC on the 345 kv bus 5. TWE Northern AC Terminal at Intermountain a. New Intermountain 500kV bus. b. Three (3) 500/345 kv transformers with an aggregated capacity of approximately 1,500 MW 3 The 500 kv bus is part of the Gateway Buildout for the TWE Project. The 500 kv bus will not be constructed until Gateway West and/or Gateway South 500 kv lines are placed in service and interconnected to the TWE Project. 4 The 500/230 kv transformers are part of the Gateway Buildout for the TWE Project. These transformers will not be installed until Gateway West and/or Gateway South 500 kv lines are placed in service and interconnected to the TWE Project. 5 See note 3. 6 See note 3. 8

9 6. TWE AC Transmission Line a. 324 miles of 500 kv, AC transmission line consisting of triple bundle of 1590 kcmil Lapwing/TW conductor per pole b. Seventy percent (70%) series compensated line. Series capacitor bank modeled approximately 162 miles from each end of the line. c. 200 MVAr shunt reactor at series compensation location. 7. TWE Southern AC Terminal a. New 500 kv substation located in Eldorado Valley b. Connected to the Nevada grid by interconnecting with the following lines: i. An existing 500 kv line between Mead and Marketplace substations ii. A new 500 kv line from the TWE Project to McCullough substation iii. A new 500 kv line from the TWE Project to Eldorado substation c. Three (3) 500/500 kv phase-shifting transformers with an aggregated capacity of approximately 1,500 MW. d. Four (4) 80 MVAr shunt capacitors at the new TWE-NV 500kV bus Planned Operating Date The plan of service provides for the facilities to be operational by Study Methods 2.1. Base Case Development The TWE Project Commercial Operation Buildout Base Case was developed starting from the WECC 2022HS1a (8/31/2016) planning base case. The TWE AC and DC Project and connected generation were added to the case. Generation in California, Nevada and Arizona was adjusted to accommodate the resources associated with the TWE AC and DC Project. Generation reductions were 1,000 MW in the SCE area, 1750 MW in the LADWP area (1,500 MW of generation was displaced at the Intermountain substation) and 250 MW in the APS area. The TWE Project Full Buildout Base Case was developed starting from the WECC 2026HS1a (4/11/2016) planning base case. The TWE AC and DC Project and connected generation were added to the case. Generation in California, Nevada and Arizona was adjusted to accommodate the resources associated with the TWE AC and DC Project. Generation reductions were 1,000 MW in the SCE area, 1750 MW in the LADWP area (1,050 MW of generation was displaced at the Intermountain substation) and 250 MW in the APS area. The phase-shift transformers at the TWE Southern Project end were adjusted to yield a flow of 1,500 MW in the north to south direction. The phase-shift transformers can be used to adjust flow to the Intermountain 345kV substation. Base cases were developed in both Siemens PSS/E (version ) and GE PSLF (version 21.0_02). Base cases in both programs are needed since PRG members utilize different in run programs during power flow and transient stability simulations. For example, in the LA Basin, the Centralized Grid Capacitor Control algorithm (cgcc.p) EPCL program is utilized, which can result in different reactive margin values with and without the program. Additional details of how each study base case was developed can be found in the Base Case Development of Section 3 in this report. 9

10 2.2. Post Transient Power Analysis Power flow contingencies are modeled with single element (N-1) outages and credible double element (N-2) outages to evaluate the NERC/WECC category P1 through P7 performance. Transmission elements were monitored for thermal and voltage violations Post-Transient Voltage Stability The WECC requires that new rated paths or facilities be increased to 102.5% and 105% of the maximum achievable transfer capability. For adequate reactive margin, 105% cases are required to converge for Category P1 and P3 7 contingencies, while 102.5% cases are required to converge for Category P6 and P7 contingencies. Studies for this analysis also simulated reactive margin for key buses throughout the system, which provides a measure of system adequacy. In addition, reactive margin was calculated for the LADWP Adelanto 500kV bus. Following a P1 contingency, the Adelanto 500kV bus must have 500 MVAr, and following a P7 contingency, the bus must have 250 MVAr Transient Stability Single element (N-1) and double element (N-2) contingencies identified in the study plan were simulated to evaluate transient stability performance. Also, critical contingencies for each path rating were simulated to evaluate transient stability performance Affected Path Stress Test (10% Test) WECC requires a screening test procedure to identify all paths that are potentially affected by the path under study. For the TWE DC contingency and TWE AC contingency, the established WECC paths with a flow increase of 10% or more were identified. The percent increase is based on the affected paths rating Path Independence Test WECC requires two (2) screening tests to be used to determine whether a path is independent of another path. Results of the tests are provided in this report to aid in determining if the TWE AC and DC proposed Project is part of the same path or a subset of an existing Path Generation Drop via Remedial Action Schemes (RAS) For loss of the TransWest Express Project, new Wyoming wind generation and/or gas generation connected to the TWE northern terminal was tripped. 100% of this generation was tripped for a TWE bi-pole contingency and approximately 40% of this generation was tripped for a TWE monopole contingency. 7 The ISO Grid Planning Standards ( April12015_v2.pdf) requires performance for P3 contingency (G-1/N-1) to meet the former Category B performance. 10

11 3. Non-Simultaneous Analysis Results The Non-Simultaneous results were simulated for single and double contingencies listed in Table 3a and 3b of the study plan. A discussion of key outages follows. Loss of the TWE DC Mono-pole (w/ras) Each TWE DC monopole has a continuous overload capacity of 1725 MW (utilizes 15% overload capability of converters) delivered to the southern DC terminal. Therefore, only 1,275 MW of new Wyoming wind generation connected to the TWE northern terminal is tripped for loss of the TWE DC mono-pole. Loss of the TWE DC Bi-pole (w/ras) The following mitigation is needed for loss of the TWE DC Bi-pole: 1. All new Wyoming wind generation at the TWE northern terminal was tripped. 2. The Intermountain (IPPDC) DC flow is ramped back quickly to ensure that there are no issues on the Intermountain Mona No.1 and No.2 345kV lines. 3. Shunt capacitors will need to be switched off-line to alleviate high voltage. Loss of the TWE Intermountain TWE Nevada 500kV line (w/ras) The TWE Project injects 1,500 MW of new Wyoming generation into the TWE 500kV line that interconnects to the AC southern terminal. Loss of this line removes the path to transfer the generation. As a result, the TWE DC flow needs to be reduced by the amount scheduled on the TWE AC line. This reduction in DC flow will require generation tripping at the northern TWE DC terminal. Loss of the Intermountain IPPDC Mono-pole or Bi-pole line (w/ras) With loss of the Intermountain IPPDC mono or bi-pole line, the TWE DC flow would be reduced by the amount that was initially flowing on the IPPDC line(s) prior to tripping. An arming RAS may be needed to determine ramp back and generation tripping amounts prior to an incident. Coordination between the IPPDC and TWE DC systems will be needed. An IPPDC bi-pole outage would require a quicker response. Depending on the amount of Wyoming generation that is needed to be tripped, the TWE DC mono-pole could be tripped (instead of ramping back) for higher flow levels that are scheduled to the Intermountain substation. Loss of the Intermountain Mona No.1 and No.2 345kV lines Post-transient power flow identifies that the IPPDC line may not need to be tripped. Presently, for loss of the Intermountain Mona No.1 and No.2 345kV lines, the Intermountain Gonder 230kV line is tripped, which also results in the IPPDC lines being tripped. For this analysis, the Intermountain Gonder 230 kv line was not tripped, which results in the Intermountain system staying intact. 11

12 3.1. Non-Simultaneous Analysis Commercial Operation Buildout A non-simultaneous Commercial Operation buildout base case was developed in order to evaluate WECC system reliability. Note, the pre-project base case was evaluated by simulating all power flow contingencies. The developed post-project base case has a TransWest Express flow of 3,000 MW on the DC portion of the Project and 1,500 MW on the AC portion Base Case Development The Non-Simultaneous base case modeled a TWE DC flow of 3,000 MW in the north to south direction and a TWE AC flow of 1,500 MW in the north to south direction. When turning the Intermountain Unit 2 generator and station service load off (displaced with TWE power), the reactive power from Unit 2 was approximately 175 MVAr. As a result, one (1) 175 MVAr shunt capacitor was modeled at the Intermountain 345 kv bus. The following Projects are included in the Commercial Operation buildout base case. Table 1 TWE Project Commercial Operation Buildout New Transmission Facilities No. Project Description 1 TWE DC and AC Project 2 Gateway West Segment D.2 3 Eldorado Harry Allen 500 kv line 4 Colorado River-Delaney 500 kv line The TransWest Express DC path is defined as the sum of flow on the following lines: TWE-INT* TWE-WY 500 kv DC No.1 and No.2 Lines The TransWest Express AC path is defined as the sum of flow on the following lines: TWE-NV* McCullough 500 kv TWE-NV* Marketplace 500 kv TWE-NV* Eldorado 500 kv TWE-NV* Mead 500 kv Note, the asterisk indicates the metering location Post-Transient Power Analysis Power flow results identified that no elements exceeded 100% of their emergency thermal limit. One (1) post-transient voltage violation was identified with inclusion of TWE AC and DC Project. Loss of the TWE DC Bi-Pole (w/ras) (P7) The outage results in voltage levels below 0.9 per unit at the Peterson 230kV buses. Two (2) 6 MVAr shunt capacitors were switched in-service to mitigate voltage levels below 0.9 per unit in the Dillon/Big Grassy 161kV area. However, this did not result in Peterson 230kV bus voltage levels above 0.9 per unit. This contingency may require additional shunt capacitors in this area with quick insertion. Eldorado Lugo 500 kv and Eldorado Mohave 500 kv Lines (P6) The outage modeled as a P7 (N-2) contingency results in a Lugo Victorville 500 kv line (WECC Path 61) flow of 99.6% of its emergency rating. This is an increase of 17% 12

13 compared to the pre-project case. However, this is actually a P6 (N-1-1) contingency, which allows the system to be adjusted after either of the line outages. Overloading of this element has been observed in other WECC path rating studies. The CAISO Transmission Plan identifies upgrades to this line targeted for 12/2018 that will increase the emergency rating by approximately 50%. Completion of these upgrades will eliminate the P7 overload identified in this study. Currently, CAISO is managing this situation by re-dispatching generation following the first outage of the P6 contingency. Prior to the completion of the upgrades, TWE will participate in the current re-dispatch procedure by reducing its schedule to Eldorado substation as required to mitigate the incremental impacts caused by TWE. However, with the TWE project planned for 2022 in-service date, the Lugo-Victorville 500 kv line upgrade is scheduled to be completed prior to TWE project at this time Post-Transient Voltage Stability Cases were created with TWE path flows increased to 105% of the maximum achievable TWE AC (1575 MW) and DC (3150 MW) transfer capability. All contingencies converged, which indicates adequate reactive margin for the system. Appendix C contains tables showing positive reactive margins at the Adelanto 500kV bus for all contingencies. Reactive margins at Adelanto met the special criteria identified in the study plan. Note: Loss of the IPP DC mono-pole results in the lowest reactive margin of 354 MVAr; however, this is with use of the +5% case. Simulating without the +5% flow yields a reactive margin of 806 MVAr, which meets the +500 MVAr requirement for N-1 contingencies Transient Stability Analysis Transient stability study simulations identified that all contingencies studied for these system conditions were damped and conformed to the NERC/WECC Planning Standards. A discussion of key outages follows. Loss of the Intermountain Mona No.1 and No.2 345kV lines Transient stability study simulation with GE identifies Stopped - network failed to converge, which indicates instability for loss of the Intermountain Mona No.1 and No.2 345kV lines. The simulation stops 5 cycles after fault clearing. Figure 4 Transient Stability Plots with PSLF Program 13

14 As a check, the contingency was simulated in the PSS/E platform to determine if both programs yield the same result. The PSS/E simulation runs without convergence issues. Figure 5 Transient Stability Plots with PSS/E Program Observing both plots, there is a large voltage spike after the fault is cleared and the lines are opened. This could be a mathematical issue causing non-convergence in the PSLF program. Another difference relates to modeling of the IPPDC. The IPPDC in the PSLF program has a user written model that is specific to the IPPDC functionality. However, this model is a black box since, the code is encrypted, which does not allow the user to discern switching actions. Only observing the output during simulations does the user get a glimpse of what the user written model is adjusting Intermountain generation is switched. The PSS/E program has a CDC6T model that represents the IPPDC. LADWP was consulted to determine if this is a modeling issue. LADWP is investigating further to determine if the TWE AC and DC Project benefits this contingency. This contingency will be further defined during the WECC Phase 2 studies. In order to get the contingency to simulate, the TWE monopole (1600 MW) was tripped and the IPPDC lines (881 MW each pole) were tripped. Transient stability results are provided in Appendix D and plots are provided in Appendix F. 14

15 3.2. Non-Simultaneous Analysis Full Buildout A non-simultaneous Full buildout base case was developed in order to evaluate WECC system reliability. Note, the pre-project base case was evaluated by simulating all power flow contingencies. The developed post-project base case has a TransWest Express flow of 3,000 MW on the DC portion of the Project and 1,500 MW on the AC portion Base Case Development The Non-Simultaneous base case modeled a TWE DC flow of 3,000 MW in the north to south direction and a TWE AC flow of 1,500 MW in the north to south direction. When turning the Intermountain Unit 2 generator and station service load off (displaced with TWE power), the reactive power from Unit 2 was approximately 70 MVAr. As a result, one (1) 70 MVAr shunt capacitor was modeled at the Intermountain 345 kv bus. The following Projects are included in the Full buildout base case. Table 2 TWE Project with Full Buildout New Transmission Facilities No. Project Description 1 TWE DC and AC Project 2 Gateway West 3 Eldorado Harry Allen 500 kv line 4 Colorado River-Delaney 500 kv line 5 Gateway South 7 North Gila Imperial Valley No.2 Project 8 Southwest Intertie Project (SWIP-N) 8 The TransWest Express DC path is defined as the sum of flow on the following lines: TWE-INT* TWE-WY 500 kv DC No.1 and No.2 Lines The TransWest Express AC path is defined as the sum of flow on the following lines: TWE-NV* McCullough 500 kv TWE-NV* Marketplace 500 kv TWE-NV* Eldorado 500 kv TWE-NV* Mead 500 kv Note, the asterisk indicates the metering location Post-Transient Power Analysis Single and double contingencies listed in Table 3a and 3b of the study plan were simulated for the Non-Simultaneous base case. Power flow results identified that only one (1) contingency results in an element to exceed 100% of its emergency thermal limit. No post-transient voltage violations were identified with inclusion of TWE AC and DC Project. 8 The Cross-Tie Project will be studied as a sensitivity without the SWIP-N Project. Since, there would be congestion with both Projects modeled. 15

16 A discussion of key outages follows. Loss of the Aeolus TWE-Wyoming No.1 and No.2 500kV lines The Platte Standpipe 230kV line loads to 101.5% (45% increase in flow) of its emergency thermal rating of 1258 amps (501 MVA). PacifiCorp has a RAS that trips up to 1600 MW of Aeolus area generation for this contingency. However, the case does not have any new Aeolus area generation modeled to trip. As a result, mitigation is required for this contingency. For this multiple contingency outage, P7, the TWE Wyoming 500/230kV transformers could be tripped, opening the path where the power is flowing. Or, the TWE Wyoming to Anticline 500kV line could be tripped to mitigate thermal issue Post-Transient Voltage Stability Cases were created with TWE path flows increased to 105% of the maximum achievable TWE AC (1575 MW) and DC (3150 MW) transfer capability. All contingencies converged, which indicates adequate reactive margin for the system. Appendix C contains tables showing positive reactive margins at the Adelanto 500kV bus for all contingencies. Reactive margins at Adelanto met the special criteria identified in the study plan Transient Stability Analysis Transient stability study simulations identified that all contingencies studied for these system conditions were damped and conformed to the NERC/WECC Planning Standards. A discussion of key outages follows. Loss of the Intermountain Mona No.1 and No.2 345kV lines Transient stability studies identify that the system is not stable. Transient stability study simulation with GE identifies Stopped - network failed to converge, which indicates instability for loss of the Intermountain Mona No.1 and No.2 345kV lines. The simulation stops 5 cycles after fault clearing. Figure 6 Transient Stability Plots with PSLF Program As a check, the contingency was simulated in the PSS/E platform to determine if both programs yield the same result. The PSS/E simulation runs without convergence issues. 16

17 Figure 7 Transient Stability Plots with PSS/E Program Observing both plots, there is a large voltage spike after the fault is cleared and the lines are opened. This could be a mathematical issue causing non-convergence in the PSLF program. Another difference relates to modeling of the IPPDC. The IPPDC in the PSLF program has a user written model that is specific to the IPPDC functionality. However, this model is a black box since, the code is encrypted, which does not allow the user to discern switching actions. Only observing the output during simulations does the user get a glimpse of what the user written model is adjusting Intermountain generation is switched. The PSS/E program has a CDC6T model that represents the IPPDC. LADWP was consulted to determine if this is a modeling issue. LADWP is investigating further to determine if the TWE AC and DC Project benefits this contingency. This contingency will be further defined during the WECC Phase 2 studies. In order to get the contingency to simulate, the TWE monopole (1600 MW) was tripped and the IPPDC lines (881 MW each pole) were tripped. Transient stability results are provided in Appendix D and plots are provided in Appendix F. 17

18 4. Affected Path Stress Test Results The WECC Affected Path Stress Test is used to determine each affected path with loss of the TWE DC Project at full output. Results for the Commercial Operation buildout, Full buildout with the SWIP-N Project and with the Full buildout with the Cross-Tie Project are provided. A simultaneous interaction is identified as a path flow change greater than or equal to 10% of the path rating. Loss of the TWE bipole outage was simulated by the following switching: 1. Block both TWE DC bi-poles 2. Tripped TWE shunt capacitors at both ends of the TWE DC line 3. Trip Wyoming wind generation 4. Tripped one (1) IPPDC Pole and Intermountain shunt capacitors Commercial Operation Buildout Thirty-one (31) simultaneous interactions were observed. Table 3. Non-Simultaneous, Commercial Operation buildout NUM NAME Post-Con 'Direction of + Pre- Con Post- Con Change Percent of Path Path (+) Path (-) 1 ALBERTA - BRITISH COLUMBIA W2E NORTHWEST - CANADA N2S WEST OF CASCADES - NORTH E2W WEST OF CASCADES - SOUTH E2W WEST OF HATWAI E2W MONTANA - NORTHWEST E2W WEST OF BROADVIEW E2W WEST OF COLSTRIP E2W WEST OF CROSSOVER E2W IDAHO - NORTHWEST W2E MIDWAY - LOS BANOS S2N IDAHO - SIERRA N2S BORAH WEST E2W MONTANA - IDAHO N2S BRIDGER WEST E2W PATH C N2S SOUTHWEST OF FOUR CORNERS E2W FOUR CORNERS 345/ PG&E - SPP E2W PACIFICORP/PG&E 115 KV N2S NORTHERN SOUTHERN CA N2S IPP DC LINE N2S INTERMOUNTAIN - MONA 345 KV E2W INTERMOUNTAIN-GONDER 230 KV E2W TOT 1A E2W

19 NUM NAME Post-Con 'Direction of + Pre- Con Post- Con Change Percent of Path Path (+) Path (-) 31 TOT 2A N2S PAVANT, INTRMTN - GONDER 230 KV E2W BONANZA WEST E2W TOT 2B TOT 2C N2S TOT 3 N2S TOT 4A NE2SW TOT 4B SE2NW TOT 5 W2E TOT 7 N2S SYLMAR - SCE N2S IID - SCE E2W SDG&E - CFE S2N WEST OF COLORADO RIVER (WOR) E2W SOUTHERN NEW MEXICO (NM1) N2S NORTHERN NEW MEXICO (NM2) N2S EAST OF COLORADO RIVER (EOR) E2W CHOLLA - PINNACLE PEAK N2S SOUTHERN NAVAJO N2S SILVER PEAK - CONTROL 55 KV E2W CORONADO-SILVER KING-KYRENE N2S BROWNLEE EAST W2E ELDORADO - MEAD 230 KV LINES N2S WALC BLYTHE - SCE BLYTHE 161 KV E2W INYO - CONTROL 115 KV TIE E2W LUGO - VICTORVILLE 500 KV LINE E2W ELDORADO - MCCULLOUGH 500 KV W2E PERKINS-MEAD-MARKETPLACE PACIFIC DC INTERTIE (PDCI) N2S COI N2S SOUTH OF ALLSTON N2S NORTH OF JOHN DAY N2S MIDPOINT - SUMMER LAKE E2W ALTURAS PROJECT N2S CRYSTAL - ALLEN S2N TOT 2B1 N2S TOT 2B2 N2S MONTANA SOUTHEAST S2N SNTI-S.NEVADA TRAN INTERFACE S2N (Imp) TOTBEAST W2E

20 NUM NAME Post-Con 'Direction of + Pre- Con Post- Con Change Percent of Path Path (+) Path (-) 83 MATL TRANSWEST EXPRESS DC LINE N2S TRANSWEST EXPRESS AC LINE N2S Full Buildout, SWIP-N Included Twenty-six (26) simultaneous interactions were observed. Table 4. Non-Simultaneous, Full buildout, SWIP-N Included NUM NAME Post-Con 'Direction of + Pre- Con Post- Con Change Percent of Path Path (+) Path (-) 1 ALBERTA - BRITISH COLUMBIA W2E NORTHWEST - CANADA N2S WEST OF CASCADES - NORTH E2W WEST OF CASCADES - SOUTH E2W WEST OF HATWAI E2W MONTANA - NORTHWEST E2W WEST OF BROADVIEW E2W WEST OF COLSTRIP E2W WEST OF CROSSOVER E2W IDAHO - NORTHWEST W2E MIDWAY - LOS BANOS S2N IDAHO - SIERRA N2S BORAH WEST E2W MONTANA - IDAHO N2S BRIDGER WEST E2W PATH C N2S SOUTHWEST OF FOUR CORNERS E2W FOUR CORNERS 345/ PG&E - SPP E2W PACIFICORP/PG&E 115 KV N2S NORTHERN SOUTHERN CA N2S IPP DC LINE N2S INTERMOUNTAIN - MONA 345 KV E2W INTERMOUNTAIN-GONDER 230 KV E2W TOT 1A E2W TOT 2A N2S PAVANT, INTRMTN - GONDER 230 KV E2W BONANZA WEST E2W TOT 2B TOT 2C N2S

21 NUM NAME Post-Con 'Direction of + Pre- Con Post- Con Change Percent of Path Path (+) Path (-) 36 TOT 3 N2S TOT 4A NE2SW TOT 4B SE2NW TOT 5 W2E TOT 7 N2S SYLMAR - SCE N2S IID - SCE E2W SDG&E - CFE S2N WEST OF COLORADO RIVER (WOR) E2W SOUTHERN NEW MEXICO (NM1) N2S NORTHERN NEW MEXICO (NM2) N2S EAST OF COLORADO RIVER (EOR) E2W CHOLLA - PINNACLE PEAK N2S SOUTHERN NAVAJO N2S SILVER PEAK - CONTROL 55 KV E2W CORONADO - SILVER KING - KYRENE N2S BROWNLEE EAST W2E ELDORADO - MEAD 230 KV LINES N2S WALC BLYTHE - SCE BLYTHE 161 KV E2W INYO - CONTROL 115 KV TIE E2W LUGO - VICTORVILLE 500 KV LINE E2W ELDORADO - MCCULLOUGH 500 KV W2E PERKINS-MEAD-MARKETPLACE PACIFIC DC INTERTIE (PDCI) N2S COI N2S SOUTH OF ALLSTON N2S NORTH OF JOHN DAY N2S MIDPOINT - SUMMER LAKE E2W ALTURAS PROJECT N2S CRYSTAL - ALLEN S2N TOT 2B1 N2S TOT 2B2 N2S MONTANA SOUTHEAST S2N SNTI-S.NEVADA TRAN INTERFACE S2N (Imp) TOTBEAST W2E MATL TRANSWEST EXPRESS DC LINE N2S TRANSWEST EXPRESS AC LINE N2S * SWIP-North: Mdpt-RobnSumt *

22 4.3. Sensitivity, Full Buildout, Cross-Tie Project Included Twenty-seven (27) simultaneous interactions were observed. Table 5. Non-Simultaneous, Full buildout, Cross-Tie Project Included NUM NAME Post-Con 'Direction of + Pre- Con Post- Con Change Percent of Path Path (+) Path (-) 1 W2E ALBERTA - SASKATCHEWAN W2E NORTHWEST - CANADA N2S WEST OF CASCADES - NORTH E2W WEST OF CASCADES - SOUTH E2W WEST OF HATWAI E2W MONTANA - NORTHWEST E2W WEST OF BROADVIEW E2W WEST OF COLSTRIP E2W WEST OF CROSSOVER E2W IDAHO - NORTHWEST W2E MIDWAY - LOS BANOS S2N IDAHO - SIERRA N2S BORAH WEST E2W MONTANA - IDAHO N2S BRIDGER WEST E2W PATH C N2S SOUTHWEST OF FOUR CORNERS E2W FOUR CORNERS 345/ PG&E - SPP E2W PACIFICORP/PG&E 115 KV INTERCON. N2S NORTHERN - SOUTHERN CALIFORNIA N2S IPP DC LINE N2S INTERMOUNTAIN - MONA 345 KV E2W INTERMOUNTAIN - GONDER 230 KV E2W TOT 1A E2W TOT 2A N2S PAVANT, INTRMTN - GONDER 230 KV E2W BONANZA WEST E2W TOT 2B TOT 2C N2S TOT 3 N2S TOT 4A NE2SW TOT 4B SE2NW TOT 5 W2E TOT 7 N2S SYLMAR - SCE N2S

23 NUM NAME Post-Con 'Direction of + Pre- Con Post- Con Change Percent of Path Path (+) Path (-) 42 IID - SCE E2W SDG&E - CFE S2N WEST OF COLORADO RIVER (WOR) E2W SOUTHERN NEW MEXICO (NM1) N2S NORTHERN NEW MEXICO (NM2) N2S EAST OF COLORADO RIVER (EOR) E2W CHOLLA - PINNACLE PEAK N2S SOUTHERN NAVAJO N2S SILVER PEAK - CONTROL 55 KV E2W CORONADO - SILVER KING - KYRENE N2S BROWNLEE EAST W2E ELDORADO - MEAD 230 KV LINES N2S WALC BLYTHE - SCE BLYTHE 161 KV E2W INYO - CONTROL 115 KV TIE E2W LUGO - VICTORVILLE 500 KV LINE E2W ELDORADO - MCCULLOUGH 500 KV W2E PERKINS - MEAD - MARKETPLACE PACIFIC DC INTERTIE (PDCI) N2S COI N2S SOUTH OF ALLSTON N2S NORTH OF JOHN DAY N2S MIDPOINT - SUMMER LAKE E2W ALTURAS PROJECT N2S CRYSTAL - ALLEN S2N TOT 2B1 N2S TOT 2B2 N2S MONTANA SOUTHEAST S2N SNTI-S.NEVADA TRAN INTERFACE S2N (Imp) TOTBEAST W2E MATL TRANSWEST EXPRESS DC LINE N2S TRANSWEST EXPRESS AC LINE N2S Cross-Tie Project

24 5. Path Independence Test Results Two screening tests were used to determine whether the TWE AC and TWE DC lines are independent of existing paths Test 1: Schedule a Fixed Amount of Power on Project The TWE AC and DC Project was added to the 2020 heavy summer base case. Since, the TWE DC inverters can control the range from 0 to 3,000 MW, it will be a new Path independent of all other paths. Also, since, the TWE AC line has phase-shift transformers that can control the power flow for the full range from 0 to 3,000 MW, it will be a new Path independent of all other paths Test 2: Do Not Schedule Power on Project The TWE AC and DC Project was added to the 2020 heavy summer base case. Since, the TWE DC inverters can control the range from 0 to 3,000 MW, it will be a new Path independent of all other paths. Also, since, the TWE AC line has phase-shift transformers that can control the power flow for the full range from 0 to 3,000 MW, it will be a new Path independent of all other paths. 6. Sensitivity Studies 6.1. Non-Simultaneous Analysis Full Buildout, Cross-Tie Project A non-simultaneous Full buildout base case with the Cross-Tie Project modeled was developed in order to evaluate WECC system reliability. Note, the pre-project base case was evaluated by simulating all power flow contingencies. The developed post-project base case has a TransWest Express flow of 3,000 MW on the DC portion of the Project and 1,500 MW on the AC portion Base Case Development The Non-Simultaneous base case modeled a TWE DC flow of 3,000 MW in the north to south direction and a TWE AC flow of 1,500 MW in the north to south direction. When turning the Intermountain Unit 2 generator and station service load off (displaced with TWE power), the reactive power from Unit 2 was approximately 70 MVAr. As a result, one (1) 70 MVAr shunt capacitor was modeled at the Intermountain 345 kv bus. The following Projects are included in the Full buildout base case. Table 6 TWE Project with Full Buildout New Transmission Facilities No. Project Description 1 TWE DC and AC Project 2 Gateway West 3 Eldorado Harry Allen 500 kv line 4 Colorado River-Delaney 500 kv line 5 Gateway South 7 North Gila Imperial Valley No.2 Project 8 Cross-Tie Project 24

25 The TransWest Express DC path is defined as the sum of flow on the following lines: TWE-INT* TWE-WY 500 kv DC No.1 and No.2 Lines The TransWest Express AC path is defined as the sum of flow on the following lines: TWE-NV* McCullough 500 kv TWE-NV* Marketplace 500 kv TWE-NV* Eldorado 500 kv TWE-NV* Mead 500 kv Note, the asterisk indicates the metering location Post-Transient Power Analysis Single and double contingencies listed in Table 3a and 3b of the study plan were simulated for the Non-Simultaneous base case. Power flow results identified that only one (1) contingency results in an element to exceed 100% of its emergency thermal limit. No post-transient voltage violations were identified with inclusion of TWE AC and DC Project. A discussion of key outages follows. Loss of the Aeolus TWE-Wyoming No.1 and No.2 500kV lines The Platte Standpipe 230kV line loads to 104.9% (49% increase in flow) of its emergency thermal rating of 1258 amps (501 MVA). PacifiCorp has a RAS that trips up to 1600 MW of Aeolus area generation for this contingency. However, the case does not have any new Aeolus area generation modeled to trip. As a result, mitigation is required for this contingency. For this multiple contingency outage, P7, the TWE Wyoming 500/230kV transformers could be tripped, opening the path where the power is flowing. Or, the TWE Wyoming to Anticline 500kV line could be tripped to mitigate thermal issue Post-Transient Voltage Stability Cases were created with TWE path flows increased to 105% of the maximum achievable TWE AC (1575 MW) and DC (3150 MW) transfer capability. All contingencies converged, which indicates adequate reactive margin for the system. Appendix C contains tables showing positive reactive margins at the Adelanto 500kV bus for all contingencies. Reactive margins at Adelanto met the special criteria identified in the study plan Transient Stability Analysis Transient stability study simulations identified that all contingencies studied for these system conditions were damped and conformed to the NERC/WECC Planning Standards. A discussion of key outages follows. 25

26 Loss of the Intermountain Mona No.1 and No.2 345kV lines Transient stability studies identify that the system is not stable. Transient stability study simulation with GE identifies Stopped - network failed to converge, which indicates instability for loss of the Intermountain Mona No.1 and No.2 345kV lines. The simulation stops 5 cycles after fault clearing. Figure 8 Transient Stability Plots with PSLF Program As a check, the contingency was simulated in the PSS/E platform to determine if both programs yield the same result. The PSS/E simulation runs without convergence issues. Figure 9 Transient Stability Plots with PSS/E Program 26

27 Observing both plots, there is a large voltage spike after the fault is cleared and the lines are opened. This could be a mathematical issue causing non-convergence in the PSLF program. Another difference relates to modeling of the IPPDC. The IPPDC in the PSLF program has a user written model that is specific to the IPPDC functionality. However, this model is a black box since, the code is encrypted, which does not allow the user to discern switching actions. Only observing the output during simulations does the user get a glimpse of what the user written model is adjusting Intermountain generation is switched. The PSS/E program has a CDC6T model that represents the IPPDC. LADWP was consulted to determine if this is a modeling issue. LADWP is investigating further to determine if the TWE AC and DC Project benefits this contingency. This contingency will be further defined during the WECC Phase 2 studies. In order to get the contingency to simulate, the TWE monopole (1600 MW) was tripped and the IPPDC lines (881 MW each pole) were tripped. Transient stability results are provided in Appendix D and plots are provided in Appendix F. 27

28 7. Study Findings and Conclusions / Recommendations Study results for the TWE AC and DC Project did not yield significant planning criteria violations. In fact, the results were positive indicating that further studies should be conducted to achieve WECC path ratings for both the AC and DC components of this Project. Key observations from the non-simultaneous studies are provided in the following summary. Both the TWE AC and DC components of the Project will be new WECC Paths since they are independent of all other paths. The Affected Path Stress Test (10% test) results indicate that there are number of existing WECC paths that will require further analysis in the WECC Phase 2 studies. Some of the paths indicate that the TWE AC and DC project have a very strong correlation. Based on power flow base case development, when scheduling power flow to the Intermountain 345kV substation, the reactive power consumption increased. As a result, an additional two (2) 160 MVAr shunt capacitors are needed. Loss of the Aeolus TWE-Wyoming No.1 and No.2 500kV lines results in the underlying 230kV system to yield a line that exceeds its thermal limit. A solution for this double line contingency would be to trip the TWE Wyoming 230kV bus from the Platte Latham 230kV line. This opens the path to mitigate the high flow during this contingency. Further discussions with PRG members will be helpful in assessing if there are any issues in coordinating operation of both the IPPDC and TWE DC lines. Furthermore, scheduling and generation tripping at the Intermountain substation should be further explored to determine trip amounts for various levels of flow scheduled to the Intermountain substation. Loss of the Intermountain Mona No.1 and No.2 345kV lines does not converge in the PSLF program for transient stability simulations. The transient stability contingency solves in the PSS/E program. However, PSLF uses a user-written model and PSS/E uses a generic CDC6T model. Need to further investigate to determine if this a numerical issue, or truly a transient instability. For this study, the TWE DC monopole and the IPPDC bi-pole was tripped for this contingency to yield a transient stability converged simulation. Based on these study results, the TransWest Express AC and DC Project does interact with a number of existing WECC path ratings. Therefore, it is recommended that the TransWest Express AC and DC Project be accepted into Phase 2A of the WECC Path process with the Plan of Service described in Appendix I. 28