TransWest Express Project

Transcription

1 TransWest Express Project Phase One--Feasibility Study Final Study Report November 2006 A subsidiary of Pinnacle West Capital Corporation

2 Executive Summary On October 21, 2005 Arizona Public Service Company (APS) announced publicly its intention of exploring the feasibility of constructing two new 500 kv transmission lines from Wyoming (Powder River Basin and nearby high-quality open range wind locations) to northern Arizona to provide Arizona and other states (NM, NV, CA and UT) access to over 6000 MW of coal and wind resources in Wyoming. The new transmission project from Wyoming to Arizona, the TransWest Express Project, is planned to be operational in 2013 and is expected to deliver 3000 MW of power to meet rapid load growth in Arizona and the southwest. The TransWest Express Project has a three-phase implementation plan. These are: Phase 1- Feasibility study Phase 2- Technical study and permitting Phase 3- Implementation APS is sponsoring the feasibility study for the project. The feasibility study entails high level technical and economic analyses. This report details the objective, scope, methodology and the results for the technical part of the feasibility study. This study evaluated six transmission alternatives capable of exporting up to 3000 MW of power from Wyoming to Arizona and the southwest. Alternatives evaluated included three 500 kv AC options (Alternatives A, B and C), a 500 kv DC only alternative (Alternative D), a 500 kv AC/DC hybrid alternative (Alternative E) and a 765 kv AC alternative (Alternative F). Alternative F was designed to serve as sensitivity to Alternative A. The study results demonstrate that each of the transmission alternatives evaluated is feasible and capable of meeting the objective of the project, which is to be able to export up to 3000 MW of power from Wyoming to Arizona and the southwest. The study also revealed that additional facilities or upgrades beyond the basic scope of each alternative are needed in order to export the 3000 MW and meet reliability standards. The study results showed that the electrical performances of Alternatives A, B and C are similar since all the three alternatives originate from the same source with same intermediate connections but slightly different termination points. The critical outages for the three alternatives were found to be the same with the same recommended mitigation plans. However, Alternative A was found to provide a more balanced flow on south of Dave Johnston 500 kv lines compared to B and C. Alternative A also results in relatively lower transmission system losses and has a lower capital cost. All the three alternatives result in inadvertent flow (up to 260 MW) on the existing system. TransWest Express Project, Final Feasibility Study Report-November 2006 i

3 The DC only and the AC/DC hybrid transmission alternatives result in relatively insignificant (about 7 MW) unscheduled flows, lowest transmission system losses, least miles of new transmission lines and lowest capital cost when compared to 500 kv AC alternatives. In particular, Alternative D has transmission system losses of about 186 MW compared to 245 MW for Alternative A, and has a capital cost approximately 55% of that of Alternative A. However, the recommended mitigation plan for the most critical outage for the DC only and the AC/DC hybrid alternatives would require tripping of up to 3000 MW of generation whereas that for the AC alternatives would require tripping of up to 1500 MW of generation. A 765 kv AC transmission alternative is found to compare favorable electrically to 500 kv AC transmission alternative. The difference between the two transmission voltage levels lies in capital cost and transmission losses. Though, transmission system losses for a 765 kv AC alternative (Alternative F) are estimated to be 90 MW while that for a 500 kv AC alternative (Alternative A) is 245 MW, the capital cost for Alternative F is about a billion dollars more than that for Alternative A. This comparison assumed 3000 MW of power schedule for both Alternatives F and A, however, Alternative F could potentially have capacity for up to 5000 MW. TransWest Express Project, Final Feasibility Study Report-November 2006 ii

4 Contents Page Introduction Objective. 2 Scope Transmission Alternatives Alternative A Alternative B Alternative C Alternative D Alternative E...7 Alternative F...8 Base Case Description Modeling of Transmission Alternatives 9 Transmission Schedules Methodology Study Results...13 Analysis and Comparison of Transmission Alternatives Conclusions...23 Appendix A...24 Appendix B...32 Appendix C...39 Appendix D...45 Appendix E...59 TransWest Express Project, Final Feasibility Study Report-November 2006 iii

5 Introduction On October 21, 2005 Arizona Public Service Company (APS) announced publicly its intention of exploring the feasibility of constructing two new 500 kv transmission lines from Wyoming (Powder River Basin and nearby high-quality open range wind locations) to northern Arizona to provide Arizona and other states (NM, NV, CA and UT) access to over 6000 MW of coal and wind resources in Wyoming. The new transmission project from Wyoming to Arizona, the TransWest Express Project (See Figure 1), is planned to be operational in 2013 and is expected to deliver 3000 MW of power to meet rapid load growth in Arizona and the southwest. TransWest Express Project Wyoming All Lines are 500 kv TransWest Express Project Existing Lines Upgrades Other Planned Projects Power Plant Substation California Nevada Los Angeles Las Vegas N.Gila Salt Lake City Utah Navajo Arizona Phoenix/ Tucson Four Corners New Mexico Figure 1: TransWest Express Project The TransWest Express Project has a three-phase implementation plan. These are: Phase 1- Feasibility study Phase 2- Technical study and permitting Phase 3- Implementation APS is sponsoring the feasibility study for the project. The feasibility study entails high level technical and economic analyses. This report details the objective, scope and methodology for the technical part of the feasibility study. It provides a high level electrical performances characteristics of the various TransWest Express Project, Final Feasibility Study Report-November

6 transmission alternatives evaluated. The report also ranks the alternatives and recommends the most desirable transmission plan, from a technical perspective. This study is performed as a separate, project-specific study that adopted as a starting point the transmission, resource, and other assumptions and plans developed in WECC, STEP, RMATS and other regional planning processes. Study results and data will be made available to other regional planning processes. As part of this study, high level power flow, transient stability and post-transient analyses were initially performed on four different 500 kv AC and DC transmission alternatives capable of exporting 3000 MW of power from Wyoming to Arizona and the southwest. Two additional transmission alternatives including a 765 kv option were subsequently evaluated. Objective This study evaluates the electrical performance of different transmission alternatives, primarily at 500 kv level capable of exporting up to 3000 MW of power from Wyoming to Arizona, New Mexico, Utah, Nevada and California. The transmission alternatives are compared and the most technically desirable plans recommended for further detailed technical and economic evaluation under the Phase 2 of the TransWest Express implementation plan. Scope The scope of the feasibility study included: Performing high level power flow, transient and post-transient studies on all the transmission alternatives under evaluation. Determining need, size and location of series compensation on all the transmission alternatives. Determining need, amount and location of reactive power support to meet reactive margin requirements. Identifying transmission constraints and the associated critical contingencies for each transmission alternative. Quantifying transmission losses for each transmission alternative. Highlighting incremental flows on the major transmission lines and interfaces. High level capital cost estimates for the preferred transmission plans. Demonstrating that the recommended transmission alternative meets the WECC/NERC planning standards. TransWest Express Project, Final Feasibility Study Report-November

7 Demonstrating that the recommended transmission alternative is capable of exporting 3000 MW of power from Wyoming to Arizona and other southwest states subject to the different transmission schedule scenarios defined under the Transmission Schedules section. Transmission Alternatives In this study, several possible scenarios of establishing a new transmission path from Wyoming to Arizona and the southwest were considered. The study focused on 500 kv (AC and DC) transmission alternatives. Four transmission alternatives were initially evaluated, each originating from Dave Johnston substation in Wyoming. Additional alternatives including 765 kv AC is considered. Provided below are the initial four 500 kv transmission alternatives considered. 3. Alternative A This is an AC only alternative and consists of a total of 1824 miles of new 500 kv transmission lines. The transmission lines originate from the newly proposed 500 kv substation at Dave Johnston and terminate at Las Vegas and Northern Arizona with intermediate terminations at Utah and Jim Bridger. Figure 2 provides a geographical depiction of the Alternative. The transmission line configuration is as follows: Two new 500 kv lines from Dave Johnston to Mona (on separate right of ways). One of the 500 kv lines will have connections at Jim Bridger and planned W. Haven Substation in Utah. New 500 kv lines from Mona to Navajo and Crystal. With additional 500 kv line from Navajo to Pinnacle Peak. New 500 kv substations at Dave Johnston, Jim Bridger, W. Haven and Mona. New 500/345 kv transformers at Jim Bridger, W. Haven and Mona. Additional 500/230 kv transformer is modeled at Dave Johnston. Appendix A, Section 1 provides detail transmission line configuration including line and transformer impedances for this alternative. TransWest Express Project, Final Feasibility Study Report-November

8 TransWest Express Project Alterntive A Utah Wyoming Jim Bridge r Dave Johnston Nevada Salt Lake City W. Haven Mona All Lines are 500 kv TransWest Express Project Existing Lines Upgrades Other Planned Projects Power Plant Substation California Los Angeles Las Vegas N.Gila Navajo Arizona Moenkopi Phoenix/ Tucson Four Corners New Mexico Figure 2: TransWest Express Project, Transmission Alternative A 3. Alternative B Alternative B is similar in configuration to Alternative A with exception of the termination points which in this case are Crystal (Las Vegas) and Four Corners (Arizona/New Mexico border). This alternative consists of a total 1993 miles of new 500 kv AC transmission lines. The high level transmission configuration is shown in Figure 3, and the detail line/transformer impedance data are located at Appendix A, Section 2. The make up of this alternative are as follows. Two new 500 kv lines from Dave Johnston to Mona (on separate right of ways). One of the 500 kv lines will have connections at Jim Bridger and planned W. Haven Substation in Utah. New 500 kv lines from Mona to Crystal and Four Corners. With additional 500 kv line from Four Corners to Pinnacle Peak. New 500 kv substations at Dave Johnston, Jim Bridger, W. Haven and Mona. New 500/345 kv transformers at Jim Bridger, W. Haven and Mona. Additional 500/230 kv transformer is modeled at Dave Johnston. TransWest Express Project, Final Feasibility Study Report-November

9 TransWest Express Project Alterntive B Utah Wyoming Jim Bridge r Dave Johnston Nevada Salt Lake City W. Haven Mona All Lines are 500 kv TransWest Express Project Existing Lines Upgrades Other Planned Projects Power Plant Substation California Los Angeles Las Vegas N.Gila Navajo Arizona Moenkopi Phoenix/ Tucson Four Corners New Mexico Figure 3: TransWest Express Project, Transmission Alternative B 3. Alternative C The total circuit mile for this alternative is approximately 1873 miles. It is an AC only alternative and is configured (see Figure 4) similar to Alternatives A and B. It has termination points at Navajo (Northern Arizona) and Four Corners (Arizona/ New Mexico border). Detailed line/transformer data can be found at Appendix A, Section 3. Below is a summary of the alternative. Two new 500 kv lines from Dave Johnston to Mona (on separate right of ways). One of the 500 kv lines will have connections at Jim Bridger and planned W. Haven Substation in Utah. New 500 kv lines from Mona to Navajo and Four Corners. With additional 500 kv line from Four Corners to Pinnacle Peak. New 500 kv substations at Dave Johnston, Jim Bridger, W. Haven and Mona. New 500/345 kv transformers at Jim Bridger, W. Haven and Mona. Additional 500/230 kv transformer is modeled at Dave Johnston. TransWest Express Project, Final Feasibility Study Report-November

10 TransWest Express Project Alterntive C Utah Wyoming Jim Bridge r Dave Johnston Nevada Salt Lake City W. Haven Mona All Lines are 500 kv TransWest Express Project Existing Lines Upgrades Other Planned Projects Power Plant Substation California Los Angeles Las Vegas N.Gila Navajo Arizona Moenkopi Phoenix/ Tucson Four Corners New Mexico Figure 4: TransWest Express Project, Transmission Alternative C 3. Alternative D This is a two-pole 892-mile, 500 kv DC line from Dave Johnston to Pinnacle Peak. Figure 5 below depicts the geographical configuration of Alternative D. Line /transformer impedance data for this alternative is located at Appendix A, Section 4. Provided below is a summary of the components of this transmission alternative. New 500 kv DC line from Dave Johnston to Pinnacle Peak New 500 kv substation at Dave Johnston New 500 kv converter stations at Dave Johnston and Pinnacle Peak TransWest Express Project, Final Feasibility Study Report-November

11 TransWest Express Project Alterntive D Wyoming Dave Johnston Nevada Utah All Lines are 500 kv TransWest Express Project Existing Lines Upgrades Other Planned Projects Power Plant Substation California Los Angeles Las Vegas N.Gila Navajo Arizona Moenkopi Phoenix/ Tucson Four Corners New Mexico Figure 4: TransWest Express Project, Transmission Alternative D 3. Other Alternatives Considered In addition to the four initial alternatives, two other alternatives are considered. These are an AC/DC hybrid alternative (i.e. Alternative E) and a 765 kv level version of Alternative A (i.e. Alternative F). The detailed configurations of these alternatives are as follows. a) Alternative E This alternative comprises of a 512-mile two-pole 500 kv DC line from Dave Johnston to Mona (Utah) and a two 500 kv AC lines originating from Mona and terminating at Crystal (Las Vegas) and Navajo (Northern Arizona). The total transmission circuit length (including the DC portion) is approximately 1318 miles. TransWest Express Project, Final Feasibility Study Report-November

12 The technical detail of this alternative can be found at Appendix A, Section 6. Figure 5 below depicts the geographical configuration of the alternative. TransWest Express Project Alterntive E Wyoming Dave Johnston Utah Nevada Salt Lake City Mona California Las Vegas Navajo Moenkopi Four Corners All Lines are 500 kv TransWest Express Project Existing Lines Upgrades Other Planned Projects Power Plant Los Ange les N.Gila Arizona Phoenix/ Tucson New Mexico Substation Figure 5: TransWest Express Project, Transmission Alternative E b) Alternative F This 765 kv level alternative is similar in configuration to Alternative A. All the new transmission lines are operated at 765 kv level with exception of Navajo- Pinnacle Peak which is operated at 500 kv level. Alternative F is designed to serve as sensitivity to Alternative A. TransWest Express Project, Final Feasibility Study Report-November

13 Base Case Description The approved WECC 2014 heavy summer peak load (14hs1a) case is used as the starting power flow base case for the feasibility study. This base case is modified to reflect forecasted in-10 heat wave load for Arizona and the southwestern states. New transmission and generation projects that are approved and planned to be online by 2013 in Arizona, Wyoming, Utah and the southwest were modeled. Pre-project case also modeled all transmission projects which are in Phase 2 or 3 of the WECC path rating process. The following projects were included in the pre-project case: STEP short term upgrade project (2006) Harquahala-Devers 500 kv line (2009) Palo Verde TS5 500 kv line (2009) EOR project (2008) Moenkopi-Eldorado series capacitor upgrade (2009) Path 51 upgrade (2009) Hassyampa- Pinal West 500 kv line (2008) VV1 500 kv switching station (2009) Navajo Transmission Project (2010) Pinal West- Browning 500 kv line (2013) TS5-Raceway 500 kv line (2012) Raceway -Pinnacle Peak 500 kv (2010) Hassyampa- N. Gila #2 500 kv line (2012) The post-project cases modeled a total of 3000 MW of new resources at Dave Johnston 500 kv Substation. These resources were scheduled to stress the new transmission lines south of Dave Johnston based on the transmission schedule scenarios provided under Table 1 for each transmission alternative. Modeling of Transmission Alternatives All 500 kv AC alternatives were modeled using MCM Aluminum Conductor Steel Reinforced (ASCR) bundle per phase. The 500 kv AC transmission lines were initially compensated 70%. Transmission lines of circuit length less than 120 miles were compensated at one end. Series compensation was modeled at both ends for transmission lines of circuit length greater than 120 miles, while the total line compensation was maintained at 70%. Shunt reactors were modeled at both ends of a transmission line section. The shunt compensation of the reactors was modeled to be 60% of the respective line charges. TransWest Express Project, Final Feasibility Study Report-November

14 765 kv transmission lines were modeled using MCM ACSR bundle per phase. The 765 kv transmission lines were not series compensated because of loading below surge impedance loading. Shunt reactors were modeled and estimated similarly as the 500 kv transmission lines. DC transmission lines were modeled as a bipole with earth/ground return. Each pole is modeled using MCM ASCR. The DC resistances of the conductors were assumed to be 93.5% of the conductor s AC resistance. Each converter station was equipped with filters and shunt capacitors sized 50% of the transmitted DC power. DC converter and associated transformer losses were estimated to be 1.5% of the total DC power transmitted. Transmission Schedules The following transmission schedules were adhered to in the evaluation of the transmission alternatives. Transmission Transmission Schedules (MW) Alternative Arizona Utah S. Nevada S. California Alternative A Alternative B Alternative C Alternative D Alternative E Alternative F Table 1: TransWest Express Project, Transmission Schedules Methodology The pre-project base case was tested to ensure compliance with WECC/NERC planning standards. The 3000 MW new resource was modeled as coal-fired plants for this feasibility study. The output of the coal plants were injected at the proposed Dave Johnston 500 kv Substation. For each transmission alternative, transfers were made according to transmission schedule scenarios provided under Table 1 until the flow on the new transmission line(s) south of Dave Johnston is 3000 MW or a critical transmission facility limit is reached. The limiting facility and the associated transfer levels were noted for each transmission alternative. The 3000 MW transferred power replaced generators in Arizona (Red Hawk, Mesquite and Harquahala Units), California (Mohave Units), Utah (Hunter Emery Units) and Nevada (Duke Units) according to the transmission schedules provided under Table 1. The generators selected for displacement in Arizona TransWest Express Project, Final Feasibility Study Report-November

15 were chosen to create a stressed base case condition to expose the most transmission constraints south of Navajo and the relative performance differences between the various transmission alternatives with respect to those transmission constraints were evaluated. The initial phase of the study focused on power flow analysis. Subsequent phases of the study examined at high level post-transient voltage and transient stability performances. As part of the power flow study, critical contingencies in Arizona and the southwest were simulated, including the following: Navajo-Crystal 500 kv line South of Navajo 500 kv lines Moenkopi-El Dorado 500 kv line Moenkopi Four Corners 500 kv line Moenkopi Westwing 500 kv line Perkins-Mead 500 kv line Four Corners- Cholla 345 kv line Palo Verde-Westwing 500 kv line Palo Verde Devers 500 kv Harquahala-Devers 500 kv line Hassyampa-N. Gila 500 kv line Palo Verde 2 units outage Navajo 2 units outage The study also focused on outages of the transmission sections of the individual transmission alternatives evaluated. Appendix E depicts the list of all outages simulated. The power flow study is performed and the results analyzed based on the assumption that no single element is loaded above its normal continuous thermal rating under pre-contingency conditions or above its emergency ratings under contingency conditions. The post-transient analysis is conducted and evaluated based on the assumption that the maximum voltage deviations allowed under contingency conditions in the post-transient time frame are 5% for N-1 and 10% for N-2 unless a lower standard has been previously adopted on selected buses. TransWest Express Project, Final Feasibility Study Report-November

16 Transient stability runs are simulated for 20 seconds to ensure the transmission system is stable and adequately damped. System stability is assessed based on damping of the rotor angles and also using WECC/NERC transient voltage dip and transient frequency criteria 1. All outages were simulated using governor power flow tools. Remedial actions for each outage were modeled according to the latest Operating Studies Subcommittee Handbook. 1 WECC transient voltage dip criteria: The transient voltage dip should not exceed 30% at any bus. For transient voltage dips 20% or more, the maximum duration should not exceed 20 cycles for a single contingency or 40 cycles for a double contingency. WECC transient frequency criteria: The minimum transient frequency for a single contingency is 59.6 Hz; if below 59.6 Hz, the duration should not exceed 6 cycles. For double contingencies, the minimum transient frequency is 59.0 Hz; if below 59.0 Hz, the duration should not exceed 6 cycles TransWest Express Project, Final Feasibility Study Report-November

17 Study Results 1. Benchmark Case The pre-project or benchmark case is tested to ensure compliance with WECC/NERC planning standards. Power flow diagram that highlights critical path flows can be found in Appendix B, Section 1. All outages studied yielded a power flow, post-transient and transient solutions. No thermal overload was identified following the outages studied. Bus voltage deviations during post-transient time frame were found to be within established planning limits. Transient voltage and frequency dips were within limits for all the outages studied. 2. Transmission Alternative A Power Flow Study All outages with exception of Dave Johnston-Bridger 500 kv line yielded power flow solution. Summary of the study results can be found in Appendix C, Table C.1. Dave Johnston-Bridger 500 kv line outage is identified as the most critical contingency for this case. Power flow solution for this outage was obtained by adding up to 600 Mvar of voltage support equipment at Dave Johnston Substation. Other potential solution to this outage is an installation of Special Protection System (SPS) to trip up to 750 MW of generation at Dave Johnston. Shiprock 345/230 kv transformer overloads up to 3% following an outage of Navajo-Pinnacle Peak 500 kv line. Replacing the transformer with a higher rated one will resolved the observed overload. Transient Stability Most of the contingencies studied yielded a stable and well-damped transient stability performance. Other critical outages such as Dave Johnston-Bridger 500 kv and Bridger-Mona 500 kv lines however resulted in unstable transient stability performances. An outage of Dave Johnston- Bridger 500 kv line results in transient voltage and frequency dip violations at several load buses. To address this system instability will require tripping up to two of the four generation units (1500 MW generation trip) connected to Dave Johnston following the outage. Similarly, Bridger-Mona 500 kv single line outage resulted in several bus voltage and frequency dip criteria violations. Tripping up to 1500 MW of generation at Dave Johnston will mitigate the observed criteria violations. TransWest Express Project, Final Feasibility Study Report-November

18 An outage of Dave Johnston- Mona 500 kv line also results in transient voltage and frequency dip criteria violations at several load buses. To mitigate this requires an installation of an SPS that will trip one generation unit or 750 MW of generation following the outage. Appendix D, Section 1 depicts the transient voltage and frequency plots for selected critical buses following the outages of Dave Johnston-Mona, Dave Johnston-Bridger and Bridger-Mona 500 kv lines. Post-transient With exception of the outage of Dave Johnston-Bridger 500 kv line, all outages studied yielded solution during post-transient time frame. No posttransient voltage deviation criteria violation was observed for majority of the outages. To achieve post-transient solution without post-transient voltage deviation criteria violation following the outage of Dave Johnston- Bridger 500 kv line will require the installation of up to 800 Mvar voltage support at Dave Johnston. Alternatively, installing an SPS to trip up to 750 MW of generation at Dave Johnston immediately following the outage will facilitate the achievement of post-transient solution and mitigate the observed voltage deviation criteria violation. Post-transient voltage deviation violations were also recorded for outage of Dave Johnston-Mona 500 kv line. To mitigate the recorded violations will require the installation of up to 200 Mvar of voltage support equipment at Bridger substation. Other potential mitigation plan includes tripping up to 750 MW of generation at Dave Johnston via SPS. 3. Transmission Alternative B Power Flow Study Summary of the power flow study is provided in Appendix C, Table C.1. No power flow solution was obtained following Dave Johnston-Bridger 500 kv line outage. Voltage support equipment or generation tripping scheme will be required for a solution to be achieved. Shiprock 345/230 kv transformer overloads by 1% following the outage of Four Corner-Pinnacle Peak 500 kv line. Replacing the existing transformer with a higher rated one will mitigate this overload. Transient Stability Three outages resulted in transient voltage and frequency dip violations at several buses. These outages are Dave Johnston-Bridger 500 kv line, Dave Johnston Mona 500 kv line and Bridger- Mona 500 kv line. TransWest Express Project, Final Feasibility Study Report-November

19 Transient voltage and frequency violations associated with the outage of Dave Johnston-Bridger 500 kv line could be mitigated by tripping up to 1500 MW of generation at Dave Johnston following the outage. Installing an SPS to trip up to 750 MW of generation at Dave Johnston will mitigate the transient voltage and frequency dip criteria violations following Dave Johnston-Mona and Bridger Mona 500 kv single line outages. Appendix D, Section 2 shows the transient voltage and frequency plots for selected critical buses following the outages of Dave Johnston-Mona, Dave Johnston-Bridger and Bridger-Mona 500 kv lines. Post-transient No solution was obtained following an outage of Dave Johnston- Bridger 500 kv line. Up to 800 Mvar voltage support will be required for posttransient solution and to remain with the voltage deviation criteria. Alternatively, installing an SPS to trip up to 750 MW of generation at Dave Johnston immediately following the outage will mitigate the observed criteria violation. Post-transient voltage deviation violations were recorded for outage of Dave Johnston-Mona 500 kv line. To mitigate the recorded violations will require the installation of up to 200 Mvar of voltage support equipment at Bridger substation. Other potential mitigation plan includes tripping up to 750 MW of generation at Dave Johnston using SPS. 4. Transmission Alternative C Power Flow study Summary of power flow results can be found at Appendix C, Table C.3. No power flow solution was obtained following Dave Johnston-Bridger 500 kv line outage. 600 Mvar of SVC or generation tripping scheme is required for a solution to be achieved. Moenkopi - RME 500 kv line overloads by 155% following the outage of Navajo-Crystal 500 kv line. This overload exceeds the line s short-term rating by 26%. The observed overload could be mitigated by upgrading the line s series capacitor for higher ampacity. Transient Stability Single line outages of Dave Johnston-Bridger 500 kv line, Dave Johnston- Mona 500 kv line and Bridger-Mona 500 kv line yielded an unstable transmission system performance. Transient voltage and frequency dip criteria violations were recorded at several buses following these outages. TransWest Express Project, Final Feasibility Study Report-November

20 Transient voltage and frequency criteria violations recorded with the outage of Dave Johnston-Bridger 500 kv line could be mitigated by tripping up to 1500 MW of generation at Dave Johnston following the outage. Installing an SPS to trip up to 750 MW of generation at Dave Johnston will mitigate the transient voltage and frequency dip criteria violations following Dave Johnston-Mona and Bridger Mona 500 kv single line outages. Transient voltage and frequency plots for selected critical buses following the outages of Dave Johnston-Mona, Dave Johnston-Bridger and Bridger- Mona 500 kv lines can be found in Appendix D, Section 3. Post-transient No solution was obtained following an outage of Dave Johnston- Bridger 500 kv line. Up to 800 Mvar voltage support will be required for posttransient solution without voltage deviation criteria violation to be achieved. Alternatively, installing an SPS to trip up to 750 MW of generation at Dave Johnston following the outage will mitigate the observed criteria violation. Post-transient voltage deviation violations were recorded for outage of Dave Johnston-Mona 500 kv line. To mitigate the recorded violations will require installing up to 200 Mvar of voltage support equipment at Bridger substation. Other potential mitigation plan includes tripping up to 750 MW of generation at Dave Johnston using SPS. 5. Transmission Alternative D Power Flow Study Appendix C, Table C.4 depicts the summary of the power flow and posttransient study results. Pinnacle Peak-Cactus 230 kv line loads up to 124% under normal operating conditions. Pre-project overload on the line was found to be 10%. Dave Johnston-Pinnacle Peak 500 kv DC bipole outage is the most critical contingency for this alternative. A power flow solution could only be obtained for this outage by tripping all the generators (3000 MW) connected to Dave Johnston. Losing one pole of the DC line will require the tripping of 1500 MW without ramping power onto the remaining pole. An outage of any one of the four Pinnacle Peak 500/230 kv transformers overloads the remaining in-service transformers by 15%. Adding a fifth transformer bank or installing a 500/345 kv transformer at Pinnacle peak will mitigate this overload. TransWest Express Project, Final Feasibility Study Report-November

21 Pinnacle Peak-Reach 230 kv line outage overloads Pinnacle Peak-Cactus 230 kv line by 5%. Re-conductoring of this line will resolve the observed overload. Transient Stability Stable and well damped transient performances were achieved for all outages studied. An outage of Dave Johnston-Pinnacle Peak 500 kv DC line (both poles), following by tripping of all the generators (3000 MW) connected to Dave Johnston yielded a stable transmission system performance during transient conditions. No transient voltage and frequency dip criteria violations were recorded following the outage. An outage of one of the DC poles without ramping power on to the remaining pole yielded a stable transmission system performance. An SPS to trip up to 1500 MW is required to achieve the stable transient solution. Transient voltage and frequency plots for selected critical buses following the Dave Johnston-Pinnacle Peak 500 kv DC bipole outage are located at Appendix D, Section 4. Post-Transient Post-transient solution was achieved for all outages studied. No voltage deviation criteria violation was recorded. 6. Transmission Alternative E Power Flow Study Summary of the power flow and post-transient study results for this alternative can be found at Appendix C, Table C.5. Dave Johnston-Mona 500 kv DC bipole outage is the most critical contingency for this alternative. A power flow solution for this outage could only be achieved by tripping all the generators (3000 MW) connected to Dave Johnston. One pole outage of the DC line will require tripping up to 1500 MW. Navajo-Pinnacle Peak 500 kv line outage overloads Shiprock 345/230 kv transformer by 1%. Replacing the existing transformer with a higher rated one will resolve the observed overload. TransWest Express Project, Final Feasibility Study Report-November

22 Transient Stability Stable and well damped transient performances were achieved for all outages studied with exception of Mona-Navajo and Mona-Crystal 500 kv single line outages. Transient Stability plots for selected critical outages are depicted at Appendix D, Section E. Mona-Navajo 500 kv line outage resulted in unstable transient system performance. To mitigate this unstable condition requires blocking one of the Dave Johnston-Mona 500 kv DC poles and in addition to tripping up to 1500 MW of generation at Dave Johnston. Similarly, an outage of Mona-Crystal 500 kv line will require the blocking of one of the Dave Johnston-Mona DC poles in addition to tripping up to 1500 MW of generation at Dave Johnston in order to achieve a stable transient stability performance without criteria violation. An outage of Dave Johnston-Mona 500 kv DC line (both poles), following by tripping of all the generators (3000 MW) connected to Dave Johnston yielded a stable transmission system performance during transient conditions. No transient voltage and frequency dip criteria violations were recorded following the outage. An outage of one of the DC poles without ramping power on to the remaining pole yielded a stable transmission system performance. An SPS to trip up to 1500 MW is required to achieve the stable transient solution. Post-Transient Post-transient solution was achieved for all outages studied. No voltage deviation criteria violation was recorded. 7. Transmission Alternative F The power flow, transient and post-transient performances for this sensitivity case are similar to the performances achieved using transmission alternative A. Key similarities are: Transmission line, path and interface flows are similar. Dave Johnston-Bridger outage is the most critical outage. Special protection schemes are required in order to achieve stable operation following outages of Dave Johnston-Bridger, Bridger-Mona and Dave-Johnston Mona 500 kv lines. Differences in performance were identified in areas of transmission line losses and the number of series capacitors. TransWest Express Project, Final Feasibility Study Report-November

23 Analysis and Comparison of Transmission Alternatives One of the objectives of this feasibility study is to rank the transmission alternatives evaluated. This section analyses and compares the transmission alternatives based on the following: Electrical performance Miles of transmission lines Number of transformers Number of series capacitors needed Number of shunt reactors Number of shunt capacitors Number of AC/DC converters Transmission losses Unscheduled flows Number of potential SPS required Transmission facilities to be upgraded Incremental flows on major transmission paths High level cost estimates. It is demonstrated in the study that all the alternatives including the 765 kv option are technically feasible in exporting up to 3000 MW of power from Wyoming to Arizona and the southwest. However, an upgrade to existing transmission facilities will be required for any of the alternatives to meet WECC/NERC reliability standard. On electrical performance, the study showed that Alternatives A, B and C exhibit similar electrical performances since all the three alternatives originate from the same source with same intermediate connections but slightly different termination points. Dave Johnston-Bridger 500 kv, Dave-Johnston-Mona 500 kv and Bridger-Mona 500 kv lines were found to be the critical outages for these alternatives. Impact of these outages could be mitigated by installing SPS to trip generation at Dave Johnston. The electrical performance of the 765 kv option (Alternative F) is similar to Alternative A. Flows on the two transmission lines south of Dave Johnston were found to be nearly balanced for the three alternatives. Alternative A, however has a better balanced flow on the two lines south of Mona when compared to B and C. This is because the power angle between Mona and Four Corners is small compared to the angle between Mona and other terminating points such as Crystal and Navajo. A balanced flow on Mona to Four Corners and Mona to Crystal or Navajo could be achieved by installing a phase shifting transformer on the Mona- Four Corners 500 kv line. Unscheduled flow (i.e. flows from the underlying transmission system on to the new transmission lines) is higher for Alternative A than B and C. Thus, Alternative A would result in a better balanced of flows on TransWest Express Project, Final Feasibility Study Report-November

24 parallel lines but has higher unscheduled flows. Alternatives D and E result in relatively lower inadvertent flows compared to A, B and C. The most critical outage for the DC only (Alternative D) or AC/DC hybrid (Alternative E) alternatives is the simultaneous outages of the DC poles. This outage could only be mitigated by tripping all the generators (3000 MW) connected to Dave Johnston. Whilst, Alternative D would require SPS for only the DC line outage where as Alternative E would require SPS for outages of the DC line and any of the line segments south of Mona. Loss of a line segment between Dave Johnston and Mona is the most critical outage for the AC alternatives. The mitigation plan for an outage of these outages would be to trip 1500 MW of generation at Dave Johnston. Table 2 below compares the transmission alternatives based on miles of transmission lines, transmission facilities needed, transmission losses and costs. As can be seen from Table 2, in terms of miles of transmission line to be constructed, Alternative D is the least, requiring 892 miles of new transmission lines and B is the most (1993 miles of new transmission line). Alternative D would require the least number of transmission equipment (such as transformer, shunt capacitors and converters) as part of its plan of service whilst B requires the most. Furthermore it is evident from Table 2 that Alternative D results in relatively lowest increase in WECC transmission system losses (186 MW) compared to the other 500 kv level alternatives. Alternative C has the highest increase in WECC transmission system losses (308 MW). In all, the 765 kv option (Alternative F) recorded the lowest increase in WECC transmission system losses, approximately 90 MW. High level project capital cost estimates were computed for each alternative based on the basic plan of service provided under section Transmission Alternatives. As depicted on Table 2, Alternative D will cost less to implement and F will cost most. It must be noted that the cost estimates provided on Table 2 does not capture the additional facilities or upgrades to the existing system required to meet WECC/NERC reliability standards. TransWest Express Project, Final Feasibility Study Report-November

25 Items Transmission Alternatives A B C D E F Miles of transmission lines No. of transformers No. of series capacitors No. of shunt capacitors No. of shunt reactors No. of AC/DC converters No. of Potential SPS Required Increase in WECC system losses (MW) Unscheduled (MW) Facility upgrades required High level cost estimate ($ Million) flows 263 1) Install a 4th 500/230 kv transformer at Pinnacle Peak. 2) Replace Shiprock 345/230 kv transformer 4, ) Install a 4th 500/230 kv transformer at Pinnacle Peak. 2) Replace Shiprock 345/230 kv transformer 1) Install a 4th 500/230 kv transformer bank at Pinnacle Peak. 2) Upgrade the series capacitors on Moenkopi-RME 500 kv line 1) Install 500/345 kv transformer at Pinnacle Peak. 2) Re-conductor Pinnacle Peak- Cactus 230 kv line 1) Replace Shiprock 345/230 kv transformer 1) Install a 4th 500/230 kv transformer at Pinnacle Peak. 2) Replace Shiprock 345/230 kv transformer 4,897 4,589 2,347 3,190 5,338 Table 2: Comparison of Transmission Alternatives TransWest Express Project, Final Feasibility Study Report-November

26 Next, incremental flows on major transmission paths in the southwest are monitored to ascertain how they are impacted by implementing any of the alternatives. Table 3 below compares interface flows for the alternatives and the benchmark case. Transmission Path Flows (MW) Alternatives Navajo South Four Corner West East of River California- Oregon Intertie Benchmark A B C D E F Table 3: Major Transmission Path Flows As can be seen from Table 3, Alternative D off-loads the flow on Navajo South path and Alternative C causes the flow south of Navajo to increase. All the other alternatives have minimal impact on the Navajo south path. Four Corner West path flow is impacted most by Alternative B and C where as Alternatives A, D, E and F have relatively small impacts. Alternative D causes the EOR flow to increase up to 1000 MW where as Alternative B off-loads the path by up to 450 MW. The EOR Path is least impacted by the implementation of Alternative A. All the transmission alternatives evaluated have minimal or no impact on the California Oregon Intertie and thus no potential effect on the operations of both the Pacific DC Intertie and the Palo Verde nuclear plants. TransWest Express Project, Final Feasibility Study Report-November

27 Conclusions The study results demonstrate the feasibility of each of the transmission alternatives capable of meeting the objective of the project, which is to be able to export up to 3000 MW of power from Wyoming to Arizona and the southwest states. The study also revealed that additional facilities or upgrades beyond the basic scope of each alternative are needed in order to export the 3000 MW and meet reliability standards. The study results showed that the electrical performances of Alternatives A, B and C are similar since all the three alternatives originate from the same source with same intermediate connections but slightly different termination points. The critical outages for the three alternatives were found to be the same with the same recommended mitigation plans. However, Alternative A provides a more balanced flow on south of Dave Johnston 500 kv lines compared to B and C. Alternative A also results in relatively lower transmission system losses and lower capital cost. The DC only (Alternative D) and the AC/DC hybrid transmission (Alternative F) alternatives result in relatively least unscheduled flows, lowest increase in system losses, least miles of new transmission lines and the associated capital cost when compared to 500 kv AC alternatives. In particular, Alternative D has transmission system losses of about 186 MW compared to 245 MW for Alternative A, and has a capital cost approximately 55% that of Alternative A. However, DC line outage would result in tripping of up to 3000 MW of generation whereas critical outage for the AC alternatives would require the tripping of 1500 MW of generation. A 765 kv AC transmission alternative is found to compare favorable electrically to 500 kv AC transmission alternative. The difference between the two transmission voltage levels lies in capital cost and transmission losses. Though, transmission system losses for a 765 kv AC alternative (Alternative F) are estimated to be 90 MW while that for a 500 kv AC alternative (Alternative A) is 245 MW, the capital cost for Alternative F is about 1 billion US Dollars more than that for Alternative A. This comparison assumed 3000 MW of power schedule for both the Alternatives F and A, however, Alternative F could potentially have capacity for up to 5000 MW. TransWest Express Project, Final Feasibility Study Report-November

28 Appendix A Section 1: Technical Details - Transmission Alternative A Section 2: Technical Details - Transmission Alternative B Section 3: Technical Details - Transmission Alternative C Section 4: Technical Details - Transmission Alternative D Section 5: Technical Details - Transmission Alternative E Section 6: Technical Details - Transmission Alternative F TransWest Express Project, Final Feasibility Study Report-November

29 Section 1: Technical Details-Transmission Alternative A States Traversed: Wyoming, Utah, Colorado, Nevada and Arizona Line length: Dave Johnston Jim Bridger, approximately 203 miles Jim Bridger West Haven, approximately 202 miles West Haven Mona, approximately 101 miles Dave Johnston Mona, approximately 512 miles Mona Crystal, approximately 340 miles Mona Navajo, approximately 220 miles Navajo Pinnacle Peak, approximately 246 miles TransWest Express Project Existing Lines Upgrades Other Planned Projects Power Plant TransWest Express Project Alterntive A All Lines are 500 kv Substation California Nevada Los Ange le s Las Vegas N.Gila Utah Salt Lake City 340 mi Navajo 246 mi 101 mi 220 mi Mona Arizona Phoenix/ Tucson Wyoming Jim Bridger 202 mi W. Haven Moenkopi 203 mi 512 mi Four Corners Dave Johnston Total 1824 miles New Mexico Figure A-1: Transmission Alternative A with line lengths Voltage level: 500 kv AC Conductor type: MCM ASCR bundle per phase Line impedance: For up to 150 miles; R= ohm/mile, X=0.530 ohm/mile, B=2.0 Mvar/mile. For transmission lines of length more than 150 miles, R= ohm/mile, X=0.519 ohm/mile, B=2.0 Mvar/mile. Series capacitors: 60% compensation on Mona-Crystal, Compensation on all other new lines modeled at 70%. TransWest Express Project, Final Feasibility Study Report-November

30 Shunt reactors: Modeled at both ends of each transmission line section with shunt compensation equivalent to 60% of respective line section charges. Transformer: Dave Johnston (500/230 kv, 600 MVA, R= p.u, X= p.u), Jim Bridger and Mona (500/345 kv. 672 MVA, R= p.u, X= p.u). Section 2: Technical Details-Transmission Alternative B States Traversed: Wyoming, Utah, Colorado, Nevada and Arizona Line length: Dave Johnston Jim Bridger, approximately 203 miles Jim Bridger West Haven, approximately 202 miles West Haven Mona, approximately 101 miles Dave Johnston Mona, approximately 512 miles Mona Crystal, approximately 340 miles Mona Four Corners, approximately 322 miles Four Corners Pinnacle Peak, approximately 313 miles TransWest Express Project Existing Lines Upgrades Other Planned Projects Power Plant TransWest Express Project Alterntive B All Lines are 500 kv Substation California Nevada Los Ange le s Las Vegas N.Gila Utah Salt Lake City 340 mi Navajo 101 mi Mona Arizona Phoenix/ Tucson Wyoming Jim Bridger 202 mi W. Haven 322 mi Moenkopi 313mi 203 mi 512 mi Four Corners Dave Johnston Total 1993 miles New Mexico Figure A-2: Transmission Alternative B with line lengths TransWest Express Project, Final Feasibility Study Report-November

31 Voltage level: 500 kv AC Conductor type: MCM ASCR bundle per phase Line impedance: For up to 150 miles; R= ohm/mile, X=0.530 ohm/mile, B=2.0 Mvar/mile. For transmission lines of length more than 150 miles, R= ohm/mile, X=0.519 ohm/mile, B=2.0 Mvar/mile. Series capacitors: 45% compensation on Mona-Crystal, Compensation on all other new lines modeled at 70%. Shunt reactors: Modeled at both ends of each transmission line section with shunt compensation equivalent to 60% of respective line section charges. Transformer: Dave Johnston (500/230 kv, 600 MVA, R= p.u, X= p.u), Jim Bridger and Mona (500/345 kv. 672 MVA, R= p.u, X= p.u) Section 3: Technical Details-Transmission Alternative C States Traversed: Wyoming, Utah, Colorado and Arizona Line length: Dave Johnston Jim Bridger, approximately 203 miles Jim Bridger West Haven, approximately 202 miles West Haven Mona, approximately 101 miles Dave Johnston Mona, approximately 512 miles Mona Navajo, approximately 220 miles Mona Four Corners, approximately 322 miles Four Corners Pinnacle Peak, approximately 313 miles TransWest Express Project, Final Feasibility Study Report-November