Houston Region Import Capacity Project

Transcription

1 Houston Region Import Capacity Project July 25, 2013 Prepared by: CenterPoint Energy Transmission Planning

2 Executive Summary 3 1. Introduction 5 2. Methodology and Study Assumptions Case Description Methodology Description 9 3. Phase I - Study Case Analysis AC Contingency Analysis Years Houston Region Capacity Demand and Reserves Analysis Phase II - Identification of Interconnection Options and Initial Screening Description of the Interconnection Options Transfer Capability Analysis Preliminary Cost Estimates Initial Screening of Options Phase III Selected Interconnection Options Studies Steady State Voltage Stability Analysis Detailed Cost Analysis AC Contingency Analysis Primary Options Short Circuit Analysis Primary Options Conclusions References 43 Appendix A. Transfer Capability of Identified Options 44 Appendix B. Preliminary Cost Estimates of Identified Options 52 Appendix C. Detailed Cost Estimates of Selected Options 58 Appendix D. PV Analysis of Selected Options 64 2

3 Executive Summary CenterPoint Energy Houston Electric, LLC (CenterPoint Energy) completed projects in 2007, 2009, and 2011 that increased the import capacity into the Houston Region. However, as the load continues to grow in the Houston Region and the potential for additional generation in the region remains limited, the need for additional import capacity increases. In its Long-Term System Assessment report dated December 28, 2012, ERCOT concluded the following: The Houston Region will need at least one additional import path within the next ten years. In the Transmission Needs Analysis section of the same report, ERCOT stated the following: ERCOT observed the need for expanded import paths into the Houston Metropolitan Region in every scenario studied in the context of this LTSA. In most scenario base cases, existing import paths into Houston were overloaded within the 10-year initial planning horizon. The results from the various scenarios evaluated are consistent and clear: the Houston Region will need incremental or expanded import capacity absent a significant amount of generation development within the area. CenterPoint Energy has completed a reliability evaluation of the need for additional transmission import capability into the Houston Region. This study identified potential reliability issues beginning in 2018 with respect to ERCOT s Planning Criteria: Planning uide (1)(b) This criterion includes the outage of any generating unit, with any other generation pre-emptively redispatched, followed by the loss of a double-circuit tower line with a length greater than 0.5 miles. This system performance criterion will not be satisfied for anticipated system conditions starting in 2018 unless additional resources are added in the Houston Region that more than offset potential unit retirements and load additions. CenterPoint Energy identified and evaluated 25 transmission interconnection options for improving import capability in the Houston Region and recommends building one of three preferred interconnection options, which are summarized below: Preferred Interconnection Options Transfer Increase (MW) New 345 kv Structure-miles ** Cost ($ MM) MW/$ MM Option 15 : Twin Oak-Zenith (including system improvements) Option 24 : Ragan Creek-Zenith* (including system improvements) Option 25 : Limestone-Ragan Creek-Zenith* (including system improvements) *Ragan Creek is a future CenterPoint Energy 345 kv Switching Station to be constructed as part of the interconnection option. **New 345 kv structure-miles include a 20 percent increase from their point-to-point straight-line distances to account for uncertainty in routing. Transfer capability into the Houston Region and estimated project cost were the primary factors used when comparing alternatives. CenterPoint Energy also considered other factors, such as expandability, geographic diversity, and the ability to construct the facilities without requiring long outages of existing facilities. CenterPoint Energy s specific cost estimates were used for improvements expected to be implemented by CenterPoint Energy, and ERCOT s LTSA average costs were used for improvements of non-centerpoint Energy owned facilities. CenterPoint Energy expects that ERCOT will conduct 3

4 additional analyses and recommend one project. CenterPoint Energy is willing to pursue any reasonable alternative to relieve the reliability concerns. The length of time required to construct the ERCOT-designated project depends on multiple variables, including time required for ERCOT approval, routing considerations, and right-of-way acquisition. It will be challenging to complete a significant new 345 kv transmission project to address the Houston Region import constraint by There are also various factors beyond ERCOT s or CenterPoint Energy s control that could cause the reliability need to be accelerated to earlier than 2018, such as additional load growth in the Houston Region, additional retirements of Houston Region generating units, or both. Accordingly, CenterPoint Energy believes the ultimate project determined by ERCOT s independent analysis should be designated as critical to reliability for the ERCOT Region. If the ERCOT Board of Directors approves a project by November 2013 and ERCOT designates the project as critical to reliability, CenterPoint Energy would expect to target completion of the project by May of

5 1. Introduction Background Cancellation of the Fayetteville-Zenith Import Project: In July of 2009, CenterPoint Energy submitted a report to ERCOT [1] that addressed the potential need to increase the North to Houston interface transfer capacity and, to a lesser extent, the South to Houston transfer capability. In 2010, ERCOT reviewed the study on the relative merits, performed its own study [2] to verify results and review multiple alternative options, and formalized in a report their recommendation for constructing a new Fayetteville-Zenith 345 kv double-circuit transmission line and related improvements. In the report, ERCOT noted that additional import capacity into the Houston Region was not considered necessary to meet reliability criteria in the period of the analysis, which was 2014, because the load in the Houston Region could be reliably served by generation in the Houston Region and the existing import capacity. ERCOT, however, recommended the project based on economic reasons by meeting the consumer impact, or the generator revenue reduction test, included in the ERCOT Planning Charter. Initiated by HB 971 of the 82 nd Legislature in 2011, the Public Utility Commission of Texas concluded in March of 2012 that the consumer impact or generator revenue reduction test should not be used by ERCOT and amended P.U.C. Subst. R relating to proceedings for a certificate of convenience and necessity (CCN). As a result, CenterPoint Energy discontinued pursuing the Fayetteville Zenith import project. Current State: ERCOT s most recent LTSA analysis [3] identified that the Houston Region would need incremental or expanded import capacity absent a significant generation addition within the area. ERCOT s 2012 Report on Existing and Potential Electric System Constraints and Needs [4] asserts that in the evaluation of 2015 and 2017, three of the highest congested elements are related to importing power into the Houston Region from the north. The Houston metropolitan area, one of the major load centers in ERCOT, interconnects to ERCOT at both the 345 kv and 138 kv voltage levels. A combination of local generation and import power from external sources serves the load in the area. Nine existing 345 kv import circuits, four from the north and five from the south, are the primary transmission circuits used for importing the external power. These include: North Houston Import Circuits - Singleton Zenith 345 kv circuit 98 - Singleton Zenith 345 kv circuit 99 - Singleton Tomball 345 kv circuit 74 - Roans Prairie King 345 kv circuit 75 South Houston Import Circuits - South Texas Project Dow 345 kv circuit 18 - South Texas Project Dow 345 kv circuit 27 - South Texas Project W. A. Parish 345 kv circuit 39 5

6 - W.A. Parish Hillje 345 kv circuit 72 - W.A. Parish Hillje 345 kv circuit 64 CenterPoint Energy has completed an evaluation of transmission interconnection options that focuses on the need for providing sufficient import capability into the Houston Region to meet reliability requirements, the details of which are contained in this report. 6

7 2. Methodology and Study Assumptions 2.1 Case Description CenterPoint Energy used the ERCOT Steady-State Working roup (SSW) cases created in February of 2013 as a starting point for building the Study Cases. The ERCOT SSW load flow cases for years 2015 to 2018 were modified to include the latest information with respect to future generation to be installed in the Houston Region as described in this section Table 2-1 below lists prospective generator projects located within CenterPoint Energy s service territory that have a signed Standard eneration Interconnection Agreement (SIA). Effective February 1, 2013, ERCOT Planning uide Section 6.9 was revised to clarify that a SIA, notice to proceed, and any necessary security are required to include a prospective generator in planning models built by the SSW. The WA Parish addition is part of a post-combustion carbon capture system planned for The combustion turbine will be providing power to the grid in 2013, but by 2015 all of the power is expected to be used for carbon capture and, therefore, was not included in the Study Cases for 2015 to The Deer Park and Channel Energy Center expansions have signed a SIA, provided a notice to proceed, and provided security, so they were included in the Study Cases for analysis. Pondera signed a SIA in 2010; however, Pondera has not provided a notice to proceed nor the financial security required to proceed with interconnection facilities. Therefore, CenterPoint Energy removed the Pondera project from the Study Cases. Deepwater Energy Storage facility is an energy storage facility that can only operate for a limited time before requiring to be recharged, so it was not added to the Study Cases. Agrifos Fertilizer Inc. signed a SIA in January 2013, but had not provided a notice to proceed nor financial security at the time of the study, so it was not included in the Study Cases for analysis Table 2-1: New Resources in the Houston Region with Signed Standard eneration Interconnection Agreements as of March 15, 2013 rid Included Unit in Study eneration Modeled (MW) MW Cases Yr 2015 Yr 2016 Yr 2017 Yr 2018 WA Parish Addition 89 No Deer Park Energy Center Addition 215 Yes Pondera (New Plant) 1,300 No Channel Energy Center Addition 200 Yes Deepwater Energy Storage +/ - 40 MW No Agrifos Fertilizer Inc No Total In 2012, several generating units in the Houston Region changed from mothball to operational status. Table 2-2 provides the generating units in the Houston Region that have been in mothball status in the 7

8 past or are currently in mothball status. enerating units over 50 years of age inside the Houston Region are listed in Table 2-3. Previously and currently mothballed units as well as all of the generating units greater than 50 years old were considered to be available in the Study Cases. Table 2-2: Previously or Currently Mothballed Units Unit eneration Modeled (MW) Yr 2015 Yr 2016 Yr 2017 Yr 2018 SRB_SRBT_ SRB_SRB_ SRB_SRB_ SRB_SRB_ SRB_SRB_ BY_BY_ APD_APD_ BY_BYT Total Table 2-3: enerating Units older than 50 years in Houston Region Bus Number Bus Name kv Pmax (MW) Id Total in-service Years Yr 2017 Yr SRB_SRBT_ MB SRB_SRB_ N SRB_SRB_ N SRB_SRB_ N SRB_SRB_ N THW_THWT_ BS WAP_WAPT_ BS WAP_WAP_ N WAP_WAP_ N WAP_WAP_ N WAP_WAP_ N Total MWs for Units 50 Years or more in service

9 2.2 Methodology Description CenterPoint Energy divided the study into three phases: - Phase I: Study Case Analysis A reliability analysis was performed for years 2015 to 2018, under the existing system network configuration, for the Study Cases and for two different generation sensitivity analysis scenarios. The objective was to review system performance in serving load without additional new import projects, while satisfying ERCOT and CenterPoint Energy Planning Criteria. - Phase II: Identification of Interconnection Options and Initial Screening Following the reliability analysis performed in Phase I, 25 different interconnection options were identified and studied. The total transfer capacity provided by each option was estimated using linear transfer capability techniques. Average cost estimates, as defined by ERCOT in its latest Long Term Study from December of 2012, were determined in this phase. Some options were eliminated in this phase based on technical and cost considerations. - Phase III: Selected Interconnection Options Studies CenterPoint Energy performed a detailed cost analysis and a non-linear steady state voltage stability analysis (PV analysis) on the selected set of interconnection options remaining from the Phase II screening. Some additional options were eliminated, and an AC Contingency analysis and Short Circuit analysis were performed on the remaining primary interconnection options from which the final set of preferred interconnection options was determined. 9

10 3. Phase I - Study Case Analysis CenterPoint Energy evaluated the 2015 to 2018 Summer Peak ERCOT base cases with varying generation dispatches to model a range of possible North to Houston and South to Houston import scenarios. The SSW ERCOT 2015 to 2018 Base Cases were modified by taking out of service the Pondera units (1300 MW) and adding the Deer Park and Channel Energy Center expansions (415 MW total). CenterPoint Energy studied the reliability of the base cases with respect to ERCOT s Planning Criteria: Planning uide (1)(b). This criterion accounts for taking the largest unit inside the Houston Region out of service, which is Cedar Bayou 2 (CBY2-745 MW), creating the corresponding Study Cases and performing common tower outages or the contingency loss of a transmission circuit or transformer. In addition to the Study Cases, the ERCOT Planning Criteria was used to evaluate two additional sensitivity analysis scenarios. For Scenario 1, the previously or currently mothballed units in the Houston Region dispatched in the SSW cases are removed from service. Because there is no additional generation available within the Houston Region, load is reduced outside of the Houston Region. In Scenario 2, an additional 500 MW of generation is added inside the Houston Region by increasing five existing units in the CenterPoint Energy service area by 100 MW each to simulate a net increase. Table 3-1 provides pre-contingency interface flows through the main 345 kv ties for years 2015 to 2018 for the Study Case and sensitivity analysis scenarios. Table 3-1: Pre-contingency 345 kv Ties Interface Flow Years Scenarios Pre-contingency Interface Flows North to Houston Interface (MW) South to Houston Interface (MW) Yr 2015 Yr 2016 Yr 2017 Yr 2018 Yr 2015 Yr 2016 Yr 2017 Yr 2018 Study Case Scenario 1 - Mothballed units out-of-service Scenario MW additional generation AC Contingency Analysis Years An initial AC Contingency analysis was performed for all years for the three scenarios described above. The analysis highlights potential loading issues that may arise over the years on the most critical ties into the Houston Region. Contingency studies included ERCOT s Category B and C contingencies. Table 3-2, Table 3-3, and Table 3-4 present the results for this analysis. ERCOT s generating unit unavailability criterion (Planning uide (1)(b)) is not satisfied in the Study in 2018 due to an overload of the emergency rating of both of the Singleton to Zenith 345 kv circuits. The Scenario 1 10

11 sensitivity analysis illustrates that a net decrease in generation from the Study Case, in this case previously or currently mothballed units removed from service, would lead to very high overloads. The Scenario 2 sensitivity analysis illustrates a reduction in the contingency loading of the Singleton to Zenith 345 kv circuits, below 95% of their emergency rating, with the addition of 500 MW of generation within the Houston Region. All available generation in the Houston Region was dispatched at full output to meet the modeled load levels; therefore, there is no generation dispatch available within the Houston Region to lower the import level into Houston. Table 3-2: AC Contingency Years Study Case with CBY2 Off-line Emergency Loading % ** From bus ** ** To bus ** CKT Rating Yr 2015 Yr 2016 Yr 2017 Yr 2018 Contingency Description SNLTN_ ZENITH 345A TOMBALL SINLETON & KIN - ROANS PRAIRIE SNLTN_ ZENITH 345A TOMBALL SINLETON & KIN - ROANS PRAIRIE Table 3-3: AC Contingency Analysis Years Scenario 1 with Mothballed Units Off-line and CBY2 Off-line Emergency Loading % ** From bus ** ** To bus ** CKT Rating Yr 2015 Yr 2016 Yr 2017 Yr 2018 Contingency Description SNLTN_ ZENITH 345A TOMBALL SINLETON & KIN - ROANS PRAIRIE SNLTN_ ZENITH 345A TOMBALL SINLETON & KIN - ROANS PRAIRIE SMTHRS 345A BELAIR 345A BELLAIRE JEANETTA 345 CKT.64 & BELLAIRE WA PARISH 345 CKT SNLTN_345 to TOMBAL 345B SINLETON - ZENITH 345 CKT.98 & SINLETON - ZENITH 345 CKT.99 Table 3-4: AC Contingency Analysis Years Scenario 2 with Additional 500 MW of eneration in the Houston Region and CBY2 Off-line Emergency Loading % ** From bus ** ** To bus ** CKT Rating Yr 2015 Yr 2016 Yr 2017 Yr 2018 Contingency Description SNLTN_ ZENITH 345A TOMBALL SINLETON & KIN - ROANS PRAIRIE SNLTN_ ZENITH 345A TOMBALL SINLETON & KIN - ROANS PRAIRIE 3.2 Houston Region Capacity Demand and Reserves Analysis Another way of assessing the reliability concerns of the Houston Region is through a Capacity, Demand, and Reserves (CDR) table showing projected resources versus projected load for the area. CenterPoint Energy performed a CDR analysis for years 2015 to The Houston Region capacity is composed of the generation resources and import capability. The generation resources exclude the largest unit, which is Cedar Bayou 2, to be consistent with the ERCOT generating unit unavailability criterion. The import capability is the contingency constrained total import capacity for the existing 138 kv and 345 kv lines connecting the Houston Region to the rest of ERCOT. Load and losses are based on the Summer Peak load flow Study Cases for years 2015 to The import capability for each year corresponds to an average of the maximum pre-contingency import into the Houston Region without overloading any element under a common tower outage calculated for years 2015 to 2018 from the Study Cases. In particular, the most limiting contingency corresponds to the loss of the Roans to Tomball double-circuit tower line. Table 3-5 provides the reserve margin for the Houston Region. A deficit between demand and capacity exists starting in Additional import capacity into the Houston Region is necessary unless timely new net resources are added in the Houston Region that more than offset potential unit retirements and unplanned load additions. 11

12 Table 3-5: Capacity-Demand Balance under -1 Conditions for Cedar Bayou MW Out-of- Service Year Peak Load (MW) Peak Transmission Losses (MW) Peak Demand (MW) Installed Capacity w/o CB2 (MW) Previously and Currently Mothballed (MW) Average Import Capacity From 138 and 345 kv Ties (MW) Planned Resources with Signed IA, Air Permit, and Securitized Deposit per Table 2-1 (MW) Total Resources (MW) Surplus/Deficit (MW) (84) 12

13 4. Phase II - Identification of Interconnection Options and Initial Screening CenterPoint Energy identified 25 interconnection options and performed initial screening studies to improve the import capacity into the Houston Region to relieve the reliability concern identified in the Phase I 2018 Study Case. CenterPoint Energy chose the year 2018 Study Case, because the year corresponds to the highest loading of Houston Region import lines for all scenarios studied. The 25 interconnection options included either upgrading existing circuits or building new tie lines at 345 kv or 500 kv. The new tie line options included many different termination points, making them flexible for future expansion and geographically diverse. The merits of the 25 interconnection options were compared by performing a technical and cost analysis with the objective of narrowing the options to the most robust for further detailed analysis. The following section lists the 25 interconnection options that were identified along with a brief description. The options identified were based on prior analyses performed in 2009 and 2010 by CenterPoint Energy and ERCOT, economical alternatives discussed in ERCOT s 2012 Long Term analysis, and some new proposals by CenterPoint Energy for this study. CenterPoint Energy evaluated the interconnection options to determine the amount of increase in transfer capability into the Houston Region each provided. This evaluation was accomplished using Siemens PTI MUST software. MUST calculates the First Contingency Incremental Transfer Capability by modeling transfers from a sending subsystem to a receiving subsystem while monitoring all buses and branches in a defined group and taking contingencies one by one from a defined contingency list. The calculation demonstrates an incremental transfer capability, where the transfer is placed on top of the base case condition. The transfers were implemented by increasing load in the CenterPoint Energy area, including Texas New Mexico Power (TNMP) load pockets supplied from CenterPoint Energy, and reducing it by the same amount across the rest of ERCOT. The methodology for the initial first screening of the interconnection options took the following approach: - Evaluate the increase in additional transfer over the 2018 Study Case for each of the interconnection options. This analysis includes selected circuit reinforcements that limit the power transfer. - Estimate project costs for each of the interconnection options based on ERCOT s 2012 average transmission costs. - Rank the 25 interconnection options on a MW/$MM basis and screen them based on the incremental MW transfer, the MW/$MM, and any other additional relevant criteria such as flexibility for future expansion. 13

14 4.1 Description of the Interconnection Options The following section offers a high-level summary of each of the 25 interconnection options. The new circuit lengths include an additional 20% increase on point-to-point distance to account for uncertainty in line routing. For study purposes, any new 345 kv transmission line construction proposed, where applicable, was modelled using ACSS conductor, which has an emergency rating of approximately 3350 MVA. However, the highest substation equipment that CenterPoint Energy currently uses at 345 kv is 5000 Amps; therefore, the emergency rating (Rate B as defined in the SSW procedural manual) used for each new circuit was 2988 MVA. Figure 4-1 and Figure 4-2 show the general geographical location and the interconnection points for each option. Option 1: New Jordan Lufkin 345 kv double-circuit. This option includes building a new 126-mile 345 kv double-circuit from CenterPoint Energy s Jordan Substation to Oncor Electric Delivery Company s (Oncor s) Lufkin Substation. Option 2: New Zenith Salem 345 kv double-circuit. This option includes building a new 50-mile 345 kv double-circuit line from CenterPoint Energy s Zenith Substation to Lower Colorado River Authority (LCRA) TSC s Salem Substation. Also loop the Fayette Power Project-Salem 345 kv line into Fayetteville 345 kv substation and add a 19.5 mile second circuit on the existing towers from Fayetteville 345 kv to Salem. Option 3: New Zenith Fayetteville 345 kv double-circuit. This option includes building a new 66-mile 345 kv double-circuit from CenterPoint Energy s Zenith Substation to LCRA TSC s Fayetteville Substation and loop the Fayette Power Project-Salem 345 kv line into Fayetteville 345 kv substation. This option can be expanded by building a Salem to ibbons Creek 345 kv circuit to provide additional North to Houston transfer capability, if needed in future years as in Option 10. Option 4: New Zenith ibbons Creek 345 kv double-circuit. This option includes building a new 63- mile 345 kv double-circuit from CenterPoint Energy s Zenith Substation to Texas Municipal Power Agency s (TMPA s) ibbons Creek Substation. Option 5: New Obrien Fayetteville 345 kv double-circuit. This option includes building a new 74- mile double-circuit from CenterPoint Energy s Obrien Substation to LCRA TSC s Fayetteville Substation and loop the Fayette Power Project-Salem 345 kv line into Fayetteville 345 kv substation. Option 6: New Obrien Salem 345 kv double-circuit. This option includes building a new 63-mile 345 kv double-circuit from CenterPoint Energy s Obrien Substation to LCRA TSC s Salem Substation. Also loop the Fayette Power Project-Salem 345 kv line into Fayetteville 345 kv substation and add a 19.5 mile second circuit on the existing towers from Fayetteville 345 kv to Salem. Option 7: New Obrien Holman 345 kv double-circuit. This option includes building a new 84-mile 345 kv double-circuit from CenterPoint Energy s Obrien Substation to Austin Energy s Holman Substation. Option 8: New Zenith Salem and Salem ibbons Creek 345 kv double-circuits. This option includes building a new 50-mile 345 kv double-circuit from CenterPoint Energy s Zenith Substation to LCRA TSC s Salem Substation and a new 49-mile 345 kv double-circuit from LCRA TSC s Salem Substation to TMPA s ibbons Creek Substation.. 14

15 Option 9: New Zenith Salem and Salem TNP One 345 kv double-circuits. This option includes building a new 50-mile 345 kv double-circuit from CenterPoint Energy s Zenith Substation to LCRA TSC s Salem Substation and a new 89-mile 345 kv double-circuit from LCRA TSC s Salem Substation to Texas- New Mexico Power s (TNMP s or TNP s) TNP One Substation. Option 10: New Zenith Fayetteville and Salem ibbons Creek 345 kv double-circuits. This option includes building a new 66-mile 345 kv double-circuit from CenterPoint Energy s Zenith Substation to LCRA TSC s Fayetteville Substation and a new 49-mile 345 kv double-circuit from LCRA TSC s Salem Substation to TMPA s ibbons Creek Substation. This option would also loop the Fayette Power Project- Salem 345 kv line into the Fayetteville 345 kv substation and add a 19.5-mile second circuit on the existing towers from Fayetteville 345 kv to Salem. Option 11: New Sandow - Zenith 345 kv double-circuit. This option includes building a new 109-mile 345 kv double-circuit from CenterPoint Energy s Zenith Substation to Oncor s Sandow Substation. Option 12: New Marion - Holman - Obrien 345 kv double-circuits. This option includes building a new 84-mile 345 kv double-circuit from CenterPoint Energy s Obrien Substation to Austin Energy s Holman Substation and a new 93-mile 345 kv double-circuit LCRA TSC s Marion Substation to Holman Substation. Option 13: New Hillje - Obrien 345 kv double-circuit. This option includes building a new 65-mile 345 kv double-circuit from CenterPoint Energy s Obrien Substation to CenterPoint Energy s Hillje Substation. Option 14: New Twin Oak - Salem and Fayetteville - Zenith 345 kv double-circuits. This option includes building a new 66-mile 345 kv double-circuit from CenterPoint Energy s Zenith Substation to LCRA TSC s Fayetteville Substation and a new 89-mile 345 kv double-circuit from Oncor s Twin Oak Substation to LCRA TSC s Salem Substation. This option would also loop the Fayette Power Project- Salem 345 kv line into the Fayetteville 345 kv substation and add a 19.5-mile second circuit on the existing towers from Fayetteville 345 kv to Salem. Option 15: New Twin Oak - Zenith 345 kv double-circuit. This option includes building a new 117-mile 345 kv double-circuit from CenterPoint Energy s Zenith Substation to Oncor s Twin Oak Substation. Option 16: New Twin Oak Salem Zenith 345 kv double-circuits. This option includes building a new 138-mile 345 kv double-circuit from CenterPoint Energy s Zenith Substation to Oncor s Twin Oak Substation with one of the circuits looping through LCRA s Salem Substation and the second bypasses the Salem Substation and both circuits continue to terminate at the Zenith Substation. Option 17: New Limestone ibbons Creek Zenith 345 kv double-circuits. This option includes building a new 63-mile 345 kv double-circuit from CenterPoint Energy s Zenith Substation to TMPA s ibbons Creek Substation and a new 67-mile 345 kv double-circuit from TMPA s ibbons Creek Substation to CenterPoint Energy s Limestone Substation. Option 18: New Big Brown Jordan 500 kv double-circuit. This option includes building a new 182- mile 500 kv double-circuit from CenterPoint Energy s Jordan Substation, which would be a new 500 kv switchyard to a new 500 kv switchyard connected to Oncor s Big Brown 345 kv Substation. Option 19: New Big Brown Zenith 345 kv double-circuit. This option includes building a new 159- mile 345 kv double-circuit from CenterPoint Energy s Zenith Substation to Oncor s Big Brown Substation. 15

16 Option 20: New Navarro Zenith 345 kv double-circuit. This option includes building a new 178-mile 345 kv double-circuit from CenterPoint Energy s Zenith Substation to Lone Star Transmission Company s (Lone Star s) Navarro Substation. Option 21: Upgrade existing circuit 74, 98, 99, and kv double-circuits. This options includes upgrading the existing CenterPoint Energy circuit 74 King - Rothwood Kuykendahl Tomball - Singleton, circuit 98 Zenith Singleton, circuit 99 Zenith Singleton and circuit 75 King Kuykendahl - Roans Prairie - Singleton using ACSS conductor. The estimated length of re-conductoring is 263 miles. Option 22: New Limestone Zenith 345 kv double-circuit. This option includes building a new 130- mile 345 kv double-circuit from CenterPoint Energy s Zenith Substation to Limestone Substation. Option 23: New Limestone Singleton Zenith 345 kv double-circuits. This option includes building a new 66-mile 345 kv double-circuit from CenterPoint Energy s Limestone Substation to Singleton Substation and a 64-mile 345 kv double-circuit from Singleton Substation to Zenith Substation on a different corridor than the existing Zenith Substation to Singleton Substation circuits. Option 24: New Ragan Creek Zenith 345 kv double-circuit. This option includes building a new 69- mile 345 kv double-circuit from CenterPoint Energy s Zenith Substation to a proposed new CenterPoint Energy 345 kv substation identified as Ragan Creek located at a to-be-determined position between TMPA s Jack Creek Substation and ibbons Creek Substation. The circuits connecting ibbons Creek Substation Jack Creek Substation and ibbons Creek Substation Twin Oak Substation would be looped into the new Ragan Creek Substation. This option can be expanded by building a Ragan Creek Limestone 345 kv double-circuit to provide additional North to Houston transfer capability (see Option 25). Option 25: New Limestone Ragan Creek - Zenith 345 kv double-circuits. This Option expands on Option 24 by also building a new 61-mile 345 kv double-circuit from CenterPoint Energy s new Ragan Creek Substation to CenterPoint Energy s Limestone Substation.. 16

17 Figure 4-1: Interconnection Options 1 to 16 17

18 Figure 4-2: Interconnection Options 17 to 25 18

19 4.2 Transfer Capability Analysis An initial transfer capability analysis was performed on the 2018 Study Case for each of the 25 identified interconnection options using linear transfer capability evaluation (Siemens MUST). The detailed output is located in Appendix A. Table 4-1 shows the initial transfer through the existing ties and the new tie prior to increasing transfer, and the potential maximum total transfer power into the Houston Region after increasing transfer to the thermally constrained contingency limit. In defining the maximum transfer, selected system reinforcements were simulated with the objective of further increasing the total transfer until major system reinforcements, defined as Limiting Element on the table, were necessary. The transfers were modelled by increasing load in the Houston Region, including TNMP load pockets supplied from CenterPoint Energy, and reducing load by the same amount across the rest of ERCOT. All the 345 and 138 kv transmission lines connecting the Houston Region with the rest of ERCOT were monitored using Rate B, and the contingencies were evaluated utilizing ERCOT s NERC Category B and C contingency files. Table 4-1: Transfer Capability Analysis Alternative Tie Flows No Transfer (MW) Maximum Transfer with Selected Reinforcements (MW) Option North to Houston Flow South to Houston Flow 138 kv Circuits New Tie Increase from 2018 Study Case Total Transfer Limiting Element 2018 Study Case N/A N/A 6450 Singleton-Zenith 345 kv Option 1 : Lufkin-Jordan Singleton-Zenith 345 kv Option 2 : Salem - Zenith Singleton-Zenith 345 kv Option 3 : Zenith - Fayetteville Singleton-Zenith 345 kv Option 4 : Zenith- ibbons Creek Jewett - Singleton 345 kv Option 5 : Obrien - Fayetteville Singleton-Zenith 345 kv Option 6 : Obrien -Salem Singleton-Zenith 345 kv Option 7 : Holman -Obrien Singleton-Zenith 345 kv Option 8 : Zenith- Salem -ibbons Creek Zenith - T.H. Wharton 345 kv Option 9 : Zenith-Salem-TNPONE Singleton-Zenith 345 kv Option 10 : Zenith - Fayetteville & Salem-ibbons Creek Singleton-Zenith 345 kv Option 11 : Sandow to Zenith Singleton-Zenith 345 kv Option 12 : Marion-Holman-Obrien Singleton-Zenith 345 kv Option 13 : Hillje-Obrien Singleton-Zenith 345 kv Option 14 : Twin Oak-Salem -Fayetteville-Zenith Singleton-Zenith 345 kv Option 15 : Twin Oak-Zenith Zenith - T.H. Wharton 345 kv Option 16 : Twin Oak-Salem-Zenith Singleton-Zenith 345 kv Option 17 : Limestone-ibbons Creek-Zenith Zenith - T.H. Wharton 345 kv Option 18 : Big Brown - Jordan 500 kv Singleton-Zenith 345 kv Option 19 : Big Brown-Zenith Singleton-Zenith 345 kv Option 20 : Navarro-Zenith Singleton-Zenith 345 kv Option 21 : Upgrade 345 kv conductors Jewett - Singleton 345 kv Option 22 : Limestone-Zenith Singleton-Zenith 345 kv Option 23 : Limestone-Singleton-Zenith Zenith - T.H. Wharton 345 kv Option 24 : Ragan Cr-Zenith Jewett - Singleton 345 kv Option 25 : Limestone-Ragan Cr-Zenith Zenith - T.H. Wharton 345 kv 19

20 4.3 Preliminary Cost Estimates A preliminary project cost estimate for each of the 25 interconnection options was developed using ERCOT s average generic dollar per transmission mile cost as shown in Table 4-2. The preliminary estimates were used to provide a relative cost comparison of the interconnection options and to calculate a ratio of MW per million dollars spend for comparing transfer improvement performance. The preliminary project cost estimates for the interconnection options, including their selected reinforcements, are listed in Appendix B. Table 4-2: Average Cost Estimates - ERCOT Rural Urban ($ MM/mi) ($ MM/mi) 345 kv New Single circuit (on double circuit capable towers) New double circuit Re-conductoring of existing single circuit line Re-conductoring of existing double circuit line Rebuilt existing single (complete tear down of towers and conductors) Rebuilt existing double (complete tear down of towers and conductors) add second circuit to an existing double circuit capable line kv New Single circuit (on double circuit cpable towers) New double circuit Re-conductoring of existing single circuit line Re-conductoring of existing double circuit libe Rebuilt existing single (complete tear down of towers and conductors) Rebuilt existing double (complete tear down of towers and conductors) add second circuit to an existing double circuit capable line kv New Single circuit (on double circuit capable towers) 2.7 New double circuit 2.98 HVDC 3000 MW capacity 3.01 Transformer ($ MM) 138/345 lesser than or equal to 600 MVA /345 lesser than or equal to 800 MVA /500 transformer 1200 MVA eneral Substation ($ MM) 138 kv Substation kv -ring bus 6-line terminals kv substation breaker&1/2 > 6 - line terminal breaker 500 kv ring substation Two - HVDC 3000 MW Converter Station 510 Expand substation with one additional line terminations 2 500kV substation breaker&1/2 > 6 - line terminal 35 Series Compensation (50%) 39 Series Comp > 100 mi 25 20

21 4.4 Initial Screening of Options Once the preliminary project cost estimates were calculated, the interconnection options were ranked according to the ratio of MW of increased transfer per million dollars cost (i.e. MW/$MM) as listed in Table 4-3. From the initial 25 interconnection options, CenterPoint Energy selected Options 8, 15, 21, 24, and 25 as the five leading options to consider further due to their relatively high transfer performance results compared to their preliminary project cost. These options are similar in that they include building a new 345 kv double-circuit transmission line from Zenith to the north to Twin Oak, ibbons Creek, Limestone or the proposed Ragan Creek Substations. A discussion of the selection process for the leading options follows. Options 17, 22, 23, and 25 are very similar projects as they begin at Zenith Substation and end at Limestone Substation. Three of the options (17, 23, and 25) connect into a switching station (ibbons Creek, Singleton, or the proposed Ragan Creek) before continuing to the Limestone Substation. Option 23 performs the best of these four options; however, this would terminate all six North to Houston tie lines at a single substation (i.e. Singleton Substation), which would be a significant reliability concern. Therefore, despite its performance advantages, CenterPoint Energy eliminated Option 23 from further consideration. Options 15 and 22 are similar and both perform very well; however, Option 15 was chosen based on slightly better performance and cost. Option 17 has one of the shortest assumed mileages, because ibbons Creek Substation is located very near a straight line distance between Zenith and Limestone Substations. However, because ibbons Creek Substation is a fixed tie point, if the final route alignment deviates several miles to the west of ibbons Creek, the cost of Option 17 would increase and approach the cost of Option 25. Option 25 has the advantage of being able to adjust to route alignment uncertainty by locating the new Ragan Creek Substation anywhere along the ibbons Creek to Jack Creek path; thus, minimizing the length of the transmission line. If the actual route is located very close to either Jack Creek or ibbons Creek, it may be appropriate to consider terminating into one of those substations rather than building a new Ragan Creek Substation. If either of these options are considered, additional short circuit analysis will be required. For this reason, CenterPoint Energy will proceed with analysis on Option 25; however, CenterPoint Energy recognizes that Option 17 and 25 are almost identical in performance. Options 4 and 24 are very similar with Option 4 terminating into ibbons Creek, and Option 24 terminating into a new Ragan Creek Substation. Both options yield similar Transfer Capability, with Option 24 slightly higher, but Option 4 has a better transfer increase to cost ratio. Because Option 4 expands an existing substation (i.e. ibbons Creek Substation, which is a fixed point), while Option 24 builds a new substation at a flexible location, the cost difference between the two diminishes greatly if the final route alignment falls approximately six miles west of the existing ibbons Creek Substation. Due to the routing flexibility offered by Option 24, CenterPoint Energy proceeded with analysis of Option 24 rather than Option 4. However, CenterPoint Energy recognizes that Option 4 and Option 24 are almost identical in performance. Option 8 provided the largest transfer increase of the options connecting CenterPoint Energy s service area with the 345 kv grid to the west and was included as one of the five leading options based on performance. Options 16, 10, and 9 are similar to the options discussed above, but were not as cost effective, so they were eliminated from further consideration. Option 21, the upgrade of the existing 345 kv conductors, 21

22 was selected as a leading option based on its Transfer Capability and preliminary project cost. However, the preliminary project cost may be artificially low because its cost basis only considers the reconductoring cost and does not take into account any tower reinforcements nor the cost of temporary solutions for the time period in which the work would be performed on the existing circuits. Option 21 would minimize landowner impact, because it is confined in scope to upgrading existing 345 kv lines. The other options presented in Table 4-3 were not selected, because they either have a relatively low increase in Transfer Capability (i.e. Options 2, 3, 5, 6, 7, 12, and 13) or have a lower MW/$MM value (i.e. Options 1, 11, 14, 18, 19, and 20). The five selected interconnection options are shown in Figure 4-4 through Figure 4-8 and were further evaluated in Phase III using a more detailed cost analysis, a voltage stability analysis, an AC contingency analysis, and a Short Circuit analysis. Figure 4-3 depicts the system configuration in the 2018 Study Case. 22

23 Table 4-3: Initial Comparison of Interconnection Options Based on Preliminary MW per $ MM Option Transfer Increase (MW) Preliminary Project Cost ($ MM) MW per $ MM (Thermal limit) Continue to Evaluate Option 4 : Zenith- ibbons Creek N Option 24 : Ragan Creek-Zenith Y Option 8 : Zenith- Salem -ibbons Creek Y Option 15 : Twin Oak-Zenith Y Option 23 : Limestone-Singleton-Zenith N Option 22 : Limestone-Zenith N Option 17 : Limestone-ibbons Creek-Zenith N Option 25 : Limestone-Ragan Creek-Zenith Y Option 16 : Twin Oak-Salem-Zenith N Option 10 : Zenith - Fayetteville & Salem-ibbons Creek N Option 9 : Zenith-Salem-TNPONE N Option 21 : Upgrade 345 kv conductors Y Option 3 : Zenith - Fayetteville N Option 19 : Big Brown-Zenith N Option 11 : Sandow to Zenith N Option 14 : Twin Oak-Salem -Fayetteville-Zenith N Option 1 : Lufkin-Jordan N Option 5 : Obrien - Fayetteville N Option 2 : Salem - Zenith N Option 7 : Holman -Obrien N Option 20 : Navarro-Zenith N Option 18 : Big Brown - Jordan 500 kv N Option 6 : Obrien -Salem N Option 12 : Marion-Holman-Obrien N Option 13 : Hillje-Obrien N 23

24 Figure 4-3: 2018 Study Case Configuration Limestone Twin Oak Jewett Jack Creek Sandow ibbons Creek Singleton ROANS PR 2018 Bobvle Tomball Salem Zenith T.H. W North Belt Addicks Fayetteville Fayette Plant O Brien Brazos Valley Holman WAP Oasis DOW Hillje STP 24

25 Figure 4-4: Option 8 Zenith Salem ibbons Creek 345 kv Twin Oak Jewett Jack Creek ibbons Creek Singleton ROANS PR 2018 Bobvle New 345 kv Tomball Salem Zenith T.H.W North Belt Addicks Fayette Plant Fayetteville O Brien Figure 4-5: Option 15 Twin Oak - Zenith 345 kv Limestone Twin Oak Jewett TNPONE Jack Creek ibbons Creek Singleton ROANS PR 2018 Bobvle Tomball New 345 kv Zenith T.H.W North Belt 25

26 Figure 4-6: Option kv Upgrade Jewett ibbons Creek Singleton ROANS PR 2018 Conductor upgrades in green Conductor upgrades in green Bobvle Kuykendahl Conductor upgrades in green Tomball Rothwood Kuykendahl Zenith T.H.W North Belt King Figure 4-7: Option 24 Zenith Ragan Creek 345 kv Limestone Twin Oak Nucor Jewett Jack Creek Ragan Creek ibbons Creek Singleton ROANS PR 2018 Bobvle Tomball New 345 kv Zenith T.H.W North Belt 26

27 Figure 4-8: Option 25 Limestone Ragan Creek Zenith 345 kv Limestone Twin Oak Nucor Jewett Jack Creek New 345 kv Ragan Creek ibbons Creek Singleton ROANS PR 2018 Bobvle Tomball Zenith T.H. W North Belt 27

28 5. Phase III Selected Interconnection Options Studies 5.1 Steady State Voltage Stability Analysis PV Analysis was performed on the 2018 Study Case load flow for each of the five selected interconnection options to determine the impact on the voltage stability when transferring power into the Houston Region. This methodology was chosen in order to illustrate the transfer effect of new lines in conjunction with the already existing tie lines into the Houston Region. The analysis was performed using PowerTech Labs VSAT software by increasing the load in the Houston Region and reducing the load in the remaining ERCOT system. Figure 5-1 below compares the voltage stability of various known limiting contingencies for load-to-load transfer into the Houston Region in the 2018 Study Case. The contingency with the lowest collapse point for this case is the loss of the Roans Prairie to Tomball corridor; similar results were obtained for the PV analysis on the five selected interconnection options as described in Appendix D. For evaluating the voltage stability performance, this worst contingency was used. Figure 5-2 includes the PV curves for the five selected interconnection options for the Roans Prairie to Tomball 345 kv corridor outage. These curves plot the total ERCOT to Houston pre-contingency interface flow versus the bus voltage at the Bellaire 345 kv, which is central to CenterPoint Energy s transmission system. The ERCOT to Houston interface for each option includes the flow on the new line. The maximum total transfer for each of the options is defined by the interface transfer at the point of voltage collapse. Figure 5-3 includes the PV curves for the five selected interconnection options for the Roans Prairie to Tomball 345 kv corridor outage. These curves plot the total Houston Region load versus the bus voltage at the Bellaire 345 kv bus. ERCOT Transmission Planning Criteria requires a voltage stability margin of 2.5% increase in load above expected peak supplied from resources external to the transmission service provider-defined areas and NERC Category C operating conditions. It is observed that all the alternatives have a higher margin, with the most limited being Option 21. Table 5-1 includes a comparison of the total power transfer between thermal and voltage limits for the five selected interconnection options. It is observed that Options 8 and 15 have their total transfer limited by voltage stability considerations. CenterPoint Energy correspondingly added a 200 MVAR capacitor bank at the Zenith 345 kv Substation with the objective of increasing its power transfer, because it has slightly lower voltage stability limits than thermal transfer limits into the Houston Region. The additional cost of $3 MM for this reinforcement is included in the detailed project costs. 28

29 Table 5-1: Thermal and Voltage Stability Total Transfer into Houston Selected Interconnection Options Option Total Transfer Thermal Total Transfer PV Margin Option 8 : Zenith- Salem -ibbons Creek Option 15 : Twin Oak-Zenith Option 21 : Upgrade 345 kv conductors Option 24 : Ragan Creek-Zenith Option 25 : Limestone-Ragan Creek-Zenith

30 Figure 5-1: Study Case Interface Transfers (MW) vs. Bellaire 345 kv Bus Voltage (p.u.) 2018 Base Case - ERCOT to Houston Transfer PV curves for Various Contingencies Base Case Roans - Tomball corridor Jewett - Singleton corridor 1 Singleton - Roans corridor Bellaire 345 kv Voltage (p.u.) Singleton - Zenith corridor Pre-contingency Singleton - ibbons Creek corridor STP - Dow corridor ERCOT to Houston Pre-Contingency Interface Flow (MW) Figure 5-2: ERCOT to Houston Flow (MW) vs. Bellaire 345 kv Bus Voltage (p.u.) Roans to Tomball 345 kv Outage PV - Selected Options Bellaire 345 kv (p.u.) Base Case Option 8 Option 15 Option 21 Option 24 Option ERCOT to-houston Pre-Contingency Interface Flow (MW) 30

31 Figure 5-3: Houston Region (MW) vs. Bellaire 345 kv Bus Voltage (p.u.) Roans to Tomball 345 kv Outage PV - Selected Options Bellaire 345 kv (p.u.) Option 15 Option 21 Option 25 Base Case Option 8 Option Houston Region load (MW) 5.2 Detailed Cost Analysis New, more detailed, transmission and substation cost estimates are used in this phase of analysis and are based on CenterPoint Energy s internal cost assessments. The detailed project cost estimates utilized in Phase III are higher than the Phase II preliminary project cost estimates that were based on ERCOT s average generic estimates, but they reflect CenterPoint Energy s recent historical costs for building new transmission lines. The estimated cost for each of the five selected interconnection options includes the cost to build the new transmission lines, to expand each substation for the new line terminations, and to make other necessary upgrades to existing facilities to achieve the full benefits of the project. ERCOT s average generic costs provided in Table 4-2 are only utilized in Phase III for non- CenterPoint Energy proposed reinforcements. The new detailed project cost estimates are provided in Appendix C and summarized below in Table 5-2. Figure 5-4 shows the geographical location for the final set of the five selected interconnection options. 31

32 Figure 5-4: Selected Interconnection Options Limestone Twin Oak Ragan Cr 24 ibbons Cr Singleton 8 Salem Zenith 32

33 Table 5-2: Detailed Cost Analysis Selected Interconnection Options Option Transfer Increase (MW) Detailed Project Cost ($MM) MW/$MM (Thermal limit) Option 8 : Zenith- Salem -ibbons Creek Option 15 : Twin Oak-Zenith Option 21 : Rebuild existing 345 kv circuits Option 24 : Ragan Creek-Zenith Option 25 : Limestone-Ragan Creek-Zenith Based on Table 5-1 and Table 5-2, CenterPoint Energy selected Options 15, 24, and 25 as its three primary interconnection options for additional analysis. Option 8 was eliminated, although it had a similar incremental transfer to Options 15 and 25, because it provides a less robust voltage stability improvement. Also, Option 8 ties to the west and then to the north, while Options 15, 24, and 25 provide a more direct path to the North. The best performing options all feature a tie to the North. Option 24 is advantageous, because it can be expanded in future years by adding a double-circuit transmission line into the Limestone Substation to provide a higher transfer increase, thus transforming it into Option 25. Option 21 was eliminated due to its lower thermal and PV limits coupled with its relatively high cost. The selected three primary interconnection options shown in Figure 5-5 would supply the Houston Region with power to serve the load for a period of approximately 10 years for Option 25 and Option 15, and 8 years for Option 24 considering an average annual load increase of 1.3% and no changes in the total installed generation. 33

34 Figure 5-5: Primary Interconnection Options Limestone Twin Oak Ragan Cr 24 ibbons Cr Singleton Zenith 34

35 5.3 AC Contingency Analysis Primary Interconnection Options In addition to transfer capability analysis, CenterPoint Energy performed normal steady-state power flow contingency analysis on the 2018 Study Case and the three selected primary interconnection options, Options 15, 24, and 25. CenterPoint Energy also evaluated the sensitivity analysis scenario corresponding to the Study Cases without previously or currently mothballed units. The contingency analysis should identify any underlying overloads that may exist for the different options not captured by the transfer analysis. Table 5-3 to 5-5 provide the results for the contingency analysis for the following load flow cases: the ERCOT 2018 Base Case (with CBY2); the 2018 Study Case; and the three primary interconnection options. All elements that are 69 kv and above are monitored inside CenterPoint Energy s system, while elements 138 kv and above are monitored in the other ERCOT areas. For the tables, loading is calculated using the emergency Rate B line rating. For the contingency studies, the overloaded branches listed are only those branches where any option had a non-trivial effect on the loading. None of the proposed circuit reinforcements as previously described in Appendix B have been implemented in this analysis. As shown in Table 5-3, the different configurations of the interconnection options do not create significant increases in circuit loading when compared to the 2018 Study Case. For the contingency loss of a common tower, 345 kv the existing overload in the 2018 Study Case is not observed for any of the three primary interconnection options. As shown in Table 5-4 and Table 5-5, for the scenarios where the mothballed generating units are out of service, the different interconnection options eliminate the existing overloads in the 2018 Study Case. Table 5-3: Common Mode and Category C Contingencies- Maximum Overload Overloaded Branch CKT 99 SNLTN_345 to ZENITH 345A WNDTR CKT A2 N_BELT 138A to M WNDTR CKT A2 N_BELT 345A to M Rating (MVA) Contingency DB_ID_7651: CKT 75 ROANS 345C TO BOBVLE 345X & CKT 74 TOMBAL 345B TO SNLTN_345 DB_ID_6089: CKT A1 N_BELT 345A TO N_BELT 138A & CKT A3 N_BELT 345A TO N_BELT 138A DB_ID_6089: CKT A1 N_BELT 345A TO N_BELT 138A & CKT A3 N_BELT 345A TO N_BELT 138A ERCOT 2018 Base Case 100.6% (1x) 102.1% (1x) 2018 Study Case 100.8% (2x) 98.3% (0x) 99.4% (0x) Option 15 Option 24 Option % (0x) 99.9% (0x) 98.7% (0x) 99.8% (0x) 98.7% (0x) 99.9% (0x) 35

36 Table 5-4: Single (N-1) Contingencies with Mothballed Units Out-of-Service Maximum Overload Overloaded Branch CKT 98 SNLTN_345 to ZENITH 345A CKT 99 SNLTN_345 to ZENITH 345A CKT 99 SNLTN_345 to IBN_CREK_5 Rating (MVA) Contingency CKT 99 SNLTN_345 TO ZENITH 345A CKT 98 SNLTN_345 TO ZENITH 345A T 75 SNLTN_345 TO BN_CREK_5 3 ERCOT 2018 Base Case 2018 Study Case 98.9% (0x) 98.9% (0x) 95.7% (0x) Option 15 Option 24 Option 25 36

37 Table 5-5: Common Mode and Category C Contingencies with Mothballed Units Out-of-Service Maximum Overload Overloaded Branch CKT 1 L_BRENNO8_1Y to L_SANDHI8_1Y CKT 1 L_SALEM_8_1Y to L_HIH368_1Y CKT 1 PETERS 138B to L_BELLSO8_1Y CKT 1 RICHLND2_5 to BIBRN CKT 1 SNLTN_345 to JEWETT_N CKT 1 SNLTN_345 to JEWETT_S CKT 66 RAYFRD to RTHWOD 138A CKT 74 SNLTN_345 to TOMBAL 345B Rating (MVA) Contingency DB_ID_10984: CKT 1 L_HIH368_1Y TO L_SALEM_8_1Y & CKT 1 L_HIH368_1Y TO L_BRENHA8_1Y DB_ID_10505: CKT 1 L_SALEM_8_1Y TO L_BRENHA8_1Y & CKT 1 L_SALEM_8_1Y TO L_UYBUR8_1Y DB_ID_8263: CKT &1 BOBVLE 345X TO KIN 345A & CKT 74 SNLTN_345 TO TOMBAL 345B DB_ID_16115: CKT 1 WATMLL_W5 TO TRINDAD1_5 & CKT 1 WATMLL_E5 TO TRICRN1_5 DB_ID_8281: CKT 75 IBN_CREK_5 TO SNLTN_345 & CKT 99 IBN_CREK_5 TO SNLTN_345 DB_ID_8281: CKT 75 IBN_CREK_5 TO SNLTN_345 & CKT 99 IBN_CREK_5 TO SNLTN_345 DB_ID_8624: CKT &1 TOMBAL 138A TO PINHUR 138A & CKT &1 TOMBAL 138A TO WESFLD 138B DB_ID_8611: CKT 98 SNLTN_345 TO ZENITH 345A & CKT 99 SNLTN_345 TO ZENITH 345A ERCOT 2018 Base Case 95.6% (0x) 95.2% (0x) 100.8% (1x) 96.4% (0x) 96.0% (0x) 2018 Study Case 106.2% (1x) 101.5% (1x) 99.6% (0x) 98.9% (0x) 99.6% (0x) 97.2% (0x) 99.5% (0x) 108.5% (1x) Option 15 Option 24 Option % (1x) 95.2% (0x) 97.7% (0x) 96.1% (0x) 100.9% (1x) 95.2% (0x) 100.9% (1x) 37

38 Overloaded Branch CKT 98 SNLTN_345 to ZENITH 345A CKT 99 SNLTN_345 to ZENITH 345A CKT 99 SNLTN_345 to IBN_CREK_ WNDTR CKT A2 N_BELT 345A to M Rating (MVA) Contingency DB_ID_8263: CKT &1 BOBVLE 345X TO KIN 345A & CKT 74 SNLTN_345 TO TOMBAL 345B DB_ID_7651: CKT 75 ROANS 345C TO BOBVLE 345X & CKT 74 TOMBAL 345B TO SNLTN_345 DB_ID_8263: CKT &1 BOBVLE 345X TO KIN 345A & CKT 74 SNLTN_345 TO TOMBAL 345B DB_ID_7651: CKT 75 ROANS 345C TO BOBVLE 345X & CKT 74 TOMBAL 345B TO SNLTN_345 DB_ID_16569: T 2 IBN_CREK_5 TO IBN_CREK_8 & CKT 75 IBN_CREK_5 TO SNLTN_345 DB_ID_6089: CKT A1 N_BELT 345A TO N_BELT 138A & CKT A3 N_BELT 345A TO N_BELT 138A ERCOT 2018 Base Case 113.2% (2x) 113.3% (2x) 101.2% (1x) 2018 Study Case 134.3% (3x) 134.4% (3x) 95.9% (0x) 98.0% (0x) Option 15 Option 24 Option % (0x) 98.9% (0x) 99.6% (0x) 38

39 5.4 Short Circuit Analysis Primary Interconnection Options Three phase and single line to ground (SL) fault analyses were performed on the three primary interconnection options (Options 15, 24, and 25) to determine the required fault duty rating of any new or existing substations and to identify potential circuit breaker upgrades that may be required. Table 5-6 and Table 5-7 include the results of the analyses. CenterPoint Energy s short circuit rating criteria require that three-phase and single-phase fault currents not exceed 99% of any facility s short circuit rating. All CenterPoint Energy substations were found to be within this criteria. Ratings for Oncor s Twin Oak 345 kv and TMPA s Jack Creek 345 kv buses were not available for this study. The new short circuit levels indicate some significant deviation with respect to their base case values. The Twin Oak 345 kv three-phase fault values exceeded 50 ka for Options 15, 24, and 25 with Option 15 having the worst case with a 8.2% increase over the 2018 Study Case. The Jack Creek 345 kv three-phase fault value for Option 24 was the worst case with a 41.9% increase over the 2018 Study Case. Because the short circuit ratings for Twin Oak 345 kv and Jack Creek 345 kv were not available for this study, no reinforcement costs were assumed or added for the fault duty upgrades at these substations. Table 5-6: Three-Phase Short Circuit Results Bus Rating (ka) 2018 Study Case OPT_15 OPT_24 OPT_25 ka Loading ka Loading ka Loading ka Loading Addicks % % % % Clodine % % % % Fayetteville % % % % Fayetteville % % % % ib Creek % % % % ib Creek % % % % Jack Creek Kluge % % % % Limestone % % % % Obrien % % % % Obrien % % % % Peters % % % % Rag Creek N/A N/A N/A N/A % % Roans Pr % % % % Salem % % % % Salem % % % % Singleton % % % % THW % % % % THW % % % % Tw in Oak Zenith % % % % Zenith % % % % 39

40 Table 5-7: Single-line-to-ground Short Circuit Results Bus Rating (ka) 2018 Study Case OPT_15 OPT_24 OPT_25 ka Loading ka Loading ka Loading ka Loading Addicks % % % % Clodine % % % % Fayetteville % % % % Fayetteville % % % % ib Creek % % % % ib Creek % % % % Jack Creek Kluge % % % % Limestone % % % % Obrien % % % % Obrien % % % % Peters % % % % Rag Creek N/A N/A N/A N/A % % Roans Pr % % % % Salem % % % % Salem % % % % Singleton % % % % THW % % % % THW % % % % Twin Oak Zenith % % % % Zenith % % % % 40

41 6. Conclusions The primary objective of the study was to determine solutions for reliability concerns related to import capacity limitations into the Houston Region under the current projected generation and demand scenarios for years 2015 to CenterPoint Energy created Study Cases for years 2015 to 2018 from ERCOT s SSW base cases and analysed them according to ERCOT s Planning Criteria: Planning uide (1)(b) Consistent with previous ERCOT assessments, the results shown in this report for the different scenarios under consideration indicate that ERCOT s generating unit unavailability criterion is not satisfied in the Study Case for anticipated system conditions beginning in 2018 unless new import transmission paths are constructed. In the initial screening studies, CenterPoint Energy evaluated 25 interconnection options to improve the import capacity into the Houston Region and selected the following three preferred interconnection options: Option 15: New Twin Oak - Zenith 345 kv double-circuit. The transfer capability is improved by approximately 2,701 MW with an estimated project cost of $462 million and a transfer improvement value of 5.85 MW/$MM invested. This option affects Oncor s and CenterPoint Energy s substations and possibly positions at Twin Oak owned by TNMP. The proposed reinforcements to achieve this transfer affect LCRA s and CenterPoint Energy s transmission networks. New and additional system improvements included: o o o Build new 117 mile 345 kv double-circuit from Zenith Substation to Oncor's Twin Oak Substation Add two 345 kv line terminations at Zenith Substation Add two additional 345 kv line terminations at Oncor s Twin Oak substation o Upgrade Bellaire Substation to Smithers Substation 345 kv circuit 98 o o o o Upgrade 138 kv substation equipment at Rayford Substation Upgrade 138 kv tie-line and substation equipment from Peters Substation to LCRA's Bell South Substation Re-conductor single 138 kv circuit between LCRA's Salem and Hwy3613 Substations Build new 200 MVAR capacitor bank at Zenith Substation. Option 24: New Ragan Creek - Zenith 345 kv double-circuit. The transfer capability is improved by approximately 1,960 MW with an estimated project cost of $297 million and a transfer improvement value of 6.60 MW/$MM invested. This option affects only CenterPoint Energy s substations. The proposed reinforcements to achieve this transfer affect Oncor s, TMPA s, LCRA s, and CenterPoint Energy s transmission networks. This option can be expanded in the 41

42 future to interconnect the Limestone Substation, the same as considered in Option 25. New and additional system improvements included: o Build new 69 mile 345 kv double-circuit from Zenith Substation to new Ragan Creek 345 kv Substation o o Add two 345 kv line terminations at Zenith Substation Build new 345 kv Ragan Creek Substation with eight positions located along and looping in the double-circuit line from TMPA's ibbons Creek Substation to Oncor's Twin Oak Substation o Upgrade Bellaire Substation to Smithers Substation 345 kv circuit 98 o o Upgrade 138 kv substation equipment at Rayford Substation Re-conductor single 138 kv circuit between LCRA's Salem and Hwy3613 Substations. Option 25: New Limestone - Ragan Creek - Zenith 345 kv double-circuits: The transfer capability is improved by approximately 2,532 MW with an estimated project cost of $532 million and a transfer improvement value of 4.76 MW/$MM invested. This option affects only CenterPoint Energy s substations. The proposed reinforcements to achieve this transfer affect LCRA s and CenterPoint Energy s transmission networks. New and additional system improvements included: o Build new 69 mile 345 kv double-circuit from Zenith Substation to new Ragan Creek 345 kv Substation o o o o Add two 345 kv line terminations at Zenith Substation Build new 345 kv Ragan Creek Substation with 8 positions located along and looping in the double-circuit line from TMPA's ibbons Creek Substation to Oncor's Twin Oak Substation Build new 61 mile 345 kv double-circuit from new 345 kv Ragan Creek Substation to Limestone Substation Add two 345 kv line terminations at Limestone Substation o Upgrade Bellaire Substation to Smithers Substation 345 kv circuit 98 o o o Upgrade 138 kv substation equipment at Rayford Substation Upgrade 138 kv tie-line and substation equipment from Peters Substation to LCRA's Bell South Substation Re-conductor single 138 kv circuit between LCRA'S Salem and Hwy3613 Substations. CenterPoint Energy is willing to pursue any reasonable alternative to relieve the reliability concerns. Due to the critical need for these facilities, CenterPoint Energy is seeking an ERCOT determination that the ERCOT selected project to relieve the Houston Import Constraint is critical to reliability. If the ERCOT Board of Directors approves a project by November of 2013 and ERCOT designates the project as critical to reliability, CenterPoint Energy may be able to complete the ERCOT selected project by May

43 . 7. References [1] North to Houston Constraint Mitigation Project, CenterPoint Energy, July 2009 [2] Houston Import Project, Version 1, ERCOT, July 2010 [3] LTSA 2012 Transmission Needs Analysis, ERCOT December 2012 [4] ERCOT Report on Existing and Potential Electric System Constraints and Needs, ERCOT, December

44 Appendix A. Transfer Capability of Identified Options 44

45 Rating B (MW) 2018 Study Case Init Init OPTION FCITC Limiting Constraint Contingency Description OPTION 1 Lufkin-Jordan L: 3118 LUFKNSS_ LUFKIN_ Open 3109 STRYKER_ LUFKNSS_ L: N_BELT 345A 345 B$0097 M A Open N_BELT 345A 345 B$0035 ALM A Open N_BELT 138A 138 B$0035 ALM A1 Open N_BELT_A1TER23.0 B$0035 ALM A1 Open N_BELT 345A 345 B$ A Open N_BELT 138A 138 B$ A3 Open N_BELT_A3TER23.0 B$ A L: SNLTN_ ZENITH 345A Open ROANS 345C BOBVLE 345X Open SNLTN_ TOMBAL 345B OPTION 2 Salem - Zenith L: 7056 L_FPPYD15_1Y L_FAYETT5_1Y Open 7056 L_FPPYD15_1Y L_FAYETT5_1Y L: 7057 L_FAYETT5_1Y L_FAYETT8_1Y Open 7057 L_FAYETT5_1Y L_SALEM_5_1Y Open 7057 L_FAYETT5_1Y L_SALEM_5_1Y L: SNLTN_ ZENITH 345A Open ROANS 345C BOBVLE 345X Open SNLTN_ TOMBAL 345B OPTION 3 Zenith - Fayetteville L: 7056 L_FPPYD15_1Y L_FAYETT5_1Y Open 7056 L_FPPYD15_1Y L_FAYETT5_1Y L: SNLTN_ ZENITH 345A Open ROANS 345C BOBVLE 345X Open SNLTN_ TOMBAL 345B OPTION 4 Zenith- ibbons Creek 1437 L: SMTHRS 345A BELAIR 345A Open W_A_P 345B BELAIR 345A Open BELAIR 345A JENETA 345B L: CLODIN 138B OBRIEN73138D C:DB_ID_6139 Open CLODIN 138B CCLODIN_138C Open OBRIEN 138A OBRIEN25138C Open MASON 138A OBRIEN 138A Move percent load from bus OBRIEN25138C138 tobus OBRIEN73138D L: 7289 L_SALEM_8_1Y L_HIH368_1Y Open 7289 L_SALEM_8_1Y L_BRENHA8_1Y Open 7289 L_SALEM_8_1Y L_UYBUR8_1Y L: 3391 JEWETT_N SNLTN_ C:DB_ID_15655 Open 967 IBN_CREK_ TWIN_OAK Open 975 JKCREEK TWIN_OAK OPTION 5 Obrien - Fayetteville L: 7056 L_FPPYD15_1Y L_FAYETT5_1Y Open 7056 L_FPPYD15_1Y L_FAYETT5_1Y L: 7056 L_FPPYD15_1Y L_FAYETT5_1Y Open 7056 L_FPPYD15_1Y L_FAYETT5_1Y L: SNLTN_ ZENITH 345A Open ROANS 345C BOBVLE 345X Open SNLTN_ TOMBAL 345B OPTION 6 Obrien -Salem L: 7056 L_FPPYD15_1Y L_FAYETT5_1Y Open 7056 L_FPPYD15_1Y L_FAYETT5_1Y L: 7057 L_FAYETT5_1Y L_FAYETT8_1Y Open 7057 L_FAYETT5_1Y L_SALEM_5_1Y Open 7057 L_FAYETT5_1Y L_SALEM_5_1Y L: SNLTN_ ZENITH 345A Open ROANS 345C BOBVLE 345X Open SNLTN_ TOMBAL 345B OPTION 7 Holman -Obrien 222 L: 7055 L_FPPYD25_1Y HOLMAN Remove unit U1 from bus STP_STP_ MWdispatch Remove unit U2 from bus STP_STP_ MWdispatch L: SNLTN_ ZENITH 345A Open ROANS 345C BOBVLE 345X Open SNLTN_ TOMBAL 345B Base Case Final 45

46 OPTION FCITC Limiting Constraint Contingency Description OPTION 8 Zenith- Salem - ibbons Creek L: SMTHRS 345A BELAIR 345A Open W_A_P 345B BELAIR 345A Open BELAIR 345A JENETA 345B L: CLODIN 138B OBRIEN73138D Open CLODIN 138B CCLODIN_138C Open OBRIEN 138A OBRIEN25138C Open MASON 138A OBRIEN 138A Move percent load from bus OBRIEN25138C138 tobus OBRIEN73138D138 Rating B (MW) 2018 Study Case Init Init Base Case Final L: RAYFRD RTHWOD 138A Open PINHUR 138A CTOMBAL_ Open TOMBAL 138A CTOMBAL_ Open TOMBAL 138A TOMBAL Open LOUETA WESFLD 138B Move percent load from bus TOMBAL tobus TOMBAL Move percent load from bus LOUETA tobus LOUETA L: 7056 L_FPPYD15_1Y L_SALEM_5_1Y Open 967 IBN_CREK_ TWIN_OAK Open 975 JKCREEK TWIN_OAK L: ZENITH 345A T_H_W 345B Open ZENITH 345A 345 B$0244 ZENITH A Open ZENITH 138A 138 B$0244 ZENITH A1 Open _STAR 23.0 B$0244 ZENITH A1 Open ZENITH 345A T_H_W 345B OPTION 9 Zenith-Salem- TNPONE L: SMTHRS 345A BELAIR 345A Open W_A_P 345B BELAIR 345A Open BELAIR 345A JENETA 345B OPTION L: CLODIN 138B OBRIEN73138D Open CLODIN 138B CCLODIN_138C Open OBRIEN 138A OBRIEN25138C Open MASON 138A OBRIEN 138A Move percent load from bus OBRIEN25138C138 tobus OBRIEN73138D L: RAYFRD RTHWOD 138A Open PINHUR 138A CTOMBAL_ Open TOMBAL 138A CTOMBAL_ Open TOMBAL 138A TOMBAL Open LOUETA WESFLD 138B Move percent load from bus TOMBAL tobus TOMBAL Move percent load from bus LOUETA tobus LOUETA L: SNLTN_ ZENITH 345A Open ROANS 345C BOBVLE 345X Open SNLTN_ TOMBAL 345B Zenith - Fayetteville & Salem-ibbons Creek L: 7056 L_FPPYD15_1Y L_FAYETT5_1Y Open 7056 L_FPPYD15_1Y L_FAYETT5_1Y L: RAYFRD RTHWOD 138A Open PINHUR 138A CTOMBAL_ Open TOMBAL 138A CTOMBAL_ Open TOMBAL 138A TOMBAL Open LOUETA WESFLD 138B Move percent load from bus TOMBAL tobus TOMBAL Move percent load from bus LOUETA tobus LOUETA L: CLODIN 138B OBRIEN73138D Open CLODIN 138B CCLODIN_138C Open OBRIEN 138A OBRIEN25138C Open MASON 138A OBRIEN 138A Move percent load from bus OBRIEN25138C138 tobus OBRIEN73138D L: SMTHRS 345A BELAIR 345A Open W_A_P 345B BELAIR 345A Open BELAIR 345A JENETA 345B L: SNLTN_ ZENITH 345A Open ROANS 345C BOBVLE 345X Open SNLTN_ TOMBAL 345B

47 OPTION FCITC Limiting Constraint Contingency Description OPTION 11 Sandow to Zenith L: SNLTN_ ZENITH 345A Open ROANS 345C BOBVLE 345X Open SNLTN_ TOMBAL 345B OPTION 12 Rating B (MW) 2018 Study Case Init Init Base Case Final Marion-Holman- Obrien L: SNLTN_ ZENITH 345A Open ROANS 345C BOBVLE 345X Open SNLTN_ TOMBAL 345B OPTION 13 Hillje-Obrien L: SNLTN_ ZENITH 345A Open ROANS 345C BOBVLE 345X Open SNLTN_ TOMBAL 345B OPTION 14 Twin Oak-Salem - Fayetteville-Zenith L: 7056 L_FPPYD15_1Y L_FAYETT5_1Y Open 7056 L_FPPYD15_1Y L_FAYETT5_1Y L: CLODIN 138B OBRIEN73138D Open CLODIN 138B CCLODIN_138C Open OBRIEN 138A OBRIEN25138C Open MASON 138A OBRIEN 138A Move percent load from bus OBRIEN25138C138 tobus 1725 L: RAYFRD RTHWOD 138A Open PINHUR 138A CTOMBAL_ Open TOMBAL 138A CTOMBAL_ Open TOMBAL 138A TOMBAL Open LOUETA WESFLD 138B Move percent load from bus TOMBAL tobus TOMBAL Move percent load from bus LOUETA tobus LOUETA L: SMTHRS 345A BELAIR 345A Open W_A_P 345B BELAIR 345A Open BELAIR 345A JENETA 345B L: SNLTN_ ZENITH 345A Open ROANS 345C BOBVLE 345X Open SNLTN_ TOMBAL 345B OPTION 15 Twin Oak-Zenith L: SMTHRS 345A BELAIR 345A Open W_A_P 345B BELAIR 345A Open BELAIR 345A JENETA 345B L: CLODIN 138B OBRIEN73138D Open CLODIN 138B CCLODIN_138C Open OBRIEN 138A OBRIEN25138C Open MASON 138A OBRIEN 138A Move percent load from bus OBRIEN25138C138 tobus 1856 L: RAYFRD RTHWOD 138A Open PINHUR 138A CTOMBAL_ Open TOMBAL 138A CTOMBAL_ Open TOMBAL 138A TOMBAL Open LOUETA WESFLD 138B Move percent load from bus TOMBAL tobus Move percent load from bus LOUETA tobus L: 7270 L_BELLSO8_1Y PETERS 138B Open FLEWLN 138A OBRIEN 138A Open MASON 138A OBRIEN 138A L: ZENITH 345A T_H_W 345B Open ZENITH 345A 345 B$0244 ZENITH A Open ZENITH 138A 138 B$0244 ZENITH A1 Open _STAR 23.0 B$0244 ZENITH A1 Open ZENITH 345A T_H_W 345B

48 OPTION FCITC Limiting Constraint Contingency Description OPTION 16 Twin Oak-Salem-Zenith 1657 L: SMTHRS 345A BELAIR 345A Open W_A_P 345B BELAIR 345A Open BELAIR 345A JENETA 345B L: CLODIN 138B OBRIEN73138D Open CLODIN 138B CCLODIN_138C Open OBRIEN 138A OBRIEN25138C Open MASON 138A OBRIEN 138A Move percent load from bus OBRIEN25138C138 tobus OBRIEN73138D L: RAYFRD RTHWOD 138A Open PINHUR 138A CTOMBAL_ Open TOMBAL 138A CTOMBAL_ Open TOMBAL 138A TOMBAL Open LOUETA WESFLD 138B Move percent load from bus TOMBAL tobus TOMBAL Move percent load from bus LOUETA tobus LOUETA L: SNLTN_ ZENITH 345A Open ROANS 345C BOBVLE 345X Open SNLTN_ TOMBAL 345B OPTION 17 Limestone-ibbons Creek-Zenith L: SMTHRS 345A BELAIR 345A Open W_A_P 345B BELAIR 345A Open BELAIR 345A JENETA 345B L: CLODIN 138B OBRIEN73138D Open CLODIN 138B CCLODIN_138C Open OBRIEN 138A OBRIEN25138C Open MASON 138A OBRIEN 138A Move percent load from bus OBRIEN25138C138 tobus OBRIEN73138D L: RAYFRD RTHWOD 138A Open PINHUR 138A CTOMBAL_ Open TOMBAL 138A CTOMBAL_ Open TOMBAL 138A TOMBAL Open LOUETA WESFLD 138B Move percent load from bus TOMBAL tobus TOMBAL Move percent load from bus LOUETA tobus LOUETA L: 7270 L_BELLSO8_1Y PETERS 138B Open FLEWLN 138A OBRIEN 138A Open MASON 138A OBRIEN 138A L: ZENITH 345A T_H_W 345B Open ZENITH 345A 345 B$0244 ZENITH A Open ZENITH 138A 138 B$0244 ZENITH A1 Open _STAR 23.0 B$0244 ZENITH A1 Open ZENITH 345A T_H_W 345B Rating B (MW) 2018 Study Case Init Init Base Case Final 48

49 OPTION FCITC Limiting Constraint Contingency Description OPTION 18 Big Brown - Jordan 500 kv L: N_BELT 345A 345 B$0097 M A Open N_BELT 345A 345 B$0035 ALM A Rating B (MW) 2018 Study Case Init Init Open N_BELT 138A 138 B$0035 ALM A1 Open N_BELT_A1TER23.0 B$0035 ALM A1 Open N_BELT 345A 345 B$ A Open N_BELT 138A 138 B$ A3 Open N_BELT_A3TER23.0 B$ A L: 3133 RICHLND2_ BIBRN C:DB_ID_16038 Open 2427 WATMLL_W TRINDAD1_ Open 2428 WATMLL_E TRICRN1_ Base Case Final 1828 L: SMTHRS 345A BELAIR 345A Open W_A_P 345B BELAIR 345A Open BELAIR 345A JENETA 345B L: RAYFRD RTHWOD 138A Open PINHUR 138A CTOMBAL_ Open TOMBAL 138A CTOMBAL_ Open TOMBAL 138A TOMBAL Open LOUETA WESFLD 138B Move percent load from bus TOMBAL tobus TOMBAL Move percent load from bus LOUETA tobus LOUETA P_H_R 345E 345 B$0032 ALM A Open P_H_R 345E 345 B$ A Open P_H_R 138A 138 B$ A4 Open P_H_R A4TER23.0 B$ A4 Open P_H_R 345E 345 B$0105 PHR A1 NEW A Open P_H_R 138C 138 B$0105 PHR A1 NEW A1 Open P_H_R A1TER23.0 B$0105 PHR A1 NEW A L: SNLTN_ ZENITH 345A Open ROANS 345C BOBVLE 345X Open SNLTN_ TOMBAL 345B OPTION 19 Big Brown-Zenith L: 3133 RICHLND2_ BIBRN Open 2427 WATMLL_W TRINDAD1_ Open 2428 WATMLL_E TRICRN1_ L: SMTHRS 345A BELAIR 345A Open W_A_P 345B BELAIR 345A Open BELAIR 345A JENETA 345B L: RAYFRD RTHWOD 138A Open PINHUR 138A CTOMBAL_ Open TOMBAL 138A CTOMBAL_ Open TOMBAL 138A TOMBAL Open LOUETA WESFLD 138B Move percent load from bus TOMBAL tobus TOMBAL Move percent load from bus LOUETA tobus LOUETA L: CLODIN 138B OBRIEN73138D Open CLODIN 138B CCLODIN_138C Open OBRIEN 138A OBRIEN25138C Open MASON 138A OBRIEN 138A Move percent load from bus OBRIEN25138C138 tobus OBRIEN73138D L: SNLTN_ ZENITH 345A Open ROANS 345C BOBVLE 345X Open SNLTN_ TOMBAL 345B OPTION 20 Navarro-Zenith L: SMTHRS 345A BELAIR 345A Open W_A_P 345B BELAIR 345A Open BELAIR 345A JENETA 345B L: SNLTN_ ZENITH 345A Open ROANS 345C BOBVLE 345X Open SNLTN_ TOMBAL 345B

50 OPTION FCITC Limiting Constraint Contingency Description OPTION 21 Upgrade 345 kv conductors L: RAYFRD RTHWOD 138A Open PINHUR 138A CTOMBAL_ Open TOMBAL 138A CTOMBAL_ Open TOMBAL 138A TOMBAL Open LOUETA WESFLD 138B Move percent load from bus TOMBAL tobus TOMBAL Move percent load from bus LOUETA tobus LOUETA L: 7289 L_SALEM_8_1Y L_HIH368_1Y Open 7289 L_SALEM_8_1Y L_BRENHA8_1Y Open 7289 L_SALEM_8_1Y L_UYBUR8_1Y L: SMTHRS 345A BELAIR 345A Open W_A_P 345B BELAIR 345A Open BELAIR 345A JENETA 345B L: 3391 JEWETT_N SNLTN_ Open 967 IBN_CREK_ SNLTN_ Open 967 IBN_CREK_ SNLTN_ Open 967 IBN_CREK_ SNLTN_ OPTION 22 Limestone-Zenith L: SMTHRS 345A BELAIR 345A Open W_A_P 345B BELAIR 345A Open BELAIR 345A JENETA 345B L: CLODIN 138B OBRIEN73138D Open CLODIN 138B CCLODIN_138C Open OBRIEN 138A OBRIEN25138C Open MASON 138A OBRIEN 138A Move percent load from bus OBRIEN25138C138 tobus OBRIEN73138D138 Rating B (MW) 2018 Study Case Init Init L: RAYFRD RTHWOD 138A Open PINHUR 138A CTOMBAL_ Open TOMBAL 138A CTOMBAL_ Open TOMBAL 138A TOMBAL Open LOUETA WESFLD 138B Move percent load from bus TOMBAL tobus TOMBAL Move percent load from bus LOUETA tobus LOUETA L: 7270 L_BELLSO8_1Y PETERS 138B Open FLEWLN 138A OBRIEN 138A Open MASON 138A OBRIEN 138A L: SNLTN_ ZENITH 345A Open ROANS 345C BOBVLE 345X Open SNLTN_ TOMBAL 345B Base Case Final 50

51 OPTION FCITC Limiting Constraint Contingency Description OPTION 23 Limestone-Singleton- Zenith L: SMTHRS 345A BELAIR 345A Open W_A_P 345B BELAIR 345A Open BELAIR 345A JENETA 345B L: CLODIN 138B OBRIEN73138D Open CLODIN 138B CCLODIN_138C Open OBRIEN 138A OBRIEN25138C Open MASON 138A OBRIEN 138A Move percent load from bus OBRIEN25138C138 tobus OBRIEN73138D L: RAYFRD RTHWOD 138A Open PINHUR 138A CTOMBAL_ Open TOMBAL 138A CTOMBAL_ Open TOMBAL 138A TOMBAL Open LOUETA WESFLD 138B Move percent load from bus TOMBAL tobus TOMBAL Move percent load from bus LOUETA tobus LOUETA L: 7270 L_BELLSO8_1Y PETERS 138B Open FLEWLN 138A OBRIEN 138A Open MASON 138A OBRIEN 138A L: ZENITH 345A T_H_W 345B Open ZENITH 345A 345 B$0244 ZENITH A Open ZENITH 138A 138 B$0244 ZENITH A1 Open _STAR 23.0 B$0244 ZENITH A1 Open ZENITH 345A T_H_W 345B OPTION 24 Ragan Creek-Zenith L: SMTHRS 345A BELAIR 345A Open W_A_P 345B BELAIR 345A Open BELAIR 345A JENETA 345B L: CLODIN 138B OBRIEN73138D Open CLODIN 138B CCLODIN_138C Open OBRIEN 138A OBRIEN25138C Open MASON 138A OBRIEN 138A Move percent load from bus OBRIEN25138C138 tobus OBRIEN73138D L: 7289 L_SALEM_8_1Y L_HIH368_1Y Open 7289 L_SALEM_8_1Y L_BRENHA8_1Y Open 7289 L_SALEM_8_1Y L_UYBUR8_1Y L: 3391 JEWETT_N SNLTN_ Open 3400 TWIN_OAK RA_CR Open 975 JKCREEK TWIN_OAK OPTION 25 Limestone-Ragan Creek- Zenith 1567 L: SMTHRS 345A BELAIR 345A Open W_A_P 345B BELAIR 345A Open BELAIR 345A JENETA 345B L: CLODIN 138B OBRIEN73138D Open CLODIN 138B CCLODIN_138C Open OBRIEN 138A OBRIEN25138C Open MASON 138A OBRIEN 138A Move percent load from bus OBRIEN25138C138 tobus OBRIEN73138D L: RAYFRD RTHWOD 138A Rating B (MW) 2018 Study Case Init Init Base Case Final Open PINHUR 138A CTOMBAL_ Open TOMBAL 138A CTOMBAL_ Open TOMBAL 138A TOMBAL Open LOUETA WESFLD 138B Move percent load from bus TOMBAL tobus TOMBAL Move percent load from bus LOUETA tobus LOUETA L: 7270 L_BELLSO8_1Y PETERS 138B Open FLEWLN 138A OBRIEN 138A Open MASON 138A OBRIEN 138A L: ZENITH 345A T_H_W 345B Open ZENITH 345A 345 B$0244 ZENITH A Open ZENITH 138A 138 B$0244 ZENITH A1 Open _STAR 23.0 B$0244 ZENITH A1 Open ZENITH 345A T_H_W 345B

52 Appendix B. Preliminary Cost Estimates of Identified Options 52

53 ERCOT ESTIMATES Rural Urban Option 1 Option 2 Option 3 Option 4 Option 5 Lufkin-Jordan Salem - Zenith Zenith - Fayette Zenith- ibbons Creek Obrien - Fayetteville ($ MM/mi) ($ MM/mi) mi/units $ MM mi/units $ MM mi/units $ MM mi/units $ MM mi/units $ MM 345 kv New Single circuit (on double circuit capable towers) New double circuit Re-conductoring of existing single circuit line Re-conductoring of existing double circuit line Rebuilt existing double (complete tear down of towers and conductors) add second circuit to an existing double circuit capable line kv New Single circuit (on double circuit capable towers) New double circuit Re-conductoring of existing single circuit line Re-conductoring of existing double circuit libe kv New Single circuit (on double circuit capable towers) 2.70 Transformer 138/345 lesser than or qual to 600 MVA /345 lesser than or qual to 800 MVA /500 transformer 1200 MVA eneral Susbstation 345 kv -ring bus 6-line terminals kv substation breaker&1/2 > 6 - line terminal breaker 500 kv ring substation Expand substation with one additional line terminations kV substation breaker&1/2 > 6 - line terminal 35 TOTAL - TIE ONLY REINFORCEMENTS $ MM/mi mi 7055 L_FPPYD25_1Y HOLMAN L_FAYETT5_1Y L_FAYETT8_1Y L_SALEM_8_1Y L_HIH368_1Y LUFKNSS_ LUFKIN_ T_H_W 345B 345 B$ A L_FPPYD15_1Y L_SALEM_5_1Y N_BELT 345A 345 B$0097 M A L_FPPYD15_1Y L_FAYETT5_1Y SMTHRS 345A BELAIR 345A RAYFRD RTHWOD 138A CLODIN 138B OBRIEN73138D L_BELLSO8_1Y PETERS 138B ZENITH 345A 345 B$0244 ZENITH 1.00 A ZENITH 345A T_H_W 345B JEWETT_N SNLTN_ RICHLND2_ BIBRN T_H_W 345B ADICKS 345A L_WILLSP8_1Y L_FAYETT8_1Y IBN_CREK_ SNLTN_ P_H_R 138C 138 B$0032 ALM A COST of REINFORCEMENTS Capacitor banks 3 1 TOTAL ESTIMATE

54 ERCOT ESTIMATES Rural Urban Obrien -Salem Holman -Obrien Creek Creek ($ MM/mi) ($ MM/mi) mi/units $ MM mi/units $ MM mi/units $ MM mi/units $ MM mi/units $ MM 345 kv New Single circuit (on double circuit capable towers) New double circuit Re-conductoring of existing single circuit line Re-conductoring of existing double circuit line Rebuilt existing double (complete tear down of towers and conductors) add second circuit to an existing double circuit capable line Option 6 Option 7 Option 8 Option 9 Option 10 Zenith- Salem Salem-ibbons Zenith-Salem- TNPONE Fayeteville -Zenith Salem-ibson 138 kv New Single circuit (on double circuit capable towers) New double circuit Re-conductoring of existing single circuit line Re-conductoring of existing double circuit libe kv New Single circuit (on double circuit capable towers) 2.70 Transformer 138/345 lesser than or qual to 600 MVA /345 lesser than or qual to 800 MVA /500 transformer 1200 MVA eneral Susbstation 345 kv -ring bus 6-line terminals kv substation breaker&1/2 > 6 - line terminal breaker 500 kv ring substation Expand substation with one additional line terminations kV substation breaker&1/2 > 6 - line terminal 35 TOTAL - TIE ONLY REINFORCEMENTS $ MM/mi mi 7055 L_FPPYD25_1Y HOLMAN L_FAYETT5_1Y L_FAYETT8_1Y L_SALEM_8_1Y L_HIH368_1Y LUFKNSS_ LUFKIN_ T_H_W 345B 345 B$ A L_FPPYD15_1Y L_SALEM_5_1Y N_BELT 345A 345 B$0097 M A L_FPPYD15_1Y L_FAYETT5_1Y SMTHRS 345A BELAIR 345A RAYFRD RTHWOD 138A CLODIN 138B OBRIEN73138D L_BELLSO8_1Y PETERS 138B ZENITH 345A 345 B$0244 ZENITH 1.00 A ZENITH 345A T_H_W 345B JEWETT_N SNLTN_ RICHLND2_ BIBRN T_H_W 345B ADICKS 345A L_WILLSP8_1Y L_FAYETT8_1Y IBN_CREK_ SNLTN_ P_H_R 138C 138 B$0032 ALM A COST of REINFORCEMENTS Capacitor banks TOTAL ESTIMATE

55 345 kv ERCOT ESTIMATES Rural Urban ($ MM/mi) ($ MM/mi) mi/units $ MM mi/units $ MM mi/units $ MM mi/units $ MM mi/units $ MM New Single circuit (on double circuit capable towers) New double circuit Re-conductoring of existing single circuit line Re-conductoring of existing double circuit line Rebuilt existing double (complete tear down of towers and conductors) add second circuit to an existing double circuit capable line Option 11 Option 12 Option 13 Option 14 Sandow to Zenith Marion-Holman- Obrien Hillje-Obrien Twin Oak-Salem- Fayeteville -Zenith Option 15 Twin Oak-Zenith 138 kv New Single circuit (on double circuit capable towers) New double circuit Re-conductoring of existing single circuit line Re-conductoring of existing double circuit libe kv New Single circuit (on double circuit capable towers) 2.70 Transformer 138/345 lesser than or qual to 600 MVA /345 lesser than or qual to 800 MVA /500 transformer 1200 MVA eneral Susbstation 345 kv -ring bus 6-line terminals kv substation breaker&1/2 > 6 - line terminal breaker 500 kv ring substation Expand substation with one additional line terminations kV substation breaker&1/2 > 6 - line terminal 35 TOTAL - TIE ONLY REINFORCEMENTS $ MM/mi mi 7055 L_FPPYD25_1Y HOLMAN L_FAYETT5_1Y L_FAYETT8_1Y L_SALEM_8_1Y L_HIH368_1Y LUFKNSS_ LUFKIN_ T_H_W 345B 345 B$ A L_FPPYD15_1Y L_SALEM_5_1Y N_BELT 345A 345 B$0097 M A L_FPPYD15_1Y L_FAYETT5_1Y SMTHRS 345A BELAIR 345A RAYFRD RTHWOD 138A CLODIN 138B OBRIEN73138D L_BELLSO8_1Y PETERS 138B ZENITH 345A 345 B$0244 ZENITH 1.00 A ZENITH 345A T_H_W 345B JEWETT_N SNLTN_ RICHLND2_ BIBRN T_H_W 345B ADICKS 345A L_WILLSP8_1Y L_FAYETT8_1Y IBN_CREK_ SNLTN_ P_H_R 138C 138 B$0032 ALM A COST of REINFORCEMENTS Capacitor banks TOTAL ESTIMATE

56 ERCOT ESTIMATES Rural Urban Big Brown-Zenith Navarro-Zenith Zenith ($ MM/mi) ($ MM/mi) mi/units $ MM mi/units $ MM mi/units $ MM mi/units $ MM mi/units $ MM 345 kv New Single circuit (on double circuit capable towers) New double circuit Re-conductoring of existing single circuit line Re-conductoring of existing double circuit line Rebuilt existing double (complete tear down of towers and conductors) add second circuit to an existing double circuit capable line Option 16 Twin Oak-Zenith - Salem Option 17 Option 18 Option 19 Option 20 Limestone- ibbons Creek- Big Brown - Jordan 500 kv 138 kv New Single circuit (on double circuit capable towers) New double circuit Re-conductoring of existing single circuit line Re-conductoring of existing double circuit libe kv New Single circuit (on double circuit capable towers) Transformer 138/345 lesser than or qual to 600 MVA /345 lesser than or qual to 800 MVA /500 transformer 1200 MVA eneral Susbstation 345 kv -ring bus 6-line terminals kv substation breaker&1/2 > 6 - line terminal breaker 500 kv ring substation Expand substation with one additional line terminations kV substation breaker&1/2 > 6 - line terminal TOTAL - TIE ONLY REINFORCEMENTS $ MM/mi mi 7055 L_FPPYD25_1Y HOLMAN L_FAYETT5_1Y L_FAYETT8_1Y L_SALEM_8_1Y L_HIH368_1Y LUFKNSS_ LUFKIN_ T_H_W 345B 345 B$ A L_FPPYD15_1Y L_SALEM_5_1Y N_BELT 345A 345 B$0097 M A L_FPPYD15_1Y L_FAYETT5_1Y SMTHRS 345A BELAIR 345A RAYFRD RTHWOD 138A CLODIN 138B OBRIEN73138D L_BELLSO8_1Y PETERS 138B ZENITH 345A 345 B$0244 ZENITH 1.00 A ZENITH 345A T_H_W 345B JEWETT_N SNLTN_ RICHLND2_ BIBRN T_H_W 345B ADICKS 345A L_WILLSP8_1Y L_FAYETT8_1Y IBN_CREK_ SNLTN_ P_H_R 138C 138 B$0032 ALM A COST of REINFORCEMENTS Capacitor banks 3 1 TOTAL ESTIMATE

57 \ 345 kv ERCOT ESTIMATES Rural Urban New Single circuit (on double circuit capable towers) ($ MM/mi) ($ MM/mi) mi/units $ MM mi/units $ MM mi/units $ MM mi/units $ MM mi/units $ MM New double circuit Re-conductoring of existing single circuit line Re-conductoring of existing double circuit line Rebuilt existing double (complete tear down of towers and conductors) add second circuit to an existing double circuit capable line Option 21 Option 22 Option 23 Option 24 Option 25 Upgrade 345 kv conductors Limestone-Zenith Limestone- Singleton-Zenith Ragan Creek- Zenith Limestone-Ragan Creek-Zenith 138 kv New Single circuit (on double circuit capable towers) New double circuit Re-conductoring of existing single circuit line Re-conductoring of existing double circuit libe kv New Single circuit (on double circuit capable towers) 2.70 Transformer 138/345 lesser than or qual to 600 MVA /345 lesser than or qual to 800 MVA /500 transformer 1200 MVA eneral Susbstation 345 kv -ring bus 6-line terminals kv substation breaker&1/2 > 6 - line terminal breaker 500 kv ring substation Expand substation with one additional line terminations kV substation breaker&1/2 > 6 - line terminal 35 TOTAL - TIE ONLY REINFORCEMENTS $ MM/mi mi 7055 L_FPPYD25_1Y HOLMAN L_FAYETT5_1Y L_FAYETT8_1Y L_SALEM_8_1Y L_HIH368_1Y LUFKNSS_ LUFKIN_ T_H_W 345B 345 B$ A L_FPPYD15_1Y L_SALEM_5_1Y N_BELT 345A 345 B$0097 M A L_FPPYD15_1Y L_FAYETT5_1Y SMTHRS 345A BELAIR 345A RAYFRD RTHWOD 138A CLODIN 138B OBRIEN73138D L_BELLSO8_1Y PETERS 138B ZENITH 345A 345 B$0244 ZENITH 1.00 A ZENITH 345A T_H_W 345B JEWETT_N SNLTN_ RICHLND2_ BIBRN T_H_W 345B ADICKS 345A L_WILLSP8_1Y L_FAYETT8_1Y IBN_CREK_ SNLTN_ P_H_R 138C 138 B$0032 ALM A COST of REINFORCEMENTS Capacitor banks TOTAL ESTIMATE

58 Appendix C. Detailed Cost Estimates of Selected Options 58

59 Option 8 - Zenith Substation to Salem Substation to ibbons Creek Substation Description Transmission Cost ($) Substation Cost ($) Build new 50 mile 345 kv double circuit from Zenith Substation to TSC's Salem Substation using ACSS. Add two 345 kv line terminations at Zenith Substation rated at least 5000 Amps. Add two 345 kv terminations at Salem Substation Build new 49 mile 345 kv double circuit from TSC's Salem Substation to TMPA's ibbons Creek Substation using ACSS. Add two 345 kv terminations at Salem Substation Expand TMPA's ibbons Creek Substation with two additional 345 kv line terminations with 5000 amp equipment. Upgrade 27 mile 345 kv circuit from TSC's Salem Substation to Fayeteville Substation using ACSS. Upgrade Bellaire Substation to Smithers Substation circuit 98 to at least 1900 Amps continuous rating and at least 2010 Amps emergency rating. 190,909,000 8,000, ,364,000 4,000, ,000,000 19,440,000 10,000 0 Upgrade Substation equipment at Rayford Substation to increase rating of Rothwood Substation to Rayford Substation Circuit 66 to at least 3000 Amps. Upgrades circuit between Oncor's Twin Oak and and TMPA's ibbons Creek substations (one circuit loops into Jack Creek) 0 200,000 5,000, MVAr Capacitor banks at Zenith 3,000,000 TOTAL COST ALTERNATIVE ($ MM)

60 Option 15 - Zenith Substation to Twin Oak Substation Description Build new 117 mile 345 kv double circuit from Zenith Substation to Oncor's Twin Oak Substation using ACSS. Add two 345 kv line terminations at Zenith Substation rated at least 5000 Amps. Expand Oncor's Twin Oak Substation with two additional 345 kv line terminations with 5000 amp equipment. Upgrade Bellaire Substation to Smithers Substation circuit 98 to at least 1900 Amps continuous rating and at least 2010 Amps emergency rating. Upgrade Substation equipment at Rayford Substation to increase rating of Rothwood Substation to Rayford Substation Circuit 66 to at least 3000 Amps. Upgrade tie-line Peters Substation to LCRA's Bell South Substation to at least 2000 Amps. Re-conductorin single 138 kv circuit between LCRA'S Salem and Hwy3613 substations Transmission Cost ($) Substation Cost ($) 443,182,000 4,000, ,000,000 10, ,000 5,145, ,000 1,983, MVAr Capacitor banks at Zenith 3,000,000 TOTAL COST ALTERNATIVE ($ MM)

61 Option 21 - Reconductor Existing N-H Tielines Description Upgrade 345 kv circuit 74 King Substation to Rothwood Substation with miles of ACSS and 5000 amp equipment. Upgrade 345 kv circuit 74 Rothwood Substation to Kuykendahl Substation with 2.62 miles of ACSS and 5000 amp equipment. Upgrade 345 kv circuit 74 Kuykendahl Substation to Tomball Substation with 7.49 miles of ACSS and 5000 amp equipment. Upgrade 345 kv circuit 75 King Substation to Kuykendahl Substation with miles of ACSS and 5000 amp equipment. Rebuild 345 kv circuit 74 and circuit 75 common tower double circuit from Tomball Substation corner to Singleton Substation with double circuit miles of ACSS and install 5000 amp equipment at terminal substations. Rebuild 345 kv circuit 98 and circuit 99 common tower double circuit from Zenith Substation to Singleton Substation with double circuit miles of ACSS and 5000 amp equipment at terminal substations. Upgrade Bellaire Substation to Smithers Substation circuit 98 to at least 1900 Amps continuous rating and at least 2010 Amps emergency rating. Upgrade Substation equipment at Rayford Substation to increase rating of Rothwood Substation to Rayford Substation Circuit 66 to at least 3000 Amps. Re-conductoring single 138 kv circuit between LCRA'S Salem and Hwy3613 substations Transmission Cost ($) Substation Cost ($) 16,500,000 1,500,000 1,700, ,800,000 1,500,000 17,900,000 1,500, ,000,000 4,700, ,000, ,000 10, ,000 1,983,000 0 TOTAL COST ALTERNATIVE ($ MM)

62 Option 24 - Zenith Substation to Ragan Creek 345 kv Substation Description Build new Ragan Creek 345 kv Substation with 8 positions located along and looping in the line TMPA's ibbons Creek Substation to Oncor's Twin Oak Substation. Loop in adjacent circuit TMPA's ibbons Creek Substation to TMPA's Jack Creek Substation. Substation equipment rated 5000 Amps. Build new 69 mile 345 kv double circuit from Zenith Substation to new 345 kv Substation using ACSS. Add two 345 kv line terminations at Zenith Substation rated at least 5000 Amps. Upgrade Bellaire Substation to Smithers Substation circuit 98 to at least 1900 Amps continuous rating and at least 2010 Amps emergency rating. Re-conductoring single 138 kv circuit between LCRA'S Salem and Hwy3613 substations Upgrades circuit between Oncor's Twin Oak and and TMPA's ibbons Creek substations (one circuit loops into Jack Creek) TOTAL COST ALTERNATIVE ($ MM) Transmission Cost ($) Substation Cost ($) 5,000,000 20,000, ,364,000 4,000,000 10, ,983, ,000,

63 Option 25 - Zenith Substation to Ragan Creek to Limestone Substation Description Transmission Cost ($) Substation Cost ($) Build new Ragan Creek 345 kv Substation with 8 positions located along and looping in the line TMPA's ibbons Creek Substation to Oncor's Twin Oak Substation. Loop in adjacent circuit TMPA's ibbons Creek Substation to TMPA's Jack Creek Substation. Substation equipment rated 5000 Amps. Build new 69 mile 345 kv double circuit from Zenith Substation to new 345 kv Substation using ACSS. Add two 345 kv line terminations at Zenith Substation rated at least 5000 Amps. 5,000,000 20,000, ,364,000 4,000,000 Build new 61 mile 345 kv double circuit from new 345 kv Substation to Limestone Substation using ACSS. Add two 345 kv line terminations at Limestone Substation rated at least 5000 Amps. 231,818,000 4,000,000 Upgrade Bellaire Substation to Smithers Substation circuit 98 to at least 1900 Amps continuous rating and at least 2010 Amps emergency rating. 10,000 0 Upgrade Substation equipment at Rayford Substation to increase rating of Rothwood Substation to Rayford Substation Circuit 66 to at least 3000 Amps ,000 Upgrade tie-line Peters Substation to LCRA's Bell South Substation to at least 2000 Amps. 5,145, ,000 TOTAL COST ALTERNATIVE ($ MM)

64 Appendix D. PV Analysis of Selected Options 64

65 2018 Base Case - ERCOT to Houston Transfer PV curves for Various Contingencies Option Roans to Tomball Corridor' 1.02 Singleton to Roans Corridor' 1 Singleton to Zenith Corridor' Bellaire 345 kv Voltage (p.u.) Pre-contingency' ibbons Creek to Singleton' STP to Dow Corridor' Ercot to Houston Pre-Contingency Interface Flow (MW) 2018 Base Case - ERCOT to Houston Transfer PV curves for Various Contingencies Option Roans to Tomball Corridor' Jewett to Singleton Corridor' 1 Singleton to Roans Corridor' Bellaire 345 kv Voltage (p.u.) Singleton to Zenith Corridor' Pre-contingency' ibbons Creek to Singleton' STP to Dow Corridor' ERCOT to Houston Pre-Contingency Interface Flow (MW) 65

66 2018 Base Case - ERCOT to Houston Transfer PV curves for Various Contingencies Option Roans to Tomball Corridor' Jewett to Singleton Corridor' 1 Singleton to Roans Corridor' Bellaire 345 kv Voltage (p.u.) Singleton to Zenith Corridor' Pre-contingency' ibbons Creek to Singleton' STP to Dow Corridor' ERCOT to Houston Pre-Contingency Interface Flow (MW) 2018 Base Case - ERCOT to Houston Transfer PV curves for Various Contingencies Option Roans to Tomball Corridor' Jewett to Singleton Corridor' 1 Singleton to Roans Corridor' Bellaire 345 kv Voltage (p.u.) Singleton to Zenith Corridor' Pre-contingency' ibbons Creek to Singleton' STP to Dow Corridor' ERCOT to Houston Pre-Contingency Interface Flow (MW) 66

67 2018 Study Case - ERCOT to Houston Transfer PV curves for Various Contingencies Option Roans to Tomball Corridor' Jewett to Singleton Corridor' 1 Singleton to Roans Corridor' Bellaire 345 kv Voltage (p.u.) Singleton to Zenith Corridor' Pre-contingency' ibbons Creek to Singleton' STP to Dow Corridor' ERCOT to Houston Pre-Contingency Interface Flow (MW) 67