Updated SYSTEM IMPACT STUDY OF NEW ENGLAND AREA

Transcription

1 CROSS SOUND CABLE PROJECT 330MW HVdc INTERCONNECTION BETWEEN NEW HAVEN, CONNECTICUT AND SHOREHAM, NY Updated SYSTEM IMPACT STUDY OF NEW ENGLAND AREA Subordinate Status Removal and Amendment of Approved NEPOOL SECTION 18.4 THERMAL & VOLTAGE ANALYSIS VOLUME 1 of 2 OCTOBER 2001 Prepared by TransÉnergie U.S. Ltd. 110 Turnpike Road, Suite 300 Westborough, MA

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3 Cross Sound HVdc Cable Project Executive Summary The Cross Sound Cable (CSC) is a 330 MW, HVdc interconnection between Shoreham on Long Island, New York and New Haven, Connecticut. System Impact studies were completed and conditional Subordinate Section 18.4 approval received from the New England Participants Committee in November 2000 based on the following Section 18.4 applications. This report assesses the impact of the CSC Project under Minimum Interconnection Standards (MIS) with other relevant queued resources that have received NEPOOL Section 18.4 approval since November 2000 and were not previously included in previous CSC studies. The intent is to remove the Subordinate approval status of the Project and to determine is any changes are required to the approved system upgrades for interconnection. The Section 18.4 approved Relevant Queued Resources in Connecticut that have a higher queue priority include Towantic, Wallingford, Meriden, and Lake Road. Other Relevant Queued Resources that the Cross Sound HVdc Cable Project is subordinate to such as AES Carpenter and Haddam Station are also included prior to these projects receiving Section 18.4 approval. Analysis indicates that replacement of a wave trap on the 1777 line is required with the relevant queued resource in the Connecticut area considered. Northeast Utilities has indicated that this is not a cost responsibility of the project and will be pursued by them. Analysis also indicates that the previously required addition of a 345 kv breaker at Scovill Rock 1 for a stuck breaker condition at Scovill Rock is no longer necessary. Concerns for this condition may be alleviated by modifying the currently approved 387 line-end-open (LEO) NPCC Type III that initiates runback the HVdc converter to also include runback of the facility for the Scovill Rock stuck 7T breaker condition. Full runback of the facility for either the 387 LEO or Scovill Rock 7T breaker condition is initially proposed. Since possible overload of local 115 kv transmission for either condition would only occur during export of power from Connecticut on the CSC Project, SPS runback under the CSC Project imports to Connecticut would be disabled. Based on the conditions studied, interconnection of the proposed Cross Sound HVdc Cable Project will not have a significant adverse impact on the New England bulk power system. The necessary system upgrades identified for the Project under MIS to remove the subordinate approval status of the CSC HVdc Project are as follows: Cross Sound SPS at Scovill Rock 2 - Installation of a Type III SPS at Scovill Rock 345 kv substation to runback the Cross Sound HVdc facilities for either o a 387 line-end-open condition at Scovill Rock or o a stuck 7T 345 kv breaker condition at Scovill Rock Replace wave trap on NU s 1777 line (N. Bloomfield x Bloomfield 115 kv) 1 Application NU-00-T25 will need to be withdrawn. 2 Application NU-00X26 will need to be revised. TransÉnergie U.S. Ltd.

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5 Cross Sound HVdc Cable Project Table of Contents Page 1.0 INTRODUCTION STUDY AREA AND INTERCONNECTION CONFIGURATION STUDY METHODOLOGY AND SYSTEM CONDITIONS System Load Representation Interfaces Modes of Operation of Cross Sound HVdc Cable EXPORT Mode: 330 MW New Haven to Shoreham Transfer IMPORT Mode: 330 MW Shoreham to New Haven Transfer Dispatches Sensitivity to Local Generation: Export Mode Only Sensitivity to New York New England Transfers Sensitivity to Millstone 1: Export Mode Only Contingency List Project Data Thermal-Voltage Guide STUDY RESULTS Thermal Analysis: Export Mode- Up to 330 MW from New Haven to Shoreham Peak Load Dispatch % Load Dispatch Sensitivity to Local CT Generation Sensitivity to New York-New England Transfers Sensitivity to Millstone 1: Export Mode Only Thermal Analysis: Import Mode- Up to 330 MW from Shoreham to New Haven Peak Load Dispatch % Load Dispatch Sensitivity to New York-New England Transfers Voltage Analysis: Export and Import Mode of Operation Cross Sound Cable SPS: Modified 387 LEO SPS Impact on Reactive Resources HVdc Converter AC Filter Bank Switching Subsynchronous Torsional Interaction SSTI SYSTEM UPGRADES REQUIRED CONCLUSIONS i TransÉnergie U.S. Ltd.

6 Cross Sound HVdc Cable Project APPENDIX I Study Area and Interconnection Configuration APPENDIX II Dispatch Summaries APPENDIX III Contingency List APPENDIX IV Project Data APPENDIX V System Dispatch Summary APPENDIX V Export Mode: 330 MW to Long Island Thermal Results Appendix Va Peak Load Level Appendix Vb 75% Load Level Appendix Vc Local CT Generation Sensitivity Appendix Vd NY-NE Transfer Sensitivity Appendix Ve Millstone 1 Sensitivity APPENDIX VI Import Mode: 330 MW From Long Island Thermal Results Appendix VIa Peak Load Level Appendix VIb 75% Load Level Appendix VIc NY-NE Transfer Sensitivity Appendix VId Millstone 1 Sensitivity APPENDIX VII Voltage Analysis VOLUME 2 Loadflow Summaries ii TransÉnergie U.S. Ltd.

7 Cross Sound HVdc Cable Project List of Tables Table 3.1 Export Mode Case Set..6 Table 3.2 Import Mode Case Set..7 Table 3.3 Peak Load with CT Generation Sensitivity: CSC HVdc 330 MW Net Export to Long Island Table Thermal Criteria Applied in Study Page Table Voltage Criteria Applied in Study Table 4.1 Summary of Transfer Levels With and Without Cross Sound HVdc Cable EXPORT Mode Transfers Connecticut to Long Island.13 Table 4.2 Summary of Transfer Levels With and Without Cross Sound HVdc Cable IMPORT Mode Transfers Long Island to Connecticut Table 4.3 Summary of Overloaded Resulting From Scovill Rock Stuck 7T Breaker Contingency..18 Table 4.4 Incremental Reactive Demand on Local Units...19 List of Figures Page Figure 2.1 Existing System...2 Figure 2.2 Previously Approved Cross Sound Cable Project Figure 5.1 Proposed Cross Sound Cable Project Interconnection. 21 iii TransÉnergie U.S. Ltd.

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9 Cross Sound HVdc Cable Project 1.0 INTRODUCTION The Cross Sound Cable (CSC) Project proposes the development of bi-directional +/- 150 kv HVdc Voltage Source Converter facilities and 23 miles of submarine cable with the ability to transfer up to 330 MW (net of losses) between the New England and Long Island electric power systems. The HVdc facilities will connect into the Shoreham 138 kv bus. Project inservice date is Summer System Impact studies were completed and conditional Subordinate Section 18.4 approval received from the New England Participants Committee in November 2000 based on the following Section 18.4 applications. TE R1 - Construct a 330 MW (net of losses), +/- 150 kv HVdc line and associated HVdc Converter Facilities. NU-00-T25 Scovill Rock Breaker Addition NU-00-X26 Cross Sound Cable SPS at Scovill Rock This report assesses the impact of the CSC Project with other relevant queued resources that have received NEPOOL Section 18.4 approval since November 2000 and were not previously included in previous CSC studies. The intent is to remove the Subordinate approval status of the Project and to determine is any changes are required to the approved system upgrades for interconnection. The relevant queued resources in Connecticut that have a higher queue priority than the CSC Project and associated approval status is listed below. Towantic - studies complete, 18.4 approval received Wallingford - studies complete, 18.4 approval received Meriden - studies complete, 18.4 approval received Lake Road - studies complete, 18.4 approval received Other Relevant Queued Resources that the Cross Sound HVdc Cable Project is subordinate to such as AES Carpenter and Haddam Station are included prior to these projects receiving Section 18.4 approval. This report summarizes the system impact of the project on the New England area thermal and voltage performance and has been prepared for review by the NEPOOL Transmission Task Force (TTF) to support a NEPOOL Section 18.4 Application (Subordinate) for the project under Minimum Interconnection Standards. 1 TransÉnergie U.S. Ltd.

10 Cross Sound HVdc Cable Project 2.0 STUDY AREA AND INTERCONNECTION CONFIGURATION The project facilities in New York (Long Island) will interconnect with the Long Island 138 kv electric transmission system adjacent to the decommissioned Long Island Power Authority (LIPA) Shoreham Nuclear Power Station. The HVdc facilities will connect into the Shoreham 138 kv bus. Appendix I provides information on the study area and interconnection of the HVdc cable and preliminary design of the HVdc facilities. The project facilities in Connecticut will interconnect with the New England 345 kv electric transmission system at New Haven, adjacent to the United Illuminating Company's existing East Shore kv Substation. The HVdc facilities would connect into the 387 (East Shore x Scovill Rock) 345 kv circuit via a single 345 kv breaker arrangement. Figures 2.1 and 2.2 show the existing system and the Section 18.4 approved interconnection to date. 353 to Manchester 353 to Manchester Middletown #4 W 4T 5T 7T 8T 376 to Haddam Neck Middletown #4 W 4T 5T 7T 8T 376 to Haddam Neck 387 Scovill Rock 345 kv Station *387 LEO SPS to runback HVdc 387 9T Scovill Rock 345 kv Station New Breaker and Line retermination New Haven HVdc Converter Facilities To Shoreham (LIPA) W W East Shore W W East Shore 115 kv 115 kv Figure Existing System 115 kv 115 kv Figure 2.2 Previously Approved Cross Sound Project Interconnection 2 TransÉnergie U.S. Ltd.

11 Cross Sound HVdc Cable Project The analysis of this report only addresses the impacts to the New England area. A separate report addressing the impact in New York was reviewed and approved by the NYISO Operating Committee in February STUDY METHODOLOGY AND SYSTEM CONDITIONS All studies were performed in conformance with the applicable NPCC, NEPOOL and local utility criteria on system representations derived from current library loadflows. The impact on the New England bulk power system was performed using the Power Technologies, INC. (PTI) Power System Simulator/Engineering (PSS/E) Program Package. The following sections describe the conditions for the thermal and voltage analysis conducted System Load Representation The system representation used in this analysis was based on loadflow cases provided by Northeast Utilities (NU) that were used in the analysis for the Haddam Neck Project (800 MW) in Connecticut 3. The cases from the Haddam Neck study reflect the most up-to-date cases available system representations of Connecticut and provide consistency of system impact study results from proposed Projects in the area. The cases represent a summer 2002 peak load (plus losses) of 24,174 MW and are consistent with the adjusted reference load of 24,140 in NEPOOL 2001 NEPOOL CELT report. Two load levels were evaluated, as based on the Haddam Neck study: 100% and 75% 4 of the anticipated summer peak load. The Connecticut area system modeled included the recently approved generation increases at Lake Road (840 MW), Towantic (549 MW), Meriden (560 MW) and Wallingford (255 MW). These facilities expected to be in-service by the year 2002 and were modeled in the same manner in which they were approved. In addition, Haddam Neck (800 MW) which is currently under review and AES Southington (786 MW) which has received both Stability Task Force (STF) and Transmission Task Force (TTF) approval, but has not yet been presented to the Reliability Committee (RC) for 18.4 approval, were included in the analysis. Existing generation in the local Connecticut area also includes the following units. Bridgeport Energy Bridgeport Harbor 2 and 3 Devon 7 and 8 Devon GTs 11,12,13, and 14 Norwalk Harbor 1 and 2 New Haven Harbor Middletown 2, 3 and 4 Milford Power English Units 7 & 8 3 System Impact Study for the Haddam Neck Project, Thermal and Short Circuit Report, May 2001, by Northeast Utilities Service Company 4 Intermediate load level is approximately 73% of the peak load and is based on Haddam Neck study cases. 3 TransÉnergie U.S. Ltd.

12 Cross Sound HVdc Cable Project 3.2. Interfaces Interfaces in the area of the Project that could be impacted by the Project include CT Import, CT Export, NY-NE and NE-NY. For consistency of system impact study results, the Haddam Neck cases with these interfaces stressed were used and modified as necessary to include the CSC HVdc Project Modes of Operation of Cross Sound HVdc Cable The CSC HVdc facilities are fully controllable and can transfer power in either direction between New Haven and Shoreham. Both import and export mode of operation was studied to investigate the bilateral transfer capability of the Project EXPORT Mode: 330 MW New Haven to Shoreham Transfer For the purpose of these studies, transfers up to 330 MW from Connecticut to Long Island, NY, is termed as the EXPORT Mode of operation for the Project. The 1385 Norwalk x Northport ac cable and phase shifter tie line between Connecticut and Long Island was scheduled for 200 MW to Long Island in the export mode cases. The Cross Sound HVdc was modeled as negative generator For cases where Cross Sound Cable (CSC) exporting to Long Island and CT was importing power, CSC HVdc was dispatched against Milford Power, Wallingford and or New Haven Harbor to maintain a similar CT Export interface loading with and without the Project. For cases where CT was exporting (maximum CT generation), no additional generation was dispatched with the Project in-service to maintain similar total CT Export and NY-NE transfers (total CT export = CT export + CSC export). Sensitivity to local CT generation, NY-NE transfer and Millstone 1 unit were included in the export mode analysis IMPORT Mode: 330 MW Shoreham to New Haven Transfer A transfer up to 330 MW in the reverse direction, from Long Island NY to Connecticut, is termed as the IMPORT Mode of operation for the Project. The 1385 Norwalk x Northport ac cable and phase shifter tie line between Connecticut and Long Island was scheduled for 0 MW to Long Island in the import mode cases. For cases where Cross Sound Cable (CSC) importing to Long Island, Cross Sound HVdc was dispatched against New Haven Harbor if in-service or Middletown #4 4 TransÉnergie U.S. Ltd.

13 Cross Sound HVdc Cable Project otherwise to maintain a similar CT Export interface loading with and without the Project. Sensitivity analysis was limited NY-NE transfer for the import mode Dispatches Testing followed same dispatch methodology used in the analysis of the Haddam Neck plant. Cases were developed with and with out the HVdc Project and for both modes of operation - Export and Import mode at both peak and 75% load levels. In addition, dispatches also considered conditions with and without Haddam Neck plant. For consistency between studies, Haddam Neck was dispatched against the same set on units used Haddam Neck study. Table 3.1 denotes the naming convention used for CSC HVDC operating in Export Mode. This case set includes sensitivity cases discussed in following sections. Cases with CSC in-service in export mode are prefixed with CSC-. Table 3.2 provides the case set used for CSC HVDC operating in Import Mode. Cases with CSC in-service are prefixed with CSCi-. Dispatch summaries of CT generation for case of Tables 3.1 and 3.2 are provided in Appendix II Full case summaries with area flow plots for all base condition loadflows used in the analysis are provided in Volume II. NY-NE positive is flow into NE on all ties and the CT Import/Export flow reported does not include the CSC HVdc project. The HVdc flow would be in addition to the reported values. 5 TransÉnergie U.S. Ltd.

14 Cross Sound HVdc Cable Project Table 3.1 Export Mode Case Set Dispatch Peak Load 75% Load Peak Load NY-NE Transfer Sensitivity Millstone #1 Sensitivity CT 115 kv Generation Dispatches CT Export/ Import Interface Export Import Export Import Import Export Import Export Export Import Export Haddam Neck Dispatched Against NY-NE Interface Transfer Loadflow Cases Without Project With Project Out-of-service Peakexp Csc-peakexp Montville, Midd#4, Meriden, AES Thames Pkex-1 Csc- pkex-1 Midd#4, Milford 0 Pkex-4 Csc- pkex-4 Out-of-service Peakimp Csc-peakimp Out-of-service Pkimp-1 Csc- pkimp-1 Midd#4, Milford, Meriden Pkimp-6 Csc- pkimp-6 Out-of-service Midexp Csc-Midexp Montville, Midd#4, Meriden, AES Thames Mdexp-1 Csc-Mdexp-1 Midd#4, Milford 0 Mdexp-4 Csc-Mdexp-4 Out-of-service Midimp Csc-Midimp Montville, Midd#4, Meriden, AES Thames Mdimp-1 Csc-Mdimp-1 Out-of-service NYNE7PKIMP CSC-NYNE7PKIMP Montville, Miid#4, Meriden, AES Thames NYNE7PKIMP-1 CSC-NYNE7PKIMP-1 Montville, Midd#4, 700 Meriden, AES Thames NYNE7PKEX CSC-NYNE7PKEX Montville, Midd#4, Meriden, AES Thames NYNE7PKEX-1 CSC-NYNE7PKEX-1 Out-of-service NENY7PKIMP CSC-NENY7PKIMP Montville, Miid#4, Meriden, AES Thames NENY7PKIMP-1 CSC-NENY7PKIMP Out-of-service NENY7PKEX CSC-NENY7PKEX Montville, Miid#4, Meriden, AES Thames NENY7PKEX-1 CSC-NENY7PKEX-1 Out-of-service Peakexp-M1 Csc-Peakexp-M1 Montville, Miid#4, Meriden, AES Thames Pkex-1-M1 Csc-Pkex-1-M1 Out-of-service 0 Midexp-M1 Csc-Midexp-M1 Montville, Miid#4, Meriden, AES Thames Mdexp-1-M1 Csc-Mdexp-1-M1 Out-of-service 700 NENY7PKIMP-2 CSC-NENY7PKIMP-2 Midd#4, Montville NENY7PKIMP-3 CSC-NENY7PKIMP-3 Out-of-service NENY7PKIMP-4 CSC-NENY7PKIMP-4 Out-of-service -700 NENY7PKIMP-5 CSC-NENY7PKIMP-5 Out-of-service NENY7PKIMP-6 CSC-NENY7PKIMP-6 Out-of-service -145 NENY7PKEX-2 CSC-NENY7PKEX-2 Midd#4, Montville -544 NENY7PKEX-3 CSC-NENY7PKEX-3 Out-of-service 425 NYNE7PKEX-2 CSC-NYNE7PKEX-2 Midd#4, Meriden 352 NYNE7PKEX-3 CSC-NYNE7PKEX-3 Midd#4, Milford, Meriden -171 Mdexp-6 CSC-Mdexp-6 Project Mode 330 MW Net Export from CT to Long Island 6 TransÉnergie U.S. Ltd.

15 Cross Sound HVdc Cable Project Table 3.2 Import Mode Case Set Dispatch Peak Load 75% Load Peak Load NY-NE Transfer Sensitivity CT Export/ Import Interface Export Import Export Import Import Export Import Export Haddam Neck Dispatched Against Out-of-service Midd#4, Meriden, AES Thames Out-of-service Midd#4, Meriden, AES Thames NY-NE Interface Transfer Without Project Ipeakexp Ipkex-2 Ipeakimp Ipkimp-2 Loadflow Cases With Project Csc-peakexp Csc- pkex-1 Csci-peakimp Csci- pkimp-2 Out-of-service Montville, Midd#4, 0 Imidexp Csci-Midexp Meriden, AES Thames Imdexp-2 Csci-Mdexp-2 Out-of-service Montville, Midd#4, -165 Imidimp Csc-Midimp Meriden, AES Thames Idimp-1 Csci-Mdimp-1 Out-of-service 290 INYNE7PKIMP CSCI-NYNE7PKIMP Meriden, AES Thames 490 INYNE7PKIMP-2 CSCI-NYNE7PKIMP-2 Midd#4, Meriden, AES Thames INYNE7PKEX CSCI-NYNE7PKEX 700 Montville, Miid#4, Meriden, AES Thames INYNE7PKEX-2 CSC-NYNE7PKEX-2 Out-of-service Montville, Midd#4, -900 NENY7PKIMP CSC-NENY7PKIMP Meriden, AES Thames NENY7PKIMP-2 CSCI-NENY7PKIMP-2 Out-of-service NENY7PKEX CSCI-NENY7PKEX Montville, Midd#4, -700 Meriden, AES Thames NENY7PKEX-1 CSCI-NENY7PKEX-2 Project Mode 330 MW Net Import from Long Island 7 TransÉnergie U.S. Ltd.

16 Cross Sound HVdc Cable Project Plant Sensitivity to Local Generation: Export Mode Only The following Table 3.3 summarizes system dispatches used in the analysis to test the sensitivity to local generation near the project with a net 330 MW transfer from CT to Long Island on the CSC HVdc. These dispatches test possible impact of the CSC HVdc project on the system for various outage scenarios of the New Haven Harbor, Middletown #4, Wallingford, English and Towantic plants at peak load. Two similar dispatches were also developed for the 75% load level having New Haven Harbor, Middletown #4 and the English units out-of-service, and with and without Haddam Neck in-service. Corresponding base system dispatches with out the Project are provided in Appendix II. Similar analysis for import mode operation was not considered necessary under minimum interconnection standards. Under import mode, the project was dispatched against New Haven Harbor or Middletown #4, as required. CSC- NYNE7PKIMP-2 Table 3.3 Peak Load with Local CT Generation Sensitivity: CSC HVdc 330 MW Net Export to Long Island CSC- NYNE7PKIMP-3 CSC- NENY7PKIMP-4 CSC- NENY7PKIMP-5 CSC- NENY7PKIMP-6 Case Names CSC- NENY7PKEX-2 CSC- NENY7PKEX-3 CSC- NYNE7PKEX-2 CSC- NYNE7PKEX- 3 English Units (#7&8) New Haven Middletown Wallingford Towantic Haddam Neck Bridgeport Milford Bridgeport Energy Lake Road Meriden AES Southington Interfaces CT Export NY-NE SW Conn Import East West Flow to LI on Sensitivity to New York New England Transfers Dispatches were developed in the analysis to test the sensitivity to the New York New England transfers with and without the CSC HVdc project in-service under both export and import mode of operation. NY-NE transfers at peak load within a range of about +/- 700 MW and were based on similar dispatches from the Haddam Neck analysis. Dispatches used in the analysis are summarized in Appendix II. 8 TransÉnergie U.S. Ltd.

17 Cross Sound HVdc Cable Project In addition to this, the TWG asked analysis of the NY-NE transfer capability with and without the CSC HVdc Project. This linear Transfer Interchange Limit analysis was performed using TLTG activity of the PSS/e program Sensitivity to Millstone 1: Export Mode Only Dispatches were developed to test sensitivity to the Millstone 1 unit at both peak and 75% load levels. This 650 MW nuclear unit was shut down in 1996 for decommissioning, but no Section 18.4 application for retirement has been submitted on behalf of the plant. Until submitted, this unit should be considered in analysis of the system. Sensitivity with the Millstone 1 unit, and with and without Haddam Neck and with and without CSC HVdc was performed for CSC HV operating in export mode with a net 330 MW transfer from CT to Long Island. Similar analysis for import mode operation was not considered necessary. Dispatches used in the analysis are summarized in Appendix II Contingency List Both normal design and extreme contingencies, required by NPCC, NEPOOL Reliability Standards and local utility criteria were tested. Appendix III provides the list of contingencies tested Project Data PTI is in the process of developing a Voltage Source converter HVdc model for the PSS/E program. Since the model was not available, a two generator method was used to model the CSC Project in the program. This model assumes the sending end (rectifier) output of 346 MW and a receiving end (inverter) output of +330 MW. The 16 MW difference is to account for HVDC system losses of the Project. For transfers in the opposite direction the output of the generators are interchanged. The net reactive capability of the Project is approximately +/- 72 MVars delivered to the high side (ac system side) of the converter transformer. This amount includes about MVars of ac filters connected to the ac filter bus and necessary for the operation the HVdc facility. The reactive capability of the inverter is slightly higher (approx. +/-90 MVars) than that of the rectifier. Output of the fictitious generators representing the HVdc facilities at New Haven was kept within this approximate range for the studies. The ac filter bus of each converter is controlled to 200 kv and connected the ac system through three single phase 120 MVA converter transformers. The system model in the study used the following for the converter transformer. 5 Note initial design was 105 MVar was used in study. Current design is 103 MVar comprised of one 61 MVar, one 32 MVar and one 10 MVar bank. Net reactive capability to the system remains the same. 9 TransÉnergie U.S. Ltd.

18 Cross Sound HVdc Cable Project Rated Voltage = (New Haven), (Shoreham) Tap Changer = secondary, +/- 14 steps, 1.5% each step Impedance=17.4 % on 360 MVA Additional Project data for the HVdc facilities is provided in Appendix III Thermal-Voltage Guide The thermal and voltage analysis used guidelines set forth in the Reliability Standards for NEPOOL, United Illuminating Company Transmission Planning Criteria 6 and Northeast Utilities Planning Standards 7. Table 3.4 identifies the thermal criteria applied. Table 3.5 identifies the voltage criteria applied. NU has additional guidelines that the Millstone 345 kv voltage should not fall below 1.0 pu post-contingency. Postcontingency incremental differences with and without the project were used to determine the impact of the project. Increase in flow of greater than 1% for thermal analysis and differences greater than 0.5% for voltage analysis resulted in further investigation of the results. Table 3.4 Thermal Criteria Applied in Study SYSTEM CONDITION TIME FRAME MAXIMUM ALLOWABLE FACILITY LOADING Pre-contingency (All Lines In) Post-contingency Continuous Normal Rating Less than 15 minutes see note 1 after contingency occurs STE Rating More than 15 minutes after contingency occurs LTE Rating Note 1) Post-contingency loadings above Long Term Emergency (LTE) rating, but below Short Term Emergency (STE) rating were considered acceptable as long as prompt action (local phase shifter adjustment or generation runback) could reduce all facility loadings below LTE within 15 minutes. Operation of existing special protection systems (SPS) were used, where available, to alleviate overload conditions. Table 3.5 Voltage Criteria Applied in Study All Lines Single Contingency Overlapping In Contingencies High Limit 1.05 pu +5%, maximum 1.05 pu +10%, maximum 1.05 pu Low Limit 0.95 pu -5%, minimum 0.95 pu -10%, minimum 0.9 pu 6 Transmission Planning Criteria, Planning Department dated April 23, Transmission Reliability Standards for Northest Utilities, May TransÉnergie U.S. Ltd.

19 Cross Sound HVdc Cable Project 4.0 STUDY RESULTS Some facilities in the study area are protected by Special Protection Systems (SPS) that result in an automatic action upon detection of an overload. The following SPSs were included in the study and were found to alleviate overloads seen on the associated circuits. Operation of the SPSs did not result in additional facilities being overloaded. Also included is the approved 387 LEO SPS that is associated with the CSC HVdc project SPS Opens R-5 circuit switcher at Ansonia for loading above the 150 MVA LTE rating on 1570 (Derby x Indian Wells 115 kv) following loss of 1545 (Devon x trap Falls 115 kv) 1870 SPS- trips 1870 (Mystic x Wood River 115 kv) for directional flow on 1870 line from Wood River above 110 MVA 1732 SPS opens 1732 line (Canton x Weingart Jct x Campville 115 kv) at Canton for 1732 line flow above 107 MVA LTE rating 387 LEO SPS 8 Runback the CSC HVdc to 0 MW flow for 387 (East Shore x CSC HVdc x Scovill Rock 345 kv) line-end-open (LEO) at Scovill Rock 345 kv Substation It should be noted that NU has a Canton-Weingart 18.4 Study currently under review and proposes to upgrade the 1732 circuit to 1272 kcmil ACSR conductor with a expected rating of 297/382/434 MVA for normal/lte/ste. The associated 1732 SPS would be removed after reconductoring. No 1732 loading shown in this analysis would exceed the new 1732 line ratings. Loss of the CSC HVdc project was included in all analysis performed and no overload condition was experienced. This is based on the existing 1385 connection between Norwalk and Northport on Long Island with a summer normal/lte/ste rating of 270/335/450 MVA as provided by LIPA and NU. Thermal results are discussed in the following sections and are summarized in tables of Appendix V and VI LEO SPS was identified as a requirement for the CSC HVdc Project and received Section 18.4 approval based on previous study of the project. 11 TransÉnergie U.S. Ltd.

20 Cross Sound HVdc Cable Project 4.1. Thermal Analysis: Export Mode- Up to 330 MW from New Haven to Shoreham Peak Load Dispatch Facilities where postcontingency thermal loadings exceed 99% of the LTE rating for conditions with net transfers of 330 MW on the CSC HVdc from New Haven to Shoreham were reviewed for the peak load dispatches. All postcontingency loadings with and without the CSC HVdc project were within the +1% comparison criteria. Some loadings above the LTE rating were noted with and without the Project. These overloads would be resolved by insertion of reactors associated with other generator projects and switching operations. No new system upgrades for the CSC HVdc project were identified. Peak load thermal results, with and without the CSC HVdc project, are summarized in Appendix Va % Load Dispatch All postcontingency loading violations with and without the CSC HVdc project were within the +1% comparison criteria. The 1732 SPS would be expected to operate for several contingencies with or without the CSC HVdc project. As noted before, if the 1732 line is upgraded, the new ratings would be adequate for the flows seen in this analysis. No new system upgrades for the CSC HVdc project were identified. 75% load thermal results, with and without the CSC HVdc project, are summarized in Appendix Vb Sensitivity to Local CT Generation Analysis of this section was performed to determine impact of the project when certain local generation may be unavailable. The more critical conditions are when either or both New Haven Harbor and Middletown #4 are off-line. Analysis confirms the system upgrades previously required by the project, namely the 387 LEO SPS and the addition of a 345 kv breaker at Scovill Rock. The 387 LEO SPS would be expected to operate for several of the system dispatches in this analysis where New Haven Harbor generation was off-line and the CSC HVdc project in-service. Runback of the CSC HVdc would alleviate overloads seen in this analysis. It should also be noted that runback of the CSC HVdc would also alleviate any overloads that may be associated with the Scovill Rock stuck 7T breaker contingency. This is discussed in more detail in Section 4.4. With the system upgrades previously required by the project, all postcontingency loading violations with and without the CSC HVdc project were within the +1% comparison criteria with the exception to the 1777 circuit (N. Bloomfield x Bloomfield 115kV). Incremental increase in load on this circuit postcontingency with the project in-service was about 2%. Although this circuit may become overloaded without the 12 TransÉnergie U.S. Ltd.

21 Cross Sound HVdc Cable Project CSC HVdc Project following a simultaneous loss of either the 1207 and 1775 circuits or the 395 and 1751 circuits, Northeast Utilities indicated that upgrade of the 1777 circuit should be considered a requirement of the CSC HVdc project. Overload seen on the 1777 circuit may be alleviated by replacement of a limiting 115 kv wave trap. The line would become conductor limited at 178/228/242 MVA with replacement of the wave trap. Northeast Utilities has indicated that it will pursue the wave trap replacement, but that the project will not be responsible for the cost. Thermal results, with and without the CSC HVdc project, are summarized in Appendix Vc Sensitivity to New York-New England Transfers All postcontingency loadings with and without the CSC HVdc project were within the +1% comparison criteria. The 1732 SPS would be expected to operate for several contingencies with or without the CSC HVdc project. As noted before, if the 1732 line is upgraded, the new ratings would be adequate for the flows seen in this analysis. The 1777 wave trap line limitation noted for the 75% load analysis was also seen in one case dispatch (csc-neny7pkimp-1 & neny7pkimp-1) with and without the CSC HVdc project. No new additional system upgrades for the CSC HVdc project were identified. Thermal results, with and without the CSC HVdc project, are summarized in Appendix Vd. Table 4.1 summaries impact on the NY-NE interface with and without the CSC HVdc project. As shown in the table, the Project does not result in any significant adverse impact ( 1%) to the transfer capability. The project does increase the transfer capability with New York. Table 4.1 Summer Transfer Levels With and Without Cross Sound HVdc Cable EXPORT Mode: Transfers Connecticut to Long Island Summer Normal Transfer Direct Tie Limit (MW) 1 Summer Emergency Transfer Direct Tie Limit (MW) 1 With Without See With Project Without See Interface Project Project Note Project Note ISONE NYISO /1116* /1524* NYISO ISONE *With Cross Sound HVdc tie flow included Notes: 1) Cross Sound HVdc Project at 330 MW net export from Connecticut cable (Northport Norwalk) at 200 MW export from Connecticut. 2) 395 Ludlow-Meekville-Manchester at 1605 LTE rating for loss of 347S line (Lake Road Card 345kV) SPS. 3) Pleasant Valley-Long Mountain 345kV at 1317 LTE rating for loss of Seabrook G1 13 TransÉnergie U.S. Ltd.

22 Cross Sound HVdc Cable Project 4) Pleasant Valley-Long Mountain 345kV at 1135 normal rating for no contingency Sensitivity to Millstone 1: Export Mode Only All postcontingency loadings with and without the CSC HVdc project were within the +1% comparison criteria. Loss of the 398 line (Long Mountain Pleasant Valley 345 kv) resulted in a loading of about 109% of LTE on the 1385 (Norwalk Harbor Northport 138 kv) tie line with LIPA only for conditions without the CSC HVdc project. With the project in-service the loading was less than 99% of LTE. Thermal results, with and without the CSC HVdc project, are summarized in Appendix Ve Thermal Analysis: Import Mode- Up to 330 MW from Shoreham to New Haven Peak Load Dispatch Facilities where postcontingency thermal loadings exceed 99% of the LTE rating for conditions with net transfers of 330 MW on the CSC HVdc from Shoreham to New Haven were reviewed for the peak load dispatches. All postcontingency loadings with and without the CSC HVdc project were within the +1% comparison criteria. Some loadings above the LTE rating were noted with and without the Project. These overloads could be resolved by insertion of reactors associated with other generator projects and switching operations. The 1732 SPS would be expected to operate for several contingencies with or without the CSC HVdc project. No new system upgrades for the CSC HVdc project were identified. Peak load thermal results, with and without the CSC HVdc project, are summarized in Appendix VIa % Load Dispatch All postcontingency loadings with and without the CSC HVdc project were within the +1% comparison criteria. The 1732 SPS would be expected to operate for several contingencies with or without the CSC HVdc project. No new system upgrades for the CSC HVdc project were identified. 75% load thermal results, with and without the CSC HVdc project, are summarized in Appendix VIb Sensitivity to New York-New England Transfers All postcontingency loadings with and without the CSC HVdc project were within the +1% comparison criteria. The 1732 SPS would be expected to operate for several contingencies with or without the CSC HVdc project. As noted before, if the 1732 line is upgraded, the new ratings would be adequate for the flows seen in this analysis. No new system upgrades for the CSC HVdc project were identified. Thermal results, with and without the CSC HVdc project, are summarized in Appendix VIc. 14 TransÉnergie U.S. Ltd.

23 Cross Sound HVdc Cable Project Table 4.2 summaries impact on the NY-NE interface with and without the CSC HVdc project. As shown in the table, the Project does not result in any significant adverse impact ( 1%) to the transfer capability. The project does increase the transfer capability with New York. Table 4.2 Summer Transfer Levels With and Without Cross Sound HVdc Cable IMPORT Mode: Transfers Long Island to Connecticut Summer Normal Transfer Direct Tie Limit (MW) 1 Summer Emergency Transfer Direct Tie Limit (MW) 1 With Without See With Project Without See Interface Project Project Note Project Note ISONE- NYISO NYISO- ISONE 1363 /1693* *With HVDC tie flow included /2407* Notes: 1) Cross Sound HVdc Project at 330 MW net export to Connecticut cable (Northport-Norwalk) at 0 MW import from Connecticut. 2) 395 Ludlow-Meekville-Manchester at 1605 LTE rating for loss of 347S line (Lake Road Card 345kV) SPS. 3) 1385 Northport-Norwalk at 335 LTE rating for loss of 398 line (Pleasant Valley-Long Mountain 345kV) and 321 line (Long Mountain-Plum Tree 345kV). 4) 1385 Northport-Norwalk at 450 STE rating for loss of 398 line (Pleasant Valley-Long Mountain 345kV) and 321 line (Long Mountain-Plum Tree 345kV) Voltage Analysis: Export and Import Mode of Operation For conditions studied, the postcontingency voltage profile in the southwestern Connecticut area demonstrated signs of a weak supply for the existing system as has been found in previous studies of the area. The CSC HVdc project slightly aggravated this area under some conditions with postcontingency voltages with the project in-service generally less than +/- 1% of the voltages without the project. Consistent with the Haddam Neck studies, the following contingencies in the southwestern CT resulted in voltage violations with post contingency voltages below 0.9 pu for many of the dispatches reviewed. loss of 1770 (Plum Tree x Stony Hill x Bates Rock 115 kv) results in low voltages in the Shepaug and Bates Rock area simultaneous loss of 1710 and 1730 (Devon x Old Town x Pequonnock 115 kv and Devon x Hawthorn x Pequonnock 115 kv) results in low voltages at the Hawthorn and Old Town substations (becomes radial feed from Norwalk 115 kv) simultaneous loss of 1770 and 321 (Plum Tree x Stony Hill x Bates Rock 115 kv and Long Mountain x Plum Tree 345 kv) results in low voltages in the Shepaug and Bates Rock area 15 TransÉnergie U.S. Ltd.

24 Cross Sound HVdc Cable Project It should be noted that NU is currently investigating the addition of reactive compensation in the area to address poor voltage performance and ISO-NE is also conducting a Southwest Connecticut reliability study to address concerns in the area. Considering the overall voltage performance in the southwest CT area following these contingencies, the CSC HVdc project is not responsible for correcting system voltage. For the rest of the Connecticut postcontingency voltage profiles for either Export or Import mode of operation of the CSC HVdc project were within acceptable limits or within 0.5% of the cases without the project. Voltage analysis results for voltage violations comparing of the impact with and without the project are provided in Appendix VI Cross Sound Cable SPS: Modified 387 LEO SPS As noted in Section 4.1.3, previous Section 18.4 approval of the project required the addition of a new 345 kv breaker at Scovill Rock to avoid loss of both 353 and 376 circuits for failure of the 7T breaker in addition to the 387 LEO SPS. When the CSC HVdc project was downsized from 600 MW to 330 MW, the impact of the Scovill Rock 7T breaker contingency was not evaluated due to uncertainty with other relevant queued resources that had not had studies completed at the time. The local 115 kv transmission serving the New Haven area load may exceed emergency ratings under very limited system conditions of high CT area load, heavy CT power transfers, export to NY via the Project and no local generation at New Haven Harbor. If New Haven Harbor is available, the 387 LEO is not a concern. Operation of the 387 LEO SPS to runback the HVdc facilities would alleviate thermal overload concerns. It is under similar conditions with New Haven Harbor unavailable that the stuck 7T 345 kv breaker at Scovill Rock resulting in the loss of the 353 (Scovill Rock x Manchester 345 kv) and 376 (Scovill Rock x Haddam Neck 345 kv) circuits could result in a possible overload of (Sackett x Mix Ave 115 kv) and Sackett phase shifter. Under this condition as with the 387 LEO, power transfer on the CSC HVdc is supplied entirely from the local 115 kv transmission. Results of the current analysis with the relevant resources included indicate postcontingency loadings associated with the Scovill Rock 7T breaker contingency are within 2% of the LTE rating of facilities and below STE rating. This is significantly less of an impact as was previously expected when the CSC HVdc project was 600 MW, where several transmission facilities could be expected to be a concern above STE rating. Table 4.3 summarizes all conditions where the Scovill Rock 7T breaker contingency resulted in loadings at or above LTE ratings based on the current analysis of this report. These overloads may also be alleviated by runback of the CSC HVdc. An alternative to the approved Scovill Rock breaker upgrade is modification of the approved 387 LEO SPS to include 7T breaker failure indication as another runback trigger. This may be 16 TransÉnergie U.S. Ltd.

25 Cross Sound HVdc Cable Project easily accomplished and would require same runback indication signal as the 387 LEO condition. The proposed Cross Sound Cable SPS would initiate runback to 0 MW for either a 387 LEO condition (open 5T and 8T breaker at Scovill Rock) or backup breaker failure of 7T breaker and only is required when CSC HVdc is operating in the export mode. For simplicity, runback to 0 MW is considered. Additional operational analysis may be conducted at a later date to determine if another level runback may be implemented that would cover both the 387 LEO and the 7T stuck breaker condition. SPS Triggering and Arming - The proposed SPS would be armed 100% of the time and triggered by breaker status of the breakers associated with the 353, 376 and 387 circuits at Scovill Rock. Operation of the SPS would result in full runback of the HVdc facilities to 0 MW under export mode transfer from CT on the CSC HVdc facilities. SPS operation would be blocked when CSC HVdc is operating in import mode. Inadvertent SPS Operation - The resulting impact to the interconnected system for an inadvertent operation of the SPS to runback the HVdc facilities would be similar to loss of the Project. It has been demonstrated in system impact studies that loss of the Project would have no adverse impact to either the New York or New England systems. Failure of SPS to Operate - Failure of the SPS to operate during HVdc export to Long Island and during heavy system stress conditions of high CT area load, heavy CT power transfers could result in overload on local 115 kv transmission serving the local New Haven area loads. Depending on local CT generation dispatch and assuming the local New Haven Harbor unit is unavailable, this may result in loadings of about 100% to 102 % of the LTE rating on the 88005A and 88005B 115 kv circuits (Devon Switching Station Milvon) and (Sackett - Mix Ave) 115 kv transmission loaded above LTE, but below STE rating. Manual runback of the HVdc facilities in event of a failure of the SPS to operate may be initiated to alleviate overloads. Impact would be limited to the local CT area. NPCC SPS TYPE Type III - No inter-area impact results for either failure of the SPS to operate when required or from inadvertent SPS operation. As noted above, it is only during limited system conditions of high CT area load, heavy CT power transfers, export to NY on the Project and no local generation at New Haven Harbor and/or Middletown #4 that there may be a need for the Cross Sound Cable SPS to operate. 17 TransÉnergie U.S. Ltd.

26 Cross Sound HVdc Cable Project Table 4.3 Summary of Overload Conditions Resulting From Scovill Rock Stuck 7T Breaker Contingency Cross Sound Export Mode 330 MW Net to Long Island Cases with New Haven Harbor, Middletown #4 and English #7&8 Off-Line (Wallingford, Milford, Bridgeport, Towantic on-line) LIMITING Normal/LTE/STE % LOADFLOW CASE COMPARISON LINE BUS NAME BUS NAME CONTINGENCY RATING FLOW LTE neny7pkex-2 and *SACKETT SACKPHS SCVRK_7T_STK 129/138/ csc-neny7pkex SACKPHS *MIX AVE SCVRK_7T_STK 129/138/ neny7pkex-3 and *SACKETT SACKPHS SCVRK_7T_STK 129/138/ csc-neny7pkex SACKPHS *MIX AVE SCVRK_7T_STK 129/138/ neny7pkimp-4 and *SACKETT SACKPHS SCVRK_7T_STK 129/138/ csc-neny7pkimp SACKPHS *MIX AVE SCVRK_7T_STK 129/138/ nyne7pkimp-2 and SACKPHS *MIX AVE SCVRK_7T_STK 129/138/ csc-nyne7pkimp A 3688 *MILVON A DEVON SCVRK_7T_STK 221/284/ nyne7pkimp-3 and SACKPHS *MIX AVE SCVRK_7T_STK 129/138/ csc-nyne7pkimp A 3688 *MILVON A DEVON SCVRK_7T_STK 221/284/ B 3689 *MILVON B DEVON SCVRK_7T_STK 221/284/ Notes: 1) SCVRK_7T_STK = Scovill Rock Stuck 7T breaker. Results in loss of 353 and 376 circuits from Scovill Rock. As such, Scovill Rock become radial to East Shore. 2) Runback of Cross Sound HVdc alleviates all overloads. 3) Scovill Rock stuck 7T breaker is a concern only for Cross Sound HVdc exporting to Long Island. Import mode into Connecticut is not a concern. 18 TransÉnergie U.S. Ltd.

27 Cross Sound HVdc Cable Project 4.5. Impact on Reactive Resources To prevent voltage instability of the Connecticut area, guidelines have been developed for the reactive output of generation at Millstone, Montville #6, Middletown #4 and New Haven Harbor. The Millstone units should be limited to about 150 MVAr output and the Montville and Middletown units to about 60 MVAr. The guidelines were developed prior to the approval of new generation in the area that includes Towantic, Milford, Wallingford, Lake Road, Meriden etc. which will support the reactive demands of the system. The associated I 2 X losses for a 330 MW net export (346 MW with losses) via the CSC HVdc project could increase the reactive demand on these units above these levels for conditions when closest unit of New Haven Harbor or others are not available. To determine the amount of incremental reactive demand from the 330 MW transfer, the Millstone, Middletown #4 units one Meriden unit were run as synchronous condensers and the MVAR output compared with and without the HVdc project in-service. The New Haven Harbor unit, English units and the Haddam Neck were not in-service. The 103 MVar of ac filters required by the HVdc facilities are modeled in this analysis. Table 4.4 summarizes the incremental reactive demand. About 12 MVar less is required from the local units with the HVdc in-service, based on a net 65 MVar flow from the HVdc facilities. This may be considered a worse case scenario for reactive demand in the area. Table 4.4 Incremental Reactive Demand on Local Units Generator No HVdc With HVdc Delta Unit MW MVAR MW MVAR MW MVAR Middletown # Montville New Haven Harbor Millstone # Millstone # Wallingford Haddam Neck Meriden Towantic CSC HVdc net at 345 kv East Shore Total Notes: 1) Information based on peak load conditions with (case csc-neny7pkimp-4) and without HVdc (case neny7pkimp-4). Units run as synchronous condensers scheduled to control pu voltage for this analysis. 2) 103 MVar of filters at East Shore HVdc converter modeled. HVdc facility delivers a net of 65 MVar to the system. 4) Loadflow model includes 16 MW of losses for HVdc facilities. 19 TransÉnergie U.S. Ltd.

28 Cross Sound HVdc Cable Project 4.6. HVdc Converter AC Filter Bank Switching Present design includes the installation of 1X 61 MVar filter bank (25 th harmonic), 1 x 32 Mvar filter bank ( 41 st harmonic) and 1 x 10 MVAr ( 21 st harmonic) to be located at the East Shore Converter terminal with a similar design for the Shoreham converter. The 32 MVar and 10 MVar banks are switched together with the converter transformer when connecting to the ac system. The 61 MVar bank will be switched separately by a separate breaker during deblock and ramping of the HVdc converter. Powering down would be in the reverse order. Based on a weak system with New Haven Harbor and Wallingford out of service and the 387 line open at Scovill Rock, switching the largest bank (61 MVar) would result in a 2% voltage change at the East Shore 115 kv bus. This is a worse case scenario and not an expected mode of operation with 387 out-of-service. Harmonic impact on local electric railroad filters/capacitors and impacts on high voltage capacitor switching is not included as part of the scope of this study and will be investigated in a separate study reviewed by ISO-NE, UI, NU and their respective consultants Subsynchronous Torsional Interaction SSTI Subsynchronous torsional interaction (SSTI) of the HVdc with local generation is not included as part of the scope of this study and will be investigated in a separate study reviewed by ISO-NE, UI, NU and their respective consultants. 5.0 SYSTEM UPGRADES REQUIRED System upgrades identified in this analysis are as follows Upgrade of the 1777 line wave trap Scovill Rock SPS (NPCC Type III) to runback the CSC HVdc facilities under export mode to 0 MW for the following conditions o 387 LEO at Scovill Rock o Stuck 7T breaker at Scovill Rock Figure 5.1 illustrates the new proposed interconnection for the Cross Sound HVdc Project without the Scovill Rock breaker addition and 376 line retermination previously approved under Section TransÉnergie U.S. Ltd.