Northport - Norwalk Harbor Cable (NNC) Tie line

Transcription

1 September 9, 008 Northport - Norwalk Harbor Cable (NNC) Tie line Technical Assessment of Operating up to NNC Inter Tie STE Ratings Executive Summary Three (3) 38kV submarine cable circuits (Lines 60, 60, and 603) have been installed from Northeast Utilities (NU) Norwalk Harbor 6J Substation to Long Island Power Authorities (LIPA) Northport 6F Substation to replace the existing single 38kV circuit. The new cables were put in service on July 9, 008. NNC single cable operation while switching has caused a concern with ISO-NE and the NYISO. The switching method presently agreed upon involves switching one cable at a time, each cable requiring approximately 45 minutes to properly operate disconnects, fuses and ground switches. The single cable operation scenario has caused transaction cuts between New England and New York and poses system reliability concerns. In order to prevent single cable operation from causing transaction cuts or having emergency states invoked, the NYISO is being requested to grant an exception to Normal Transfer Criteria and allow the NNC tie line to be solved to the post contingency STE rating instead of the LTE rating (for any one cable; 60, 60 or 603). Such an exception will benefit both ISOs as well as both Connecticut and New York state electric customers. Thermal and voltage analysis study results demonstrate that there will be no adverse impact on system reliability as a result of granting the exception by the NYISO / NYSRC to allow any one NNC cable to be solved to the post contingency STE rating instead of the LTE rating. Phase angle regulation capability is available at Northport to reduce NNC loading to the NNC LTE rating within 5 minutes without causing any other facility to be loaded beyond its LTE rating. Use of the STE rating rather than the LTE rating provides for a consistent operating practice with ISO-NE. References: New York State Reliability Council (NYSRC) Reliability Rule B-R and E-R. Study Assumptions Study time period: Summer 008 Load flow base case: - Summer 008 peak load case - All lines in service - LIPA imports from NYISO via Y49 and Y50 maximized - 86 MW wheel to Jamaica - Shoreham CSC set at 330 MW import to Long Island - Neptune set at 660 MW import to Long Island

2 September 9, NNC single cable operation thermal ratings: 55 / 9 / 430 MVA (normal / LTE / STE) for any individual cable - For reference: NNC three (3) cable operation thermal ratings for any individual cable: 00 / / 75 MVA (norm / LTE / STE); respecting prior cables (#385) thermal ratings Norwalk Harbor 5/38kV Auto Transformer Data - Thermal Ratings: 40/ 40/ 449 MVA (normal / LTE / STE) - Impedance: assume the impedance of the new replacement auto (data provided by ISO-NE), as this auto is scheduled for replacement in October/November 008 Thermal and Voltage Technical Assessment Two main load flow base cases were set up for this technical assessment. These cases represent the bounds of flows for imports to and exports from LI at the present normal FERC scheduling limit of 00 MW. - Import to LI from CT o Case simulates a 00 MW flow from Connecticut to Long Island over the NNC inter tie (single cable operation) - Export from LI to CT o Case simulates a 00 MW flow from Long Island to Connecticut over the NNC inter tie (single cable operation) To determine the impact of operating to the post contingency STE rating, a severe system contingency was simulated for each of the above cases. For testing Long Island imports, case, the loss of the Shoreham Cross Sound Cable (CSC) HVDC (loss of 330 MW) was simulated. For testing Long Island exports, case, the loss of Millstone Unit #3 (loss of approximately 00 MW) was simulated. Pre and post contingency PSS/E load flow plots for a portion of the power system in the vicinity of Northport (Long Island) and Norwalk Harbor (Connecticut) are provided in the attached Appendix for reference. These plots summarize pre and post contingency line flows and bus voltages. Discussion of Results Case - Import to LI of 00 MW No normal overloads are observed in this case. Assuming operation to post contingency LTE ratings, the following contingency overload(s) were observed: Table 008 Summer Peak Load Flow Analysis Results NNC single cable operation Pre-contingency flow = 00 MW to L.I. Limiting Element Loss of PERCENT LOADING NNC (LTE = 9 MVA) Shoreham CSC 5% of LTE

3 September 9, 008 Since the post contingency flow is well below the single cable STE rating of 430 MVA, solving to the STE rating will mitigate this overload. The Northport phase angle regulator (PAR) associated with NNC is available to reduce NNC loading to the NNC LTE rating within 5 minutes without causing any other facility to be loaded beyond its LTE rating. No pre or post contingency voltage violations were detected. Case - Export to CT of 00 MW No normal overloads are observed in this case. Assuming operation to post contingency LTE ratings, the following contingency overload(s) were observed: Table 008 Summer Peak Load Flow Analysis Results NNC single cable operation Pre-contingency flow = 00 MW to CT. Limiting Element Loss of PERCENT LOADING NNC (LTE = 9 MVA) Millstone #3 8% of LTE Since the post contingency flow is well below the single cable STE rating of 430 MVA, solving to the STE rating will mitigate this overload. The Northport phase angle regulator (PAR) associated with NNC is available to reduce NNC loading to the NNC LTE rating within 5 minutes without causing any other facility to be loaded beyond its LTE rating. No pre or post contingency voltage violations were detected. Conclusions This technical assessment demonstrates that there will be no adverse impact on system reliability as a result of granting the exception by the NYISO / NYSRC to allow the NNC tie line to be solved to the post contingency STE rating instead of the LTE rating (for any one cable; 60, 60 or 603). Phase angle regulation capability is available at Northport to reduce NNC loading to the NNC LTE rating within 5 minutes without causing any other facility to be loaded beyond its LTE rating. For single cable operation, it is expected that the maximum post contingency phase angle regulator adjustment will be on the order of 50 to 60 MW. 3

4 September 9, 008 This exception will not adversely impact existing transfer capabilities between New England and New York and is expected to improve overall system reliability by: - relieving existing restrictions on New York New England transfer limits which may arise in real time due to: o loss of Millstone Unit #3 o loss of Pleasant Valley Long Mountain 398 line o loss of Shoreham CSC o other NY or CT system contingencies - mitigating the need for transaction curtailments 4

5 September 9, 008 APPENDIX NNC One Line Diagram & Pre and Post Contingency Load Flow Summary Plots 5

6 DRAFT

7 938 ELWOOD 934 NRTHPRT CASE : NNC - one cable I/S 00 MW Import to LI NRTPTG GLNBROOK ELWOOD 48.6R 907 NRTPTG4 037 NWLK HAR R 904 NRTPTG 0369 RYTN J A NORWALK PILGRIM R 9343 NRTHPT P NNC Inter tie (one cable I/S) NRTPTG 0366 NORHR R NRTHPT ELYAVE SASCO CR R NORHAR# Bus - VOLTAGE (KV/PU) Branch - MVA/% OF RATE A NORHAR# RYTN J B FLAX HIL Equipment - MW/MVAR 00.0%RATEA.050OV0.950UV H

8 938 ELWOOD 934 NRTHPRT CASE a: NNC - one cable I/S Post Contingency loss of Shoreham CSC ELWOOD 5% I NRTPTG3 60% I 63.R 907 NRTPTG4 037 NWLK HAR GLNBROOK % I % I 60.3R 904 NRTPTG 0369 RYTN J A % I NORWALK 9355 PILGRIM % I 59% I R NRTHPT P NNC Inter tie (one cable I/S) % I % I % I % I NRTHPT 6% I % I NRTPTG 59% I 5.4R % I 55% I NORHR NORHAR# % I 80.0H % I ELYAVE % I 44% I SASCO CR % I Bus - VOLTAGE (KV/PU) Branch - MVA/% OF RATE B Equipment - MW/MVAR 00.0%RATEB.050OV0.950UV NORHAR# % I 60.0H % I RYTN J B % I FLAX HIL % I

9 938 ELWOOD 934 NRTHPRT CASE b: NNC - one cable I/S Post Contingency loss of Shoreham CSC NNC flow reduced to LTE rating ELWOOD 6% I NRTPTG3 60% I 63.5R 907 NRTPTG4 037 NWLK HAR GLNBROOK % I % I 60.6R 904 NRTPTG 0369 RYTN J A % I NORWALK 9355 PILGRIM % I % I % I NRTHPT 58% I % I % I 48.7R 905 NRTPTG 59% I 53.0R NRTHPT P % I 47% I NNC Inter tie (one cable I/S) 0366 NORHR NORHAR# % I 80.0H % I 43% I ELYAVE % I 45% I SASCO CR % I 37% I Bus - VOLTAGE (KV/PU) Branch - MVA/% OF RATE B Equipment - MW/MVAR 00.0%RATEB.050OV0.950UV NORHAR# % I 60.0H % I RYTN J B % I FLAX HIL % I

10 938 ELWOOD 934 NRTHPRT CASE : NNC - one cable I/S 00 MW EXPORT to CT NRTPTG GLNBROOK ELWOOD 5.R 907 NRTPTG4 037 NWLK HAR R 904 NRTPTG 0369 RYTN J A NORWALK PILGRIM R 9343 NRTHPT P NNC Inter tie (one cable I/S) NRTPTG 0366 NORHR NRTHPT 33.0R ELYAVE SASCO CR R NORHAR# Bus - VOLTAGE (KV/PU) Branch - MVA/% OF RATE A NORHAR# RYTN J B FLAX HIL Equipment - MW/MVAR 00.0%RATEA.050OV0.950UV R

11 938 ELWOOD 934 NRTHPRT CASE a: NNC - one cable I/S Post Contingency loss of Millstone # ELWOOD 9% I NRTPTG3 7% I 5.R 907 NRTPTG4 037 NWLK HAR GLNBROOK % I % I 50.3R 904 NRTPTG 0369 RYTN J A % I NORWALK 9355 PILGRIM % I 70% I R % I 44% I 4% I NRTHPT % I NRTPTG 70% I 30.9R NRTHPT P % I 6% I NNC Inter tie (one cable I/S) 0366 NORHR NORHAR# % I 54.R % I 9% I ELYAVE % I 60% I SASCO CR % I 44% I Bus - VOLTAGE (KV/PU) Branch - MVA/% OF RATE B Equipment - MW/MVAR 00.0%RATEB.050OV 0.950UV NORHAR# % I 54.R % I RYTN J B % I FLAX HIL % I

12 938 ELWOOD 934 NRTHPRT CASE b: NNC - one cable I/S Post Contingency loss of Millstone #3 NNC flow reduced to LTE rating ELWOOD 3% I NRTPTG3 7% I 49.5R 907 NRTPTG4 037 NWLK HAR GLNBROOK % I % I 47.8R 904 NRTPTG 0369 RYTN J A % I NORWALK 9355 PILGRIM % I 70% I R % I 45% I 4% I NRTHPT % I NRTPTG 70% I 9.6R NRTHPT P % I 46% I NNC Inter tie (one cable I/S) 0366 NORHR NORHAR# % I 46.9R % I 3% I ELYAVE % I 58% I SASCO CR % I 44% I Bus - VOLTAGE (KV/PU) Branch - MVA/% OF RATE B Equipment - MW/MVAR 00.0%RATEB.050OV0.950UV NORHAR# % I 46.9R % I RYTN J B % I FLAX HIL % I