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Southwest Connecticut Reliability Study Update

This presentation provides an update on the Southwest Connecticut Reliability Study, with the objectives of formulating a long-term transmission solution that satisfies reliability criteria, eliminates operating difficulties, and mitigates congestion. The presentation covers the current status, history, problems found, transmission alternatives, and recommended solutions, including the proposed 345-kV loop.

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Southwest Connecticut Reliability Study Update

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  1. Southwest ConnecticutReliability Study Update Presentation to the TEAC January 24, 2002 Frank Mezzanotte

  2. Study Objective • Formulate a long-term transmission solution for Southwestern Connecticut that • Satisfies reliability criteria • Eliminates operating difficulties • Eliminates first contingency (including double circuit) overloads • Eliminates threat of voltage collapse • Mitigates congestion by increasing SWCT and Nor-Stam transfer limits

  3. Study Objective • And that • Provides the base transmission infrastructure to support additional generation expansion and retirements • Eliminates short circuit restrictions • Eliminates conditional dependence of generator operation • Provides an operable system during construction periods • Allows increased bi-directional transfer capability to other areas

  4. Staged Analysis • Stage 1: Perform thermal and voltage analysis @ 27700MW; Formulate solution; Check field feasibility with design engineers; Perform preliminary short-circuit analysis. • Stage 2: Further test thermal & voltage @ other load levels; Perform preliminary dynamic analysis & transfer limit analysis; finalize short circuit & dynamic analyses

  5. Current Status - Stage 1 • Draft Report for Stage 1 Complete • Text portion of Volume I will be available today after the presentations • Volume I Appendices & Volumes II-IV output listings will be available through ISO Customer Service by request only

  6. Current Status - Stage 2 • Preliminary dynamic analysis complete • Transfer limit analysis in the works • Preparing additional base cases • Thorough area short circuit analysis underway • Plan to have Stage 2 draft report complete by end of 1st quarter

  7. History • 345 kV loop originally proposed in 1970s postponed due to • Fluctuations in economy and load growth • 115 kV system improvements • Emphasis on optimum coordination of local generator and transmission maintenance

  8. History (cont.) • Loads increased 25% in 1990s • Sale of existing generators resulted in loss of control of optimum coordination of local generator and transmission maintenance • More uncertainty surrounding future availability and performance of local generation

  9. Problems Found • 28 instances of post contingent load flow non-convergence due to voltage collapse • 24 instances of normal overloads with all facilities normally in service (1% to 33% overloaded)

  10. Problems Found (cont.) • Most severe single line contingencies • L/O Devon-Trumbull-Old Town (1710) creates a 10% LTE overload on the 1730 line • L/O Devon-Trumbull-Weston (1730) creates a 15% LTE overload on the 1710 line • L/O Pequonnock-Compo (1130) creates a 13% LTE overload on Pequonnock-Ash Creek (91001) • L/O Pequonnock-Ash Creek (91001) creates a 14% LTE overload on Old Town-Hawthorn

  11. Problems Found (cont.) • Critical double circuit contingencies • L/O 1710 & 1730 lines (23 miles) • Up to 42% LTE overloads on lines along the Plumtree to Norwalk path & the Pequonnock to Glenbrook path • L/O 1130 & 91001 lines • Up to 69% LTE overloads on lines along the Devon to Norwalk path & the Norwalk to the south path

  12. Transmission Alternatives 1) Various scenarios upgrading 115 kV lines from Frost Bridge, Southington and East Shore 2) 115 kV Plan • Upgrade Devon to Norwalk 115, Ckt 1 • Upgrade Devon to Norwalk 115, Ckt 2 • Upgrade Peaceable to Norwalk 115 • Build new Devon to Norwalk 115 • Build new Pequonnock to Norwalk 115 • Reconfigure Norwalk - Norwalk Harbor - Glenbrook 115 kV System

  13. Transmission Alternatives (cont.) 3) Case 2 with Plumtree 115 kV Phase Angle Regulator 4) Case 3 with with Beseck to Devon 345 kV 5) 230 kV Loop: Plumtree - Norwalk - Beseck

  14. Recommended Solution: 345-kV Loop • Plumtree - Norwalk - Pequonnock - Devon - Beseck 345kV • 2005 / 2006 In-service date • ~100 miles - mostly on existing ROW • Includes associated 115kV improvements • ~$500 to 600 million • Meets study objectives

  15. Recommended Solution: 345-kV Loop • Preliminary Planning transfer limits • SWCT: in excess of 2900 MW • Nor-Stam: in excess of 1300 MW • Will probably eliminate the need for the Nor-Stam interface definition • Construction Sequencing • NU has proposed a phased approach • ISO is currently investigating impacts

  16. Upgrade Recommendations 1. Add new 345kV Substations at Plumtree, Norwalk, Pequonnock, Devon, & Beseck Junction2. Add new 345kV loop from Plumtree to Beseck Junction3. Add (2) 3-150MVA auto transformers at Norwalk, (1) at Pequonnock, and (1) at Devon4. Add (1) 3-200 MVA auto transformers at Pequonnock to shift Bridgeport Energy output to 345kV5. Rearrange / add to 115kV between Norwalk, Norwalk Harbor and Glenbrook 6. Establish new 115kV substation adjacent to Devon (East Devon)7. Other 115kV work a/w new 345kV structures

  17. 1/9/02 8

  18. 1/9/02 5

  19. Existing‘Simplified’1-Line Long Mountain FrostBridge Southington Plumtree BeseckJunction Devon SWCT Pequonnock Norwalk Key: 115 kV 345 kV Interface NOR-STAM 1/9/02 6

  20. Proposed‘345 kV Loop’1-Line Long Mountain FrostBridge Southington Plumtree BeseckJunction Devon SWCT Pequonnock Norwalk Key: 115 kV 345 kV Proposed 345 kV NOR-STAM Interface 1/9/02 7

  21. In Summary • Stage 1 draft report complete -recommending the 345-kV loop as the ultimate solution • Stage 2 in progress - aiming for completion by end of 1st quarter

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