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Central MA Transmission Study

Central MA Transmission Study. Long-term Needs and Solutions Presentation to: NEPOOL Reliability Committee January 18, 2005. Central MA Infrastructure Study. Study Initiated in 2001 Identified Short-term and Long-term Upgrades to ensure reliability of service

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Central MA Transmission Study

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  1. Central MA Transmission Study Long-term Needs and Solutions Presentation to: NEPOOL Reliability Committee January 18, 2005

  2. Central MA Infrastructure Study • Study Initiated in 2001 • Identified Short-term and Long-term Upgrades to ensure reliability of service • Study area covers region bounded by: • Sandy Pond (NE) • Pratts Jct (NW) • Carpenter Hill (SW) • Northboro Rd (SE)

  3. Geographic Location of Central MA

  4. Short-term Upgrades • 18.4 applications approved in February 2002 • 63 MVAr Capacitor Bank at Millbury • 54 MVAr Capacitor Bank at Northboro Road • Also adjusted taps on Ayer 115-69 kV transformers • In-service for Summer 2002

  5. Long-term Upgrades • 18.4 applications approved in April 2004 • Install 69 kV circuit breaker at Woodside • Install 2nd 115-69 kV transformer at Wachusett • Replace Millbury T1 and T2 115-69 kV transformers • Install two additional 115-69 kV transformers at Pratts Junction, replace 69 kV circuit breakers, and transfer one-half Prospect Street load • Wachusett 345-115-69 kV substation • Reconductor 115 kV lines O-141N, P-142, W-175 • Reconductor 69 kV lines M-39, N-40 • Replace 115 kV circuit breaker at Rolfe Ave • Upgrade W. Boylston protection systems • Replace W-23E 69 kV line disconnect

  6. Long-term Upgrades • Transmission Cost Allocation presentation made to NEPOOL RC in April and May 2004 • Uncertainty regarding GIS costs for Wachusett substation resulted in deferral of application • Additional engineering has been performed for the three 345-115 kV substation sites • Firm bids received for the GIS

  7. Long-term Needs in Central MA • Needs identified in three main areas • Millbury • 115-69 kV transformer loading • 115 kV voltage • Sandy Pond • 345-115 kV transformer loading • Ayer • 115-69 kV transformer loading • 69 kV voltage

  8. Existing Problems 4. Ayer 69 kV Area voltage drops below 0.9 pu for K-137 + L-138W DCT contingency 3. Ayer T4 & T6 Overload for loss of each other 2. Sandy Pd T1 & T2 overload for loss of each other 5. Shrewsbury 69 kV Breaker overdutied 1. Millbury T1 & T2 Overload for loss of each other

  9. Review of Recommended Solutions • Millbury: • Replace existing T1 and T2 with larger transformers • Ayer: • Transfer Prospect Street from 69 kV line V-22E to U-21S; install two (2) 115-69 kV transformers at Pratts Jct and replace eight (8) 69 kV breakers • Wachusett: • Install two (2) 345-115 kV transformers and 345 kV and 115 kV GIS at existing Wachusett substation and associated upgrades

  10. Millbury Alternatives • Recommendation: • Replace existing T1 and T2 with larger transformers ($1.5 M) • Alternatives: • Add fourth 115-69 kV transformer into dedicated bus position ($3.8 M) • Add fourth 115-69 kV transformer tapped off Q-143, relocate I-35 ($2.1 M) • Convert 69 kV line X-24 to 115 kV to unload existing transformers ($14.9 M)

  11. Millbury Substation 56 MVA 56 MVA Replace T1 and T2 (50 MVA) w/ 56 MVA Transformers Millbury – Replace Two (2) 115-69 kV Autotransformers

  12. Millbury Solution • The recommendation is based on: • Lowest cost • Simpler construction compared to adding a 4th transformer • Existing Millbury transformers can be relocated to Wachusett substation

  13. Ayer Alternatives • Recommendation: • Transfer Prospect Street from 69 kV line V-22E to U-21S; install two (2) 115-69 kV transformers at Pratts Jct and replace eight (8) 69 kV breakers ($2.47 M) • Alternatives: • Install (2) 115-69 kV transformers at Ayer ($4.5 M) • Convert 69 kV line V-22 to 115 kV to unload existing transformers ($13.7 M)

  14. Transfer ½ of Prospect St Load from V-22E to U-21S 56 MVA 56 MVA Two Additional 115-69 kV Autos at PJ Pratts Jct Sub – Install Two (2) Additional 115-69 kV Autotransformers

  15. Ayer Solution • The recommendation is based on: • Lowest cost • Simpler construction at Pratts Junction compared to Ayer

  16. Sandy Pond 345-115 kV Transformers • Loss of either T1 or T2 overloads the remaining transformer • Considered installation of new 345-115 kV transformers at: • Sandy Pond • Tewksbury • Pratts Junction • Millbury • Wachusett • Quinsigamond Junction

  17. Sandy Pond Alternatives • Preliminary analysis indicated: • Sandy Pond and Tewksbury do not support Central MA voltage • Millbury and Tewksbury not effective at unloading Sandy Pond transformers • Pratts Junction, Wachusett, and Quinsigamond Junction locations meet both needs

  18. Evaluation of Alternatives • The Pratts Junction, Wachusett, and Quinsigamond Junction sites were fully evaluated to provide: • A list of associated upgrades based on thermal and voltage analysis • Study grade estimates for all upgrades associated with each option

  19. Recommended Sandy Pond Solution • Initial recommendation made based on air-insulated substation estimates for Wachusett, Pratts Junction, and Quinsigamond Junction • Wachusett alternative recommended based on: • Lowest cost • Wachusett PW = $32.2 M • Pratts Junction PW = $32.3 M • Quinsigamond Junction PW = $36.1 M (based on ±25% study grade estimates) • Better system performance compared to Pratts Junction option • Less environmental impact than Pratts Junction option (N-40/W-23 conversion) or Quinsigamond Junction (new substation)

  20. Transient Stability Analysis • Analysis conducted for the preferred alternative • West Boylston substation becomes a bulk power system substation • High-Speed pilot protection required for P-142 line from Wachusett to West Boylston • Incremental Cost = $0.880 M • Did not change recommendation

  21. Wachusett Construction Issues • Construction Grade estimate developed for the preferred alternative • Identified wetland issues that limit use of existing Wachusett site • Encroachment on intermittent stream and associated wetlands that are tributaries to Wachusett Reservoir • Wetland replication not permitted if alternatives exist • Gas Insulated Substation required

  22. Review of Alternatives • Additional engineering required to evaluate alternative sites to obtain MA DTE, NEPOOL, and National Grid approval • Additional engineering identified issues with Pratts Junction and Quinsigamond Junction sites

  23. Pratts Junction Site • Site preparation work required for air insulated substation would encroach on perennial stream • Impacts to estimated habitat and priority habitat for species protected by MA Endangered Species Act • Gas Insulated Substation requires filling an environmentally critical area • High likelihood this location would not be approved if alternatives exist

  24. Quinsigamond Junction Site • Air insulated substation would impact perennial stream and associated wetlands • Gas Insulated Substation required • Research identified former use of substation site as oil company tank farm • Records not available to assess additional cost if soil contamination is identified

  25. Wachusett GIS Layout

  26. Wachusett Alternative - Costs • Woodside 69 kV Breaker 2004 0.700 M • Wachusett 2nd 115-69 kV Xfmr 2006 2.530 M • Wachusett 345-115-69 kV 2006 41.959 M • O-141/P-142 Protection Upgrades 2006 0.440 M • Reconductor O-141N 2006 1.500 M • Reconductor P-142N 2006 0.125 M • Reconductor M-39 2006 1.000 M • Reconductor N-40 2006 1.181 M • Replace Rolfe Ave Breaker 2006 0.366 M • Reconductor W-175 2006 0.475 M • W. Boylston Upgrades 2006 0.440 M • Replace W-23E Disconnect 2006 0.020 M

  27. Pratts Jct Alternative - Costs • Woodside 69 kV Breaker 2004 0.700 M • Pratts Jct Substation 345-115 kV 2006 25.700 M • Pratts Jct Substation 115-69 kV 2006 4.885 M • Replace Pratts J 115 kV Breakers 2006 3.225 M • Replace Pratts J 69 kV Breakers 2006 0.840 M • Reconductor N-40 2006 1.180 M • Reconductor O-141N 2006 0.750 M • Replace W-23E Disconnect 2006 0.020 M • Convert N-40/W-23 to 115 kV 2012 18.300 M

  28. Quinsigamond Jct Alternative - Costs • Woodside 69 kV Breaker 2004 0.700 M • Quinsigamond Jct Sub 2006 41.484 M • Wachusett 115-69 kV Upgrades 2006 5.475 M • Replace O-141S Terminal Equip. 2006 0.500 M • Reconductor M-39 2006 1.000 M • Reconductor N-40 2006 1.180 M • Replace Rolfe Avenue Breaker 2006 0.366 M • Reconductor W-175 2006 0.475 M • Replace Pratts J 69 kV Breakers 2006 0.840 M • Replace W-23E Disconnect 2008 0.020 M

  29. Cost Comparison Alternative Total Cost Present Worth Pratts Jct $55.623 M $50.886 M* Quinsigamond Jct $52.041 M $52.041 M Wachusett $54.696 M $54.696 M * 2012 cost to convert 69 kV lines N-40/W-23 to 115 kV discounted to 2006

  30. Technical Comparison • All three alternatives provide adequate voltage support and unload Sandy Pond transformers • Wachusett and Quinsigamond Junction provide the most reliable system • Most balanced system power flows • Better line out (n-1) performance • Less sensitive to future system changes (e.g. load forecast)

  31. Environmental Comparison • All three sites require Gas Insulated Substations • Pratts Junction: • Requires filling an environmentally sensitive area • Requires conversion of 69 kV lines to 115 kV • Quinsigamond Junction • Development of a new site • Potential soil contamination issues from past use as tank farm • Wachusett • Existing site • Gas Insulated Substation addresses environmental concerns

  32. Operational Comparison • Similar cutover plans for 345 kV substations • Two outages of four days to relocate lines and cutover substation • Pratts Junction requires outage of N-40/W-23 lines in 2012 for conversion to 115 kV • Impacts to voltage support in the Northboro Road area

  33. Recommendation • The Wachusett alternative is recommended • Additional 7% cost compared to Pratts Junction is offset by: • Better technical performance • Less environmental impact • Less operational impact during construction • Less uncertainty regarding cost and schedule • Additional 5% cost compared to Quinsigamond Junction offset by: • Less environmental impact • Less uncertainty regarding cost and schedule

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