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Central MA Transmission Study

Central MA Transmission Study. Long-term Needs and Solutions. 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)

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Central MA Transmission Study

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  1. Central MA Transmission Study Long-term Needs and Solutions

  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 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

  6. 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

  7. Millbury 115-69 kV Transformers • Loss of either T1 or T2 overloads the remaining small transformer

  8. Recommended Solution to Millbury T1 and T2 Overload Millbury Station – Replace T1 and T2 (115-69 kV) w/ Larger Transformers Cost: $1.5M In-Service Year: 2004

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

  10. Millbury Alternatives • Recommendation: • Replace existing T1 and T2 with larger transformers ($1.5M) • 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 Solution • The recommendation is based on: • Lowest cost • Simpler construction compared to adding a 4th transformer • Less permitting risk than 69 kV line conversion to 115 kV • Existing Millbury transformers can be relocated to Wachusett substation

  12. Ayer 115-69 kV Transformers • Loss of either T1 or T2 overloads the remaining transformer

  13. Recommended Solution to Ayer T4 & T6 Overload Transfer 69 kV Load from Ayer to Pratts Jct, and Install two additional 115-69 kV transformers at Pratts Jct Cost: $1.4M In-Service Year: 2004

  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 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 ($2.46 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)

  16. Ayer Solution • The recommendation is based on: • Lowest cost • Simpler construction at Pratts Junction compared to Ayer • Less permitting risk than 69 kV line conversion to 115 kV

  17. 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

  18. Sandy Pond Alternatives • Preliminary analysis indicates: • Tewksbury location • not effective at unloading Sandy Pond transformers • does not support Central MA voltage • Millbury location • not effective at unloading Sandy Pond transformers • Sandy Pond 3rd transformer • does not support Central MA voltage • design challenges to prevent loss of two transformers for a breaker failure contingency • Pratts Junction, Wachusett, and Quinsigamond Junction locations • off-load Sandy Pond transformers • support Central MA voltage • these alternatives identified for further analysis

  19. Sandy Pond 345-115 kV Transformers • 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

  20. Sandy Pond Alternatives • Install two (2) 345-115 kV transformers at existing Pratts Junction substation and associated upgrades • Install two (2) 345-115 kV transformers at existing Wachusett substation and associated upgrades • Install two (2) 345-115 kV transformers at new Quinsigamond Junction substation and associated upgrades

  21. Pratts Jct Alternative - Costs • Woodside 69 kV Breaker 2004 0.700 M • Pratts Jct Substation 345-115 kV 2006 10.400 M • Pratts Jct Substation 115-69 kV 2006 4.390 M • Replace Pratts J 115 kV Breakers 2006 1.628 M • Replace Pratts J 69 kV Breakers 2006 0.840 M • Reconductor N-40 2006 1.180 M • Reconductor O-141N 2008 0.750 M • Replace W-23E Disconnect 2008 0.020 M • Pratts Jct Substation 345 kV 2010 2.700 M • Convert N-40/W-23 to 115 kV 2012 18.300 M

  22. Wachusett Alternative - Costs • Woodside 69 kV Breaker 2004 0.700 M • Wachusett 345-115 Substation 2006 25.750 M • Wachusett 115-69 kV 2006 2.530 M • Reconductor O-141N 2006 1.500 M • Reconductor M-39 2006 1.000 M • Reconductor N-40 2006 1.000 M • Replace Rolfe Ave Breaker 2006 0.600 M • Reconductor W-175 2006 0.475 M • W. Boylston Upgrades 2006 0.670 M • Replace W-23E Disconnect 2008 0.020 M • Reconductor P-142N 2008 0.175 M

  23. Quinsigamond Jct Alternative - Costs • Woodside 69 kV Breaker 2004 0.700 M • Quinsigamond Jct Sub 2006 27.700 M • Wachusett 115-69 kV Upgrades 2006 4.400 M • Replace O-141S Terminal Equip. 2006 0.500 M • Reconductor M-39 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 • Reconductor N-40 2006 1.180 M • Replace W-23E Disconnect 2008 0.020 M

  24. Recommended Solution to: Sandy Pd T1 and T2 OverloadLow Voltage in Central MA Wachusett Station – Install two new 345-115 kV Transformers (448 MVA) Cost: $25.75M In-Service Year: 2006

  25. Install 345-115 kV Transformers and Substation at Wachusett Sandy Pd 314N 343N Replace Breakers Pratts Jct P-142N 448 MVA 50 MVA O-141N M-39 B-54 G G G G G G G G G G Wachusett 115 kV 69 kV G 345 kV G G G G 448 MVA G G G G 50 MVA A-53 P-142 O-141 Greendale Boylston Millbury Wachusett – Install Two 345-115 kV Autotransformers (448 MVA)

  26. Associated Thermal and Voltage Upgrades Replace all 69 kV breakers at Pratts Jct for Short Ckt Duty. Reconductor N-40 & M-39 w/ 795 ACSR Reconductor P-142 [Wachusett – W Boylston] w/ 1113 ACSR in 2008 Reconductor O-141N [Quinsigimond Jct – Nashua St] w/ 636 ACSS Replace Rolfe Ave 115 kV Breaker

  27. Preferred Sandy Pond Solution • The Wachusett alternative was identified as the preferred alternative based on: • Lowest cost • Better system performance compared to Pratts Junction option • Less permitting risk than Pratts Junction option (W-23 conversion) or Quinsigamond Junction (new substation)

  28. 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 = $0.890 M • Does not change recommendation

  29. Recommended Sandy Pond Solution • Wachusett recommended as the preferred alternative based on: • Lowest cost • Wachusett PW = $32.2 M • Pratts Junction PW = $32.3 M • Quinsigamond Junction PW = $36.1 M (all estimates are study grade – ±25%) • Better system performance compared to Pratts Junction option • Less permitting risk than Pratts Junction option (W-23 conversion) or Quinsigamond Junction (new substation)

  30. Wachusett Construction Issues • Construction Grade estimate developed for the preferred alternative • Identified wetland issues that limit use of existing Wachusett site • Requires construction of Gas Insulated Substation

  31. Wachusett GIS Layout

  32. Revised Wachusett Cost • GIS design increases cost of Wachusett substation by $5 M (+19%) • Revised Comparison of Project Costs • Wachusett (Air): PW = $32.2 M • Pratts Junction: PW = $32.3 M • Quinsigamond Junction: PW = $36.1 M • Wachusett (GIS): PW = $37.2 M

  33. Assessment of Alternatives • Wachusett Alternative • PW = $37.2 M • NEP land at existing substation • Balanced system flows • Supports Millbury/Northboro Rd voltage

  34. Assessment of Alternatives • Quinsigamond Junction Alternative • PW = $36.1 M • Requires purchase of land • Higher permitting risk • Balanced system flows • Supports Millbury/Northboro Rd voltage • Transient Stability analysis and detailed site engineering may identify additional costs

  35. Assessment of Alternatives • Pratts Junction Alternative • PW = $32.3 M • NEP land at existing substation • Requires conversion of N-40/W-23 circuit from 69 kV to 115 kV • Higher permitting risk • Requires construction of a new 345-115 kV substation near Millbury if line cannot be permitted • Unbalanced system flows • Eight (8) 115-69 kV transformers at Pratts Junction • Heavy reliance on converted N-40/W-23 circuit to Northboro Road • Support for Millbury/Northboro Rd voltage • Transient Stability analysis and detailed site engineering may identify additional costs

  36. Recommendation • The Wachusett location is still the recommended option • Technically superior and less permitting risk than Pratts Junction option • Similar cost and less permitting risk than Quinsigamond Junction option • Changing recommendation will delay installation by at least one year • Additional engineering minimizes uncertainty with the Wachusett option compared to Pratts Junction or Quinsigamond Junction

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