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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

Central MA Transmission Study

Long-term Needs and Solutions

Presentation to:

NEPOOL Reliability Committee

January 18, 2005

central ma infrastructure study
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)
short term upgrades
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
long term upgrades
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
long term upgrades1
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
long term needs in central ma
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
existing problems
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

review of recommended solutions
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
millbury alternatives
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)
millbury replace two 2 115 69 kv autotransformers

Millbury Substation

56 MVA

56 MVA

Replace T1 and T2 (50 MVA) w/ 56 MVA Transformers

Millbury – Replace Two (2) 115-69 kV Autotransformers
millbury solution
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
ayer alternatives
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)
pratts jct sub install two 2 additional 115 69 kv autotransformers

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
ayer solution
Ayer Solution
  • The recommendation is based on:
    • Lowest cost
    • Simpler construction at Pratts Junction compared to Ayer
sandy pond 345 115 kv transformers
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
sandy pond alternatives
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
evaluation of alternatives
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
recommended sandy pond solution
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)
transient stability analysis
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
wachusett construction issues
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
review of alternatives
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
pratts junction site
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
quinsigamond junction site
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
wachusett alternative costs
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
pratts jct alternative costs
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
quinsigamond jct alternative costs
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
cost comparison
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

technical comparison
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)
environmental comparison
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
operational comparison
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
recommendation
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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