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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

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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)


Geographic location of central ma

Geographic Location of Central MA


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

      • WachusettPW = $32.2 M

      • Pratts JunctionPW = $32.3 M

      • Quinsigamond JunctionPW = $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 gis layout

Wachusett GIS Layout


Wachusett alternative costs

Wachusett Alternative - Costs

  • Woodside 69 kV Breaker2004 0.700 M

  • Wachusett 2nd 115-69 kV Xfmr2006 2.530 M

  • Wachusett 345-115-69 kV2006 41.959 M

  • O-141/P-142 Protection Upgrades2006 0.440 M

  • Reconductor O-141N2006 1.500 M

  • Reconductor P-142N 2006 0.125 M

  • Reconductor M-392006 1.000 M

  • Reconductor N-402006 1.181 M

  • Replace Rolfe Ave Breaker2006 0.366 M

  • Reconductor W-1752006 0.475 M

  • W. Boylston Upgrades2006 0.440 M

  • Replace W-23E Disconnect2006 0.020 M


Pratts jct alternative costs

Pratts Jct Alternative - Costs

  • Woodside 69 kV Breaker2004 0.700 M

  • Pratts Jct Substation 345-115 kV200625.700 M

  • Pratts Jct Substation 115-69 kV2006 4.885 M

  • Replace Pratts J 115 kV Breakers2006 3.225 M

  • Replace Pratts J 69 kV Breakers2006 0.840 M

  • Reconductor N-402006 1.180 M

  • Reconductor O-141N2006 0.750 M

  • Replace W-23E Disconnect2006 0.020 M

  • Convert N-40/W-23 to 115 kV201218.300 M


Quinsigamond jct alternative costs

Quinsigamond Jct Alternative - Costs

  • Woodside 69 kV Breaker2004 0.700 M

  • Quinsigamond Jct Sub200641.484 M

  • Wachusett 115-69 kV Upgrades2006 5.475 M

  • Replace O-141S Terminal Equip. 2006 0.500 M

  • Reconductor M-392006 1.000 M

  • Reconductor N-402006 1.180 M

  • Replace Rolfe Avenue Breaker2006 0.366 M

  • Reconductor W-1752006 0.475 M

  • Replace Pratts J 69 kV Breakers2006 0.840 M

  • Replace W-23E Disconnect2008 0.020 M


Cost comparison

Cost Comparison

AlternativeTotal CostPresent 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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