Central MA Transmission StudyLong-term Needs and Solutions Presentation to:

NEPOOL Reliability CommitteeJanuary 18, 2005

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

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 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 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 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

1. Millbury T1 & T2 Overload for loss of each other

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

4. Ayer 69 kV Area voltage drops below 0.9 pu for K-137 + L-138W DCT contingency

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 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

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

56 MVA

Millbury Substation

56 MVA

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 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

56 MVA

56 MVA Two Additional 115-69 kV Autos at PJ

Transfer ½ of Prospect St Load from V-22E to U-21S

Ayer Solution The recommendation is based on:

Lowest cost Simpler construction at Pratts

Junction compared to Ayer

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 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 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 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 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 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 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 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 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 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 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 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 ComparisonAlternative Total Cost Present

WorthPratts Jct $55.623 M $50.886 M*Quinsigamond Jct $52.041 M $52.041 MWachusett $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 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 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 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 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