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Southwest ConnecticutReliability Study Update

Presentation to the TEAC

January 24, 2002

Frank Mezzanotte

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Study Objective

• Formulate a long-term transmission solution for Southwestern Connecticut that

– Satisfies reliability criteria• Eliminates operating difficulties• Eliminates first contingency (including double

circuit) overloads• Eliminates threat of voltage collapse

– Mitigates congestion by increasing SWCT and Nor-Stam transfer limits

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Study Objective

And that•Provides the base transmission infrastructure to support additional generation expansion and retirements

•Eliminates short circuit restrictions•Eliminates conditional dependence of generator operation•Provides an operable system during construction periods•Allows increased bi-directional transfer capability to other areas

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Staged Analysis

• Stage 1: Perform thermal and voltage analysis @ 27700MW; Formulate solution; Check field feasibility with design engineers; Perform preliminary short-circuit analysis.

• Stage 2: Further test thermal & voltage @ other load levels; Perform preliminary dynamic analysis & transfer limit analysis; finalize short circuit & dynamic analyses

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Current Status - Stage 1

• Draft Report for Stage 1 Complete

• Text portion of Volume I will be available today after the presentations

• Volume I Appendices & Volumes II-IV output listings will be available through ISO Customer Service by request only

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Current Status - Stage 2

• Preliminary dynamic analysis complete

• Transfer limit analysis in the works

• Preparing additional base cases

• Thorough area short circuit analysis underway

• Plan to have Stage 2 draft report complete by end of 1st quarter

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History

• 345 kV loop originally proposed in 1970s postponed due to– Fluctuations in economy and load growth– 115 kV system improvements– Emphasis on optimum coordination of local

generator and transmission maintenance

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History (cont.)

• Loads increased 25% in 1990s

• Sale of existing generators resulted in loss of control of optimum coordination of local generator and transmission maintenance

• More uncertainty surrounding future availability and performance of local generation

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Problems Found

• 28 instances of post contingent load flow non-convergence due to voltage collapse

• 24 instances of normal overloads with all facilities normally in service (1% to 33% overloaded)

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Problems Found (cont.)

• Most severe single line contingencies– L/O Devon-Trumbull-Old Town (1710) creates

a 10% LTE overload on the 1730 line– L/O Devon-Trumbull-Weston (1730) creates a

15% LTE overload on the 1710 line– L/O Pequonnock-Compo (1130) creates a 13%

LTE overload on Pequonnock-Ash Creek (91001)

– L/O Pequonnock-Ash Creek (91001) creates a 14% LTE overload on Old Town-Hawthorn

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Problems Found (cont.)

• Critical double circuit contingencies– L/O 1710 & 1730 lines (23 miles)

• Up to 42% LTE overloads on lines along the Plumtree to Norwalk path & the Pequonnock to Glenbrook path

– L/O 1130 & 91001 lines• Up to 69% LTE overloads on lines along the Devon

to Norwalk path & the Norwalk to the south path

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Transmission Alternatives

1) Various scenarios upgrading 115 kV lines from Frost Bridge, Southington and East Shore

2) 115 kV Plan– Upgrade Devon to Norwalk 115, Ckt 1

– Upgrade Devon to Norwalk 115, Ckt 2

– Upgrade Peaceable to Norwalk 115

– Build new Devon to Norwalk 115

– Build new Pequonnock to Norwalk 115

– Reconfigure Norwalk - Norwalk Harbor - Glenbrook 115 kV System

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Transmission Alternatives (cont.)

3) Case 2 with Plumtree 115 kV Phase Angle Regulator

4) Case 3 with with Beseck to Devon 345 kV

5) 230 kV Loop: Plumtree - Norwalk - Beseck

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Recommended Solution: 345-kV Loop

• Plumtree - Norwalk - Pequonnock - Devon - Beseck 345kV– 2005 / 2006 In-service date

– ~100 miles - mostly on existing ROW

– Includes associated 115kV improvements

– ~$500 to 600 million

• Meets study objectives

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Recommended Solution: 345-kV Loop

• Preliminary Planning transfer limits– SWCT: in excess of 2900 MW

– Nor-Stam: in excess of 1300 MW

– Will probably eliminate the need for the Nor-Stam interface definition

• Construction Sequencing– NU has proposed a phased approach

– ISO is currently investigating impacts

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1. Add new 345kV Substations at Plumtree, Norwalk, Pequonnock, Devon, & Beseck Junction2. Add new 345kV loop from Plumtree to Beseck Junction3. Add (2) 3-150MVA auto transformers at Norwalk, (1) at Pequonnock, and (1) at Devon4. Add (1) 3-200 MVA auto transformers at Pequonnock to shift Bridgeport Energy output to 345kV5. Rearrange / add to 115kV between Norwalk, Norwalk Harbor and Glenbrook6. Establish new 115kV substation adjacent to Devon (East Devon)7. Other 115kV work a/w new 345kV structures

Upgrade Recommendations

1/9/02 8

1/9/02 5

Long Mountain

FrostBridge

Southington

BeseckJunction

Devon

PequonnockNorwalk

Plumtree

Existing‘Simplified’

1-Line

115 kV345 kV

InterfaceInterfaceNOR-STAMNOR-STAM

SWCTSWCT

Key:

1/9/02 6

Long Mountain

FrostBridge

Southington

BeseckJunction

Devon

PequonnockNorwalk

Plumtree

Proposed‘345 kV Loop’

1-Line

NOR-STAMNOR-STAM

SWCTSWCT

115 kV345 kVProposed 345 kVInterfaceInterface

Key:

1/9/02 7

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In Summary

• Stage 1 draft report complete -recommending the 345-kV loop as the ultimate solution

• Stage 2 in progress - aiming for completion by end of 1st quarter