NSTAR 345KV TRANSMISSION RELIABILITY PROJECT PLAN

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NSTAR 345KV TRANSMISSION RELIABILITY PROJECT PLAN
Presentation to the New England
Stakeholders January 31, 2005
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AGENDA

• 345 kV Project Overview
• Project Need
• Project Cost
• Project Alternatives
• Project Design

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345 KV PROJECT OVERVIEW
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Planned 345kV Supply To Downtown Boston Mitigates
These Concerns
Proposed 345 kV Transmission Cable
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NSTAR 345 kV Reliability Project One-Line Diagram
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CONSTRUCTION SEQUENCE
Stage I Construction - 2006 Stage II Construction
- 2007
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PROJECT NEED
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Emerging Transmission Concerns 2004-2010
115 kV Cable to Brighton overloads for loss of
companion cable 2005-2008
115 kV Lines to Lexington overload for loss of
DCT Line from Framingham 2004-2006
115 kV Cable to K Street overloads for loss of
companion cable 2005-2007
345 kV Cable to Kingston overloads for loss of
companion cable 2005-2007
115 kV Cable to K Street overloads for loss of
companion cable 2006-2008
Framingham 230A Auto overloads under normal
conditions 2008-2010
115 kV Cables to Baker St. overload for loss of
Needham DCT Lines 2005-2007
Medway 345A Auto overloads under normal
conditions 2008-2010
115 kV Line to Needham overloads under normal
conditions 2007-2009
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NEMA/BOSTON AREA
2006 SYSTEM
Transfer Capability Increased by 1000 MW
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Project Cost
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Project Cost Breakdown
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PROJECT ALTERNATIVES
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Alternatives Considered

• Upgrade Overloaded Facilities
• Requires 14 individual upgrades including
• 2 New Mystic to Kingston 345 kV underground
  circuits (5 miles)
• 2 New Needham to Newton 115 kV underground
  circuits (5 miles)
• 2 New Waltham to Watertown 115 kV underground
  circuits (10 miles)
• 1 New Walpole to Needham 115 kV overhead circuit
  (10 miles)
• Addition of 3 new autotransformers
• Replacement of 2 existing autotransformers
• Requires 4 simultaneous regulatory review
  proceedings
• Provides minimal transfer capability improvement

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Alternatives Considered

• Construct New 115 kV or 345 kV Overhead Facility
• New 115 kV lines lack sufficient capacity
• New 345 kV lines would require the following
• Expansion of existing ROW from Walpole to Needham
  (10 miles) from 100 foot width to 300 foot width
• Existing Right of Way ends 4 miles from Baker
  Street Station, obtaining new ROW over this 4
  mile section is estimated to cost over 60 M and
  would require at least 3 years to obtain and
  license
• Overhead routes from Baker Street into Boston
  unattainable and very costly
• Highly congested area of the system
• All existing utilities are underground
• Licensing and eminent domain proceeding would
  take many years
• Numerous Underground 345 kV Facility Route
  Alternatives Were Evaluated

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• South Boston Area
• Densely populated area of the city
• No overhead facilities exist in these areas
• Property takings and removal of structures would
  be required

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Overhead TransmissionCost of Right of Way
Acquisition
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PROJECT SCHEDULE
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PRELIMINARY PROJECT SCHEDULE
DEC 2003
DESIGN
MAR 2005
PERMITTING
JUN 2006
STATION CONST
MAR 2006
STREET CIVIL
JUNE 2006 In-service
CABLE SPLICING
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Appendix
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Transient Analysis Results
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What Was Studied

• Frequency Scan / Harmonic Resonance Analysis
• Energization Cases
• Cables Transformers
• Synchronous closing versus pre-insertion resistor
  breakers
• Fault Clearing Cases
• 1 ph-gnd 3 ph faults
• Reclosing OH lines
• 15 fault locations

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EMTP Model
Transmission System Study Area
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Harmonic Resonance Screening

• Analysis used to identify locations to monitor
• Harmonic resonance below 3rd can aggravate
  transient problems but is not a problem itself
• Value and intent is to target locations where
  overvoltage conditions may be introduced

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Study Results

• Energizing cases simulated for
• 345 kV cables from Stoughton to K Street and Hyde
  Park
• 345/115 kV Transformers at K Street, Hyde Park
  Holbrook
• Above cases with Stoughton - Walpole / Stoughton
  - Holbrook out of service
• Above cases for closing into a fault
• Results indicate need for point on wave switching
  (i.e. synchronous closing) or pre-insertion
  resistors for breakers at Stoughton
• Fault clearing cases for faults at K Street, Hyde
  Park, Stoughton, Walpole Holbrook
• Results indicate that line out of service
  conditions at Stoughton call for a Special
  Protection System

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Breaker Selection

• Based on results for equipment energization the
  following breaker types will be employed
• Stoughton 345 kV Ring Bus Pre-Insertion
  Resistor
• Stoughton 345 kV Reactors Synchronous Closing
• K Street 345 kV Bus / Reactors Synchronous
  Closing
• Hyde Park 345 kV Bus Normal Closing
• The 345 kV cables will only be energized from the
  Stoughton 345 kV bus

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Study Results No SPS
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Study Results With SPS
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SPS Design

• SPS will be armed whenever either the Stoughton
  to Walpole or the Stoughton to Holbrook 345 kV
  lines are out of service
• Reclosing for the 345 kV line that remains in
  service will be disabled when the SPS is armed
• 345 kV Reactors will be set to a total
  compensation level of at least 400 MVAR any time
  the Stoughton Walpole line is out. (Insures
  acceptable response for faults at Holbrook)