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NSTAR 345KV TRANSMISSION RELIABILITY PROJECT PLAN

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... Walpole to Needham 115 kV overhead circuit (~10 miles) Addition of 3 new ... populated area of the city. No overhead facilities exist in ... for closing into ... – PowerPoint PPT presentation

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Title: NSTAR 345KV TRANSMISSION RELIABILITY PROJECT PLAN


1
NSTAR 345KV TRANSMISSION RELIABILITY PROJECT PLAN
Presentation to the New England
Stakeholders January 31, 2005
2
AGENDA
  • 345 kV Project Overview
  • Project Need
  • Project Cost
  • Project Alternatives
  • Project Design

3
345 KV PROJECT OVERVIEW
4
Planned 345kV Supply To Downtown Boston Mitigates
These Concerns
Proposed 345 kV Transmission Cable
5
NSTAR 345 kV Reliability Project One-Line Diagram
6
CONSTRUCTION SEQUENCE
Stage I Construction - 2006 Stage II Construction
- 2007
7
PROJECT NEED
8
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
9
NEMA/BOSTON AREA
2006 SYSTEM
Transfer Capability Increased by 1000 MW
10
Project Cost
11
Project Cost Breakdown
12
PROJECT ALTERNATIVES
13
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

14
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

15
  • 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

16
Overhead TransmissionCost of Right of Way
Acquisition
17
PROJECT SCHEDULE
18
PRELIMINARY PROJECT SCHEDULE
DEC 2003
DESIGN
MAR 2005
PERMITTING
JUN 2006
STATION CONST
MAR 2006
STREET CIVIL
JUNE 2006 In-service
CABLE SPLICING
19
Appendix
20
Transient Analysis Results
21
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

22
EMTP Model
Transmission System Study Area
23
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

24
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

25
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

26
Study Results No SPS
27
Study Results With SPS
28
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)
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