Appendix D Underground Route Study - Bonneville Power

136 Pages·2012·2.97 MB·English

Appendix D
Underground Route Study

January 21, 2011

BONNEVILLE POWER ADMINISTRATION

I-5 Transmission Corridor Project
Underground Route Study

Issued Final

PROJECT NUMBER:
119864

PROJECT CONTACT:
DENNIS JOHNSON
EMAIL:
[email protected]
PHONE:
[phone]
POWER ENGINEERS, INC

UNDERGROUND ROUTE STUDY

PREPARED FOR: BONNEVILLE POWER ADMINISTRATION
PREPARED BY: DENNIS JOHNSON
[phone]
[email protected]

REVISION HISTORY
DATE REVISED BY REVISION
07/06/10 Dennis Johnson A
11/05/10 Dennis Johnson B
01/21/11 Dennis Johnson 0

HLY 019-381 (SR-02) BPA (01/21/2011)BH 119864
POWER ENGINEERS, INC
TABLE OF CONTENTS

1.0  EXECUTIVE SUMMARY ........................................................................................................... 1 
1.1  SCOPE OF WORK ................................................................................................................. 1 
1.2  OVERVIEW OF PROJECT DESIGN ......................................................................................... 1 
1.3  COST ESTIMATES ................................................................................................................ 2 
1.4  SUMMARY ........................................................................................................................... 2 
2.0  PROJECT DESCRIPTION .......................................................................................................... 3 
3.0  UNDERGROUND CABLE SYSTEMS ....................................................................................... 5 
3.1  EXPERIENCE ........................................................................................................................ 5 
3.2  CABLE SYSTEM RATING ..................................................................................................... 7 
3.3  CONSTRUCTION METHODS ................................................................................................. 7 
3.3.1  Open Trench .......................................................................................................... 8 
3.3.2  Trenchless Installation ........................................................................................... 8 
3.3.3   Manholes .............................................................................................................. 11 
3.3.4  Cable Installation and Testing ............................................................................. 12 
3.4  LAND USE ......................................................................................................................... 13 
3.5  ELECTRICAL CONSIDERATIONS ........................................................................................ 15 
3.5.1  Reactive Compensation ....................................................................................... 15 
3.5.2  Electric and Magnetic Fields ............................................................................... 17 
3.6  TRANSITION STATIONS/SUBSTATIONS .............................................................................. 17 
3.7  MAINTENANCE .................................................................................................................. 18 
3.7.1  System Maintenance ............................................................................................ 21 
3.8  CABLE SYSTEM RELIABILITY ........................................................................................... 22 
3.9  CABLE FAILURE LOCATING AND REPAIR ......................................................................... 22 
3.9.1  Fault Locating ...................................................................................................... 22 
3.9.2  Cable Repair ........................................................................................................ 23 
4.0  OVERHEAD TRANSMISSION SYSTEM ............................................................................... 24 
4.1  OVERHEAD EXPERIENCE ................................................................................................... 24 
4.2  SYSTEM DESIGN ................................................................................................................ 24 
4.2.1  Conductor Size ..................................................................................................... 24 
4.2.2  Tower Type .......................................................................................................... 24 
4.2.3  Foundation Type .................................................................................................. 25 
4.3  CONSTRUCTION METHODS ............................................................................................... 25 
4.3.1  Conventional ........................................................................................................ 25 
4.3.2  Aerial Construction .............................................................................................. 26 
4.3.3  Line Crossings ..................................................................................................... 26 
4.4  LAND USE ......................................................................................................................... 26 
4.5  ELECTRICAL CONSIDERATIONS ........................................................................................ 27 
4.6  MAINTENANCE .................................................................................................................. 28 
4.7   FAULT LOCATING.............................................................................................................. 28 

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POWER ENGINEERS, INC
5.0  UNDERGROUND CONCEPTUAL DESIGN .......................................................................... 29 
5.1  CABLE SYSTEM DESIGN .................................................................................................... 30 
5.1.1  Open Cut Trench Design ..................................................................................... 30 
5.1.2  Trenchless Design ................................................................................................ 31 
5.2  ELECTRICAL CHARACTERISTICS ....................................................................................... 34 
5.3  MAGNETIC FIELD CALCULATIONS .................................................................................... 35 
5.4  SYSTEM OPERATION ......................................................................................................... 36 
6.0  OVERHEAD CONCEPTUAL DESIGN ................................................................................... 38 
6.1  FACILITIES DESIGN ........................................................................................................... 38 
6.2  CONSTRUCTABILITY ......................................................................................................... 38 
6.3   SPECIAL CONSTRUCTION AREAS ...................................................................................... 39 
7.0   COST ESTIMATES .................................................................................................................... 40 
7.1  COST ESTIMATE ASSUMPTIONS ........................................................................................ 40 
7.2  UNDERGROUND COST ESTIMATES .................................................................................... 41 
7.3  OVERHEAD COST ESTIMATES ........................................................................................... 42 
7.4  COST ESTIMATES COMPARISON ........................................................................................ 42 

APPENDIX A – ENVIRONMENTAL REPORT

APPENDIX B – DISCUSSION OF AVAILABLE UNDERGROUND CABLE SYSTEMS

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1.0 EXECUTIVE SUMMARY
1.0 EXECUTIVE SUMMARY

1.1 Scope of Work

Bonneville Power Administration (BPA) is proposing to install a new single circuit 500 kilovolt (kV)
alternating current (AC) transmission line from a proposed substation near Castle Rock, Washington
extending approximately 70 miles south to a proposed substation near Troutdale, Oregon. The line is
being developed to proactively counter the growing demand within BPA’s existing electrical transmission
system in southwest Washington and northwest Oregon. To ease congestion and keep pace with these
growing demands, an in depth analysis at implementing a new transmission line through the proposed
project area has been undertaken to comply with the provisions of the National Environmental Policy Act
(NEPA). The NEPA process is intended to promote better agency decisions by ensuring that high quality
environmental information is available to agency officials and the public before the agency decides
whether and how to undertake a federal action. As part of the NEPA scoping process, BPA has enlisted
POWER Engineers, Inc. (POWER) to investigate the feasibility and prepare estimated costs to place the
proposed transmission line underground as well as a comparative overhead line cost assessment. This
report provides an overview of available underground transmission technologies, applications, and
capabilities; as well as construction, operation, maintenance, repair, and estimated costs for a 500kV
underground and comparable overhead line.

Narrowing the Project area to two possible routes, BPA provided both the study area as well as a number
of route segments for POWER to base the feasibility study and estimates on. Additionally, BPA made
available their typical estimating practices, overhead structure families, and intended operation of the line
to assist POWER in its work.

To minimize the overall scope of design work, the underground portion of the study focuses solely on
high voltage extruded dielectric cable (HVED); namely cross-linked polyethylene (XLPE). While other
cable technologies do exist, the current US trend is to utilize XLPE cable because of its favorable traits in
reliability, constructability, and long term operation and maintenance.

1.2 Overview of Project Design

The basis of the underground design and installation is developed from the target power transfer
requirement, from which a cable size and the total number of cables can be determined using
predetermined environmental and system operating characteristics. For the anticipated underground
project, it is assumed that four cables per phase will be required which will be installed in four
independent concrete encased duct banks. The duct banks would be installed via open-cut trench and
backfilled with thermally corrective fill to improve cable operating performance. A number of major
waterways, railroad tracks and roadways would be encountered along each evaluated route. It has been
assumed that major waterways and wetlands would be crossed using horizontal directional drilling (HDD)
and major roadways would be crossed by means of a jack and bore (J&B). Reactor stations would be
installed at two intermediate points, approximately every 25 miles and at each end.

The assumption for the overhead estimate is standard 500kV lattice tower construction according to BPA
standards.

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1.3 Cost Estimates

Using the predefined route segments, estimated costs for each route were developed taking into account
the environmental conditions, geology, and anticipated construction method. Detailed assumptions have
been included in Section 7 of this report. The estimated installed costs for the proposed transmission line
for each route can be seen in Table 1-1.

TABLE 1-1 COMPARISON COST ESTIMATES
Length
Route/Installation Overhead Cost Underground Cost
(mi)
Eastern Route 76 $151,215,000 $2,369,721,000
Western Route 68.5 $147,080,000 $2,051,490,000

1.4 Summary

While installing an underground 500kV transmission line of the proposed length appears to be technically
feasible, there is a significant cost increase compared to the overhead alternative of nearly 15 times. In
addition to the cost, there are significant operational, system loss, performance and reliability concerns.

 Operational Concerns – With the addition of the capacitance and reactors, BPA will need to do an
extensive system analysis to determine the operational impact to their system. It may require
replacement of downstream equipment as well.

 System Losses – No analysis was performed to determine the additional system losses associated
with the underground cable system compared with an overhead line. However, it is well
understood that the systems losses for the underground system will be significantly higher than
the overhead.

 Performance and Reliability – With only a few land installations throughout the world, totaling
less than 30 circuit miles, the cable and accessories have not proven themselves to maintain the
high reliability demands of today’s electric grids.

While a direct current (DC) cable system was not evaluated for this report, recent studies have shown that
for lengths greater than 40 miles, the cost of the DC converters and DC cable system would be equivalent
and may be less expensive compared to the proposed AC cable system.

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2.0 PROJECT DESCRIPTION