345 kV Underground Report - CapX2020

1 POWER ENGINEERS, INC. STL 085-247 (SR) CapX2020 REV B (02/24/2010) MM 117910 February 24, 2010 PROJECT NUMBER: 117910 PROJECT CONTACT: Mike Mueller Richard C. Mues, PE EMAIL: PHONE: 314-851-4050 314-851-4014 345 kV Underground Report POWER ENGINEERS, INC. STL 085-247 (SR) CapX2020 REV B (02/24/2010) MM 117910 PREPARED FOR: CapX2020 PREPARED BY: POWER ENGINEERS For additional information contact: Mike Mueller (314) 851-4050 Richard C.

2 Mues, (314) 851-4014 Rev. Issue Date Issued For Prep By Chkd By Appd By Notes A 2/10/2010 Prelim SA MRM RCM Issued for review B 2/24/2010 Appvl SA MRM RCM Issued for approval Issued For Definitions: - Prelim means this document is issued for preliminary review, not for implementation - Appvl means this document is issued for review and approval, not for implementation - Impl means this document is issued for implementation - Record means this document is issued after project completion for project files POWER ENGINEERS, INC.

3 STL 085-247 (SR) CapX2020 REV B (02/24/2010) MM 117910 PAGE i TABLE OF CONTENTS I. EXECUTIVE SUMMARY .. 1 SCOPE OF WORK .. 1 SUPERCONDUCTING CABLES .. 1 Underground CABLE SYSTEMS .. 1 Extruded Dielectric Cable Systems .. 1 HPFF Pipe Type Cable Systems .. 2 CABLE CASE SUMMARY .. 2 COST ESTIMATE SUMMARY .. 3 II. PROJECT DESCRIPTION .. 4 INTRODUCTION .. 4 XLPE CABLE system DESIGN .. 4 system Description and Trench Design .. 4 HPFF CABLE system DESIGN .. 5 system Description and Trench Design .. 5 AMPACITY STUDIES .. 5 Ampacity Calculations .. 6 ELECTROMAGNETIC FIELDS.

4 7 III. Underground CABLE SYSTEMS .. 9 INTRODUCTION .. 9 SUPERCONDUCTING CABLE SYSTEMS .. 9 General .. 9 Experience .. 10 RELIABILITY OF 345 KV CABLE SYSTEMS .. 11 EXTRUDED DIELECTRIC CABLE SYSTEMS .. 11 Cable .. 11 Cable Accessories .. 12 Civil Installation .. 13 Vault Design and Installation .. 14 Cable Maintenance and Repair .. 15 pros and cons .. 15 HIGH-PRESSURE FLUID-FILLED CABLE SYSTEMS .. 16 Cable .. 16 Cable Accessories .. 18 Cable Pipe Installation .. 18 Vault Design and Installation .. 18 Maintenance and Repair .. 19 pros and cons .

5 19 TRENCHLESS INSTALLATIONS .. 20 IV. TERMINATIONS .. 21 GENERAL .. 21 DESCRIPTION .. 21 POWER ENGINEERS, INC. STL 085-247 (SR) CapX2020 REV B (02/24/2010) MM 117910 PAGE ii Transition Structure .. 21 Termination Station .. 21 V. COST ESTIMATE .. 22 INTRODUCTION .. 22 COST ESTIMATE ASSUMPTIONS .. 22 SUMMARY OF COST ESTIMATES .. 22 VI. COMPARISON OF ENVIRONMENTAL IMPACTS OF OVERHEAD AND Underground TRANSMISSION LINE CONSTRUCTION .. 24 RIGHT OF WAY WIDTHS .. 24 XLPE Right Of Way Requirements .. 24 HPFF Right Of Way Requirements .. 24 Trenchless Crossings.

6 24 GROUND DISTURBANCE .. 25 LAND USE AND AESTHETICS .. 25 ELECTRIC FIELDS, MAGNETIC FIELDS AND NOISE .. 25 RIGHT OF WAY CLEARING AND VEGETATION CONTROL .. 26 EROSION CONTROL IN UNSTABLE AREAS .. 26 APPENDICES APPENDIX A - AMPACITY STUDIES APPENDIX B - EMF CALCULATIONS APPENDIX C - TRENCH DETAILS APPENDIX D TERMINATION AND MANHOLE DETAILS APPENDIX E COST ESTIMATES POWER ENGINEERS, INC. STL 085-247 (SR) CapX2020 REV B (02/24/2010) MM 117910 PAGE 1 I. EXECUTIVE SUMMARY Scope of Work Xcel Energy (Xcel) requested that a study be made of alternative 345 kV Underground cable systems for the CapX2020 Project, including cost estimates to install double circuit 345 kV Underground transmission line.

7 No specific route was selected, but a distance of approximately miles was assumed. Superconducting Cables Superconducting cable systems were researched regarding the viability of using high temperature superconductors (HTS) for a 345 kV Underground installation. Details of HTS cable systems are included in Section III. Underground Cable Systems Two basic types of Underground cable systems were considered for this Report , namely an extruded dielectric, cross-linked polyethylene (XLPE) cable system and a high-pressure fluid-filled pipe-type (HPFF) cable system .

8 Details of the construction of the cables and major accessories for each of these cable systems are included in Section III. The major pros and cons of each of these cable systems are: Extruded Dielectric Cable Systems pros : cons : Essentially no operation and maintenance requirements. Appropriate reliability reported for systems of modern design at voltages 230 kV and below in the USA, Japan and European countries. Higher normal operating and short circuit temperature ratings as compared to HPFF systems.

9 Installation environmental condition requirements for splicing and terminating less stringent. Lower dielectric losses. Shorter time required for repair. Concrete encased duct bank systems provide mechanical protection from dig-ins and allow for short lengths of trench to be opened for construction activities. Susceptible to damage from dig-ins if direct buried, more so than HPFF pipe-type cable systems. Potential for induced sheath voltages and losses. Trench for installation of each cable length (direct buried) must be left open for the entire length during cable installation.

10 Duct bank/conduit installation may reduce thermal performance and increases cost. XLPE insulation not as forgiving (fluid-impregnated paper insulation is more tolerant of manufacturing defects, and variances). Limited use at 345 kV in US. POWER ENGINEERS, INC. STL 085-247 (SR) CapX2020 REV B (02/24/2010) MM 117910 PAGE 2 HPFF Pipe Type Cable Systems pros : cons : Long experience and service life record dating from 1930 s with extensive use in the Higher reliability than XLPE cable systems based on utility records.