Offshore Electrical Cable Burial For Wind Farms: State Of .

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Offshore Submarine Power CableCONTRACT #M10PS00204Offshore Electrical Cable Burial for Wind Farms: Stateof the Art, Standards and Guidance & AcceptableBurial Depths, Separation Distances and Sand WaveEffectProject No. 671, Contract M10PC00102Prepared for:Bureau of Ocean Energy Management, Regulation &Enforcement - Department of the InteriorTh is report has been reviewed by the Minerals Management Service and approvedfor publication. Approval does not signify that the contents necessarily reflect the viewsand policies of the Service, nor does mention of trade names or commercial productsconstitute endorsement or recommendation for use.November 2011Malcolm Sharples, P.E.

Bureau of Ocean Energy Management, Regulation and EnforcementOffshore Electrical Cable Burial for Offshore Wind Farms on the OCS

Offshore Submarine Power CableCONTRACT #M10PS00204Front Page Acknowledgement[Courtesy ABB]REPORT AVAILABILITYA complete copy of this report may be downloaded from the BOEMRE Technology Assessment &Research (TA&R) Program’s website at This project isnumbered as TA&R project 671.ACKNOWLEDGMENTSThe authors wish to thank the Bureau of Ocean Energy Management, Enforcement andRegulation Technology Assessment and Research Branch for funding this study and LoriMedley, and John Cushing for critical and insightful comments associated with the work.AUTHORS’ NOTE, DISCLAIMER AND INVITATION:This document has been written by engineers experienced in the offshore oil and gas industryalthough much information, advice and comment has been provided by those with years ofexperience in various aspects of the wind turbine industry. Many of the points made in this reportmay be subject to a different interpretation, and the facts may differ from the information relied uponwhich is believed to be factual. This report has been written without prejudice to the interests of anyparties mentioned or concerned and the Company and authors shall not in any circumstances beresponsible or liable for any act, omission, default, or negligence whatsoever.While we have used our best efforts to provide an impartial report, errors of fact or interpretation mayhave resulted: consequently, an invitation is issued to any readers to provide written comment for alimited period of time which will be reviewed for possible inclusion in an addendum to this report.Comments may be sent by email to [email protected]: Risk & Technology Consulting Inc.Dr. Malcolm Sharples [email protected]

Offshore Submarine Power CableCONTRACT #M10PS00204Table of ContentsABBREVIATIONSEXECUTIVE SUMMARY. 21. INTRODUCTION . 61.1 Planning Overview .61.2 Cable Selection on Wind Farm Submarine Cables to Date .91.3 References .152. REGULATIONS AND REGULATORY ISSUES . 162.1 Regulatory Requirements of 30 CFR 285 on Subsea Power Cables.162.2 Cables and Mariners/ Fishermen .162.3 Legal Restrictions to Cable Vessel Operations and the Jones Act .172.4 USCG and Customs & Border Protection.182.5 United States Army Corps of Engineers (USACE) Viewpoint .192.6 References .203.0 HISTORICAL INCIDENTS WITH CABLES . 223.1 References .234.0 CABLE TYPE SELECTION & INSTALLATION CONSIDERATIONS IN CABLE DESIGN. 274.1 Types and Manufacture.354.1.1 Basic Information on Cable Construction.354.1.2 Conductors.364.1.3 Insulation.374.1.4 Screening.384.1.5 Bending Radius.384.1.6 Sheathing.384.1.7 Armoring.384.1.8 Jacket .394.1.9 Fiber Optic Cables .394.1.10 Cable Joints.404.2 Cables and Heat .404.3 Electromagnetic Fields (EMF).474.3.1 EMF and Alternating current.474.3.2 EMF and Direct current .484.3.3 Further Explanations of EMF .484.4 Cables for Floating Wind Turbine Application .504.5 Cable Type Selection Summary.514.6 References .515.SPECIAL CONSIDERATIONS. 535.1 Installations in Seismically Active Areas.53Offshore: Risk & Technology Consulting Inc.Dr. Malcolm Sharples [email protected]

Offshore Submarine Power CableCONTRACT #M10PS002045.1.1 Newfoundland 1929 .535.1.2 Hengchun Earthquake near Taiwan 2006 .545.1.3 Other Seismic Events and Discussion of Potential Effects on Submarine Cables.545.1.4 Historical Seismic Events in the US.555.1.5 Seismic Design Considerations .565.1.6 Seismic Areas of United States.575.1.7 Mitigating Actions for Seismic Areas.595.1.8 References.605.2 Sand Wave Effects on Route Selection.625.2.1 Overview of Sand Wave Issue.625.2.2 Installation Issues in Sand Waves .635.2.3 Mitigating Actions for Sand Waves .645.2.4 References.645.3 Separation Distances.655.3.1 Vertical Separation .655.3.2 Cable Protection at Vertical Crossings .675.3.2 Horizontal Separation.695.3.3 Non-Technical Issues .695.3.4 Separation Distance Recommendations.705.3.5 References.706. ROUTE SELECTION. 726.1 Desktop Study.756.2 Metocean Information .766.3 Route Assessment Field Survey.766.4 Burial Assessment Survey.786.4.1 Burial Assessment Survey by Pulling the Plow .786.4.2 Burial Assessment Survey with Instrumented Sled .796.5 Route Selection Summary.856.6 References .857. NAVIGATION RISK ASSESSMENT. 877.1 Information Needed.877.2 Sources of Information.887.3 Recreational Vessels.927.4 Fishing Gear .927.5 Construction Vessels .947.6 Ship Anchors: Depth of Potential Damage from Anchor Release .947.7 Quantitative Risk Analysis : Step-by-Step Method.997.8 Qualitative Risk Analysis: Step-by-Step Method.1027.9 Effects of Cables on Marine Navigation .1067.10 Assumptions of Due Diligence .1067.11 Acceptance of Risk.1067.12 Mitigation of Risk.1067.12.1 Mitigation by Exclusion Zones.106Offshore: Risk & Technology Consulting Inc.Dr. Malcolm Sharples [email protected]

Offshore Submarine Power CableCONTRACT #M10PS002047.12.2 Mitigations Available from Signs, Beacons and Potential Exclusion Zones .1077.13 References .1098. CABLE PROTECTION . 1118.1 Burial Protection Index. .1158.1.1 A Simulation Model: Building on the BPI Index Concept.1198.2 Repair and Armoring Issues.1198.3 Decommissioning of Cable .1198.4 Protection at the Shore Landing.1208.5 Protection from Ice Rafting: Offshore Maine and Alaska .1208.6 Rock Dumping and Plastic Sheaths.1208.7 Scour Protection.1228.8 Post Installation Survey.1248.9 In-Service Inspection Plan .1248.10 References .1259.0 INSTALLATION CONSIDERATIONS. 1269.1 Installation Vessels .1269.2 Trenching and Burial Equipment.1299.2.1 Mechanical Plows.1309.2.2 Jet Plows.1339.2.3 Rock Saw .1369.2.4 Dredging.1379.2.5 Horizontal Directional Drilling.1379.2.6 Interface at the Turbine .1389.2.7 Vessel Functions to Deploy Inter-Array Cables.1419.2.8 Activities to Deploy Shore Connections.1429.4 References .14310. DOCUMENTATION. 14511. RECOMMENDATIONS . 14611.1 Specific Information Recommended for Inclusion in the Facility Design Report .14611.2 Recommendations for Research Topics .14711.3 Other Recommendations.148APPENDIX A: HISTORICAL CABLE INCIDENT DETAILS AND REFERENCES. 149A.1 Arklow Bank .149A.2 Barrow .149A.3 Blyth .149A.4 Bockstigen .150A.5 Burbo Bank .151A.6 Horns Rev.151A.7 Kentish Flats.152A.8 Lynn and Inner Dowsing.152A.9 Middelgrunden.152Offshore: Risk & Technology Consulting Inc.Dr. Malcolm Sharples [email protected]

Offshore Submarine Power CableCONTRACT #M10PS00204A.10 Nysted.152A.11 Robin Rigg .152A.12 Scroby Sands.153A.13 Skegness Offshore Wind Farm .155A.14 Teeside OffshoreWind farm.155A.15 Utgrunden.155A.16 Oil & Gas Platform “Hogan”, Offshore California – Repair/Replacement Cable. .155A.17 General Review of Historical Experience .157A.18 For Further Reading.163A.19 Germanischer Lloyd Advice .163APPENDIX B DESIGN OF, REPAIR OF, and LIFE OF SUBMARINE CABLES . 165B.1 Design Issues.165B.2 Repairing Cables .169B.2.1 Contingency Cable Lengths .171B.2.2 Issues for Repair .171B.2.3 Repair Costs .172B.3 Life of Cable & Maintenance.173B.4 References .174APPENDIX C: TOOLS TO DETERMINE SUITABILITY OF ROUTE. 175C.1 Bottom Profile .175C.2 Side Scan Sonar.177C.3 Remote Operated Vehicle – Camera.179C.4 Geophysical Survey on Site.179C.4.1 Sub Bottom Profiler .179C.4.2 Magnetometer .180C.5 Soil Surveys in the Field.181C.5.1 Cone Penetrometer Test (CPT) .182C.5.2 Thermal Conductivity Probe.184C.5.3 Soil Samples.186C.5.4 Vane Shear Test .186C.5.5 Soil Testing .187C.6 Report on Soils & Bottom Conditions.189C.7 References .191APPENDIX D: TYPICAL INSTALLATION VESSELS USED TO DATE. 192APPENDIX E: SUBMARINE CABLE INSTALLATION EXAMPLE OFFSHORE WIND FARMBLYTH. 203E.1 Overview.203E.2 Beach Preparatory Work.205E.3 Cable Landing at the Turbines.205E.4 Diving Operations .205E.5 Cable Lay Operations between the Northern & Southern Turbines .206Offshore: Risk & Technology Consulting Inc.Dr. Malcolm Sharples [email protected]

Offshore Submarine Power CableCONTRACT #M10PS00204E.6 Cable Lay Operations Across the River Blyth .206Table of FiguresFigure 4.1: Horns Rev Export Cable 170 kV 3 29Figure 4.2: Subsea Cable details of Cross Section 30Figure 4.3: Sheringham Shoal, Lincs & London Array (Courtesy Nexans) 30Figure 4.4: Cross Section of 70 Sq. mm Double Armor with 16 fibers Optic Package 31Figure 4.5: Cable Terminations at Horns Rev 2 (Courtesy Nexans) 31Figure 4.6: Accessory Hangoffs (Courtesy Nexans) 32Figure 4.7: Hangoff and Termination – London Array (Courtesy JDR). 32Figure 4.8: Typical 3 Phase AC Cable bundled with Fiber optic and Single Cable 35Figure 4.9: Nominal Power for 2 applications of HVDC and various Conductor Cross-sections 37Figure 4.10: Rocky Terrain Offshore Maine – 39Figure 4.11: Temperature contours around a pair of submarine HVDC cables. 42Figure 4.12: Temperature contours around a pair of submarine cables on the left and a pipeline on the right with a 50 o Csurface temperature. 43Figure 4.13: Temperature rise at -0.2m and -0.3m below the sea floor. 44Figure 4.14: Temperature as a function of time and burial depth in meters. 45Figure 4.15: Temperature profile in a single-core cable and surrounding soil 45Figure 4.16: Current Rating as a Function of Burial Depth (Example) 46Figure 4.17: Magnetic field around a parallel bipolar cable (left), with currents in opposite directions. 49and around a co-axial cable (right), with opposite currents in the inner and outer conductors. 49Figure 4.18: Floating Power Plant potentially proposed offshore Oregon. 50Figure 5.1: Map of Taiwan area Illustrating the Cable Break Issue 54Figure 5.2: The largest landslide in Anchorage occurred along Knik Arm between Point Woronzof and Fish Creek, 55Figure 5.3: International Offshore Cable Routes (from Global Marine Systems Ltd.) currently in use. 56Figure 5.4 (a): 5% damped Spectral Response Accelerations for offshore North America 57Figure 5.4 (b): 5% damped Spectral Response Accelerations for offshore North America 58Figure 5.5: Seismic Risk in U.S. Coastal Waters (0 is low, 5 is high) 59Figure 5.6: Diagram showing the relationship between stream velocity and ability to transport material of varying sizes.63Figure 5.7: ROV deployment of concrete protection 68Figure 5.8: Concrete mattress in place protecting pipeline from cable laid above it.Figure 5.9: Concrete Bags ProtectionFigure 5.10: Mattress Protection68Figure 6.1: Cartoon examples of various geohazards. 73Figure 6.2: Four Alternates Routes form one location to another as a function of topography. 75Figure 6.3: Mini-Plow 79Figure 6.4: Basic Assessment Plow 79Figure 6.5: Typical Burial Assessment Survey Sled 81Figure 6.6: GAMBAS – Tow Sled for Seismic Refraction [Ref. 6.14] 83Figure 6.7: Progress rate as a function of undrained shear strength for 2 jet pressures. 83Figure 6.8: Burial Assessment Example Graphic Final Product 85Figure 7.1: Screen Shot of East Coast Ports March 12, 2011 6:30 pm. 91Figure 7.2: Showing the Load Line on a ship: 92Figure 7.3: Relationship between Trawl Door Penetration and Soil Shear Strength 94Figure 7.4 Fluke Angle of Typical Ship Anchor 97Figure 7.5: Frequency vs Consequence Matrix 103Figure 7.6: Risk Analysis Matrix

Offshore Submarine Power Cable CONTRACT #M10PS00204 Offshore: Risk & Technology Consulting Inc. Dr. Malcolm Sharples [email protected] Front Page Acknowledgement [Courtesy ABB] REPORT AVAILABILITY A complete copy of this report may be downloaded fro