CCI Feasibility Study for 500 KV AC Underground Cables

8/9/2019 CCI Feasibility Study for 500 KV AC Underground Cables

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CCIC ab l e C o n s u l t i n g I n t er n a t i o n a l L t d Feasibility study for 500 kV AC underground cables

for use in the Edmonton region of Alberta, Canada

ER 381PO Box 1, Sevenoaks TN14 7ENUnited Kingdom 19

thFebruary 2010

Distribution: AESO, HPT, CCI

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Cable Consulting International LtdRegistered in England and Wales No. 4234974

Registered office: 74 College Road, Maidstone, Kent, ME15 6SL, United Kingdom

TITLE: FEASIBILITY STUDY FOR 500 kV AC UNDERGROUND CABLES

FOR USE IN THE EDMONTON REGION OF ALBERTA, CANADA

REPORT No: ER 381

CUSTOMER: AESO

AUTHORS: Alan Williams BSc CEng MIET

Brian Gregory BSc CEng FIEE

DATE: 18 February 2010

INTRODUCTION

CCI has been engaged to perform a feasibility study into the use of 500 kV underground cables for theEdmonton region of Alberta. The design requirements used within this study are generic and based onthose of the 500 kV 3,000 MW system known as the Heartland Project.

This document contains a description of the available cable technology, recommendations on thefeasibility of the cable technology and how underground cable technology needs to be developed so asto be suitable for use in the Edmonton region.

Also included are:

Definitions and glossary (Section 16) for words that have been Capitalised.

An appendix recording individual studies, including:

Total cost estimates (in 2009 Canadian dollars) for nine scenarios comprisingdifferent proportions of underground cable and overhead line, which wereprovided by the Heartland Project Team (HPT) based on estimated cable systemcosts provided by cable manufacturers and estimated civil cable installation costs

provided by HPT. HPT also provided the estimated costs of the overhead line andall of the other equipment required for each scenario.

Preliminary project schedules, which were provided by HPT.


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CCIC ab l e C o n s u l t i n g I n t er n a t i o n a l L t d Feasibility study for 500 kV AC underground cables for

use in the Edmonton region of Alberta, Canada


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CONTENTS

INTRODUCTION .................................................................................................................................... 11 EXECUTIVE SUMMARY............................................................................................................. 13

1.1 Introduction............................................................................................................................. 131.2 Method of approach ................................................................................................................ 141.3 Technical feasibility findings.................................................................................................. 16

1.3.1 Choice of cable technology............................................................................................. 161.3.2 500 kV XLPE cable system: supply capability and experience...................................... 171.3.3 Choice of installation technology ................................................................................... 181.3.4 500 kV Study Project size............................................................................................... 19

1.3.5 Project specific requirements.......................................................................................... 191.3.6 Low ambient temperatures.............................................................................................. 201.3.7 Proving the performance of the cable system before it is supplied ................................ 21

1.4 Estimates of reliability ............................................................................................................ 221.5 Estimates of capital cost.......................................................................................................... 24

1.5.1 Scenarios considered for costing..................................................................................... 261.5.2 Estimated capital cost: comparison between scenarios................................................... 281.5.3 Estimated Net Present Value: comparison between scenarios........................................ 291.5.1 Summary of cost estimates ............................................................................................. 301.5.2 Cost differences between cable and overhead line ......................................................... 31

1.6 500 kV Study Project duration................................................................................................ 32

1.7 Power losses ............................................................................................................................ 331.7.1 Relationship of power loss to power transfer for the 500 kV Study Project .................. 341.7.2 Cumulative power losses for the 500 kV Study Project ................................................. 361.7.3 Estimated NPV of cumulative power losses................................................................... 37

1.8 Recommendations for next steps ............................................................................................ 381.8.1 Study of end to end reliability and availability............................................................... 391.8.2 System and design studies............................................................................................... 391.8.3 Carry out additional engineering studies, as required..................................................... 39

2 REQUIREMENTS FOR UNDERGROUND POWER TRANSMISSION SYSTEM FOR THE500 KV STUDY PROJECT.................................................................................................................... 44

2.1 Functional requirement: .......................................................................................................... 44

2.1.1 Functional requirement: power transmission.................................................................. 442.1.1 Functional requirement: ambient temperatures............................................................... 462.2 Scenarios considered............................................................................................................... 48

3 BASIC DESCRIPTION OF 500 KV AC UNDERGROUND TECHNOLOGY ........................... 563.1 Alternating current transmission system................................................................................. 563.2 Voltage, current and power..................................................................................................... 56

3.2.1 Voltage ............................................................................................................................ 563.2.2 Power .............................................................................................................................. 583.2.3 Current ............................................................................................................................ 58


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3.3 Component parts of the cable.................................................................................................. 593.4 Cable system ........................................................................................................................... 61

3.4.1 Component parts of the cable system ............................................................................. 653.4.2 Cable spans ..................................................................................................................... 653.4.3 Cable Terminations ......................................................................................................... 663.4.4 Cable Joints ..................................................................................................................... 683.4.5 Bonding equipment. ........................................................................................................ 69

3.5 Ancillary equipment................................................................................................................ 713.6 Hydraulic system for SCFF cable systems only ..................................................................... 723.7 Thermal design........................................................................................................................ 723.8 Thermomechanical design ...................................................................................................... 72

3.9 Installation design ................................................................................................................... 733.9.1 Cable installation............................................................................................................. 733.9.2 Assembly of joints and terminations............................................................................... 76

3.10 Route protection and identification......................................................................................... 783.11 Forced cooling......................................................................................................................... 793.12 Operation, maintenance and repair ......................................................................................... 813.13 Testing..................................................................................................................................... 81

3.13.1 Proving tests.................................................................................................................... 823.13.2 Quality tests..................................................................................................................... 85

3.14 Permissible length of an AC underground cable circuit ......................................................... 874 STATE OF THE ART FOR 500 KV UNDERGROUND POWER TRANSMISSION ................ 90

4.1 Introduction............................................................................................................................. 904.2 Self-Contained Fluid Filled Cables (SCFF)............................................................................ 914.3 Cross-Linked Polyethylene Cable (XLPE)............................................................................. 944.4 Advantages of extruded cross-linked polyethylene cables ..................................................... 96

4.4.1 XLPE cable has the advantage over the SCFF type of : ................................................. 964.4.2 XLPE cable technology .................................................................................................. 97

4.5 Accessories for XLPE cable systems...................................................................................... 984.6 Cumulative service experience of XLPE cable systems....................................................... 1054.7 Electrical tests for XLPE cable systems ............................................................................... 111

4.7.1 Importance of prequalification tests for EHV XLPE cables......................................... 1124.7.2 Prequalification test recommendations for the 500 kV Study Project .......................... 113

4.8 Low temperature operation ................................................................................................... 1154.8.1 Ambient temperature levels for the Edmonton region of Alberta ................................ 1154.8.2 Low temperature risks................................................................................................... 118

4.9 Types of cable installation .................................................................................................... 1234.9.1 Direct Buried Installation.............................................................................................. 1234.9.2 Duct-manhole system.................................................................................................... 1264.9.3 Tunnel Installation ........................................................................................................ 1284.9.4 Service experience with different methods of installation at 400 kV and 500 kV ....... 1294.9.5 Service experience with forced cooled systems............................................................ 130


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4.10 Gas insulated lines ................................................................................................................ 1304.10.1 Description of GIL........................................................................................................ 1314.10.2 GIL Experience ............................................................................................................. 1344.10.3 GIL: Advantages and Disadvantages............................................................................ 136

4.11 High Temperature Superconducting Cable........................................................................... 1374.11.1 Superconductivity ......................................................................................................... 1374.11.2 Low temperature superconductors ................................................................................ 1384.11.3 High temperature superconductors ............................................................................... 1394.11.4 Construction of a conceptual HTSC cable.................................................................... 1404.11.5 HTSC Cable System Experience .................................................................................. 1444.11.6 Installation of a conceptual HTSC cable system for the Study project ........................ 147

5 ESTIMATES OF RELIABILITY................................................................................................. 1525.1 Repair times for 500 kV XLPE cable ................................................................................... 1535.2 Fault statistics for underground 500 kV XLPE cable ........................................................... 153

5.2.1 Cable system fault statistics.......................................................................................... 1535.2.2 Application of fault statistics to the 500 kV Study Project scenarios........................... 1555.2.3 500 kV Study Project fault rate..................................................................................... 1595.2.4 Types of cable faults ..................................................................................................... 159

5.3 Overhead line fault statistics................................................................................................. 1606 OVERVIEW OF POTENTIAL ENVIRONMENTAL EFFECTS OF UNDERGROUNDING.. 1617 PRELIMINARY 500 KV UNDERGROUND CABLE SCOPING STUDY ............................... 163

7.1 Description of the cable type used for the preliminary scoping study.................................. 163

7.2 Cable installation options...................................................................................................... 1667.3 General installation configuration......................................................................................... 1677.4 Preliminary scoping study: duct-manhole system ................................................................ 169

7.4.1 Configuration of cables in ducts ................................................................................... 1697.4.2 Duct for scoping study .................................................................................................. 1707.4.3 Trench filling................................................................................................................. 171

7.5 Preliminary scoping study: Cable installation direct in the ground...................................... 1727.6 Minimum spacing between groups of cables of each circuit ................................................ 1757.7 Installation Swathe and spacing between circuits,.............................................................. 1767.8 Sample ampacity calculation (XLPE cable) ......................................................................... 1787.9 Stabilised backfill.................................................................................................................. 180

7.10 Effect of obstructions on the route........................................................................................ 1817.10.1 Methods of maintaining the ampacity where the cable depth must be increased. ........ 1817.10.2 Installation at increased phase spacing. ........................................................................ 1817.10.3 Installation in tunnels.................................................................................................... 1847.10.4 Further methods of obstruction crossing....................................................................... 185

7.11 Cable lengths between joint bays.......................................................................................... 1867.11.1 Outline reel dimensions ................................................................................................ 1867.11.2 Cable reel transportation study ..................................................................................... 188

7.12 Manholes and joint bays ....................................................................................................... 188


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7.13 Tunnels.................................................................................................................................. 1907.13.1 Tunnel ampacity............................................................................................................ 1907.13.2 Cable installation in tunnels.......................................................................................... 1917.13.3 Tunnel cross sections .................................................................................................... 192

7.14 Staging of the cable installation............................................................................................ 1947.15 Staged duct manhole cable installation................................................................................. 196

7.15.1 Installation layout.......................................................................................................... 1967.15.2 Reasons for proposal..................................................................................................... 197

7.16 Staged cable installation direct in the ground ....................................................................... 1987.16.1 Installation layout.......................................................................................................... 1987.16.2 Reasons for proposal..................................................................................................... 199

7.17 Staged cable installation in deep tunnel................................................................................ 1997.17.1 Installation layout.......................................................................................................... 2007.17.2 Reasons for proposal..................................................................................................... 200

7.18 Staged cable installation in cut and cover tunnel.................................................................. 2007.18.1 Installation layout.......................................................................................................... 2017.18.2 Reasons ......................................................................................................................... 202

7.19 Alternative staging arrangements.......................................................................................... 2027.20 Alternative SCFF cable type for scoping study .................................................................... 203

7.20.1 SCFF cable power losses .............................................................................................. 2057.20.2 SCFF LPP cable installation configuration................................................................... 205

7.21 Cable system routine maintenance........................................................................................ 207

7.21.1 Maintenance for 500 kV XLPE cable systems ............................................................. 2077.21.2 Recommended routine maintenance on 500 kV SCFF cable systems.......................... 2107.22 500 kV cable system spares and repairs................................................................................ 211

8 ELECTROMAGNETIC FIELD PROFILE .................................................................................. 2139 DESIGNS PROPOSALS FROM PROSPECTIVE SUPPLIERS: SYSTEM DESIGN............... 215

9.1 Inquiry and questionnaire documents ................................................................................... 2159.1.1 Inquiry document .......................................................................................................... 215

9.2 Requests for technical information from prospective suppliers of 500 kV cable systems ... 2169.3 System designs proposed by prospective suppliers .............................................................. 219

9.3.1 Duct-Manhole systems.................................................................................................. 2229.3.2 Direct buried systems.................................................................................................... 222

9.3.3 Tunnel systems.............................................................................................................. 2229.3.4 Sheath bonding systems ................................................................................................ 2229.4 Designs proposals from prospective suppliers: cable ........................................................... 223

9.4.1 XLPE cable designs: general ........................................................................................ 2249.4.2 Conductors for XLPE cable designs ............................................................................. 2249.4.3 Core design for XLPE cable designs ............................................................................ 2249.4.4 Sheath design for XLPE cable designs ......................................................................... 2249.4.5 Distributed Temperature Sensing.................................................................................. 2259.4.6 Jacket design for XLPE cable designs .......................................................................... 226


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9.4.7 SCFF cable designs ....................................................................................................... 2269.4.8 GIL design..................................................................................................................... 2269.4.9 Cable design types proposed......................................................................................... 227

9.5 Cable electrical values provided by suppliers....................................................................... 2379.6 Splice designs proposed by prospective suppliers ................................................................ 238

10 TRANSITION STATION......................................................................................................... 24011 POWER LOSSES ..................................................................................................................... 242

11.1.1 Relationship of power loss to power transfer for the 500 kV Study Project ................ 24211.1.2 Cumulative power losses for the 500 kV Study Project ............................................... 24411.1.3 Estimated Net Present Value of Losses ........................................................................ 246

12 GENERIC COST STUDY FOR THE 500KV STUDY PROJECT ......................................... 248

12.1 Cable system unit costs ......................................................................................................... 24812.2 End-to-end estimated capital costs for the 65 km route length............................................. 24912.3 Capital cost estimates: comparison of components in each scenario.................................... 25012.4 Estimated Net Present Value of the life cycle costs for the 65 km route length................... 25512.5 Comparison of the cost of each scenario ............................................................................ 25612.6 Differences between the estimated cost of underground cable and overhead line ............... 25712.7 Sensitivity studies on the estimated capital cost of the cable system ................................... 261

12.7.1 Sensitivity: Effect on cost of SCFF cable ..................................................................... 26112.7.2 Sensitivity: Canadian Dollar value falls against other currencies by 20% ................. 26112.7.3 Sensitivity: Metal prices change by 50%...................................................................... 263

13 500 kV STUDY PROJECT DURATION................................................................................. 265

13.1 Cable ..................................................................................................................................... 26613.2 Transition station................................................................................................................... 26614 UNDERGROUNDING THE ENTIRE 65 KM ROUTE LENGTH ......................................... 267

14.1 Scenarios considered............................................................................................................. 26714.2 Technical limitations............................................................................................................. 267

14.2.1 Voltage control.............................................................................................................. 26714.2.2 Reduction in useful power transmission capacity because of cable charging current .. 267

14.3 Supplier capability ................................................................................................................ 26814.4 Cost estimates ....................................................................................................................... 26914.5 Cable system fault statistics for 65 km underground route length........................................ 269

15 500 kV STUDY PROJECT RISKS .......................................................................................... 271

15.1 Technical risks ...................................................................................................................... 27115.1.1 Inability of the accessories to meet the required minimum winter design temperatures.271

Remedial Action: .......................................................................................................................... 27115.1.2 Uncertainty of the winter minimum design temperature .............................................. 27115.1.3 Failure of the joints to demonstrate reliability in the Proving Tests............................. 27215.1.4 Failure of the cable system to achieve reliable service performance............................ 27215.1.5 Inability to repair the circuit at winter minimum ambient temperature:....................... 273

15.2 Contractual risks ................................................................................................................... 274


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15.2.1 Failure to attribute responsibility: ................................................................................. 27415.3 Schedule risks ....................................................................................................................... 274

15.3.1 Delayed development:................................................................................................... 27415.3.2 Delayed manufacture: ................................................................................................... 27515.3.3 Delayed installation and commissioning: ..................................................................... 27515.3.4 Damage to cable during delivery or installation ........................................................... 27615.3.5 Commissioning test failure and repair .......................................................................... 277

15.4 Common mode failure .......................................................................................................... 27815.4.1 Repeated latent defect in manufactured cable or accessories ....................................... 27815.4.2 Repeated jointing error.................................................................................................. 27915.4.3 Third party damage. ...................................................................................................... 279

15.4.4 Fire in tunnel. ................................................................................................................ 28015.5 Collateral Damage................................................................................................................. 28015.5.1 Failure of one cable causes damage to another............................................................. 28015.5.2 Failure of one joint causes damage to another.............................................................. 28115.5.3 Failure of one termination causes damage to another................................................... 28115.5.4 Testing of one cable system causes damage to another ................................................ 28115.5.5 Repair of one cable causes damage to another ............................................................. 282

15.6 Cost risks............................................................................................................................... 28216 DEFINITIONS AND GLOSSARY .......................................................................................... 284FEASIBILITY STUDY REFERENCES.............................................................................................. 299APPENDICES ...................................................................................................................................... 304

1 Appendix: Overhead line performance and statistics ................................................................... 3042 Appendix : Total capital cost estimate for each scenario.............................................................. 3043 Appendix : Economic comparison of scenarios for the 500 kV underground cable feasibility report

3044 Appendix: Project schedule .......................................................................................................... 3045 Appendix: System study (reactor requirements, voltage profiles and losses) .............................. 3056 Appendix: Generic crossings route maps: East TUC.................................................................... 3057 Appendix: Generic crossings route maps: West TUC .................................................................. 3068 Appendix: Transmission System Requirements ........................................................................... 3069 Appendix: Analysis of the minimum winter temperatures recorded on the 240kV DESS circuit inEdmonton in 2009................................................................................................................................. 306

10 Appendix: The Damage Prevention Process In Alberta ........................................................... 30611 Appendix: Potential overview of environmental effects of undergrounding............................ 30712 Appendix: Cable reel transportation study of feasibility and costs .......................................... 30713 Appendix: Magnetic fields for cable and overhead line ........................................................... 30714 AESO introduction letter for CCI ............................................................................................ 30715 500kV Heartland inquiry .......................................................................................................... 30716 Appendix: 500kV Heartland transmission project response template ...................................... 30817 Appendix : AIS transition station scope of work...................................................................... 30818 Appendix: Heartland underground construction: construction overview ................................. 308


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19 Appendix : Heartland underground line-civil estimate............................................................. 30820 Appendix: Heartland underground crossing requirements..................................................... 30921 Appendix : Heartland overhead line scope of work.................................................................. 30922 Appendix : Substation 1 scope of work .................................................................................... 30923 Appendix : Substation 2 scope of work .................................................................................... 30924 Appendix: Owners risk briefing................................................................................................ 31025 Appendix: Overhead and underground line maintenance......................................................... 31026 Appendix: Drawings of termination stations, cable trenches, and obstruction crossings......... 310

TABLE OF FIGURES

Figure 1. 500 kV Study project estimated capital cost main components ........................................... 25Figure 2 Comparison of scenario trench cross sections.......................................................................... 27Figure 3. Estimated capital costs in 2009 dollars.................................................................................... 29Figure 4 Estimated NPV of the life cycle costs for each scenario.......................................................... 30Figure 5. Power losses for selected scenarios at different levels of transmitted power.......................... 35Figure 6. Overhead line: Normal operation ............................................................................................ 45Figure 7. Overhead line: Contingency operation.................................................................................... 46Figure 8 Comparison of scenario trench cross sections.......................................................................... 50Figure 9 Scenario 1A.10 and 1B.20........................................................................................................ 52Figure 10 Scenario 2A.10 and 2B.20...................................................................................................... 52

Figure 11 Scenario 3A.10 and 3B.20...................................................................................................... 53Figure 12 Scenario 4A.10 and 4B.20...................................................................................................... 53Figure 13 Scenario 5A.65 ....................................................................................................................... 54Figure 14 Scenario 5B.65........................................................................................................................ 54Figure 15 Scenario 6 : No cable.............................................................................................................. 55Figure 16 Key to scenario diagrams ....................................................................................................... 55Figure 17. Three parallel lines or cables are required to form an AC circuit ......................................... 56Figure 18. Relative voltages of a 500 kV system ................................................................................... 57Figure 19. Voltages between individual 500 kV cables.......................................................................... 57Figure 20. Voltage across the insulation of a 500 kV cable ................................................................... 58Figure 21. Component parts of a 500 kV XLPE cable ........................................................................... 59

Figure 22. The component parts of a cable system................................................................................. 61Figure 23. Two circuits comprising four groups of underground cables................................................ 62Figure 24. 400 kV transition station with terminal gantry..................................................................... 63Figure 25. 400 kV transition station with terminal tower....................................................................... 64Figure 26. Two overhead line circuits connect to four groups of underground cable ............................ 64Figure 27. Delivery with cable reel axle cross-wise ............................................................................... 65Figure 28. Delivery with cable reel axle length-wise ............................................................................. 65Figure 29. Loading cable reels in ships hold ......................................................................................... 66Figure 30. Outdoor cable terminations ................................................................................................... 67


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Figure 31, Cable terminations into gas immersed switchgear ................................................................ 68Figure 32. A joint on a 400 kV XLPE cable prepared for burial............................................................ 69Figure 33. Part assembly of a joint on 240 kV XLPE cable inside a vault in Edmonton....................... 69Figure 34. An above-ground link box housing the components for a cross bonded position................. 70Figure 35. Above ground link kiosks connected to 400 kV underground cable..................................... 71Figure 36. Duct-manhole cable installation ............................................................................................ 73Figure 37. Direct buried cable installation.............................................................................................. 74Figure 38. Typical formations for cables installed in ducts.................................................................... 74Figure 39. Typical formations for direct-buried cables .......................................................................... 75Figure 40. Preparation of cable trench crossing agricultural land .......................................................... 75Figure 41. Jointing in progress in clean conditions ................................................................................ 77

Figure 42. Completed joints.................................................................................................................... 77Figure 43. Temporary cable termination assembly structure.................................................................. 78Figure 44: 400 kV cable system being prepared..................................................................................... 83Figure 45: A Cable being prepared for type approval ............................................................................ 83Figure 46. High voltage AC commissioning test equipment .................................................................. 86Figure 47. Three reactors located in a substation.................................................................................... 87Figure 48. SCFF 525 kV 1,000 mm2 cable commissioned in Grand Coulee Dam in 1976.................... 92Figure 49. SCFF LPP 2,500 mm2 cable, similar to that commissioned in Japan in 1994 ...................... 93Figure 50. 500 kV XLPE cable............................................................................................................... 94Figure 51. Increase of cable shield stresses at higher transmission voltages.......................................... 95Figure 52. Chart of XLPE cable design stress with system voltage. ...................................................... 99

Figure 53. Extrusion moulded joint (EMJ) schematic ............................................................................ 99Figure 54. 500 kV XLPE cable and extrusion moulded joints in a tunnel .......................................... 100Figure 55. One-piece joint (OPJ) schematic ......................................................................................... 101Figure 56. 275 kV EPR OPJ in manufacture ........................................................................................ 101Figure 57. 400 kV silicone OPJ in manufacture and routine test ........................................................ 102Figure 58. Prefabricated composite joint (PJ) schematic...................................................................... 103Figure 59. Prefabricated composite joint (PJ) during assembly ........................................................... 103Figure 60. 500 kV PJ joints on test ....................................................................................................... 105Figure 61, Outdoor termination with capacitor stress control .............................................................. 120Figure 62. Outdoor termination with prefabricated composite, premoulded stress cone ..................... 121Figure 63. Typical direct buried 400kV cable trench containing one Group of Cables ....................... 124

Figure 64. Component parts of a 400 kV gas insulated line................................................................. 131Figure 65. Two groups of 275 kV gas insulated line installed in a tunnel........................................... 134Figure 66. One group of 400 kV gas insulated line installed on stilts in a substation .......................... 134Figure 67. Cross section of a conceptual HTSC cable.......................................................................... 141Figure 68. 13 kV, three phase, concentric HTSC cable construction ................................................... 144Figure 69. Conceptual arrangement of an HTS cable in buried trough ................................................ 149Figure 70. Conceptual cross section dimensions of a HTSC buried, three phase group / trench

arrangement.................................................................................................................................... 150Figure 71. Conceptual installation swathe dimensions for a HTS cable trenches ................................ 151


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Figure 72: Construction and dimensions of Scoping Study 500 kV, 2500 mm, XLPE cable............. 164Figure 73 Scenario 1 ............................................................................................................................. 167Figure 74: Preliminary duct block arrangement ................................................................................... 169Figure 75: Preliminary direct burial arrangement................................................................................. 172Figure 76: Trench with sloped sides ..................................................................................................... 174Figure 77: Spacing between Groups of Cables..................................................................................... 176Figure 78: Arrangement of circuits and construction Swathe.............................................................. 177Figure 79: Photograph of construction swathe for four trenches.......................................................... 178Figure 80: Sample ampacity calculation............................................................................................... 179Figure 81: Required phase spacing at increased laying depth .............................................................. 182Figure 82: Requirement for cable installed by trenchless method........................................................ 183

Figure 83: Typical directional drill arrangement, plan view ................................................................ 183Figure 84: Typical naturally ventilated tunnel...................................................................................... 184Figure 85: Compound containing two headhouses for naturally ventilated tunnels............................. 185Figure 86: Typical reel dimensions and weight .................................................................................... 186Figure 87: Conventional delivery ......................................................................................................... 187Figure 88: Longitudinal reel on lowboy ............................................................................................... 187Figure 89: Plan of typical joint bay....................................................................................................... 188Figure 90: Longitudinal elevation of typical joint bay ......................................................................... 189Figure 91: Elevation cross section across typical joint bay .................................................................. 189Figure 92:Tunnel temperatures over a 10 year period .......................................................................... 191Figure 93: Typical tunnel cable clamp (cleat) for a sagged system...................................................... 192

Figure 94:Tunnel cross section: deep tunnel......................................................................................... 193Figure 95:Tunnel cross section: cut and cover...................................................................................... 193Figure 96 Scenario 2, one group per circuit installed initially (black), the second later ...................... 194Figure 97: Staging summary................................................................................................................. 195Figure 98: Scenario 2, staging for the duct-manhole system................................................................ 196Figure 99:Scenario 2, staging for cables direct buried in the ground ................................................... 198Figure 100: Scenario 2, staging for cables installed in deep tunnels .................................................... 199Figure 101: Scenario 2, staging for cables installed in cut and cover tunnels ...................................... 201Figure 102: Alternative SCFF 500 kV cable ........................................................................................ 204Figure 103. Underground cable: design requirement............................................................................ 220Figure 104 Cable spacing...................................................................................................................... 221

Figure 105. Cross bonding schematic................................................................................................... 223Figure 106. Detail of cross bonding components ................................................................................. 223Figure 107: Proposed 500 kV design: extruded lead sheath................................................................. 228Figure 108: Proposed 500 kV design: welded aluminium sheath......................................................... 229Figure 109: Proposed 500 kV design: corrugated aluminium sheath ................................................... 230Figure 110: Proposed 500 kV design: copper wire screen and corrugated stainless steel sheath......... 231Figure 111: Proposed 500 kV design: copper wire screen and lead sheath.......................................... 232Figure 112: Proposed 500 kV design: wire screen and smooth aluminium sheath .............................. 233Figure 113: Proposed 500 kV design: copper wire screen and aluminium laminate............................ 234


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Figure 114: Proposed 500 kV design: self contained fluid filled ......................................................... 235Figure 115: Proposed 500 kV design: GIL ........................................................................................... 236Figure 116 One piece prefabricated joint (OPJ) ................................................................................... 239Figure 117. Prefabricated composite joint (PJ)..................................................................................... 239Figure 118. Indoor GIS switchgear....................................................................................................... 240Figure 119. Power losses for selected scenarios at different levels of transmitted power.................... 243Figure 120. Power losses for an average load of 457.3 MW................................................................ 245Figure 121. Estimated capital cost components in $M for 4 groups of Cables, 10 km long ................ 251Figure 122. Estimated capital cost components in $M for 3 groups of Cables, 10 km long ................ 252Figure 123. Estimated capital cost components in $M for 4 groups of Cables, 20 km long ................ 253Figure 124. Estimated capital cost components in $M for 3 groups of Cables, 20 km long ................ 254

Figure 125. Estimated capital cost components in $M for all overhead line (Scenario 6) ................... 255Figure 126. Historic variation in the value of Canadian dollar............................................................. 262Figure 127. Historic variation in copper price (USD) .......................................................................... 264

TABLES

Table 1. Description of Scenarios........................................................................................................... 26Table 2. Table of Scenarios..................................................................................................................... 27Table 3. 500 kV Study Project costs, cost differences and cost ratios compared to all-overhead line ... 31Table 4. Ratio of cost of underground cable and transition stations to an equal length of overhead line

.......................................................................................................................................................... 32Table 5. Duration of cable supply and installation for each scenario..................................................... 33Table 6. Power losses for each scenario at an average load of 457.3 MW............................................. 36Table 7. Power losses per circuit for each scenario at an average load of 1,000 MW ........................... 37Table 8. PV of losses and of revenue requirement ................................................................................. 38Table 9. Number of suppliers for each undergrounding scenario........................................................... 43Table 10. Minimum design temperatures for cable ................................................................................ 47Table 11. Minimum design temperatures for splices (joints) ................................................................. 47Table 12. Maximum and minimum design temperatures for air insulated terminations ........................ 48Table 13. Maximum and minimum design temperatures for gas insulated terminations....................... 48Table 14. Scenarios considered............................................................................................................... 51

Table 15 Cumulative quantities of underground cables of all types in each country ........................... 106Table 16 Commercial applications of large conductor XLPE cable with joints by voltage,conductors size, and circuit length ................................................................................................. 109

Table 17 Summary of the cumulative lengths at each voltage of major XLPE circuits with largeconductors, long lengths and joints ............................................................................................... 109

Table 18 XLPE Cable system component statistics: 315 kV to 500 kV............................................... 110Table 19 SCFF Cable system component statistics: 315 kV to 500 kV ............................................... 110Table 20 Total cable system components installed up to end 2005: 315 kV to 500 kV....................... 111Table 21 Comparison of statistics of XLPE circuit from three sources................................................ 111


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Table 22 EHV installation types, three phase cable lengths and number of projects........................... 129Table 23. Details of significant GIL applications................................................................................. 135Table 24. Details of some HTSC cables and applications .................................................................... 147Table 25 CIGRE failure rates of components in 220 kV to 500 kV XLPE cable systems................... 154Table 26 Failure rates of components in 220 kV to 500 kV XLPE cable systems by cause................ 155Table 27 Conditioned failure rates of components in 220 kV to 500 kV XLPE cable systems ........... 156Table 28 Unconditioned cable system failure rates for the study scenarios for one year in-service.... 156Table 29 Conditioned cable system failure rates for the study scenarios for one year in-service........ 157Table 30 Unconditioned cable system failure rates for the study scenarios for 40 years in-service .... 158Table 31 Conditioned cable system failure rates the study scenarios for 40 years in-service.............. 158Table 32 Numbers of faults in all types of 220 kV-500 kV AC land circuits by installation type....... 159

Table 33 OHL failure rates for the study scenarios for one year in-service ......................................... 160Table 34 OHL failure rates for the study scenarios for forty years in-service...................................... 160Table 35 Tunnel dimensions for scoping study .................................................................................... 190Table 36. Magnetic field from EMF report (Appendix, Section 13) .................................................... 213Table 37 Supplier responses: Average capacitance and dielectric losses for XLPE cable................... 237Table 38 Supplier responses: Average capacitance and dielectric losses for SCFF cable ................... 237Table 39 Supplier responses: Average capacitance for GIL................................................................. 237Table 40 Combined conductor and sheath losses: XLPE cable mean and maximum ....................... 238Table 41 Conductor and enclosure losses of GIL................................................................................. 238Table 42. Power losses for each scenario at an average load of 457.3 MW ......................................... 245Table 43. Power losses per circuit for each scenario at an average load of 1,000 MW ....................... 246

Table 44. Estimated NPV of power losses over a forty year period..................................................... 247Table 45. Capital cost estimates for each scenario (2009 dollars)........................................................ 250Table 46. Estimated NPV of the life cycle cost for each scenario........................................................ 256Table 47. Effect on estimated cost of number of Groups of Cables ..................................................... 257Table 48. Effect on estimated cost of staging ....................................................................................... 257Table 49. 500 kV Study Project Estimated costs, cost differences and cost ratios compared to all-

overhead line .................................................................................................................................. 258Table 50. Ratio of estimated installed cost of underground cable to an equal length of overhead line 259Table 51. Ratio of estimated cost of underground cable and transition stations to an equal length of

overhead line .................................................................................................................................. 259Table 52. Estimated capital cost increase if SCFF cable is used .......................................................... 261

Table 53. Estimated capital cost change if Canadian dollar value should vary by 20% ...................... 263Table 54. Estimated capital cost change if cable metal prices should vary by 50%............................. 264Table 55. Duration of cable supply and installation for each scenario................................................. 265Table 56 Unconditioned failure rates for a 65 km cable route length for one year in-service ............. 269Table 57 Conditioned failure rates for a 65 km cable route length for one year in-service ................. 270Table 58 Unconditioned failure rates for a 65 km cable route length for forty years in-service.......... 270Table 59 Conditioned failure rates for a 65 km cable route length for forty years in-service.............. 270


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1 EXECUTIVE SUMMARY

1.1 Introduction

CCI has been engaged to perform a study into the feasibility of using 500 kV underground cable for atransmission system in the Edmonton region of Alberta. The example used for the 500 kV StudyProject is generic and based on the two 3,000 MVA circuits known as the Heartland Project, with theunderstanding that the findings could be applied to other 500 kV transmission applications in theEdmonton region of Alberta. This report does not include an economic optimisation of the design asthis would be performed at some future stage should it be decided to proceed with an underground

option.

The scope of the feasibility study also includes the identification of the next steps to be taken if it isdecided to proceed with a detailed evaluation of an option that includes underground cable.

While the AESO and others have provided information to CCI relevant to the study, the findings andrecommendations are those of CCI alone.

The main issues that have been addressed are:

Techni cal f easibi li ty of 500 kV undergr ound cable systems

This is summarised in Section 1.3 and is discussed in Sections 4, 7 and 9.

Reliability

Reliability of the 500 kV cable system is summarised in Section 1.4 and is discussed withinSection 5.2.1.Reliability of the 500 kV overhead line systems is discussed within Section 5.3 andinformation is given in Appendix, Section 1.

Estimated costs

These are summarised in Section 1.5 and is discussed in Section 12, with detailedinformation being given in the Appendices, Sections 2 and 3.

500 kV Study Proj ect schedul e

This is summarised in Section 1.6 and is discussed in Section 13, with detailed informationbeing given in Appendix, Section 4.

Power losses

This is summarised in Section 1.7 and discussed in Section 11, with detailed informationbeing given in Appendix, Section 5.


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Recommendations for next stepsThese are summarised in Section 1.8.

500kV Study Proj ect ri sks

These are discussed in Section 15.

1.2 Method of approach

This report is based on the prospective requirement to use underground cable for all or part of two500 kV Transmission circuits in the Edmonton region of Alberta. This is referred to as the 500 kV

Study Project. The example upon which the design parameters and the terrain of the route of the500 kV Study Project have been based is the proposed Heartland Project, which consists of two parallel500 kV, 3,000 MVA circuits with a route length of 65 km per circuit.

A summary of the division and sequence of work between CCI, HPT and AESO is given below:

CCI

Performed a scoping study as the basis for :

Invitation to cable suppliers to provide outline designs, budgetary costs andmanufacturing times.

Outline trench cross-section dimensions to be provided to HPT for a) normal

installation conditions and b) for special construction at a generic obstructioncrossing.

Participated in visits to Tokyo with AESO and HPT to evaluate a) the only operational, longlength 500 kV cable system in the world and b) the premises of two of the manufacturerswho supplied it.

Analysed the manufacturers design responses to provide averaged:

Cable sizes.

Installation layouts.

Manufacturing and jointing times.

Estimated capital costs of cable, accessories and spares; these were normalised toallow for common metal prices and exchange rates.

Cable system energy losses.

Reviewed the state of the art of cable technology with respect to the 500 kV Study Project.

Advised:

Feasibility of the available cable technologies to the 500 kV Study Project.

Risks associated with 500 kV cable technology for use in the Edmonton region ofAlberta.

Next steps to be followed if an underground option is to be investigated further.


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HPT Selected preliminary routes for indicative civil and installation costing purposes, comprising

installation of a) cable laying in normal conditions and b) cable crossings of routeobstructions.

Selected the installation type, i.e. that the cable should be direct buried in the ground. Thisbeing considered to be the lowest cost option.

Compiled a project schedule.

Compiled the total estimated capital costs of nine scenarios comprising a) differentproportions of underground cable to overhead line and b) transition stations.

AESO

Studied the effect of the underground cable on the operation of the system. Studied the effect of reactive compensation on the operation of the transmission system

containing underground cable.

Compiled the lifecycle costs of nine different scenarios.

Calculated the cost of losses of the cable, reactors and overhead line.

In order to obtain information for the 500 kV Study Project on the availability of 500 kV cable systemsand the estimated costs for cable systems, a number of prospective manufacturers were contacted andtechnical proposals and budgetary prices were requested. The request was based on the requirementsfor the Heartland Project, with a generic underground route length of nominally 10 km. The ambient airand ground temperature information given to suppliers was based generally on the design parameters

that had been used for the 240 kV Downtown Edmonton Supply and Substation (DESS) undergroundcable project.

The estimated cost provided by each prospective cable supplier was given on the basis that, forcommercial reasons, it would remain confidential. The estimated cost and design information havetherefore been presented in this report a non attributable manner. A summary of the designs proposed

by prospective suppliers is given in Section 9.

Different scenarios, which each include some underground cable, were agreed for study; Figure 9,Figure 10, Figure 11 and Figure 12. Each scenario comprises different combinations of undergroundcable length, overhead line length and numbers of parallel Groups of Cables. These scenarios include

options for undergrounding the following generic lengths in a nominal 65 km route:

10 km underground cable (55 km overhead line)

20 km underground cable (45 km overhead line)

The estimated costs of the scenarios containing either a 10 km or 20 km length of underground cablewere compared with the estimated cost of a 65 km all-overhead line scenario, with no undergroundcable. Some consideration was also given to the engineering implications of undergrounding the entire65 km route, Section 14, although the costs were not estimated.


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To obtain representative costs for installation conditions, indicative routes in the EdmontonTransportation Utility Corridor (TUC) were chosen by the HPT. The lengths of these indicative routesdo not necessarily correspond with the generic 10 km and 20 km lengths chosen for the study. Theseare shown in Appendix, Sections 6 and 7. The work by the HPT is acknowledged with thanks.

Indicative installation designs were prepared by CCI so that the feasibility of undergrounding could beevaluated and to determine the civil cost and practicability. These were based on the ground conditionsthrough which the cable system would have to be installed and the types of obstruction which wouldhave to be crossed. Details of these indicative designs are given in Section 7.

Information was collected and compiled for inclusion in this report by CCI from information supplieda) on the cable system by the cable manufacturers and b) on the type of civil works installation suppliedby the HPT.

The estimated costs given in this feasibility study were expected to be within a range of plus or minusthirty percent.

1.3 Technical feasibility findings

The conclusions are that:

Cable is technically feasible for the underground part of the 500 kV Study Project. Cable with extruded, cross-linked polyethylene (XLPE) is the best choice of cable type.

The proviso is that the performances of the particular 500 kV XLPE designs of cable and accessories tobe offered by selected manufacturers must be validated on test as described in Section 1.3.7. Key testsare:

Accelerated aging conditions at elevated voltage and high current loading for one year toIEC 62067[1]

Simulated low ambient temperature for a representative period, this being a specialrequirement for this 500 kV Study Project.

The reasons for the choice of this technology and the need to demonstrate performance are givenbelow.

1.3.1 Choice of cable technology

The most appropriate cable system technology for the 500 kV Study Project is cableinsulated with extruded, cross-linked polyethylene (XLPE). XLPE cable has the benefits of:


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Low energy loss. Solid insulation that does not require impregnation with insulating fluid and

consequently a) risk of leakage into the environment is eliminated b) maintenanceis reduced and c) risk of fire spread is reduced.

XLPE cable is preferred to the alternative pre-existing design of cable, which is the self-contained fluid-filled (SCFF) type insulated with polypropylene paper laminate (LPP) tape.The numbers of applications and suppliers of SCFF cable are presently falling to a levelwhere it is foreseen that it will soon become obsolete for land cable applications. Thesuitably trained and experienced personnel and specialist equipment which would berequired for a SCFF cable system for the 500 kV Study Project will consequently become

increasingly difficult to obtain. There are also environmental concerns regarding possibleleakage of insulating fluid from SCFF cable systems.

Other technologies of Gas Insulated Line (GIL) and High Temperature Superconducting(HTS) cable have also been evaluated. GIL is a possible alternative for a tunnel application,

but is not recommended for a long length buried application. (No proposals for buried GILsystems have been received from any prospective suppliers.) GIL has the advantages of ahigh power carrying capacity and reduced need for reactive compensation. A long lengthGIL circuit contains large volumes of Sulphur Hexafluoride (SF6) insulating gas and thereare some environmental concerns regarding possible leakage. HTS cable has not beensufficiently developed for use in a high power, long length application with joints, such as

the 500 kV Study Project and so is not considered further.

1.3.2 500 kV XLPE cable system: supply capability and experience

The typical design of direct buried XLPE cable system proposed by prospectivemanufacturers to meet the requirement to transmit 3,000 MW comprised two cables per

phase each having a copper conductor with a cross sectional area of 2,500 mm. Thisconductor size is at the top end of the range that has been installed to date. Conductor sizesof up to 3,500 mm have been developed for 500 kV cable.

The majority of the prospective manufacturers who were contacted were willing to offer a500 kV XLPE underground cable system for the Heartland Project. From a supplier

perspective a 500 kV XLPE underground cable system is thus indicated to be technicallyfeasible. The cables and joints are prospectively suitable for installation either in the ground(buried or in ducts), or in tunnels.

A fully tested and service proven off the shelf design of 500 kV XLPE cable system(cables, accessories and ancillaries) does not exist for the 500 kV Study Project. Suitabledesigns of proven 500 kV XLPE cables and terminations exist, but the analysis of


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manufacturers responses shows that only a small number of commercially available,prefabricated, joints have commenced service experience at 500 kV. To date their initialservice experience is judged to be insufficient to accept the designs as service proven for thesubstantially greater numbers required for the 500 kV Study Project. Some limited 500 kVtest experience exists, but has not been sufficiently quantified by manufacturers. A utility inShanghai[2] has awarded a major contract to two manufacturers for two 17 km long-length

parallel circuits of 500 kV 2,500 mm cable, which are at present at an advanced stage ofconstruction in a tunnel. Two different types of 500 kV prefabricated joint are beinginstalled. Other manufacturers submissions for the 500 kV Study Project indicated thatsimilar designs of 500 kV joints exist, in the form of either prototype joints undergoing in-house evaluation tests, or as design proposals.

Three suppliers have commercial experience with the manufacture and installation of largeconductor 500 kV cable and joints. There are many 400 kV cable systems in operation thatcontain XLPE insulated cables having the same 2,500 mm conductor size that would beneeded for the 500 kV Study Project. Many of these include the prefabricated joint types

proposed for the 500 kV Study Project. However, the 400 kV cables and joints operate at alower electrical stress than is required for the 500 kV Study Project. The existence of these400 kV circuits is a good indicator that there are several more manufacturers who have theright level of capability and experience to develop, manufacture and install a long length,high power 500 kV cable system.

It is normal for manufacturers to custom-design underground EHV transmission circuits foreach particular application, including the necessary supporting development work andProving Tests.

1.3.3 Choice of installation technology

The most appropriate cable installation technology for the 500 kV Study Project is directburied, naturally cooled, in terms of simplicity and anticipated total costs. A forced cooledsystem is more complex than a naturally cooled cable system. Because of the need for

planned or unplanned outages to maintain the cooling equipment, it is less likely to be

available for service. A naturally cooled system has no cooling equipment.

Prospective cable system suppliers provided designs and cost estimates for cable systemssuitable for installation in naturally cooled direct buried, naturally cooled duct-manhole andforced ventilated tunnel arrangements. The HPT have provided installation cost estimatesfor the direct buried, naturally cooled, method.

The layout proposed by most manufacturers comprised four trenches each containing oneGroup of Cables. This is shown in Figure 23 and with installation dimensions typically as


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shown in Figure 78. This arrangement consists of two circuits, each comprising two Groupsof Cables. Each Group of Cables has three individual single core cables installed in onetrench. For the purpose of this feasibility study a total of eleven layout scenarios wasconsidered in varying levels of detail. The scenarios have either different lengths ofunderground cable, different numbers of Groups (trenches) and different phased installationtime Stages. The scenarios are described in Section 2.2.

1.3.4 500 kV Study Project size

An underground cable system for the 500 kV Study Project would be one of the largest in

the world to date. If the route length were to be 20 km, and if two circuits, each consistingof two Groups of Cable were to be selected, the quantities of cable would be equal to thosein the only very long 500 kV circuit in commission to date (in Tokyo). The Tokyo tunnelcircuit was supplied by four cable manufacturers and commissioned nine years ago. (Sincethe installation of the Tokyo project, there has been a consolidation in the number ofJapanese cable makers from four to two). The quantities required for the 500 kV StudyProject are within the supply capabilities of cable manufacturers.

This would be the first application of direct buried, long length, large conductor 500 kVXLPE cable.

The 500 kV Study Project has the combination of the highest system voltage of 500 kV andone of the highest power ratings of 3,000 MVA, which results in a large conductor area of2,500 mm and a large diameter cable. The large cable size poses challenges to themanufacture, delivery and installation of worthwhile drum lengths of cable and in particularto the designs and performance of the accessories (joints and terminations) required.

1.3.5 Project specific requirements

The location-specific requirements for the 500 kV Study Project are the crossing of routeobstructions; such as wide roads, railroads, wetlands and many oil and gas pipelines.

If a major obstruction is encountered in a particular future route, such as the NorthSaskatchewan River valley, which is deep and wide, a separate feasibility study would berequired to select a suitable method of crossing.

Low temperature operation (see below).


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1.3.6 Low ambient temperatures

The winter air and ground temperatures that occur in the vicinity of Edmonton are lowerthan those previously reported for any other 400 kV and 500 kV applications of XLPE cablesystems. Some manufacturers submitted their experience lists for transmission voltages ofless than 400 kV. These showed that some long length, large conductor cable systems have

been supplied into locations in which the minimum winter ambient temperature is possiblyless than zero degrees Celsius. However, no evidence of recorded minimum ambienttemperatures was provided. For the 500 kV Study Project cable system to be acceptable itis necessary to demonstrate the operational reliability at low temperature of the cables andaccessories. The cable accessories are prospectively the most vulnerable, because the

elastomeric insulation would be operating closer to the glass transition temperature atwhich the properties of high elasticity, believed to be essential for reliable electrical

performance, are lost.

Temperature records from the 240 kV DESS duct-manhole project in Edmonton, show that:

240 kV elastomeric joints and XLPE cable installed at 1.3 m depth have beenexposed to a winter ground temperature of -8oC.

To give an adequate margin of safety for the 500 kV Study Project, designtemperatures are recommended of:

500 kV joints in a direct buried installation: -15oC

500 kV joints in a duct-manhole installation: -20oC

240 kV outdoor terminations have been exposed to a temperature of -46oC.To give an adequate margin of safety for the 500 kV Study Project, the designtemperature is recommended to be in line with Alberta practices for outdoorelectrical equipment:

500 kV outdoor terminations in open air: -50oC

To demonstrate suitability for winter operation it is recommended as mandatory thatprospective manufacturers participate in a series of development activities to demonstratethe low temperature performance of their 500 kV XLPE cable system.

The winter design temperatures can be raised to higher and more acceptable temperatures atwhich more service and test experience exists. Joint temperatures could be raised by burialat greater depths, for example to a depth of 2.5 m, at which depth the minimum groundtemperature may be above 0oC, thus allowing the design temperature to be raised to, say,-5oC. Cable termination temperatures can be increased by installation within a specially


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constructed and temperature controlled building. This should allow the minimum airtemperature to be maintained above, say, 0oC and the design temperature to be raised to,say, -5oC. (It is recommended that these alternatives be investigated in the next steps)

A consequence of installing the cable system at greater depths is that system ampacity isreduced under the limiting summer rating condition. To ensure that the cable at greaterdepth does not exceed its maximum design temperature in summer the following studies arerecommended to be performed:

A cyclic ampacity calculation be performed to take advantage of the reduction inheat generation due to the hourly fluctuating nature of the load current, in place of

the continuous ampacity calculation that was applied to the 500 kV Study Projectto meet the 3,000 MW requirement.

An investigation be performed to see if a more favourable ampacity can becalculated in summer by taking into account the temperature of the ground at the

proposed increased depth of cable burial. The present ampacity calculationmethod assumed that all of the ground is at a constant temperature, similar to thetemperature close to the ground surface. This is the conventional assumption usedin ampacity calculations for cables at depths of approximately 1 metre; but may be

pessimistic for the Edmonton region of Alberta where the temperature of theground at greater depths is significantly lower than that near the surface during thesummer period.

An evaluation be performed on increasing the number of cables per phase fromtwo to three to take advantage of the reduction of heat generation in each cable.

1.3.7 Proving the performance of the cable system before it is supplied

Both long term prequalification tests and low temperature tests must be performed

It is normal practice to require manufacturers to perform tests of proof on their systemsbefore providing supplies to applications such as the 500 kV Study Project. Therequirements for these tests are stated in international specifications[1] for cables. Some

cable system users formulate their own additional tests of proof to cover any specialrequirements for a particular application.

It is recommended that the cable systems must pass the following proving tests before theyare supplied to the 500 kV Study Project:

Prequalification test: a one year test to demonstrate performance when theparticular cable voltage, cable conductor and joints have not been previouslyprequalified.


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Type test: a six week long series of high voltage laboratory tests to prove thesuitability of the cable system design selected for the study project.

Special proving tests: tests to demonstrate the reliability of the cable systems atEdmonton cold winter temperatures. It is recommended that a specific series oftests be specified and performed.

Most of the manufacturers expressed an interest in supplying the 500 kV cable systems forthis Project and in performing the necessary tests. Some manufacturers provided details ofthe 500 kV proving tests that they had already commenced or completed, or are planning,

for 2,500 mm conductor cables and joints. None have yet completed a full series of testson the size of cable, type of joints and type of direct buried installation that would be usedfor the Study Project. This is not considered to be an obstacle to them performing therequired 500 kV prequalification tests.

1.4 Estimates of reliability

Expectations of reliability

Utilities throughout the world are now purchasing XLPE cable systems at voltages up to the

highest EHV levels, which demonstrates their confidence in the reliability of thistechnology.

Quality assurance and testing, care and maintenance

The 500 kV underground cable system can be expected to give reliable service, subject to:

Successful completion of proving tests before supply.

Quality control test programs during manufacture and installation.

Protection of the cable system from third party damage throughout its service life.

The objective in the design, Provi

Documents

CCI Feasibility Study for 500 KV AC Underground Cables