Tài liệu Electrical transmission and substation structures 2018 dedicated to strengthening our critical infrastructur

d from ascelibrary.org by RMIT UNIVERSITY LIBRARY on 01/03/19. Copyright ASCE. For personal use only; all right Electrical Transmission and Substation Structures 2018 Dedicated to Strengthening our Critical Infrastructure Proceedings of the Electrical Transmission and Substation Structures Conference 2018 Atlanta, Georgia  November 4–8, 2018 Edited by Michael Miller, P.E. Downloaded from ascelibrary.org by RMIT UNIVERSITY LIBRARY on 01/03/19. Copyright ASCE. For personal use only; all rights reserved. ELECTRICAL TRANSMISSION AND SUBSTATION STRUCTURES 2018 Dedicated to Strengthening our Critical Infrastructure PROCEEDINGS OF THE ELECTRICAL TRANSMISSION AND SUBSTATION STRUCTURES CONFERENCE 2018 November 4–8, 2018 Atlanta, Georgia SPONSORED BY Structural Engineering Institute of the American Society of Civil Engineers EDITED BY Michael Miller, P.E. Published by the American Society of Civil Engineers Downloaded from ascelibrary.org by RMIT UNIVERSITY LIBRARY on 01/03/19. Copyright ASCE. For personal use only; all rights reserved. Published by American Society of Civil Engineers 1801 Alexander Bell Drive Reston, Virginia, 20191-4382 www.asce.org/publications | ascelibrary.org Any statements expressed in these materials are those of the individual authors and do not necessarily represent the views of ASCE, which takes no responsibility for any statement made herein. No reference made in this publication to any specific method, product, process, or service constitutes or implies an endorsement, recommendation, or warranty thereof by ASCE. The materials are for general information only and do not represent a standard of ASCE, nor are they intended as a reference in purchase specifications, contracts, regulations, statutes, or any other legal document. 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Errata: Errata, if any, can be found at https://doi.org/10.1061/9780784481837 Copyright © 2018 by the American Society of Civil Engineers. All Rights Reserved. ISBN 978-0-7844-8183-7 (PDF) Manufactured in the United States of America. Electrical Transmission and Substation Structures 2018 iii Preface Downloaded from ascelibrary.org by RMIT UNIVERSITY LIBRARY on 01/03/19. Copyright ASCE. For personal use only; all rights reserved. The planning and preparation of the Electrical Transmission and Substation Structures Conference 2018 required an extraordinary amount of time, effort, and dedication by the members of the conference steering committee and the ASCE/SEI staff. The success of the conference is a direct reflection of the level of effort by this group of volunteers. The steering committee would also like to acknowledge the critical support of the sponsors and exhibitors who made this conference a success through their exhibition displays and substantial financial support. This conference takes place every three years and provides sessions on Structural Analysis, Special Design Considerations, Foundations, Structural Failure Analysis and Investigation, Substation Design Issues, Seismic, Construction Challenges, Structure Upgrading, and much more. On behalf of our dedicated volunteers and SEI staff, we would like to thank you for spending your valuable time attending the Electrical Transmission and Substation Structures Conference. It is our hope that you and your colleagues will benefit greatly from the information provided and make professional connections that last for years Acknowledgments Conference Steering Committee Michael Miller, P.E., M.ASCE Conference Steering Committee Chair SAE Towers Anthony Di Gioia, Jr., Ph.D., P.E., .M.ASCE DiGioia Gray and Associates, LLC Frank Agnew, P.E., M.ASCE Alabama Power Company Leon Kempner, Jr., Ph.D., P.E., F.SEI, M.ASCE Bonneville Power Administration Joel Bryant, P.E., M.ASCE TAPP, Inc. Gary E. Bowles, P.E., F.SEI, M.ASCE ECI Engineers Ronald Carrington, P.E., M.ASCE POWER Engineers Timothy Cashman, P.E., M.ASCE Cashman Engineering, LLC Dana Crissey, P.E., M.ASCE Oncor Electric Delivery Company © ASCE Otto Lynch, F.SEI, M.ASCE Power Line Systems, Inc. Mary Jane McMillen, P.E., F.SEI, M.ASCE AEP Robert E. Nickerson, P.E., F.SEI, M.ASCE Consulting Engineer Wesley J. Oliphant, P.E., F. SEI, F.ASCE EXO Group LLC Archie Pugh, P.E., PMP. M.ASCE American Electric Power Downloaded from ascelibrary.org by RMIT UNIVERSITY LIBRARY on 01/03/19. Copyright ASCE. For personal use only; all rights reserved. Electrical Transmission and Substation Structures 2018 iv Ronald Randle, P.E., F.SEI, M.ASCE EDM International Marlon Vogt, P.E., M.ASCE Ulteig Engineers David Todd, P.E., M.ASCE LG&E-KU Services Company C. Jerry Wong, Ph.D., P.E., F.SEI, M.ASCE DHW Engineering LLC Sponsors Premier Powerline Systems Silver Beta Engineering Black & Veatch Corporation PLH Group, Inc. Mitas Energy Platinum Valmont Utility Sabre-FWT TransAmerican Power Products Electrical Consultants, Inc. Trinity Meyer Utility Structures Bronze Fabrimet, INC. Falcon Steel, Inc. IEEE/NESC NV5 Osmose Utilities Services EXO Leidos Engineering Gold SAE Towers Ltd. DIS-TRAN Steel, LLC TRC Engineers SA-RA Group POWER Engineers Exhibitors (5/16/18) 3M Electrical Markets All-Pro Fasteners, Inc. Almita Piling AMPIRICAL Ampjack Industries, Ltd. ASC ASEC Inc. Bell Lumber & Pole Company Beta Engineering Bold Transmission LLC Boundry Layer Wind Tunnel Laboratory Brooks Manufacturing Co. Burns & McDonnell Cantsink Manufacturing CEATI International Chemline © ASCE Commonwealth Associate, Inc. Creative Pultrusions, Inc. Custom Engineering Solutions, Inc. DiGioia Gray, Inc. DIS-TRAN Steel EDM International, Inc. Electrical Consultants Inc. External Sun Steel Mast (Shanghai) Co., LTD. EXO Group LLC Fabreeka Fabrimet Falcon Steel America FDH Velocitel Frank X. Spenser & Associates, Inc. (FSXA) Electrical Transmission and Substation Structures 2018 Downloaded from ascelibrary.org by RMIT UNIVERSITY LIBRARY on 01/03/19. Copyright ASCE. For personal use only; all rights reserved. GAI Consultants, Inc. Gonzaga University Hanson Professional Services, Inc. HDR Helical Pier Systems, Inc. Highland Composites Hubbell Power Systems Hughes Brothers IEEE/NESC Kalpataru Power Transmission Karamtara Engineering Private Limited Keller: Cyntech, Hayward Baker, McKinney Drilling, Seaboard Foundations Kleinfelder Klute Inc. Steel Fabrication Laminated Wood Systems, Inc. Locweld Inc. Magnum Piering McWane Poles Mesa Associates, Inc. Metalogalva North America Inc. Mitas Energy and Metal Construction Inc. Network Mapping Group Oldcastle Enclosure Solutions Osmose Utilities Services, Inc. Paul J. Ford and Company PFISTERER LAPP North America Pile Dynamic, Inc./GRL Engineers, Inc. PLH Group Inc. Power Consulting Associates Powerline Systems Preformed Line Products © ASCE v PUPI (Geotek) Quanta Subsurface Rohn Products RS Poles Sabre-FWT SAE Towers Sanpec SA-RA Group Sediver USA Shaner Industries Stella Jones Summit Utility Structures Superior Concrete Products Surveying & Mapping, LLC TAPP, Inc Terra Remote Sensing (USA) Inc. The Stresscrete Group Threaded Fasteners, Inc. Tower Drafting Services, Inc. TransDesign International, LLC TRC Trinity Meyer Utility Structures Ulteig Utility Pole Solutions, Inc V&S Schuler Utilities Valmont Utility W.E Gundy & Associates Inc. Westwood Professional Services Williams Form Engineering Worley Parsons Zhejiang Shengda Steel Tower Co., LTD. Electrical Transmission and Substation Structures 2018 Contents Downloaded from ascelibrary.org by RMIT UNIVERSITY LIBRARY on 01/03/19. Copyright ASCE. For personal use only; all rights reserved. Construction Challenges Structural Design and Construction Challenges on the South and West of Edmonton Area Development Project ................................................................................. 1 Jondy Britton, Meagan Moeller, Wellan Cowan, Jacob Merriman, and Chih-Hung Chen Keeping the Project on Schedule—A Case Study about Emergency Weld Repairs Required on a Newly Installed Vibratory Caisson ......................................... 11 Zachary J. Oliphant, Justin W. Curtis, Benjamin S. Jessup, and Christopher W. Schnetzler Mechanically Spliced Full Length Anchor Bolts—Bringing It All Together ........................ 23 Kolleen L. Backlund, Adam G. Bowland, Aaron P. Darby, Keith S. Yamatani, and Nancy Z. Fulk Construction Challenges in Paradise Hawaiian Electric Company—138 kV System Rebuild ........................................................................................................................ 36 Mitchell Cowen and Garett Muranaka Foundations Guide for Transmission Line Foundations with Least Impact to Environment ................... 47 Peter M. Kandaris, Ashley E. Evans, and Asim Haldar Practical Collaborative Approach to Alternative T-Line Foundations ................................ 62 Bridget Honsey, Jacob Hexum, Cole Vosters, Michael Bradley, and Cliff Van Den Elzen The Value of Structure-Specific Borings: Statistical Analysis of Electrical Transmission Line Structure Foundation Costs Based on Structure-Specific Borings versus No Borings or Variable Boring Spacing ........................................................ 70 Robert Chantome, James Knutelski, Darren Ratliff, Kevin Schilling, and Daniel Whalen Groundwork for Developing Comprehensive Transmission Line Foundation Design Guidelines .................................................................................................................... 84 Peter M. Kandaris, Steve Davidow, and Ashley E. Evans Posters Composite Transmission Towers: Analysis, Behavior, Slip Investigation, and Interaction Diagrams ....................................................................................................... 94 Mustafa Mahamid, Kamel Bilal, and Cenk Tort © ASCE vi Electrical Transmission and Substation Structures 2018 Failure Analysis on Transmission Tower Struck by Tropical Storms ................................ 108 Jian Zhang and Qiang Xie Downloaded from ascelibrary.org by RMIT UNIVERSITY LIBRARY on 01/03/19. Copyright ASCE. For personal use only; all rights reserved. Effective Length Factor of Leg Member in Latticed Steel Tower ....................................... 122 M. L. Lu, M. Hao, and D. Chakrabarti Seismic Effects on Transmission Lines and Their Major Components .............................. 132 Leon Kempner Jr., Scott Schlechter, and Asim Haldar Program Considerations for Analysis of Drilled Shaft Foundations .................................. 146 Sanchit Chitre, Joel Coker, and Brian Sedgwick Flood Design of Substation Structures ................................................................................. 157 Jared Augustine, Emily Larson, and Emily Bonini Consideration of Sustained Loads and Creep Effects in Specifying and Designing Fiber Reinforced Polymer (FRP) Utility Poles ................................................... 167 Diego S. Arabbo, Matthew C. Richie, and Scott J. DiFiore A Full-Scale Crash Test for a Transmission Wood Pole...................................................... 176 Haijian Shi Seismic Design of Substation Steel Structures: What Code Should I Follow? ................... 185 Hannah M. Hillegas and Prapon Somboonyanon Analysis, Prediction, and Mitigation of Vortex Induced Vibrations in Substation Structures ............................................................................................................ 191 Hossein Qarib and Diaaeldin Mohamed Managing Aging Substation Structures ............................................................................... 199 Harinee Trivedi and Stefanie Gille Seismic Evolution of Electrical Grid Seismic Resiliency ................................................................... 209 John Dai, John Eidinger, Florizel Bautista, and Roderick Dela Cruz Seismic Design of Substations—IEEE Standard 693 Gets a Major Update ....................... 219 Eric Fujisaki, Leon Kempner Jr., Brian Knight, and Craig Riker Seismic Resiliency: What Utilities Should Know to Keep the Lights On............................ 233 Robert S. Cochran Special Design Considerations Aesthetics and Infrastructure: Accomplishing Both with Better Overall Results for Power Delivery Projects ..................................................................................... 244 Kenneth Sharpless and Lynda Kiejko © ASCE vii Electrical Transmission and Substation Structures 2018 Downloaded from ascelibrary.org by RMIT UNIVERSITY LIBRARY on 01/03/19. Copyright ASCE. For personal use only; all rights reserved. Case Study for Behaviour of Transmission Line Structures under Full-Scale Flow Field of Stockton, Kansas, 2005 Tornado .................................................................... 257 Ashraf A. El Damatty, Nima Ezami, and Ahmed Hamada Evaluation and Implementation of Alternate Pole Materials to Meet Regulatory Aesthetic Requirements ..................................................................................... 269 Clinton Y. Char and Alaira Bilek Question: What Is an Acceptable Target Reliability for High-Voltage Transmission Lines? ............................................................................................................. 281 Leon Kempner Jr. Securing Steel Davit Arms: When and How? ...................................................................... 290 Meihuan Fulk, Blake Tucker, and David Parrish Modeling and Quantifying the Aerodynamic Characteristics of Transmission Line Structures to Avoid and Mitigate Aeolian-Induced Vibrations .................................. 302 Erik Ruggeri Embrittlement in T.L. Lattice Steel Structures Specifying Energy Absorption Criteria .................................................................................................................................. 312 Katherine Bridwell, Bhargava Vantari, Jonathan Kell, and Cesar Aguilar Structural Analysis Lattice Tower Deflection and Modeling of the Structure and Spans in Practice ............... 325 Saumya Nag, Steve Beilstein, Loren Jessen, Jonathan Frantz, Matthew Nicholson, Khaled Kator, and Kevin Heller Recent Duke Energy Studies to Develop Transmission Pole Standard ............................... 337 Prasad Yenumula, Jimmy Robinson Jr., and Neal Murray Lattice Transmission Structures: Challenging Modeling Scenarios That Require Non-Traditional Analysis Methods ........................................................................ 349 Kevin M. Wortmann and Ryan Z. Hann Wood v. Steel: Dawn of Justice............................................................................................. 362 Otto J. Lynch Heel or Toe? The Transmission Engineer’s Guide to Single Angles in Flexure ................. 372 Aaron Darby, Mary Jane McMillen, Nancy Fulk, and Robert Nickerson Crossing the Delaware with PECO and a 300 ft Tall H-Frame Structure .......................... 385 Guy Faries and Kalpesh Patel Updated Fall Protection Efforts for Transmission Structures ............................................ 393 David E. O’Claire and Mark D. Nelson © ASCE viii Electrical Transmission and Substation Structures 2018 Structural Failure Analysis and Investigation Downloaded from ascelibrary.org by RMIT UNIVERSITY LIBRARY on 01/03/19. Copyright ASCE. For personal use only; all rights reserved. Evaluation of Typical Arm-to-Pole Connections in Slender Steel Pole Transmission Structures for Wind Induced Vibration and Fatigue ................................... 407 Lawrence G. Griffis and Karl H. Frank Fatigue Testing and Finite Element Modeling of Arm-to-Pole Connections in Steel Transmission Pole Structures .................................................................................. 419 Francisco J. Bonachera Martin, Jason B. Lloyd, Robert J. Connor, and Amit Varma Welding Challenges in Typical Connections Used in Steel Pole Transmission Structures .............................................................................................................................. 435 Jim Merrill and Wesley J. Oliphant Challenges in Design and Mitigation of Wind-Induced Vibration for Slender Steel Pole Transmission Structures ...................................................................................... 445 Daryl Boggs Structure Upgrading Great River Energy Transmission Line Tower Repairs ...................................................... 458 Kerby M. Nester and James M. McGuire Teaching an Old Line New Tricks ........................................................................................ 472 Jimmy Buker and Deborah Knudtzon Steel Transmission Pole Structural Capacity Uprating for High Voltage Transmission Line and Substation Upgrade Projects ......................................................... 484 Chad Hines, Matthew Lohry, and Christopher Facklam Substation Design Issues Prefabricated Foundations—Construction Efficiencies and Economic Impacts ................ 496 Daniel S. Cuffman, Aaron P. Darby, and Olivialin A. Miller Design and Construction of Riser Structures in Alberta ..................................................... 506 Kumar Kishor and Andrew Rees Going against the Current: Short Circuit Force Background ............................................ 519 Alex J. Kladiva © ASCE ix Electrical Transmission and Substation Structures 2018 Structural Design and Construction Challenges on the South and West of Edmonton Area Development Project Jondy Britton, P.E., M.ASCE1; Meagan Moeller, P.E., M.ASCE2; Wellan Cowan3; Jacob Merriman, P.E., P.Eng., M.ASCE4; and Chih-Hung Chen, P.E., P.Eng.5 Downloaded from ascelibrary.org by RMIT UNIVERSITY LIBRARY on 01/03/19. Copyright ASCE. For personal use only; all rights reserved. 1 Burns & McDonnell, 9400 Ward Pkwy., Kansas City, MO 64114. E-mail: [email protected] 2 Burns & McDonnell, 9400 Ward Pkwy., Kansas City, MO 64114. E-mail: [email protected] 3 Burns & McDonnell, 9400 Ward Pkwy., Kansas City, MO 64114. E-mail: [email protected] 4 Burns & McDonnell, 9400 Ward Pkwy., Kansas City, MO 64114. E-mail: [email protected] 5 Burns & McDonnell, 9400 Ward Pkwy., Kansas City, MO 64114. E-mail: [email protected] ABSTRACT In 2013, AltaLink initiated work on the South and West of Edmonton Area development project comprised of multiple 138-kV and 240-kV circuit modifications. Scopes included greenfield construction, rebuilding existing lines, and tapping existing lines to new substations. The complicated project scopes were challenging to construct due to outage constraints, environmental restrictions, and the need for multiple foundation solutions. Proper outage planning with the AltaLink Control Center was imperative and directly impacted the construction sequencing of the project. Environmental concerns affected the project in multiple ways: work restrictions during bird nesting and migration seasons, requirements for rig matting in environmentally sensitive and wet areas, and the use of vehicle wash stations. A variety of structure types were implemented on the project including double-circuit latticed steel towers, single-, double-, and triple-circuit tubular steel poles, and wood poles. Foundation types, including drilled shafts, helical foundations, and direct embed foundations, were selected based on structure type and location. Construction commenced in early 2017, and the project was placed in service in December 2017. PROJECT DEVELOPMENT PROCESS Continued residential, commercial, and industrial growth south and southwest of Edmonton, Alberta, has resulted in increased electric load in the area. The Alberta Electric System Operator (AESO) forecasted that the winter peak load in the Edmonton planning region was expected to grow from approximately 2,100 MW in 2011 to approximately 2,800 MW by 2022. The AESO also forecasted that generation in the region would grow from approximately 4,600 MW in 2010 up to 5,400 MW by 2020 (AESO 2012). The AESO concluded that transmission system reinforcement was needed to alleviate system constraints created by load growth and generation expansion, and to comply with reliability criteria. Following identification of the areas requiring transmission development, shown in Figure 1, the AESO filed a Needs Identification Document (NID) with the Alberta Utility Commission (AUC) for system reinforcement designated as the South and West of Edmonton Area Transmission Development (SWEATD). The NID contained several alternatives, but the © ASCE 1 Electrical Transmission and Substation Structures 2018 Downloaded from ascelibrary.org by RMIT UNIVERSITY LIBRARY on 01/03/19. Copyright ASCE. For personal use only; all rights reserved. preferred option included four smaller sub-developments with scopes including the construction of new substations, the modification of existing substations, and the construction of 240-kV and 138-kV transmission lines. The sub-developments were designated as Harry Smith, Cooking Lake, Saunders Lake, and Leduc. The locations of the sub-developments relative to the area requiring reinforcement are also identified in Figure 1. Figure 1. Greater Edmonton Transmission Development Area (AESO Newsletter) Once the SWEATD project was identified, the project process shifted toward public notification and participation. The AUC notified the public of the AESO’s NID filing through the commission’s website and local newspapers. After a public hearing process, the NID was approved and the project progressed to the development of a Facility Application (FA) by the selected Transmission Facility Operator, AltaLink. Throughout the FA process, AltaLink’s project team narrowed the scope of each sub-development and incorporated feedback from the public consultation process. AltaLink compared the options for each sub-development by completing transmission line optimization studies and conducting an involved public consultation process. Selection of the preferred option required consideration of the environmental, aesthetic, and cultural impact of the project, both during construction and post-energization. After public hearings and a review of the FA, the AUC issued the permit and license to AltaLink to construct the transmission facilities. The facilities were energized as planned at the end of 2017, meeting AESO transmission system reinforcement requirements with an engineered solution that minimized impacts to the environment and community. A PORTFOLIO OF PROJECTS Early in the planning stages of the project, a single-line diagram of the overall system was developed to allow the project team to better visualize the scope of work, sequence of work, and schedule dependencies between the sub-developments, and to start high-level outage planning. © ASCE 2 Downloaded from ascelibrary.org by RMIT UNIVERSITY LIBRARY on 01/03/19. Copyright ASCE. For personal use only; all rights reserved. Electrical Transmission and Substation Structures 2018 3 The Leduc and Harry Smith sub-developments were grouped in a sequence diagram to support outage planning. The Saunders Lake and Cooking Lake sub-developments also were grouped in a sequence diagram, as their outages and construction requirements were closely interrelated. Using these sequence diagrams, the project team worked with the AltaLink Control Center to develop a high-level outage schedule with milestone completion dates in support of the ultimate in-service dates for all sub-developments. See Table 1 for a summary of the scope required for each sub-development. Table 1 - SWEATD Development Scope Development 1 Development 2 Development 3 Harry Smith Saunders Lake Cooking Lake 240/138-kV Sub. 240/138-kV Sub. Single-circuit New 240-kV trans. line Construction Triple-circuit 138-kV trans. line (2) 138-kV Substations Development 4 Leduc Double-circuit Double-circuit 240-kV trans. line 138-kV trans. line Double-circuit 138-kV trans. line (2) Substations Double-circuit 240-kV trans. line Leduc Sub. Facility Single-circuit Double-circuit Single-circuit 138Modifications 138-kV trans. line 138-kV trans. line kV trans. line Single-circuit Single-circuit Single-circuit 138240-kV trans. line 138-kV trans. line kV trans. line ROUTE AND SCHEDULE CONSTRAINTS In addition to determining the optimal structure types for the project described in later sections, there were many non-engineering considerations incorporated in design and project execution for SWEATD, including environmental, visual, cultural, and land use impacts. Throughout the transmission line route selection process, the routing team considered longer span lengths to span wetlands, or the addition of angle structures to divert the alignment around environmentally sensitive areas. The location of structures in proximity to roads determined the types of foundations that could be used. Most structures near roads were located on road allowance, a pre-arranged joint use right-of-way agreement between the Alberta Ministry of Transportation and utilities in the province. Structure foundations located in the road allowance were required to be less than two meters in diameter. The construction team also had a number of work and schedule constraints to consider in its execution planning. Construction required the use of rig matting. What started as a way for the construction team to minimize impacts to wetlands ended up as a necessity to execute work. An early spring thaw made it difficult for construction equipment to maneuver across the project site without rig mats. The construction execution plan would also need to consider protocol if certain bird species were encountered during their breeding seasons. During migratory nesting season (March-July), bird and nest sweeps were required each day before construction could commence. If a nest was encountered, the project team could be restricted to setbacks of up to 100 meters, depending on the species, or could be required to stop work. Another constraint was clubroot © ASCE Downloaded from ascelibrary.org by RMIT UNIVERSITY LIBRARY on 01/03/19. Copyright ASCE. For personal use only; all rights reserved. Electrical Transmission and Substation Structures 2018 infestation spread by infested farm machinery in canola fields near Edmonton. To minimize clubroot spread due to project construction equipment, cleaning stations were required where equipment crews entered or exited farm fields. In addition to these development-wide requirements, certain sub-developments had additional unique requirements to consider. Cooking Lake Sub-Development: Part of the transmission line associated with the Cooking Lake sub-development was proposed to be on the road allowance shared with the Alberta Ministry of Transportation when parallel with Highway 14 and Range Road 220. While locating the line within the road allowance minimized land impact since the land is designated for transportation and utility use, there is a chance that the property could be reclaimed if the road would need to be widened in the future. Additionally, the structures within the road allowance along Highway 14 at the Highway 21 crossing were required to be taller than typical to accommodate the Alberta Transport High Load Corridor clearance requirements. Additional complications arose when transmission line alignment passed through a historical cemetery. AltaLink conducted surveys adjacent to the alignment to determine if human remains would require relocation prior to foundation installation. Figure 2. Tubular Galvanized Steel 240-kV H-Frame (Courtesy of Burns & McDonnell) Harry Smith Sub-Development: The Harry Smith sub-development presented unique challenges due its proximity to a local private airport. The airport requested that the 240-kV transmission line either be diverted from near its property or installed underground. Airport officials believed an overhead transmission line could interfere with airport operations and would be a safety hazard. However, moving the transmission line underground would significantly increase project cost. AltaLink agreed to use H-frame structures with a maximum height of 25 meters above ground, shown in Figure 2, to remain below the airport’s Obstacle Limitation Surface. STRUCTURE AND FOUNDATION DESIGN Overall, the SWEATD project involved designing and constructing eighty circuit-kilometers of new 138-kV and 8 circuit-kilometers of new 240-kV transmission lines. The project team had © ASCE 4 Electrical Transmission and Substation Structures 2018 5 Downloaded from ascelibrary.org by RMIT UNIVERSITY LIBRARY on 01/03/19. Copyright ASCE. For personal use only; all rights reserved. to consider AESO reliability requirements that vary by line voltage and circuit configuration. The reliability requirements and their application to the SWEATD sub-developments are outlined in Table 2. Each of these Return Period (RP) requirements result in different ice and wind loads, which added complexity to the project design effort by increasing the number of transmission structural load cases required. Table 2 – AESO Reliability Requirements (AESO Reliability) Transmission Line Voltage Circuit Configuration Development RP (Years) RP Gust Wind (km/h) RP Combined Wind / Ice (km/h / mm) 138-kV/144-kV Single/Double All 50 130 63 / 40 240-kV Single Harry Smith 75 140 65 / 45 240-kV Double Saunders Lake 100 140 67 / 50 500-kV Single/Double N/A 100 140 67 / 50 In addition to varying structural load cases, multiple conductor types were required for the different sub-developments. The 138-kV circuits utilized 266 kcmil ACSR “Partridge”, 477 kcmil ACSR “Hawk”, and 1033 kcmil ACSR “Curlew”. Structures used to facilitate taps to existing lines also needed to support existing custom self-dampening conductor (SDC), which was equivalent in diameter to a 477 kcmil conductor. The 240-kV circuits within the Harry Smith sub-development required double-bundled 1033 kcmil ACSR “Curlew” conductor while the 240-kV transmission lines within the Saunders Lake sub-development required single 1590 kcmil ACSR “Falcon” conductor. The different design parameters required to satisfy AESO’s project functional specifications, conductor sizes, environmental restrictions, reliability and stakeholder requests made it necessary to use a wide range of structure types throughout the sub-developments. There were several drivers that affected the structure selection process for the different line segments. Right-of-way (ROW) requirements, conductor size, matching existing structure types, and AltaLink preference were all considerations during the structure selection process. Structure Design – Cooking Lake: Due to the length of the double-circuit lines within the Cooking Lake sub-development, AltaLink completed a line optimization study. AltaLink’s system predominantly uses wood pole structures for 138-kV lines but other structure material types were considered for this sub-development. For the optimization study, the project team considered the pre-determined ROW width and sought to maximize span lengths. The study determined that wood poles were not practical for a double-circuit configuration and steel structures would be required to support the circuits. Wood poles were only suitable for line segments with a single-circuit configuration and either single 266 kcmil ACSR “Partridge” or 477 kcmil ACSR “Hawk” conductor. Structure Design – Saunders Lake: The existing structure type had the largest impact on selecting the optimal structure type for 240-kV line segments within the Saunders Lake subdevelopment. The existing 240-kV line being tapped for connection to the new Saunders Lake substation was supported by latticed steel towers, so the new tap portion was designed with a similar structure type. The new latticed steel towers were based on the existing structure family, but the loading was revised to incorporate current requirements and a new conductor type; the © ASCE Downloaded from ascelibrary.org by RMIT UNIVERSITY LIBRARY on 01/03/19. Copyright ASCE. For personal use only; all rights reserved. Electrical Transmission and Substation Structures 2018 original towers were designed to support bundled custom 477 kcmil self-damping conductors per phase, but the new line segments required one 1590 kcmil ACSR “Falcon” conductor per phase. Instead of evaluating tower performance based on a comparison of the original tower design loads to the proposed loading, the project team engaged a tower manufacturer for additional engineering support. The project team modified structure design requirement drawings to incorporate updated loading and considerations for construction and maintenance to provide to the tower manufacturer. The tower manufacturer then analyzed tower performance under the proposed loading and developed modified designs that included angle member size updates and minor framing adjustments. The final towers installed for Saunders Lake are shown in Figure 3. Figure 3. 240-kV Latticed Steel Towers (Courtesy of Burns & McDonnell) Structure Design – Harry Smith: Similar to those in the Saunders Lake sub-development, the existing structures near the new Harry Smith substation drove structure type selection for new lines installed nearby as part of SWEATD. The existing structures near the new Harry Smith substation were steel H-frames and the new transmission structures at Harry Smith were designed to match the configuration. The existing 240-kV H-frame line would be segmented with an in-and-out tap to the new Harry Smith substation, so two new H-frame circuits would run parallel to each other as single-circuit 240-kV lines. While this arrangement required more ROW than ideal, AltaLink engaged with landowners to identify optimal placement of structures on their properties. The H-frame structure type also allowed the project team to minimize structure heights and meet the adjacent airport requirements as previously discussed. The Harry Smith sub-development also used unique triple-circuit structures, shown in Figure 4. Part of the scope of the Harry Smith sub-development included cutting in to the existing Stony Plain-to-Acheson transmission line to create a single-circuit connection between the new Harry Smith and Stony Plain substations and a double-circuit connection between the Harry Smith and Acheson substations. While various routes and configurations were investigated, during project development the team identified an opportunity to minimize landowner impact by combining all three circuits on one structure and one connection point to the existing transmission line. © ASCE 6 Downloaded from ascelibrary.org by RMIT UNIVERSITY LIBRARY on 01/03/19. Copyright ASCE. For personal use only; all rights reserved. Electrical Transmission and Substation Structures 2018 7 Figure 4. 138-kV Triple-Circuit Tubular Steel Poles (Courtesy of Burns & McDonnell) Line Volt. (kV) # Ckts Table 3- SWEATD Structure and Foundation Types Structure Structure Conductor Type Foundation Types Framing Material Type 1 266 kcmil ACSR Partridge 477 kcmil ACSR Hawk 138 2 477 kcmil ACSR Hawk 1033 kcmil ACSR Curlew 138 3 240 240 138 Wood & Steel Direct Embedment Helical Can Drilled Shafts Monopole Steel Direct Embedment Helical Cans Drilled Shafts 1033 kcmil ACSR Curlew Monopole Steel Drilled Shafts Helical Grillage 1 2x1033 kcmil Curlew ACSR H-Frame Steel Helical Cans Helical Grillage 2 1590 kcmil ACSR Falcon Lattice Tower Steel Helical Grillage Monopole While the triple-circuit structure minimized the number of structures and negotiations with landowners, it introduced additional challenges. From a maintenance perspective, the structure configuration introduced increased risk and complexity. Any energized maintenance work performed on the upper circuits would require additional precautions to avoid the circuit below. Reliability was also a concern with the triple-circuit design. By grouping three circuits together, a failure of a single structure would remove three circuits from operation. As shown in Table 2, the AESO reliability requirements do not address a triple-circuit design. The project team used a © ASCE Downloaded from ascelibrary.org by RMIT UNIVERSITY LIBRARY on 01/03/19. Copyright ASCE. For personal use only; all rights reserved. Electrical Transmission and Substation Structures 2018 75-year return period for developing loading requirements to mitigate the risk associated with the triple-circuit structure. The project team expected the ground-line reactions for the triple-circuit structure to be substantially higher than the reactions associated with a double-circuit structure of similar height due to the addition of the “underbuilt” third circuit and the more severe loading requirements associated with the 75-year return period loads. Once structure designs were completed, however, the magnitude of the impact of the additional third circuit was more extreme than anticipated. The ground-line moments associated with the triple circuit structures were almost double the ground-line moments associated with a double-circuit structure of the same height. This increase in ground-line reactions limited the types of foundations that could be used to support the triple-circuit structures. Foundation Design: The predominant drivers for the selection of foundation types were installed cost, soil conditions, magnitude of loads, and restrictions to the size of the final foundation footprint. Table 3 contains a list of the structure and foundation types used within each sub-development. The geotechnical investigation revealed the presence of sand layers of varying thicknesses interspersed with clay layers creating very soft subsurface conditions. There were also many areas with high water tables. These soil profiles presented complications with sloughing and seepage during excavation work. Figure 5. Helical Can Installation (Courtesy of Burns & McDonnell) Direct Embedment: Since direct-embedded structures can minimize foundation cost and have a small footprint, the project team used them as often as possible. Early in the project, a desktop analysis was performed to determine where direct-embedded foundations were feasible. Throughout the project process, proposed locations for direct-embedded foundations were often re-evaluated for suitability. As the project moved into construction, the on-site crews noted that soil conditions in some locations were poorer than anticipated. An early spring thaw also caused site conditions to worsen. This change in conditions led the project team to determine that a number of locations originally identified as suitable for direct embedded foundations would require the additional support of helical cans. Helical Cans: When a structure could not be direct embedded, the first alternative considered was a helical can. Helical cans, also referred to as bucket piles, are commonly used in © ASCE 8 Downloaded from ascelibrary.org by RMIT UNIVERSITY LIBRARY on 01/03/19. Copyright ASCE. For personal use only; all rights reserved. Electrical Transmission and Substation Structures 2018 Alberta. They provide additional support for structures that may not require substantial foundations like drilled shafts or grillages, but cannot be direct embedded. A helical can is comprised of a helical pile base and a hollow upper section, as shown in Figure 5. Once the helical cans are screwed into the ground, poles are embedded into the hollow upper section and backfilled. The helical can foundation has a small footprint that allowed it to be used adjacent to and parallel to roads. The largest bucket diameter used on the project was less than the 2-meter maximum foundation size. The piles could also be bolstered with additional battered piles to increase capacity if required. Helical Grillages: The helical grillage foundations used for the project consisted of multiple helical piles configured in an array. The individual helical piles were then connected to a grillage comprised of wide flange steel members. This grillage connected to either latticed steel or tubular steel structures via various baseplate adapters or transition plates. The footprint for most helical grillage foundations exceeded the 2-meter limit, so the use of these foundation types was limited to structures located on the ROW and not the road allowance. If a grillage was needed on a structure located in the road allowance, the project team opted to bury the grillages as shown in Figure 6. To accommodate burial, the foundation design was modified to consider the added soil pressure on top of the grillage structure. The depth of the grillage also needed to be below the frost depth, so extension bridges were used to connect the structure baseplate to the grillage attachment point. Figure 6 shows the construction crew lifting the extension bridge into place on a subgrade helical grillage foundation. Figure 6. Buried Helical Grillage Installation (Courtesy of Burns & McDonnell) Drilled Shafts: While some portions of the project alignments could accommodate burying large helical grillage caps to minimize permanent above-ground land impacts, locations such as structure installations adjacent to roads could not. Drilled-shaft foundations are not commonly used in Alberta due to the soil conditions, cost of concrete, and distance to construction sites from batch plants. However, the SWEATD project was close enough to Edmonton that drilledshaft foundations were an economically viable option in some situations. Due to the soil © ASCE 9 Electrical Transmission and Substation Structures 2018 Downloaded from ascelibrary.org by RMIT UNIVERSITY LIBRARY on 01/03/19. Copyright ASCE. For personal use only; all rights reserved. conditions determined from the geotechnical investigation, foundation installation procedures for the project included the use of temporary casing, permanent partial casings, and permanent fulllength casings. The smaller footprint of drilled-shaft foundations, compared to those of the helical grillage foundations, helped support permitting compliance. Drilled shafts were used primarily on the triple-circuit portion of the Harry Smith sub-development and on heavily loaded dead-end structures located within the road allowance or alongside roadways. CONCLUSION The expanded region, multiple voltages, loading requirements, and construction challenges made SWEATD a more complex project than typical. With a diligent plan of execution and coordination and a design offering a wide range of options to tackle challenges, the project team was able to keep construction efforts on schedule. The SWEATD project was energized in December 2017, providing the necessary infrastructure for expected growth in Edmonton, Alberta. REFERENCES Alberta Electric System Operator. “South and West of Edmonton Transmission System Development Newsletter.” AESO Grid. Accessed February 1, 2018. https://www.aeso.ca/assets/Uploads/SW-Edmonton-Newsletter-WEB.pdf. Alberta Reliability Standards. Alberta Standard. Calgary, Alberta. Alberta Electric System Operator. Accessed April 27, 2018. https://www.aeso.ca/rules-standards-and-tariff/albertareliability-standards/complete-set-of-standards/. Alberta Electric System Operator. (June 2012) AESO Long Term Transmission Plan. https://www.aeso.ca/downloads/AESO_2012_LTP_Sections_1.0_to_5.0.pdf © ASCE 10