Electrical Transmission and Substation Structures 2015: Technical Challenges and Innovative Solutions in Grid Modernization

In 2012, Dominion rebuilt their 115kV transmission line (T/L 64) that crosses the five-mile wide Albemarle Sound in North Carolina. GAI Consultants, Inc. designed the 24 foundations located in the waterway, which consisted of 35-foot long precast concrete pilecaps and 66-inch diameter prestressed cylinder piles. The pilecaps were designed for bending moment plus torsion from the steel H-frame structure base reactions, combined with wave loading. The unique challenge for this project was the design of the connections between the pilecaps and the piles to meet the fabrication and installation tolerances. The innovative solutions implemented into the design included the use of self-consolidating concrete to bond the piles to the reinforcing steel cages that projected 9′-6″ from the pilecap. The installation procedure required rotating the 80-ton pilecaps 180 degrees with a barge-mounted crane, and setting the pilecaps on top of the cylinder piles.

The Orlando Utilities Commission (OUC) engaged Black & Veatch to oversee an inordinately complex upgrade of a critical 230 kV transmission line. This line links the Taft Substation near Orlando to the McIntosh Power Plant substation near Lakeland, Florida. The project nearly doubled the capacity of the 46-mile line, but over the eight-year project period it presented OUC and Black & Veatch a significant number of planning, technical, environmental and permitting challenges, many of which were not anticipated during the initial planning stages. As planned, the project involved installation of trapezoidal wire to increase capacity, a structure-by-structure condition assessment of each tower, and the use of PhaseRaisers® for some structure modifications. However, strict enforcement of environmental regulations and the discovery of endangered species added further complexity, including the creation of new wetlands and large earthmoving operations to create flood-storage compensation areas. The need for expanded access roads and maintenance pads to facilitate live-line maintenance added to the complexity. All of this led to a complex permitting and design process, highlighting the need to collaborate with numerous state and federal agencies, and multiple legal issues relating to the expansion of an adjacent interstate highway corridor. All of this work was managed by OUC and Black & Veatch personnel over a six-year period. By the end of the presentation, attendees should take away: (1) an understanding of the key interrelationships of all the components of this very intricate project; (2) a basic understanding of the project methodology to manage such a complex project; the importance of inter-agency coordination and collaboration between shareholders; and (3) the benefits of using a very intense engineering program to effectively develop the approach for permitting, design, and construction.

The Jack Rabbit–Big Sky 161 kV Transmission Line is partially located in the Gallatin National Forest and parallels a busy two-lane road, US Highway 191, and the Gallatin River, all which fall within the confines of the steep narrow Gallatin Canyon. The 8.5 mile segment of transmission line that falls within the canyon has 22 concrete pier foundations. Access was not permitted before the special use permit was issued; therefore, subsurface investigation information was not available to aid in design of the pier foundations. An on-site geotechnical engineer performed the subsurface investigation during the excavation of the foundations. Once the soil stratum was known, the pier foundations could be modified accordingly. Limited access was available due to difficult terrain and requirements set by the United States Forest Service (USFS), requiring excavation of numerous holes by hand, some up to 8 feet in diameter and 15 to 20 feet deep. Helicopters were used to aid construction, such as flying in structures, equipment, aggregate backfill, as well as string conductor. This paper will cover in detail the design and construction challenges, solution options, and final design decisions.

This paper will discuss the use of micropiles as a specialty deep foundation solution to limited construction access challenges within the Troy Meadows wetland portion of PSE&G’s 500 kV Susquehanna to Roseland Electric Reliability Project. Micropile foundations were constructed utilizing primarily helicopter access for seven 500 kV double-circuit tubular steel pole structures within the protected habitat. The successful implementation of a design-build strategy between the overhead design team and the contractor led to significant refinements in the foundation design. Value engineering efforts focused on refinement of tower loading geometry and load cases, assessment of geotechnical conditions, and reduction of foundation footprints within the wetlands environment. The paper will detail design and routing of the overhead alignment, as well as permitting restrictions and area of impact limitations. It will then provide an in-depth analysis of concrete cap micropile design and detailed construction methodologies.

River crossings are often unavoidable when designing and constructing foundations for long-range cross-country transmission lines. Factors such as dynamic terrain changes, unique structure loading, unfavorable access conditions, enhanced permitting restrictions, and poor soil conditions almost always create significant challenges for utilities, engineers, and contractors. This paper will present a case history of one of the three challenging river crossings on the 250-mile CapX2020 Brookings County–Hampton 345 kV Transmission Project. It will lay out how the engineering team, utilities, and contractors worked together in an effort to overcome several challenges encountered in the foundation planning, design, and construction process. Following the development of multiple design alternatives, large-diameter vibratory caissons were selected as the preferred solution. Each alternative will be presented, and a detailed discussion of the selected alternative will be provided. Additional discussion will include project management, scheduling, and contracting strategies as well as permitting challenges, detailed design, and construction challenges of the 345 kV vibratory caisson foundations.

Bonneville Power Administration (BPA) has committed to adoption of a 100% fall protection policy on its transmission system by April 2015. The vast majority of BPA’s transmission system consists of traditional wood pole structures and lattice steel structures; most fall protection efforts to date have centered around those two structure categories. Fall protection on wood pole structures was completed in late 2013 through work practice modification and changes to Personal Protective Equipment (PPE) utilized by lineman and maintenance personnel. Fall protection efforts for lattice structures are ongoing and in addition to work practice and PPE modifications, structural solutions will almost surely be implemented. The structural efforts are divided into two main categories: (1) devising methods that will allow linemen to climb and work safely on BPA’s 42,000-plus lattice structures while minimizing the need for costly retrofits and (2) developing designed-in fall protection characteristics for BPA’s next iteration of standard lattice tower families. For existing lattice structures, the challenges largely involve identification of existing brace points available for anchorage that can withstand the appropriate fall protection loads and also ensuring there is an existing climbing system or one that can be easily and quickly retrofitted to allow for 100% fall protection for the “first man up.” For new designs, efforts involve a number of additions to traditional tower design activities, including development of climbing systems with permanent, engineered fall protection capabilities (including possible vertical lifelines), provisions for lateral movement on the structure (e.g. horizontal lifelines), engineered and clearly identified attachment points throughout the structure, and horizontal members specifically designed for standing and working.

Cross Texas Transmission was selected to design, construct, and operate approximately 235-miles (378 km) of 345-kV double circuit CREZ transmission lines in the Texas Panhandle. Truly, starting from a blank paper, the design team had to create utility standard practices and designs from the ground up, including conductors, hardware, loading criteria, structures, and foundations. This process resulted in the creation of new steel monopole and steel lattice tower structure families and the implementation of a blended solution using both structure types for the final design. A significant challenge was the design of a half mile river crossing, which was solved with the use of a high temperature low sag ACCR conductor for that crossing to minimize structure heights. The selected monopole design was a direct embedded weathering steel structure, which led to unique construction challenges with the specified concrete backfill material. This paper will describe these challenges and their solutions.

The Fargo – Saint Cloud 345 kV transmission line project led by Xcel Energy as part of the CapX2020 transmission expansion initiative includes about 52 miles containing 284 tubular steel structures located in the lakebed of Glacial Lake Agassiz (GLA) in northwest Minnesota and eastern North Dakota. GLA was an immense glacial lake. It was larger than all of the Great Lakes combined and held more water than all lakes in the world today. When GLA drained about 8,500 years ago, it left deep soft clay deposits that can create a challenge for foundation installation and can introduce potential for long-term creep in foundation deflections. A study, which included full scale constructability testing, was conducted to evaluate appropriate design and construction methods to address these concerns. This paper will describe the study and the design and construction methods used to install foundations in the deep soft clay deposits of GLA.

Deep foundations in the transmission line industry are increasingly being inspected using Non-Destructive Testing (NDT) methods such as sonic, seismic, and temperature methods of determining structural integrity of new and existing assets. The variety of testing methods, combined with differences in engineering designs, construction methods, inspection protocols, and other project-specific variables challenge owners and engineers when deciding if, when and how to conduct NDT testing. Several guidelines should be used when considering these variables to not only determine the method of testing, but also the frequency and rejection criteria.

Three (3) major river crossings [one (1) across the Mississippi River and two (2) across the Illinois River] with tower spans potentially as great as 3,700 feet are part of Ameren Transmission Company of Illinois (“Ameren”) Illinois Rivers Transmission Line Project. Hanson Professional Services Inc. (“Hanson”) is working closely with Ameren to provide geotechnical, civil, structural, and hydrologic and hydraulic engineering services to design steel tripod foundations for the 14 lattice towers, potentially as tall as 470 feet, that are part of these crossings, as well as the necessary access roads and barge landings. Soil test borings advanced to rock depths up to 120 feet at each tower location; soil laboratory testing; land and bathymetric surveying; and engineering analysis of design load cases, geotechnical parameters, and hydraulic aspects of the river crossings, were utilized to develop foundation design parameters and performance criteria (strength and displacement) for the evaluated conditions, including flood levels, scour, debris forces, hydraulic forces, and ice forces. This paper summarizes how accessibility and permit-related challenges can be overcome on major transmission line projects such as this project. Many of the towers are on the river side of flood protection levees and in wetland areas. Some are on islands within the rivers. Part of the strategy to overcome such challenges was to design 100% steel foundations to preclude the need for concrete and minimize ground disturbance areas and required earth excavation. Additionally, barges will be utilized to transport all necessary components, machinery, and workforce to many of the tower locations. In the interest of brevity, this paper focuses on the Mississippi River crossing.

This paper presents a parametric study evaluating the impact of various deflection and rotation criteria for self-supporting, double circuit, 138kV steel pole structures and their foundations on the performance of the overall wire system. The study was used to develop guidelines for determining structure and foundation deflection, and rotation design criteria. The impact on conductor sag and blowout were evaluated by using PLS-Pole to model pole behavior and flexibility, PLS-Cadd to model the interaction between pole and wires, and MFAD to model foundation behavior. This study was conducted using a representative transmission line consisting of structures designed to varying levels of flexibility. This study focuses on the complex interactions between foundations, structures, and wires, and emphasizes the important effects these interactions can have on the overall system. Guidelines are developed for determining the deflection criteria for self-supported transmission structures, and their foundations, based on structure type and line angle.

This paper presents the results of the full scale testing of longitudinal loads on a 132kV wood H-frame line. The load cases are broken insulators and broken conductor/wire conditions. The longitudinal events were filmed and three cameras were used to capture the events that occurred. One camera was strategically placed at each structure adjacent to the event to capture the response to the respective longitudinal loads. One camera was placed to record the event itself. An independent study was conducted to model the same line using industry accepted software including PLS-Cadd^™ and Solid Works^™. These two programs were used in an attempt to replicate the actual results. This paper should be of interest to anyone who is responsible for the maintenance, design or relocation of comparable lines or for PLSCadd and Solid Works users modeling comparable lines.

Following the last ASCE Electrical Transmission and Substation Conference (Columbus, OH in 2012), the current roster of the Task Committee on Electrical Transmission Line Structural Loading was assembled to work towards updating ASCE Manual of Practice No. 74: Guidelines for Electrical Transmission Line Structural Loading (ASCE-74). ASCE-74 is currently in its 3^rd Edition, published in 2010, and provides guidance on loading criteria, weather-related loads (i.e., wind and ice), additional load considerations for transmission structures and wires (e.g., longitudinal loads), and an example design considering all relevant load cases. As well, an extensive set of appendices contains useful information relevant to the design and analysis of transmission lines. The 4^th Edition of ASCE-74 is scheduled to be published in 2016, and will contain a number of revisions to the previous edition. Many of these revisions are relevant to weather-related loading (Chapter 2), which is currently the largest section of the Manual. This paper, written on behalf of the ASCE Task Committee on Electrical Transmission Line Structural Loading, outlines significant changes to the weather-related loading (Chapter 2) made for the upcoming edition of the Manual and discusses the reasoning behind some of the revisions.

Institutional knowledge on the history of damaging ice storms in a utility’s service area often resides with the members of the utility’s line crews. As they retire that information is lost. This paper describes our compilation of freezing rain storms in the United States and southern Canada that were severe enough to damage trees, power lines, and communication towers. This compilation is available online in an ice storm Geographic Information System (GIS) that maps each storm’s damage footprint and includes information compiled primarily from newspaper reports on the storm severity, including comparisons to previous storms and any disaster declarations. By clicking on the map, users generate a list of ice storms at that location. Choosing one of the listed storms brings up the storm description and a map of the damage footprint. The presentation will include a demonstration of the GIS.

Electrical utilities are interested in building well engineered new and replacement transmission lines that balance the many elements of their design. The public is concerned about impacts on land use and how the aesthetics of the line will impact their quality of life and the value of their property. The utilities and the public are both concerned about reliability, and both are also concerned about the cost effectiveness of the balance between the competing forces of aesthetics, reliability, and economy. A guide was developed with the objective of providing a comprehensive, single, document that discusses the elements of 115kV to 230kV transmission lines, including materials, configurations, insulation, reliability, EMF, and economics. The guide also includes some other (non-design-related) aspects of transmission lines, such as routing, permitting, and public acceptance. This paper summarizes information presented in the guide. The topic of this paper will be of interest to both US and international utilities.

There may one day be a new generation of transmission line engineers (or wind turbine blade specialists, or bridge engineers, or pipeline technicians, or even agricultural engineers). The next wave of youths into the workforce will be well-equipped with the hand-eye coordination and virtual acumen necessary to handle the controls required to carefully navigate a small-unmanned aircraft system (sUAS) (better known as a “Drone”) around obstacles like an energized high voltage transmission line. They will be looking through first person view (FPV) goggles, or watching streaming video to find cracked welds, corroded, or worn line hardware, broken insulators, or burned strands on the conductor. Or, they may be writing computer code that will turn these sUAS into “smart” devices that can autonomously fly to a predetermined GPS location, and through feature recognition algorithms, zoom in on programmed elements of interest, and snap photos/videos, or capture important data and stream it to a ground station instantaneously for further technical analysis. Or, perhaps with a robotic arm, manipulate it to reach out and touch or grab something. Such innovation is developing so rapidly that if you blink, you might well miss the technology train. Just as LIDAR has transformed line siting and design, sUAS technologies may well transform the industry once again. These flying systems are “cool”, but the payload they will carry – the micro sensors, etc. will rapidly advance vision and data collection technologies to a point beyond belief.

The use of weathering steel, or Cor-ten®, for transmission line structures appeals to many utilities. This is partly due to its ability to blend in with the environment. It’s also slightly lower in initial cost due to eliminating the need for galvanizing. Celanese – Peters Mountain is an approximately 20 year old 138kV weathering steel tubular pole line located on American Electric Power’s (AEP’s) system in western Virginia. The line is showing signs of heavy corrosion. The environment is characterized by steep terrain, heavy vegetation and humid conditions. An arm failure on one of the structures initially led to the discovery of corrosion issues on this line. In this paper, we will discuss the nature of the corrosion found, the criticalness to the structural integrity of the poles, the repairs performed, modifications of our standard pole details, and the inspection and maintenance programs. This line is being used as a case study for other AEP weathering steel lines located in the region.

A successful transmission line asset management program has many components. One of the major components includes collecting data on asset conditions based on sound inspection techniques. The primary purpose of the study reported herein was to develop best practices guidelines against which electric utilities could benchmark their current inspection programs and make appropriate adjustments. The study included three primary tasks: (a) conducting a survey of utilities on an international scale to collect key information to assess the types of patrols being performed on their systems, (b) conducting a literature search to document tools and instruments available on the market to enable various inspection techniques, and (c) analyzing the survey results to develop best practices guidelines. In addition, a database was created that stores information on commercially available tools, techniques, and instruments to perform condition assessments of overhead line components. This topic is of international interest.

This paper covers the worlds first use of Aluminum Conductor Composite Reinforced (ACCR) conductor on a 500-kV transmission line and the first use of ACCR in a three conductor bundle. The ACCR conductor was used by the Tennessee Valley Authority (TVA) to span over a lake utilizing existing structures while maintaining adequate clearance. The lake and surrounding land were controlled by state and federal agencies that complicated schedules and activities and threatened to delay the project.

Increased load requirement from the RTO required improvements to the existing transmission system in PSE&G’s southern region. The Southern Reinforcement Project addressed this requirement through a combination of new underground 230 kV transmission lines and improvements to the existing 230 kV overhead system. This paper will focus specifically on the various engineering and construction challenges encountered on one, three mile section of the overhead line built over a heavily utilized railway corridor. A summary of the challenges are: (1) comparative analysis of expanding and reinforcing existing railroad overbuild structures versus installation of new structures in order to support the replacement of an existing circuit and the installation of a new circuit; (2) right of way is owned by a major railroad company. ROW widths between 50 and 100 feet for 230 kV double circuit construction, surrounded by major roadways, numerous buildings, and regulated wetlands; and (3) legal/permitting restrictions which prevented any excavation on the ROW and forced the need for an atypical foundation solution consisting of helical cluster foundation types.

Recently, ITC needed to raise 25 steel lattice towers by 10 or 20 feet each to enable the line to operate at its design rating. This paper will communicate the methodology and cost considerations involved in raising existing lattice towers vs. constructing new structures. It will also cover the project’s critical path items, and potential improvements. By the end of the paper, readers will learn: (1) Why did we need to raise steel lattice towers? (2) How did we raise the steel lattice towers during construction? (3) What were the key steps that made the project a success?

All linear projects, including transmission lines crossing federal jurisdictions, must comply with the National Environmental Policy Act (NEPA). Most projects of any significance require an Environmental Impact Statement (EIS) under NEPA. Large projects encounter numerous permitting challenges that must be navigated and overcome to obtain a Record of Decision and Right-of-Way Grant. This paper provides suggested approaches for completing the NEPA process successfully by presenting the unique role that engineering played in enabling several large projects with permitting challenges to complete the NEPA process intact, or nearly so.

The enduring visual presence of transmission lines gives cause for appropriate consideration of aesthetic impacts. While remaining in the realm of traditional design, improvements can be realized by applying basic architectural concepts to guard against poor aesthetic designs that result in disproportionate, uncomfortable, and unnecessarily awkward structures. Second-level aesthetic enhancements can be employed to modify traditional structures without substantially altering the core elements of standard structures. There are also “out of the box” approaches, as seen in past and current projects in Russia, Spain, Finland, the United States and elsewhere, that freely apply architectural concepts to push the limits of engineering and construction as well as operational reliability and cost-effectiveness. This paper shows that to the degree that designers apply appropriate aesthetic treatment, transmission line structures can exhibit responsibility and earn their place in the built environment.

Electric utilities are increasingly considering projects to either upgrade or replace existing infrastructure and sometimes new construction needs to address system expansion. In addition to resource availability, regulatory concerns, lack of outages and associated requirements for energized work, some of the key technical considerations are material availability, design requirements, structure reliability, and constructability. Fiber reinforced polymer (FRP) materials present an opportunity for utility engineers to partner with manufacturers and vendors in developing innovative alternatives to structures built with conventional materials. The goal is to achieve a safe, reliable, and maintainable structure to support electrical infrastructure under challenging environmental and in-service conditions. This paper describes BC Hydro’s practice for the design, construction and maintenance of FRP structures including a case study of a 230kV project completed by BC Hydro. The paper also covers BC Hydro’s field experiences with FRP and provides an overview of BC Hydro’s criteria for using FRP components.

BOLD (Breakthrough Overhead Line Design) is a high-capacity, high-efficiency transmission line design. A single steel pole with two curved arms was desired for the first BOLD suspension structure, combining a simple, elegant appearance with performance. Two BOLD circuits are symmetrically supported, with the bundled conductor phases of each circuit chained together by an innovative arrangement of V-string insulator assemblies. This paper describes the engineering and fabrication challenges encountered. Close collaboration between the BOLD developer, American Electric Power (AEP) and the fabricator, Valmont-Newmark (VN) was necessary to ensure the success of the project.

In order to mitigate possible environmental concerns on portions of Southern California Edison’s Tehachapi Renewable Transmission Project, double circuit 500kV tubular steel poles of heights between 150’ and 195’ were chosen. During the design phase of the project, SCE decided to perform a thorough analysis of the double circuit 500 kV TSP designs. To coordinate this effort, SCE teamed with Valmont to develop a program to test and confirm the pole designs. The test program consisted of three analyses/tests, which were performed on select critical TSP designs. Valmont performed the static analyses. SAP2000 finite element models were developed by W. E. Gundy & Associates Inc. to perform seismic analyses using site specific ground motion records. Full scale static load tests were performed at a China test facility. The maximum longitudinal, transverse, and torsional design load cases were individually applied on a tangent and running angle design. The poles successfully carried the applied loads.

The Heartland Transmission Project is a recently built 500kV double circuit transmission line near Edmonton, Alberta, Canada. The scope of the project was to connect the existing Ellerslie Substation, located within Edmonton, to the new Heartland Substation, located approximately 65 kilometers northeast of Edmonton in the Heartland Industrial Area, near Fort Saskatchewan, Alberta. Approximately half of the line was built within a designated Transportation and Utility Corridor (TUC) with a section passing between the communities of Edmonton and Sherwood Park. The Alberta Utility Commission (AUC) declared that a 10 km section of the line passing between the communities of Edmonton and Sherwood Park were to be built using tubular steel structures rather than the traditional lattice steel towers. The process of developing a family of tubular monopoles consisting of tangent, light, and medium angle suspension towers and site-specific dead-end towers is outlined. The design, from a conceptual stage through to the project’s completion is discussed. Topics will cover the development of pole design requirement drawings, structure design, manufacturing, full scale testing, and foundation design.

A recent project required a 345 kV single circuit transmission line to cross a lake for a portion of the alignment. Structure spotting and route constraints required two adjacent spans of approximately 2800 feet. Structures were located on each side of the lake with 0 to 5 degree line angles, and a third structure was located on an island in the center of the lake with a 25 degree line angle. The allowable height of all three structures was less than 200 feet, and the required minimum clearance from the energized conductor to the water surface was 50 feet. Traditional design methodologies would suggest using a lattice tower as the structure design of choice. However, the transmission line owner did not possess a previously engineered tower design that would accommodate the project conditions, and the project schedule could not support the timeframe that a new tower design would require. Therefore, a tubular steel design was investigated. Multiple structure configurations were designed and analyzed to develop the most efficient solution that would meet the project needs. Several commonly used configurations were analyzed and compared with other nontraditional options. The configuration selected was an innovative tripod structure. It consisted of three tubular steel legs oriented in a triangular pattern at the base, converging at a central point 170 feet above ground line. The overall structure height was 195 feet. This paper will discuss in detail the project challenges and design requirements, the process used to evaluate the multiple design options, and the results of the analysis which led to the development of a unique and innovative structure design. This topic is of international interest and will help readers understand the structural analysis process, and learn how to combine creative thinking with engineering judgment to develop new and efficient structure designs.

Slip joint connections are the most common splice connection used for tubular steel transmission structures. Historically, they have performed well and generally allow for a lower installed cost. However, the behavior of this commonly specified joint is not clearly understood by both engineers and fabricators alike. Available research is limited and designs are based on geometry rather than limit states. While this approach has proven reasonable in the design of a new structure assembled within tolerances, it makes it difficult to assess the joint capacity when less than ideal conditions exist. This paper and presentation will explore the slip joint in detail from research and design through fabrication and assembly. It will provide informative details and present an approach to analyze and calculate slip joint capacity.

Failures can occur during full-scale load testing. The behavior of the structure can differ from the theoretical model for several reasons: included among them are the effects of the eccentricities at the connections. In this paper, the analysis of an eccentric connection using the finite element method (FEM) will be presented. The example of an eccentric connection occurs on a guyed 500kV lattice tower, which has been full-scale tested at the Brametal Structural Testing Station, located in Linhares, Brazil. During the load test, there was a failure at an important connection. As a solution, the size of the failed member was increased, using the same connection detail. This resulted in a second failure. It was determined at this time, the connection eccentricity impacted the member capacity, resulting in the premature failure. The final solution was to redesign the connection, eliminating the eccentricity in the connection. The result of these solutions using the FEM will be presented.

The process of creating a new lattice tower structure family is complex and requires the involvement of multiple engineering disciplines. Based on the design and construction of the BC Hydro 287-kV AC 344-km (213-mile) Northwest Transmission Line, this paper discusses lattice tower structure family development from initial concept through delivery, construction and energization, and how configuration changes affect tower erection, structure placement and the construction schedule. Topics to be covered include tower types, both self-supported and guyed towers, load development, and tower geometry. Special attention will be given to load development, including statutory, security, and reliability-based loads. To address loading conditions, we provided structure-type alternatives and the benefits of each alternative. Lastly, we addressed the key role of electrical engineers, structural engineers and tower erection firms in the process. The goal of this paper is to help you gain a better understanding of lattice tower family development. More specifically, you will learn more about the benefits of different structure types, special load cases to consider and overall constructability of lattice towers in the context of a design-build project in British Columbia, Canada.

Many years ago, when widespread access to electronic computers revolutionized structural analysis, the older analysis methods were gradually set aside along with their techniques and requirements. Even with the advancement of technology, the use of classical methods of analysis to aid development of new designs is still beneficial. One classical method used extensively in the design of lattice electrical transmission towers is graphical static analysis. The identifying feature of this method is the uniquely patterned force diagrams found on analysis sheets of old designs. This paper will demonstrate the relevance of the graphical method for designing new lattice transmission towers, even with the wealth of powerful software available. Explanation of the fundamental methods and diagrams, underlying assumptions for analysis, interpretation of historical diagrams, and development of efficient geometry will also be shown. Knowledge of fundamental statics is presumed.

Seismic isolation technology is well established within the building industry and has frequently been employed to provide superior seismic protection for buildings that are required to remain fully functional after an earthquake. Seattle City Light is among the first utilities in the world to utilize seismic isolation to protect a new high voltage transformer in a working substation. Seismic isolation is an ideal solution for protecting this type of heavy, expensive, and fragile equipment from earthquake damage. The process of seismically isolating the transformer included the following steps: obtaining in-house approval; analysis; preparing the existing foundation for the isolation system; addressing interconnection of the transformer to both underground and overhead lines; procuring and testing isolation devices; and construction of pier, isolation bearings, float slab, and transformer embed plates. The total construction schedule was four months, and the transformer was energized in November of 2014. Those interested in using seismic base isolation will find that it is not only cutting edge technology but cost effective and practical for actual implementation. In many ways, it diminishes the complexity of foundation design and provides actual confidence that the equipment will achieve the post disaster operational performance goal.

To increase reliability of the bulk electric system (BES), and due to media reports concerning the safety of key transmission stations from physical attacks, the Federal Energy Regulatory Commission (FERC) requested that the North American Electric Reliability Corporation (NERC) develop a physical security standard. This standard, CIP-014-01: “Physical Security” (NERC, 2014), requires transmission system owners to identify key stations and control centers that pose a system instability risk, identify potential threats and vulnerabilities for those stations, develop and implement a security plan to protect those stations from physical attack, and obtain third-party verification. This paper will provide an overview of this new standard, and then discuss how substation civil engineers, working with transmission owner’s planning and operations staff, can cost-effectively design for increased physical security of vital assets. Topics will include: (1) Station layout – considerations for protection of critical equipment. (2) Fencing and screening to block line of sight – pros and cons, methods. (3) Vehicular barriers – site-specific considerations, types. (4) Transformer firewalls for protection against projectiles – design considerations and latest technology. (5) New technologies in security measures.

On April 4th, 2010, a magnitude 7.2 earthquake occurred in northern Mexico, causing shaking as far away as Los Angles, California. The earthquake caused significant damage to the 500kV yard of San Diego Gas & Electric’s (SDG&E) Imperial Valley Substation. Damaged equipment included transformer bushings, surge arrestors, disconnect switch corona rings, and bus support connectors. Post-earthquake surveys revealed downed flexible bus due to the failure of multiple bus support connectors throughout the yard. Part of SDG&E’s post-earthquake mitigation plan involved performing detailed study of the flexible bus conductor in the 500kV yard at Imperial Valley to determining the causes of the damage, identify where weaknesses currently are, and study how to best address them. As part of this study, non-linear analysis was used to assess the cause of first-failure and investigate seismic retrofit options to protect the substation bus system from damage during future earthquakes. The analysis was performed using a two-step process. First, the modeling techniques were validated by replicating the damage observed in the 2010 substation configuration and ground motions. Next, the current 2014 substation configuration was subjected to design level (2500yr) ground motions and the resulting damage prediction was evaluated. After estimating the damage patterns, several of possible retrofits schemes were considered and evaluated. The retrofit scheme chosen uses a spring damping system which absorbs significant energy while limiting the seismic drift of the bus support structure. The chosen retrofit scheme was judged to have minimal construction impact to the substation operation and would provide maximum protection for the bus support connectors and bus support insulators in the 500kV yard for the design basis earthquake. This paper will discuss the regional seismicity and the wide spread damage from the El Mayor - Cucapah earthquake, including specific damage at the Imperial Valley Substation. This paper will also highlight the issues and complexity of analyzing and retrofitting flexible bus substations, including the interaction of substation equipment connected by flexible bus jumpers. In addition, the unique challenges of the analysis and development of the retrofit options including constraints on schedule, allowable substation outages, and performance of the system in extreme environmental conditions are discussed.

Transmission line foundations often consist of concrete piers. Examples of construction situations that may result in problematic piers are presented to motivate the use of deep foundation non-destructive testing methods. Advantages and shortcomings of established testing methods are briefly reviewed. A newer technology, Thermal Integrity Profiling (TIP), is then discussed and compared with established ones. TIP is based on the premise that heat energy released during cement hydration depends on cement content and on total concrete volume. Temperature measurements obtained inside a curing foundation correlate with the effective radius of the foundation and with concrete quality. The theoretical background of thermal integrity profiling is summarized; descriptions of alternate ways of obtaining internal temperature measurements follow. Measurement interpretation is discussed, including relating data measured at the reinforcement cage during curing to concrete quality, shaft diameters, local concrete cover, and reinforcement cage alignment. Case studies of electrical transmission line construction where this technology was employed are presented.

Equations for the gust response factors (GRF) for transmission line loading were presented by Dr. Alan Davenport in 1979 and have since been used by numerous parties in the design of transmission lines for wind loading, including ASCE Manual of Practice No. 74: Guidelines for Electrical Transmission Line Structural Loading (ASCE-74). This technique provided an efficient method of estimating peak responses based on the consideration of the underlying statistics of the approaching wind, the dynamic characteristics of the transmission tower and wires, and a sustained wind speed. Although various measures of sustained wind speeds were used at the time (e.g., fastest-mile, hourly mean, 10-minute mean), the basic idea remained the same: to estimate a peak response based on a mean wind speed. When ASCE Standard 7 (Minimum design loads for buildings and other structures) adopted a 3-second gust wind speed as the averaging time for design wind speeds (as of ASCE 7-95), the existing GRF equations were no longer compatible. Thus, an update to the original Davenport GRF equations is required for compatibility. This process has been carried out, and has been proposed for the upcoming 4^th Edition of ASCE-74. This paper describes the reasoning and theory leading to an update of Davenport’s GRF approach for transmission line loading, which is compatible within the existing framework of ASCE-74 and consistent with the wind nomenclature in ASCE 7. A worked example is included at the end of the paper.

Hollow steel tubes (HSS) are frequently used in electrical substations to support various equipment. Even though they are made of galvanized steel, poor details, and/or deficiencies during the galvanizing process can result in corrosion due to the accumulation of moisture inside the base of these tubes. Unfortunately, the deterioration is usually concentrated at the base of the structure columns, where the stresses are at maximum. If repairs to the columns are not performed, the structural integrity is compromised. This paper reports on the newly developed Fiber Reinforced Polymer (FRP) SuperLaminate^™ and its use in repair of nearly sixty corrosion-damaged structures at two Tucson Electric Power (TEP) substations. The laminates are supplied in 4-ft wide rolls that are approximately 0.025 inch thick. The tensile strength of these laminates varies from 60,000 to 150,000 psi depending on whether they are constructed with glass or carbon fiber. In the field, the laminate is cut to the desired length and coated with an epoxy paste. The laminate is wrapped around the column a minimum of two wraps, creating a 4-ft tall cylindrical shell around the column. The annular space between the column and the shell is filled with concrete or grout. Additional reinforcing steel can be added in the annular space. The lower portion of the column is also filled with grout and a drain is added to prevent future accumulation of moisture. All repairs can be performed while the structure remains in service.

Upgrading aging transmission towers to meet the requirements of increased loads due to additional equipment and updated loading standards has attracted interest from researchers and engineers throughout the world. Retrofitting of tower leg members by adding parallel reinforcing members has been verified as an effective way to increase structural load-carrying capacity. The structural performance of the connector between reinforcing members and main members is the controlling factor in this kind of retrofitting design. In this paper, the static structural performance of bolted cruciform/splice connections in reinforced leg members was reviewed and numerical models were developed for dynamic analysis of the connections under cyclic loads using ANSYS. The bolt pretension relaxation was simulated and its structural effect on bolted cruciform/splice connections was studied. Results demonstrated that the bolt pretension loss causes high initial stiffness degradation and this effect is more influential on cruciform connections than splice connections.

Taking into account future needs, the transmission line in the river crossing was designed for higher voltage with fiber optic as overhead ground wires. Two different types of structures were studied to arrive at optimum design. Also, since the height of the pole is about 188 ft. and subject to vortex shedding force due to wind, the pole was designed to minimize the vibration with a chain inside as a damping device. The design and construction challenges of reinforced concrete caissons with a smooth steel pipe casing in a river will be discussed in further detail. The limestone rock and cavity at some depths below the river mud level provided both design and construction considerations. The caisson foundations were extended 11’-0” above normal river water level so that the steel structures supported by caissons were not required to be designed for barge protection. This paper describes the various design and construction challenges encountered in the project.

For the Thumb Loop 345 kV transmission line project, ITCTransmission (ITC) chose to evaluate the feasibility of modifying existing single-circuit 765 kV lattice steel towers for a double-circuit 345 kV application. In order to establish the feasibility of converting the single-circuit 765 kV structure to double-circuit 345 kV, structural and electrical evaluations were performed. Structural analysis using current ITC loading criteria indicated that the structural capacity of the towers would be sufficient and that no structural modifications would be required. Electrical analysis of clearances, lightning protection, insulation coordination, and electromagnetic field (EMF) performance indicated that electrically, the existing single-circuit 765 kV lattice steel towers could be modified to function adequately in a double-circuit 345 kV application. Furthermore, the existing single-circuit quad-bundle conductor could be reconfigured in a double-circuit twin-bundle configuration.

Guyed and self-supported transmission towers are typically comprised of two unique geometries: the vertical tower body and the horizontal conductor support cross-arm. Much research has been directed towards the evaluation of aerodynamic coefficients of the compact and symmetric geometry often used in the vertical portion of towers, however, much less information is available for cross-arm or non-symmetric sections. Wind tunnel tests carried out on a typical tower cross-arm design indicate that the drag loads vary significantly with wind direction, and exhibit a relationship which differs from the design procedure in the current (3^rd Edition) of ASCE Manual of Practice No. 74: Guidelines for Electrical Transmission Line Structural Loading (ASCE-74). Two additional methods are presented, which show better agreement with the experimental data: the IEC equation for yawed wind (which was recommended in the 2^nd Edition of ASCE-74); and a modified version of the yawed wind formula in ASCE-74. These approaches have been proposed for the upcoming edition of ASCE-74. The implications of the different equations are shown with reference to the wind loading on the structure only, as well as the overall tower-line system. The results are also compared with those obtained using PLS-TOWER. The paper reviews how force coefficients (i.e., drag coefficients) are developed and applied in wind load calculations, and describes the implications of the current and proposed approaches to yawed wind loads.

This paper introduces pioneering solution for upgrading 45 km, 115 kV double circuit line, built in 1922, in Ontario. To double the circuits’ power transfer, the existing 605 kcmil ACSR was replaced with 997.2 kcmil ACSR/WT conductor and the thermal rating was increased from 85°C to 150°C. Visual inspection and probabilistic corrosion model were used to determine the severity of corrosion and to incorporate corrosion damages into analysis of the steel towers. Relocating the bottom phases to modified middle arms did not provide sufficient ground clearance and using conventional vertical extensions on existing grillage footings were impractical because it require large crane to lift the fully dressed tower, which was impossible in populated areas. Innovative solution using lighter shaft extension inserted above the tower’s bend line was designed allowing the use of smaller crane thus considerably lowered material and construction costs. Further, galloping performance was improved by installing inter-phase spacers.

High Intensity Wind (HIW) associated with tornadoes and microbursts pose a major threat to transmission line networks in Ontario and many other regions around the world. Almost all transmission structures failures in Ontario in the last 15 years can be attributed to HIW, particularly microbursts. However, when assessing the structural adequacy in accordance to current designs codes, the codes assume that synoptic wind profile provides the basis of wind loading in the design process and does not consider the HIW components associated with severe thunderstorms. Such assumptions may be leaving transmission networks exposed to an unquantified level of threat to a meteorological events associated with severe thunderstorms. In this paper, the models for tornadoes and microbursts are discussed and a case study is presented to demonstrate the destructive effects of these extreme wind events. Recommendations for revising the design criteria for extreme weather are given.

This abstract outlines the process and challenges of designing and constructing a new 230kV-115kV Transmission Substation (TS) and a new 115kV-12kV Distribution Substation (DS) adjacent to an existing operating 115kV-12kV TS/DS. Once the new TS and DS were constructed, the old substation was disassembled and demolished to make room for a Static Var Compensator (SVC) substation on the old substation property. The design and construction of this project presented many challenges such as limited property for expansion, existing utilities onsite, Florida Department of Environmental Protection (FDEP) and Army Corp of Engineers (ACOE) jurisdictional wetlands onsite requiring dredge and fill permitting, FDEP and Bay County Florida stormwater permitting requirements, high groundwater levels, and poor soils onsite with PEAT layers at approximately 10’ - 20’ of depth requiring deep foundations to support substation equipment. The use of direct embedded concrete poles for dead end structures as well as for bus support and switch structures was used for both the TS and DS. What made this project successful was the close coordination between Gulf power, civil design, transmission line design, and physical substation design to provide innovative solutions to accommodate project size on limited property with many site challenges including a short project timeframe.

Electrical system transmission line structures are typically supported by deep foundations such as concrete drilled shafts, driven piles, micropiles, and helical piles. Although a number of industry guidelines describe the fundamental design principles and construction/installation procedures of these foundation types, there is no comprehensive electrical system guideline, which relates all the elements needed to properly characterize loads imposed by electrical structures and extreme environmental conditions on foundations. There is a lack of guidance on relating electrical system loads developed from various industry codes to foundations governed by traditional civil engineering design standards. A task force assembled by the Deep Foundation Institute has conducted a survey of utility design professional to assess the state of the practice for transmission structure foundation design. This survey, in conjunction with a thorough literature review, will be used to develop a guideline design document with recommendations for uniform analysis and design of electrical system deep foundations. This paper provides a summary of task force efforts to date and the initial industry survey results. Included are discussions of existing design and code documents as they relate to electric transmission line foundations, and elements needed in a guide document to improve the efficiency and reliability of electrical transmission line foundation design.