Electrical Transmission and Substation Structures 2022: Innovating for Critical Global Infrastructure

The Port of Wilmington, operated by the North Carolina State Ports Authority (port), is a significant economic driver for the state of North Carolina. Following the Panama Canal’s expansion in 2016, they embarked on a $200M capital improvements plan to service the larger “Neo-Panamax” container vessels that are now calling on ports in the United States. The port added larger “Neo-Panamax” lifting cranes and requested Duke Energy Progress (DEP) raise the pair of 230kV lines crossing the Cape Fear River at least 12 feet. The new cranes are so large that their delivery also required the lines to be temporarily raised. The port needed quick, innovative, and cost-effective solutions. The project team immediately began working on a plan to meet their needs. The transmission lines are supported by 335-foot lattice towers that were installed in 1972 and are the tallest of their type on the East Coast. They were analyzed in PLS-TOWER to determine which members needed to be retrofitted to support the tower modifications, while also meeting today’s wind loading criteria. The structural evaluation considered each phase of construction and the associated loads. This sequencing was complex because at least one of the two circuits had to always remain energized. The existing lattice tower legs are supported by concrete pier caps founded on concrete piles. These were analyzed and validated against the new loading. This assessment avoided significant environmental impacts to the Cape Fear River estuary. The optimal solution was determined to be: 1) reconfigure the tower arms from a vertical to a delta conductor arrangement, and 2) reconductor the line with a high-temp, low-sag ACCR conductor. This redesign provided more than 41 feet of air clearance that could be implemented within a reasonable timeframe and cost. This solution not only exceeded the NCSPA’s expectations, but it also benefited Duke Energy Progress customers. The structures were upgraded to current engineering wind standards and the conductors were replaced with state-of-the-art cables that are smaller, lighter, and less sensitive to wind. These improvements enhance power reliability and resiliency in a severe-weather and hurricane-prone area, which will benefit customers for years to come. The strategy came to fruition and history was made in May 2020 when the MV Hyundai Hope docked at the state port. It was the largest container ship to ever dock at the Port of Wilmington.

As utility professionals we are responsible for infrastructure spanning all over the country through a myriad of environmental and ecological challenges. We know the importance of being good stewards of the environment while also balancing the need for progress and development. Regardless of your operating territory, on some level, all engineering and O&M teams have needed to coordinate with other agencies to mitigate damage or disturbance of the environment while maintaining existing or constructing new transmission lines. And in some instances, we are forced to respond to situations born out of factors that were out of our control entirely. The SR529 Mitigation Project is a wonderful example of multiple agencies responding to a need with some “out of the box” thinking. In 2018, the Washington Department of Transportation (WSDOT) notified Snohomish County Public Utility District (SNOPUD) of their intention to create a new estuary along the Snohomish River that would reclaim damaged wetland from years of transportation, residential, and commercial development, as well as offset the future destruction of ecologically sensitive areas from subsequent highway expansion projects. The estuary would be critical for declining salmon populations and other connected species in the area. The issue for SNOPUD was that the proposed estuary happened to encompass the right of way for a major transmission line serving the region. Once flooded, SNOPUD would have no way to access and maintain a major river crossing structure for that line. It also meant that the foundation and base section of the galvanized tubular steel tower would be subject to high salinity tidal flows that would regularly submerge those structurally critical components. Of course, the tower was not designed or installed with this kind of exposure in mind. SNOPUD had a decision to make. They could either move the line out of the intended flood zone or upgrade the affected crossing structure to withstand these new environmental conditions, knowing that once WSDOT completed their project, the only way to access this tower would be via inland barge (a costly endeavor). Complicating this decision further was the aggressive timeline that WSDOT outlined for having all utility work completed before they intended to breach the dike of the main river. This paper outlines the technical challenges and decision-making process that SNOPUD endured as well as the corrosion mitigation and structural upgrade efforts that were undertaken to extend the life of the transmission tower in its new environment.

The Badger Coulee transmission line is a 180-mile 345 kV transmission line that extends from the Briggs Road Substation in Holmen, Wisconsin, to the Cardinal Substation in Middleton, Wisconsin. With routing and siting efforts starting in May 2010 and construction completing in December 2018, the 8 ½ years in-between provided the project team with some of the most unique and interesting challenges that designing and constructing a transmission line in the state of Wisconsin has to offer. First, navigating the routing and siting effort to complete the state regulatory process to obtain project approval from the Public Service Commission of Wisconsin. Once project and route approval were received, the detailed design and construction of the line commenced. This paper and presentation will detail some of the more unique challenges the project team had to tackle and what they did to overcome those challenges. These challenges included: considerable variation in terrain from the low-lying lands of south-central Wisconsin to the coulee regions of western Wisconsin; construction adjacent to a major interstate for approximately 100 miles; single, double, and triple circuit configurations; single-pole, three-pole, and H-Frame structure designs; long-span river crossing in excess of 2,200’; direct embed, reinforced concrete, and micropile foundation designs; helicopter, including heavy-lift, construction; DOT communication fiber and railroad signal interference; and planning, scheduling, and sequencing man-power and efforts.

As the most critical portion of the 500KV Zhenhai~Zhoushan transmission line project. The Xihoumen Crossing is also one of the largest transmission line crossing projects in the world. The crossing scheme is "Strain-Suspension-Suspension-Strain", and the crossing spans are 1016m-2656m-521m respectively for each span; the total crossing length is 4.193km. The height of two ultra-long span tubular crossing towers is 380m, which currently ranks as the tallest transmission crossing tower in the world, based on the weather conditions of the area, the towers were designed under the high wind and wind plus ice conditions. Concrete-Filled Steel Tubes (CFT) were used for the main legs below 260m, and tubular steel members were used for other components. The production process and key fabrication technics will be introduced, which include the fabrication of the large diameter steel tubes, large sized X joints and K-joints, stiffened ball-joints, and trial assembly. Construction is the most challenging portion for such a heavy and tall tower, construction methodology will be discussed to cover installation plans and lifting equipment, erection of tower legs and cross arms, and pouring concrete into tower legs.

Transmission power transformers are the Achilles’ heel of the bulk electric system, since they perform voltage transformations and are located at the beginning and end of the transmission system. Designing a foundation and other associated elements to support a transformer installation is a critical, and sometimes daunting, task. Transmission power transformer installations may require different means and methods than for other substation equipment and structures. This is especially true for large power transformers, which can exceed 750,000-pounds after assembly. Additionally, code revisions and Critical infrastructure protection (CIP) requirements have added a new level of complexity to the design process. In order to achieve a functional, maintainable, and reliable transformer foundation design, it is important for structural engineers to have a working knowledge of the various construction means and methods used for transformer installation, and the supporting components.

Based on experience with four large lattice tower projects in the United States during the past five years, the authors have assessed the potential cost savings and performance of guyed lattice structures in comparison with self-supporting alternatives. Three projects used guyed vee structures as tangents, and the fourth used a guyed delta structure (a “banjo”). Guyed lattice masts as deadend structures were also used. This paper presents a general description of guyed lattice structures and evaluates cost savings related to steel, foundations, assembly, and erection. Two projects allowed a direct comparison between guyed vee and self-supporting tangent towers, owing to identical structural loading criteria. The other two projects had very similar criteria and can corroborate the information provided by the prior two. Aspects of the performance of guyed structures are also examined. Findings are summarized in table form.

American Electric Power (AEP) recently developed base shoe and standoff anchor bolt designs for their 765-kV lattice tower family. A review of publications from the American Society of Civil Engineers (ASCE), American Institute of Steel Construction (AISC), and American Association of State Highway and Transportation Officials (AASHTO) produced a variety of alternate approaches available for undertaking this design. These included the selection of an effective bend line length, considerations for anchor bolt flexure, and methods for calculating the required anchor bolt area for combined loads. Anchor bolt flexure was included in the final design approach, even though the standoff distance between the concrete and base plate was kept below the two-diameter limit. Finite element analysis used to refine the design approach revealed that assuming a rigid base plate for calculating anchor bolt forces was not always accurate, and that additional design rules for anchor bolt location and minimum base plate and stiffener thickness are required for this assumption to be valid. This paper presents the final design methodology selected to achieve a balance between economy and reliability. It uses a formulation that is consistent with current approaches, and incorporates the findings of the finite element analysis and full-scale installations.

As engineers, we work to refine our designs to ensure the most efficient use of material to provide an optimized design and best service to our clients. In doing so, we’re able to design some very slender members that will still meet the project design criteria. However, when left unchecked and so narrowly focused on material usage and efficiency, in some cases, these slender designs may be susceptible to the detrimental effects of vortex shedding and wind-induced vibration. While wind-induced vibration is largely a location-based phenomenon, it may be possible for owners, line designers, and fabricators to work together to reduce the probability of problematic vibration. Cross braces and cross arms for H and A Frame structures are two examples where overly efficient designs can lead to some unintended consequences with structures installed in susceptible locations. This paper and presentation will provide a real-world example of one such design. Based on analysis, investigation, and research, this paper and presentation will also propose slenderness limits and equations that any engineer can use to determine the approximate critical wind velocity for vibration to occur and help them assess the risk for their cross brace or cross arm design to the effects of vortex shedding and wind-induced vibration.

Transmission tower designers are left with little to no guidance on how to design and analyse towers when considering seismic excitation. There are few valuable published works with suggestions on how calculate and lump a tributary mass of the span of conductors, insulators, etc. to the attachment points on the tower supporting the span. This is normally followed by analysing the tower using simplified, quasi-static, or response spectrum methods to obtain the straining action necessary to perform the design. There are several valuable investigations and data collection on the real-life behaviour of transmission towers after seismic events that suggest the majority, if not all, of the recorded failures are attributed to foundation issues. It is still necessary, however, for a transmission tower designer to conclude with higher level of certainty whether a seismic load case is likely to govern the design of the tower, member of a tower or group of members, or not. As part of BC Hydro’s design plan for a new transmission project including three new, short 500 kV transmission lines, analysing the self-supporting lattice towers on these lines was required. The analysis is performed using several methods: 1. Simplified analysis of the towers with conductors lumped masses; 2. Response spectrum analysis of the towers using conductors lumped masses; 3. Full time history analysis of towers using conductor lumped masses and synthesized earthquake acceleration; and 4. Full time history nonlinear analysis of one of the three lines as coupled system consisting of towers and conductors using synthesized earthquake acceleration from the site design spectrum. This paper presents the results obtained from each of the four methods, comparison between forces obtained in several members as well as a discussion of the level of effort involved with each method.

The transmission industry is evolving continuously as customer expectations, reliability, and resiliency play an ever-important role in the engineer’s selection of a transmission line structure. Transmission Engineers have an array of tools available to satisfy overhead transmission line project requirements. Most importantly, the engineer must select the most appropriate and economic supporting structure and foundation type. Factors to evaluate include project-specific electrical performance, weather-related loads, land use, terrain, geotechnical conditions, and constructability. When these are considered in combination, it is a challenging decision for the engineer to select the best structure for the project. This paper describes the advantages, disadvantages, and economy for various configurations of common overhead transmission line structure types. The engineer may consider latticed steel towers and tubular steel poles when selecting the most effective site-specific structure or structures for an entire project. This paper presents analytical procedures for comparing structure weights of common transmission structures, and their relationship to applied load versus weight. In addition, this paper includes project-specific parameters and their effects on structure selection: voltage class, structure type, terrain, cable size and tension, and structure loading.

Some transmission lines require very long span crossings over rivers and other obstacles. The increased height and heavy loading may make lattice towers and tubular H-frames inefficient designs for these structures. This paper presents an innovative tubular 3D frame design as an effective solution for tall, long span transmission structures. The design of tubular 3D frames follows the requirements in ASCE 48 Standard Design of Steel Transmission Pole Structures. The three-dimensional configuration significantly increases the structural capability in resisting heavy longitudinal loads due to broken wire or unbalanced wire tensions. While the overall configuration may appear similar to lattice towers, all main members in this type of frame are tubular sections that provide much higher loading capacities. This paper discusses general structure configuration, geometry optimization to improve design efficiency, typical connection joints, Finite Element Analysis (FEA) for static loadings, and full-scale load testing. Examples of installed tubular 3D frames in operation are presented as well.

Historically, direct embed H-frame foundations were installed using the "rule of thumb" 10 percent plus 2 feet. This rule does not address changes in soil conditions, backfill type, or different loading conditions. The embedded portion of the pole behaves similarly to a drilled concrete foundation because the backfill material resists lateral and axial forces and overturning moments. Due to the presence of a backfill material and surrounding soil, multiple failure modes may exist for a direct embed foundation. The interaction between the pole and the backfill, and the interaction between the backfill and the surrounding soil may not be easily predicted and can vary depending on the line location and contractor installation. Little consideration has been given to accurately predict the foundation capacity of direct embed structures. Prior to our research, several projects were planned on the Ameren Transmission system using tubular steel H-frame structure with direct embed foundations. Full scale load tests were conducted to determine an effective direct embed foundation design. Multiple structure heights and configurations were tested, and the results were compared to common structural and foundation software. The results showed that the combination of quality backfill material, proper backfill installation, and proper structure bracing can reduce structure overturning and improve foundation resistance. These results also provided a cost-effective design for all future projects using direct embed structures.

Vibratory caissons (circular or multi-sided, tubular, smooth wall steel piles) are increasingly utilized as a preferred foundation type for transmission line projects in poor subsurface conditions due to their limited spoil generation and ease of installation with the proper application. However, without a thoughtful approach, the use of vibratory caissons can lead to significant project schedule delays and increased project costs. How do we get the information necessary to reduce the risk of design or construction issues for projects with very challenging environmental or construction access conditions? How do we effectively coordinate with the various stakeholders involved in the successful implementation of vibratory caissons? How do we improve the likelihood of accurately predicting the performance of vibratory caissons? How do we set up contractors for installation success? This paper will answer these questions while discussing key considerations to select, design, and construct vibratory caisson foundations as a suitable alternative to traditional direct embed or drilled shaft foundation systems. Based on project experience with multiple utilities along much of the East Coast and Southeast parts of the country, the authors will discuss how project teams can identify when vibratory caisson foundations are favorable over traditional foundation systems. In addition, the authors will discuss important design methodology, fabrication, and installation elements that require consideration for improved probability of successful implementation of vibratory caissons.

The Xcel Energy W3408 69kV overhead transmission line was originally constructed in 1934 and extends 2.7 miles (4.3 km) from the Nelson Substation in Wisconsin to the Wabasha Substation in Minnesota, crossing the Mississippi River and its backwaters through the Federal Upper Mississippi River National Wildlife Refuge. Xcel Energy identified 2.2 miles (3.5 km) of direct embed wood H-frame structures in Wisconsin through the backwaters area for a rebuild in 2018–2019 due to age and condition. Design and construction challenges include the following: the presence of 2 to 3ft (0.6 to 0.9 m) of standing water over a significant portion of the project; winter ice; environmental/wildlife concerns; a limited service interruption (outage) for the transmission line, and poor soils. The design team selected a high-strength conductor, minimizing sag and decreasing the total structure count from 27 to 17. The chosen principal foundation consists of groups of four (4) 3.5-inch (90 mm) outer diameter helical piles connected by a grillage at each structure leg. All required materials could be transported to the structure locations by airboat and installed using specialized marsh equipment without an extended, non-restorable outage of the transmission line. The grillage cap design consists of W-beams interconnecting grouted collars that accept the helical piles and transfer loads from the structure legs. This configuration develops a fixed head condition for the piles. The use of battered piles creates a stiffer load-deflection response thus improving capacity. Drifting and expanding ice loads were addressed by identification of risk-prone areas and development of a secondary foundation system consisting of vibratory steel caissons for the four (4) structures that could not be spotted in low-risk areas. These caissons consist of 0.563-inch (14.3 mm) thick galvanized steel in a dodecagonal shape with a 3.5-ft (1.05 m) outer diameter. They range in length from 56 to 62 feet (16.8 to 18.6 m) and are designed for up to 6.5 feet (1.95 m) of scour potential.

Over the past few years, several large Extra High Voltage (EHV) transmission line projects have enabled a North American renaissance in latticed tower design and testing. POWER Engineers, Inc. was recently involved in multiple EHV tower family designs and subsequent full-scale testing efforts. In addition to compressed project schedules, design modifications to accommodate permitting and test facilities located around the globe, the COVID-19 pandemic added unprecedented challenges to the latticed tower testing programs. Our experiences and lessons learned on tower testing from the Owner’s and Owner’s Engineer perspectives are the subject of this paper. Tower testing for multiple projects and multiple tower types, over a short period of time enables the engineer a unique opportunity to witness, evaluate, and compile high-level best practices and lessons learned. In this light, the following topics are addressed: reasons why an Owner would or would not test towers; timing and schedule for design and tower testing; general guidelines, key elements, and suggestions for lattice tower testing; development and sequencing of test load cases; potential pitfalls and testing challenges; and witnessing of tower testing including remote witnessing.

When combined, OSHA 1926.502 and IEEE 1307 provide requirements and considerations for qualified electrical workers to safely climb transmission and distribution structures. Meeting these requirements is especially challenging for transmission line lattice towers as most were designed and constructed prior to these standards. Most industry-specific transmission line design software are incapable of proper analysis; therefore, manual calculations must be performed to determine the viability of safely climbing and anchoring to these structures. This paper provides a brief overview of these requirements, an approach to selecting walkable members and anchoring points, and practical methods for calculating the structural capacity of these structures for climbing. Calculations will include the required loading requirements for anchor points and the combined axial and flexural calculations for walkable members using ASCE 10-15 and AISC 360.

The lattice steel transmission tower-line system serves as a critical component of the electrical power grid. To meet community economic development and power demands, tall high-voltage towers connected by long spans have been built in recent years. Due to the complex structural performance of transmission tower-line systems leading to knowledge gaps in system responses and failure mechanisms, tower collapses and line breaks remain threats under extreme weather loading even when following established transmission design codes and specifications. Under various meteorological threats, such as hurricanes, tornadoes, and thunder or ice storms, individual structural component failures can lead to progressive collapse and large area blackouts, producing devastating economic losses and societal consequences. Improved modeling of the wind-infrastructure dynamics and resulting structural failures and power outages is consequently necessary to better inform local decision-makers on effective storm preparation and grid hardening actions to reduce outages and recovery time. In the present study, a mechanistic model is developed using finite element analysis to evaluate tower and line performance under various climatological parameters, including wind, rain, and ice storms, for physical damage predictions. Material imperfections and environmental loading uncertainties are considered and evaluated to develop fragility surfaces. This physics-based model is integrated into a Monte Carlo model to predict cumulative tower failure probabilities using weather simulations. Copulas are used to model the joint distribution of wind and rain or ice, and the methodology is applied to a case study for the northeastern United States. The results indicate the coupling of ice accretion and strong winds has a substantial impact on the tower fragility. Over a 10-year period, an average cumulative failure probability of 0.33% is projected, indicating a generally reliable design. For demonstration, climate change scenarios were projected where rains and winds were increased 10% while ice thicknesses decreased by 10%, increased by 10%, or remained constant. Under these simulated future climate change scenarios, the failure probabilities could be projected to increase up to over 1.5%, indicating the reliability in the future could be compromised under a changing climate.

The province of British Columbia, Canada, is prone to snow avalanches in its mountainous regions. Overhead transmission lines are often built along mountain sides and may trespass avalanche zones. From time to time, damages to transmission lines are observed due to avalanche impacts. The most phenomenal case was observed on a tangent structure of a 287kV transmission line located in the Northwest of British Columbia. Since its service in late 1960s, damages have occurred to the same structure four times in 1977, 1989, 2007, and 2018, respectively. The last one occurred on April 02, 2018, that destroyed the self-supported lattice tower. A temporary lattice tower had to be installed as an emergency response to restore the power supply as soon as possible. Driven by the 2018 incident, a systematic investigation was carried out to mitigate the avalanche impact on this power line. As a result, a rational design methodology was developed and implemented in this project. This paper is intended to describe the details of the design methodology. First, the phenomena of a snow avalanche are described. Second, design avalanches are established. Semi-empirical equations are recommended to determine the key parameters of a design avalanche. Third, the method of applying avalanche load on a power line and the ensuing structural analysis of the entire section of a transmission line consisting of towers, foundations, conductors, insulators, etc. is illustrated using the above-mentioned project as the case study. As a result of lesson and learn, the following principles are recommended to mitigate damage from avalanches effectively: (a) Conductors and structures shall be located away from an avalanche zone if feasible. Conductors shall be located high enough from ground to minimize the avalanche impact. (b) Conductors and structures shall have minimized area facing the avalanche to minimize avalanche impact, if feasible. (c) Various components in a transmission line shall be properly coordinated in terms of their relative strengths to minimize the consequences of avalanche induced failures if it occurs.

Keeping an electrical substation operational is one of the top priorities for every utility. In recent years, severe weather-related and extraordinary events have occurred more frequently, e.g., floods, hurricanes, tornados, and tsunamis. For substation structural designs, utilities often refer to ASCE 113, which is generally based on ASCE 7-05 edition with modifications to better suit substation designs. Although ASCE 113 provides guidelines on extreme conditions, such as high wind and seismic, there are no provisions on other extreme events. In this paper, load determinations for different extreme events, including hurricanes, tornados, and tsunamis, are first described based on various available resources. Then, how extreme event loadings are combined with all other applicable loads is presented. Several suggestions that may be applicable to substation applications are also provided. The goal of this paper is to provide utilities with a better awareness on extreme event loadings that could affect how utilities perform substation designs and allow them to better prepare, harden, and protect their assets during extreme events.

Load effects due to extreme wind events are considered in the design of most structures. A component of this calculation in ASCE Standard 7 (i.e., ASCE 7-16) is the effect of wind directionality, which acts to reduce the nominal design wind load imposed on the structural system. A reduction such as this is traditionally not applied in transmission line design for many reasons, including a large geographic extent of the line, varying line orientations, and that the load factor used in design is typically 1.0. This creates a difference between the wind loading procedures used for transmission lines and those used for other structures, although the base criteria (i.e., mean recurrence interval or MRI) are often directly compared. In light of the ever-increasing reliance of society on a constant and reliable electricity source, there is currently debate as to the classification of transmission lines as more critical structures and therefore greater design loads than those used currently. This is relevant at the time of writing as a committee for a new ASCE Loading Standard is under formation and the implications of the above differences are under review. This paper is intended to begin a discussion on developing wind loading procedures for this new ASCE Loading Standard which achieve the intended performance and how the level of intended performance compares with structures designed using ASCE 7.

The first transmission line in the United States was constructed in 1889. The U.S. has since designed and installed 240,000 miles of high voltage transmission lines. Most of this infrastructure was developed prior to the 1960s, and some of the tallest river crossing towers (greater than 400’ in height) were constructed in the early 1900s and are still in active service today. While analyzing structures of this magnitude with a design origin from the early 20^th century, the original design criteria and drawings needed for analysis may not be available. Connections may have used rivets, steel, and bolt strength may not be specified, and section sizes used may be obsolete. This paper will present ways to overcome these challenges, reference historical design resources, and provide analysis recommendations. Furthermore, there have been significant changes in the design and analysis of lattice structures over the last 120 years. To understand these advancements, this paper presents a study comparing the latest design standards with those from the 1900s and the 1960s.

Aging infrastructure is a critical issue for utilities, and for The United Illuminating Company, it has led to the need to replace the two 115 kV transmission circuits attached to the Metro-North Railroad structures. Rebuilding a high voltage river crossing is daunting by itself, but add in removing the existing wires from 100-year-old 200-foot tall towers built over one of the busiest commuter railroads in America next to a heavily traveled interstate highway bridge, and you must get creative. After almost two years of planning, the major stakeholders finally agreed that the solution would consist of two parts: the removal of the conductors on the north side would be performed using a helicopter, and the removal of the conductor on the south side would be performed by shifting three lanes of high-speed traffic to make room for a 180-foot-tall man-lift on the deck of the Moses Wheeler Bridge (I-95). The removals were completed ahead of schedule and without any safety issues.

There are several critical customers located in Southern Maryland Electric Cooperative, SMECO territory. Until recently, one customer had been served by Potomac Electric Power Company, PEPCO, up until 2012 when the feed to the facility was purchased from PEPCO by SMECO. The feed to this customer is a radial, 69-kilovolt line dating back to the mid 1940s. When SMECO purchased the line, it was in need of extensive repair. A significant section of the line needed to be rebuilt entirely. The line rebuild presented numerous challenges that had to be addressed, including: The only back up source for the line is onsite generation that cannot support the entire facility at once. Extended outages were not an option and were limited to weekends in late fall and early spring. The line would have to be rebuilt while the existing line remained energized. The railroad, parallel to the line, had been converted to a hiker/biker trail with significant pedestrian traffic. The line traverses part of the Mattawoman Creek watershed, which is recognized to be a critical area by the EPA. Given the critical nature of the line and surrounding limitations, SMECO realized that standard construction practices would not be practical within the project’s parameters. In conjunction with the project engineer, Booth & Associates, SMECO evaluated several options for rebuilding the line and determined the most practical option was to rebuild the line using composite poles on an offset centerline 10 feet from the existing centerline. Composite poles have a life expectancy comparable to steel poles, and the lightweight nature of composite material allowed the contractor to use lighter construction equipment resulting in no significant damage to the bike path. The base sections were set first, and the pole tops were set using only the material handler on the contractor’s bucket trucks. Only two outages under two days each spread over two weekends were required to complete the line cutover and retire the old line.

On occasion, a transmission line might be terminated on, or supported by, the oddest of structures: to anchors in the face of cliff, to powerhouse walls or rooftop structures, or to a dam. When challenged to rebuild or reconductor existing transmission lines, it is often difficult for the designer to confidently assess the condition of atypical termination structures and determine their serviceability for the loads to which it may be subjected. This paper discusses some inspections and tests that were performed on 230kV termination structures anchored to a dam for a project in Montana. These activities included weld inspection, ultrasonic condition testing, bolt cluster pull-tests, and load development. Testing protocol is explained, and the results presented.

While helical piles and screw anchors have been around for decades and used in a variety of industries, they haven’t been widely used to support substation structures. By employing an innovative structural grillage with integrated multi-pile foundation design, which allows for adjustment in multiple directions for ease of installation, the grillage can be designed to transfer the forces from the substation structure to the helical piles. This paper will demonstrate how using some basic principles of structural engineering coupled with finite element analysis, an innovative structural grillage was developed to transfer typical substation structure forces into the helical foundations. The designs were confirmed by full scale testing. This paper will provide detailed and informative design information and test results.

Early collaboration between the utility and its line and foundation designers provides sequencing and adjustment to field geotechnical data collection protocols and associated foundation design. This paper presents application of the demonstrated benefits of adaptive foundation design for several projects across the U.S. Grid modernization, renewable energy integration, and demand changes have been driving rebuilding of power transmission lines within existing right-of-way and construction of new lines built in green fields, often through difficult terrains. Design and optimization of foundations for tower structures have critical impacts to cost and schedule. Traditionally, geotechnical investigations involving drilling of soil borings with heavy machineries have been conducted in the early phase of projects to obtain soil data. However, obtaining such field data early in the project poses several difficulties such as addressing access issues, landowner sensitivity and coordination requirements, synchronizing with de-energizing schedule, mitigating safety hazards including fire risks, noises, avoiding impact to vegetation, and sensitive species. In addition, accurate foundation locations and loads are often not established in early project planning phases and weather events add huge variability to the schedule. Over the last two decades desktop studies have been increasingly used in the industry to address some of these challenges. Desktop studies collect published geological information to further target field data collection locations often reducing or better targeting the needed number of borings. A natural progression is to further refine desktop studies with soil mapping and limited soil borings to customize preliminary soil design parameters. These parameters are then employed for estimating foundation sizes and sensitivity analyses are performed, where needed. Many utilities also have standard foundation designs for established soil profiles which further aids this approach. When access and tower locations are better established at, or before construction, a targeted verification soil boring program can validate earlier assumptions and adjust foundation sizes. This adaptive foundation design provides greater flexibility to the project. Verification borings at the actual locations of heavily loaded towers provides greater accuracy. Construction contracting mechanisms can accommodate for some anticipated changes to length and size of foundations through pre-established unit rates. The phased approach blends the limited availability of access, the schedule, and the risk tolerance to provide a dependable means of foundation design.

Those of us in the overhead line business are constantly checking out lines and structures as we travel. Our distraction with our craft undoubtedly amuses and annoys our families. What do you see when you drive around? We take pride because we understand that the electric grid is ‘the largest machine in the world’ and that power delivery is critical life-line infrastructure. We appreciate the size and complexity of power line projects, we admire unique solutions and we notice examples of excellent execution. Far too often, however, we see sloppy and neglected installations. It makes us question how the design was originally conceived and wonder how it can stay in service much longer. If it is something we notice and ponder, how do these neglected lines impact the general public? Should we turn a blind eye to haphazard conductor arrangements and leaning poles? Or, should we put forth our best effort to keep the grid looking organized, professional, and tidy? This paper will explore the responsibility engineers have to consider aesthetics and the functional benefits that can result by examining ASCE Policy 117 on aesthetics as it applies to power line projects. Attention to good cable management designing power lines has parallels to an electrician routing electric or data cable, leaving an elegant, safe, and easy to maintain installation. Further, the human response to organization or disorganization ultimately affects public opinion and acceptance to power lines. As we invest and maintain our overhead lines and structures, making design decisions with the mindset of being right and tight will result in improved public safety, grid reliability, and visual quality. We should take inspiration from the beauty and functionality displayed by thoughtfully executed cable management and strive to impress upon the greater pubic the professionalism and attention to detail that is pervasive in our industry.

The power transmission industry has grown increasingly interested in new approaches to generate economic design. For high-voltage transmission lines, opportunities for greater efficiencies exist primarily in structure design. Guyed engineered steel poles have become a desirable option for those seeking to minimize cost while satisfying performance requirements. Lightweight and easily erected, guyed steel poles minimize structure deflections and can ordinarily be built on relatively economical foundations. Because they depend upon a complex system of load transfers, however, guyed engineered steel structures introduce many unique design considerations. For instance, engineers must calculate how a load will transfer from the structure to the guy wire to the anchor, as well as how it will transfer from the structure to the foundation. They need to determine how construction tolerances will be accounted for in the design and the feasibility of accomplishing this added design work without significantly increasing cost. They must consider which decisions impact cost and add margin to the design, as well as what could potentially limit the proposed guy wire size. They must determine if guy loading should be limited to reduce anchor size and related installation costs. They must verify the ready availability of hardware that meets strength requirements. Failure to acknowledge these design considerations can result in lost efficiencies, construction schedule delays, or inadequate performance. Drawing on their years of high-voltage transmission line experience, the authors examine key design considerations on projects where guyed engineered steel poles were used and discuss approaches to account for these considerations in coordination with steel suppliers.

Steel lattice towers are commonly used in overhead power lines. Key elements of these towers are gusset plates, which connect and transmit forces between members. This paper presents an evaluation of the behavior and strength of lattice towers’ gusset plates (LTGP) based on experimental investigation. The study presented herein was carried out at the Université de Sherbrooke and deals with a set of geometrically distinct conventional configurations subjected to monotonic tensile loading until failure. Digital image correlation (DIC) method was employed as a means of elucidating the mechanisms governing the behavior of bolted assemblies with gusset plates. The study revealed the influence of geometry in the behavior of bolted connections, a parameter which is generally not considered in detail in most design guidelines.

Hurricanes are one of the main causes for blackouts and related infrastructure damage in the United States. Electrical transmission towers, which are key parts of the electrical transmission networks, are vulnerable to high wind speeds during storms. This research introduces a framework to develop fragility curves that describe collapse probabilities of transmission towers under hurricanes. The intensity measure of fragility curves is the storm-maximum gust wind speed, and incremental dynamic analysis (IDA) is used to capture the collapse phenomenon. The fragility curve is expressed as the cumulative distribution function of the intensity measure at the onset of collapse, which is assumed to follow a lognormal distribution. The record-to-record randomness of different hurricanes is considered by running IDA analysis for a suite of hurricane wind speed and direction time histories, which are selected from 10,000-year synthetic hurricanes. The two parameters of the lognormal distribution are estimated using the method of moments.

Tubular steel poles with davit arms are used extensively as high-voltage transmission line support structures—a double-circuit tubular steel pole with davit arms and I-string insulators is one of the quintessential tangent pole configurations. A davit arm’s length in a suspension application is often dictated by the combination of the I-string insulator’s swing and the required clearance from energized conductor or hardware to the structure under the conditions that produced the swing. To maximize design efficiency of a transmission line, the line designer should be aware of all factors that influence system performance. The pole shaft and arm deflections are factors often overlooked for clearance to structure calculations. National Electrical Safety Code (NESC) Rule 235E states that a flexible structure’s deflection shall be considered in clearance calculations to the supporting structure. Since most davit arms are not designed considering arm deflection limits, arm deflection could result in significant variability in the actual clearance values. With limited design information available during the early phases of a project, most transmission line designers must make reasonable allowances over required clearance values to accommodate the anticipated pole shaft and arm deflection’s impact. This paper will study how the additional clearance allowances established during the initial phases of design to accommodate pole shaft and arm deflection compare to the final installed condition. The study will include analysis of typical configurations of double-circuit tubular steel poles with davit arms and I-string insulators. This study will also examine some of the controls that could be established during various phases of the design process, such as using a deflected structure shape for allowable insulator swing calculations, limiting arm deflection, and communicating an arm rise value to counteract the arm deflection. These controls, among others, may limit the variability between the allowable swing angles established during the early phases of the design and the actual clearance to structure observed.

Due to advancements in silicon and fiberglass rod technology there are now seemingly limitless options to customize high voltage braced post insulator designs for new or existing poles and lattice structures. This paper covers the optimization process for transmission line design using braced post insulation for 138 and 240 kV circuits and reviews examples of custom applications where braced post insulators have been used for the purpose of clearance mitigation without replacing structures. This paper will break down the steps of line optimization and benefits of braced post insulators for new line construction compared to traditional pole and crossarm designs. Some of the benefits that will be covered include reduced construction and assembly time, reduced hardware requirements, better contamination resistance, bird perch reduction, reduced right-of-way requirements, smaller structure footprint, and fire hardening. Also discussed in the paper is the process of modifying existing structures with custom compact braced post insulator designs to increase clearance without losing full functionality of the structure. This paper will provide examples where traditional cross arms with suspension insulators and lattice tower arms have been replaced with specialized braced post insulator assemblies to mitigate clearance violations in Alberta, Canada. Some of the drawbacks of braced post insulators such as reduced longitudinal capacity and increased galloping risk, are also summarized in this paper.

Overhead transmission line towers may be subjected to a severe level of earthquake-related forces if the line lies in a seismically active region. However, the traditional practice in the industry generally overlooks the effect of seismic forces on the structural demand in parallel with universally valid design codes claiming that the base shear that emerges on an earthquake would generally be less than wind or wind + ice combined conditions. On the other side, in recent years, a rising number of scientific articles in relation to the possibility of severe consequences of an earthquake on the components of a transmission line (e.g., towers) have been published. Additionally, in late 2019, the Ministry of Environment and Urbanization of the Turkish Republic put a comprehensive earthquake code along with a new seismic map of the country into effect, also covering transmission line towers. Preliminary studies revealed that earthquake-related forces might be critical for specific components of towers, especially in case the line was located close to the fault zones. In this regard, modal analyses of towers have become a must for the industry of transmission line engineering in some countries. In addition, even the most common commercial software packages used in tower analysis and design do not have the option to perform the modal analysis. In order to determine the modal response of towers, the finite element model (FEM) of the tower or whole tower family must be generated or be transferred to an alternative FEM software, which is a cumbersome procedure. At this point, artificial neural networks (ANN) can be a practical solution. In brief, this study aims to construct and train an ANN architecture in order to determine the relationship between the structural parameters related to the mass and stiffness of the tower with first mode frequencies. In this way, required modal response data of the considered tower can be obtained rapidly with a high accuracy rate.

While the Iron Age spanned between 1200 and 600 B.C., significant advances have been made in iron manufacturing over the last 60 years, allowing for new applications which capitalize on its performance properties. One of these applications includes ductile iron poles. Consisting of an older, proven metal, ductile iron has been transformed into a relatively new pole product through the application of state-of-the-art manufacturing processes and an engineered product design. While ductile iron has seen widespread use in various applications since the 1940s, its application as a pole material has only been experienced in the past dozen years, making it a relative newcomer to the utility industry. Ductile iron is like A588 steel, with just a few percent differences in iron content. But that is where the similarity ends. There are distinct structural performance differences between steel and ductile iron that need to be understood if one is to utilize ductile iron poles as a structural support. This paper provides a basic study of the properties and performance of ductile iron as a pole material technology, with comparisons to other materials, and is intended to provide engineers and designers with a basic understanding of the pole technology when considering their use and application for everyday or new design challenges.

The current industry design standard for short circuit forces in substations prescribes a static analysis considering peak instantaneous force. Various complex dynamic analyses and full-scale tests have demonstrated that this approach is highly conservative. The response spectrum for short circuit loads was developed to account for dynamic effects and reduce design forces for aluminum bus, insulators, supports, and foundations. It is significantly simpler and less labor intensive than the rigorous dynamic analysis option described in IEEE 605-2008. The approach also produces results that correlate extremely well with rigorous dynamic analysis.

This paper presents the seismic risk assessment of the electrical substations located in Colombia of ISA (Interconexión Eléctrica S.A. E.S.P), which is the largest energy transmission company in Latin America. Seismic forces are not usually considered in the design of the transmission lines as tension and wind are more critical loads. In order to perform the seismic risk analysis exposure, vulnerability and seismic hazard models were generated. Risk metrics such as average annual loss, the probable maximum loss, and loss values for different return periods are used to present the results of the risk assessment. In the interest of interpreting and visualizing more clearly the consequences of a particular seismic event, scenarios were selected in which the number and distribution of the collapse of the substation’s components and associated economic losses are calculated.

There is ambiguity and confusion within the power industry related to codes and standards that define structural design criteria for electromotive forces due to a short-circuit condition. The lack of cohesive guidance throughout the industry for reliable and efficient design of substation structures subject to short-circuit loads typically results in conservative structural design. The intent of this paper is to explore the effects of short-circuit events on rigid bus support structures in substations, to recommend modification factors to the short-circuit force used in ASCE 113 (2008), suggest new strength reduction factors for insulators, and propose new load factors for short-circuit loads in ASCE 113 (2008). The final recommended design short-circuit force for use with ASCE 113 (2008) should be defined as a product of a Structural Response Factor, an Electrical Reliability and Resiliency Factor, and the IEEE 605 (2008) short-circuit force. Another recommendation is the adjustment of the safety and strength reduction factors for porcelain insulators. The strength reduction factor for ultimate strength design should be increased from 0.5 to 0.75 and the safety factor used for the design of insulators according to allowable strength design should be reduced from 2.5 to 2.0. Finally, the load factors for the short-circuit load effect used in allowable strength design should be changed to 0.67 and 0.45, for short-circuit-only and combined load combinations, respectively.

The electrical utility industry has used the National Electric Safety Code (NESC) since its first publication in 1914. This Code has been used for the specification of minimum structural loads to design poles and towers that comprise the overhead power grid as well as the minimum electrical requirements for the safe installation, operation, and maintenance of these systems. However, the NESC has a singular chartered focus on “safety”, implying electrical safety and was never intended as a structural design specification. We know this because the NESC explicitly states in its purpose statements, that the Code is to provide a “...standard of safe practices...”, and “…not intended as a design specification…”. As such, it was never intended to be a Code or Standard to provide structural loading or prescriptive performance for in-service reliability. Minimum safety standards as outlined by NESC or California GO 95 are indeed needed and should be required to be followed. As technical advancements have been made in the science of improving our understanding of meteorological events such as extreme wind, extreme ice, seismic, and flooding has evolved, a concerning structural engineering disconnect is emerging. The latest edition of ASCE Manual of Practice No. 74 Guidelines for Electrical Transmission Line Structure Loading (a non-mandatory guide, ASCE 74) reflects that improved science. The requirements of the latest edition of the NESC (a regulatory Code), is chartered to reflect safety rather than structural reliability. The reality of not having an electrical overhead line structural loading standard for the industry is that a patchwork of various levels of reliability and resiliency is being designed into our overhead lines infrastructure, and in some cases only the NESC is used for design loading criteria. When new multi-regional high voltage transmission lines are developed under the competitive environment we are in today, or when electrical distribution lines are upgraded or new lines installed, those lines can be designed based on a wide variety of structural loading requirements. The result is a wide range of inconsistences in applied structural loadings, which in addition to reliability issues, can potentially shorten the service life and increase the lifecycle costs of the overhead line infrastructure. In consideration of the overall increasing national focus on reliability and resiliency, the American Society of Civil Engineers (ASCE) and its Structural Engineering Institute (SEI) has recently approved the development of a national consensus Overhead Line Loading Standard for electrical transmission and distribution structures. Some of the major topics to be covered are minimum design loads, hazard levels, and intended performance goals for the design of structures supporting overhead electrical power lines. The standard will also address joint-use overhead electrical line structures carrying wired telecommunications infrastructure. This paper will discuss the case made for the development of that Standard.

During the course of their service-life direct embedded steel transmission and distribution structure foundations are subject to significant environmental exposure that can, over time, have a negative impact on their strength and structural integrity. Foundations are critical components and are therefore crucial to the long-term performance and reliability of a utilities overall transmission and distribution systems. Because of the aging infrastructure in the United States relative to the national power grid many of these existing structures are now beyond their original designed life span. As such, options for extending the service life of existing structures and even adding additional protection to newly installed structures is becoming more of a necessity. Corrosion control measures can be effective and economical solutions to help protect structures both above and below ground. In many instances coatings make up the primary means of corrosion protection measures. However, most coatings contain flaws or “Holidays” that allow exposure of the structure to its environment. When coatings alone are not sufficient to protect from the effects of corrosion cathodic protection is an additional measure of protection that can be applied. Cathodic protection (CP) is an advanced secondary means of corrosion control used for the protection of metal structures which are submerged or buried. CP systems are most commonly used to help protect large structures such as pipelines, storage tanks, ships, and offshore platforms. However, these systems can be readily adapted to perform well on smaller structures like steel transmission and distribution support structures. CP works by transferring the corrosion activity that would normally occur on the structure to sacrificial anodes with a higher electrochemical potential than the alloy being protected. This is achieved by placing the anode within the same electrolyte (soil, water, swamp, etc.) as the structure and placing it in electrical contact with the structure. Once applied most CP systems typically require little in the form of maintenance. However, monitoring system performance should be maintained to ensure protection.

Transmission projects are increasingly crossing remote, undulated terrain to tie resources into the grid and are experiencing a growing number of access challenges as a result. Helicopter-supported construction provides a viable solution in these circumstances but introduces different challenges and considerations to the project simultaneously. The helicopter-supported design and construction challenges faced and overcome on the Cricket Valley Transmission Project provide an example for future projects facing similar challenges. Many of the 64 tubular steel structures were located near rocky outcrops designated as threatened and endangered species habitats, and the permitting required helicopter installation of both foundations and structures to lessen the potential impacts. Proactive helicopter operation planning during the design phase of the project assisted in a simplified permitting process and was a key component to avoiding costly design revisions and schedule delays during construction.

The forces associated with flooded rivers can be incredibly destructive, causing significant damage to widespread areas. Urbanization, tiling of agricultural land, and an increasing trend in heavy precipitation are some of the suspected contributors to more frequent large-scale flooding of river basins across the United States. With this increasing commonality of flooding, a growing number of transmission structures are being put at risk. Fast flowing water carrying pieces of debris or ice can potentially damage or destroy structures within its path. Many existing transmission poles within new or changing flood zones are not robust enough to stand up to these forces. The damage can lead to costly repairs and lengthy outages because of the difficulties that accompany traversing and constructing in the flooded terrain. This paper is a case study of a structure failure along the Minnesota River. It includes an investigation into the factors that contributed to the structure failure and takes a detailed look at the difficulties associated with post-failure reconstruction. By comparing the flow data collected on the Minnesota River Basin over the past century to land use and precipitation trends, this paper draws some conclusions as to why such noticeable changes have occurred in the basin and explores the impacts those changes have had on transmission infrastructure.

Electric utilities play a pivotal role in disaster recovery. Long-term power outages will have a significant effect on the local and regional service area. From a resiliency perspective, electric power substations control the interconnected transmission and distribution lines, and points of generation and delivery. Past earthquake performance of the electric power grid has demonstrated that substation components are the most seismically vulnerable of the power delivery system. One solution for reducing the seismic vulnerability of both existing and new substation components is the application of supplemental damping devices. These devices have been used for substation equipment for decades, but on a limited basis. This paper will present past and present applications of substation equipment supplemental damping devices. Applications of supplemental damping device for three Utilities (Seattle City Light, Bonneville Power Administration, and San Diego Gas and Electric) are presented.

Following a reported vortex-induced vibration (VIV) incident at a substation located in northern Tennessee, a structural monitoring project was implemented to investigate and evaluate the severity of the vibrations in the structure. The operational monitoring involved the continuous collection of weather information including wind direction and speed, air temperature, and structural responses, such as acceleration, base strain, and video recordings of the target structure. This paper presents the instrumentation and field monitoring application, along with the processing of the collected data for vibration event extraction, vibration analysis of the structure (based on the field data), and fatigue stress analysis. The large data set from the long-term monitoring was processed to identify vibration event cases. The vibration features extracted from the vibration events were used to update a finite element model of the structure, to represent the as-built system. In addition, video processing was used to extract the vibration features and verify the results of the vibration analysis. In addition to the surveillance video, the capability of cellphone-captured videos for vibration monitoring was demonstrated. To represent the vortex shedding forces on the structure, nodal harmonic force functions were defined and applied to the model. The dynamic loading on the structure model was verified, based on the collected structural response data gathered through monitoring. The results of the analysis were presented and compared with field data. This was used for fatigue stress estimation to consider the effects of stress concentration at critical joints. The presented process can be used to estimate the maximum vortex shedding-induced stress on structures during the design stage, in order to mitigate the risk of future fatigue damage or failure. This process, with further tests and validation, can be used to develop an approved industry analysis process, without the need for computationally expensive Computational Fluid Dynamics (CFD) modeling methodologies.

This paper describes a practical application based on the results of a research project performed by EPRI to quantify the behavior of substation switchyard rigid bus and its supporting structure during a fault current event. Two key improvements to standard methodology have been proposed during the last several years compared to the traditional methods: (1) Applying dynamic force time histories to the buses in the structural FEA models, rather than applying static peak force loading; and (2) Performing the short-circuit magnetic force analysis in 3 dimensions rather than 2, which allows the effects of corners and drops to be included. These were formerly largely ignored. The research learnings were applied in conjunction with a condition assessment of a 345 kV switchyard. The new study described in this paper, along with an inspection of the current level of corrosion of the structures, concluded that it was economically feasible to upgrade the switchyard rather than to replace it, with considerable cost savings.

Electrical faults can generate significant electromagnetic forces on substation strain bus conductors resulting in large forces on supporting structures. Simplified calculations from the relevant IEEE standard are typically used to determine these forces; however, the forces are often so large that they are thought to be unrealistic. This paper/presentation summarizes research into standards and papers on electromagnetic fault forces, load application to strain bus, and resulting loads on structures. Errors in the relevant standard are identified and some differences are highlighted between standards used in the United States and used internationally. Design examples are prepared to illustrate the effects of these errors and differences. Comparisons between simplified methods and historical test data are discussed. Comparisons to testing show that simplified methods are accurate assuming the actual fault parameters match the design parameters. Cost impacts of considering short circuit forces on strain bus are presented as well as cost differences between methods in domestic and international standards. Recommendations are given regarding design for short circuit forces on strain bus. This research can have immediate impacts on design considerations.

Transmission line design and maintenance is driven mainly by regulatory requirements, professional standards, or utility-specific provisions, all of which set minimum strength requirements for both new and replacement structures. Yet transmission line structures fail every year all around the world, demonstrating that compliance with those standards does not guarantee survival. While in the United States some frequency of failure has been considered acceptable and even expected in extreme weather events, in California the tolerance for failure is dropping, in part due to catastrophic wildland fire ignitions traced to power line failures in extreme winds. California is not alone as the consequences of power line failures elsewhere are also worsening, suggesting that the target reliability inherent in regulatory standards needs to be recalibrated. In particular, the human suffering and loss of life consequences associated with transmission line structural failure in high fire threat areas should be considered when assessing strength requirements, and the associated failure rate, for engineered structures used to support overhead lines. Regulatory requirements for power line structure strength in general, but particularly in California, are lagging behind modern, risk-based design methods being adopted elsewhere in structural engineering practice. The purpose of this paper is to progress current efforts to modernize overhead transmission line design practice in California by incorporating wildland fire risks into our structural engineering standards. We explore the history and evolution of California General Order 95 regarding minimum structural design standards and identify areas in which it could be improved. We also discuss how site-specific and risk-informed methodology should now become the best-practice for both system design and hardening.

Wherever possible, utilities favor routing their transmission, sub-transmission, and distribution lines outside of urbanized areas in grassland and forested areas. This minimizes right-of-way costs, aesthetic impacts, and public objections. Recently due to global climate change, the frequency and intensity of wildfires in grassland and forested environments have dramatically increased. This has negatively impacted the utilities with higher levels of structural damage, power outages, lower system reliability, and higher system restoration costs. After experiencing overhead infrastructure losses through several wildfires, in 2017, Southern California Edison (SCE) started to explore and investigate the options for increasing the fire resistance of its assets in high fire prone areas. The investigation was extensive and included an evaluation of new and alternate structural materials as well as protective coatings and barriers which could be installed on new and existing structures. After performing a high-level analysis of all products, SCE developed a short list of viable products. SCE worked with the manufacturers of those products to test their products to simulated wildfire conditions. SCE adopted two fire test standards to which all products would be tested. One was based on an ASTM draft standard, the other was developed in consultation with a wildfire expert from the University of Alberta. These tests provided a common ground to compare the effectiveness of the products. The fire resistance of the products was determined by comparing a structure’s strength before and after the fire testing. Based on the results of the tests, SCE has developed a revised structural strategy for new and existing structures in high fire areas. The strategy includes the use of lab tested, fire-resistant structural materials for new structures and fire-resistant coatings/wraps for existing structures. Wildfires in 2020 have given SCE the opportunity to see how these new fire-resistant materials perform in actual wildfire conditions and compare the results with the simulated wildfire testing.

A great threat to our nation, costing billions of dollars annually, are wildfires. These wildfires result from tinder-dry vegetation and conditions consisting of strong winds, low humidity, and warm temperatures. The 2018 Camp Fire in Northern California is currently the costliest, deadliest, and most destructive wild fire, having killed 88 people, destroyed more than 18,500 structures, and resulted in costs of approximately $15 billion. Over the years, utilities around the nation have had to deal with wildfire-related damage to their transmission and distribution lines, especially those that traverse wilderness areas. Moreover, there is growing evidence that, in some instances, the power lines themselves could trigger the wildfire due to vegetation into electrical distribution lines. The paper presents a summary of the performance of full-scale electric distribution poles when subjected to fire. The evaluation reported here addresses poles made of two materials: spun prestressed concrete and galvanized steel. The testing protocol, developed by Ackerman and RS Technologies in Canada, was adopted as it exposes the test articles to conditions that would be considered severe to extreme in terms of actual wildfire conditions occurring in the field. After exposure and cool down the poles were removed from the ground and transported to a test facility for strength evaluation. At this facility the pole was held in a fixture and loaded to failure. The intent of this strength evaluation was to gain some insight into the remaining strength after a simulated severe wildfire exposure. The paper also provides an overview of wildfire conditions and the basis for developing the test apparatus and procedure.

Global climate change is creating many challenges which utilities need to address. One of the most critical challenges is the increased threat of wildfires. The reliable operation and maintenance of the electric infrastructure continues to increase in importance and complexity as utilities address the challenges of wildfires. Southern California Edison (SCE) has approached this challenge from two fronts. The first front is to look at methods to fire harden its system with the second front being to minimize the risk of ignition from wildfires. This paper will provide the details on SCE’s wildfire risk mitigation program. The goal of the risk mitigation program is to minimize the chances of initiating a wildfire due to electrical infrastructure issues. Extreme environmental conditions, such as high temperatures, extremely low relative humidity, and high winds, combined with an aging grid infrastructure increases the probability of some part of the electrical grid becoming an ignition source. To address this concern SCE has developed a comprehensive program to perform detailed inspections of all its transmission structures. This program uses advanced inspection and analysis tools to provide a comprehensive assessment of its structures and identifies any structures which may require remediation.