Electrical Transmission and Substation Structures 2012: Solutions to Building the Grid of Tomorrow

On April 27, 2011 an unprecedented 164 tornadoes wreaked havoc across areas of Mississippi, Alabama and Tennessee. April 2011 is ranked as the most active tornado month on record. For the Tennessee Valley Authority (TVA) the damage was immense and the worst in almost 40 years. A total of 353 transmission structures were damaged in the storms and 108 transmission lines were out of service, including fifteen 500-kV transmission lines. The line outages resulted in a shutdown of TVA's Browns Ferry Nuclear Plant and Widows Creek Fossil Plant because of partial loss of offsite power and instability of the electrical grid. TVA activated its Transmission Emergency Operations Center (TEOC) and provided an avenue for field assessments to be received. A systematic plan was developed for the engineering, materials, equipment and construction logistics to rebuild the damaged transmission lines. More than 1.4 million pounds of tower steel and 275 conductor miles were installed to rebuild the electrical system. This paper will present the approach that TVA employed to optimize engineering solutions to stretch available supplies as far as possible and that also prioritized equipment and construction personnel to return the transmission system back to service.

This paper will assess the impact of the April 27th storms that devastated the Alabama Power service territory. It will assess and scrutinize the storms' characteristics, statistics of losses, failures of materials, and the restoration efforts from the utilities perspective. Before sunrise on April 27, 2011, a round of tornados and straight line winds tore through West Central and Northwest Alabama. By 8:20 am, Alabama Power Transmission and Distribution crews were hard at work restoring power to 270,767 customers that were affected by the early morning onslaught. As mid-morning approached, office personnel and upper management became concerned about the ominous forecast coming from the National Weather Service for the afternoon storm systems headed toward Alabama. As early afternoon warnings loomed, all restoration efforts were halted and crews were sent to secure locations to ride out the deteriorating weather. By late afternoon, the true stress test for catastrophic system damage took place as 62 tornados tore through the state of Alabama. By midnight, Alabama Power had 412,229 customers in the dark, 171 transmission lines out, 438 transmission structures down or damaged, 318 substations out, 6 substations with major damage, and 2 of those 6 left unrecognizable. The seven days following the storms led to proactive and reactive restoration efforts by the Alabama Power transmission team. The value of this information lies in the opportunity for other utility companies to look inside this storm's devastation and dissect their own disaster plans to become better prepared for Mother Nature's fury.

Glade Spring, Virginia was struck by an F3 tornado on April 28, 2011. Winds were reported at 140 mph. There was loss of life. American Electric Power (AEP) Company's Broadford - Sullivan 500 kV extra high voltage (EHV) transmission line was severely damaged along a five-mile section. The damage was unusually extensive as the tornado followed the transmission line corridor for many miles. The project repairs tallied sixteen 500 kV lattice tower replacements with sixty-four newly drilled reinforced concrete foundations. The new foundations were designed and constructed using predesigned foundations with nomographs to establish site-specific foundation depths during installation based on as-drilled subsurface conditions. Seven tower repairs were also performed. Approximately five circuit miles of two-bundled Aluminum Conductor, Aluminum-Alloy Reinforced (ACAR) conductor were replaced. The line was placed into service on July 21, 2011. This was an 85 day outage with service re-established 57 days ahead of schedule. This paper summarizes the team effort to assess damage, investigate alternatives, develop a restoration plan, and design and construct replacement facilities for an extensively damaged EHV line. It focuses on tower repair, tower replacement, foundation design, and foundation installation with an emphasis upon the factors that benefited the final in-service date. These factors include the impact of the crucial assistance from FirstEnergy in furnishing the 16 lattice replacement towers, the nomograph method of foundation design and installation, and the field instrumentation and equipment utilized to install the foundations.

The US Energy Sector is listed as one of 17 critical infrastructures by the Department of Homeland Security. The widespread loss of electric power after the 2003 blackout was a wakeup call about the vulnerability of the US electricity network and the national impact of a local power grid disruption. Lattice transmission towers in overhead high-voltage lines are critical elements of the US power transmission grid. In spite of their crucial function, constant security monitoring of transmission structures is extremely challenging since they are spread across a vast geographical area; many of which are installed in remote regions. Extensive research is necessary to understand the vulnerability of lattice type towers to malevolent manmade disasters. This study is aimed to develop a basic knowledge on the vulnerability of double-circuit lattice towers to different blast scenarios. Three analytical models are created for prototype suspension, angle tension, and dead-end towers using PLS-Tower software. The blast damage is introduced to the models by eliminating specific structural members. The stability of the damaged structured is evaluated using the overstress ratios of the remaining members under service loads in accordance with ASCE 10-97. Results demonstrated that towers remain stable under limited blast damage scenarios.

While transmission lines are usually the primary focus of our electric power grids, overhead distribution lines play an equally import part of delivering power to the end users and thus are just as important in determining the Solutions to Building the Grid of Tomorrow. Overhead distribution lines are currently often designed using simplistic "back of the envelope" design methods and with bare minimum code required weather loading events. As distribution lines are most often under 60 feet, they are even exempt from Extreme Wind and Combined Ice and Wind loading requirement of the National Electrical Safety Code (NESC). With recent ice and/or wind events causing significant outages nationwide, some states in the U.S. are requiring 'storm hardening' to force a stronger distribution system to be designed and built. However, there are some that argue against the proper designing of overhead distribution lines with more reliable loadings and modern engineering methods as this would be cost prohibitive, too hard to do, and unnecessary for various reasons. This paper will explore the design and cost differences on typical distribution line designs between the existing District Loadings of the NESC (Rule 250B) and the Extreme Wind (Rule 250C) and Combined Ice and Wind (Rule 250D) Loadings. The differences between the simplistic "hand" methods of designing the distribution structures and guying systems will be compared to designs using commonly accepted modern structural engineering methods as well. Finally, a case study will be presented that shows how these modern structural engineering practices will actually reduce the pole size required and thus decrease the cost.

With the expansion of the transmission grid to accommodate renewable energy generated far from load centers, a number of High Voltage Direct Current (HVDC) lines are being proposed. Since the grid in North America is primarily comprised of highly interconnected Alternating Current (AC) transmission lines, a transmission line engineer/designer rarely is exposed to HVDC facilities. Although AC and DC transmission lines are greatly similar from a structural perspective, the fundamental electrical differences between AC and DC require the transmission design engineer to make a number of adjustments to a "normal" AC line design when designing an HVDC transmission line. This paper will provide an overview and high level discussion of the topics, components and practices that must be considered in the design of an HVDC line that are different or require modification from conventional AC design practices. Subjects to be highlighted include design approach for HVDC, corona field effects, current return path and insulation design.

The Tehachapi Renewable Transmission Project, Segments 4-11 is a series of new and upgraded transmission facilities from 69 kV to 500 kV equaling 250 miles (spanning an area of approximately 173 miles) with an estimated cost of $2.1 billion. Once complete, the project will deliver electricity from renewable wind energy generators in Kern County south through Los Angeles County and east to the existing Mira Loma Substation in Ontario, San Bernardino County. Virtually all transmission line materials were procured by SCE. Burns & McDonnell, operating in the role of Owner's Engineer was tasked with managing the material inspection contractor, Bureau Veritas, and their efforts at the suppliers' facility. This included inspections occurring simultaneously throughout the U.S. and into Mexico, Canada, and China on a very high-profile project. The paper will focus on the lessons learned and how the TRTP project benefited from transmission line material supplier inspections throughout the fabrication process.

Like many electrical utilities, Public Service Company of New Mexico (PNM) is faced with the issue of maximizing the use of existing transmission facilities. PNM owns and operates over 2,500 miles of transmission line located throughout the state of New Mexico. Many of these facilities were built in the time frame from the mid-1950's to the early 1970's. The lines were designed to standards current at the time of construction and to meet the long term system planning requirements projected at that time. These lines continue to be an integral part of PNM's system. Their lifespan has exceeded the planning horizon and the need for transmission of power has increased. In an on-going program that has now spanned over fifteen years, PNM has upgraded over a thousand miles of its 115kV, 230kV, and 345kV transmission lines. This paper addresses PNM's line rating and upgrade program including the establishment of utility line rating standards, analysis of existing field conditions, techniques for mitigating sag limited spans, and examples of typical projects.

The increasing size of transmission projects and transmission structures on those projects have put a strain on the supply of plate material commonly used for base plates. The availability of base plate material became an issue not only because of lead time (which could affect project scheduling) but because fewer mills were willing to produce base plate material meeting the specifications of our industry. This stimulated the pursuit of other available materials and sources that might be available to satisfy the increasing demand for large, thick base plates for galvanized and weathering structures. This process determined the "forged ring" material was the most advantageous for leadtime and material conformance to current design practice. It was then identified that three categories for control and validation were required: 1. Base plate design and detailing: The "forged ring" would provide a larger center hole than had previously been validated in testing. 2. Material properties: This will not be ASTM plate material. How will it be specified, controlled, certified and presented to the customer? 3. Welding procedures: Since this is new material to be welded, base weld procedures must be created for all base weld processes currently used and then independently tested.

Fabricated tapered tubular steel poles represent approximately 80% of the non-wood, electric transmission "structures" sold in the United States. Most steel poles are press brake formed, either into a round shape through a "coining" process, or are multi-sided. As the requirement for ever larger, higher capacity, tubular steel poles grows, other technologies, primarily conventional steel plate roll forming technologies are being used. Steel roll forming technologies are widely used for large, storage tanks as well as wind turbine support structure fabrication, but not so commonly thought of for use in electrical transmission structure fabrication. This paper will compare and contrast the differences in the technologies and discuss design (both pole and connection designs), material efficiency, fabrication steps and processes, quality requirements, logistics/shipping, and field assembly/erection differences.

The use of V-string insulator hardware assemblies has been utilized on transmission line structures for their control of conductor position, clearance to supporting structure, and structural advantage. In designing V-strings, a critical design criterion consideration is insulator leg compression. Specifically, the weather (wind) condition that induces V-string insulator compression impacts the V-string interior angle, arm lengths, drop bracket length, pole shaft diameter, and foundation reactions. This paper provides insight into V-string analysis methodology and comparisons of different conductors, wind loadings, wind and weight span ratio limits, and V-string internal angle configurations. Wind loading effects on insulator leg compression are specifically examined for multiple weather cases ranging from 4 to 21 psf. Also examined is the inefficiency of a set parameter design (line angle range, conductor type, wind and weight span, etc.) compared to the potential design envelope, which can be utilized with design software such as Power Line Systems PLS-CADD.

Underground coal mining is a common activity in the North East United States which often impacts surface facilities including electric transmission/substation systems. In long-wall mining, coal seams are excavated over large areas that cause near immediate, vertical and horizontal displacements of the ground surface above the mined seam. Structures located on these affected areas are subjected to varying permanent and temporary foundation displacements and rotations that may induce strains and stresses beyond the capacity of the structure. Cumberland Coal informed West Penn Power that long-wall mining would occur underneath the West Penn Power, 138kV, Whiteley Substation in early 2010. Their estimates indicated the ground would settle a total of approximately 4.5 feet. It was also necessary for West Penn Power to maintain service, from the substation during this subsidence event for its customers including the mining equipment. This paper discusses how the structural integrity of the substation components was maintained during the subsidence event by devising, implementing and monitoring various mitigation actions that reduced horizontal and vertical strains, compensated for the induced deformations in the structures, and reinforced components to tolerate anticipated deformations. Depending on the materials, geometry, and foundation layout of each structure, the impact of subsidence can be significantly alleviated by either stiffening of the panels and foundations to promote rigid body movements, and/or by softening the connections in order to facilitate limited mechanism types of movements. Whiteley substation functioned as needed during the subsidence event, as the result of these mitigation actions.

To design a rigid bus system, several design methods are available. The IEEE Std. 605-2008 design method is widely used but is conservative and has several limitations. A dynamic analysis approach offers more accurate results but is more complex and time consuming. The static analysis using a finite element program design approach was proposed and described in this paper. The IEEE Std. 605-2008 design limitations were first identified followed by design advantages from the proposed method. Proper design considerations should be accounted for when using the program to obtain meaningful results. Results were compared between the IEEE Std. 605-2008 and the proposed design methods using the same applied loads derived from IEEE Std. 605-2008 design guidelines and the same set of design inputs. Three case studies were performed, and the results from Case 1 and Case 2 showed the conservatism in the IEEE Std. 605-2008 design method. Results from Case 3 showed the impact from overload factors on the same bus arrangement. It was then concluded that the static analysis using finite element program design approach offered more accurate results than the IEEE Std. 605-2008. In addition, results showed that insulator internal forces and bus conductor fiber stresses analyzed by the proposed method were reduced comparing to the IEEE 605 Std. 605-2008 design method, which could result in overall construction cost savings due to less insulators, less bus structures, or less foundations needed.

This abstract outlines the specific challenges and unique solutions related to a substation expansion in a congested, suburban area.

Historically, AEP has used the same broken wire loading requirements in the design of EHV (230kV and above) suspension structures without differentiating between single and bundled conductor configurations. Since many EHV transmission lines are built using bundled conductor configurations for increasing power transfer capacity and for reducing corona, a review of these historic broken wire requirements and the resulting impact on the structure design was warranted. It was apparent that using the same broken wire criteria on a six-bundle 765kV suspension latticed steel tower versus a single conductor 138 kV suspension single steel pole would result in a greater impact to the former structure weight. This paper describes one method to establish cost effective and reliable broken wire design criteria for EHV transmission line suspension structures with bundled conductor configurations. This study indicates that the broken wire loads under the everyday (60°F, no ice, no wind) loading condition with a 0.8 load reduction factor provide an economical and reliable EHV suspension structure design.

High-voltage transmission line networks throughout the world have failed during earthquakes. The operators of these networks have developed a wide range of strategies for dealing with earthquake events. Over the past few years, the Bonneville Power Administration (BPA) has modeled their systems to examine network performance under earthquake conditions. This includes damage to substation components, earthquake-induced landslides and liquefaction on transmission towers. Simulation models have been developed for assessing earthquake performance of transmission lines that can be used to forecast the following types of information: for a given earthquake, what is the damage to the substations or the number of transmission towers likely to collapse; what is the forecast reliability of a circuit, from end-to-end, in a given earthquake; what is the annualized rate of damage for a network as a whole; and is it cost effective to design or upgrade high-voltage transmission lines (substations and towers) for more stringent (or less stringent) seismic criteria. This type of information can be used to develop mitigation strategies, emergency response plans, and provide benefit-cost data for making appropriate decisions to prepare for potential extreme event hazards.

Most wind-related transmission line failures have been attributed to high intensity wind (HIW) events in the form of tornados and downbursts. In the current study, a numerical model is developed to investigate the performance of two guyed transmission lines under tornado wind loads. The F2 tornado wind field used in the study is based on a computational fluid dynamics (CFD) analysis that was developed and validated in previous studies. The tornado wind forces are calculated and are then incorporated into a three-dimensional nonlinear finite-element model that simulates both the towers and the conductors. The study investigates the effect of tornado loads on the structural performance of the two different guyed transmission line systems. The tornado locations leading to maximum internal forces in various members of the towers are identified and are considered as critical load cases. The nonlinear numerical model is then extended to study the progressive failure of the two transmission lines under the critical tornado load cases by varying the velocity of the tornado wind fields incrementally. The velocities at which a total collapse is predicted are identified for both towers.

CenterPoint Energy Transmission Structural Design incorporates a "limiting" longitudinal unbalanced loading criterion into the design of tangent and small angle lattice transmission towers. This criterion ensures that a localized longitudinal failure in the arm occurs before tower body damage or failure; thereby, reducing overall structural damage and the probability of cascading failure from accidents during construction and operations. The success of the historical application of this criterion during both construction and operations and its application in the design, full-scale testing, and construction of a new 138 kV tangent tower will be presented. Full-scale testing is crucial to ensure that the parameters, loads, and capacities used during design produce results within an acceptable range. Unanticipated test results will be discussed in detail and correlation with a field construction failure provide an opportunity to prove the validity of the design requirement.

The Electric Transmission Texas/Competitive Renewable Energy Zone (ETT/CREZ) project consists of seven 345kV transmission line segments with a total length of over 400 miles. The project is located in North Central Texas. The transmission line consists of tubular steel poles supported by two types of foundations. The poles will be either direct embedded with a concrete backfill for the more lightly loaded tangent pole structures; or drilled shafts with full length anchor bolts for the more heavily loaded tangent, running angle and dead end structures. Over 2,400 or about 90% of the total number of structures will be direct embedded with concrete backfill. In the past, AEP Foundation Design Engineers, as well as most of the utility industry, traditionally assumed that a direct embedded pole behaves the same as a reinforced concrete drilled pier, however no full-scale foundation load tests have ever been performed to confirm this assumption. Due to the large number of direct embedded foundations to be installed, a tremendous opportunity for construction savings existed, even if only one foot of embedment were saved on average for each installation. To seize this opportunity, the engineering team decided to conduct two fullscale direct embedded pole tests. The primary goal was to reduce foundation construction costs, while maintaining reliability. This was accomplished by performing preliminary direct embedment depth calculations using MFAD and test site-specific soil data, installing the test poles to the calculated embedment depths, and subsequently conducting the load testing. The resulting field-measured load displacement responses were then analyzed and compared with the original design assumptions and methodology. Adjustments were made to the design approach as appropriate, and used in the final designs for all direct embedded foundations. As a result of the testing program, the engineering team was able to realize a reduction in embedment depths ranging from one to four feet, which will have a beneficial impact on foundations costs. Furthermore, the knowledge obtained from the tests allowed the team to confirm the design approach and thus improve the reliability of future, direct embedded pole designs.

In 2011, Dominion completed construction of a 60 mile long 500 kilovolt (kV) transmission line and a 22 mile long 230 kV transmission line in southeastern Virginia to meet the growing demand for electricity in the south Tidewater area of Virginia. The transmission lines are entirely within the Coastal Plain physiographic province where the subsurface conditions are characterized by deep soil deposits and a shallow groundwater table. Numerous sensitive wetlands throughout the length of the project and the subsurface conditions of the Coastal Plain were driving factors for considering alternative foundation types to reinforced concrete drilled shafts. Ultimately, to minimize impact on this environmentally sensitive area, pipe pile foundations with a grouted inner steel pipe were chosen to support the new steel lattice towers. This paper will describe the important aspects of the project such as the geotechnical exploration, the full scale prototype laboratory testing, the structural design and the quality assurance program during construction. Soil properties and insitu stresses were determined during the subsurface exploration using a flat plate dilatometer coupled with data from traditional borings and laboratory tests. During construction, geotechnical capacity was monitored by using dynamic pile testing. The foundations have been designed to support lattice tower legs that are subjected to uplift, compression and lateral loads. The legs of the lattice towers are connected to the inner steel pipe by threaded studs attached to a steel plate that is welded to the top of the inner pipe. The loads from the inner pipe are transmitted to the outer pipe pile through a combination of non-shrink concrete/steel interface and shear clips. In order to determine the total uplift capacity of the inner steel pipe/concrete interface and shear clips, a load test was performed on a full scale prototype foundation in Lehigh University's ATLSS laboratory.

This document presents a unique and cost saving solution that was developed and installed to address extremely corroded steel grillage foundations supporting a 3 tower angle structure on a critical Southern Company 230kV line in south Alabama.

Transmission lines (TL) towers are traditionally analyzed assuming fixed base. However, this assumption is questionable as foundation is not rigid in most cases. In other fields, such as seismic engineering, it has been reported in the past that the foundation stiffness and damping affects the structural behavior while in interaction with the structure specifically under dynamic loads. In this paper, the soil-structure interaction (SSI) effect on transmission line (TL) behavior is studied. The soil is replaced by foundation impedance, a set of frequency dependent spring and dashpot. For this purpose, a parametric study on a simplified case is presented for two types of dynamic loads: wind load and impulse load supposed to represent the effect of the shock wake following the breakage of a conductor of ground wire. To complement this parametric study, a real case is used in the analysis. The behaviour of the foundation is determined with software FLAC with its foundation impedance. Two types of soil are used in the analysis: (i) cohesive soil; (ii) granular soil. The paper confirms that foundations can modify structural behaviour significantly.

The conductors of transmission lines are subjected to a variety of motions caused by the wind. The most common motions are aeolian vibration, sub-conductor oscillation (bundled conductors), galloping (generally associated with a light ice coating) and wind sway. Unless controlled, motions of conductors can produce damage to the conductor and other elements of the transmission system that will negatively affect the reliability and serviceability of the system. Sub-conductor oscillations, galloping and wind sway are associated with higher wind velocities, and in the case of galloping a light to moderate ice coating is required to initiate the motion. These motions are generally characterized as low frequency, high amplitude. Aeolian vibration, which is the subject of this paper, is associated with smooth (non-turbulent) winds in the range of 2 MPH to 15 MPH, and can occur on a daily basis. In contrast to galloping and sub-conductor oscillations, aeolian vibration is characterized as high frequency, low amplitude motion. This paper describes the theory of aeolian vibration, simulation of aeolian vibration in the laboratory to test the performance of conductor and conductor hardware, with a focus on how vibration damper performance is measured and finally the methods used to monitor aeolian vibration in the field on operating transmission lines.

Bonneville Power Administration (BPA) has undergone a 500 kV transmission infrastructure build-out starting in 2002 that has resulted in construction of approximately 250 miles of new single- and double-circuit transmission lines. Several additional projects are currently in planning or design stages that may result in up to 130 miles of new 500 kV transmission line. During initial design of these projects, it was identified that there would be a number of large river crossing structures as well as heavy double-circuit dead-end structures in which main leg forces would exceed the capacity of the largest rolled single-angle imperial shapes available (typically 8x8x1 1/8). Prior to 2002, BPA countered this situation by designing single-angle welded main legs (up to 16x16x 1 3/8) but other alternatives were studied for these projects due to extreme high cost of the fabricated legs as well as considerable manufacturing difficulties. BPA eventually chose a "cruciform" shape, or four angles bolted back-to-back, for the main legs of these towers. The individual angles making up the built-up section are widely available rolled single-angle shapes. Angle sizes used on BPA towers have ranged from 5x5 to 8x8. Due to a lack of experience and published design information about this shape, BPA performed compression testing on a variety of cruciform sizes as well as theoretical modeling. The members tested satisfactorily and those results as well as published data research allowed the development of a compressive strength model that could be incorporated into BPA's overall tower modeling program. Since 2002, cruciform legs have been successfully used in six different tower types with one of those being a standard dead-end tower that has been used in multiple lines and locations.

Lattice towers are primarily constructed of steel angles of varying thickness and length with members that interact in complex ways. Analysis and design techniques had historically been slow, tedious and required a liberal amount of engineering judgment. Fortunately, analytical tools have improved significantly over the last twenty to thirty years, greatly reducing engineering time and improving the overall confidence in the final design. It has never been easier to not only produce, but optimize a tower design. So why bother testing? Because "It's all in the details". The analysis and resulting design are affected by the interpretation of the design standard and its application to the model. Additionally, the performance of the connection is highly dependent on how the tower is detailed. Both add uncertainty in which only full-scale testing can provide final verification of the design and detailing assumptions. Any "flaw" in the design or detailing discovered during the test can be mitigated at much less expense than if determined after structures are erected and the line is placed in service. Two new 138kV Double Circuit towers (164 foot suspension tower with swinging brackets, and 167 foot strain tower with square and pointed arm configurations) designed for extreme ice conditions were recently full-scale tested. The nine unexpected but significant failures experienced are evaluated in detail, clearly showing the economic justification for testing.

Structural load tests of most transmission line structural components are currently not highly regulated. For typical structural materials, users must expand the few pages of generalized information provided by ASCE documents in order to develop a more project specific test plan. These documents may include the ASCE Standard 10-97, Standard 48-11, or the new ASCE concrete pole design manual. For major structural types, such as a latticed tower or steel pole, there is often enough background information available from collective past experience within this industry to develop a representative test program. Other less common components, such as hardware or insulators, do not have such clear-cut testing practices. Granted, most of these structural components are proof-tested by manufacturers based on load cases defined by the Owner's engineer. Test procedures will then be developed, most likely by the manufacturer based on its facility limitations, to address (in all likelihood) only the maximum load required. To cover uncertainties, a safety factor is commonly assigned. As the electrical transmission industry pushes the limits on all design parameters, is this traditional approach still adequate to ensure structural integrity? How to determine that sufficient capacity has truly been achieved? What if material nonlinearity behavior exists? Do the selected test and test plan accurately represent inservice conditions? Are most test programs satisfactory enough to find potential problems? What exactly are these 'potential problems'? How to guarantee structural reliability in today's demanding environment? This article attempts to provide basic background on the mechanical load test, and hopes to stimulate further studies and discussions in this area from the utility industry.

This paper will present a historical summary of full-scale latticed steel tower and structural assembly tests. Since the first use of latticed transmission tower designs it has been common industry practice to perform full-scale latticed steel tower tests as a verification of the design capacity and connection detailing. There have been hundreds of tests with a wealth of information collected. A number of significant technical papers have been written addressing these tests. Case studies of four tower tests will be presented. These case studies will present the rationale for the continued need of full-scale tower testing for the purpose of verifying the adequacy and calibration of new tower designs. The paper will provide practical advice for conducting future full-scale tests.

Have you ever seen "As Built" drawings that barely resemble those that were issued by the engineer for construction? Various reasons cause these field changes. Nevertheless, in nearly every case, field changes to the design adversely impact the project budget and schedule. While these changes cannot always be totally eliminated, they can be reduced by ensuring the design can be efficiently built. Even an experienced design team will not always have the knowledge and insight of the construction/installation process to produce a design that minimizes the total installed cost— especially if the component being designed is an integral part of a complex system such as an electrical substation. This paper provides an overview of the design process spanning the life-cycle of a project and describes some key steps that need to be integrated into the process. These key steps enable the "constructability" of the facility and its components to be fully reflected into the design before it reaches the field.

Utilities and transmission line developers are facing regulatory challenges, public scrutiny and opposition from environmental activists in their management of avian migration, nesting and roosting issues. The presence of birds near overhead transmission lines has long been addressed during both construction and maintenance, and many issues are well defined. For example: 1) Raptor perch deterrents are installed on EHV line support structures to protect insulators from bird excrement, which can lead to line faults. 2) Distribution line design has been modified or retrofitted to reduce the chances of bird electrocution. 3) Avian nests identified in preliminary design have been taken into account during detailed design and construction planning through line routing, buffer zones and seasonal restrictions. 4) Collisions with overhead lines in flight paths have driven the development of visual devices designed to reduce bird strikes. 5) Routing of new lines must account for habitat, nesting and migration habits of threatened and endangered species. 6) Construction must be timed to avoid critical nesting and migration windows. New issues are arising in light of increasing agency interest in compliance with existing regulations, public awareness brought on by highly publicized avian mortality issues associated with wind turbine farms, environmental opposition to utility projects, and rapidly shifting landscapes and avian populations. Construction delays and new project cost increases seem to be on the rise. This paper will explore transmission line project avian protection issues, methods to mitigate those potential problems and the effectiveness of proposed solutions. It will also discuss the regulatory structure of avian protection laws and how they are being applied nationwide. The paper provides recommendations for increasing the likelihood of project success.

The Trans-Allegheny Interstate Line (TrAIL) Project began in 2006 when the regional transmission operator, Pennsylvania-Jersey-Maryland (PJM) identified congestion and the need for additional capacity in the Northern Virginia and Washington D.C. area. PJM turned to Allegheny Energy (now a subsidiary of FirstEnergy) for a solution. Allegheny Energy formed a wholly owned subsidiary, TrAILCo, to site, permit, and build the Trans-Allegheny Interstate Line. TrAILCo immediately began preparing the line surveys and routing analyses needed to submit the applications for Certificates of Public Convenience & Necessity (CPCN) in the three states the line would cross (Pennsylvania, West Virginia, and Virginia). In early 2007 TrAILCo formed an alliance partnership with Kenny Construction Company to serve as the overall project and construction management contractor. Kenny in turn, contracted with POWER to perform the environmental permitting and transmission line design for the project. The team worked throughout 2007 to develop the required permits, procure materials, develop the engineering designs for the substations and transmission line, and establish subcontracts for the major construction services. With the receipt of the CPCNs in late 2008, crews broke ground at the Western end of the TrAIL, near Mt. Morris Pennsylvania, on what would become 502 JCT Substation. This was soon followed by right-of-way (ROW) clearing, access road building, and foundation installation for the entire 151 mile 500kV TrAIL transmission line. During the peak of construction in 2009 and 2010 more than 1000 personnel worked in the field on a daily basis. Through severe weather and rugged topography the crews cleared over 2,700 acres of ROW, installed 252 miles of access roads, placed over 55,000 cubic yards of concrete, erected over 17,000 tons of lattice steel and 5,000 tons of tubular steel, and pulled in nearly 200 circuit miles of conductor. On May 19th, 2011, 12 days prior to the required in-service date, the TrAIL was energized, and a project which many had thought was impossible only five years earlier, had been deemed a success!

The demand for availability and reliability of the electrical power system service has resulted in increased use of energized work. For particular transmission line upgrade activities in electric power transmission facilities, energized re-conductoring work has become the preferred alternative over de-energized re-conductoring work. A significant number of re-conductoring activities for high voltage transmission lines, typically 110-115 kV and above, are performed energized without the need to take the transmission line out of service. Energized re-conductoring prevents congestion of the existing transmission facilities and maintains the transmission grid reliability level by avoiding taking facilities out of service. In general, high voltage transmission lines contribute considerably to the reliability and economic operation of a power system. There is a significant impact of taking these key facilities out of service (even if at all possible) on power system reliability and economics. This condition has driven electric power utilities and the industry to analyze and include the alternative of performing the maintenance and/or construction activities like re-conductoring using live work techniques. This paper will present the challenges encountered in energized re-conductoring work during the project preparation and the field execution of such work. The paper will address key challenge elements to consider in the planning of energized re-conductoring projects based on the experience obtained over the years in actual projects.

PacifiCorp began a broad expansion in 2007 of its main grid transmission system in the western United States through a program called Energy Gateway. This ongoing effort will add more than 1900 miles of 230, 345, and 500 kilovolt lines to PacifiCorp's transmission system. One key element of this transmission expansion is the development of 15 different 500-kV steel lattice towers to date with a variety of tangent, running angle, transposition and dead-ends in both single and double circuit configurations. A broad overview of the development and use of this family of 500 kV towers is detailed herein. The tower family was designed for reliable and cost-effective line construction through the wide ranging elevations, terrain, geology and climate of Utah, Idaho and Wyoming. Electrical and mechanical requirements and National Environmental Policy Act (NEPA) permitting were significant drivers for the tower design. Tower development is truly a global process. Energy Gateway towers were designed in Texas and Mexico. Full scale load tests were performed on nine towers at five test facilities in Brazil, South Africa and India. Proto-type testing occurred in Mexico during design and in Turkey with the first tower purchase. Ongoing construction of the Mona-Oquirrh 500 kV line has completed installation of more than 100 towers by June 1, 2012, with energizing scheduled for mid-2013.

Under ordinary circumstances, due to their geometry, Y-Frame structures can provide an engineer with some unique challenges. When you add strict geometry requirements in a high seismic region, the challenges can be even more daunting. This paper will describe the difficulties faced in the design of heavily loaded Y-Frame structures in a high seismic region along with a detailed seismic analysis and some very informative results. The project consisted of 54 steel structures on base plated concrete foundations located in Southern California. Due to high potential seismic activity in the region, the project specifications required a detailed and in depth seismic analysis. To facilitate permitting, an aesthetics study was performed resulting in the specific geometry requirements. In addition, the transition section of the Y-Frame created some unique design challenges including an FEA study, testing and evaluating 3 different configurations. This paper will include an in depth discussion of the seismic analysis, the geometry requirements, results of the testing, and the transition section design. Engineers will benefit from the informative results and details presented.

The South American country of Brazil is not only hosting the 2014 World Cup and the 2016 Olympic games, Brazil is currently expanding its high voltage transmission network all across their vast country. With a large number of new hydroelectric power plants in various planning and construction stages, Brazil's projects bring a new scale to the concept of green power. The implementation of the ANEEL (National Agency of Electrical Energy) Auction for defining new transmission players responsible for the design, construction and operation of the new transmission lines, are promoting healthy competition among Brazilian engineering companies to develop new design solutions. HVDC projects (±800 kV) or EHV lines (765kV AC) are currently under study, while other 500kV AC, ±600kV HVDC and a multitude of support lines are currently under construction from the Amazon Basin in the North region of Brazil, to the cities of São Paulo and Rio de Janeiro, in the Southeast region, crossing distances up to 1,500 miles (2,400 km). This paper summarizes the main projects mentioned above, with emphasis on the new transmission lines and their structural solutions.

Steel Poles are common type of structures erected to support power overhead lines of most voltage rating in the United States. Typically these poles are founded on single reinforced concrete drilled circular piers designed to resist the high bending moments of the supported poles. The principle of designing these drilled piers relies on the theory of soil resistance to the central point rotation of the pier. Soil structure interaction is simulated through a complicated system of springs acting on the circumference and base of the piers inducing a set of internal pier forces which control sizing and reinforcing these piers. Soil structure interaction is governed by several parameters, the most important of which are the soil mechanical parameters and the depth and diameter of the pier. However the design problem is further complicated by set limits on horizontal deflection and pier rotation in addition to the strength requirements. In several cases these constraints control the design of the pier rather than the loading applied. Assuming a fixed set of soil parameters the question can be narrowed down to deciding upon the best depth/diameter combination. However, currently there is no guidance on the optimum combination of depth/diameter for a particular loading and deflection constraints. This paper attempts to establish guidelines to help deciding on the optimal depth/diameter combination. The methodology adopted to define these guidelines is through parametric studies which examine the effect of varying depth and diameter on the ultimate capacity of the drilled piers and at the same time satisfy the deflection constraints under service loads. Foundation Analysis and Design (FAD) software, developed by Electric Power Research Institute (EPRI), is used in this study.

ASCE/SEI 7-10 - Minimum Design Loads for Buildings and Other Structures introduced wind maps and a new way to evaluate wind loading compared to its predecessors (e.g. ASCE/SEI 7-05, ASCE/SEI 7-02, etc.). The changes will present challenges to current codes and manuals which utilize the previous maps and methodologies, specifically the National Electric Safety Code (NESC) and ASCE Manual No. 74. The purpose of this paper will be to show a comparison of the extreme wind loading and combined ice and wind for ASCE 7-10 to the ASCE 7-05 values as they apply to Transmission Lines. To begin that discussion, the author will look back on work previously done by others. The intention of this paper is to begin a public discussion of possible directions the NESC and ASCE Manual No. 74 should consider.