Blair, Joel  (Co-Presenter: Towns Holmboe)

AACSR: The Forgotten High Strength, Low Sag Conductor

What are the considerations, issues, and solutions presented when you’re faced with rebuilding a long transmission span across an ever-changing riverbed. This paper and presentation will explore how OG&E and CEC handled the rebuild of the Fixico-Kolache transmission line crossing the Canadian River. Specifically, we’ll discuss how the project was initiated, how CEC & OG&E developed solutions and selected the best option for everyone involved, how CEC & OG&E spanned the river by using a custom design with specialized conductor, and how construction turned the prints into reality. The washed out structure was discovered during regularly scheduled inspections as part of a program called Transmission Restoration. Transmission Restoration is a vital maintenance program at OG&E where inspectors inspect existing Transmission lines for areas of concern. CEC’s inspectors carefully assess each structure and make recommendations for repair, reinforcement, or replacement. The Fixico-Kolache 138kV Canadian River Crossing project emphasizes the importance and benefits of regular inspections of a utility’s infrastructure. We will also explore the decision making process for how to re-build the river crossing. OG&E and CEC evaluated multiple options for relocation of the line and we’ll showcase the reasons why each of those options was eliminated. Details considered in making the decision included time-frame, ROW issues, environmental considerations, and the desire to eliminate any structures being placed in the river bed. After the decision was reached to span the entire river bed, CEC and OG&E’s Transmission Engineers had to take this plan from conception to reality. After CEC’s survey crew provided a land survey showing the extents of the Canadian River, the group was now faced with a 2,200’ span. This long span presented many obstacles including vertical clearance, conductor spacing, structure strength, galloping, vibration, sag of the conductor, conductor strength, ice loading, constructability, and possibly FAA paint and lighting requirements. In order to avoid the FAA requirements and future maintenance they would impose, CEC and OG&E decided to use a special high strength AACSR conductor to reduce the sag and allow for shorter poles.

   Char, Clinton, P.E. 

The Challenges of Fire Hardening the Southern California Edison Transmission and Distribution System

Due to various factors, the world’s climate is changing. In order to meet the challenges posed by climate change, utilities must recognize and prepare for these changes to ensure continued service reliability into the future. In California one of the most devastating results of climate change is the increasing frequency and intensity of wild fires throughout the state. The two worst fires in the state’s history have occurred over the past 2 years – Medocino Complex Fire (2018) where 459,123 acres were burned and the Thomas Fire (2017) where 281,893 acres were burned. As a result of the fires, electric utilities have lost a multitude of transmission and distribution lines resulting in millions of dollars in damage. To position itself to address climate change and the potential for increasing wild fires, Southern California Edison (SCE), has initiated a Grid Resiliency program to harden the SCE system against wild fires. The primary effort in the Grid Resiliency program is to look for pole materials and coatings which would increase the fire resistance of its poles. Composite poles, ductile iron poles, weathering steel poles, concrete poles were examined. Various coatings and wraps to protect new and in-service wood poles were also examined. An extensive evaluation process was conducted for each of the materials to ensure that the materials would perform well in everyday conditions. QUV testing, water intrusion testing, corrosive environment testing, strength testing and service life calculations were made to ensure that the materials would not degrade when exposed to the Southern California environment. Once it was determined that the materials would perform well under everyday conditions, the materials were subjected to fire testing to see how they would perform under simulated wild fire conditions. Two fire testing procedures were used to simulate wild fire conditions – ASTM Standard Test Method for Determination of Charring Depth of Wood Utility Poles Exposed to Simulated Wildland fires (DRAFT) and the RS Technologies Fire Testing. Upon being exposed to the fire testing, strength reduction calculations were made to determine the materials effectiveness to withstand fire conditions. Based on the testing results, SCE is making decisions on the materials which will be used to fire harden its system. The objective of this paper will be to provide the details of the materials which SCE has tested, the results of the testing and their effectiveness under simulated fire conditions.

   Estes, Bartley, CMS 

Supporting Design with Reality Capture Technology

Developments in reality capture and geospatial technologies are rapidly enhancing the approach to engineering and design in the utility sector. As current design workflows shift from 2D to 3D, precise preliminary design requires highly detailed existing information. Projects are now being “virtually constructed” before ever breaking ground, drastically reducing construction conflicts, change orders, and other issues that come along with conventional design workflows. To help achieve this, reality capture technologies are being leveraged to provide comprehensive and high-precision existing models. The general term “reality capture” encompasses many related technologies that capture the current state of something, like a project site. These technologies range from 3D laser scanning, photogrammetry, unmanned aerial systems, augmented reality, and many more. These new data capture methods are empowering designers to make more data-driven decisions. There is not one single reality capture technology that fits every situation. Choosing the right tool in the toolbox is key. Many times, this can be a blending of multiple technologies to produce the critical and actionable data needed to create a comprehensive preliminary design. Understanding how these different technologies translate to the world of design is crucial to the overall approach to a project understanding. This presentation will explore various reality capture technologies and discuss how each are implemented in preliminary design processes and 3D visualization. We will examine best-use practices for each and the benefits of their implementation.

   Fisher, Brett  (Co-Presenter: Tom Guess, Paul Barker, Jon Trout)

Reconductoring and Associated Lattice Tower Foundation Analysis and Modifications

In 2016, FirstEnergy (FE) initiated work to replace conductor and convert existing overhead ground wire to OPGW on three 69kV circuits in Pennsylvania. The project included 26 circuit miles of lattice towers and posed many challenges including an accelerated schedule, outage constraints, difficult access and the lack of existing lattice tower foundation capacity drawings. During the design phase of the project it was discovered the NESC 250C Extreme Wind loading case was causing uplift capacity issues on existing lattice tower foundations. FE, with the assistance of Burns & McDonnell (BMcD), completed a ground line reaction comparison of the existing configuration against the proposed design loading and identified each tower location where the new loading would exceed the existing configuration’s ground line reactions. FE and BMcD analyzed grillage capacities on 41 lattice towers which consisted of five different tower types. Grillage capacities were developed for these specific towers by following industry design practices. A geotechnical investigation was completed to characterize the native soil and backfill properties at the tower locations. The results of the analysis showed that the proposed loading increase would result in several of the grillages having insufficient uplift capacity. The factored capacities were compared with the extreme load case and were used to determine which structure foundations required modifications to provide adequate uplift resistance. Several mitigation options were developed to provide additional capacity to the existing foundations. The feasibility of each option was evaluated by representatives from engineering, construction, project management, real estate and transmission maintenance. Options were assessed and ranked considering cost, constructability, rights of existing easement agreements, aesthetics, land-owner impacts and long-term performance and maintenance. The uplift mitigation system included a bracket designed to attach to the existing tower leg near the ground that can accommodate connection to multiple anchor types. The attachment design had to account for induced stresses on the tower leg, additional bracing and reinforcement and constructability to properly install the anchors adjacent to the tower leg and foundation while securing the anchor to the bracket. The structural design of the attachment bracket required close coordination with construction, project management, real estate and geotechnical engineering. Several anchor systems were utilized to overcome varying rock depths and soil profiles. These anchor systems included grouted threaded rod rock anchors, helical anchors, stingray earth anchors and a hollow bar injection anchor system.

   George, Jean-Marie 

Overhead lines under extreme heat and wildfire conditions

Wildfires can have multiple causes. Overhead lines often just happen to be on the path of a fire, and in this case it is critical to understand what may happen to the line and its components. Besides the risk of having phase ground faults resulting from intense arcing activity in the smoke and heat cloud, resilience is paramount and the amount of damage to lines is a direct consequence of line designs. Distribution overhead lines are obviously much closer to fires than transmission lines and therefore suffer much more of heat damage. Wood poles are clearly identified as a weak link under such circumstances but insulators can also become critical. Even for transmission lines the heat impact can be substantial but not necessarily immediately visible in the short term. Some specific physical characteristics of overhead line insulators need to be clearly identified and taken into consideration either to evaluate the risk of having a line drop during the fire or years later as a result of a weakening of the insulators which survived the fire in the first place. Another aspect of this problem is to review insulator design features assessing the risk of insulators to be a threat triggering fires on a normal day. Insulator failures can lead to line drops and subsequently trigger fires and catastrophic situations. This is true for either distribution or transmission lines. Hardening the grid means finding more robust line designs and insulators. In the aftermath of the Californian fires, this contribution is intended to help evaluating what can be done differently and what needs to be changed in the selection of insulators.

   Mukherjee, Srijib, Ph.D., P.E.  

Frequency Response and Dynamic Power Balancing in Wind and Solar Generation

Large scale deployment of renewable resources introduces significant complexity in performing load balancing and ACE/frequency regulation. Wind and solar energy are intermittent which may diminish rapidly while system load is increasing. This operating condition places an additional burden on conventional resources that are on-line and available for load balancing and ACE/frequency regulation to meet the challenges surrounding the aspects of uncertainty and variability that come with having variable generation in the system. There are two major attributes of intermittent generation that notably impact system operations – variability (generation changes according to the availability of the primary fuel, i.e. – wind or sunlight in this case resulting in swings of the plant output) and uncertainty (magnitude and time of the generation output is unpredictable). While variability is more of a function of regulation, uncertainty can be aligned more to the need for ramping requirements. The objective of this paper will be to understand the feasibility of ramp rate limits within the present CAISO’s conventional generation fleet to meet renewable requirements in 2020 and determine the additional ramp capability required with the integration of renewables to CAISO footprint. Moreover, statistical analysis will be done to characterize the ramp effects and determine the worst hourly changes with renewable energy penetration. The objective of this paper will be to understand the feasibility of ramp rate limits within the present CAISO’s conventional generation fleet to meet renewable requirements in 2020 and determine the additional ramp capability required with the integration of renewables to CAISO footprint. Moreover, statistical analysis will be done to characterize the ramp effects and determine the worst hourly changes with renewable energy penetration.

   Salehi, Farshid, Ph.D.  (Co-Presenter: Mike Tabrizi, Ph.D.)

Sub-Synchronous Control Interaction: Overview of Modeling, Risk Assessment and Countermeasures

Power electronic-based devices such as renewable resources, battery storage and FACTs devices have been widely used in the modern power grids. Complex and multi-layer controllers associated with these elements have presented new challenges in transmission and distribution networks. Some of these challenges such as Sub-Synchronous Control Interaction (SSCI), weak grid interconnection, middle frequency resonance (MFR) and high frequency resonance have received more attention and, recent investigations have highlighted the strong tie between the nature and extent of these phenomena and the control systems and strategies utilized to parameterize the controllers of the power electronic-based devices.

Sub-synchronous control interaction is relatively new phenomena and results from the energy exchange between control system of power electronic-based devices and nearby series-compensated line within the sun-synchronous frequency range. SSCI has electrical and fast-growing nature and can cause severe damages to the grid's elements. Therefore, expeditious mitigation and detection solutions in, addition to effective and comprehensive modeling and risk assessment approaches are required to avoid the negative impact of the SSCI.

This presentation will cover the basic understanding of the SSCI, modeling and vulnerability assessment of power grids to SSCI, and propose some mitigation and detection solutions for this harmful phenomenon.

   Schrein, Nate  (Co-Presenter: Travis Layton)

Concrete Supply Options In Remote Locations For Transmission Lines And Substations

Regions of the United States that are favorable to renewable generation growth generally have sustained winds and sunny skies year around. However, the areas favorable to renewable generation are often found in remote locations with low population densities and little infrastructure in place. Transmission providers tasked with connecting these generators to the grid often deal with the logistical challenges of constructing transmission lines and substations in remote locations. When a transmission line is constructed, engineers and constructors may find that the line traverses sparsely populated areas, sometimes hours away from concrete suppliers. This paper will focus on concrete supply in remote locations as it can be a significant logistical hurdle that needs to be overcome. On the design and planning side, there are measures that can be taken to help mitigate these logistical challenges. For construction, there are several concrete supply options that can be considered. Upfront planning and concrete supply options will be discussed within this paper. Additionally, advantages and disadvantages for each concrete supply option will be reviewed.

   Wright, Joshua, P.E.   (Co-Presenter: Christopher Fornataro, P.E.)

Meeting Modern Resiliency Goals Through Cascade Failure Analysis

On August 25th, 2017, Category 4 hurricane Harvey made landfall in the Coastal Bend area of American Electric Power’s (AEP’s) Texas service territory causing significant damage to both distribution and transmission facilities. In total, over 766 transmission line structures and 5,726 distribution poles were left downed or damaged resulting in roughly 220,000 outages. One of AEP’s transmission lines significantly impacted by the storm was the Whitepoint - STP 345kV Circuit. Built by Central Power and Light in 1972 and later acquired by AEP, the Whitepoint – STP 345kV circuit stretches from outside of Corpus Christi (San Patricio County) to near Danevang (Wharton County). During hurricane Harvey, a cascading failure occurred on a more than 30-mile section of the 130-mile line leaving approximately 128 structures either downed or damaged. The cascaded section of the line consisted of a single horizontal circuit supported by steel lattice mast H-frame tangent structures and three-mast lattice guyed angle structures. The cascaded section of the line was replaced and put back in service by May of 2018 using tubular H-frame tangent and strain structures and three-pole tubular dead-end structures. In early 2018, AEP’s Transmission Engineering Services group tasked DiGioia Gray and Associates (DiGioia Gray) to study the Whitepoint – STP 345kV cascade event. In conjunction with The Electrical Power Research Institute (EPRI), DiGioia Gray developed a software tool to implement EPRI’s algorithm for evaluating the potential for line cascading failures. EPRI’s method, Cascading fAilure riSk assEssment (CASE), defines unbalanced forces on electric transmission structures and assesses the risk of progressive structure failures, or cascades, along the alignment of an overhead transmission line. The intent of DiGioia Gray’s study was to use the CASE software (CASE TOOL) to analyze the original cascade failure and the remaining uneffected100-mile sections, compare the resiliency of the replacement line to the failed line section, and provide an assessment of AEP’s current design practices regarding cascade failures. The analysis considered three weather conditions and four failure events that typically initiate cascading failures on overhead line systems. The findings revealed that the failed portion of the line did not meet current recommended industry standards and was unable to contain a cascade failure under the majority of the load conditions considered. The findings also revealed that the replacement line met all current minimum standards for cascading as specified by ASCE Manual 74. In summary, the study showed the value in using the CASE analysis and the CASE TOOL to assess resiliency levels of old and new transmission lines. The study validated that AEP’s design practices meet current industry standards, and outlined the importance of those standards to ensure safety, reliability, and resiliency are met in the design of future transmission facilities.