P35.013: Line Ratings and Increased Power Flow
Objective
The objective of the Line Ratings and Increased Power Flow project is to allow increased utilization of transmission assets to maximize power flow while managing risks. This requires balancing the need for more energy with the cost, complexity, lead time, and regulatory requirements surrounding different strategies to find the either the “right size” or a “no regrets” solution. This optimization allows more efficient, reliable, and resilient operation of the grid. Leveraging an improved understanding of risks and risk mitigation methods, utilities can balance capacity decisions against short-term risks such as maintaining statutory clearances and long-term risks such as reduced asset life.
This project intends to document knowledge regarding the selection, design, and application of transmission ratings and uprating methods. Utilities can leverage this information to better understand how legacy practices, new regulations, emerging grid-enhancing technologies, and industry disruptors can be managed.
This project addresses multiple industry needs, including the following:
- Documenting lessons learned from utility uprating projects around the globe
- Assessing the performance of commercially available uprating technologies
- Quantifying the cost, system risks, and time to complete uprating alternatives
- Testing utility conductors to increase ratings accuracy
- Exploring novel uprating technologies and identifying gaps in practices/standards
- Tracking new standards and regulations to establish best practices
- Providing reference and training materials
- Developing engineering software tools
Research Value
Research related to line ratings and increased power flow can lead to:
- Reduction in capital and operational costs by maximizing existing transmission infrastructure
- Increasing circuit ratings, which can reduce congestion and allow integration of renewables
- Increased safety and reliability by using mature models to determine the effects of increasing current on the existing system
- Reduction in operational cost by understanding where limiting conditions may be located to prioritize inspection and remediation solutions
Planned 2025 Research
To address knowledge gaps and develop improved practices, research and development (R&D) is conducted by performing literature reviews, evaluating new standards and regulations, performing historical and what-if analysis on digital twins, performing laboratory testing, and gathering data using in-service lines at member-hosted evaluation sites. The following list of tasks represents the areas of concern identified by utility members and advisors requiring additional focus in 2025.
Applying Novel and Emerging Technologies: There are many providers in the grid-enhancing technologies (GETs) space. EPRI routinely identifies the newest technologies and updates to existing technologies to increase member awareness. Information is captured in EPRI guidebooks and presented during annual meetings. In 2025, EPRI plans to add a technical report to “demystify” the array of dynamic line rating (DLR) technologies, discuss what makes them different, and describe the inherent strengths and weaknesses of their approaches.
Grid-Enhancing Technologies (GETs) Field Trials: In some cases, utilities may wish to pilot an emerging technology, such as DLR sensors, to get hands-on experience with the new tools and practices. EPRI collaborates with members to provide guidance, capture lessons learned, and provide data needed to conduct performance evaluations. The findings are brought back to members via presentations by the host utility and technical reports. This allows utilities to understand the potential benefits as well as the barriers to adoption.
Radial Conductor Temperatures and Ratings: Because of the fundamental properties of heat transfer, transmission conductors are hotter at the core than at the outer surface. The increased core heat can lead to line sag being greater than projected in software tools. A combination of literature review, modeling, and lab testing can be used to establish correction factors to prevent utilities from exceeding clearance requirements or identifying the required ampacity derates if no action is taken.
Acceptance of Increased Power Flow (IPF) Projects: Utilities face many challenges in getting upgrades and new construction projects accepted. This task maps different upgrade scenarios to the challenge areas such as corona loss, electromagnetic fields, and cybersecurity to aid engineers in identifying “least regrets” options when considering upgrades to existing lines. The primary focus in 2025 will be mapping ambient adjusted rating (AAR) and DLR technologies to the relevant communcation and cybersecurity considerations.
Increased Power Flow and Limiting Components: As part of this task, EPRI plans to work with utilities and technology providers to identify case studies where lines have been uprated. An update to the Recent Increased Transmission Line Utilization Projects report is planned for 2025. This report includes case studies that have implemented uprating solutions such as coated conductors, voltage upgrades, reconductoring, and DLR to provide real-world lessons learned and decision-making processes from around the world. Utilities may use these findings to better understand where limiting components are within the system and the potential capacity increases available.
Evaluation of Methods and Standards: Utilities are required to adjust to ever-changing regulatory requirements and industry standards. This task seeks to provide workflows and best practices to help utilities navigate these changes efficiently and to capture the potential risk exposure of different adoption strategies. Guidance is provided for ratings standards such as IEEE Std 738, FERC Order 881, and NERC FAC-008. In addition, updates to the Increased Powerflow Guidebook (The Platinum Book)—which addresses standards and regulations for rating overhead lines, underground cables, transformers, and substation components—is planned for 2025.
Weather Models and Forecasted Ratings: As utilities begin to apply AAR and FERC Order 881, there will be initial lessons learned. As part of this task, EPRI will work with utilities to capture their initial experiences, any unexptected issues, and workflow improvements that are made around handling data needed for ratings development.
Conductor Characteristics for Ratings (emissivity and absoptivity testing): EPRI offers conductor testing for emissivity and absorptivity on an ongoing basis. Using measured values improves the accuracy of ratings, light detecting and ranging (LiDAR) scans, and infrared (IR) inspections. Periodic reports share industrywide findings; however, utilities can provide samples and receive their specific results at any time.
Anticipated Deliverables
In 2025, a mix of ongoing research initiatives together with new research areas will be undertaken.
| Deliverable | Type | Date |
|---|---|---|
| Recent Increased Transmission Line Utilization Projects: 69 kV and Above | Technical Update | December 2025 |
| Technical Review of Methods Used to Determine Dynamic Line Ratings (DLR) | Technical Update | December 2025 |
| Uprating Project Stakeholder Coordination: Cybersecurity for Rating Engineers | Technical Update | December 2025 |
| Radial Temperature Effects on Conductors and Ratings: State of the Science | Technical Update | December 2025 |
| Increased Power Flow Reference Book (The Platinum Book): Increasing Power Flow in Lines, Cables, and Substations | Reference Book | December 2025 |
| Transmission Ratings Workstation (TRW) | Software | December 2025 |
Past EPRI Work on Topic
| Product ID | Title | Description | Published Date |
|---|---|---|---|
| EPRI Research Facilitating Adoption of FERC Order 881: AAR, seasonal, emergency, forecasted ratings, and concerns for next limiting elements | This report compiles five years of research on best practices for adoption of new ratings methods as outlined in FERC Order 881 within the United States. | December 2024 | |
| Understanding Historical Trends with Climate Events and Their Impact on Transmission Ampacity | This report expands past research to define how much capacity would be needed from DLR, AAR, or other upgrades to reduce congestion when responding to large outages or demand spikes. | December 2024 | |
| Cost-Effective Measures to Resolve Under-clearance Spans | This report compares the cost, complexity, and time to complete for multiple technologies that increase transmission capacity on clearance limited lines. | December 2024 | |
| 3002027093 | Improved Methods Identifying At-risk and Wind Sheltered Spans | This report addresses the knowledge gaps around identifying at-risk spans within heavily loaded circuits. The number and location of at-risk spans determine where and how many DLR sites would be needed to safely and accurately rate a circuit. | November 2023 |
| 3002024452 | Guidance for Clearance Limited Lines: LiDAR, UAS, and ratings best practices | This report identifies common errors made in determining line clearances and identifies methods to improve data collection and workflow to improve accuracy. Practical examples are given using multiple LiDAR and unmanned aerial system (UAS) technologies. | December 2022 |
| 3002019090 | Summary of Recent Increased Transmission Line Utilization Projects: 115 kV and Above | This report captures case studies where utilities have uprated lines or increased the use of a given corridor. It includes reconductoring, retensioning, structure raising, voltage upgrades, and DLR. The advantages and disadvantages of each approach are provided to help utilities identify which methods will best suit their needs. | December 2020 |