P35.013: Overhead Line Ratings and Increased Power Flow

Use of Light Detection and Ranging (LiDAR) Technologies and Unmanned Aerial Systems (UAS) for Ratings: As there is increasing industry need and pressure to apply DLR technologies, utilities are seeking faster, lower cost ways to deploy them, preferably without an outage. One method is to use UAS to install the sensors. Present experience has seen an increased failure rate of sensors during energized installation, and a number of drone crashes. For this task, EPRI’s UAS team intends to collaborate with the ratings team to extract lessons learned form past failures and provide workflows that contain improved practices, that intends to reduce the risk of failures during future installation efforts. This report is part of a series on stakeholder coordination, to help bridge the gap between technical areas which can be siloed within utilities.

Forecasted Ratings and Modeling: Both hardware and software based DLR vendors offer capacity forecasting. Accurate forecasted ratings are crucial to being able to safely adopt DLR, and to avoid both safety and economic consequences from re-dispatching capacity. EPRI has been collecting forecast data across multiple utility DLR pilots. This update intends to share anonymized learnings from the field, and show fully worked examples using publicly available weather models. Methods to reduce risks intends to be demonstrated for different forecast models and climate types. Recommendations intends to be provided for model selection, and handling the high uncertainty / variability of DLR. Low-cost alternatives to commercial DLR intends to also be demonstrated.

Wide-Area and Long Circuit Ratings and Uprating for Unique Scenarios: Datacenters, Storage, and Renewables: These two research task areas have a common thread which is high voltage direct current (HVDC) transmission lines. Internationally HVDC has been increasingly considered for scenarios where high capacity gains are needed. This is a unique tool deployed when capacity gains are needed at two times the capacity or more, or when the line constraint is due to voltage drop or stability instead of thermal/clearance limitations. A report is planned to cover the key concepts of when to consider HVDC and to capture a practical example that covers both potential benefits, and key tradeoffs for initial selection.

Life-Cycle Costing of Capacity Projects: Utilizing EPRI’s past research, web-based tools are available on the Transmission Resource Center estimating the cost of losses and life-cycle costing of DLR. Additional uprating project costing tools intends to be developed leveraging the Platinum Book and recent reports on uprating projects. These tools intend to allow utilities to rapidly access a citable resource when responding to NOFO or developing initial RFI templates for uprating projects.

Evaluating Practices and Standards: While North American utilities primarily use IEEE Std 738 for overhead ratings, there are alternatives within CIGRE, IEC, and several regional standards in use around the globe. This task intends to unpack the technical differences between the different rating methods and discuss potential methods to align the best components from each. Several ambient adjusted ratings (AAR) and DLR technology providers offer ratings from the standards which can differ by up to 10%. This review intends to allow utilities to make informed decisions about methodology selection and improve their technical justification for that selection.

Update The Platinum Book: The Increased Powerflow Guidebook (The Platinum Book) is updated annually and covers all aspects of uprating. The guide covers overhead lines, underground cables, substations, transformers, and the economics of staged upgrades. As part of this task EPRI collates materials from published EPRI reports and industry standards for power flow such as IEEE, IEC, and CIGRE. In 2026 EPRI planned to update discussions of CIGRE TB 601 ensure sections for both twisted pair and coated conductor are brought up to date.

Document Grid Enhancing Technologies (GETs) Field Trials: Many utilities are working with EPRI to pilot 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 do performance evaluations. The findings are brought back to members via presentations by the host utility which are then added to the TRC. Performance data on DLR sensors and software are used to update the “Dynamic Line Rating Technology Database”

Develop Guidance on Radial Conductor Temperatures and Ratings: Due to the fundamental properties of heat transfer transmission conductors are hotter at the core than the outer surface. The increased core heat can lead to line sag being greater than projected in software models. Neglecting this factor can cause in incorrect line ratings and increased risk of clearance violations. These challenges would be amplified by the adoption of GETs. Following the testing update from a 2026 report, modeling and analysis intends to be performed during 2027.

• Provide Tools and Resources on The Transmission Resource Center: The TRC hosts various resources. The following calculators, tools, result summaries, and references are planned to be available on the Line Ratings and Increased Power Flow Transmission Resource Center: