P35.014: High Temperature Operation of Overhead Lines
Objective
Transmission asset owners can increase the power transfer capability of a transmission line by increasing line current, which in turn raises conductor operating temperature. Elevated conductor temperatures can lead to reduced conductor‑to‑ground clearances due to increased sag, loss of mechanical strength over time, and degradation or damage to connectors and other attached hardware components. In addition to these mechanical impacts, higher operating temperatures can adversely affect corona performance, potentially resulting in electric field levels, audible noise, or radio interference that exceed utility design criteria and applicable standards.
The main objectives of this research project are to help utilities raise transmission line capacities (through increased current) safely, reliably, and with confidence, and to provide a technical basis that supports utility decisions on operating lines at elevated temperatures.
Research is aimed to:
- Understand premature failures of conductors and conductor accessories due to thermal aging from high-temperature operations.
- Determine and evaluate the mitigation and remediation options for high-temperature operation.
- Understand the high-temperature effects on corona, thermal, and other models used in evaluating electrical effects, heat-transfer capability, and other performance indicators of an overhead line.
- Determine and verify the mechanical effects of high-temperature operation on conductor performance.
Research Value
Through empirical studies, collecting utility experiences, and developing models research in high temperature operation of overhead lines can lead to a:
- Reduction in capital and operational costs by maximizing existing transmission infrastructure
- Increased safety and reliability by utilizing 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
Approach
This project undertakes tasks to develop the required information to make effective decisions when operating lines at elevated temperatures. In 2027, these tasks include:
Evaluate the Durability of Robotically Applied High Emissivity Coatings: This task intends to evaluate the durability of two high emissivity coatings on a conductor that has round strands and one that has trapezoidal strands. This research aims to provide an understanding of degradation of coated conductors to better predict the service life of the coatings.
Update HTC Matrix Software Tool: The High-Temperature Conductor (HTC) Matrix was developed as a repository for all the high-temperature overhead conductor research conducted by EPRI. The HTC Matrix includes several calculators. For 2027, the intent is to update the software for improved usability and accessibility as well as transfer another calculator to the Web-based platform.
Update Guide for High-Temperature Operation: This task intends to update the guide developed to assist utilities in safely operating lines at higher temperatures. In 2027, EPRI intends on providing an update on magnetic attraction of overhead transmission conductors.
Understand Corrosion at Elevated Temperatures: Corrosion rates increase at elevated temperatures; however, those rates have not been quantified. This task sets out to understand the increase in corrosion rate with elevated temperature. In 2027, the work on the development of equations to model corrosion rates at elevated temperatures is planned to continue.
High-Temperature Effects on Traditional Conductor-Connector Systems: This task sets out to understand the degradation mechanisms of conventional conductor-connector systems, such as copper, AAC, AAAC, ACAR, and ACSR. In 2027, the project aims to continue empirical evaluations of the effects of time and temperature on aluminum alloy conductor strands.
Evaluate 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 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. In 2027, additional empirical studies are planned to further refine predictive equations.
Develop Guidance on Magnetic Attraction: Increased current loads lead to higher potential for magnetic attraction. In 2025, EPRI initiated emperical testing to determine the effects of tension, conductor geometry, and current on magnetic attraction in hopes of developing a predictive model to provide guidance on spacer placement. In 2027, EPRI intends on providing an update in the Guide for High Temperature Operations.
Provide Tools and Resources on The Transmission Resource Center: The following calculators, tools, result summaries, and references are planned to be available on the High Temperature Operations Transmission Resource Center:
| Resource Title | Resource Type |
|---|---|
| Aluminum Annealing and High Temperature Creep Calculators | Calculator |
| Effect of High Temperature on Tensile Strength of Aluminum 1350-H19 | Research Summary |
| High Temperature Operation Standards | Reference |
Anticipated Deliverables
| Deliverable Title | Deliverable Type |
|---|---|
| High Temperature Conductor (HTC) Matrix | Software |
| Guide for High-Temperature Operation of Overhead Lines | Technical Update |
| Radial Temperature Effects on Conductors and Ratings | Technical Update |
| Robotically Applied High Emissivity Coatings for Overhead Transmission Conductors | Technical Update |
Past EPRI Work on Topic
| Product ID | Title | Description | Year Published |
|---|---|---|---|
| 3002033771 | High Temperature Conductor (HTC) Matrix: v15 | EPRI’s HTC Matrix software is a Windows application designed to provide the user with quick and directed access to all of the information developed under several EPRI projects investigating the effects of high temperature operation of conductors. | 2025 |
| 3002022795 | Guide for Operating Overhead Lines | This report provides technical information and research data to assist users in evaluating the option of raising overhead transmission line capacities by increasing the current and, therefore, the conductor temperature. | 2025 |
| 3002032790 | Radial Temperature Effects on Conductors and Ratings: State of the Science | This report explores the phenomenon of radial temperature gradients in overhead transmission conductors and their implications for line ratings, asset management, and system reliability. | 2025 |
| 3002029606 | High-Temperature Performance of Spacer-Dampers | For this evaluation, the dampening characteristics of a specific make and model of a spacer-damper utilizing elastomer-lined clamps was evaluated before and after room temperature and elevated temperature (150C) vibration aging to determine the effect of vibration and thermal stresses on its performance. | 2024 |
| 3002027109 | Overhead Transmission Connectors Operating at High Temperature | This report will summarize EPRI’s research on the effects that high temperature operations have on the performance of overhead transmission connectors to enable utilities to make informed decisions when increasing the ratings for their lines. | 2023 |
| 3002027111 | High Temperature Conductor (HTC) Matrix Practical Application: Examples of Utilizing HTC Matrix for Elevated Temperature Operation Analysis | This report’s primary aim is to educate engineers on how to navigate HTC Matrix software package to perform analysis related to elevated temperature operations of overhead transmission lines. |
2023 |