P35.014: High Temperature Operation of Overhead Lines
Objective
Transmission asset owners can raise the power transfer capacity of a transmission line by increasing the line current. This increase in line current may lead to an increase in conductor operating temperature. An elevated conductor temperature could result in reduced conductor ground clearance (increased sag), loss of conductor strength, and damage to connectors and other attached hardware accessories. In addition to these mechanical effects, the elevated temperatures can impact the line corona performance, resulting in values that exceed the utility’s design specifications.
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 emperical 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 exisiting transmission infrastructure
- Increase in 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 2026, these tasks include:
Evaluate the Effect of Emissivity on Conductor-Connector Thermal Performance: This task intends to undertake research to understand the thermal effects of having a high-emissivity surface on conductor-connector systems. In 2025, testing was performed evaluating the thermal performance of high-emissivity coatings. In 2026, testing is aimed at evaluating the durability of high-emissivity coatings placed under various simulated stresses.
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 2026, the intent is to update the software for improved usability and accessibility as well as transfer another calculator to the web-based platform. Additionally, a training video of how to utilize the tools will be produced.
Update Guide for High-Temperature Operation with Copper Annealing Predictive Model: This task intends to update the guide developed to assist utilities in safely operating lines at higher temperatures. Each year, a new chapter could be added or an existing chapter updated. In recent years, EPRI has been testing the effects of time and temperature on the mechanical strength of copper conductor strands. In 2026, EPRI plans to analyze results obtained from these copper annealing studies to provide predictive models. This work will be summarized in the guide.
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 2026, the plan is to continue work on the development of equations to model corrosion rates at elevated temperatures.
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, all-aluminum conductor (AAC), all-aluminum alloy conductor (AAAC), aluminum conductor alloy reinforced (ACAR), and aluminum conductor steel-reinforced (ACSR). In 2026, the project aims to initiate 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 2026, additional emperical studies are planned to further refine predicitive equations.
Develop Guidance on Magnetic Attraction: Increased current loads lead to higher potiential for magnetic attraction. In 2025, EPRI intiated 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 2026, EPRI intends on continuing this testing and analysis.
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-TemperatureCreep Calculators | Calculator |
| Effect of High Temperature onTensile 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 |
| Corrosion at Elevated Temperatures | Technical Update |
| Radial Temperature Gradient of Overhead Transmission Conductors | Technical Update |
Past EPRI Work on Topic
| Product ID | Title | Description | Year Published |
|---|---|---|---|
| 3002030134 | High Temperature Conductor (HTC) Matrix: v14 | EPRI’s HTC Matrix software isa Windows application designed to provide the user with a quick and directedaccess to all of the information developed under several EPRI projectsinvestigating the effects of high-temperature operation of conductors. | 2024 |
| 3002029604 | Guide for Operating Overhead Lines | This report providestechnical information and research data to assist users in evaluating theoption of raising overhead transmission line capacities by increasing thecurrent and, therefore, the conductor temperature. | 2024 |
| 3002029606 | High-Temperature Performance of Spacer-Dampers | For this evaluation, thedampening characteristics of a specific make and model of a spacer-damperutilizing elastomer-lined clamps was evaluated before and after room temperatureand elevated temperature (150°C) vibration aging to determine the effect ofvibration and thermal stresses on its performance. | 2024 |
| 3002027109 | Overhead Transmission Connectors Operating at High Temperature | This report summarized EPRI’sresearch on the effects that high-temperature operations have on theperformance of overhead transmission connectors to enable utilities to makeinformed decisions when increasing the ratings for their lines. | 2023 |
| 3002027111 | High Temperature Conductor (HTC) Matrix Practical Application: Examplesof Utilizing HTC Matrix for Elevated Temperature Operation Analysis | This report’s primary aim isto educate engineers on how to navigate HTC Matrix software package toperform analysis related to elevated temperature operations of overheadtransmission lines. |
2023 |