P35.008: Line Resiliency
Objective
Recent statistical data point to a consistent and sustained increase in the average number of weather-related outages worldwide. Aging overhead transmission infrastructure together with climate change concerns emphasizes the importance of line resiliency. Resiliency may be improved by hardening transmission structures and developing techniques to limit the extent of damage and provide effective restoration in the event of structure failure. Overhead transmission structure failures have significant negative consequences for both utilities and the public, including safety and reliability issues.
The objective of this project is to provide guidance on how to increase overhead line resiliency through the hardening of new and existing lines and, when failures do occur, to contain the extent of damage and restore lines safely and rapidly.
Value may be extracted from this research by applying technologies, tools, and design techniques to reduce or avoid unintended structural, mechanical, and geotechnical failures. Using empirical studies and modeling, guidance is provided on how intelligent hardening for both new and existing assets may be achieved. This project aims to increase knowledge relating to grid sensitivities, modes of failure, and improved accuracy in the quantification of probability and uncertain load events. In addition, the project provides resources to increase utilities’ emergency restoration capabilities through access to improved restoration strategies.
Research Value
EPRI’s research on line hardening and emergency restoration aims to:
- Increase safety by providing guidance on selecting and installing hardened structures
- Increase reliability by providing guidance on selecting and installing hardened structures
- Increase safety by providing guidance on selecting and installing hardened structures
- Decrease power outage lengths by providing guidance on quick modern restoration strategies
Planned 2025 Research
EPRI aims to enhance transmission line resiliency by applying research effort in the following areas:
Practical Determination of Dynamic Load Impact Factors. EPRI has been conducting ongoing fundamental research into quantifying loads experienced by structures during broken wire events. These loads are then translated into dynamic impact load factors used by engineers to design high-resiliency structures. In 2025, EPRI aims to conclude this research effort by developing a procedure to apply dynamic impact load factors in the transmission design process.
Failure Event Loading Workshop. Engineers looking to enhance the resiliency of their systems may incorporate failure event load cases into the design process. Not all failure events are identical, however, because broken conductors affect a system far differently than cascading structures. This workshop is planned to present EPRI’s recommendations on the subject built on research into broken conductor and cascading events. The workshop aims to enhance the knowledge of transmission engineers at all experience levels.
Learning from Failure: Case Studies in Improved Engineering. With every structural or mechanical failure event, there is a potentially valuable lesson to be learned by line design engineers. The continued increase in failure events means that there is no shortage of potential events from which valuable design lessons may be extracted. Very often the events leading to failure are multi-dimensional and not the result of a single point of discrepancy. When the root causes and possible preventive actions from these events are documented, they can teach engineers how to become better designers. In 2025, EPRI aims to add multiple case studies to its current guide on documented failures related to how structures have failed in the past and how future generations of engineers may use this information to achieve more resilient designs.
Quantification of Transverse Cascading Loads. Although EPRI and other institutions in the transmission industry have conducted research into longitudinal cascading events, transverse cascading loads remain a knowledge gap. EPRI aims to build and operate a transverse cascading test line to quantify loads experienced by structures during these events and ultimately help engineers design against them. In 2025, EPRI aims to design a test line and develop a research methodology for transverse cascades to then execute upon in subsequent years.
Impact of Soil Investigation Frequency on Design Reliability. Engineering practices with regard to soil investigation frequency for transmission line projects vary widely. Every foundation that is designed and installed without an adequate soil investigation presents risk to a utility. In 2025, EPRI aims to complete a study to correlate the impact of soil investigation frequency on foundation design reliability.
Rapid Response Emergency Tower. The Rapid Response Emergency Tower is performed under EPRI’s Technology Innovation Program, in support of P35.008. In 2025, EPRI aims to demonstrate the operation of the completed emergency restoration system and to document improvements to the prototype.
Anticipated Deliverables
In 2025, a mix of ongoing research initiatives together with new research areas will be undertaken.
| Deliverable | Type | Date |
|---|---|---|
| Practical Determination of Dynamic Load Impact Factors | Technical Update | December 2025 |
| Failure Event Loading Workshop | Workshop | December 2025 |
| Learning from Failure: Case Studies in Improved Engineering | Technical Update | December 2025 |
| Quantification of Transverse Cascading Loads | Technical Update | December 2025 |
| Impact of Soil Investigation Frequency on Design Reliability | Technical Update | December 2025 |
| Rapid Response Emergency Tower | Demonstration Event | December 2025 |
Past EPRI Work on Topic
| Product ID | Title | Description | Published Date |
|---|---|---|---|
| 3002024418 | Practical Overhead Line Hardening Techniques | Guidance on how to harden both new and existing overhead lines | December 2022 |
| 3002021172 | Rapid Emergency Restoration Concept for 220–500 kV Transmission Lines | Development of a conceptual design for a 500 kV emergency restoration structure capable of deployment in 2–3 hours | April 2021 |
| 3002019065 | CASE software, Practical Algorithms for Evaluating Line Cascading Failures | Software to determine the resilience of existing overhead lines against longitudinal load events | December 2020 |