P35.006: Lightning Performance and Grounding
Objective
Lightning is the leading cause of outages and service interruptions on transmission lines. Finding the most effective and economically viable measures to improve lightning performance can be challenging. Often confronted with several options—such as grounding improvements, insulation modifications, or application of line surge arresters—engineers seek guidance on which solution to apply. Sometimes the option chosen impacts other design aspects. For example, transmission line grounding influences both lightning performance and the public/worker safety of transmission lines.
The objective is to help overhead transmission owners and operators mitigate lightning outages and evaluate the effectiveness of grounding systems to enhance system reliability and reduce costs by:
- Developing engineering tools
- Developing resource material, such as the Lightning and Grounding Reference Book
- Developing tests to improve the reliability of components such as transmission line surge arresters or grounding systems
- Providing training (in-person and virtual)
- Developing an instrument (EPRI Zed-Meter) to measure the structure grounding impedance and soil resistivity quickly and without disconnecting the ground wire
- Transferring the research results via face-to-face meetings, webcasts, and workshops
Research Value
This project is expected to have the following impact:
- Improved lightning performance and safety of transmission lines by providing engineers with effective tools and an improved knowledge base
- Addressing the loss of institutional knowledge by providing guides, training, and software tools to engineering staff who are new to the field of lightning and grounding
- Reduced costs by providing improved knowledge and tools (for example, reference information and software tools for field inspection and engineering design)
- Improved public and worker safety by calculating the tower footing voltages and their associated step-and-touch potentials in the event of line faults
Planned 2025 Research
Improved Lightning Shielding Failure Approach for Tall Structures. Since the introduction of ultra-high voltage (UHV) lines with tall support structures, utilities have experienced a significantly high number of lightning outages caused by shielding failures. The shielding failures in most cases are not predicted by the traditional calculation methods. In 2025, this task aims to evaluate the new simplified Rizk model against documented cases of shielding failures and report the findings.
Electromagnetic Surveys to Estimate Soil Resistivity. Unanticipated grounding electrode improvements are both costly and time-consuming when constructing a new transmission line. A good estimation of the soil resistivity along the line during the planning phase of a project is necessary to correctly select a ground electrode design. Advances in electromagnetic surveying could speed the process dramatically compared to Wenner surveys, more typically used by utilities. In 2025, this task intends to review different electromagnetic technical solutions from aerial to terrestrial to estimate the soil resistivity.
Lightning Impulse Performance of Brace Post Insulators. Lightning impulse data for dimensioning polymer insulators are based on tests performed on porcelain insulator strings installed in the 1960s. This information is not always applicable because polymer insulators are applied in several different configurations today, and the flashover value for the same insulator length may be different. In 2025, this task intends to focus on brace post insulators and to test different installation arrangements that could impact their lightning impulse strength.
Lightning and Grounding Reference Book (The Gray Book). EPRI has amassed a large knowledge base of lightning and grounding information. This task intends to develop a single resource that consolidates previous EPRI lightning and grounding research. The reference material enables utilities to quickly find information and relevant tools to improve the outage performance of their overhead lines. Some of those tools are hosted on EPRI’s transmission.epri.com site to help utilities compare technical solutions and to provide additional training materials. The reference book (available in electronic format) is updated with new information each year.
Transmission Line Workstation—Generation 2 (TLW-Gen2): Lightning Performance and Power Frequency Grounding Modules. New version of the Lightning Performance Analysis Module (TFlash). This is a software module for determining the lightning performance of lines that is part of TLW-Gen2. This task intends to update this tool with the latest research results to improve and expand its modeling capabilities. Participants in this project get access to the Lightning Performance module of TLW-Gen2.
Updating the Power Frequency Grounding Module. This is a software module for calculating fault current division and circulating currents on transmission lines. This task intends to update the software to expand its capabilities. Participants in this project get access to the Power Frequency Grounding module of TLW-Gen2.
Anticipated Deliverables
| Deliverable | Type | Date |
|---|---|---|
| Evaluation of the Simplified Risk Model for Estimating Shielding Failures | Technical Update | December 2025 |
| Review of Electromagnetic Survey Techniques to Estimate the Soil Resistivity | Technical Update | December 2025 |
| Lightning Impulse Tests on Brace Post Insulator Configurations | Technical Update | December 2025 |
| New version of TLW-Gen2: Lightning Performance and Power Frequency Grounding modules | Software | December 2025 |
| Lightning Performance and Grounding Reference Book (The Gray Book) | Reference Book | December 2025 |
Past EPRI Work on Topic
| Product ID | Title | Description | Published Date |
|---|---|---|---|
| 3002024403 | Guidelines for Estimating the Lightning Impulse Strength of Overhead Transmission Lines | This report summarizes the key effects of insulator length on the lightning impulse strength of transmission lines. | December 2022 |
| 3002024474 | Sizing Overhead Ground Wires for Fault Currents: Using EPRI’s TLW-Gen2—Power Frequency Grounding Module | This report describes how to model a transmission line in TLW-Gen2 to size overhead ground wires for fault currents with the power frequency grounding module. | December 2022 |