P35.006 Lightning Performance and Grounding
Objective
Lightning is the leading cause of outages and service interruptions on overhead transmission lines. Finding the most effective and economically viable measures to improve the 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 like 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
Research Value
This project is expected to have the following impacts:
- 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
Approach
In 2026, EPRI intends on achieving the objectives of this project with the following tasks:
Develop a Lightning Attraction Model Utilizing LiDAR Data: Lightning performance calculations are usually done on a line considered in an open terrain, which leads to conservative results for shielding failures. Typically, there are trees and objects on the sides of transmission lines, which help to reduce the shielding failure flashover rate. The TFlash module, within TLW-Gen2, allows to handle trees considered as boxes on the sides of the line model. Nevertheless, adding a precise description of the sides of a line when studying a poorly performing line is time consuming. EPRI is developing a method to use LiDAR data to evaluate the effects of trees and objects on the shielding failure rate. In 2026, EPRI intends to apply this method to a specific transmission line to identify limitations and potential improvements of the approach and publish their findings in the report Using LiDAR Data to Estimate the Shielding Failure Performance of Existing Lines.
Evaluate Electromagnetic Survey Methods to Estimate the 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 the project is necessary to correctly select a ground electrode design. Advances in electromagnetic surveying could speed up the process dramatically compared to Wenner surveys more typically used by utilities. In 2026, this task intends to continue the benchmark started in 2025, but focusing on identifying the limits of the different methods on several known simulated soil configurations. EPRI intends on publishing their findings in an updated report, Electromagnetic Survey Techniques to Estimate the Soil Resistivity.
Evaluate the Use of Ground-Penetrating Radar to Assess Existing Buried Electrodes: Ground-penetrating radar (GPR) is a noninvasive method in geophysics. It is classically used to detect the presence of pipes or cables buried in the ground to prepare road works and identify potential risks before digging. EPRI intends to evaluate if GPR could be used to identify the type of grounding electrode design buried in the soil without digging and used to locate counterpoises and check their electrical continuity. In 2026, EPRI intends to share their understanding of the technology and results from a preliminary field demonstration in a report, Using Ground-Penetrating Radar to Assess Existing Buried Electrodes.
Test Lightning Impulse Performance of Polymer Brace Post Insulators: In 2026, EPRI intends to continue testing the lightning performance of brace post insulators to develop a formula to estimate their lightning impulse strength including a unique flashover path. The results of these tests are intended to be published in the Lightning Impulse Tests on Brace Post Insulator Configurations report.
Update the Lightning and Grounding Reference Book (The Gray Book): The Gray Book was developed to be a single resource that consolidates fundamental learnings from decades of research in the area of lightning performance and grounding. To facilitate understanding of content contained in The Gray Book, calculators have been developed and are housed on The Transmission Resource Center. In 2026, The Gray Book will be available on The Transmission Resource Center and the chapter on surge arresters will be updated.
Update the Transmission Line Workstation—Generation 2 (TLW-Gen2): Lightning Performance and Power Frequency Grounding Modules: In 2026, these modules will be updated to incorporate the latest research results and correct any software and usability issues.
Provide Tools and Resources on the Transmission Resource Center: The following calculators, tools, result summaries, and references are planned to be available on the Lightning Performance and Grounding Transmission Resource Center:
| Resource Title | Resource Type |
|---|---|
| Online Lightning andGrounding Applications Estimates of Soil Parameters for Sets of ResistanceMeasurements Calculation of Ground Electrode Dimensions to Obtain aDesired Value of Resistance Calculation of Ground Electrode Resistance Voltage on Tower Ancillary Circuits During Phase toGround Faults Potential and Step Potential Near a Ground Electrode Influence of Ground Electrode on Lightning Performance Propagation Model for Tower and Ground Plane Tower Footing Dynamic Resistance Ionization and Propagation Model for Counterpoise |
Calculators |
| Surge Impedance Calculator | Calculator |
| Lightning Impulse Strengthand Surge Impedance Calculators | Calculator |
| US Ground Conductivity Map | Reference |
| US Ground Flash Density Map | Reference |
| Mechanical Aging of SurgeArrestor Leads | Results Summary |
| Alternative Ground Materialsfor Counterpoises | Results Summary |
| Lightning Performance Targetsand Structure Footing Resistance Targets | Reference |
| Measuring Transmission LineGrounds Using the Fall of Potential Method | Training Video |
| Measuring Transmission LineGrounds Using the Clamp-On Method | Training Video |
| Directional Testers forMeasuring the Ground Resistance of Transmission Structures | Training Video |
| Measuring Transmission LineGrounds Using the Zed-Meter | Training Video |
Anticipated Deliverables
| Deliverable | Deliverable Type |
|---|---|
| Using LiDAR Data to Estimatethe Shielding Failure Performance of Existing Lines: A First Test | Technical Update Report |
| Electromagnetic SurveyTechniques to Estimate the Soil Resistivity: Comparison with NumericalSimulations | Technical Update Report |
| Using Ground-PenetratingRadar to Assess Existing Buried Electrodes | Technical Update Report |
| Lightning Impulse Tests onBrace Post Insulator Configurations | Technical Update Report |
| New version of TLW-Gen2:Lightning Performance and Power Frequency Grounding modules | Software |
| Lightning Performance andGrounding Reference Book (The Gray Book) | Reference Book |
| In-person Training Workshopon Transmission Line Grounding | Workshop |
Past EPRI Work on Topic
| Product ID | Title | Description | Published Date |
|---|---|---|---|
| 3002026966 | Comparison of Lightning Datawith Lightning Location Systems and TFlash: Impact of Trees on the Sides ofthe Lines |
This report shows the impacttrees on the sides of the lines have on the lightning performance oftransmission lines |
12/19/2023 |