P36.006: Principles and Practices of Underground Transmission
Objective
Reliability of an underground transmission system depends on highly skilled utility engineers working throughout the life cycle of design, construction, installation, operation, and maintenance of the system. It is essential to retain cable system institutional knowledge and support the next generation of technical leaders. The project addresses the following needs with knowledge, methods, and tools:
- Knowledge management of EPRI research and development project results and industry experiences.
- Investigation results of advanced tools and techniques for effective cable system management.
- Knowledge transfer on various topics covering design, construction, installation, operation, or maintenance of extruded and laminar dielectric cable systems.
This project intends to provide resources and technical support to current and future cable engineers. Participants may be better equipped with the latest knowledge, technologies, and educational materials, resulting in more reliable and cost-effective transmission cable systems. Utility engineers can apply the results of this project by participating in educational sessions while interacting with industry subject matter experts and other experienced utility engineers. For example:
- The educational workshops and workshop proceedings can be used to equip utility engineers and improve work productivity for long-term system performance.
- The updated Underground Transmission Systems Reference Book and Increased Power Flow Guidebook can be used to validate system designs, improve system operation and maintenance, and increase or optimize ratings of transmission cable lines.
- The fault location application guide can help utility engineers apply proper location detection techniques to efficiently locate faults and reduce outage time.
Research Value
This project may provide the following benefits:
- Improved underground transmission system design.
- Enhanced cable project execution.
- Retention and/or transfer of institutional knowledge.
Planned 2025 Research
An update of the EPRI Underground Transmission Systems Reference Book and Training Materials.
A revision of the EPRI Increased Power Flow Guidebook.
Semi-annual educational sessions.
Final investigation results on various topics related to design, installation, operation, and maintenance of underground transmission systems.
Anticipated Deliverables
| Deliverable | Description | Date |
|---|---|---|
| Underground Transmission Education Workshops (report) | EPRI intends to hold educational workshops in conjunction with the Underground Transmission Task Force meetings, twice annually. Topics include design, construction, installation, operation, and maintenance of both extruded and laminar dielectric cable systems. Workshop proceedings will be made available. | December 2025 |
| EPRI Underground Transmission Systems Reference Book (The Green Book)—2025 Edition (report) | The EPRI Underground Transmission Systems Reference Book (the Green Book) is a desk and field compendium on the general principles involved in planning, design, manufacturing, installation, testing, operation, and maintenance of underground transmission cable systems. The project team continuously updates the Green Book, focusing on one or two sections each year. | December 2025 |
| EPRI Underground Transmission Reference Book Training Proceedings – 2025 Update (report) | Report contains training session proceedings in
|
December 2025 |
| Increased Power Flow Guidebook (The Platinum Book)—2025 Edition (report) | This report will be continuously augmented with updated and additional materials on the state of the science and best practices for increasing and optimizing power flow through underground transmission cables and their associated circuit components. | December 2025 |
| Determining Root Causes of Pipe-Type Cable Failures—Impact of Fluid Freezes on Energized High-Pressure Fluid-Filled Pipe-Type Cable Insulation (report) | This report describes results of investigating the impact of low temperature on paper/oil dielectric insulation of energized pipe-type cable to ensure energized cable insulation performance. | December 2025 |
Past EPRI Research on Topic
| Product ID | Title | Description | Published Date |
|---|---|---|---|
| 3002027228 | Underground Transmission Systems Reference Book (The Green Book) | This 2023 edition includes update in Chapter 6 – Cable Construction: Self-Contained Fluid-Filled. | 2023 |
| 3002027229 | EMF Management User’s Guide for Underground Transmission Systems | A design guide for magnetic field management methods based on practical installations and for quantifying ampacity derating effects of magnetic field management methods. | 2023 |
| 3002024554 | Framework for the Comparison of Overhead and Underground Power Transmission | This report provides a comparative analysis framework for 69-kV through 500-kV overhead and underground transmission installations. | 2022 |
| 3002021332 | Life-Cycle Cost Guide for Underground Transmission Cable Systems, Survey Results, and Case Studies | This report identifies key considerations to include in a life-cycle cost (LCC) analysis and general approach to an LCC analysis for underground transmission cable systems, focusing on less-often considered aspects of cost analysis, including operation, maintenance, repair, and decommissioning. | 2021 |
| 3002019134 | Underground Transmission System Protection | Describes basic theories and options for cable system fault protection, including special considerations for hybrid overhead and underground lines. | 2020 |
| 3002015537 | Electrical Safety Practices in Underground Transmission Systems | Provides a guidance document on electrical safety management, including safe grounding requirements and practices, and calculation procedures for induced voltages and currents under normal and fault conditions. | 2019 |
| 3002012448 | Pressurization Procedures for High-Pressure Fluid-Filled and High-Pressure Gas-Filled Cable Systems | Describes a variety of repressurization and depressurization procedures for different cable constructions and offers recommendations. | 2018 |