P36.001: Design, Construction, Ratings, Operation, and Maintenance of Underground Transmission Systems
Objective
Cost-effective and reliable underground transmission cable systems depend on sound engineering practices of design, construction, operation, and maintenance. This project develops technologies, software tools, and guides, providing technical basis for safe, reliable, and efficient underground transmission systems of both extruded and laminar dielectric cables. The project addresses the following needs to equip cable users with knowledge, methods, and tools to execute required tasks throughout the life cycle of underground cable systems:
- Advanced designs and innovative techniques to reduce construction and installation costs.
- Methods and tools to assist in engineering designs and determine and improve cable circuit ratings.
- Cable accessory installation, diagnostics, and long-term performance.
- Safe and effective cable circuit inspection techniques.
- Cable and accessory failure root causes.
Underground transmission engineers, designers, and managers can use the tools, methods, and technologies developed in this project to effectively plan, design, operate, and maintain their underground transmission systems. For example:
- Laboratory and investigative results can be used to improve system long-term performance and design and implement reliable and effective cable systems.
- Software tools and analytical studies can be used to validate system designs and enhance cable project planning and management, and to increase and optimize ratings of transmission circuits.
- By applying industry best practices, especially in cable system construction and installation, utilities can reduce costs in all phases of a cable project, from design and construction to operation and maintenance.
- Development and laboratory demonstration of inspection techniques can be used to improve the health and safety of personnel working with underground cable systems.
- Performance and failure information and databases can be used for effective asset management.
Research Value
Design, construction, rating, operation, and maintenance tools and methods developed through this project could help cable users:
- Make more informed decisions about planning new transmission lines.
- Improve efficiency in underground cable system design and operations.
- Improve productivity and quality in underground cable system construction.
- Assess conditions of existing underground transmission lines and develop fact-based maintenance and replacement strategies.
- Reduce overall installation, construction, operation, and maintenance costs.
Planned 2025 Research
To address industry issues and provide adequate tools and information, this project intends to evaluate and apply industry knowledge, enhance and validate existing solutions, and investigate and develop tools and technologies by undertaking key tasks in a wide variety of activities, which may include the following:
Develop methodologies, software tools, and practices related to design, engineering, system planning, ratings, and operations of underground cable systems.
Investigate transmission cable accessory performance issues, perform aging tests on outdoor terminations with composite insulation, and develop and demonstrate inspection and monitoring techniques.
Analyze field-aged cables and accessories as well as failure and performance data to investigate long-term performance issues.
Investigate underground transmission vault inspection techniques to improve worker safety and reduce circuit outage requirements.
Anticipated Deliverables
| Deliverable | Description | Date |
|---|---|---|
| Reliable Performance of Transmission Cable Accessories: Long-Term Aging Test Result—2025 Update (report) | Built on prior EPRI research, this multi-year effort continues to investigate the reliability of transmission cable accessories. Included are technical and investigative results from accelerated aging tests at EPRI’s Lenox, Massachusetts laboratory, material deterioration test results on field-aged cable accessories, and results from the evaluation of condition assessment tools. | December 2025 |
| Underground Transmission Workstation: Functional and Technical Enhancements and Developments (software and reports) | The Underground Transmission Workstation (UTW) is an easy-to-use tool for cable engineers to plan, design, operate, and maintain their extruded and laminar dielectric cable systems. The project team is updating and enhancing the functionality of UTW and associated EPRI research results. | December 2025 |
| Pipe-Type to Extruded Dielectric Cable Conversion—Technology, Design, and Construction Options (reports) | Multiple volumes of reports include the assessment of converting existing pipe-type cables using extruded dielectric cables and existing pipe alignments. The project task evaluates available solutions, identifies leading industry practices, presents any novel ideas for design and installation of extruded cables and accessories in steel pipes, and provides guidelines and recommendations for such conversions. | December 2025 |
| Underground Transmission Cable System Construction and Installation Practices Manual – 2025 Update (report) | Recent advances in underground transmission led to increased demand for best practices and innovative ways to reduce construction and installation costs. This task identifies and assesses advanced designs and innovative construction/ installation techniques that would contribute to improved operation performance and reduced overall project costs. | December 2025 |
| Underground Transmission Vault Inspection Using Robotic Techniques – 2025 Update (report) | To improve worker safety and reduce circuit outage requirements, this task continues the investigation of underground transmission vault inspection techniques. Concepts and prototype robotic techniques have been demonstrated in laboratory and field manholes. | December 2025 |
| Performance and Failure Reports for Underground Transmission Cables and Accessories – 2025 Update (report) | Central to effective asset management is knowledge of the failure rate of specific components based on age, family, make, model, application, and environment. This task is a multi-year effort to gather available information on underground transmission cable and accessory performance issues, and failures of both extruded and laminar dielectric cable systems. | December 2025 |
Past EPRI Research on Topic
| Product ID | Title | Description | Published Date |
|---|---|---|---|
| 3002027200 | Extruded-Dielectric Pipe-Type Cable (EP Cable) for Installation in Steel Pipe | Report on EPRI cable design concepts, feasibility, and technical considerations of retrofitting pipe-type cable pipes with extruded-dielectric cables. | 2023 |
| 3002027199 | Underground Transmission Workstation (UTW) | Software tool that engineers can use to plan, design, operate, and maintain their extruded and laminar dielectric cable systems. | 2023 |
| 3002027202 | Underground Transmission Cable System Construction and Installation Practices Manual | Report on advanced designs and innovative construction/installation techniques that would contribute to improved operation performance and reduced overall project costs | 2023 |
| 3002027195 | Reliable Performance of Transmission Cable Accessories – Outdoor Aging Test Rig | Results of analytical and laboratory studies on extruded cable terminations with composite insulation and evaluation of service-aged components. | 2023 |
| 3002027205 | Failure and Performance Report of Underground Transmission Cables and Accessories | Documentation of information of underground transmission failures of extruded and laminar dielectric cable systems. | 2023 |
| 3002024523 | Shallow and At-Grade Power Transmission Cable Installation Techniques | Report on a concept of installing underground transmission cables in shallow trenches or berms, allowing a lessened economic impact of using underground cables but remaining resilient to fire. | 2022 |
| 3002021268 | Underground Transmission Cable System Construction and Installation Practices Manual | A manual that reviews relevant EPRI work and distills results into a comprehensive volume that is of immediate benefit to experienced cable users as well as those considering their first transmission cable installation project. | 2021 |
| 3002019117 | Primer for Installation of High-Voltage Cable in Tunnels | A primer on tunneling methods for installation of transmission cables in tunnels and case studies of notable installations. | 2020 |
| 3002015512 | Concept Evaluation of Pipe Bursting for Installation of Extruded Dielectric Cables | Results of evaluation of pipe bursting as a method to use existing assets to improve power transfer capability without the need to excavate major lengths of trench. | 2019 |
| 3002012433 | Feasibility Assessment of Pipe-Type Cable to Extruded Cable Conversion | Results that show that it is feasible to replace pipe-type cables with XLPE cables while keeping the same (or even higher) power flow capability. | 2018 |