The research team is happy to share our plans for this year’s R&D. Thanks to all of our utility advisors that have given input throughout the planning process. We are excited to continue working together!
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2025 Research Plans
- 1: P36.001: Design, Construction, Ratings, Operation, and Maintenance of Underground Transmission Systems
- 2: P36.002: Extruded Dielectric Cable Systems
- 3: P36.003: Laminar Dielectric Cable Systems
- 4: P36.006: Principles and Practices of Underground Transmission
- 5: P36.008: HVDC Cable and HVAC Submarine Cable Systems
1 - 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 |
2 - P36.002: Extruded Dielectric Cable Systems
Objective
Utilities rely on extruded dielectric cable systems to meet growing demands for new underground transmission lines. This project intends to address several key research issues, including specific goals:
- Improving engineering-based design and installation procedures to accommodate electrical, mechanical, and thermal requirements for long-term performance, considering thermo-mechanical behaviors of cables and accessories as well as corrosive environments of buried or in-manhole components.
- Developing effective inspection and monitoring methods for cable system condition assessment.
- Achieving a better understanding of cable and component aging, failure mechanisms, and end-of-life criteria. Underground transmission engineers, designers, and managers can use the guidelines, methods, and technologies developed or assessed in this project to improve productivity and reduce costs of designing, installing, commissioning, testing, operating, and maintaining extruded dielectric cable systems. Engineers may use the improved understanding of the behavior of extruded dielectric cables under normal and emergency loading scenarios plus analytical or software-based tools to achieve effective and economical system designs. Operators and maintenance departments can deploy new inspection and monitoring methods and tools to obtain real-time and near-real-time information on cable system conditions.
Research Value
The new materials, devices, and methods produced in this project could improve the performance of extruded dielectric transmission cable systems to meet power system safety, reliability, and maintainability requirements and to contribute to improved technical standards. For example:
- Full-scale laboratory testing may validate and improve theoretical understanding of the thermo-mechanical behavior of extruded dielectric transmission cables. The results would support improved specifications and standardized designs, leading to higher system reliability, fewer circuit outages, and lower life-cycle costs.
- Development and deployment of advanced inspection and monitoring techniques may assist in asset management, improve utility operation efficiency, and increase system reliability.
- Investigation of corrosion inspection, assessment, and remediation methods and techniques for cable components in underground vaults addresses this emerging issue and may improve the design, inspection, maintenance, and protection of these components.
- Laboratory testing can deepen the industry’s understanding of system performance and help determine the end-of-life criteria of the system.
Planned 2025 Research
This project investigates methods and technologies for extruded dielectric transmission cable systems. Solutions are applicable to design, selection, installation, commissioning, testing, operation, and maintenance of these systems. The project seeks to answer research questions and address industry issues through the following activities:
Laboratory testing to validate engineering design models.
Laboratory testing to understand failure mechanisms and end-of-life.
Development and evaluation of innovative inspection and assessment tools, methods, and technologies.
Laboratory testing and field demonstration of developed or available diagnostic methods.
Anticipated Deliverables
| Deliverable | Description | Date |
|---|---|---|
| Guidelines for Thermo-Mechanical Design of Extruded Dielectric Cable Systems (reports) | This multi-year task builds on and continues EPRI’s prior research in laboratory verification of thermo-mechanical behavior of extruded dielectric cables in ducts, pipes, and manholes. Multiple volumes of reports include development of a validated source of practical engineering knowledge to assist cable engineers in designing extruded dielectric cable systems with respect to their thermo-mechanical effects. The reports cover design principles, cable mechanical parameter measurements, finite element analysis modeling, engineering software tools, full-scale laboratory validation, applications at utility sites, and subject matter training. | December 2025 |
| Advanced Sensors and Inspection Techniques for Extruded Dielectric Transmission Cable Systems (report) | This multi-year task is a continuation of the study on advanced sensors and monitoring techniques for inspection of cable system condition and operational status. The task covers developments of test rigs and performs tests to evaluate the effectiveness of available technologies and to demonstrate emerging technologies. | December 2025 |
| Aging Characteristics of Extruded Dielectric Cable Systems and Components (report) | Many extruded dielectric cable circuits are approaching 30–40 years in service. The industry needs an approach to study their life management and expectancy. This task started as a series of laboratory experiments to better understand extruded dielectric cable system aging and failure mechanisms, and has since expanded into three different tests:
|
December 2025 |
| Underground Transmission Vault Corrosion: Inspection Assessment and Remediation (report) | This task addresses common corrosion issues within underground extruded dielectric cable joint vaults. The report discusses corrosion mechanisms within the vaults and provides inspection and assessment results on components within the vaults. It also provides remediation recommendations based on results of field inspections and laboratory testing. | December 2025 |
| Asset Vintage Guide and Technology Review of Extruded Dielectric Cable Systems (report) | How an asset degrades and fails is often dependent on how the asset was designed and manufactured. This task develops and updates vintage information for component materials, design, manufacturing, and other known issues of extruded dielectric cable systems. This task also provides a state-of-art technology review to assist utility cable users in making engineering decisions for reliable and cost-effective in-service operations. The report captures evolving technologies, success and failure experience, and lessons learned to enforce the needs for continuous vigilance during design, manufacturing, and installation processes of both cables and accessories. | December 2025 |
| Product ID | Title | Description | Published Date |
|---|---|---|---|
| 3002027208 | Experimental Verification for Thermo-Mechanical Models for Cross-Linked Polyethylene Cable in Pipes and Ducts | Results on full-scale verification tests for EPRI thermo-mechanical models of cross-linked polyethylene (XLPE) cable in pipes and ducts. Cable constructions include 345 kV, 4000 kcmil conductor, with corrugated aluminum sheath, and 230 kV, 3000 kcmil conductor, with corrugated copper sheath. | 2023 |
| 3002027212 | Mechanical Bending Test Rig for Extruded Dielectric Transmission Cables | Describes efforts in developing an EPRI bending rig and reports additional results of performed tests. This test rig determines aging performance by mechanical bending of extruded dielectric transmission cables. | 2023 |
| 3002027215 | Quality Guidelines for Grouting Procedures for Large Casings Used for Transmission Cable Systems | Utility experiences with grouting and steps required to properly design and install high-quality grouts. | 2023 |
| 3002021317 | Transmission Extruded Dielectric Cable Sheath Bonding System – Equipment Design and Performance | Guideline document for sheath bonding system and equipment design, performance, and operation and maintenance practices. | 2021 |
| 3002021319 | Guide for Application of Distributed Fiber Optic Temperature Sensing to Underground Power Cables | Reports additional results on a walk-through of setting up a distributed temperature sensing device, required calibrations, follow-up testing, and measurement process. | 2021 |
| 3002019121 | Finite Element Analysis for EPRI Thermo-Mechanical Tests of Aluminum Corrugated, Copper Corrugated, and Lead Sheath Cables | Provides results of finite element analysis modeling of cables of different metallic sheath designs, based on mechanical parameters of axial stiffness (EA) and bending stiffness (EI) as extrapolated from previous EPRI measurements. | 2020 |
| 3002012436 | Mechanical Parameter Testing of Extruded Dielectric Transmission Cables | Describes mechanical parameter test procedures and results obtained on samples of a 3000-kcmil copper conductor cable with corrugated copper sheath. | 2018 |
3 - P36.003: Laminar Dielectric Cable Systems
Objective
Laminar dielectric cable systems consist of high-pressure fluid-filled (HPFF), high-pressure gas-filled (HPGF), and self-contained fluid-filled (SCFF) system types. These cables in general have provided long-lasting service, surpassing their design life specifications. However, the advanced age of many of these assets might be a cause for concern. Replacement costs for laminar dielectric cable systems are high and the consequences of electrical failures or fluid leaks are significant. Research is needed to:
- Improve understanding of laminar dielectric cable system failure mechanisms.
- Develop and demonstrate inspection, diagnostic, monitoring, and remediation techniques.
- Provide guidance and develop strategies for effective operation, maintenance, life extension, and replacement.
Underground transmission engineers, designers, and managers may use the knowledge base, guidelines, methods, and technologies developed in this project to improve productivity, lower cost of operation and maintenance, and extend the life of laminar dielectric cable systems. Reliability and safety can be enhanced, and asset management strategies can be improved. Maintenance personnel can make more effective use of staff time and budget resources by applying new inspection methods and monitoring technologies. Planners may learn where to apply selective upgrades and retrofits through a better understanding of the relative conditions of their asset fleet, as well as where and under what circumstances cable systems are most susceptible to damage. In addition, utilities can apply the knowledge of corrosion mechanisms and detection to fine-tune the monitoring of their systems to enhance public and environmental safety.
Research Value
This research produces new understanding, methods, and tools that could improve the ability of engineers and planners to assess the condition of laminar dielectric cable systems and take proactive steps in operating and maintaining these systems to extend asset life and prevent unexpected outages. Benefits of this project may include:
- Better understanding of failure mechanisms and prevention procedures for longer asset life, fewer customer outages, and lower operations costs.
- Effective inspection and monitoring of assets, leading to increased asset utilization, rapid maintenance intervention prior to spontaneous failure, higher reliability, and lower repair costs.
- New inspection techniques and tools to increase staff productivity and reduce overall maintenance costs.
Planned 2025 Research
This project investigates and develops condition assessment methods and procedures for laminar dielectric cable systems. Efforts focus on life extension, improved reliability, reduced operation and maintenance costs, and improved support for asset management decision-making protocols. EPRI intends to direct its research at one or more of the following areas:
Evaluate and demonstrate advanced diagnostic techniques to assess conditions of laminar dielectric cables.
Develop best practices in dissolved gas analysis and insulating paper and fluid testing for effective deployment of the technologies.
Develop vintage information for laminar dielectric cable systems for improving asset management strategies.
Conduct investigations to better understand failure mechanisms of laminar dielectric cables.
Study buried steel pipe coating degradation as a function of coating types, coating ages, pipe installation environments, coating application methods, and stray current conditions.
Evaluate and develop methods to effectively detect and mitigate corrosion and corrosive environments.
Develop technical bases for best practices to improve the effectiveness of cathodic protection systems.
Anticipated Deliverables
| Deliverable | Description | Date |
|---|---|---|
| Inspection, Assessment, and Mitigation of Buried Steel Pipe Corrosion (reports) | The task applies various detection techniques to investigate their effectiveness, while studying coating degradation as a function of coating types, pipe installation environments, and stray current conditions. | December 2025 |
| New Technique Development for Online and Off-Line Condition Assessment of Laminar Dielectric Cable Systems (report) | This task will evaluate and characterize new techniques for condition assessment and diagnostics of laminar dielectric cables, with emphasis on techniques that provide localization information on potential defects or degradation and continuous online monitoring. Techniques under investigation include prototype testing of test stations for buried steel pipe corrosion monitoring. | December 2025 |
| EPRI Guide for Testing Insulating Paper and Fluid of Laminar Dielectric Transmission Cables (report) | This task is a multi-year effort to create an up-to-date guide to test and analyze insulating paper and fluid of laminar dielectric cable systems to assess insulation and system conditions. This report includes results from tests and case studies. | December 2025 |
| EPRI Dissolved Gas Analysis Guide for High-Voltage Cables and Transformers—Case Studies (report) | This task continues prior EPRI research to create a comprehensive dissolved gas analysis guide to assess conditions of laminar dielectric cable systems. This report also includes example test results and case studies. | December 2025 |
| Evaluation and Documentation of Vintage Pipe-Type Cable Performance and Experience—2025 Update (report) | This task enhances the vintage guide to document changes in component materials, design, manufacturing, and other known issues of pipe-type cable systems. | December 2025 |
| Failure Root Cause Study of Laminar Dielectric Cables (report) | EPRI has performed comprehensive research in developing an approach for life management of cable systems, including cables, terminations, joints, pressurizing plants, and others. This task will continue such investigations and perform further laboratory experiments to better understand laminar dielectric cable aging and failure mechanisms. | December 2025 |
Past EPRI Research on Topic
| Product ID | Title | Description | Published Date |
|---|---|---|---|
| 3002027224 | Utility Experience of In-Pipe Thermo-Mechanical Bending (TMB) Events on Pipe-Type Cables | Results to determine performance of different cable constructions when subjected to TMB motion. | 2023 |
| 3002027220 | EPRI Guide for Testing Insulation Paper and Fluid of Transmission Laminar Dielectric Cable Systems | A consolidated industry guide for testing and data interpretation of fluid quality and paper tests performed on samples removed from aging in-service cable systems to inform and help make sound decisions on the condition and life of these assets. | 2023 |
| 3002027221 | Dissolved Gas Analysis Guide for High-Voltage Cables | A guide for DGA sampling, analysis, and data interpretation from laboratory and field experiences. | 2023 |
| 3002027223 | EPRI Evaluation and Documentation of Vintage Pipe-Type Cable Performance Experience | A guide for cable users to record major and subtle changes in design, materials, manufacturing, and recorded issues of key components of pipe-type cable systems. | 2023 |
| 3002027217 | Mitigation, Inspection, and Monitoring of Corrosion on Buried Steel Pipes of Pipe-Type Cable Transmission Systems | Report on corrosion fundamentals, mitigation options, stray currents, coating system performance, and various inspection and assessment techniques of pipe-type cable buried steel pipes. | 2023 |
| 3002027219 | EPRI Buried Pipe Test Station Development for Condition Monitoring of Buried Steel Pipes in Pipe-Type Cable Systems | Report on development of a buried pipe test station for use in condition assessment of buried steel pipes in pipe-type cable systems. | 2023 |
| 3002024547 | Best Practices for High-Pressure Fluid-Filled (HPFF) Pipe-Type Cable Pressurization Plant Upgrades | Overview of operating principles for HPFF pipe-type cable pumping plants and a description of factors to consider when evaluating pumping plants for upgrades or replacements. | 2022 |
| 3002021328 | Evaluation of Three Laminated Paper Polypropylene (LPP) Cable Pieces with One Containing Failure | Results of an analysis of a 345-kV failed LPP cable. A series of radial electrical, physical, and chemical tests were conducted on dissected cable pieces. Exchange of pipe and impregnation fluids were investigated. Analysis determines the condition and life of the cable. | 2021 |
| 3002019131 | Determining Root Causes of Pipe-Type Cable Failures—Impact of Fluid Freezes on Energized High-Pressure Fluid-Filled Pipe-Type Cable Insulation | Report on results of investigations on impact of low temperature on paper/oil dielectric insulation of pipe-type cables and temperature limits to ensure energized cable insulation performance. | 2020 |
4 - 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 |
5 - P36.008: HVDC Cable and HVAC Submarine Cable Systems
Objective
Significant trends are developing in applications of high-voltage, direct-current (HVDC) cable systems for power grid integration and interconnections. Increasingly, HVDC cable systems and high-voltage, alternating-current (HVAC) submarine cable systems are being used for power transmission from remote renewable energy generation to power grids. The line distances of HVDC cable circuits are steadily increasing for both land and submarine applications. All these occurrences are being enabled by advances in HVDC cable and converter technologies. More cable manufacturers are offering HVDC cables or adding manufacturing capacity in anticipation of the growing demands. Research is needed to:
- Understand needs, trends, and technologies for HVDC system integration with existing power grids.
- Develop tools for effective designs and implementations.
- Understand failure mechanisms and demonstrate inspection, diagnostic, monitoring, and fault location methods.
- Provide guidance, develop strategies, and share practices for effective operation, inspection, and maintenance.
Engineers, designers, and managers of underground transmission can use the tools and methods developed in this project to effectively apply, operate, and maintain HVDC transmission and HVAC submarine cable technologies. Utility engineers may use the improved understanding of the HVDC and HVAC submarine cable systems to achieve effective and economical system designs and determine system ratings. Maintenance departments can deploy new fault location methods and tools to locate faults more efficiently, especially for long-distance HVDC and HVAC submarine cables.
Research Value
This research produces new understanding, methods, and tools that can assist engineers and designers apply, operate, and maintain HVDC and HVAC submarine transmission cable systems as well as extend asset life and prevent unexpected outages. For example:
- The use of the reference books, design tools, and other investigative results may lead to more effective designs and applications for power grid integration and interconnection.
- Effective inspection and monitoring of assets could lead to increased asset utilization, rapid maintenance intervention, improved reliability, and reduced repair costs.
- Better understanding of failure mechanisms and prevention procedures may result in longer asset life, reduced customer outages, and lower operating costs.
Planned 2025 Research
This project investigates and develops methods and tools for effective applications of HVDC cable and HVAC submarine cable technologies for system integration and interconnection. The project:
Analyzes and evaluates design tools for utility engineers to prepare feasibility studies and verify proposals and implementations.ls.
Assesses cable insulation materials and aging characteristics to optimize designs and extend the life of HVDC cable and HVAC submarine cable systems.
Evaluates operational practices in application of HVDC cable and HVAC submarine cable technologies, based on technical and economic benefits and increased power transfer capability requirements.
Measures condition assessment, maintenance, inspection, and fault location technologies to meet operation and maintenance requirements.
Anticipated Deliverables
| Deliverable | Description | Date |
|---|---|---|
| EPRI High-Voltage, Direct-Current (HVDC) Transmission Reference Book (The Olive Book)—2025 Edition (report) | The EPRI Olive Book is a state-of-the-art guidebook and comprehensive source of technical information for designing, building, operating, and extending the life of HVDC transmission systems. The project team continuously updates the Olive Book. | December 2025 |
| Underground Transmission Workstation—DC Ampacity (software and report) | This task aims to enhances the standalone Underground Transmission Workstation (UTW) DC ampacity calculation software tool for HVDC transmission cables. The calculation procedures are based on previous EPRI studies. | December 2025 |
| Guide for High-Voltage Direct Current (HVDC) Transmission Cable Ratings (report) | This report provides calculation procedures for continuous ratings of buried land or submarine HVDC transmission cables. | December 2025 |
| Guide on HVAC and HVDC Array and Export Power Cables for Offshore Wind Farms – 2025 Edition (report) | This task is a multi-year effort addressing technical challenges for exporting a large amount of energy from offshore wind collectors to land-based grid connections. Both HVAC and HVDC technologies are investigated. The task evaluates best practices and the state of technology, from design to operation and maintenance. | December 2025 |
| Off-Line Fault Location Systems for Transmission AC and DC Cables (report) | Off-line fault location is critical for determining location of a cable fault. This task provides results of a study in applying and demonstrating previously developed fault location technology for long HVDC cables to HVAC cables. | December 2025 |
Past EPRI Research on Topic
| Product ID | Title | Description | Published Date |
|---|---|---|---|
| 3002027330 | EPRI High-Voltage Direct Current (HVDC) Transmission Reference Book: 2023 Edition | Provides transmission companies with a comprehensive and single source of technical information and guidance, including HVDC cables, for designing, building, operating, and extending life. | 2023 |
| 3002027233 | Underground Transmission Workstation (UTW) – DC Ampacity | Calculates normal ratings of buried land or submarine HVDC transmission cables, taking into account environmental considerations such as soil thermal resistivity, ambient temperature, and installation. Also calculates electrical stress across the insulation wall, which needs to be considered for HVDC cables when a high maximum conductor temperature is selected. | 2023 |
| 3002027236 | EPRI Guide on HVAC and HVDC Array and Export Power Cables for Offshore Wind Farms – 2023 Edition | Describes HVAC and HVDC power cable technologies, cable reliability experience, typical static and dynamic cable configurations, system implications, environmental impacts, maintenance activities, and trends and forecasts for future development. | 2023 |
| 3002019137 | Off-Line Fault Location Systems for Long HVDC Cables | Reports on technology developed for HVDC long cable fault locations. | 2020 |
| 3002015541 | Underground Transmission Alternative for ±525 kV HVDC Grids | Summarizes a feasibility investigation of applying long HVDC underground circuits from a renewable generation collection center to an urban hub load center. | 2019 |