1 - P36.001: Design, Construction, Ratings, Operation, and Maintenance of Underground Transmission Systems
Target Start Date
01/2026
Anticipated Duration
12 months
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 a 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:
- Methods and tools to assist in engineering designs and to determine and improve cable circuit ratings
- Advanced designs and innovative techniques to reduce construction and installation costs
- Safe and effective cable circuit and manhole 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 more 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.
- 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.
- Performance and failure information and databases can be used for effective asset management.
Approach
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
- Develop pipe-type to extruded cable conversion technology, design, and construction options, including feasibility assessment, pipe bursting technology, and extruded-dielectric pipe-type cable for installation in steel pipe
- Investigate underground transmission vault inspection techniques to improve worker safety and reduce circuit outage requirements
- Analyze field-aged cables and accessories as well as failure and performance data to investigate long-term performance issues
Research Value
Design, construction, ratings, operation, and maintenance tools and methods developed through this project could help cable users:
- Make more informed decisions when planning new transmission lines
- Improve efficiency in underground cable system designs 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
Anticipated Deliverables
| Deliverable |
Description |
Date |
| UndergroundTransmission Workstation: Functional and Technical Enhancements andDevelopments and Supporting Engineering Documents (software and reports) |
The UndergroundTransmission Workstation (UTW) is an easy-to-use tool for cable engineers toplan, design, operate, and maintain their extruded and laminar dielectriccable systems. The project team is updating and enhancing the functionalityof UTW and associated EPRI research results. In addition to the softwarepackage, various supporting engineering documents are included, e.g., EMFuser’s guide, life-cycle cost procedures, electrical safety practices, HVDCcable ratings, and thermo-mechanical force calculations. |
December 2026 |
| UndergroundTransmission Cable System Construction and Installation (reports) |
Recent advancesin underground transmission have led to increased demand for best practicesand innovative ways to reduce construction and installation costs. This taskidentifies and assesses advanced designs and innovative construction/ installationtechniques that would contribute to improved operation performance andreduced overall project costs. Examples of the documents include acomprehensive practices manual, quality guidelines for grouting procedures,and primer for installation of high-voltage cable in tunnels. |
December 2026 |
| Pipe-Type to ExtrudedDielectric Cable Conversion—Technology, Design, and Construction Options (reports) |
Reports in multiplevolumes include the assessment of converting existing pipe-type cables using extrudeddielectric cables and existing pipe alignments. The project task evaluatesavailable solutions, identifies leading industry practices, presents anynovel ideas for design and installation of extruded cables and accessories insteel pipes, and provides guidelines and recommendations for such conversions.Examples of the documents include feasibility assessment, pipebursting technology, and extruded-dielectric pipe-type cable method forinstallation in steel pipe. |
December 2026 |
| UndergroundTransmission Vault Inspection Using Robotic Techniques (report) |
To improve workersafety and reduce circuit outage requirements, this task continues theinvestigation of underground transmission vault inspection techniques. Conceptsand prototype robotic techniques have been demonstrated in EPRI laboratoriesand at member utility sites. |
December 2026 |
| UndergroundTransmission Vault Corrosion: Inspection Assessment and Remediation (report) |
This task addresses common corrosion issues withinunderground cable joint vaults. The report discusses corrosion mechanisms withinthe vaults and provides inspection and assessment results on componentswithin the vaults. It also provides remediation recommendations based onresults of field inspections and laboratory testing. |
December 2026 |
| Underground Cable Fault Location Reference andApplication Guide (report) |
This report summarizes underground cable fault locationmethods and provides details in application of methods for transmission cablesystems. |
December 2026 |
| Performance and Failure Reports for Underground Transmission Cablesand Accessories (reports) |
Central to effective asset management is knowledge of thefailure rate of specific components based on age, family, make, model,application, and environment. This task is a multi-year effort to gatheravailable information on underground transmission cable and accessoryperformance issues, and failures of both extruded and laminar dielectriccable systems. |
December 2026 |
Past Example EPRI Research on Topic
| Product ID |
Title |
Description |
Published Date |
| 3002030104 |
Underground Transmission Workstation (UTW) |
Software tool that engineers can use to plan, design,operate, and maintain their extruded and laminar dielectric cable systems. |
2024 |
| 3002029490 |
Pipe-Type to XLPE Cable Conversion—Technology, Design,and Construction Options Volume 1: Feasibility Assessment of Pipe-Type Cableto Extruded Cable Conversion — 2024 Update |
Results that show it is feasible to replace pipe-typecables with extruded cables while keeping the same (or even higher) powerflow capability. |
2024 |
| 3002029491 |
Pipe-Type to XLPE Cable Conversion—Technology, Design,and Construction Options Volume 2: Concept Evaluation and Demonstration ofPipe Bursting for Installation of Extruded Dielectric Cables — 2024 Update |
Results of evaluation of pipe bursting as a method to useexisting assets to improve power transfer capability without the need toexcavate major lengths of trench. |
2024 |
| 3002029493 |
Pipe-Type to XLPE Cable Conversion—Technology, Design,and Construction Options Volume 4: Extruded-Dielectric Pipe-Type Cable (EPCable) for Installation in Steel Pipe —2024 Update |
Report on EPRI cable design concepts, feasibility, andtechnical considerations of retrofitting pipe-type cable pipes withextruded-dielectric cables. |
2024 |
| 3002029489 |
Reliable Performance of Transmission Cable Accessories –Outdoor Aging Test Rig |
Results of analytical and laboratory studies on extrudedcable terminations with composite insulation and evaluation of service-agedcomponents. |
2024 |
| 3002029496 |
Failure and Performance Report of UndergroundTransmission Cables and Accessories |
Documentation of information on underground transmissionfailures of extruded and laminar dielectric cable systems. |
2024 |
| 3002029495 |
Underground Transmission Vault Inspection Using RoboticTechniques—2024 Update |
Documentation of the approach and demonstration resultsat different utility sites. |
2024 |
| 3002027202 |
Underground Transmission Cable System Construction andInstallation Practices Manual |
Report on advanced designs and innovativeconstruction/installation techniques that would contribute to improvedoperation performance and reduced overall project costs. |
2023 |
2 - P36.002: Extruded Dielectric Cable Systems
Target Start Date
01/2026
Anticipated Duration
12 months
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 of:
- 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
- Achieving better understanding of cable and component aging, failure mechanisms, and end-of-life criteria
- Developing effective inspection and monitoring methods for cable system condition assessment
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.
Approach
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
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.
- Laboratory testing can deepen the industry’s understanding of cable and accessory performance and help determine the end-of-life criteria of the system.
- Development and deployment of advanced inspection and monitoring techniques may assist in asset management, improve utility operation efficiency, and increase system reliability.
- Assess conditions of existing underground transmission lines and develop fact-based maintenance and replacement strategies to reduce costs and improve reliability.
- Reduce overall installation, construction, operation, and maintenance costs.
Anticipated Deliverables
| Deliverable |
Description |
Date |
| Guidelines for Thermo-Mechanical Design of Extruded Dielectric Cable Systems in Pipes and Ducts (reports) |
This multi-year task builds on and continues EPRI’s research in laboratory verification of thermo-mechanical behavior of extruded dielectric cables in ducts, pipes, and manholes. Reports in multiple volumes include developments 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 2026 |
| Life Evaluation and Management of Extruded Dielectric Cable Systems and Components (reports) |
Volume 1 – Composite Cable Termination Long-Term Aging Tests:
Built on prior EPRI research, this multi-year effort continues to investigate the reliability of transmission extruded dielectric cable accessories. Included are technical and investigative results from accelerated aging tests at EPRI’s Lenox laboratory on terminations with composite insulating housing, material deterioration test results on field-aged cable terminations, and results from demonstrations of condition assessment tools.
Volume 2 – Cable Mechanical Bending Aging Tests &
Volume 3 – Cable Thermo-Mechanical Aging Tests:
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 starts 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:
• Mechanical bending aging tests (30,000 to 60,000 cycles)
• Full-scale thermo-mechanical aging tests (65, 80, 90, and 105 °C)
• Outdoor accelerated aging tests (138-kV and load currents)
The aging tests are to include both land and submarine cables as well as accessories of different designs at different transmission voltage levels.
Volume 4 - Asset Vintage Guide and Technology Review:
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 experiences, and lessons learned to enforce the needs for continuous vigilance during design, manufacturing, and installation processes of both cables and accessories.
|
December 2026 |
| EPRI Guide on Extruded Transmission Cable System Condition Monitoring and Diagnostics (report) |
This multi-year task is a continuation of study on advanced 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 2026 |
Past Example EPRI Research on Topic
| Product ID |
Title |
Description |
Published Date |
| 3002029498 |
Guidelines for Thermo-MechanicalDesign of Extruded Dielectric Cable Systems in Pipes and Ducts Volume 2:Fundamentals |
Describes fundamentals in thermo-mechanical behaviorsthat determine performance of XLPE cable systems, provides design values of thelimiting parameters and an application guide for the design of duct-manholesystems. |
2024 |
| 3002029499 |
Guidelines for Thermo-MechanicalDesign of Extruded Dielectric Cable Systems in Pipes and Ducts Volume 3:Mechanical Parameter Tests |
Describes mechanical parameter test procedures andresults on different cable types, including samples of a 3000-kcmil copperconductor cable with corrugated copper sheath and a 5000-kcmil copperconductor cable with a copper laminate sheath. |
2024 |
| 3002029500 |
Guidelines for Thermo-MechanicalDesign of Extruded Dielectric Cable Systems in Pipes and Ducts Volume 4:Finite Element Analyses |
Provides results of finite element analysis modeling ofcables of different metallic sheath designs based on mechanical parameters ofaxial stiffness (EA) and bending stiffness (EI) as extrapolated from previousEPRI measurements. |
2024 |
| 3002029501 |
Guidelines for Thermo-MechanicalDesign of Extruded Dielectric Cable Systems in Pipes and Ducts Volume 5:Full-Scale Experimental Verification Tests |
Shows results of full-scale verification tests for EPRIthermo-mechanical models of cross-linked polyethylene (XLPE) cable in pipesand ducts. Cable constructions include 345 kV, 4000 kcmil conductor withcorrugated aluminum sheath, and 230 kV, 3000 kcmil conductor with corrugatedcopper sheath. |
2024 |
| 3002029504 |
Aging Characteristics of ExtrudedDielectric Cable Systems and Components—Mechanical Bending Tests |
Describes efforts in developing an EPRI bending rig and reportsresults of performed tests. This test rig determines aging performance bymechanical bending of extruded dielectric transmission cables. |
2024 |
| 3002029506 |
Asset Vintage Guide andTechnology Review for Extruded Dielectric Cables, Terminations, and Joints |
Provides a document to capture changes in componentmaterials, design, manufacturing, and other known issues through life cycleof cable systems in terms of design, procurement, installation, operation,maintenance, and end of life. |
2024 |
| 3002029505 |
EPRI Guide on ExtrudedTransmission Cable System Condition Monitoring and Diagnostics |
Documents development of EPRI Guide on ExtrudedTransmission Cable System Condition Monitoring and Diagnostics, addressing distributedtemperature sensing, field partial discharge measurements, and EPRI evaluationof monitoring technologies. |
2024 |
3 - P36.003: Laminar Dielectric Cable Systems
Target Start Date
01/2026
Anticipated Duration
12 months
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 have generally 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:
- Provide guidance and develop strategies for effective operation, maintenance, life extension, and replacement
- Improve understanding of laminar dielectric cable system failure mechanisms
- Develop and demonstrate inspection, diagnostic, monitoring, and remediation techniques
Underground transmission engineers, designers, and managers may use the knowledge base, guidelines, methods, and technologies developed in this project to improve productivity, lower costs 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 can improve the asset fleet by identifying where to apply selective upgrades and retrofits based on a better understanding of relative system conditions. Additionally, they can determine where and under what circumstances the cable systems are most susceptible to damage. Utilities can also refine system monitoring by leveraging knowledge of component failure mechanisms, enhancing public and environmental safety.
Approach
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 to improve 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
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
- Reduction in overall installation, construction, operation, and maintenance costs
Anticipated Deliverables
| Deliverable |
Description |
Date |
| Life Evaluation and Management of Laminar Dielectric CableSystems (reports) |
Volume 1: Introduction and Approach. This task describesthe EPRI general approach in life evaluation and management of laminardielectric cable systems. |
December 2026 |
| Volume 2: Evaluation and Documentation of Vintage Pipe-TypeCable Performance and Experience. This task enhances the vintage guide todocument changes in component materials, design, manufacturing, and otherknown issues of pipe-type cable systems. |
December 2026 |
| Volume 3: EPRI Guide for Testing Insulating Paper andFluid. This task is a multi-year effort to create an up-to-date guide to testand analyze insulating paper and fluid of laminar dielectric cable systems toassess insulation and system conditions. This report includes results fromtests and case studies. |
December 2026 |
| Volume 4: EPRI Dissolved Gas Analysis Guide forHigh-Voltage Cables. This task continues prior EPRI research to create acomprehensive dissolved gas analysis guide to assess conditions of laminardielectric cable systems. This report also includes example test results andcase studies. |
December 2026 |
| Volume 5: Best Practices for High-Pressure Fluid-Filled(HPFF) Pipe-Type Cable Pressurization Plant Upgrades. This task providesoperating principles for HPFF cable pumping plants and a description of themany factors to consider when evaluating pumping plants for upgrades orreplacements. |
December 2026 |
| Volume 6: Pressurization Procedures for High-PressureFluid-Filled and High-Pressure Gas-Filled Cable Systems. This task describesresearch into a variety of repressurization and depressurization proceduresfor different cable constructions and offers recommendations. |
December 2026 |
| Pipe-Type CableSystem Buried Steel Pipe Corrosion (reports) |
The task describes fundamentals and practices of pipe-typecable system buried steel pipe corrosion, performs various tests at EPRIcorrosion test facilities, and applies various detection techniques toinvestigate their effectiveness. The task also studies pipe coatingdegradation as a function of coating types, pipe installation environments,and stray current conditions. This task evaluates and characterizes newtechniques for condition assessment and diagnostics with emphasis ontechniques that provide localization information on potential defects ordegradation and continuous online monitoring. Techniques under investigationinclude prototype testing of test stations for buried steel pipe corrosionmonitoring. Several volumes of documents are included: 1. Introduction,Fundamentals, and Practices; 2. Pipe Test Facility and Results; 3. ExtrudedCoating Test Rig and Results; 4. Corrosion Monitoring System Development andTesting; and 5. Field Assessment Approach and Case Studies. |
December 2026 |
| Failure Root CauseStudy of Laminar Dielectric Cables (reports) |
EPRI has performed comprehensive research in developing anapproach for life management of cable systems, including cables,terminations, joints, pressurizing plants, and others. This task continuessuch investigations and performs further laboratory experiments to betterunderstand laminar dielectric cable aging and failure mechanisms. This taskpublishes results in separate volumes for each completed investigation. |
December 2026 |
Past Example EPRI Research on Topic
| Product ID |
Title |
Description |
Published Date |
| 3002029509 |
EPRI Guide for Testing InsulationPaper and Fluid of Transmission Laminar Dielectric Cable Systems |
A consolidated industry guide for testing and datainterpretation of fluid quality and paper tests performed on samples removedfrom aging in-service cable systems to inform and help make sound decisionson the condition and life of these assets. |
2024 |
| 3002029510 |
Dissolved Gas Analysis Guide forHigh-Voltage Cables |
A guide for dissolved gas analysis (DGA) sampling,analysis, and data interpretation from laboratory and field experiences. |
2024 |
| 3002029511 |
EPRI Evaluation and Documentationof Vintage Pipe-Type Cable Performance Experience |
A guide for cable users to record major and subtlechanges in design, materials, manufacturing, and recorded issues of keycomponents of pipe-type cable systems. |
2024 |
| 3002027224 |
Utility Experience of In-PipeThermo-Mechanical Bending (TMB) Events on Pipe-Type Cables |
Results to determine performance of different cableconstructions when subjected to TMB motion. |
2023 |
4 - P36.006: Principles and Practices of Underground Transmission
Target Start Date
01/2026
Anticipated Duration
12 months
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, and 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 EPRI Green Book training proceedings can aid in cable engineers to better understand general principles and practices needed to provide reliable underground transmission systems.
Approach
This project focuses on knowledge management in underground transmission. It provides:
- Semi-annual educational sessions and proceedings.
- Updated EPRI Underground Transmission Systems Reference Book and Training Materials.
- Updated EPRI Increased Power Flow Guidebook.
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
- Reduction in overall installation, construction, operation, and maintenance costs
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 2026 |
| EPRI Underground Transmission Systems Reference Book (The Green Book)—2026 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 2026 |
| EPRI Underground Transmission Reference Book Training Proceedings – 2026 Update (report) |
Report contains training session proceedings in:
- Underground Transmission Cable Systems
- Pipe-Type Cable Systems
- Extruded Cable Systems
- Installation, Construction, and Operations & Maintenance
|
December 2026 |
| Increased Power Flow Guidebook (The Platinum Book)—2026 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 2026 |
Past Example EPRI Research on Topic
| Product ID |
Title |
Description |
Published Date |
| 3002029513 |
Underground Transmission SystemsReference Book (The Green Book) |
Desk and field compendium on the general principlesinvolved in planning, design, manufacturing, installation, testing,operation, and maintenance of underground transmission cable systems. |
2024 |
| 3002029514 |
EPRI Underground TransmissionSystems Reference Book Training Proceedings |
Materials from Green Book training sessions structured inaccordance with the book’s diverse subject matters. |
2024 |
| 3002030267 |
Increased Power Flow Guidebook(The Platinum Book) |
State-of-the-art and best practices reference andguidebook on increasing power flow capacities of existing overheadtransmission lines, underground cables, power transformers, and substationequipment. |
2024 |
| 3002029515 |
Underground Cable Fault LocationReference and Application Guide – 2024 Update |
Summary of underground cable fault location methods andapplication of the methods for transmission cable systems. |
2024 |
| 3002027229 |
EMF Management User’s Guide forUnderground Transmission Systems |
A design guide for magnetic field management methodsbased on practical installations and for quantifying ampacity deratingeffects of magnetic field management methods. |
2023 |
| 3002024554 |
Framework for the Comparison ofOverhead and Underground Power Transmission |
This report provides a comparative analysis framework for69-kV through 500-kV overhead and underground transmission installations. |
2022 |
| 3002021332 |
Life-Cycle Cost Guide forUnderground Transmission Cable Systems, Survey Results, and Case Studies |
This report identifies key considerations to include in alife-cycle cost (LCC) analysis and general approach to an LCC analysis forunderground transmission cable systems, focusing on less-often consideredaspects of cost analysis, including operation, maintenance, repair, anddecommissioning. |
2021 |
| 3002019134 |
Underground Transmission SystemProtection |
Describes basic theories and options for cable systemfault protection, including special considerations for hybrid overhead and undergroundlines. |
2020 |
5 - P36.008: HVDC Cable and HVAC Submarine Cable Systems
Target Start Date
01/2026
Anticipated Duration
12 months
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.
Approach
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
- 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
Research Value
This research produces new understanding, methods, and tools that can assist engineers and designers to 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.
Anticipated Deliverables
| Deliverable |
Description |
Date |
| EPRI High-Voltage, Direct Current (HVDC) Transmission Reference Book (The Olive Book) – 2026 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 2026 |
| Underground Transmission Workstation—DC Ampacity (software and report) |
This task aims to enhance the stand-alone Underground Transmission Workstation (UTW) DC ampacity calculation software tool for HVDC transmission cables. The calculation procedures are based on previous EPRI studies. |
December 2026 |
| Guide for High-Voltage Direct Current (HVDC) Transmission Cable Ratings – 2026 Update (report) |
This report provides calculation procedures for continuous ratings of buried land or submarine HVDC transmission cables. |
December 2026 |
| UndergroundTransmission Vault Inspection Using Robotic Techniques (report) |
To improve workersafety and reduce circuit outage requirements, this task continues theinvestigation of underground transmission vault inspection techniques. Conceptsand prototype robotic techniques have been demonstrated in EPRI laboratoriesand at member utility sites. |
December 2026 |
| Off-Line Fault Location Systems for Transmission AC and DC Cables (report) |
Off-line fault location is critical for determining the 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 2026 |
| Guide on HVAC and HVDC Array and Export Power Cables for Offshore Wind Farms – 2026 Edition (report) |
This task is a multi-year effort addressing technical challenges in exporting a large amount of energy from offshore wind collectors to land-based grid connections. Both HVAC and HVDC technologies are investigated, including best practices and the state of technology from design to operation and maintenance. |
December 2026 |
Past Example EPRI Research on Topic
| Product ID |
Title |
Description |
Published Date |
| 3002030235 |
EPRI High-Voltage Direct Current (HVDC)Transmission Reference Book: 2024 Edition |
Provides transmission companies with a comprehensive and singlesource of technical information and guidance, including HVDC cables, fordesigning, building, operating, and extending life. |
2024 |
| 3002030107 |
Underground TransmissionWorkstation (UTW) – DC Ampacity |
Calculates normal ratings of buried land or submarineHVDC transmission cables, considering environmental considerations such assoil thermal resistivity, ambient temperature, and installation. Alsocalculates electrical stress across the insulation wall, which needs to beconsidered for HVDC cables when a high maximum conductor temperature isselected. |
2024 |
| 3002029516 |
Guide for High-Voltage DirectCurrent (HVDC) Transmission Cable Ratings - 2024 Update |
Describes calculation procedure for normal ratings ofburied land or submarine HVDC transmission cables. |
2024 |
| 3002029518 |
EPRI Guide on HVAC and HVDC Arrayand Export Power Cables for Offshore Wind Farms – 2024 Edition |
Describes HVAC and HVDC power cable technologies, cablereliability experience, typical static and dynamic cable configurations, systemimplications, environmental impacts, maintenance activities, and trends and forecastsfor future development. |
2024 |