Overview

Introduction to the distribution underground assets project
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Project Description

Key Research Question

Utility companies that own and operate underground distribution systems face a number of challenges and changing needs. Installing and maintaining underground infrastructure is challenging due to its accessibility. Additionally, installed underground distribution infrastructure is aging, and much of the early installed plant is reaching the end of its useful life. Utility managers are charged with managing costs, improving system reliability and resiliency, increasing power throughput, and improving the health and safety of workers and the public. In addition, significant changes to underground electric distribution systems are underway, including the application of new load types, new distributed generation sources, new equipment and materials, and automation technologies. At the same time, many utilities are losing their institutional knowledge due to worker attrition.

This research aims to support utilities in the face of these challenges by focusing on:

  1. Promoting technology transfer, via multiple vehicles, of the collated and created knowledge,
  2. Investigating the impact of increased electrification on the performance and reliability of both new and legacy underground infrastructure,
  3. Providing a framework with which to understand the common asset degradation mechanisms, informing enhanced specifications, diagnostics, and workmanship,
  4. Identifying effective approaches to improve reliability and extend the practical life of underground assets.

Objective

Utility companies managing underground distribution systems are at a pivotal moment. With aging infrastructure, limited accessibility for inspections and maintenance, and the dilution of institutional knowledge due to experience exiting the workforce and the reducing tenure of replacements, the challenges are significant. The landscape is evolving rapidly, bringing both opportunities and complexities.

Underground (UG) electric distribution systems are undergoing substantial changes. Shifting load profiles due to electrification, an increased reliability requirement, and innovative equipment and materials all require integration with a complex and diverse legacy grid. Our research focuses upon new and legacy technologies and is designed to equip utility asset managers with the insights and tools needed to design, specify, and manage the underground distribution grid.

Key Focus Areas

  1. Knowledge Sharing: Foster a global culture of knowledge sharing, both from utility peers and EPRI expertise, to improve the stewardship of underground distribution systems

  2. Asset Aging and Degradation: Understand the mechanisms behind asset aging and degradation to refine specifications, diagnostics, maintenance strategies, and workmanship approaches

  3. Diagnostic and Asset Management Approaches: Identify effective methods for diagnosing, inspecting, and assessing the health of underground assets so that appropriate maintenance strategies can be deployed to extend each asset’s life and guide investment decisions

  4. Performance: Evaluating new and existing technologies, not only against industry requirements but the evolving needs of end users across the world

  5. Supply Chain: Support utilities as they navigate the complexities of a changing supplier landscape that has been further stressed by required expansions and replacements within the underground grid

  6. Next-Generation Grid: Prepare for the transformation of the UG grid occurring as a result of increased automation, distributed energy resources, changing load profiles, heightened customer expectations, and geographic needs

Approach

Approach

Research results will be provided in multiple forms, including:

  • Results from experimentation and analysis
  • Evaluation and demonstration of advanced tools and equipment
  • Reference books, practical manuals, and field guides
  • Workshops, meetings, short courses, and webcasts

In 2026, planned research tasks include five key research themes:

  • Performance

    • Cable and Accessory Performance- In 2026, EPRI plans to continue its investigation of newer cables, such as the expected long-term performance of medium-voltage conventional and transition joints. This work will be conducted within the newly developed test area at the Lenox laboratory. Using this test facility, EPRI also plans to continue researching the impact of wet aging on lead-free EPR- and EAM- insulated cables.
    • Underground Structure (Manhole) Events - This research focuses on understanding the causes of underground events that occur in ducts, manholes, and vaults, investigating methods to identify event precursors, and assessing event mitigation systems and approaches. In the 2026 research, EPRI will continue research into detecting manhole event precursors using online and offline grid monitoring/inspection technologies. The goal of this research is to identify technologies and strategies for keeping UG structures safe for utility personnel and the public.
    • Covered Conductor Research - In conjunction with overhead assets team, research will continue into the performance of covered conductors and their connector technologies. It is anticipated that utilities will derive benefit from this work through better understanding of aging factors and the development of qualification and specification principles.

  • Diagnostics

    • Diagnostics Techniques for Cable Systems - This task researches the use of various diagnostic techniques for underground systems, including investigating trigger points for action. Planned activities for 2026 include continued examination of heating in medium-voltage cable components under different conditions to inform the use of infrared thermography, leveraging an energized test bed at EPRI’s Lenox laboratory.
    • Decision Tools - EPRI also intends to continue to develop tools to assist Funders in understanding different diagnostic technologies so they are better able to leverage the information these tests can generate. Such tools can include tech briefs that describe the basics of different technologies as well as their advantages, disadvantages, and use cases.

  • Asset Health

    • New Technologies - The pace of change in distribution technology is accelerating, with new technologies, approaches, vendors, and service providers entering the market and offering new solutions. This research will scout new technologies for underground distribution and identify opportunities for further investigation and demonstrations. Areas of focus will include:
      • Online grid monitoring
      • Connectors
      • Cable rejuvenation
      • Fault locating
      • Installation/undergrounding approaches
    • Asset Management Approaches - EPRI plans to gather and collate leading practices that are leveraging monitoring (both offline and online) data to manage assets.

  • Supply and Standards

    • EPRI plans to continue supporting utilities in the industry standards space by:
      • Participating in international standards development bodies to ensure that end-user perspectives are considered
      • Providing updates and interpretations to utilities when standards are updated
    • Factory Assessment Approaches - 2022 to 2027 will have seen a tremendous expansion in manufacturing capacity of UG components. EPRI aims to continue to examine approaches used by utilities to ensure suppliers provide products that continue to comply with industry standards and utility specifications.

  • Failure Analysis

    • Failed Cable and Cable Accessories - This research task investigates cable and cable accessories, including joints, terminations, and separable connectors, to understand their life-cycle performance.
    • Asset Demographics - Building on the global data gathered in 2024 and 2025, EPRI intends to expand the asset demographic data to include failure rates for additional underground components. Funders will be able to provide their input in early 2026 on which components EPRI will investigate. These data are expected to be published for Funders on the Distribution Resource Center (DRC).

  • Knowledge Preservation

    • Update to the Underground Distribution Systems Reference Book (Bronze Book) - In 2026, EPRI plans to produce an update to the Underground Distribution Systems Reference Book with an expanded chapter on cable manufacturing and qualification.
    • Interest Groups - EPRI will continue to support the North American Dense Urban Utility Working Group (NADUUWG) and Underground for Distribution Interest Group (U-DIG).

The six areas noted above will benefit from cross cutting activities of Knowledge Engineering and Technology Scouting which seeks to ensure that the key technical knowledge is delivered to members in the most useful manner, including:

  • EPRI Underground Systems Reference Book (Bronze Book)
    • Expand to include reference cable information developed in 2024,
    • Separate Chapter 17 into four chapters: materials, qualification, quality, and manufacture.
  • Development of online cable handbook on the Distribution Resource Center (http://distribution.epri.com)
  • Gathering of key industry performance data
    • Manhole events
    • Cable system failure performance
    • Cable installation / usage
  • Tech scouting – WP
    • “Articulate” cable limiter technology
    • Medium voltage dc systems
    • Network system data uses / potential
  • Educational webinars and informational videos covering topics such as:
    • Withstand (Proof ) Diagnostics
    • Cable system ampacity
    • Partial discharge
    • Fundamentals of cables and accessories (stress distribution, materials)
    • Basics of water treeing and the effects
    • Manufacturing fundamentals

Research Value

With the knowledge acquired through this research program, distribution underground utility engineers and managers will have access to information and products that can help them:

  • Improve the quality of underground distribution assets
  • Increase engineering staff knowledge in underground distribution
  • Lower underground distribution installation and maintenance costs
  • Gain more accurate and timely knowledge about asset condition and life expectancy
  • Improve system reliability and safety
  • Reduce environmental impacts while achieving the benefits of underground systems
  • Enhance strategic intelligence on emerging technologies
  • Improve specifications, inspection and maintenance approaches, and workmanship practices associated with underground assets (cable, cable accessories, transformers, structures, automation devices, etc.)

Task-Force Roles

The Underground Assets Task Force advises the Distribution Underground Assets Project. This task force is generally staffed by subject-matter experts in underground distribution components, and work practices associated with managing underground system, both urban and URD / UCD.

This task force meets several times per year by WebEx or in person. There is usually one in-person meeting per year held in conjunction with the other P180 task forces. The in-person meeting is normally held in either Lenox, MA, or Charlotte, NC.

Members are encouraged to participate in several ways:

  • Attend task-force meetings
  • Review and comment on reports and findings
  • Provide materials for testing or evaluation, including new, aged or failed underground devices
  • Provide information on your company’s standards or practices (a survey for example)
  • Provide data for analysis, including asset and asset performance data
  • Attend testing at EPRI laboratories
  • Present to the task force on company issues or initiatives

This task force is also a good opportunity to meet peers at other participating companies, and collaborate to address common challenges.

Common Questions

Who can attend task-force meetings?

  • Task-force meetings are for funders of the appropriate P180 project. This includes task-force members and guests from sponsoring companies.

Are there specific membership requirements?

  • The only requirement is to fund P180.002, Underground Assets. Membership is rather loose. There are no meeting attendance requirements.

How do I join this task force?

Can my company have more than one task-force member?

  • Yes.

Can I share task-force material within my company?

  • Yes.

Can I share task-force material outside my company?

  • Generally not. There are exceptions, so if you have a need, please contact Josh Perkel.

Are discussions covered by a non-disclosure agreement?

  • Yes. All EPRI member agreements include non-disclosure clauses.

If my company isn’t funding this, how can I sign up?

  • Each company has their own methods for selecting components of the annual EPRI research portfolio. If my company isn’t funding this, how can I sign up? Technical advisors from EPRI’s member services can also help. Find contact information here.

Supplemental Projects

EPRI participants can engage EPRI with supplemental projects. When a company funds EPRI annual research, 25% of the funds are set aside as self-directed funds (SDF). Utilities can use this to fund supplemental projects. Options for these projects can include:

  • Field pilots of technologies
  • Integration of research results
  • Teardowns of failed equipment
  • Test specific equipment or scenarios

Collaborative Supplemental Projects

Structure Underground Structure Monitoring -Guiding Alarm Settings and Monitor Deployment

As underground cables and components degrade, they can generate a variety of gases from chemical reactions caused by heating, overheating, arcing, and general aging. These gases may be combustible and, should the presence of these gases not be identified, can build up and lead to an explosive event which can endanger the public, utility workers, and damage equipment.


This research is expected to increase industry understanding of combustible gas behavior in underground structures to inform detection sensor placement within the structures, required sensitivities, and alarm settings.


Findings from this research will enable utilities to better leverage underground structure monitoring technologies to identify precursor conditions of underground structure events, enabling them to respond and minimize or prevent these events from occurring, and increase public safety.
Structure Evaluating Remote Inspection Technologies for the Underground Structures

This project is aimed at providing the industry with information to: 1) understand and compare the technologies that can be leveraged to remotely ascertain conditions in UG structures, including technology for creating a visual capture of the UG distribution system, 2) explore how the information captured by different technologies can be applied and the potential benefits and limitations associated with each approach and 3) understand the potential to remove workers from hazards while still performing necessary inspection and assessment activities.

For more on supplemental projects, see here. To discuss project ideas, please e-mail Josh Perkel or Nigel Hampton.

Implementation Opportunities

Supplemental projects can also be one-on-one efforts. Companies allocate their self-directed funds in different ways. Options for these projects can include:

  • Field pilots of technologies
  • Integration of research results
  • Teardowns of failed equipment
  • Test specific equipment or scenarios

Examples related to current research could include:

  • Forensic examination of particular UG components
  • Testing performance of a cable accessories in a submerged environment

Services and Capabilities

EPRI has several capabilities available to utilities as part of research work, supplemental projects, or service agreements:

  • Arc-flash testing of equipment
  • Forensics and material analysis of equipment failures
  • Custom tests of Underground components
  • Full-scale testing of UG structure events
  • Evaluation of online condition monitoring equipment

Other EPRI Underground Research

EPRI research related to distribution underground assets in several other areas.

TASK FORCE

P36 Underground Transmission

Portfolio

Underground transmission systems consist of extruded and laminar dielectric cables and accessories.

This program intends to assist utilities in resolving challenges related to design, construction, installation, operation, and maintenance of underground transmission systems. Cross-cutting research addresses issues such as design calculations, cable ratings, and inspection technologies.

Research specific to extruded dielectric cable systems focuses on cable thermo-mechanical behaviors, sensing and monitoring, and component and system aging characteristics. Research specific to laminar dielectric cable systems is concentrated on cable and system diagnostics, buried steel pipe corrosion, and failure root causes.

One project is designed to focus on principles, experiences, and knowledge capture for transmission cable engineers of utilities installing or considering underground transmission lines.

The HVDC Land and Submarine Cable Systems project addresses the emerging issue of grid integration and interconnections and long-distance transmission from remote renewable energy generation sources.

Program 180: Distribution Systems

Research into automated underground devices is also occurring in P180.003, Distribution Automation project.