Introduction to the distribution underground assets project

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 produce results that support utility managers in addressing these challenges, including the knowledge to better acquire, maintain, and optimize underground distribution infrastructure. These results can improve the industry’s understanding of the expected performance, failure modes, and service life of underground assets. Key focus areas include:

  • Understanding asset aging and degradation mechanisms to inform asset specification, diagnostic, and maintenance approaches
  • Identifying effective inspection, assessment, and maintenance approaches to understand asset health, extend asset life, and inform investment decisions
  • Identifying, capturing, and sharing key practices and knowledge for managing underground distribution systems


This objective of this research is to produce results to support utilities as they manage underground distribution systems, where the challenges include dealing with aging plant, assessing asset health and performance, improving specification and selection, and understanding and leveraging new technologies. This research also emphasizes knowledge capture and transfer to address the challenge of maintaining expertise in managing underground distribution systems.

Results take the form of reports, online repositories, and guidebooks, including periodic updates to the Underground Distribution Systems Reference Book (The Bronze Book).


Research 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, and webcasts

2022 Research Tasks

Underground Asset Health and Performance

  • Underground Switch Forensics: This research investigates medium-voltage underground switch life-cycle performance. The research includes analysis of new, field-aged, and damaged units, as provided by utilities, to better understand degradation and failure modes. Research results can inform equipment specifications and inspection and maintenance approaches, reducing the likelihood of failure and aiding utilities in optimizing the life-cycle performance of these devices. Results from this research can reduce system operating costs and enhance reliability.

  • Cable and Cable Accessory Forensics: This research task will investigate cable and cable accessories, including joints, terminations, and separable connectors, to understand their life-cycle performance. Forensics may be performed on aged/failed units supplied by utilities, or on new components, subjected to accelerated aging to expose degradation and failure modes. Findings can be used to inform equipment specifications, inspection and maintenance approaches, and workmanship practices, resulting in reduced system operating costs and enhanced reliability.

  • Infrared Thermography: This task will investigate thermography for underground systems and cable accessory diagnostics, including research aimed at informing trigger points for action. Planned activities include development of an energized test bed for examining heating in medium voltage components under different conditions.

  • Monitoring of Network Transformers: In 2021, EPRI completed initial testing of a single gas (H2) submersible dissolved gas analysis (DGA) monitor. In 2022, EPRI will continue to research network transformer monitoring and investigate trigger points for action associated with monitored conditions.


  • Manhole Events: This research focuses on understanding the causes of manhole events, determining methods to identify precursors to such events, and assessing various event mitigation systems. In 2021, research included testing of new and aged low-voltage cable systems to understand the types of gases formed when cables are subjected to overheating and arcing. For 2022, EPRI will continue testing to understand gas production associated with low voltage cable systems, and research combustible gas production rates associated with selected causes, including arcing. Results could inform selection and placement of monitoring systems to identify manhole event precursors.

  • Inspection: This research will explore practices and approaches for performing corrosion inspection and assessment of padmounted equipment. The use of AI / image processing technology to aid inspectors will be explored.

Knowledge Capture and Transfer

  • Underground Distribution System Practices: This research is focused on identifying, assessing, and sharing industry underground practices. To share practices, EPRI has developed an online application that houses results from over ten years of peer practice information gathered from EPRI targeted investigations (called “immersions”), and surveying. For 2022, EPRI will present the content of the Practices Repository through the Distribution Resource Center (DRC), Distribution.EPRI.com.

  • Bronze Book: For 2022, EPRI will produce an update to the Underground Distribution Systems Reference Book.

  • Network Reference: For 2022, EPRI produced The EPRI Low-Voltage Secondary Network Systems Reference Book (Network Reference), a comprehensive, stand-alone reference on network systems, a design type that utilizes a meshed or “networked” secondary system supplied by multiple primary feeders.

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 accomplish the following:

  • Improve specifications, inspection and maintenance approaches, and workmanship practices associated with underground switches and cable accessories
  • Enhance strategic intelligence on emerging technologies
  • Increase engineering staff expertise in underground distribution
  • Improve the quality in underground distribution system design
  • Lower underground distribution maintenance costs
  • Gain more accurate and timely knowledge about asset condition and life expectancy
  • Improve system reliability and safety and reduce environmental impacts

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 John Tripolitis.

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

New Supplemental Offering

  • Underground Structure Monitoring Guiding Alarm Settings and Monitor Deployment

    Please view the following links for more information on the project: PDF | PPT

Supplemental projects can be one-on-one efforts, or projects can be collaborative. Companies allocate their self-directed funds in different ways. Please contact your METT for more information.

For more on supplemental projects, see here. To discuss project ideas, contact John Tripolitis.

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.

For more on supplemental projects, see here. To discuss project ideas, please e-mail John Tripolitis.

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

Other EPRI Underground Research

EPRI research related to distribution underground assets in several other areas


P36 Underground Transmission

Cockpit | 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.

41.05.02 Plant Engineering (Nuclear Sector)

Cockpit | portfolio

The Plant Engineering Program performs research to inform decisions related to the continued safe, reliable, and efficient operation of nuclear power plants. Research activities address key equipment issues and the effectiveness of plant engineering programs. Active and ongoing research includes but is not limited to: component aging and mitigation (flow-accelerated corrosion, electric cables, buried piping, cathodic protection, nuclear grade coatings, electric relays), system reliability (offsite power, emergency power, single point vulnerabilities), plant performance (heat exchangers, transformers, service water system, plant thermal performance), and other engineering and operational support areas (procurement engineering, seismic qualification, workforce and skills development). The program also supports technology transfer through technical assistance programs, user groups, interest groups, and training.

Program 180: Distribution Systems

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