December 2017 Vol. 72 No. 12


Unique Undergrounding Program Reduces Outages, Maximizes Response Time

In late August, Hurricane Harvey devastated Houston and other areas in Southeast Texas, leaving more than 750,000 customers without electric power. Immediately after Harvey, Hurricane Irma struck Florida, leaving much of the state and more than 6 million customers in the dark.

Discussions about converting overhead power lines to underground frequently occur after every weather event that downs lines and causes power outages. New power lines have gone underground for decades, and outages from weather-related causes can be significantly less in areas were infrastructure is buried.

“Why don’t they bury them where they’ll be ‘safe’,” is an often-asked question following every major storm-related outage.
But immediately after a major storm isn’t the time to begin planning an undergrounding program – the priority is public safety and restoring services as fast as possible. However, undergrounding is a viable option for many power suppliers, and the number of carefully planned programs to replace aerial infrastructure under the ground is increasing.

Cost always has been the primary roadblock for undergrounding – it costs more to bury power cable than to suspend it from poles. However, considering repeated replacements in storm-prone areas, along with other factors, many power companies are considering ways to go underground in areas with older, established infrastructure.


In Virginia, Dominion Energy has had an underground program underway for several years. Alan Bradshaw, Dominion director of electric distribution-underground, said the company’s Strategic Underground Program identifies the most outage-prone areas with overhead tap lines and targets them for underground placement.

“The goal of the program,” Bradshaw explained, “is to reduce the number of work repair locations required to restore power outages. Our data suggest that converting just 10 percent, or 4,000 miles, of the most outage-prone lines could reduce restoration times following severe weather events by up to 50 percent.”

Since July 2014, Dominion has converted more than 650 miles of outage-prone, overhead tap lines to underground. This includes more than 1,900 individual tap lines across the company’s Virginia service territory.

Bradshaw said legislation passed by the Virginia General Assembly enables investor-owned electric utilities to bury overhead electric distribution lines that are most prone to outages during major storms, and to recover costs for doing so. The law declares undergrounding outage-prone tap lines to be in the public interest and cost beneficial by providing local and system level benefits for customers.

Funding for the program comes from a small rate adjustment called a rider, which must be approved by the State Corporation Commission (SCC) that monitors the costs for the program. The Strategic Underground Program is subject to annual regulatory reviews and approvals by the SCC.
Evaluating the cost

Dominion’s underground program is based on research.

In 2003, Hurricane Isabel left some Virginia customers without power for more than two weeks. Following that storm, Bradshaw said the Virginia Corporation Commission estimated the cost to underground the overhead electric distribution system in the state would be $83 billion. Since that time, costs will have increased.

“When we started to look at the data,” Bradshaw said, “we found that a significant number of outage events occur on the tap line portion of our distribution system.

“Looking deeper, we found that over 60 percent of the outage events that occur on tap lines actually occur on about 20 percent of those tap lines, many located in backyards with heavy tree canopies, exposing lines to damage from trees.”

Such areas are the most difficult and time consuming to repair, frequently requiring additional crews to hand-carry poles, wires and climb poles while bucket trucks and auger trucks are parked on the roadway because they cannot gain access to where the repairs need to be made.

“These labor intensive repairs can sometimes take days and pull resources from other restoration efforts,” Bradshaw said. “Eliminating these difficult-to-repair locations will lead to a significantly more efficient restoration.

“We believe that a program aimed at burying only the most outage-prone tap lines will cost less than three percent of the ‘underground everything’ estimate from 2005.”

Targeting areas

To select which overhead tap lines to convert, Bradshaw said Dominion uses a data-driven process that begins with a review of 10 years of outage data for each tap line. Data is used to develop an events-per-mile metric to ensure selection of a group of tap lines that have the greatest impact for the lowest cost.

”We take this data and then perform a site review to ensure that the tap lines are, indeed, good candidates for conversion to underground,” said Bradshaw.

Horizontal directional drilling (HDD) is used almost exclusively.

“Directional drilling minimizes impact to our customers’ properties,” Bradshaw said. “This installation method, as opposed to open trenching, has been key to customer acceptance and willingness to install underground lines in their area. These projects serve established properties where customers have installed sheds or built fences and planted gardens. The ability to safely install facilities using trenchless technology allows for minimal impact on established properties.”

Construction is being performed by five contractors assigned to seven geographic areas throughout the Virginia service territory.

“Each contractor,” said Bradshaw, “provides design, right-of-way and construction services. While they are installing new underground facilities, they are also securing easements and completing designs for future work. They build their own backlog and in many ways are responsible for their own success. We have been very pleased with our contracted partners. They also have a high regard for the customer experience associated with the program.”

Bradshaw said that as expected, converted tap lines have seen significant improvement in reliability, going from an annual average outage duration of 372 minutes prior to underground conversion, to less than two minutes after conversion.

“As conversions continue,” he said, “we believe we will have a slight decrease in the number of customers impacted while having a significant reduction in the number of work repair locations, so we expect our traditional restoration curve will look different as we complete the program.”

Satisfied customers

Post construction surveys show that Dominion customers are “very” satisfied with the underground program, scoring more than 4.5 out of 5.
“We make it a priority,” Bradshaw explained, “to communicate regularly with customers impacted when securing easements for new underground facilities and to review construction schedules, safety and landscaping once a project is complete.

“We use a variety of communication mediums including letters, postcards, telephone calls and door hangers. We have also created a portfolio of reference pieces on topics such as easements, meter base conversions and how directional boring mitigates impact to tree roots.“

On larger projects, Dominion hosts community informational meetings to review proposed layouts and discuss project schedules.

“We have had an overwhelmingly positive response to easement requests, which is critical to the completion of any project,” said Bradshaw. “We recognized early on that respecting personal property was important to our customers, so we make a commitment to leave private properties at least as good as we found them.

“Because we rely so heavily on vendors to help us with the program, we are very conscientious about sharing feedback with our contractors and hold them to the same standards we hold our own employees.”

Related Articles

From Archive


{{ error }}
{{ comment.comment.Name }} • {{ comment.timeAgo }}
{{ comment.comment.Text }}