Is it time for you to consider undergrounding some of your distribution lines?

worker and green grass
Workers plan to underground a tap line to a home in Virginia as part of Dominion Energy's Strategic Undergrounding Program. Credit: Dominion Energy.

Two North American utilities are burying more than 6,000 miles of power lines combined. Project managers from each one describe why they did it, how they did it, and what lessons they have learned along the way.

Utilities are in the business of providing reliable, affordable electricity service to customers but what happens when there is an area that just keeps getting pummeled with storms and reliability can’t be improved? For both Dominion Energy and WEC Energy Group, that’s when strategic undergrounding came into play.

Undergrounding transmission and distribution wires has historically been so cost prohibitive that utilities dismiss the idea before even exploring it. But that’s a mistake, says Mike Beehler, PE and spokesperson for the Power Delivery Intelligence Initiative (PDII).

“Engineers and planners need to evaluate overhead and underground and no longer work under the assumption that there is a rule of thumb that says, ‘Underground is just too expensive. I’m not going to evaluate it,” said Beehler in an interview.

“It’s the 21st century [and] we’re not building transmission and distribution lines like our grandfathers did on the legacy grid,” he added.

Underground VS Overhead: Power Line Installation-Cost Comparison and Mitigation

Indeed, the cost to bury electricity lines has fallen and new technologies make power lines not only easier to bury but also more robust once in the ground. Those lower costs and improved technologies are what led both Virginia’s Dominion Energy and Wisconsin’s WEC Energy Group to embark on decade-long projects to seriously increase reliability in hard-to-harden areas.

Dominion Energy — Strategic Undergrounding

For Karen Kinslow, Director of Electric Distribution Grid Resiliency at Dominion Energy, the decision to go underground with some of its wires was actually prompted by the state legislature. Frustration with extra-long customer restoration times (sometimes up to 14 days) following storms, hurricanes, and even a derecho led the state government to ask Dominion Energywhat else they could be doing to speed up electric recovery.

“So, one of our VPs said ‘Look OK, we can’t do everything but we can do something.’”

That’s where the utility came up with the term ‘strategic’ undergrounding. The plan was to dig into the outage data and try to determine where putting wires underground would really affect restoration time.

“Back lot was big,” said Kinslow, “you built it [the electric overhead wires] then you built the house and now we can’t get our truck to it so that takes longer to restore,” she explained.

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After looking over a lot of data (all Excel, said Kinslow), and running scenarios on number of minutes out or number of customers out, the utility eventually landed on a metric of outages per mile.

“We focused on tap lines (other companies call them laterals) and we found that if we converted 20% of our overhead taps to underground we could cut our customers’ outage time by half after a multi-day storm,” she said.

Legislative Support

Because Dominion Energy’s underground proposal was spurred by the state legislature, the state itself passed a law allowing the utility to recover some of its costs for the program via a small rate adjustment called a rider included on customer bills. An excerpt from the Virginia Electric Utility Regulatory Act is below:

“The replacement of any subset of a utility’s existing overhead distribution tap lines that have, in the aggregate, an average of nine or more total unplanned outage events-per-mile over a preceding 10-year period with new underground facilities in order to improve electric service reliability is in the public interest. 

“That is one way we are different from other states,” explained Kinslow, we do get a rider on top of the base rates.”

“As long as an area has so many outages per mile and we can eliminate them, then it’s deemed in the public interest and has to be approved,” she explained.

Dominion Energy’s Program

The project, which began in 2014 will likely run through 2028 according to Kinslow, will eventually result in about 4,000 miles of overhead distribution lines being converted to underground. Dominion Energy has been averaging about 300 miles per year and has completed about 1,700 miles of undergrounding already.

What’s great she explained is that it is already showing results. These days when a storm rolls through and knocks out power, Dominion Energy can see which devices went out and note whether they are on the list to be undergrounded or not. This is giving the team the peace of mind knowing that they are hitting the right spots.

The total cost will be about $2 billion for the 4,000 miles of underground taps, she said.

Wisconsin Public Service – System Modernization and Reliability Project

It was improvements to cable and drilling technology coupled with rising vegetation management costs that led WEC Energy Group’s utility subsidiary, Wisconsin Public Service (WPS) to consider undergrounding, according to Paul Gogan, Director of Electric Distribution Asset Management for WEC Energy Group.

“We saw that a lot of the construction techniques had changed with directional drilling and trenching and boring and we realized that we could do underground lines in a much more cost-effective manner,” he said in an interview. Further, there were parts of its service territory that just weren’t seeing the reliability improvements the company wanted.

“We weren’t able to make a game-change on it,” said Gogan.

In order to gain approval for the project the utility commission told WPS to survey customers to see if and how much they would be willing to pay for better reliability. And lo and behold, the vast majority of customers said they were willing to pay more on their electric bill for reliability improvements. The utility estimated that the average residential customer would experience an approximate increase of 5% or $4.30 per month. Surprisingly, even customers who did not have service interruptions in the previous year were willing to pay more for the utility to make upgrades.

With approvals in hand, WPS began the 8-year $425 million project to underground 1294 miles of overhead lines with 1629 miles of underground circuits. Part of the project included automating mainline circuits to provide fault location, isolation and service restoration (FLISR) capabilities.

Like the Dominion Energyproject, WPS decided to underground the tap lines and keep the main line overhead. Locations were determined based on customer minutes of interruption (CMI). Currently in the last year of the project, the project has resulted in a 97% reduction in outages for customers.

Communications are key

Keeping customers informed about the project was key for both WPS and Dominion. Gogan explained that WPS took lessons learned from other utilities who had undertaken similar projects in the past. Using those learnings, WPS said they would cover the cost of bringing the wires to the customers’ home.

Workers meet with homeowners in Virginia as part of Dominion Energy’s Strategic Undergrounding Program. Credit: Dominion Energy

“It was a one-time opportunity,” said Gogan, adding “they had to decide and commit to it because they couldn’t go back say two years later and say now they wanted it.”

That’s what got the ball rolling, said Gogan. He said the utility started fielding calls from customers who weren’t even in the undergrounding area but still requested the utility bury their lines.

Kinslow echoes the fact that keeping customers informed is incredibly important. “We look at this as a customer program,” she said, “so communications are the cornerstone of everything we do.”

For Dominion, that means there are always two dedicated points of contact for customers wo are part of the undergrounding program. It’s their job to make sure the communications are going well and that there are no surprises for customers.

“It’s a big deal,” she said.

WPS also needed to make sure that customers were satisfied with the project, per the original order from the utility commission. In addition to surveying customers before the project began to see if they would be willing to pay for it, the commission asked WPS to survey customers afterward to make sure they were happy, which they did for a few years.

“Eventually the results were all so glowingly positive that we didn’t have to do surveys anymore,” Gogan said.

Mike Beehler, Karen Kinslow and Paul Gogan will be participating in a panel discussion on this topic during September’s DISTRIBUTECH+ series. The session, Strategic Undergrounding: A Panel Discussion, will take place on September 29 from 11:30-12:15 Central. Learn more and register to attend here.

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Jennifer Runyon is a Content Director at Clarion Energy, writing, editing and posting content on POWERGRID International and planning conference sessions for DISTRIBUTECH's live and virtual events. She as the conference advisory committee chair for DISTRIBUTECH International. You can reach her at

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