These areas are the most difficult and time-consuming to
repair, frequently requiring additional crews to hand-carry
poles and wires and climb poles while bucket trucks and auger
trucks are parked on the roadway because they cannot access
the locations where 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.”
Costs of undergrounding
In 2003, Hurricane Isabel left some customers without power
for two weeks. The Virginia State Corporation Commission
estimated the cost to underground the overhead electric distribution system in Virginia to be $83 billion. Bradshaw said
that cost has increased since then, especially when considering the advances in automated equipment currently used by
“Tap lines generally have fewer wires, smaller wires and
certainly less automation than main feeders,” he said. “So, we
shifted our focus from burying all distribution lines to concen-
trating on those that were most outage-prone. We believe that
a full-scale strategic underground program aimed at burying
only the most outage-prone tap lines (or approximately 4,000
miles) will cost about $2 billion, or less than 3 percent of the
‘underground everything’ estimate from 2005.”
To select areas to convert, Dominion Energy uses a data-
driven process that begins with a review of 10 years of outage
data for each tap line. The information is used to develop an
events-per-mile metric to ensure the 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,” Bradshaw said.
Horizontal directional drilling (HDD) is heavily used.
“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
Most of the cabling in Dominion Energy’s
undergrounding program is installed by
horizontal directional drilling.