June 2015, Vol. 70, No.6
Features
Strategic Undergrounding
After hurricanes, tornadoes, ice storms and other natural disasters that disrupt vital infrastructure services by downing overhead power and communications lines, there invariably is the question: “Why don’t they put those wires underground?”
There are two obvious answers:
• Immediately after such disasters the priority is restoring services, not planning and executing projects to convert aerial to underground; and
• It costs too much – funds simply are not available for costly overhead-to-underground conversions.
Of course, much of today’s electrical distribution and telecommunications cable infrastructure is already underground; utility lines have been routinely buried in new developments since the 1970s. However, in older neighborhoods of most American cities, distribution lines remain suspended from utility poles, often in areas with many exposed to mature trees, and these are the lines usually most vulnerable to wind and ice storms.
However, in areas that experience frequent weather-related outages, consumers and regulatory agencies are considering at what point it becomes more cost effective to bury power lines, rather than incur costs of repeatedly repairing and replacing the same overhead infrastructure.
With severe weather affecting much of the country over the past two years, more underground projects are being planned and executed.
For example, Dominion Virginia Power has an impressive underground plan that was initiated in 2014 that ultimately could replace up to 350 miles of power lines per year at an annual cost of $175 million. The first year, 50 miles of conversion were completed.
“By the end of 2015, we should be able to complete 250 miles before we fully roll out our program in 2016,” said Alan Bradshaw, director of distribution, underground.
Fresh perspective
What changed?
“Past studies,” Bradshaw explained, “took an all-or-nothing approach to replacing overhead power lines. For example, a 2005 study by the Virginia State Corporation Commission placed the cost of undergrounding all overhead electric distribution lines in Virginia at $83.3 billion, or about $27,000 per customer. A project of that magnitude would take generations to complete.
“Dominion is analyzing 10 years of outage data to determine which overhead distribution lines throughout our Virginia service area have historically sustained the most damage and repairs. The program will impact our entire Virginia service territory. Initial projects are underway that will help us develop our processes.”
Dominion’s system is made up of high voltage transmission lines that carry electricity from power stations to substations, and distribution lines that deliver the electricity to homes and businesses. The largest of the distribution lines – the main feeder lines – carry power from substations. Tap lines then connect the main feeder lines to homes and businesses. Dominion’s Strategic Underground Program focuses on the tap lines deemed to be the most outage-prone.
Underground lines come into the ground-level pad-mount transformer from below, where connections are kept safely inside and out of view. The location of each pad-mount transformer is ultimately determined by the electric load calculations and the route of the underground lines.
Construction will be minimally invasive.
“To minimize disruption to landscaping,” said Bradshaw, “Dominion plans to use horizontal directional drilling (HDD) rather than open trenching. Directional drilling provides a low impact way to install conduit and cables horizontally underground. A small construction hole will be used as an entrance point for the directional drill to enter. The directional drills used can go out to distances of 500 feet from the single entrance hole. We will work with property owners as we determine the acceptable routing for underground lines. Dominion will also work in partnership with property owners to obtain the rights necessary to perform the work. Property owners along a tap line would have to agree on a plan before it could be implemented.”
Dominion is working with six contractors, who in addition to directional drilling, will also provide design and right-of-way services. There currently are more than 20 HDD crews working within Dominion’s service territory. Drilling is used to install conduit through which cable is pulled through. The equipment used by contractors is able to create pilot holes between 2 and 12 inches in diameter and use several different drill sizes as dictated by the requirements of each job. The number of HDD crews is expected to triple in 2016.
Schedule
Bradshaw said the time required to complete construction will vary among projects.
“Property owners and neighborhood organizations will be advised what to expect throughout the project,” he said. “Once the new underground facilities have been installed, there will be a short, planned outage in order to make the necessary connections. Property owners will be notified in advance of the scheduled outage. An outage to make the final conversion from overhead service to underground would typically be four hours or less.
“Some of Dominion’s system will remain above ground and subject to extreme weather such as high winds and ice storms, so outages could occur,” stressed Bradshaw. “Dominion makes clear there can still be power outages during major storms but the Strategic Undergrounding Program will improve the reliability of the system and shorten the time for restoring service to all affected customers following a major storm.
“However, when this program to underground selected tap lines is implemented, there will be fewer lines to fix and fewer repairs to make on a house-by-house basis. Therefore, it would take much less time to restore service to our customers. We expect by the end of the multi-year undergrounding program, the restoration time following major storms could be reduced by up to 50 percent.”
Funding for this program comes from a special rate adjustment that must be approved by the State Corporation Commission (SCC). The SCC will monitor and implement the costs for the program. Rate adjustments would affect monthly bills of all residential and small commercial customers.
“To ensure the cost remains low for our customers,” Bradshaw said, “we will request a small, gradual increase over time to cover the costs of this program.”
In its preliminary stages, the program has received overwhelming support from customers, he added.
One Urbana, VA, customer wrote to the project manager saying: “We are extremely impressed by the operation. It is important to acknowledge excellence and dedication, and particularly for an endeavor of this scope and purpose. In fairly miserable conditions . . . the team worked extremely hard to bury the cable. Not only did they face poor conditions with great attitude, they were challenged to locate old water pipes, some dating as far back as the late 20s. Throughout the work, the [workers] reflected consideration for the environment, from existing landscaping, to the safety of those of us around.”
FOR MORE INFORMATION:
Dominion Virginia Power, http://www.dom.com/
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