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From Overhead to Underground: It Pays to Bury Power Lines

BEADLE COUNTY, SD - On a drive across the mostly flat, seemingly endless prairie of South Dakota, a few features are likely to stand out – the road ahead, the vastness of the land and sky, and the rhythmic repetition of power poles next to the road. Throughout the state, overhead lines deliver electricity to cities and farms, providing power for people’s livelihoods and personal lives and helping to keep livestock healthy and productive.

As widespread and vital as the overhead power lines are, they also are vulnerable, particularly during tornadoes, ice storms, and severe winter weather. Constant vibrations caused by wind or the weight of ice alone can exert enough pressure to break power lines or bring down poles. When the two forces are combined, the effects are multiplied.

“While we’re trying to keep the lines in the air, Mother Nature is trying to get them on the ground,” said Lynn Kruse, manager of operations for Dakota Energy Cooperative, one of approximately 28 such organizations in the tate. “Occasionally she wins; most of the time we win.”

Following a 1996 severe ice storm, Dakota Energy, a non-profit cooperative, used funds available through the Hazard Mitigation Grant Program (HMGP) of the Federal Emergency Management Agency (FEMA) to bury a 5.5-mile segment of line in Beadle County just west of Huron. The cost of the burying the line was approximately $11,570 per mile, for a total cost of $57,850. The HMGP paid 75 percent of the cost, or $43,387, while Dakota Energy paid the remaining $14,463. The project was part of a larger strategy to bury select power lines.

Following presidential disaster declarations, the HMGP provides funds for long-term measures that reduce future disaster risks. The purpose of the program is to reduce the loss of life and property due to natural disasters and to enable mitigation measures to be implemented during disaster recovery. The state administers the grants and selects projects for funding, which must be consistent with FEMA-approved state and local hazard mitigation plans.

Farmer Rodney Liebnow remembers the 1996 ice storm. He was helping to herd 30 to 40 yearling calves from the pasture into a barn when he saw poles leaning in the distance. The poles bowed about three times and then they snapped and fell over.

“We heard a crack and it was like dominoes coming down,” he said. “They started breaking all at once. It was really odd.” Lines came down in every direction.

The segment that Dakota Energy buried after the 1996 storm provided direct service to 59 people in 17 homes, a small portion of Dakota Energy’s approximately 2,400 patrons with 3,460 meters in seven counties. However, it was a main feeder line. Users included chicken confinements and the Liebnow family’s milking barn, as well as one person with special needs.

The storm occurred during pheasant season, and a group of Minnesota hunters who came every year to the Liebnows’ farm were there. Most of the hunters were in the flooring business, but the lone electrician in the party helped the Liebnows set up their generator, using a tractor, so they could milk their 80 to 90 dairy cows. “That really saved us,” Liebnow said, adding that the hunters stayed in a Huron hotel that had not lost power.

The generator, which ran for about two weeks, was an expensive temporary solution. After paying for about 300 gallons of fuel to run the generator for two weeks, Liebnow said, “I told the cooperative I’d never complain about an electric bill after that.”

Despite the expense, Liebnow feels he was luckier than those who did not have generators. “Their houses were freezing up and they had to find other places to stay,” he said. “They didn’t have generators and there was no way to run furnaces or thaw pipes.”

After the power line was buried, storms continued with events that were severe enough to result in presidential disaster declarations for Beadle County in 2001, 2005, and 2007. But with the power lines buried four feet below the ground, neither these events nor others caused significant damage to the lines. A tornado in August 2006 resulted in no damage or disruption of service. “Obviously, a tornado can’t get at a line that’s underground,” Kruse said. After a 2008 heavy snow, the only damage was on an overhead line that was fed from the underground line. It included broken conductors, broken ties on insulators, and other minor damage.

In light of the frequent storms, burying the line proved to be a good investment. Installing underground lines costs more initially than overhead lines, but the underground lines are less prone to damage and disruptions, and maintenance is less expensive. In early 2010, Kruse roughly estimated the cost of installing one mile of overhead line might be $18,000, compared to $24,000 for one mile of underground line. He explained that the cost for the underground wire fluctuates because it is tied closely to the costs of metals that are used for the wire and petroleum products that are used in the insulation.

In addition to sharing the cost for burying the line west of Huron, Dakota Energy budgets for new underground cable each year, selecting segments based largely on their cost effectiveness.

“For the majority of new homes, we can justify the underground lines,” Kruse said. On the other hand, the utility is unlikely to install underground lines where development is sparse. “If you put in underground line and the load disappears, that line would most likely be abandoned,” Kruse said.

At any rate, the underground line would have paid for itself in just two damaging weather events. If the overhead line had been in place and damaged during all of the weather events after 1996, the cumulative cost of replacing it after each storm would have been far greater than the cost of burying it once.