Electric utilities going underground for aesthetics, reliability

Utility workers have finished laying power lines under the ground on Mathis Ferry Road in Mount Pleasant. Once the line is hooked up, they will take down the above-ground power lines and poles. (Brad Nettles/staff)

A new 115,000-volt transmission line will double the electricity supply for the Isle of Palms and Sullivan's Island without adding new power poles to the scenic vista of the Intracoastal Waterway.

Instead, the $35 million, five-mile-long line will go underground, a welcome change for some.

“I think what we would all like is fewer above-ground poles. In this case, we did get the line underground so that we don't see it,” said Isle of Palms City Manager Linda Tucker.

The line will run from Mount Pleasant underneath the marshes and waterway to IOP. It is scheduled for completion by the end of the year.

“It will just increase the reliability. Power to the Isle of Palms and portions of Sullivan's Island as well as northern Mount Pleasant could be restored in minutes, instead of hours or days,” said SCE&G spokeswoman Kim Asbill.

Currently, an above-ground 115,000-volt transmission line runs from Mount Pleasant to Sullivan's Island.

SCE&G told IOP officials that without the new line there is an eventual possibility of rolling blackouts or brownouts because of increased power demand spurred by residential growth on the northeast end of the island, Tucker said.

Across the South and around the country, utilities and communities weigh the issue of whether to bury power lines. Usually, the discussion is spurred by a massive power outage caused by a storm. In such situations, calls for “undergrounding” are common from customers, elected officials and sometimes state utility commissions.

North Carolina investigated the cost of burying the state's power infrastrucure and found that it would increase electric rates by more than 125 percent. In Anaheim, Calif., the city decided to completely convert its system for aesthetic reasons. To minimize the impact on customer bills, the undergrounding of power lines is taking place slowly over 50 years. It is funded by a 4 percent surcharge on electric bills, according to the U.S. Energy Information Administration.

Buried power lines are protected from wind, ice and tree damage that commonly cause outages, but they are vulnerable to flooding and can still fail. Problems with underground lines are harder to locate and repair, the EIA says.

Santee Cooper has two underground transmission lines running two miles to Pawleys Island that provide redundancy in case one line fails.

“It's a whole lot more expensive to go underground. It's never a decision that it is the most cost-effective solution,” said Santee Cooper spokeswoman Mollie Gore.

Avoiding issues with wetlands permitting for above-ground towers is one reason for the work to go underground, she said.

In another underground project, Mount Pleasant and SCE&G are splitting the $830,000 cost of burying power lines on two miles of scenic Mathis Ferry Road.

“The neighborhoods over there are ecstatic,” said Town Councilwoman Linda Page.

Residents had complained that the grand oak trees were disfigured by work done to maintain a path for the powerlines, said Town Administrator Eric DeMoura.

The final phase of the project will start in about a year, he said.

Currently about 77 percent of SCE&G's distribution system and nearly all of its transmission lines are overhead. SCE&G says the frequency of outages on underground systems is 50 percent less than for overhead systems.

On the Isle of Palms, the city donated right of way for the new underground transmission line. The town of Mount Pleasant granted right of way and is deeding property to SCE&G for the Hungryneck power substation that is part of the project.

“These contributions of right of way and property helped to reduce the total cost of the project. The remaining cost will go into SCE&G's asset base and is paid for by customers,” the utility said.

The cost of subterranean power is up to 10 times more than above-ground systems, according to the EIA.

Santee Cooper put in a quarter-mile underground line in Blythewood. A small airport there paid for the work. In Hilton Head, a developer paid for an underground line, Gore said.

Most new distribution lines serving developments and communities are being placed underground. The cost is usually paid by developers, who prefer underground lines for aesthetic reasons, officials said.