What is the best choice: underground T&D or overhead T&D?
BY PHILL FELTHAM, Executive Editor
Electricity Today Magazine
Overhead transmission lines used to be the no-brainer choice when it came to the overhead versus underground transmission line comparison. Two decades ago, costs for underground lines were 20 times higher than their overhead counterparts. Therefore, utilities would naturally choose the less-expensive solution. However, that no-brainer choice that existed 20 years ago has become more difficult.
The cost to bury power lines has decreased dramatically. According to the American Transmission Company, costs to install underground transmission lines are now only 2.5 to 10 times the cost of an equivalent overhead line. Consequently, the number of underground power line projects has exploded in recent years and the significant lengths of underground power lines operating in the United States have dramatically increased.
However, the cost to burying power lines still carries a hefty price tag. Many electric utilities, such as Alberta’s AltaLink, are still cautious about pursuing underground power line projects because ratepayers would have to absorb the cost on their electricity bills. According to the Post and Courier, North Carolina investigated the cost of burying the state’s infrastructure and found that electricity rates would increase more than 125 percent. Therefore, most distribution lines serving communities and developments are being placed underground where developers, who prefer these lines for aesthetic reasons, can pay for most of the cost.
South Carolina Electric & Gas Company (SCE&G) recently finished laying a 115,000-volt, five-mile-long transmission line below ground in the suburban town of Mount Pleasant for aesthetics and reliability. The local communities benefiting from the new buried line (Mount Pleasant and city of Isle of Palms) donated either right of ways or deeded property to SCE&G to reduce the overall cost of the $35 million project.
Aesthetics has been the driving factor for many new underground power line projects. Anaheim, California has aggressively been converting their overhead transmission system to, in their words; beautify the city’s streets for years. In general, residents prefer the underground solution because overhead power lines and electric substations are not attractive to the public eye.
Many electric utilities pursuing permits from their public utilities commissions for new overhead power line projects have encountered opposition from nearby residents at public hearings. This opposition, among others, can stall approval procedures and delay construction on new overhead transmission lines for an undetermined amount of time.
Lastly, reliability plays a major part in a utility’s decision to bury their power lines underground. AltaLink states that overhead lines fail more quickly than their underground counterparts. The Post and Courier reports that conversations about installing underground power lines usually occur after a major power outage due to a storm. In these situations, calls for “undergrounding” from elected officials, customers, as well as public utilities commission are common. Underground power lines are protected from the elements (wind, ice and tree damage), which are common causes for outages.
AltaLink points out that, while overhead lines can frequently fail, workers can repair overhead lines more quickly due to accessibility; whereas, underground transmission lines are less accessible, leading to slower repair times that can take days, even months. Another caveat, according to the U.S. Energy Information Administration, is that problems with underground lines are harder to locate and repair. Furthermore, underground lines are vulnerable to flooding, which could result in failure.
THE BOTTOM LiNE
While underground power lines are clearly the ideal choice for most consumers due to their aesthetic benefits, those same consumers have no desire to pay a substantially higher electricity bill to bury their community’s infrastructure. Cost alone makes overhead power lines a more attractive option for utilities.