OKLAHOMA CITY – Even after a destructive ice storm, Public Service Co. of Oklahoma rarely buries electric lines. As a general rule, PSO buries power lines “to address specific operational issues such as voltage or capacity issues,” said Stan Whiteford, the utility’s region communications manager.
As an example, several years ago PSO had a section of line in Bartlesville that was in an older established neighborhood full of mature trees. An undersized substation served that area, so, “We needed to upgrade the circuit,” Whiteford said.
To perform that upgrade, “The answer was not to go into the back yards,” he said. “Those overhead lines were in a forest.” Instead, PSO buried the power lines in front yards, “where they are much more accessible.”
Placing electric lines belowground is not usually cost-effective “on a wide scale,” Whiteford said.
“We do an occasional conversion from overhead to underground when needed to improve voltage or capacity,” he said, “but not solely for aesthetics.”
A study performed 12 years ago by the Oklahoma Corporation Commission estimated the cost of burying all electricity transmission and distribution lines in this state at $57.5 billion. That figure is more than seven times greater than the $7.7 billion state budget the Legislature adopted for the current Fiscal Year 2021, and almost nine times greater than the 2020 fair cash value of all public service electric companies in Oklahoma.
2007 ICE STORM LED TO STUDY: AERIAL VS. BURIED
A brutal three-day ice storm in December 2007 interrupted electric service to more than 600,000 homes and businesses across the state – many for several days and some for more than a week – and was blamed for 29 storm-related deaths.
Consequently, the Corporation Commission performed a study in 2008 that compared the cost of burying power lines versus over-head electric lines.
The commission staff gathered information from the state’s two largest investor-owned electric utilities, PSO and Oklahoma Gas & Electric Co., from the Office of Emergency Management, and from Edmond Electric. The commission’s Public Utility Division staff also requested data from all retail electric utilities and cooperatives operating in Oklahoma.
The staff also met with members of the Oklahoma Climatological Survey to discuss the impact of severe weather conditions and the frequency of such conditions, which will likely continue to have a negative impact on Oklahoma’s electrical plant and Oklahoma customers.
The commission’s review included a study performed by the Edison Electric Institute and other studies completed for and by the states of Florida, Maryland, North Carolina, Virginia and Michigan.
Information also was gathered from the Oklahoma Insurance Department, the Oklahoma Tax Commission, the Highway Traffic Safety Office within the Department of Public Safety, and from Oklahoma Forestry Services within the state Department of Agriculture, Food and Forestry.
Information collected from the various in-depth studies that were analyzed “clearly indicated that requiring electric utilities to underground all of their facilities is generally not a feasible solution,” the Corporation Commission concluded. The cost to install all transmission and distribution facilities underground would soar into billions of dollars, and the potential impact on customers would be significant.
AERIAL FACILITIES SUSCEPTIBLE TO SEVERE STORMS
Overhead electric facilities are generally hit hard by severe storms, but the most widespread damage happens when severe icing occurs along with high winds. That ice weighs 57 pounds per cubic foot.
When ice develops on an overhead line during high winds, the ice forms into the shape of a “wing” and gives “lift” to the electric line, causing the line to start moving. In more extreme cases, electric lines will move severely up and down, which is referred to as a “galloping line.” The combination of the heavy ice and wind creating movement in overhead electric lines is often sufficient to snap the supporting poles and causing outages to customers.
PSO reported having to replace approximately 250 utility poles and 713 cross-arms, along with more than 89,000 feet (approximately 17 miles) of electric lines, because of the three-day ice storm in October.
Federal law allows cooperatives to receive Federal Emergency Management Agency assistance for such storm losses.
Electric utilities, though, are unable to insure their power lines from storm damage. The private insurance industry — following cataclysmic losses in Hurricane Andrew and other wide-spread storms — has stopped writing affordable policies to cover catastrophic weather-related losses sustained by electric utilities.
“This information was provided through telephone interviews with numerous insurance providers and utility risk managers,” the Corporation Commission said.
POTENTIAL BENEFITS OF BURYING LINES
Potential benefits of placing power lines underground would include:
• improved aesthetics, by eliminating unsightly aerial lines and poles (although all utilities that share space on a pole with a power line, such as cable TV and internet providers, must coordinate efforts and bury their lines, too);
• less damage to facilities, resulting in fewer outages from wind, rain and ice storms;
• fewer lost electricity sales, day-to-day and after storms;
• fewer damages caused by animals (such as the grass fire Sunday near Medicine Park that was sparked by a squirrel on an electric line);
• significantly fewer outages with underground electric circuits than with aerial power lines;
• reduced vegetation management costs (from trimming overhanging tree limits). Information the Corporation Commission staff received from investor-owned and regulated electric cooperatives indicated the utility companies spent an estimated $63 million in 2007 on vegetation management.
DISADVANTAGES OF BURIED LINES
• In 2008, the cost in Oklahoma would have ranged from an estimated $8,800 per person to bury just electricity distribution lines, or $16,600 per person to place both transmission and distribution lines underground. At that time electric utilities and cooperatives indicated Oklahoma had approximately 8,551 miles of main distribution lines and about 34,600 miles of lateral distribution lines.
• Burying high-voltage transmission lines costs 10 to 14 times as much per foot as overhead conductors (wires). The cost is affected by the voltage of the line and the project location: whether the line is placed in an urban, suburban or rural area, and whether the site has soil consisting of sand or clay or if the line must be trenched through rock.
• Although electric lines are buried at least 48 inches below ground, the possibility of cutting a power line during routine excavation activities increases, and the risk of injury or death from such an event is high. “Dig-ins are extremely hazardous to heavy-equipment operators as well as to backyard gardeners,” the Corporation Commission staff noted.
• In some cases, higher voltage lines must be placed in concrete-encased conduit to protect them from excavation damage and possible injury or death from dig-ins. Typical trenches for high-voltage lines are 5 to 8 feet in depth and 4 feet in width, officials said.
• Underground cable is much thicker and heavier than overhead conductors designed to carry the same amount of power.
“The expensive design is necessary to minimize damage from water and to meet insulation and heat dissipation requirements,” the commission staff wrote.
• Finding and repairing failures in buried transmission lines usually consumes “considerably more time” than it takes to repair an overhead power line, the commission staff reported.
All studies indicated that underground power lines have fewer outages per mile than overhead lines, but when an outage does occur “it undoubtedly takes longer to repair” if the line is buried, the commission staff reported.
• Since a transmission line affects far more customers than a lower voltage distribution line, any problems from an underground transmission line “will result in vastly more customer outage hours” than will a distribution feeder line.
• Life expectancy of buried power lines may be less than that of overhead lines, “so future replacement costs will likely be higher with under-ground facilities.”
During discussions with PSO and OG&E, both companies indicated that overhead facilities have a life expectancy “in the range of 50 or perhaps 60 years ... primarily because individual components are easy to replace,” the commission staff wrote. But underground facilities have an anticipated life “in the range of 30 years.”
• Underground costs can quickly inflate with obstructions such as roads, driveways, above and below-grade obstructions including trees, soil stability and rock content, and the presence of other utilities. Also, difficulty in acquiring easements from property owners “could drive the costs” of moving aerial power lines underground higher.
• Moving an aerial power line underground before it has been fully depreciated resulted in a “stranded asset cost”. The Michigan Public Service Commission equated it to “tearing down a house that still has an existing mortgage.”
Regulatory commissions nationwide have tackled this problem the way PSO did in Bartlesville: “by addressing specific parts of the electric grid, e.g., poorly performing circuits, lines along road rights-of-way undergoing construction, all secondary line extensions, etc.,” the Corporation Commission staff wrote.