Oklahoma Electric Utility Mounts Successful Overhead-To-Underground Program

By Jeff Griffin, Senior Editor | September 2008 Vol. 63 No. 9
Most power cable in the Public Service Co. Of Oklahoma’s conversion to underground program uses HDD for installation. (Photo cou

The Public Service Co. of Oklahoma (PSO), provider of electricity for metropolitan Tulsa and portions of eastern and southwestern Oklahoma, has an ongoing program to replace aerial distribution lines with underground cable in selected neighborhoods in its service area.

The underground conversions are part of a reliability improvement program that includes trimming tree limbs around power lines on a regular basis.

To date, PSO has completed conversion or construction is under way to convert aerial to underground power lines in more than 30 neighborhoods, most in the Tulsa metropolitan area, said PSO spokesperson Stan Whiteford. In addition, conversion programs are under way in McAlester and Weatherford with work scheduled to begin on another program in Lawton. A neighborhood in Bartlesville is expected to be added to the list soon.

Whiteford said anecdotal information from the severe ice storm of December 2007 indicates areas where conversions are complete experienced fewer outages and that for those where power was lost, it was restored sooner than other neighborhoods.

Cost always is a primary factor when utilities consider aerial to underground conversions.

Costs

Whiteford said average cost of conversions completed by PSO is approximately $580,000 per mile, a significant expenditure, but substantially less than the "$1 million per mile" figure often cited by utilities, sometimes to justify not undertaking aerial to underground projects.

Proponents for burying more power cable point out that this figure often is presented out of context and that the $1 million a mile estimate or citing other "average" costs, usually do not reveal specifically what is included in the estimate. Every project is different, and actual costs are influenced by many factors.

PSO conversions leave feeder lines on poles and replace back lot aerial laterals and service lines with new underground cable at the front of the property. Most underground cable is buried primarily by horizontal directional drilling which limits the amount of excavation required and reduces surface restoration needed after cable is in the ground.

"Because feeders usually are on poles along street right of way and are easy to access, they are not buried," explained Whiteford. "The problems in areas we convert relate directly to heavy tree growth and difficulty accessing rear lots."

Laterals are buried in front right of ways, usually within eight feet of the curb.