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.
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.
“We place a 2 by 2 by 3 foot, pad mount transformer every three or four houses,” said Whiteford. “We directionally drill services to each house and replace existing meters with RF meters which are read from the street. When a neighborhood is complete, we never have to go in the back yard again. All future repairs can be made in the front. Whether the access service point is a transformer or flush mount pedestal, repairs are much quicker with less impact to the homeowner. No worry about downed lines, no locked gates, no dog bites.”
During planning stages of the reliability improvement program, PSO evaluated neighborhoods to identify the best candidates for replacing aerial lines underground.
“Most of those selected,” he explained, “are older neighborhoods, usually with many old, large trees. In looking at the process we identified between 700 and 800 miles of overhead distribution cable that converting to underground would have a significant impact to improving reliability.”
Criteria considered when targeting areas included:
• Accessibility – Without alleys in the city, back yards can be difficult to access for repairs;
• Terrain – Is it conducive to directional drilling? Planners wanted to utilize this technique and avoid trenching; and
• History of reliability.
“For the first underground conversion,” said Whiteford, “we selected an area that was reasonably representative of the city – one where trees were causing problems, but not one of the worst areas in terms of reliability problems. It was a good starting point.”
Considering all factors, Whiteford said PSO is pleased with progress.
“We have converted more than 70 miles of aerial cable to underground,” he said. “We believe we are getting better at it as we proceed – engineering is more nailed down, contractor crews are more efficient.”
PSO currently uses three contractors for underground conversions, all working on a turnkey basis. In some instances, contractors make connections and perform other tasks in addition to burying cable.
“Much of the time is spent coordinating with other utilities and the city,” continued Whiteford. “Existing utilities must be located and marked. Typically, natural gas lines are in the back yards, so they are not an issue for work we do in the front. Soil conditions are suitable to directional drilling. We have encountered rock in a few areas, but for the most part, drilling is not difficult.”
Paying for the program
The OCC has provided PSO a mechanism for the raising the $20 million per year for the capital investment in the underground program.
Whiteford said costs are submitted to the commission quarterly and must be reviewed and approved before customers are billed. The cost per month for the overall reliability program, including tree trimming on a four year cycle and conversions to underground, is about $2 per month with less than half that amount going to underground costs.
Whiteford said feedback to PSO is that most residents are pleased with the underground conversions.
“We had complaints in two neighborhoods where residents objected to the placement of boxes in the front yard,” he said. “In one area, property owners mounted a ‘Stop the Box’ campaign, urging the boxes be placed in back yards.”
Plans for converting both areas to underground were dropped.
As planned, PSO’s conversion program will take 25 years to complete. However, company representatives have advised the commission that the time could be reduced by approximately half if a proposed accelerated program is approved. The additional cost to accomplish that would be initially adding 25 cents to monthly bills.
PSO is a business unit of American Electric Power.
FOR MORE INFORMATION:
Public Service Company of Oklahoma, (888) 216-3523, www.psoklahoma.com