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Oklahoma Electric Utility Mounts Successful Overhead-To-Underground Program
"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