Omaha Public Power District (OPPD) is in the midst of a comprehensive review of undergrounding its power lines.
The review began earlier in 2021 but its importance was underscored July 10 when a severe thunderstorm left 188,000 customers of the Nebraska public power utility without electricity.
Initially, the study was a way to evaluate least-cost methods of construction for new and rebuilt facilities. OPPD has studied undergrounding in the past, but “as materials and construction methods evolve it’s a good effort to revisit,” Guy Lucey, manager of distribution engineering at OPPD, said via email.
“Comparing the entire life-cycle cost of overhead and underground facilities gives direction on how OPPD should move forward as our system continues to grow,” Lucey said. “Initial studies have shown that there are cases where underground cable has a lower lifecycle cost than overhead conductor.”
Lifecycle includes the upfront cost of installation, maintenance over the expected life, tree trimming costs, locate costs, attachment income, outage performance, and cost to replace in the future.
The undergrounding study draws on different areas of the utility. “We approached it from many different directions including Engineering, Planning, and Maintenance,” Mike Herzog, manager of distribution planning at OPPD, said via email. As the project expanded into more of a case study approach, “our Land Rights team was specifically engaged to bring in their expertise,” Herzog said. “This ended up being a really critical step because it established that areas of the service territory may have differing levels of documentation.”
The review applies to all neighborhoods and portions of the system, but areas of particular impact are the more established parts of OPPD’s service territory that tend to be built with overhead construction and now have mature trees and landscaping.
“Almost all new residential and commercial developments in our metro areas are being constructed underground,” Lucey said. “We’re really looking to understand what underground facilities would look like in dense areas that were initially constructed with overhead facilities.”
OPPD is approaching the undergrounding cautiously. It can be expensive, and it is not always a cure-all solution. The study is still in its early stages but, as expected, “the upfront capital cost and resource commitment to execute something looks to be very high,” Herzog said. A large-scale rollout of undergrounding “would represent a significant commitment by OPPD over a decade or more,” he said.
In addition, areas that are hit hardest during severe weather are also the areas where burying existing overhead lines would be the most difficult, Herzog said. Those tend to be older, established neighborhoods with mature vegetation, landscaping, sheds, pools, patios, and other obstacles that have to be worked around.
OPPD is also looking at other options to boost reliability. “We increased our tree-trimming budget and have programs in place to make improvements on circuits that haven’t been performing as well,” Lucey said.
OPPD is aiming to have a summary of the undergrounding study by year end, which would enable the results to be included in OPPD’s Grid Modernization Strategic Initiative “The expectation is that this work will also continue to become an integrated part of our normal T&D practices,” Herzog said. “As technology continues to improve and construction methods may change, we want to build a framework where we can continue to reevaluate the long-term cost and benefit of multiple solutions to provide the best overall service to our customers,” he said.
“The expectation is that we will have guidelines, especially around new construction, but also looking at existing construction,” Lucey said. “New facilities going in as overhead have traditionally been identified as the least cost method. But with the improvements in cost and durability, we’re initially finding that there are some circumstances where underground facilities are the better economic choice.”