A Tall Order: Duke Energy’s NCSPA Project

The Port of Wilmington, operated by the North Carolina State Ports Authority (port), is a significant economic driver for the state of North Carolina. Following the Panama Canal’s expansion in 2016, they embarked on a $200M capital improvements plan to service the larger “Neo-Panamax” container vessels that are now calling on ports in the United States. The port added larger “Neo-Panamax” lifting cranes and requested Duke Energy Progress (DEP) raise the pair of 230kV lines crossing the Cape Fear River at least 12 feet. The new cranes are so large that their delivery also required the lines to be temporarily raised. The port needed quick, innovative, and cost-effective solutions. The project team immediately began working on a plan to meet their needs. The transmission lines are supported by 335-foot lattice towers that were installed in 1972 and are the tallest of their type on the East Coast. They were analyzed in PLS-TOWER to determine which members needed to be retrofitted to support the tower modifications, while also meeting today’s wind loading criteria. The structural evaluation considered each phase of construction and the associated loads. This sequencing was complex because at least one of the two circuits had to always remain energized. The existing lattice tower legs are supported by concrete pier caps founded on concrete piles. These were analyzed and validated against the new loading. This assessment avoided significant environmental impacts to the Cape Fear River estuary. The optimal solution was determined to be: 1) reconfigure the tower arms from a vertical to a delta conductor arrangement, and 2) reconductor the line with a high-temp, low-sag ACCR conductor. This redesign provided more than 41 feet of air clearance that could be implemented within a reasonable timeframe and cost. This solution not only exceeded the NCSPA’s expectations, but it also benefited Duke Energy Progress customers. The structures were upgraded to current engineering wind standards and the conductors were replaced with state-of-the-art cables that are smaller, lighter, and less sensitive to wind. These improvements enhance power reliability and resiliency in a severe-weather and hurricane-prone area, which will benefit customers for years to come. The strategy came to fruition and history was made in May 2020 when the MV Hyundai Hope docked at the state port. It was the largest container ship to ever dock at the Port of Wilmington.