Replacing and maintaining aging infrastructure is important for the power industry to continue to deliver reliable and resilient power. Xcel Energy recently replaced and repaired some transmission and distribution structures near Glenwood Springs, Colorado, on the side of a steep canyon above the heavily trafficked I-70 corridor.
The transmission and distribution poles are part of the state power grid, which consists of hundreds of miles of high-voltage transmission lines that run across the State of Colorado. The pole replacement work would take place on the 6584 Shoshone-Glenwood Springs 69kV transmission line, which runs between the Shoshone Hydroelectric Plant – built in 1906 – and the Glenwood Springs Substation. Work would also be performed on the distribution-owned lines, including some distribution under-build as part of the circuit 6584 pole replacement work occurring between the plant and the Grizzly Creek Rest Area in Glenwood Canyon.
Many of the transmission structures had reached their end-of-life, with some dating back to their initial placement in the early 1900s.
The rebuild meant removing the existing wood structures, insulators and hardware, and installing new monopole wood structures, insulators and hardware. This work would be critical to allow Xcel Energy to continue to deliver reliable power to Western Colorado – today, tomorrow, and well into the future.
Ensuring Safety, Minimizing Disruption
“Xcel Energy and line construction crews were facing some unique project challenges,” said Black & Veatch Project Engineer Joshua Jirsaraie. “They had to access these deteriorating transmission and distribution poles, which happen to be in some challenging spots. For example, one area was only accessible by foot, and the crew had to climb through a series of rope systems to get there.”
Xcel Energy turned to Black & Veatch for engineering and design services of the project.
The work was challenging. The transmission structures were located on the side of a very steep canyon adjacent to I-70, a heavily trafficked artery that rises above the Glenwood Canyon Recreation Trail, a paved pedestrian trail popular with walkers, hikers, runners and cyclists, and the Colorado River, a major area for recreational water sports.
The area is revered for its beauty and environmental significance, and extra care had to be taken to minimize any disruption. This meant that no new access roads could be built, and thus the project had to be designed and executed to utilize helicopter construction methods.
“Due to the proximity to I-70 and the recreation trail, public safety was a major concern throughout the life of the project,” said Jirsaraie. “The work had to be very carefully planned and executed to minimize any disruption to the vehicular traffic, as well as the trail, environmental, and river activities. Plus, the project could only take place during specific seasons due to wildlife concerns, outage constraints, constructability issues, weather and access.”
The work took place between the Shoshone Hydroelectric Plant and the City of Glenwood Springs during the summer and fall of 2019. Approximately 30 transmission structures were replaced during this pole replacement scope effort.
Delivering from the Air and Ground
Helicopters were used to set up the new transmission and distribution structures. Lane closures were monitored by the Colorado Department of Transportation (CDOT) in coordination with Xcel Energy and the line contractor.
Helicopters were used to fly equipment and poles to the project site from a staging site located on private land. The helicopters delivered one pole per trip via winch line and hovered 200 to 300 feet above grade at each site, depending on the terrain, above where ground personnel were stationed. This required careful coordination with CDOT, which implemented complete shutdowns of I-70 to ensure the safety of the passengers and vehicles during all live helicopter flights.
Black & Veatch worked closely with Xcel Energy to provide engineering construction support as required during all construction activities.
Embracing Technology in Construction
Technology also played a significant role in helping the project come to life. Black & Veatch used sophisticated 3D engineering modelling with PLS-CADD software to model the full system, including transmission PLS-Pole structure models, with all wires modelled in the full system. The engineering team also incorporated LiDAR survey data to ensure that adequate clearance was kept between the wires, ground and any above-ground obstacles or crossings meeting Xcel Energy engineering design guides along with NESC code, and applicable industry design standards.
“Using PLS-CADD and LiDAR allowed transmission line engineering to improve from prior legacy line design methods – not only to account for the exact conditions present in the field, but to ensure that the rebuilt line will meet current Xcel Energy design criteria and current Xcel Energy design guides,” said Jirsaraie.
Prior to flying the new structures to the project site, the structures were framed with crossarms, insulators and ground wires to help reduce the amount of work required in the canyon along the interstate. When feasible, the old structures were planned to be removed from their existing holes and the existing holes were to be filled in with rock. When removal was not an option, the old structures were cut off at the base and disassembled, then removed via helicopter.
The holes for the new transmission and distribution structures were dug by hand, with assistance from jackhammers powered by air compressors.
To reduce visual impacts and disturbance in Glenwood Canyon, the team placed distribution underbuild on some of the transmission structures. By underbuilding distribution on the structures, the team was able to eliminate 10 distribution-only pole structures.
“Black & Veatch’s engineering design team did a great job on this one-of-a-kind project, with zero safety incidents resulting,” said Jirsaraie. “Using new technologies and delivery methods helped ensure the successful replacement of all poles required for the project, and even allowed us to reduce the number of structures in the canyon. This project really helps ensure that Xcel Energy can continue to deliver reliable, resilient power to the people of Western Colorado.”