Overhead Line Moves Underground

Jan. 1, 2013
Utility relies on in-house crews to perform an overhead-to-underground transmission conversion for the University of Colorado at Colorado Springs.

With the vista that inspired “America the Beautiful,” Colorado Springs instills pride in its residents with its spacious skies and mountain majesties. Pikes Peak, also known as America's Mountain, fills the residents' every view and attracts more visitors than any other mountain in North America.

This extraordinary community asset was a primary driver for the creation of Colorado Springs Utilities' System Improvement program, established in 1993 to allocate funds to proactively install electric transmission underground and provide funding assistance for requests to convert existing overhead lines. Since the program's inception, Springs Utilities' crews have placed nearly a quarter of their 110-mile, 115-kV transmission system underground.

The University of Colorado at Colorado Springs recently took advantage of this 50-50 cost-sharing program to have the overhead 115-kV transmission lines that fronted its property placed underground. The university's desire to further develop the land as well as enhance its view of Pikes Peak and the Rocky Mountains was part of a comprehensive effort by the Colorado Springs Urban Renewal Association to revitalize a blighted business corridor within the city. Together, these two groups contracted with Springs Utilities to convert about 1 mile of the overhead transmission circuit underground.

Installing Underground Infrastructure

After the project contract was signed in the summer 2011, crews commenced site work under the expert direction of Rod Glover, a 26-year Springs Utilities employee whose extensive experience dates back to the utility's first foray into underground transmission. His team was comprised of in-house crews who executed the vast majority of the project's work — from excavating trenches and installing duct banks to setting vaults and termination structures. Springs Utilities linemen also pulled, spliced and terminated the new transmission cable.

The underground infrastructure required for this project consisted of approximately 5,700 ft of a 3-ft by 3-ft concrete duct structure as well as three vaults measuring 21 ft long by 9 ft wide by 8 ft deep. The duct bank was designed and built to hold four 6-inch conduits — one conduit for each phase and one spare — and buried with 5 ft of ground cover along the route. The three massive vaults, built to the utility's specifications by Colorado Precast Concrete, were installed at the end points and midpoint of the route to facilitate cable pulling and splicing.

Cable Pulling, Splicing and Terminating

Springs Utilities crews returned to the site in late May 2012 to complete the cable installation phase of the project. This schedule gap was driven primarily by the several-month lead time on the Prysmian 1750-kcmil aluminum cable and the Trinity Steel Cor-Ten termination structures. However, the delay played into the team's favor by timing construction with both favorable weather and the college students' summer vacation.

When the nearly 21,000 ft of cable arrived on seven 3,000-ft reels, the Springs Utilities linemen spent the next six weeks pulling the cable into the new duct structure, splicing the cable in the midpoint vault, building the terminations and transitioning the cable from the underground duct bank to the new overhead Cor-Ten structures.

On many projects of this type, these particular tasks normally would be completed by outside contractors. Springs Utilities is a rare exception in its ability to self-perform this work. Given the volume of underground transmission in its 115-kV system, the utility has invested in specialized equipment and training to support these assets.

For example, utility personnel custom built their own motorized cable pay-out trailer, and linemen received ongoing training and certification to splice and terminate transmission cable. Such equipment and expertise is a hot commodity. In fact, Springs Utilities crews have been called on by neighboring utilities to assist in their underground transmission projects.

Overhead Modifications

Since the new underground cable segment replaced a portion of a 3-mile overhead circuit, modifications were required to connect the new underground cable to the existing overhead lines.

The overhead work, led by crew supervisors Justin Mitchell and Warren Stewart, took place in four stages: setting two new 100-ft-tall Cor-Ten termination structures, tying the new structures in to the existing overhead system, completing the connections from the cable terminations to the existing overhead conductor and removing the original overhead infrastructure.

This project staging, particularly the interim step of incorporating the new structures into the existing system, allowed the existing overhead circuit to remain energized while the underground cable was being installed. After successful installation and testing of the underground cable and reenergization of the circuit, the overhead crews wrecked out the now-defunct 20,000 ft of all-aluminum alloy conductor and 12 85-ft-tall to 95-ft-tall steel towers.

Overcoming Project Challenges

Many projects face obstacles on their path to completion, and this overhead-to-underground conversion was no exception. While the technical challenges of installing underground transmission cable are familiar to the experienced team, other difficulties encountered during the project execution phase were considerable. As the team members strived to meet the university's deadline of Aug. 1, 2012, they dealt with substantial material lead times, stringent system operational and reliability requirements, logistical accommodations for local businesses and an unexpected natural disaster.

Operating within these constraints forced the project team to develop creative ways to satisfy all project stakeholders. For example, significant adjustments were made to crew schedules to lessen the intrusion on business owners and traffic flow along the circuit's route. Tasks that encroached on driveways, parking areas and intersections — such as assembling the termination structures, pulling cable and removing overhead conductor — were performed at night and on weekends. These activities are complicated enough in broad daylight, so performing them under floodlights made the tasks far more difficult to execute.

While schedule problems can be prevented with pre-project planning, no amount of preparation could have predicted the Waldo Canyon Fire. On the afternoon of Tuesday, June 26, 2012, the linemen were working on the cable terminations when they witnessed the wildfire roar out of control, crest the mountain ridges and threaten the neighborhoods in the foothills west of the city. As one of the worst disasters in Colorado Springs history unfolded — claiming two lives, destroying nearly 350 homes and scorching tens of thousands of acres — Springs Utilities resources were redirected to firefighting and utility service restoration efforts.

When employees were called to duty on the Wildland Fire Team, evacuated from their homes or prevented from coming to work, project crew resources were stretched thin. Despite this monumental interruption, the team quickly regrouped and kept the project moving.

In the end, the challenges were not enough to deter the skilled and driven Springs Utilities linemen from safely and efficiently accomplishing the task set before them. The newly configured overhead-underground hybrid circuit was energized in early July 2012, and overhead wreckout was completed well in advance of the university's deadline.

The success of this project reinforced the value in-house expertise brings to the execution of complex projects, demonstrating once again the hometown crew has what it takes to restore unobstructed views of America's Mountain.

Jacqueline Brusoe ([email protected]) has been with Colorado Springs Utilities for two years and currently works as a senior project engineer for transmission for the substation and transmission engineering department.

Heather Engle ([email protected]) has been with Colorado Springs Utilities for 18 years and currently works as an engineering support coordinator for the substation and transmission engineering department. She handled all aspects of project management, material and services procurement, and civil infrastructure design.

Shannon O'Driscoll ([email protected]) is an electric section lead for electric for Colorado Springs Utilities. As a Springs Utilities employee for more than 25 years, he is an experienced lineman who has particular expertise in the utility's underground transmission construction, operation and maintenance.

Companies mentioned:

Colorado Springs Utilities | www.csu.org

Colorado Precast Concrete | www.coloprecast.com

Prysmian Cable | www.prysmianusa.com

Trinity Steel | www.trinitysteel.com

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