Rebuilding and reconductoring just under 12 miles (19.3 km) of transmission line is not unique or considered to be a major accomplishment; unless that line is rebuilt and re-conductored while it remains continuously energized. That was the case for UtiliCorp United's Cripple Creek 69-kV transmission line.
UtiliCorp's WestPlains Energy operating unit found itself faced with rapidly declining service from a radial 69-kV transmission line in a rugged region of Colorado's Rocky Mountains. The line's copper conductor had reached the end of its reliable life--it often broke under ice or high wind loads. UtiliCorp's engineers also determined faulty insulators, poor grounding and, in some places, inadequate clearances for conductor blowout were causing an unacceptable level of momentary outages.
The fact that this line was the only source to Colorado's largest gold mine and to one of the state's most successful gambling resort towns only heightened the need to address the situation. Outages were out of the question. Revenues at the Pikes Peak gold mine and in the gambling resort town of Cripple Creek are measured in tens of thousands of dollars per hour. In addition, the Cripple Creek transmission line serves the historic mining town of Victor, Colorado and the surrounding ranches, businesses, hospital and other vital services.
UtiliCorp's engineers vigorously investigated a variety of options to address the problem. They considered building a temporary circuit, constructing a parallel line, building an additional circuit from another source and even installing generation facilities. Then, they developed and documented estimated costs and project completion dates.
When the engineers evaluated costs and environmental and customer impacts, they found that none of the conventional options were desirable. The generation option was quickly dismissed given the 10,000-ft (3048-m) elevation and lack of fuel source. Acquiring new rights-of-way and the associated tree clearances was not desirable given the fact that the area is located in some of the Rocky Mountain's most beautiful and rugged terrain. The majority land owner, the U.S. Bureau of Land Management, is charged with protecting the local habitat, and as such, supported developing a solution with little impact on the environment.
To develop an alternative solution, UtiliCorp engineers teamed with Danford, L.C., Lees Summit, Missouri, U.S., to implement an innovative solution. Danford is an international firm that specializes in the energized maintenance and construction of overhead electrical lines. It has developed proprietary techniques and apparatus that makes energized work on transmission lines safer and more efficient. Prior to the subject project, Danford principals had completed three projects in which a transmission line was reconductored and refurbished while remaining energized. Working closely with UtiliCorp engineering staff, Danford developed a plan to reconductor and rebuild the Cripple Creek line on the same center line without taking a single outage. This plan met all of the safety, environmental, customer service and economic criteria set forth by all parties involved in the project.
The Cripple Creek line was originally built as a 22-kV line in the late 1800s. In 1918 it was rebuilt to 69 kV. The construction varies from single wood poles with 300-ft (91.5-m) spans in milder terrain, to three pole structures with spans up to 1700 ft (518-m) in the rough areas. Over the years, poles were replaced and general maintenance was performed, however, the 1918 vintage copper conductor remained in service because the line could not be de-energized.
By 1995 the conductor had become brittle and unreliable. It was clear to UtiliCorp that measures needed to be taken to continue the high level of service the utility is committed to providing.
The project was given high priority in the spring of 1995 after enduring a winter of icing, broken wires and less than acceptable outage statistics. Danford developed a detailed written construction plan that was reviewed by UtiliCorp engineering and operations personnel. After the plan was accepted, UtiliCorp engineering staff completed line design and procured materials for the job. UtiliCorp and Danford jointly developed a detailed construction mitigation plan, which the U.S. Bureau of Land Management approved. Construction began less than nine weeks after the first field inspection of the circuit in May 1995.
The construction mitigation plan included a detailed listing of construction equipment and materials to be used on the project, the number of equipment trips in and out of the right-of-way, and the length and location of construction activities, among other details. Because of wildlife and archeological concerns only about half of the project was approved for construction during the summer of 1995. The second half of the project was performed in the summer of 1996 after wildlife and archeological studies were completed.
Special equipment such as low pressure tracked vehicles, all-terrain vehicles and horses minimized disturbance to the ground in the rugged, remote and pristine mountain environment. One requirement for the area was that no new roads or additional grading could be performed; however, back blading of existing trails was permitted. Danford's patented LineMaster robotic arm was the essential piece of equipment used on this energized project. In fact, the UtiliCorp review team claimed that the project could not have been performed safely without the LineMaster.
The LineMaster is a patented, hydraulically powered, boom-mounted robotic arm designed and intended for use at both distribution and transmission voltage levels. The Line-Master telescopes and pivots through a range of rotary motion in excess of 130 degrees. It captures, supports and moves all standard conductor configurations from flat to phase-over-phase. Conductor capture and motion is remotely controlled by one man on the pole, in the bucket, on the truck, or on the ground.
During the course of the project UtiliCorp's concern over the likelihood of conductor failure was confirmed. The line crew discovered four sections of the line that were damaged by line fatigue or, in one case, rifle shots. The damage was severe enough that any heavy wind, ice or construction loading would cause the conductor to break, creating a major outage in the Cripple Creek district. The outages, as with past broken wire events, would have been lengthy given the region's rough terrain and snow depth. The LineMaster allowed the crew to handle the fragile conductor remotely in a smooth, controlled motion, increasing the safety of conductor movement operations.
At the time this project began, Danford did not yet possess a group of skilled linemen trained in the specialized techniques required to perform energized transmission re-conductor projects. Likewise, no such workforce was available from UtiliCorp's WestPlains operation. Undaunted, Danford and UtiliCorp joined forces to train the specialized workforce required. Cliff Devine and Dan O'Connell, the two Danford principals who directed the project, were certified instructors in hot-stick, rubber glove and barehand techniques and procedures.
Together, UtiliCorp's safety and training department and Danford provided the required training to a group of linemen with no previous transmission construction experience. Theyperformed two weeks of classroom and field trial training during the nine weeks prior to the start of the project. Due to the concern over the condition of the Cripple Creek line and the short window of opportunity to perform the construction in the Rocky Mountains, a good deal of training was performed "on the job." In all, more than 5000 man-hours of training were provided.
The Cripple Creek project was completed for less than half the cost of more conventional construction alternatives. The cost of the project was US$1.1 million, which compared to the original estimates of US$2.3 million and US$3.0 million using more conventional approaches. These estimates may have been conservative given the higher than anticipated costs to mobilize in rugged terrain and to obtain the required permits and construction rights.
In conclusion, the Cripple Creek project as well as previous and future energized reconductor projects substantiate and prove the value of energized transmission line reconductoring and rebuilding to the industry.
In this new age of increasing com-petition and heightened customer reliability concerns, energized transmission line reconductoring and rebuilding is an important new tool that utility asset managers can use to balance competitive pressures with the reliability demands of their customers.
Dan Slaven is a transmission engineer with UtiliCorp United, Kansas City, Missouri, U.S., which he joined nine years ago. He has the BSCE degree from Kansas State University. He is responsible for the design and management of all transmission line projects in the Missouri Public Service and WestPlains Energy divisions of UtiliCorp United, which includes facilities in Colorado, Kansas and Missouri.
Cliff Devine is a founding principal of Danford, L.C. He started his 33-year career in the utility industry with West Kootenay Power. During his tenure at West Kootenay, he developed and implemented high voltage, live-line techniques as well as managed all facets of the electric and commercial operation in the Okanagan Valley. He co-developed the patented LineMaster robotic arm, invented the patented High-Test insulator tester and co-authored the British Colombia Lineman's Apprenticeship Training Program.
Steve Powell is a principal of Danford, L.C. He is a registered professional engineer who started his 17-year utility career designing and managing transmission line projects with Burns & McDonnell Engineering. Most recently, he was the director of transmission engineering for UtiliCorp United, responsible for planning, design, right-of-way acquisition and project management for all transmission line, substation and system protection projects for U.S. operations.