Transmission congestion on the Kansas City Power & Light (KCP&L; Kansas City, Missouri, U.S.) 345-kV LaCygne-Stillwell Line represented a serious bottleneck for members and customers of the Southwest Power Pool (SPP) who rely on the line for service. A serious constraint to upgrading the line was KCP&L's limited opportunity to take the line out of service for extended times for upgrades.
Built in 1972, the line was designed to carry a maximum load of 1251 MVA. The power flow over this line is controlled by the SPP, which consists of 50 members serving more than four million customers over all, in parts of eight states. Pool membership is comprised of investor-owned utilities, municipal systems, generation and transmission coops, state authorities, federal agencies, wholesale generators and power marketers.
Studying an Upgrade
Previously, KCP&L investigated the possibility of upgrading the line by rebuilding with larger conductor. The use of larger conductor would have required at least five or six months of construction time for replacing existing structures, which were not capable of handling the larger, heavier conductor. KCP&L did not implement this option because of the required outage. Building a parallel line was not practical because a large number of estates had been built along critical sections of the right of way. In addition, siting and permitting issues would have been problematical.
KCP&L had done significant work to address the capacity limitations of the transmission circuit by upgrading substation apparatus at each end of the line. Additionally, weather related equipment in conjunction with dynamic real-time rating apparatus (CAT-1) was installed to evaluate the actual conductor capacity during changing climatic conditions. Although these measures provided incremental capacity increases, the capacity increases did not meet the immediate or long-term requirements for KCP&L or the region.
In April 2002, the utility contracted with ETG Mapping to conduct a fly-over survey. KCP&L used the data to determine if there was some way to increase capacity without rebuilding the line. ETG Mapping discovered that several sections on the line would violate the NESC code ground clearance if capacity were boosted beyond 100°C (212°F) design limits. With the advent of high-temperature conductor, the ACSS (aluminum conductor steel supported), KCP&L renewed its consideration of an upgrade, assuming the line could be reconductored while energized. The ACSS conductor could carry almost twice the load of the original ACSR conductor with about the same weight, diameter and tensions. If the line could be reconductored, the existing H-frames could be used. Working with Quanta Services (Houston, Texas, U.S.), KCP&L considered this possibility because of Quanta's experience in energized line work and its proprietary tools and work methods. The aerial photogrametrics were examined and survey work completed to develop ground line features and to analyze conductor behavior. Using line-design software PLS-CADD, the old conductor was compared with the high-temperature conductor for differences in sag and tension, after which the bundled 954 kcmil type 13 ACSS/TW (aluminum conductor steel supported/trapezoidal wire) with mischmetal coasted core was selected as the replacement. The lines were configured to match sag at maximum operating temperature and allow the 15.5°C ambient sag of the new conductor to float where it would. The goal was to match design working tension so that it would not be necessary to change out structures or anchors.
To allow for an increase in the transmission line capacity, an agreement between the SPP transmission owners was implemented. Previously, the SPP did not expect to renew several firm power reservations at the end of their terms that was granted under the SPP filed Open Access Transmission Tariff (OATT). Recent FERC orders concerning the filing required the SPP to renew the transmission transactions at the close of their terms. The line did not have sufficient available transfer capacity to allow for their renewal.
Getting the Money
The financing was solved by an innovative solution developed by the SPP and KCP&L, in which SPP transmission owners agreed to pool future revenues to pay for the upgrade. A plan was put into place whereby the cost of the upgrade would be paid out of the revenues that would be generated by the additional capacity resulting from the upgrade. With this innovative scenario, ratepayers would not see higher rates, KCP&L would not face budget-busting construction costs and transmission customers would have an efficient, high-capacity transmission system. The go-ahead for the project was issued in February 2003.
While financing details were being engineering team used computer aided design (CAD) software to locate structures on the right of way, captured connection points and sagged the wire. The entire project was predicated on reconductoring the line while energized at 345 kV, an ambitious project for Quanta, which had worked many lines while energized for KCP&L in the recent past, but none of this magnitude.
The original 32-mile (52-km) line, with 234 H-frame structures, had three phases suspended in traditional horizontal configuration. Quanta developed detailed work plans to enable the sequential transfer of electrical load between the three existing phases and a temporary transfer bus.
Material acquisition was critical. Even though vendors responded with fast deliveries, there were a few times when management had to use existing material dedicated to other jobs in process to maintain the tight project timeline. KCP&L managed all of the material acquisition, since almost $1 million of the material would be recovered and restocked for use on other ongoing projects.
The Safety Issue
The important considerations for the project revolved around the mitigation of potential hazards created by induced voltages during conductor installation at 345 kV, the estimate of how much induced current there might be and assurance that both the electrical crews and the public would be protected. To ensure safe handling of the conductor being strung, Quanta used the Equal Potential Stringing Method, which isolated the working area and the conductor being pulled. This technique permitted all work on the conductor to be carried out without mishap at the induced voltage. In this configuration, the induced voltages ranged from 2000 to 30,000 V, while the circulating currents did not exceed 30 A.
Among the problems solved during the construction was how to handle the wire at night when the crews were not working. Normally, under de-energized conditions, the wire is tied or “caught off” to a Caterpillar front-end loader (Cat), which was not possible since the wire could not be caught off to any equipment that was at ground potential. The Quanta crews developed a proprietary dead-end structure, which safely insulated and isolated the wire from other equipment and from the public.
An additional problem involved the transfer of large loads from the existing conductor to the temporary line, and from the temporary line to the new conductor. Quanta solved the problem with a proprietary 26-step process and a large mobile breaker used for high-voltage switching.
The project ran smoothly and finished almost a month ahead of schedule, which was a major accomplishment considering the team endured hostile weather from the start in February with frozen ground, snow, mud, copious spring rains and May tornados. Following completion of the upgrade, KCP&L infrared-tested all of the connections and released the line fro service. The rating was increased from 1251 MVA to 1972 MVA. Although the line's conductor rating is actually greater, other components on the system limit the capacity to 1972 MVA.
The Final Results
The reconductoring job was successful because KCP&L and Quanta worked as a team to solve problems as they arose. The team emphasis was reflected by the following factors:
- The right contractor with the skills, experience, tools and engineering expertise is a requisite for a project of this size.
- Safety is of prime importance.
- Partnership and trust are key ingredients. This was illustrated on this project by the fact that the PAR operating unit of Quanta has been a primary transmission contractor for KCP&L since the early 1980s, which fostered a spirit of trust and cooperation. KCP&L and Quanta were able to streamlined the process by actively working together to insure that all work was properly completed.
- Flexibility is essential and was demonstrated here as the project evolved by making changes, as required.
- Good relationships with vendors help to smooth the way to a successful conclusion even with the late start. Vendors demonstrated a high level of cooperation when supplies were required on short notice.
In summary, the project broke new ground in solving the transmission congestion problem by upgrading conductors in an energized state. The project was completed ahead of schedule in less than five months for less than $8 million. Construction of a new transmission line would have required a significant increase of funds as well as a considerable increase in time required to complete the project.
John E. White is the director of Energized Services for Quanta Services Inc. He has more than 20 years experience in the electric utility industry and has managed major transmission, substation and distribution projects throughout the United States. He is responsible for the development, application and integration of live-line technology for all the Quanta companies. He is a certified instructor in barehand techniques, hotsticks and the LineMaster Robotic Arm.
Paul S. Beaulieu is senior engineer in the transmission and substation engineering for KCP&L. He graduated from the University of Missouri in 1983 with a master's degree in mechanical and aerospace engineering, with emphasis in material science, fatigue and fracture mechanics. He began his career with KCP&L in 1982 and is responsible for the design and development of overhead and underground transmission lines and mechanical/civil aspects of substations and apparatus with the high-side voltages of 69 kV through 345 kV.
Rick Albertson is supervisor of transmission construction and maintenance for KCP&L.
Equal Potential Stringing Method
The technique for the Equal Potential Stringing Method requires wire mesh to support working personnel and to be connected by a traveling ground to the pulled conductor and to the pulling equipment. With the crew on the wire mesh, everything is at the same potential as the conductor. A double fence around the area prevents ground contact by the crew, and an insulated walkway to the area ensures workers are protected from step potential when they cross to the isolated area. Although this method has been around for many years, it is used only infrequently because of the expense and training required.