With a bridge scheduled for demolition, KCP&L faces the challenge of relocating the attached electric circuits.
In 2007, when the Missouri Department of Transportation notified Kansas City Power & Light that the Highway 240 bridge over the Missouri River in Glasgow, Missouri, U.S., was scheduled for demolition, it came as no surprise to the utility. Constructed in 1925, the bridge looked its age and needed to be replaced.
The problem for KCP&L was that the bridge carried two electric circuits on its superstructure: the 34-kV line was part of a sub-transmission loop in the utility's east district, and the 12-kV circuit served customers out of the Glasgow substation.
Overhead Becomes Underground
Initially, the task of replacing the circuits seemed obvious. The utility's transmission department was enlisted to design an overhead river crossing for the two circuits. With a route selected, after much evaluation, and the soil borings taken, work began on obtaining easements and consent for the new route. However, when negotiations failed in June 2008, with the Aug. 1, bridge demolition date approaching, KCP&L decided to go under the river.
Since the 34-kV line was a loop system, the line could be taken out of service without losing power to the Glasgow substation or the substations serving the towns of Slater and Gilliam, Missouri, on the opposite side of the river. But with winter approaching, there was a concern storms could take out what would become radial feeds on either side of the river for an extended period of time, causing entire towns to be without power. The solution to this problem was to prepare for the deployment of emergency generators in the event the line could not be rebuilt in two to three days. Areas near the substations in Slater, Gilliam and Glasgow were prepared (by being leveled and rock surfaced) to receive from one to three 2000-kW emergency generators, which would be rented as needed. Additional line hardware was also staged so the generators could be connected into the existing distribution system quickly.
Concurrent with planning for the emergency generators, KCP&L developed a plan for boring under the river and rebuilding the 12-kV and 34-kV lines to new terminal poles on each side of the river. This endeavor would be a joint effort between a contractor, to be selected by KCP&L, for the under river crossing and KCP&L line crews from Marshall, Missouri, for the overhead line construction.
Since this type of crossing of the Missouri River was a first for KCP&L, the engineering and project management team explored options for completing the work. Time was a critical factor as the utility hoped to get the new line energized by the end of 2008. Could it be done?
An Unconventional Approach
The conventional approach to a job of this magnitude at KCP&L would be to design the crossing and overhead lines. Contracts would then be issued to bore under the river and install conduits for the cables. Finally, KCP&L would pull the cables and terminate them on both sides of the river while crews would construct the overhead lines. The project team concluded the conventional approach would take longer than desired and alternatives should be explored. In the end, the utility abandoned its traditional approach and sought a turnkey solution for the river crossing. The scope of this contract would include boring the river and installing conduits, supplying and installing the cable, and terminating the cable on terminal poles installed by KCP&L.
Before the contract was prepared, KCP&L had discussions with four cable manufacturers to gain an early consensus that the distances involved would not be a major problem during cable installation and to determine the manufacturers' interest in and experience performing a turnkey contract of this magnitude. The decision was also made to have all six cables under the river be rated 34 kV even though one set would be operated on the 12-kV circuit. The design of the overhead on either side of the river would include provisions for a contingency plan to switch the 12-kV circuit cables into the 34-kV circuit if a 34-kV circuit cable failed. The failed cable could then be replaced later, but the integrity of the 34-kV loop would be re-established quickly.
Once it was determined there were no technical show-stoppers, the task of developing a turnkey contract began. Building on the work previously done by the transmission department, routes were reviewed and other potential obstacles addressed. Ultimately, the following requirements were made part of the scope of work for the turnkey contract:
Two possible routes were identified as acceptable to KCP&L. The contractor could choose either.
Based on the route chosen, the contractor would be responsible for securing easements or agreements from landowners required for both the underground conduits and extending the overhead line from existing locations to the new terminal poles.
Boring is Not Boring
Two circuits were required. The cables could be installed three to a conduit or pulled in separate conduits.
A single 2-inch (51-mm) conduit with fiber-optic cable was required for KCP&L's future relaying and communications needs.
All permits required by legal entities, such as the Corps of Engineers and Missouri Department of Natural Resources, would be obtained by the contractor.
Any one of four cable manufacturers would be acceptable. Either cross-linked polyethylene or ethylene polypropylene rubber (EPR) insulation would be accepted, although EPR was preferred. The cable was to be rated 35 kV, with 500 kcmil copper conductor and 133% insulation.
Once installed, the cable would be terminated and high-potential (hipot) tested to certify quality.
The installation was to be completed by Dec. 31, 2008.
On July 3, 2008, a request for proposal was issued to six bidders. A pre-bid meeting was held to answer questions, and bids were received from three contractors on Aug. 4. After a technical and commercial evaluation, Mark One Electric was awarded the contract on Aug. 26. Mark One immediately began ordering the cable and securing permits and easements. It also awarded a subcontract to Larry Dunn's ICS Inc. boring under the river. Mark One teamed with Dunn because of the subcontractor's previous experience boring under the Missouri River at Glasgow. About a year earlier, Dunn had successfully completed a bore under the river for AT&T after another AT&T contractor failed to get across after two attempts. When problems developed the week before Thanksgiving, Dunn's experience and determination to successfully complete the job proved Mark One had made the right decision.
After securing the necessary easements and permits, the boring crew set up and began the first of two bores across the river on Oct. 2, 2008. The plan was to directionally drill two 16-inch (406- mm) channels under the river and install a total of nine 4-inch (102-mm) conduits and one 2-inch conduit in the bore holes. This would provide three spare 4-inch conduits — which were not required by KCP&L, but which Mark One wanted as insurance — and a single 2-inch conduit for the fiber-optic cable.
With the bridge out, crews working on the project could only pass from one side of the river to the other by taking either a ferry operated by the Department of Transportation or a 62-mile (100-km) road trip. Ferry passes were purchased in bulk. The two 16-inch channels were ready just before Thanksgiving.
The problems started when the conduits being pulled into the first of the two bored channels became stuck 250 ft (76 m) short of the river's edge. The boring machine encountered a mechanical problem requiring 24 hours to repair. This 24-hour shutdown allowed the boring mud to harden in the channel. Mark One's contingency plan to increase the size of the second bore became the immediate focus. The second bore would need to be enlarged to 22 inches (559 mm) in diameter to accept six 4-inch conduits. A second boring machine was brought in to enlarge the second channel while the first machine worked to free the stuck conduits in the first channel.
As the diameter of the second bore was being enlarged, efforts to free the conduits in the first hole continued. Throughout December, various materials were pumped through the first bore in an attempt to loosen the pipe. During this process, Mark One was able — with the aid of a third boring machine — to push a rod under the stuck conduits and pull back the 2-inch fiber-optic conduit. As temperatures fell, keeping the materials liquid and flowing became an additional challenge.
By Jan. 9, 2009, the six 4-inch conduits were in place under the river, and the effort to complete the rest of the duct work began in earnest. Once the conduits were through to both sides of the river, Mark One mobilized the duct bank crews from Kansas City in a convoy of crews and equipment. These crews worked from before dawn to after dark seven days a week in bitter temperatures to complete the conduit runs from pole to pole and install the cables.
The duct bank from the river bore to the dip poles on each side of the river transitioned from high-density polyethylene roll conduit to red flex conduit and, finally, to standard gray polyvinyl chloride conduit. Once complete, the ducts were encased in concrete and topped off with the natural soil. Arrangements were made to ensure concrete would be available after hours, so work could continue into the evening. Also, by early January, ice floes on the Missouri River were frequently shutting down the ferry service. In spite of this challenge, the conduit runs were completed by Jan. 14.
Companies mentioned in this article:
As the conduit runs were completed, the cable-pulling equipment was mobilized from Kansas City in another convoy. Because of the length of the runs, special measures were taken to manage the pulls. The rope was kept coiled in consecutive barrels as it was pulled in and out of the conduits. Multiple ropes were joined to make the length.
Prysmian was selected as the cable supplier, in part for its ability to provide the required continuous length of cable and also in part for the smooth surface increasing the ease of pulling. All six 2300-ft (701-m) cable pulls were completed by Jan. 20, and the cable was independently tested and verified good the next day. These represent some of the longest continuous cable runs in the KCP&L system.
While boring operations were under way, KCP&L contracted with Finley Engineering to design the double-circuit overhead line portions of the job. Once complete, the design was issued to KCP&L crews in Marshall, and the first order of business was to set the terminal poles on each side of the river. This was done on Jan. 12.
As cable installation under the river was in progress, overhead-line construction continued. Work was hampered by bad weather on occasion, and when ice was too bad on the river, the ferry was shut down, making the trip to the east side much longer. On March 17, 2009, the overhead lines were complete and the two circuits across the Missouri River were ready to be restored to their normal operating configuration.
Richard Ruppert (firstname.lastname@example.org) is a project manager in the engineering and asset management department at Kansas City Power & Light. He has worked more than 39 years as an engineer or project manager on domestic and international turnkey engineering, procurement and construction generation, transmission and substation projects. He has a BSEE degree and is a registered professional engineer in three states.
Tony Privitera (email@example.com) is vice president and part of the ownership group of Mark One Electric Co. in Kansas City, Missouri. He had more than 20 years in the electrical contracting business.
Finley Engineering Co. www.fecinc.com
ICS Inc. www.icshdd.com
Kansas City Power & Light www.kcpl.com
Mark One Electric Co. www.markone.com