By Rajesh (Roger) Gupta and Kenny Chaix, Entergy Corporation
Louisiana’s wetlands, which support an amazing range of wildlife and a healthy outdoor recreation industry, are essential to the state’s economy. They’re also essential to the nation’s long-term ecological health, since Louisiana is home to approximately 40 percent of the lower 48 states’ coastal wetlands. Yet, as Entergy CEO Wayne Leonard has noted, every year approximately 40 square miles, an area the size of Manhattan, of this valuable recreational and income-producing property disappears.
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Environmental concerns have halted more than a few transmission projects in recent years, so when it came time for Entergy to upgrade two 1.7-kilometer-long sections of its transmission lines that cross marshlands east of New Orleans, it was vitally important that the construction not harm that portion of the fragile ecosystem.
New 230-kV Line Needed to Serve Load Growth
Analysis performed in 2002 established that a single contingency loss of Entergy’s Chalmette-Meraux 115-kV transmission line would load the submarine section of its Behrman-Port Nickel line to 133 percent. That same analysis found that a single contingency loss of the Behrman-Port Nickel line would load the Chalmette-Meraux 115-kV line to 103 percent.
Switching load, starting an additional combustion turbine located at Entergy’s Buras, La., power station, and automatically shedding load were steps that would mitigate, but not eliminate, the overloads caused by either of those single contingency failures.
Based on its evaluation, Entergy acted to eliminate the overload on the Behrman-Port Nickel line and allow for load growth on its 115-kV system south of Chalmette, La. The company accomplished this by removing the entire load at Meraux from the 115-kV system and putting it on the 230-kV system. To serve the load at Meraux from the 230-kV system, a new 230-kV loop feed was constructed from the Kaiser-Michoud line to the Meraux substation, and the Meraux substation was converted to 230-kV operation. At project completion, the Kaiser-Michoud 230-kV line was renamed Kaiser-Meraux-Michoud 230-kV line and the Chalmette-Meraux-Poydras 115-kV line became the Chalmette-Poydras 115-kV line.
Without harming the fragile ecosystem, Entergy recently upgraded two 1.7-km-long sections of transmission lines that crossed marshlands east of New Orleans to better serve customers.Click here to enlarge image
The project called for totally converting the existing Meraux 115-kV substation to the 230-kV system, thus removing it from the 115-kV system. That could be done by breaking the existing Kaiser-Michoud line at a point just east of Paris Road where the line turns to go to Michoud, and extending it into Meraux, approximately 2 miles, picking up four 67-mvA transformers that feed large residential and petro chemical loads, and then routing the line back to Michoud. This new line would become the Kaiser-Meraux-Michoud 230-kV line. A portion of the new line would be built on 22 new independent structures that would join the two existing lines.
Reconfiguring this portion of the company’s transmission system would allow for load growth on the 115-kV system south of Chalmette by reducing non-industrial 115-kV load at Meraux thus providing a stronger voltage source to customers in St. Bernard Parish and surrounding areas.
Labeled the “Kaiser-Meraux-Michoud T-Line” project, this transmission upgrade was completed in the second half of 2003 and continued Entergy’s initiatives to expand service and capacity and ensure reliability for its greater New Orleans customers.
An interlocking composite mat system allowed access to install new transmission towers with higher capacity conductors through the marshlands.Click here to enlarge image
Wetlands Access the Key
But completion of the project was not without its challenges. Access to a protected wetlands area was essential, but Entergy had to find a way to gain access to the area without harming the ecosystem. Tidal marsh covering several square miles forms a transition zone between Lake Pontchartrain, Lake Borgne and the Mississippi River. The site is bordered on the south by a protective levee system and a canal network known as the 40 Arpent Canal.
All work had to be done while protecting the integrity of the levee system and preserving the wetlands environment. Options for access included flying in the new transmission towers with helicopters, building a temporary mobile bridge to each location or constructing a temporary road. With assistance from regional civil contractor, Barriere Construction Co., and Jackson, Miss., electrical contractor Irby Construction, Entergy’s Transmission group was able to minimize impact on the wetlands, limit planned outages, and complete the project safely, economically and on schedule.
Oilfield Construction Techniques Play Key Role
The key to meeting these project objectives boiled down to selecting the right kind of temporary road–one that neither Entergy nor Barriere had used before.
A technique developed in the oilfield, where year-round operations demand all weather access, was the key. Workers laid down an interlocking composite mat system that allowed access for the heavy equipment needed to install new transmission towers with higher capacity conductors through the marsh.
According to Chris Gremillion, Entergy construction engineer, “The first challenge was getting an access road across the levee–stretching out its width so we could drive trucks over it, while protecting the levee.”
The road had to be flexible enough to allow travel over the steep levee and into the marsh zone, yet stable enough to support cranes, concrete trucks and other heavy equipment. These factors, combined with the requirement to expeditiously and completely remove the road system at the end of the project, were among the reasons Entergy chose the oilfield matting.
Research by Kenny Chaix, Entergy Transmission South Louisiana construction supervisor, established that the mat system could be adapted to fit the project’s demands. Chaix found that matting was not only a good fit, but was within project budget and was environmentally friendly.
Chaix contacted temporary road contractor SOLOCO of Lafayette, La., and learned that a new composite matting system, DURA-BASE Composite Interlocking Mats, developed as an alternative to wooden mats, provided the ideal flexible solution to access over the levee and into the standing water of the protected wetlands. Untreated wood chips were chosen to serve as the road base since the untreated chips are environmentally neutral and biodegradable.
Construction took place over several months, during which severe weather was a factor. Eleven spur roads, each crossing the levee, linked traffic from the primary access road to each tower location. The mat system, supported by the wood chip base, formed an interlocking network that resisted tidal movement and wind action, offsetting the impact adverse weather posed to the project schedule.
Construction Contractor Stays High and Dry
The composite mats also proved to be of benefit to Irby Construction, the contractor responsible for setting poles and stringing the 230-kV lines. Access to the location was easier, and Irby’s cranes and trucks maneuvered well on the matted surface.
“The biggest surprise was we didn’t get wet,” commented Tom Dickson, Irby Construction project foreman. Dickson continued, “We’d never worked on anything like this before. The mats stayed clean and worked very well for us.”
Overall, the Kaiser-Meraux-Michoud project benefited from a versatile, new technology that provided a stable, consistent base of operations and allowed Entergy to meet its environmental protection, schedule, budget and safety objectives. The result was a successfully completed transmission line project in an environmentally sensitive area–no small accomplishment in this day and age. Entergy was able to bolster the reliability of its system, while maintaining the health of a wetland area vitally important to Louisiana and the nation as a whole.
Rajesh (Roger) Gupta is the transmission program manager for New Orleans-based Entergy Corp. He is currently managing a portfolio of system upgrade and IPP interconnection transmission and distribution projects. He holds a Bachelor of Science in Civil Engineering from Indore University in India and a MBA in Finance from Tulane University in New Orleans.
Kenny Chaix is the construction management supervisor for Entergy’s South Louisiana jurisdiction. His professional experience includes two decades in construction management disciplines associated with transmission and distribution substations and transmission lines.