Nashville District, Hydroelectric Design Center charged to assess switchyards
By Lee Roberts
CARTHAGE, Tenn. — The process of collecting and transmitting electricity generated from hydropower charged a team of experts March 6, 2012, to assess and determine the status of structures and components at the Cordell Hull Dam Switchyard.
The technical team consisted of civil, mechanical and electrical engineers from the U.S. Army Corps of Engineers Nashville District and Hydroelectric Design Center in Portland, Ore., which is the Corps' national center of excellence for hydroelectric and large pumping plant engineering services. It is the first stop in a district-wide switchyard assessment intended to identify critical power train equipment needs in the Cumberland River Hydropower System.
Jim Carter, who leads hydropower design activities in the Nashville District Civil Design Branch Mechanical and Electrical Section, said the team is working to assess all nine switchyards within the district by the end of the fiscal year in order to generate a report and develop work items for the Cumberland River System Hydropower Rehabilitation Program Master Plan.
"It's very important that we move forward, and this assessment helps us focus on how to effectively and efficiently fund any capital improvements," Carter said.
In this endeavor, the Nashville District is partnering with HDC experts on the first two switchyard assessments at Cordell Hull and Center Hill Lakes. The district then plans to finish the remaining assessments, but will rely on HDC to perform a technical review of findings. HDC will also provide additional quality assurance oversight, and help shape options and recommendations on possible replacement and upgrades of structures, equipment and technology.
Scott D. Cotner, senior electrical engineer at HDC, said his team has extensive experience performing these types of hydro and electrical equipment assessments at Corps projects throughout the country, and they are doing everything possible to support the Nashville District with relevant insight and recommendations.
"There's a lot of opportunity that we can provide for each other, to learn from each other, and make things better," Cotner said. "I think that it's good the work the Nashville District has started, doing a system-wide assessment of their hydropower facilities. It's important and should provide a good framework for guiding capital investments in the future to maintain the reliability of these public assets."
Cotner said that some other districts in the country tend to fund things on a project-by-project basis. "While it's hard to get your hands around something as big as all nine power plants and all the equipment that you might have to worry about in those power plants, it's a good first step to know where to start," he said.
Sharon Demeaux, lead structural engineer, and Kevin Florence, electrical engineer, were also at Cordell Hull Dam's switchyard with Cotner to collaborate with district officials during the inspection.
James Graham, senior electrical engineer for the Nashville District Engineering Design Group, explained that the district-wide switchyard assessment involves interviewing the senior electrician and power plant superintendent at each dam to learn about equipment history, maintenance, testing, and operational issues.
The assessment team then performs a detailed inspection of switchyard components such as the generator busses, cable galleries and bus ducts, oil circuit breakers, disconnects, current and potential transformers, coupling capacitors, current limiting reactors, wavetraps, high voltage conductors, insulators, and other structural items such as concrete pads, steel structures, fencing, and switchyard lighting.
The Nashville District's Electronic Service Section electricians perform all electrical testing on the switchyard electrical components, grounding mat, and lightning arrestors, Graham said.
Carter added that although the operations and maintenance staff has done an outstanding job maintaining and preserving the lifecycle of the district's switchyards, it's time now to consider recommended improvements based on the findings of these site inspections.
"Almost all of the equipment in the Nashville District is original. Actually, some of the equipment is obsolete and it's hard to find replacements for it," Carter said. "It needs to be upgraded with current technology for both safety and environmental concerns."
Carter said environmental concerns such as transformer oil containment and safety issues such as arc-flash in the switchyard are also being examined in the assessment and will be important considerations in any plan to improve or replace current power structures and equipment.
The district's nine hydroelectric power plants and 28 generating units were built between 1948 and 1977 and have an aggregate capacity of more than 914 megawatts. Southeastern Power Administration sells the power from these plants though negotiated power sales and operating agreements with the Tennessee Valley Authority and regional utility companies.
Ryan Frye, Nashville District Hydropower Branch maintenance manager, noted that funding for capital improvements from hydropower preference customers for switchyard upgrades is dependent on the findings of the district-wide assessment and future inclusion into the Master Plan.
The purpose of the Master Plan is to establish scope, schedule, budgets, and technical performance requirements for the management and control of the Cumberland River System Program's Hydropower Modernization Initiative.
Frye said it's a dynamic plan, which promotes efficiency and reduces operations and maintenance costs through design enhancements and equipment standardization across the Cumberland River system.