The 85-MW Ohio Falls hydropower plant in Kentucky is actively providing clean, renewable electricity in an area known for its coal-fired facilities. Currently, the plant is undergoing modernization to further make its imprint on the region's energy resource map.
By Donn Dunker and Kyle Burns
Located in a state with a large percentage of coal-fired electricity, the 85-MW Ohio Falls hydropower plant, on the Ohio River near Louisville, Ky., stands out on the landscape. Public utilities Louisville Gas and Electric Company (LG&E) and Kentucky Utilities Company (KU) have embarked on a modernization project to update the 86-year-old hydro facility.
Fire and water
To coin a phrase, "coal rocks in Kentucky." The state is blessed with an abundance of coal, which enables residents to enjoy among the lowest electric rates on average nationwide. In fact, state law requires electric utilities to provide customers with the most cost-effective, dependable supply of power, and coal fits the bill. It's a resource that generates more than 90% of the state's electricity and fuels some $9 billion in economic activity.
Headquartered in Louisville, Ky., LG&E and KU are the regulated utilities of LG&E and KU Energy LLC. The companies have a combined generation capacity of about 8,185 MW and serve 1.2 million customers. LG&E and KU Energy is a subsidiary of PPL Corporation in Allentown, Pa., which operates 11 additional hydroelectric projects with a total capacity at 784 MW.
At LG&E and KU - which provide electricity, natural gas and retail services in 94 Kentucky counties plus five counties in Virginia - coal facilities have about a 90% availability rate among the entire fleet of coal-fired plants.
For LG&E's single hydroelectric facility, the Ohio Falls Generating Station, however, the availability rate is significantly lower than the rest of the fleet. This run-of-the-river hydro facility, about 3 miles west of downtown Louisville, is located at a dam owned and operated by the U.S. Army Corps of Engineers. The Corps' responsibilities for flood control, navigation management and preservation of marine wildlife limit its ability to make flow in the river available for power generation.
Despite these challenges, LG&E is dedicated to maximizing its hydro capacity at Ohio Falls, allowing the company to get the most from this clean form of energy. For LG&E, electric generation is really a story of fire and water.
"Although we operate a fleet of mostly coal-fired power stations, the company's history of hydropower dates back all the way to the '20s," said Kyle Burns, manager of generation and engineering at LG&E and KU. "And the companies are making investments to ensure hydro generation continues into the 22nd century."
|Ohio Falls opened in 1927 with eight 10.4 MW, the seventh largest hydroelectric facility at the nation at the time.|
Hydro's deep history
Among the milestones LG&E and KU have seen over the past 100 years is the development of hydroelectricity. LG&E dove into the hydro world in 1923 when it began construction of the Ohio Falls project on Shippingport Island.
Shippingport Island has a rich history as well. The land was once a peninsula that supported a village of mostly French settlers, a horse racing park and a six-story flour mill. However, the digging of the Louisville and Portland Canal in 1825 turned the peninsula into an island, which led to the settlement's demise.
Yet, as with milling grain, the Ohio River's currents were useful for generating electricity, and in 1927, Ohio Falls opened as the nation's seventh largest hydro station at the time. It generated enough electricity to meet the entire demand of the city of Louisville, undoubtedly benefitting some descendants of those early settlers.
Highlights of the original design
The original design of Ohio Falls was governed largely by the river's extreme water-level fluctuations. Low-stage headwater is about 420 feet and tailwater elevation at about 384 feet, providing an operating head of roughly 36 feet. Ohio Falls was built with eight 10.4-MW units, each operating at 13,500 horsepower. The original facility and all units, each of which was comprised of Allis Chalmers turbines and General Electric generators, were built within two years by the Byllesby Engineering and Management Corp., which also conducted preliminary studies on the plant.
At the time, the units' ventilation system was unusual among hydro plants yet common among steam turbines in that the stators employed a water-based cooling system. Water tubes were mounted outside of each stator, with a continuous water supply placed just outside the stator frames.
Engineers opted for this design due to Louisville's hot summers and the increased generation that would result from water cooling instead of relying on air for cooling. Less heat equals less resistance, which enables the units run more efficiently for increased output. Writing in 1926, an electrical engineer with Byllesby Engineering and Management Corp. noted, "The additional cost of the coolers and water piping, water pumps, etc., is offset by the saving in cost of generation due to the positive and continuous results which may be expected from this system ... a considerably greater output will be obtained from the plant during hot weather."
|Installation of this fixed-blade turbine is part of a larger rehabilitation under way at the 86-year-old Ohio Falls hydropower plant in Kentucky. When finished in 2015, the work is expected to boost electric output by 27%.|
Highlights of the modernization
Although repairs have been made to the Ohio Falls plant over the years, the facility needed a full modernization to repair the natural wear resulting from more than eight decades of service. This will ensure optimum reliability and performance because a rehabilitated plant means fewer work stoppages to make repairs. And it allows LG&E to continue to generate power from a renewable and low-cost energy resource.
It's a three-phased project that, when finished in 2015, will boost combined plant capacity from 80 to 101 MW, a 27% increase. Voith Hydro Inc. of York, Pa., was hired to design and implement the modernization effort.
The initial phase, which began in 2002 and was completed later that year, involved the design, procurement and installation of equipment and software that allows the company to monitor and control the units from a remote location.
The second phase, which was completed in 2005, included the design, procurement and installation of equipment to upgrade the trash-removal systems. This includes deployment of a three-story Kuenz America gantry crane that moves on rails to raise the submerged trash-intake screens for cleaning. The work also included installation of a new sluice gate and new intake screens.
The remaining phase, which is in progress and scheduled to be complete by 2015, is the full rehabilitation of all eight units, which includes fabricating and installing new runners, rewinding the generators, wicket gate refurbishments and converting the rotating exciters into a static excitation system.
As part of the fabrication process, computer modeling was performed at a York laboratory in early 2001 to help engineers determine the precise shape of the turbine blades for maximum performance. This led to the construction of a scale model of the runners at a Voith Hydro laboratory. The computer and scale modeling allowed engineers to design "mixed-flow" runners made of stainless steel with blades at a variety of angles, pitches and curvatures to reduce cavitation damage and maximize performance. Vivid computer imagery allowed engineers to examine how gas bubbles form then burst on the scale-model blades, a process that leads to cavitation damage.
|Rewinding the generators is one of the tasks still in progress in the last phase of the modernization, slated for completion in 2015.|
"As a result of the testing, the finished units can operate over a broader range of water levels, which allows them to run more often at a higher load," said Kerry Johnson, plant supervisor at Ohio Falls.
The new runners consist of five cast stainless steel hub/blade segments held together with carbon steel rings shrunk into annular grooves at the hub's top and bottom. A new carbon steel adapter plate was provided to accommodate the bolting configuration of the turbine shaft. A fabricated carbon steel runner cone provides guides water as it leaves the runner.
The original draft tube liner has been modified for the installation of a new single-piece bottom ring/discharge ring. The discharge ring is shipped in two pieces, made of stainless steel and is assembled just above the draft tube. It is installed with very close tolerances in eccentricity and concentricity which also improves the efficiency and additional power per megawatt output of the unit.
A carbon steel liner plate was welded between the new equipment and the existing draft tube liner. The bottom ring serves as the annular structure member of the discharge ring and contains the wicket gate stem's lower bushings. The wicket gates are angularly adjustable so that, when closed, they are flush with finished stainless steel surfaces to provide a positive shut-off with minimal leakage. The position of the wicket gates is controlled by the governor system through the servomotors and the gate mechanism. Twenty wicket gates are used in the assembled unit.
Old and new
Amid the clamor of the construction work, signs of the modernization are becoming increasingly visible around the venerable station. Employees now monitor the units by watching flat-screen monitors, and the computerized gear of the new exciters is now a familiar sight around the powerhouse.
Despite the technological advancements to the Ohio Falls site, vintage control panels and other historic materials will remain for facility tours. A new structure outside the entrance serves as a visitors' center and offices complete with old photos depicting the plant's storied history. A kiosk will be added in 2014 so visitors can watch a short video about Ohio Falls, including its history, the modernization effort and its ability to generate power for the next 100 years.
Donn Dunker is a corporate communications contractor and Kyle Burns is manager of generation engineering with Louisville Gas and Electric Company and Kentucky Utilities.