Improvements in the insulating material surrounding the copper coils in the generators will permit a higher copper to insulation ratio. The intent is to significantly reduce that time,” Floyd said. “Operation’s staff spends about two weeks per year per unit on cavitation repair. Utilizing stainless steel for the various components that have historically shown the most vulnerability to cavitation should significantly reduce that maintenance effort. “With hydroelectric dams you can’t eliminate cavitation, you can only protect against it.”Īccording to Floyd, each turbine is allotted three weeks of annual periodic maintenance, most of which is spent repairing cavitation. “Cavitation is a major concern with any hydroelectric system,” said Lehman. Over time, these implosions produce pits or cavities in the components that have to be repaired. When these bubbles implode near or against the component materials, they create powerful shockwaves that act like millions of micro-sized hammers. As the water passes through the turbine blades, the pressure drops below the vapor pressure and bubbles form. Now, they can get a better understanding of how the stressors will affect the materials.”Īn additional challenge not unique to Webbers Falls is cavitation. “They didn’t have the computer modeling or technology we have today, and they couldn’t analyze all the stressors. “The fatigue stresses weren’t properly analyzed when the system was designed,” said Ken Lehman, a contract engineer at Webbers Falls. A single turbine at Webbers Falls can generate four times that output but the efficiencies of the smaller European tilt-axis turbines didn’t transfer as well to the larger turbines. Slant-axis turbines were popular in Europe when the turbines were installed but the European models were significantly smaller, capable of producing five megawatts or less of electricity. Webbers Falls produces electricity with three Kaplan-type, slant-axis turbines. “In the early 1980s all of the shafts on the turbines were replaced but this is the first complete rehabilitation since the dam was brought online in the 1970s.”
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“Some of the problems the plant has encountered over the years included cracked turbine shafts, and failed bolts at major connections that would put each unit out of commission as well as significant amounts of cavitation,” said Floyd. The improvements will increase power generating capacity and reduce mechanical failures. In addition to turbine replacement, the project includes rehabilitation of four cranes, rewinding the coils on three generators and rehabilitating the roller gates, intake bulkheads and tailrace bulkheads. Once the second turbine is replaced, rehabilitation of the last turbine will begin said Byron Floyd, resident engineer, Tulsa District Army Corps of Engineers. The first turbine was completed and accepted in December 2013 and a second is about 90 percent complete. Workers at the Webbers Falls Powerhouse have completed more than 60 percent of the required upgrades on turbines and generators scheduled for rehabilitation.
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