Extreme Turbine Makeover

Kingston Fossil Plant’s Unit 3 turbine remained hidden for 16 years, spinning at 3,600 revolutions per minute inside a cast iron shell, until the unit came offline for repair last fall. Now, with the conclusion of the 99-day maintenance outage — ending Jan. 13 — images of the rarely seen turbine tell a story of a rebuild that required more than 35,000 combined man hours from TVA’s precision craftsmen.

Repairing everything from blades to bearings, Power Service Shops machinists used the latest technology to refurbish the 65-year-old turbine, which still produces about 120 megawatts of power — enough for 60,000 homes.

To accomplish the feat, PSS craftsmen relied heavily on computer-based machines and programs to fabricate new parts, such as the turbine’s bull gear, a heavy-duty cog that is attached to the turbine’s rotor. The part looks and acts like the flywheel on a car.Bull Gear
PSS Machinist Ernest Corum bores holes in new KIF Unit 3 bull gear.

Before and after the turbine comes online, a turning gear locks into the bull gear like a car starter, spinning the turbine slowly at 3 RPMs. The practice keeps the turbine’s shaft from warping due to extreme temperature fluctuations inside the turbine.

“The way things are done today versus the way it was done in the 70s is night and day,” said Corey Saint, PSS senior manager. “With something like the bull gear, back in the day a machinist would have had to take measurements in the field and then machine the piece from scratch. Now, we can put the old part on a machine, write a computer program, then let the machine bore the coupling holes in the new part for an exact fit.”

Saint compared the new process to a child tracing his or her hand on a piece of paper.

“The process is simply more accurate and reduces the mathematical hurdles that were once an everyday challenge,” he said. “Years ago, if you did something and missed a measurement on one of those holes, you wouldn’t discover the error until you took the part back to the site where it was then refitted. If a part has to be refitted or adjusted on site, it affects quality.”

Getting it Right

While machining quality parts for the turbine is essential, perfection in its reassembly is also critical. The turbine rotor weighs more than 22 tons, but the margin for error is about .003 inch—about the thickness of a sheet of notebook paper.

“Effective communication and teamwork are paramount when you’re doing these types of lifts. Our shift turnovers take at least 30 minutes,” said Matt Craft, Generation Projects and Field Services construction manager. “Everyone has got to be on the same page. The most valuable thing we do is communicate with each other as we plan each task safely.”

Saint agreed.

“One of the greatest assets we have here is our people,” he said. “Safety is number one, and quality is right there behind it. We take pride in that.”

Outage Overview

Some of the many upgrades the PSS performed included improvements and repairs to the intermediate-pressure and low-pressure turbine sections, Kingsbury thrust bearing, turbine rotor bearings, governor valves, main steam stop valves, intercept valves, generator hydrogen coolers and exciter.

“When that unit comes up and we’re making megawatts again, it’s a pretty good sense of accomplishment to know that we were able to break the turbine down to the half shell, then put it back together so it’s making money again,” Craft said.

In addition to the turbine rebuild, more than 300 plant employees and contractors supported improvements to Unit 3, which included a major overhaul of a tube section inside the boiler. The replacement required more than 600 welds.

The total cost of the Kingston outage was $16 million, furthering the life of the fleet asset by an estimated 10-15 years.

“The outage was accelerated due to an unexpected tube failure inside the boiler, which happened six months prior to the scheduled outage. To be able to execute this outage successfully with zero injuries involved a tremendous amount of effort from everyone involved,” said Kingston Outage Manager Rhyne Douglas, Generation Field Services. “The support we received by the Power Service Shops on such short notice was a testament to the skill and focus that our employees and contractors brought to the table. We couldn’t have done it without them.”