Every year, the hydroelectric power generators at the Gavins Point Dam powerhouse, operated by the U.S. Army Corps of Engineers, Omaha District, are brought down one at a time to undergo annual maintenance. The maintenance begins in the fall when water releases are lower and concludes in early spring.
These comprehensive mechanical and electrical inspections ensure the units are operating safely and at peak performance.
“It keeps the unit in tip-top shape and makes sure everything is functional so that the unit and alarm systems perform as it is designed,” said Eric Johnson, assistant Gavins Point Dam powerhouse superintendent, in late November. “Right now, on unit three, we’re focusing on cavitation welding and fixing the cavitation down on the runner and in the draft tube.”
Cavitation welding repairs cavities caused by air bubbles that burst along the steel components inside the hydropower unit as water flows through.
Before maintenance can begin, gates on the upstream and downstream sides of the powerhouse generators are lowered and draft tubes are dewatered so mechanics can repair the damage.
“It will eat through the metal if you don’t repair it,” said Michael Schnetzer, lead mechanic at the Gavins Point Dam powerhouse . “We’ll go in and use a tool called an air arc [welder], which will excavate that damaged metal out.”
Once the damaged metal is removed, mechanics use a metal inert gas welder to replace the void with stainless steel. They will then polish the area smooth with a grinder to reduce turbulence on the blades.
In addition to cavitation welding, mechanics also inspect mechanical components to include the wicket gates, adjustable turbine blades, governor pumps and cooling systems. Oil is removed, filtered and reintroduced, and filters are replaced.
Schnetzer said zebra mussels, just introduced to Lewis and Clark Lake within the last decade, also bring additional challenges. The invasive species attach to any substrate surface that touches water. This includes pumps and piping that must be regularly cleaned to avoid clogging.
The rest of annual maintenance focuses on the electrical systems.
“This year, we’re replacing brushes on the unit,” said Andy Kilgore, Gavins Point Dam powerhouse senior electrician. “They are part of the [direct current] excitation system - they are the transfer point from stationary electrical potential to the rotating shaft of the field.”
Kilgore and his team will perform functional tests of electrical components under a scheduled outage. This includes inspections of low, medium and high voltage auxiliary equipment. All of this ensures the systems continue to produce hydroelectric power.
“With unit maintenance, it’s more preventative,” Kilgore said. “It can prevent premature degradation of the unit. It provides system reliability and is an important part of the hydro plant.”
The Gavins Point Dam powerhouse includes three generators, each capable of producing 44,099 kilowatts for a total of 132.297 megawatts annually.
Crews recently completed maintenance on unit three and are now focusing on the remaining two units. Annual maintenance is scheduled for completion in April 2025.