The deafening hum of a single, 15,000-horsepower generator filled the powerhouse downstream from the Thomson Dam on Thursday for the first time in 28 months.
“That sound is music to our ears,” said Brad Oachs, Minnesota Power’s chief operating officer.
The powerhouse was knocked offline, flooded and badly damaged in the June 19-20, 2012, flood that devastated the Duluth region.
Perhaps no other area was harder-hit than Thomson and the lower St. Louis River, where the 10-inch deluge of rain upstream pushed river flows to never-before-seen levels 10 times above normal. Highways and bridges were washed away. Entire hillsides sloughed into the river. Giant trees were uprooted like twigs. The powerhouse flooded nearly up to the second level, submersing the paddle wheels and gears that turn the generator upstairs.
All six generators in the Thomson Powerhouse were silenced, and it’s taken a herculean construction effort, and some $90 million, to get the system up and running after the flood.
The Duluth-based utility on Thursday started running water through one of the generator’s paddle wheels, producing about 12 megawatts of electricity. It’s going to get a lot louder when all six are working in the 1906-vintage hydro station.
The facility should be back up to full capacity by spring, said Thomas Donofrio, Minnesota Power’s director of hydro operations, producing a full 72 megawatts - the largest hydro station in Minnesota and enough electricity to light and power 30,000 homes.
Construction crews and Minnesota Power engineers have taken advantage of 28 months of downtime to not just repair broken parts but also to refurbish much of the hydro system, from new 12-foot-diameter pipes that bring water into the powerhouse to all-new electrical control panels. The adjacent electrical substation is raised to avoid future floods, and many of the repairs were done with another 500-year or even 1,000-year flood in mind.
“Everything we’ve done has taken into account that something like that (2012 flood) could happen again,” Oachs said.
There are three other generating stations, and several dams, along this portion of the lower St. Louis River just west of Duluth, that combine to produce 88 megawatts of electricity. That’s not a lot compared to Minnesota Power’s giant coal-fired power plants, but still enough to help the utility produce electricity without producing air emissions such as mercury and carbon dioxide, the greenhouse gas blamed for global climate change.
“Our local hydro, combined with wind power and with hydro we’re bringing down from Manitoba, are a big part of our Energy Forward effort to reduce our dependence on coal,” Oachs said as he walked through the powerhouse Thursday afternoon. “This one generator may not be a huge part of our total system, but it’s part of that larger renewable effort, and we need every part.”
The Thomson Powerhouse is supplied by water from the Thomson Reservoir, held back by the Thomson Dam, just above the hamlet of Thomson, about 10 miles west of Duluth. Water is diverted into a man-made canal and then funneled about a mile into giant tubes - one to each of the six generators.
Water rushes through the tubes faster and with more vertical drop than the river flows naturally, Minnesota Power engineers explained, and thus provides more generator-turning power than if the powerhouse were on the river itself.
Once the water turns the paddle wheels, it’s released back into the river.
Minnesota Power currently is seeking approval from the Minnesota Public Utilities Commission to incorporate the $90 million flood recovery cost into customers’ rates.
