Hydropower has a decent claim to being the most dependable thing on the American grid. Water runs downhill, turbines spin, and some of the hardware doing the work has been at it since before your grandparents met. Fort Peck Dam in northeastern Montana is about as good an example as you’ll find. The Army Corps of Engineers has been running it since 1940, and it’s the kind of infrastructure nobody thinks about, which is exactly what you want from a dam.<\/p>\n
Then, a little after 10:30 p.m. on Thursday, September 3, a transformer failed next to its powerhouse, and a few thousand Montanans suddenly started thinking about it.<\/p>\n
According to Valley County Emergency Services Manager Ed Malone, the failed transformer knocked a live power line to the ground and the grass around it caught. KFYR reported<\/a> that the outage hit 3,157 NorthWestern Energy customers in the Glasgow area, and the last of them got their lights back at about 12:17 a.m. Glenn Meier, Valley County’s sheriff between 2002 and 2016, lives about two miles from the dam and told Montana’s Q2 News he got “a blast of light that lit up our house in our backyard,” followed by the boom. Friends of his happened to be fishing near the plant and sent him video of the flames.<\/p>\n Nobody on site got hurt, everyone on duty was evacuated, and local fire crews working alongside project staff put the grass fire out. All three of the hydroelectric generating units running that night spent roughly four hours offline while the Corps checked things over.<\/p>\n Four hours is, honestly, about as gentle as a night like that gets.<\/p>\n And if 3,157 customers sounds like a small number for a dam this size, you’re right, and that’s kind of the point. Fort Peck’s output goes out through a federal transmission line run by the Western Area Power Administration, which ties into the Eastern Interconnection. If you’ve never heard of that one, don’t feel bad. It’s the giant shared grid covering most of the country east of the Rockies, and your toaster’s probably on it. WAPA crews bypassed the damaged equipment during the night, and that’s why Glasgow got its electricity back well before the generators did.<\/p>\n Here’s the two-sentence version of what a switchyard does. Generators make electricity at a fairly low voltage, and the transformers sitting next to the plant step it up to something that can travel hundreds of miles without wasting a chunk of it as heat along the way. Cut that link and the plant has nowhere to send its power, so operators disconnect the generators before something expensive breaks.<\/p>\n That’s basically what happened here. The units themselves were fine. In the Corps’ official release<\/a>, the agency said the three units came offline to protect the machinery and the grid, went through safety inspections and grid stability checks, and came back to full operation. The fire stayed outside the powerhouse, and the Corps says nothing inside the plant was immediately affected.<\/p>\n What made the transformer fail is a different question, and as far as I can tell, nobody’s answered it in public yet. The Corps and WAPA are still investigating, and the Corps’ own release never actually uses the word transformer. It only mentions a big grass fire outside the building. The transformer account comes from the county’s emergency services manager, and from Meier, who told Q2 News the fire looked to him like it involved the switchyard transformer while being careful to call himself a speculator. Grass right up against high-voltage gear isn’t a great combination whichever way the sequence ran.<\/p>\n Fort Peck isn’t a concrete monolith like Hoover. It’s an earthen embankment 250 feet high and 21,026 feet long, which works out to just about four miles of dam, and it’s the biggest hydraulically filled dam in the country. Hydraulically filled means nobody trucked all that dirt in. The Corps built a shipyard on site in the middle of the Great Depression, launched a fleet of dredges the workers called the Fort Peck Navy, and pumped river-bottom slurry into place until a dam existed. Yes, the Army ran a navy. In Montana.<\/p>\n The workforce topped out at nearly 11,000 people in 1936, the project survived a major slide in 1938 with the end in sight, and the final load went in during October 1940. The dam’s been holding the Missouri back ever since, and the Army Corps’ Fort Peck project page<\/a> credits the two powerhouses with averaging 1.1 billion kilowatt hours annually, roughly what a city of 100,000 people uses.<\/p>\n We’re talking about five turbines split between two powerhouses, three units in the first and two in the second, and only three of the five were spinning that Thursday night. The Corps hasn’t said which ones. I couldn’t find that detail anywhere, and frankly it doesn’t change the story much.<\/p>\n The Glasgow Courier reported that power dropped again across a big chunk of Valley County on the afternoon of Friday, September 4, including Glasgow and St. Marie, and came back within the hour. The Corps and NorthWestern didn’t answer the paper’s question about whether that second outage was tied to the fire, and nothing’s gone dark since. When residents started worrying about flooding on Facebook, the Corps told the Courier that any flood risk in the area would come from localized rain, which is a bureaucratic way of saying the dam itself is fine.<\/p>\n Powerhouse tours were canceled for the Labor Day weekend while the investigation got moving. The Fort Peck Interpretive Center next door stayed open on its normal holiday hours, which frankly tells you how contained this whole thing was.<\/p>\n Dams on the Missouri system have been keeping us busy lately. Downstream on the same river, crews at another mainstem dam are scraping 25,000 pounds of zebra mussels off every intake gate<\/a> they clean, and fire has treated other hydro plants far worse than it treated Fort Peck, like the 142-megawatt station that burned to the frame<\/a>.<\/p>\n Nobody’s put a cause on paper yet. In the Corps’ most recent statement on the fire, which local papers ran on September 9, the agency confirmed all three generating units were back on the grid and producing power, and said a full assessment of the technical and structural damage is underway to work out what the repairs will take.<\/p>\n","protected":false},"excerpt":{"rendered":" Hydropower has a decent claim to being the most dependable thing on the American grid. Water runs downhill, turbines spin, … <\/p>\nSo how does one transformer knock out a whole powerhouse?<\/h2>\n
They built this dam by pumping mud<\/h2>\n
The week after came with a couple of hiccups<\/h2>\n