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The Sherburne County Generating Station, also known as Sherco, is a massive coal-fired power plant in Becker, Minnesota, which is in Sherburne County. Its three units have a combined capacity of 2,400 megawatts, making it the largest power plant in the state. In comparison, the single-unit Monticello Nuclear Generating Plant located less than 4 miles away has an output of 671 MW. The state's other nuclear power plant, the 2-unit Prairie Island facility, is rated at 1,096 MW, so Sherco has a larger peak output than those plants put together. The station uses 20,000 to 30,000 tons of coal per day. Up to three 115-car trains per day are required to deliver fuel to the plant from mines in the Powder River Basin.
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In addition to generating electricity, some steam is also sent from the plant to a nearby paper plant, Liberty Paper Incorporated. The power plant has a normal staff of about 350 people, but up to 800 more employees are on site when the generating units are shut down and undergoing maintenance. The city borders of Becker extend around the plant, making the town heavily dependent on the plant for property tax revenue. The plant's annual $4 million property tax bill covers about 75% of the total for the city of about 4,600 people.
The plant was initially constructed by Northern States Power Company (NSP), now a subsidiary of Xcel Energy. Units 1 and 2, which each have a capacity of 750 MW, came online in 1976 and 1977, respectively. The plant is still mostly owned by NSP/Xcel, although Southern Minnesota Municipal Power Agency has a 41 percent stake in the 900-MW Unit 3, which was built from 1983 to 1987 at a cost of about $1 billion.
Notable outages
Generating capacity at Sherco was reduced to 1,500 MW following the catastrophic failure of Unit 3 on November 19, 2011. Repairs were completed at the facility on October 21, 2013 at a cost exceeding $200 million. The incident occurred during a test cycle following an upgrade to the steam turbine where it was intentionally spun up beyond 3,600 rpm to check that safety mechanisms functioned properly. However, a severe vibration soon developed and pieces of the turbine began to disintegrate. The machine went from over 3700RPM to 0 in less than 10 seconds. Some turbine buckets sliced through the outer casing of the turbine. One cylindrical piece of the exciter the size of a five-gallon (19 liter) bucket landed next to the control room door and was still spinning at sufficient speed to drill a divot into the floor. A hydrogen and lubricant oil fire also erupted in the unit, which was extinguished within a few hours. Two men were standing between the steam turbine and generator when the incident began, but luckily escaped unharmed. Some men were treated for smoke inhalation but no serious injuries were reported in the incident.
Plans for future operation
On October 2, 2015, Xcel Energy filed plans with the Minnesota Public Utilities Commission to shut down the plant's Unit 2 in 2023 and Unit 1 in 2026. Prior to this filing, Xcel had planned to reduce its carbon dioxide emissions across the Upper Midwest by 40% by the year 2030 (from 2005 levels), but closing both of these units will contribute to a new goal of a 60% reduction in the same time frame. Generating capacity will be partly replaced with a new natural gas-fired power plant and partly through renewable energy investments. More detailed information was expected to be released in January 2016, with a ruling by the PUC expected later that year. Initial notes made by the PUC indicate a desire to instead cease operations at the nearby Monticello Nuclear Generating Plant as a reduction in total carbon emissions would come at a greater cost to the rate paying customers in the state of Minnesota. Recent conclusions drawn from Xcel Energy's ongoing rate case with the PUC found that the Monticello plant would cost the customers significantly more than expected. In 2008, Xcel had estimated the expected cost of the project to be $320 million, but during the course of the 2012 electric rate case the company informed the Commission that the actual costs would total $665 million. Subsequent information show costs of approximately $748 million. As a result the PUC has redirected efforts away from ceasing operations at Sherco and the plant is expected to stay open for longer than initially anticipated in order to reduce the impact on low cost electricity supply in the state. Regulators approved the plan in October 2016.