St. Louis-based Ameren, meanwhile, agreed to report any similar incidents at its Missouri power plants in the future.
The trade-off was at the center of agreement filed with the PSC on Thursday, in which the parties asked the five-member commission to resolve the dispute to clarify how to handle such situations in the future.
But the new filing confuses the question of exactly what occurred at the plant last spring. A PSC staff report two weeks ago cited an "extensive fire," though Thursday's filing states that no fire was actually "witnessed or extinguished" even though local fire crews responded to the plant's powerhouse.
What's not disputed is that one of the plant's two 220-megawatt generators automatically shut off and began smoking on the night of June 6, and that repairs to the equipment will cost $11 million.
The Taum Sauk plant, located in Reynolds County about two hours southwest of St. Louis, was put back into service in the spring of 2010, more than four years after the kidney-shaped reservoir atop Proffit Mountain ruptured, releasing a flood that scoured the mountainside and badly damaged Johnson Shut-Ins State Park.
The incident earlier this year didn't affect the plant's second of two generators, and Ameren expects the disabled unit to be back online this spring.
The PSC staff brought the complaint against Ameren in June for failing to immediately report the incident, which was discovered by a staff member on a visit to the plant more than a week later.
The complaint cited rules that require Missouri utilities to report within a day "any accident or event at a power plant" that involves serious injury, death or property damage in excess of $200,000. The regulations also require reporting of any outage at a fossil fuel or nuclear generating plant.
Ameren blamed the incident on an insulated copper winding that failed inside the generator.
The utility classified the incident as a power plant outage rather than an "accident or event" as defined by the PSC, and believed it didn't require immediate notification since it occurred at a hydroelectric plant, not at a coal or nuclear plant.
The plant originally began operations in 1963. It is the only pumped storage plant in Missouri, generating electricity during the afternoon when water from the upper reservoir flows through a tunnel to spin turbines. At night, when electricity is cheaper, electric pumps move water back up the mountain to refill the reservoir.