A Colorado electric cooperative that is part owner of Public Service Company of Colorado’s (PSCo) Comanche 3 coal plant sued the Xcel Energy (NYSE:XEL) subsidiary Tuesday, saying the utility’s mismanagement had cost it “tens of millions of dollars” in repair costs and purchases of replacement power.

Comanche 3, a 750-MW super-critical generator, has been plagued by repeated unplanned outages since it began commercial operation in 2010 and is now expected to be retired long before its expected 60-year lifespan.

CORE Electric Cooperative, which serves customers from Colorado’s Eastern Plains to its Front Range, agreed to purchase a share of Comanche along with Holy Cross Electric Association, with PSCo owning a majority share and operating the plant.

But in a breach of contract suit filed in Denver County District Court, CORE said PSCo failed to properly maintain the plant, causing it be out of service an average of 91 days per year, only 27% planned, the “worst reliability record of any of PSCo’s generation facilities.”

The suit quotes from a March 2021 Colorado Public Utilities Commission report that concluded the reliability issues resulted from “poor maintenance practices” and “lack of thoroughness in procedures and training.”

The suit says outages between 2010 and 2020 resulted from “boiler tube leaks and equipment replacements” resulting from PSCo’s “imprudent utility practices and failure to maintain proper water chemistry.”

The plant suffered a yearlong outage beginning in January 2020 when two turbine blades broke off while spinning at high speed, shutting the plant down for 141 days. When the utility attempted to restart the plant after repairs, technicians improperly shut of all lubrication to the turbines, causing another 231-day outage, CORE said.

“Without lubrication, metal-on-metal contact occurred between various components of Comanche 3’s rotor train. According to the PUC staff report, ‘observers noted sparks coming from some of the turbine bearings, and a flash fireball was seen coming from the top of the [turbine lubrication oil] tank,’” CORE said.

Under its agreement, CORE agreed to purchase replacement power from PSCo when Comanche 3 was out of service. The yearlong outage cost the co-op more than $38.5 million in replacement power — $20 million more than it would have paid from power from Comanche, it said. “PSCo enjoyed an unjust enrichment, at CORE’s detriment, by receiving much higher payments for replacement power from CORE as a result of PSCo’s failure to properly operate Comanche 3,” the suit alleges.

The cooperative said it was unaware of PSCo’s poor maintenance until recently because the utility intentionally withheld information from a joint committee, including CORE and Holy Cross, to oversee the plant.

CORE asked the court to force PSCo to pay damages and to relieve the cooperative from paying for any share of the costs of repairs or reconstruction.

Xcel spokeswoman Michelle Aguayo said the company is “still reviewing the documents and generally [doesn’t] comment on pending lawsuits.”

“That said, Xcel Energy remains committed to ensuring the safe, reliable operation of the plant through its proposed early retirement in 2040. Comanche 3 is one of the lowest-cost generating plants on our system and has proven valuable to the system over its life.”