Xcel Energy has been cited for three “serious” safety violations in connection with an electrical explosion at its Becker, Minn., power plant last summer that left three workers significantly injured.

The Minnesota Occupational Safety and Health Administration (OSHA) recently declared that Xcel had violated standards for “personnel protection” and “use of equipment.” OSHA, which didn’t disclose further details, has fined Xcel $21,000, or $7,000 per violation.

Three workers at Xcel’s Sherco plant were hurt when a breaker failed. They were taken to the burn unit at Hennepin County Medical Center for treatment.

Xcel said in a statement to the Star Tribune on Monday that it has “worked hard to build a culture of safety. … We strongly disagree with the OSHA findings and have filed to contest them.”

Employers often contest OSHA violations, usually agreeing to settlements and lower fines in the process.

Minneapolis-based Xcel is Minnesota’s largest utility. Sherco is a huge coal-fired electricity operation in Becker, about an hour northwest of downtown Minneapolis. On July 17, when three workers entered a room to investigate a tripped circuit breaker, an “arc flash and explosion occurred,” Minnesota OSHA said.

In an arc flash, electric current leaves its intended path, instead traveling through air and any person who happens to be in its way.

Arc flashes generate intense heat and can cause severe burns.

Each of the three workers injured at Sherco “sustained burns to a large percentage of their bodies,” according to a July post on the Facebook page of the International Brotherhood of Electrical Workers Local 160, the union that represents workers at Sherco.

OSHA standards for “personnel protection” involved safety gear and equipment for employees working near electrical hazards.