An attack on the Tennessee Valley Authority's power grid, which serves almost the entire state of Tennessee, could take down critical services and leave residents in the dark.

The TVA has reported five instances of physical attacks, suspected attacks and vandalism on its Tennessee infrastructure since January 2011, a USA TODAY analysis of federal energy records finds.

While these attacks have not caused major problems, they raise concerns about vulnerabilities in the system that powers Tennessee.

TVA would not release the incident reports to The Tennessean because of security concerns and ongoing criminal investigations. But spokesman Jim Hopson said the Federally owned Corporation takes significant steps, both physically and procedurally, to protect its transmission infrastructure and the equipment that supports it.

"We, of course, take these things very seriously," Hopson said.

While he wouldn't go into specifics, Hopson said each of the five incidents that were reported between 2011 and December 2014 had the potential to affect the TVA's transmission infrastructure, either a transmission tower or a substation.

The authority investigates unauthorized access of its facilities, including cut locks and fences. It is also concerned with damaged and stolen equipment, including theft of copper conductors and sabotage, Hopson said.

TVA serves seven Southern states, including Tennessee, and is required to report electrical emergencies and disturbances on its system immediately to the U.S. Department of Energy, Hopson said.

Stephen Smith, executive director of the Southern Alliance for Clean Energy, sees the potential for security breaches of the country's power grid as a sleeper problem. He said he thinks some utilities are uncomfortable talking about vulnerabilities.

"We've got wires hanging all over the place. We've got substations that are very accessible and can be damaged," Smith said. "If a determined group of individuals wanted to create havoc, I am absolutely certain that could be done ... with relative ease."