American Transmission Co. shuts down damaged transmission lines in the Straits of Mackinac
As a result of yet-undetermined damage, American Transmission Co. (ATC) shut down two submarine cables in the Straits of Mackinac on Tuesday that electrically connect the Upper Peninsula to lower Michigan.
The cables went offline about 30 seconds apart on April 1.
A patrol of the overhead elements of the system between Point Lebarbe in St. Ignace and the McGulpin Riser Station in Mackinac City revealed no damage.
ATC monitored the submarine cables overnight, which contain a mineral-based fluid for insulation, and determined that they were leaking. The company reduced pressure on the system to minimize the fluid leak.and deployed maintenance, environmental and operations personnel to locate the compromised section of the cables on April 2. The investigations included aerial patrols, cable testing, and system reconfiguration options.
Extreme weather conditions, however, hindered the damage investigations and contributed to the decision to shut down the cables on Tuesday.
ATC notified the National Oceanic and Atmospheric Administration, Environmental Protection Agency, U.S. Coast Guard, U.S. Fish & Wildlife Service, Michigan Department of Environmental Quality, Michigan Department of Natural Resources and the Michigan Public Service Commission of its decision to shut down the cables.
“It was an extraordinary set of circumstances, but ultimately, the decision to shut down the cables had to be made,” ATC Chief Operating Officer Mark Davis said. “We will continue to investigate the cause of the incident, determine any necessary remediation efforts and continue communicating with the appropriate regulatory agencies.”
The electric transmission grid in the Upper Peninsula, much of which ATC owns operates, is operating normally, the company said. ATC is coordinating with the Midcontinent Independent System Operator and Midwest Reliability Organization to determine short-term and long-term solutions and will take steps to determine the condition of other cables in the Straits.
