American Transmission Co.

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ATC electrically reconnects the Upper Peninsula and lower Michigan

Three undamaged cables combined to form a powerline across Straits of Mackinac

PEWAUKEE, Wis. – American Transmission Co. has restored the electrical connection between the Upper Peninsula and lower Michigan. Two powerlines made up of six submarine cables in the Straits of Mackinac tripped offline Sunday, April 1. Three cables are needed to make one circuit, or powerline. Two of the cables – one in each circuit – were damaged, possibly by vessel activity, and were subsequently decommissioned after they were found to be releasing dielectric insulating fluid. Subsea inspections revealed that at least three of the remaining cables were undamaged and operable; ATC reconfigured and tested those cables to create a circuit across the Straits. The new circuit went into operation on Tuesday, May 1.

“This connection is essential for reliability for the eastern U.P. and the northern portion of lower Michigan,” said Mark Davis, chief operating officer for ATC. “We were able to maintain reliability by implementing conservative operating procedures during the month the connection was lost, but re-establishing this powerline will give us greater flexibility and an added measure of reliability to help us keep the lights on.”

The damaged cables have been soldered, capped, sealed and returned to the bottom of the Straits. ATC is making plans to permit and construct two new circuits in the Straits using a solid dielectric insulator, and to eventually decommission the six fluid-filled insulating cables. No firm timeline or cost has been established.

“We thank all the participants in the Unified Command, led by the U.S. Coast Guard, for the safe and efficient response to this incident,” Davis said. “The coordinated response helped minimize impacts to the environment and local community.”

Note to editors:
For additional information, please visit http://www.atcllc.com/straitscables/

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American Transmission Co. is a Wisconsin-based company that owns and operates the electric transmission system in portions of the Upper Midwest. Formed in 2001 as the nation’s first multi-state transmission-only utility, ATC has invested $4.5 billion to improve the adequacy and reliability of its infrastructure. ATC now has $4.7 billion in assets, including more than 9,600 miles of transmission lines and 554 substations. The company is a member of the MISO regional transmission organization, and provides nondiscriminatory service to all customers, supporting effective competition in energy markets without favoring any market participant. For more information, visit our website at www.atcllc.com.

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