American Transmission Company restarts grid transmission upgrades to support Port Washington data center power requirements.

The American Transmission Company (ATC) refiled its application on Monday for a sweeping series of grid upgrades in eastern Wisconsin, restarting the state's six-month regulatory review of infrastructure needed to serve a new Port Washington data center.

ATC initially sought Wisconsin Public Service Commission approval in September, with plans to break ground as early as May 2026. That application outlined a $1.3 billion infrastructure package—including a high-voltage transmission line and five new substations across Fond du Lac, Ozaukee, Sheboygan, and Washington counties—required to reliably serve the data center by December 2027.

The commission rejected the application last month after ATC repeatedly revised the project's design throughout the review process, leaving the public unable to fully assess the proposal. PSC Environmental Affairs Coordinator Adam Ingwell testified in July that he could not recall "any other comparable cases in my experience with as many application material document revisions and ongoing design changes throughout the process." He warned that "the sheer volume of documents and revisions, without adequate explanation, likely makes it more challenging than typical for a member of the public to find specific information about the project."

ATC characterized the revisions as routine, arguing that applications routinely evolve during review. The company's attorneys cited a Barron County solar farm approved by the PSC in March despite an "eleventh-hour" overhaul that included "relocating an entire substation," contending that "there is simply no principled basis on which to treat ATC's lesser and earlier changes more harshly."

The three-member PSC unanimously sided with ATC's critics in August. Chair Summer Strand called the decision "an unfortunate outcome," but stated that the application represented "a cautionary tale of when unrealistic and unreasonable speed-to-power expectations collide with a deliberative regulatory process."

ATC's refiled application departs from its predecessor by removing a transmission line segment through Trenton in Washington County and Saukville in Ozaukee County. "The need for this project has not changed, but the application has," said Jared Winters, ATC's executive vice president and chief assets officer.

The PSC will solicit new public comment before determining whether the application can proceed. That review begins once the commission certifies the new application as complete.