ATC Sets First Structure on Wisconsin 345 kV Grid Forward Line, Now 5% Built

American Transmission Co. has moved its Grid Forward – Central Wisconsin project from planning into construction. The utility set the first transmission structure and reports the work about 5% complete as of August 12, 2026. Line construction started in the second quarter of 2026. The project rebuilds roughly 160 miles of existing line. It adds a new 345 kV line of about 200 miles. It also expands a substation near Arpin, Wisconsin. The Midcontinent Independent System Operator approved the work inside its Long Range Transmission Planning Tranche 1 portfolio. ATC still targets a December 2030 in-service date. A revenue requirement analysis filed with the project puts net savings to Wisconsin customers at about $1.75 billion over its life. On a discounted basis that figure is about $142 million.

What Is Being Built

The scope splits between rebuild and new build. ATC rebuilds about 160 miles of existing corridor. The new 345 kV segment runs roughly 200 miles. The substation expansion near Arpin ties that capacity into the existing network.

ATC listed four current milestones. The first structure is up. Detailed engineering and design continue across several line segments and substations. Permitting and material procurement continue. The December 2030 date holds. Eric Lundberg, senior vice president of asset delivery, said construction is underway and the project remains on track.

Read the Cost Claim Carefully

ATC says the forecast stays inside the cost range the Public Service Commission of Wisconsin approved. It also says the forecast sits within about 2.5% of MISO’s original estimate on a time value of money basis. That last phrase carries the weight. MISO built its estimate during planning and stated it in 2022 dollars. The current forecast absorbs several more years of inflation, refined engineering, development work, and approved project changes.

Lundberg made the framing explicit. He said a simple comparison between an early planning estimate and a current forecast does not always tell the whole story. That is a fair point about escalation. It also means the 2.5% figure is not a nominal dollar comparison. ATC did not publish the nominal forecast next to it. MGRID could not independently verify the current nominal cost from the released materials.

Why It Matters

Tranche 1 is the first real test of whether MISO’s long range portfolio lands near its promised cost. Grid Forward is one of the larger Wisconsin pieces of that portfolio. Utilities across the footprint will cite this project when they defend their own Tranche 1 and Tranche 2 budgets before state commissions. Large loads in central Wisconsin now get a firmer date to plan against. The December 2030 target sits behind a started construction schedule rather than a permit. Treat 2030 as the earliest relief from the current constraint, not a hedge. Watch the annual cost updates in the PSCW docket rather than the headline percentage.

Sources

• T&D World: ATC Advances Central Wisconsin Transmission Project to Enhance Grid Reliability
• Public Service Commission of Wisconsin: Grid Forward – Central Wisconsin Transmission Line Project
• WisBusiness: Grid Forward – Central Wisconsin Project advances into construction
• American Transmission Co.: Grid Forward project overview

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