MISO has opened a third review of a long-range transmission project, this time because three substations are needed more than five years ahead of schedule to accommodate new data center load.
MISO’s third variance analysis focuses on the South Fond du Lac–Rockdale–Big Bend–Sugar Creek–Kitty Hawk Long-Range Transmission Project in southeastern Wisconsin that was approved under a $22 billion portfolio at the end of 2024.
At the beginning of 2026, MISO awarded Chicago-based Viridon Midcontinent some of the project build — 106 miles of 345-kV lines and four, 345-kV substations at $350 million, nicknamed the Wisconsin Southeast (WISE) project. (See MISO Picks AEP, Berkshire’s Joint Venture to Build $1.2B 765-kV Line.)
Now, MISO said Viridon “is unlikely to secure required regulatory approvals in time to meet the recently accelerated Dec. 1, 2027, in‑service date” for the Sheboygan River, Mullet River Junction and Cedar Creek Junction substations, part of the WISE project.
MISO originally projected the project would be in service by mid-2033.
MISO said the project is bumping up against a separate, expedited transmission project in east-central Wisconsin from American Transmission Co. designed to address anticipated data center load.
The expedited project, which ATC submitted to MISO in September 2025, relies on the trio of substations. MISO said it approved the expedited Ozaukee County Distribution Project in late February “in light of the urgency of the anticipated data center load.”
Viridon’s regulatory snags include “acquiring public utility status and receiving appropriate certification(s) required to construct the three referenced substations,” according to MISO.
Viridon was founded in 2023 and is owned by Blackstone Energy Transition Partners, one of Blackstone’s private equity funds.
“As the Sheboygan River, Mullet River Junction and Cedar Creek Junction substations are already included in the WISE competitive transmission project, Viridon maintains the responsible entity for the construction, implementation, ownership and operation of said substations,” MISO said in a late February notice for the variance analysis.
MISO included footnotes in its selected developer agreement with Viridon that timelines for the three substations were subject to change pending the outcome of ATC’s Ozaukee County Distribution Interconnection Project.
The Ozaukee project involves rebuilding and upgrading existing 345-kV lines and construction of up to five new substations at a cost of $1.36 billion to $1.64 billion. The Wisconsin Public Service Commission said it likely has until December 2026 to approve, modify or deny the project (137-CE-221).
“This process will review the likelihood of being able to meet the accelerated timeline, assess potential impacts, and determine next steps to resolve the issue,” MISO said of its variance analysis in a statement to RTO Insider.
MISO conducts variance analyses on regionally cost-shared transmission projects when they encounter schedule delays, permitting challenges, significant design changes or experience at least a 25% cost increase from original estimates. The reevaluation studies are also triggered when developers find themselves unable to complete the project or if they default on the terms of their selected developer agreement.
After completing the analysis, MISO can either let projects stand, develop a mitigation plan for them, cancel projects or assign them to different developers if possible. A committee of MISO employees selected by RTO executives make calls on how to deal with projects.
“Viridon is committed to delivering the WISE Project, including the three substations, and will meet MISO’s requirements with respect to timeline and all other requirements,” the developer said in a statement to RTO Insider.
Viridon said it “can’t speculate” on PSC actions, including why the commission is unlikely to grant approvals in the near term.
“Viridon will follow the PSC’s defined process, which will allow for completion of the substations on the timeline required,” it said.
Neither Viridon nor MISO would comment on whether there’s a possibility ATC could take over some of the substation work because of data center development.
MISO didn’t respond to RTO Insider’s question on whether it’s anticipating other instances where timelines on long-range transmission projects will need to be accelerated to meet demand for new transmission capacity to accommodate other data centers.
Viridon said it “is committed to the best outcome for all customers in Wisconsin and across MISO.”
In its selection report at the beginning of 2026, MISO said it was concerned Viridon may have underestimated the capital costs of the project in its bid. Three other bidders estimated the project would cost anywhere from $471 million to $481 million; MISO itself estimated the project would cost $662 million to complete.
However, MISO said its confidence in its selected developer was buoyed by the fact Viridon already executed an agreement with an experienced general contractor and strong cost containment measures.
MISO is conducting two other variance analyses on long-range transmission projects — for cost overruns instead of schedule and regulatory hitches. Two transmission projects in Minnesota and Illinois/Indiana have crossed MISO’s 25% overrun threshold from an original cost estimate. (See MISO Launches 2nd Review of Long-range Tx Project for Cost Overruns; Stakeholders Suggest Cost Overruns Ubiquitous as MISO Reviews Long-range Tx Project.)
