160 miles of transmission lines planned for eastern SD, costing upward of $2 billion

South Dakota regulators are considering permit applications for projects that would add about 160 miles of electrical transmission lines along the eastern edge of the state. 

Transmission lines carry high-voltage power over long distances.

The larger proposal is part of the PowerOn Midwest Project, from companies including Xcel Energy and Otter Tail Power. It calls for about 90 miles of 765-kilovolt transmission line in South Dakota through Grant, Deuel and Brookings counties. It would run south from the Big Stone South Substation in Grant County, in the northeastern corner of the state, and turn into Minnesota at a point east of Brookings.

It also includes expansions at the Big Stone and Brookings County substations and about 5 miles of 345-kilovolt transmission line. Further segments would be constructed across southern Minnesota.

The companies estimate construction of the South Dakota segment would cost between $1.3 and $1.7 billion, with completion in 2034.

The route includes a 250-foot-wide right-of-way for the 765-kilovolt line and a 150-foot-wide right-of-way for the 345-kilovolt line, according to the project application. The 765-kilovolt line has landowner access agreements, known as easements, for 81 of the required 274 parcels in South Dakota, or 30%. The 345-kilovolt line has 7 of 19, or 37%. 

The second proposal, filed by Otter Tail Power Company, is the Big Stone South to Hankinson to Bison Project. That proposal would run 71 miles of 345-kilovolt transmission line in South Dakota from the Big Stone South Substation north through Grant and Roberts counties into North Dakota. The project would continue to a substation west of Fargo.

The line would have a 150-foot right of way, and the South Dakota segment is estimated to cost $191 million to $229 million with completion in 2034. The project application says the company “will work collaboratively with landowners to obtain necessary rights through voluntary agreements.” The application does not say how many agreements have been obtained. 

The companies say the projects are intended to improve reliability and increase transmission capacity for more power plants and customers consuming large amounts of electricity, including “data centers and other industrial demands.” South Dakota has some small data centers but none of the larger hyperscale data centers proliferating across the country, including in North Dakota and Minnesota.

Maps show the routes of proposed transmission-line projects in eastern South Dakota. Hover over the PDF and use the controls to see the second page. (Courtesy of the South Dakota Public Utilities Commission)