S.D. Codified Laws § 49-32-20
Any incumbent electric transmission owner may construct, own, and maintain an electric transmission line that connects to facilities owned by the incumbent electric transmission owner. The right to construct, own, and maintain an electric transmission line that connects to facilities owned by two or more incumbent electric transmission owners belongs individually and proportionally to each incumbent electric transmission owner, unless otherwise agreed in writing. If an electric transmission line has been approved for construction in a federally registered planning authority transmission plan, the incumbent electric transmission owner may give notice to the commission, in writing, within ninety days of approval, of its intent to construct, own, and maintain the electric transmission line. If no notice is provided, the incumbent electric transmission owner shall surrender its first right to construct, own, and maintain the electric transmission line. Within eighteen months after the notice, the incumbent electric transmission owner shall file an application for a permit in accordance with chapter 49-41B.
SDCL 49-32-20