SPP will complete its third major expansion of its RTO footprint when it begins administering the regional transmission grid under its tariff for several Western organizations overnight March 31 into April 1.

C.J. Brown, the grid operator’s vice president of operations, said staff have been encouraged by the status of their system and readiness activities, and they are expecting a successful cutover.

“After years of planning and testing, it’s exciting to be close enough to April 1 that SPP’s forward‑looking studies now include data from the western part of our expanded territory,” he said in a statement to RTO Insider. “This is obviously a major milestone, but it’s just the beginning of something bigger. Our operators and support staff are already looking ahead to April 2 and every day that follows, when we’ll be just as focused on our ongoing mission to keep the lights on.”

The RTO Expansion (RTOE) members affirmed their support to go live April 1 with a unanimous vote of support in March. (See SPP RTO Expansion Members Affirm April 1 Go-live.)

The expansion will add three states to the RTO’s 14-state footprint: Arizona, Colorado and Utah. It follows the previous additions of the Integrated System (IS) in 2015 and Nebraska’s public utilities in 2009. Those expansions added the Dakotas and parts of Iowa, Minnesota, Montana and Wyoming to the RTO’s footprint. (See Integrated System to Join SPP Market Oct. 1.)

The key organizations joining RTOE are:

• • Basin Electric Power Cooperative;
  • Colorado Springs Utilities;
  • Deseret Power Electric Cooperative;
  • Municipal Energy Agency of Nebraska (MEAN);
  • Platte River Power Authority;
  • Tri-State Generation and Transmission Association; and
  • Several Western Area Power Administration (WAPA) regions: Upper Great Plains (UGP)-West, Colorado River Storage Project and Rocky Mountain.

Basin Electric, MEAN, Tri-State and WAPA’s UGP-East Region already are members of SPP, having placed their respective facilities in the Eastern Interconnection under SPP’s tariff as part of the IS.

Several other load-serving and embedded entities that are part of WAPA’s Colorado-Missouri balancing authority also will become part of the SPP RTO on April 1.

The expansion began in 2020 when several utilities decided to explore RTO membership. A Brattle Group study found the move would be mutually beneficial and save $49 million annually.

SPP’s members will have access to seven of the eight back-to-back DC ties, with a combined capacity of 1,320 MW, that connect the asynchronous Eastern and Western interconnections.