Rocky Mountain Power seeks regulatory approval in Wyoming of 500-kV, 230-kV transmission lines

Rocky Mountain Power said that the transmission projects serve the public interest as an investment of about $2bn in energy infrastructure, $915m of which is located in Wyoming

Rocky Mountain Power on Aug. 26 filed with the Wyoming Public Service Commission an application “for situs and non-situs” certificates of public convenience and necessity (CPCNs) to build the Gateway South 500-kV transmission line and the Gateway West Segment D.1 230-kV transmission line, as well as accompanying facilities.

Listing reasons why the transmission projects are necessary, the company noted that its 2019 Integrated Resource Plan (IRP) demonstrates the need for additional resources to serve load by 2024, and that the transmission projects would allow the interconnection of an additional 1,920 MW of cost-effective generation resources in eastern Wyoming. In addition, time-limited federal tax incentives associated with new renewable generation enabled by the transmission projects offset the transmission projects’ costs, Rocky Mountain Power said.

The company further noted that it is obligated under its Open Access Transmission Tariff (OATT) to reliably accommodate nearly 2,500 MW of interconnection and transmission service requests governed by 13 executed contracts that require the construction of one or both of the transmission projects. The projects are also necessary because they will improve grid reliability by providing better operational control of the backbone transmission system by interconnecting two areas of the PacifiCorp transmission system — wind-rich eastern Wyoming with the solar-rich area of southern Utah, the company said.

Rocky Mountain Power said that the transmission projects serve the public interest as an investment of about $2bn in energy infrastructure, $915m of which is located in Wyoming.

Noting that the transmission projects are a key component of its Energy Gateway Transmission Expansion Project, and have long been recognized as an integral component of the long-term transmission plan of the company and of the region, Rocky Mountain Power said that it is moving forward with the transmission projects at this time because current circumstances make them necessary and economic.

The company said that it requests CPCNs now so that the transmission projects can be built and energized by the end of 2023.

To complete the transmission projects by that time, Rocky Mountain Power said that it proposes a phased CPCN review process:

  • The company requests conditional CPCNs that allow it to start by Dec. 31 the process to finalize acquisition of the rights of way (ROWs) necessary to build the transmission projects
  • Start work by June 1, 2021, on the transmission projects on a limited notice to proceed basis
  • The company requests completion of the Advanced Review Process and issuance of final CPCNs to allow construction to commence on a final notice to proceed basis by Aug. 1, 2021

Describing the projects, Rocky Mountain Power noted that Gateway South is a 414-mile, high-voltage, 500-kV transmission line that connects southeastern Wyoming to northern Utah. Gateway South would begin at the Aeolus substation, which is located near Medicine Bow, Wyo., and was recently built as part of the Aeolus-to-Bridger/Anticline transmission project. The company added that from the Aeolus substation, the line extends west to Wamsutter, Wyo., and then generally south to the Colorado border. The line then crosses through the northwest corner of Colorado, enters Utah, and eventually terminates at the Clover substation near Mona, Utah.

Due to the length of Gateway South, the company said that it would build two series compensation substations along the line to reduce net transmission line impedance and improve the power transfer capability of the line. Rocky Mountain Power noted that construction of Gateway South would require modifications to the Aeolus, Anticline, Clover, and Mona substations to accommodate the new line.

Of Gateway West Segment D.1, the company said that the new 59-mile, high-voltage, 230-kV transmission line extends from the Shirley Basin substation in southeastern Wyoming to the Windstar substation near Glenrock, Wyo. Rocky Mountain Power said that it would also rebuild the existing Dave Johnston-Amasa-Difficulty-Shirley Basin 230-kV transmission line, which runs about 57 miles from the Shirley Basin substation to the Dave Johnston substation near Glenrock, Wyo.

Rocky Mountain Power said that Gateway West Segment D.1 also requires construction of the new 230-kV Heward substation that would be sited adjacent to the Difficulty substation, which is owned by Tri-State Generation & Transmission. Gateway West Segment D.1 also requires additions to the Shirley Basin, Dave Johnston, Windstar, and Anticline substations, the company said.

Among other things, the company said that before building a transmission line located outside Wyoming, a public utility is required to obtain a “nonsitus certificate of public convenience and necessity determining that the present or future need for the nonsitus resource is prudent and in the public interest,” if the “nonsitus resource is intended by the public utility to be a capital investment in a plant on which return is earned in Wyoming” and the “capital investment in the nonsitus resource exceeds one percent … of the total capital investment in the plant on which return is earned, that is assigned or allocated to Wyoming customers, based on the public utility’s most recent general rate case determination.”

In this case, the company said, the transmission projects would be built in Wyoming, Colorado, and Utah. Rocky Mountain Power said that it intends to include the transmission projects in rates and the capital investment exceeds 1% of the company’s Wyoming-allocated rate base; therefore, the company is required to obtain a non-situs CPCN.




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About Corina Rivera-Linares 3286 Articles
Corina Rivera-Linares was TransmissionHub’s chief editor until August 2021, as well as part of the team that established TransmissionHub in 2011. Before joining TransmissionHub, Corina covered renewable energy and environmental issues, as well as transmission, generation, regulation, legislation and ISO/RTO matters at SNL Financial from 2005 to 2011. She has also covered such topics as health, politics, and education for weekly newspapers and national magazines.