Entities file with Arizona regulators Ten-Year Plans detailing transmission projects in the works

Various entities, including ATC Development Company (ATC DevCo), a development branch of American Transmission Co. (ATC), and Southline Transmission, L.L.C., a subsidiary of Hunt Power L.P., recently filed Ten-Year Plans with the Arizona Corporation Commission (ACC), detailing several transmission projects that are in the works, including Southline’s Southline Transmission Project.


In its Jan. 31 filing, ATC DevCo said that it expects a subsidiary company, such as ATC Southwest, will be responsible for activities relating to electric transmission development within Arizona.

As TransmissionHub reported, Arizona Electric Power Cooperative (AEPCO) and ATC DevCo have entered into a joint operating agreement under which ATC Southwest will develop needed transmission projects in Arizona and the southwest United States.

ATC DevCo said in its filing that it has been an active participant in regional and sub-regional transmission planning efforts within the Western Interconnection for several years through participation in the Western Electricity Coordinating Council (WECC) activities and membership in WestConnect. ATC DevCo also noted that it is involved in such committees and workgroups of the WECC as the Data Working Group and the Operating Transmission Expansion Planning Policy Committee.

ATC participates in the open and collaborative WestConnect transmission planning process, the company noted, adding that WestConnect completed its initial abbreviated planning cycle in December 2015, and began its first full two-year planning cycle beginning on Jan. 1, 2016. The planning cycle is scheduled to conclude with the issuance of a Regional Plan in early 2018, the company said.

Under “planned projects,” the company said that it has “none at this time.” The company said that it is studying the feasibility of transmission projects for inclusion as planned projects in future Ten-Year Plans. ATC DevCo said that it will continue to hold discussions with prospective project participants throughout 2017, and if refined scopes have been developed, those changes would be reflected in next year’s Ten-Year Plan.

The company said that transmission projects that it is studying include:

  • The approximate 15-mile Topock to Needles 230-kV Transmission Line; the point of origin is the Topock substation or Southpoint switchyard, and the point of termination is the Firehouse substation. The project is being developed by the City of Needles, Calif., with cooperation from the Western Area Power Administration (WAPA) in order to meet Needles’ growing load needs. The project would bring a new 230-kV radial feed from Arizona into a new 230-kV switchyard at the Firehouse switching station in Needles. Two new 230-kV/69-kV transformers would be added at Firehouse. ATC DevCo has been in discussion with the City of Needles regarding being the transmission developer for the project, and technical studies are ongoing
  • The Gila River to Pinal West 500-kV Transmission Line; the point of origin is the Gila River switchyard, and the point of termination is the Pinal West substation. The project is proposed in cooperation with Tucson Electric Power (TEP) to reinforce the existing transmission grid and increase capacity between the Gila River power plant and points east. ATC DevCo and ATC Southwest have been in discussion with TEP regarding the conceptual project, and technical studies are ongoing


AEPCO, in its Jan. 30 Ten-Year Transmission Plan, said that it has been an active participant in regional and sub-regional transmission planning efforts within the Western Interconnection for many years through the Southwest Area Transmission (SWAT), as well as membership in WECC and WestConnect.

AEPCO noted that its Board of Directors last November approved the 2017-2020 Construction Work Plan, which identified a number of projects that will be included in the Ten-Year Plan as planned projects. Projects that have projected in-service dates outside of the current Construction Work Plan window but still have a high likelihood of being built are also included as planned projects, AEPCO said. Additional projects that have a higher degree of uncertainty and no firm in-service dates are included as “additional projects under consideration.”

AEPCO added that planned projects include the:

  • Marana-Thornydale-Saguaro Interconnect project, which involves the construction of a new 115-kV line from the existing Marana substation to the Thornydale substation and to acquire a single circuit of TEP’s quad-circuit line from a TEP substation, disconnecting from Tortolita, and connecting it to Saguaro, reenergizing the quad-circuit line to 115-kV and interconnect with AEPCO’s Thornydale substation. The driving factor for the project is reliability. The project’s location is in Pima and Pinal counties, and its in-service date is in 2020; AEPCO’s estimated cost is about $16.2m
  • Tombstone Junction Project in Cochise County, which involves looping the AEPCO Butterfield to San Rafael 230-kV line into a new Scheiffelin substation with a 230/69-kV transformation to the existing Sulphur Springs Valley Electric Cooperative, Inc., Tombstone Junction substation and the Arizona Public Service (APS) Boot Hill substation. AEPCO and APS are discussing project configuration and cost allocations for the project; the driving factor for the project is reliability. The project’s in-service date is in 2021, and AEPCO’s estimated cost is about $13.8m
  • Valencia to Central Arizona Project (CAP) Black Mountain 115-kV Line – this line segment was approved by the Arizona Corporation Commission (ACC) Line Siting Committee in February 2010, and by the commission in April 2010, as part of the North Loop to Rattlesnake 115-kV Line Project. The project proposes a new 2.6-mile, 115-kV line that will extend from the existing AEPCO Valencia substation to tie to the turning structure of the 115-kV CAP line that heads directly north two miles to the existing CAP Black Mountain substation. The driving factor for the project is reliability on AEPCO and CAP systems. The project is located in Pima County, and its in-service date is in 2019; AEPCO’s estimated cost is about $2.5m
  • APS Bagdad Interconnection Project, which involves expanding AEPCO’s Bagdad Interconnect substation by installing a used 115/69-kV transformer and connecting it to APS’ Bagdad substation via a new 115-kV line. That connection will provide mutual backup for APS loads in the town of Bagdad, and Mohave Electric Cooperative Inc.’s loads west of Bagdad. AEPCO and APS are discussing project configuration and cost allocations for the project. The driving factor for the project is reliability for APS and Mohave Electric Cooperative. The project’s location is in Yavapai County and the in-service date is in 2018; AEPCO’s estimated cost is about $2.4m

Additional projects under consideration include the Thornydale to Twin Peaks 115-kV Line, AEPCO said, adding that the ACC Line Siting Committee approved the line segment in February 2010, and the commission approved it in April 2010. The project proposes a new, eight-mile, 115-kV line between AEPCO’s Thornydale substation and the CAP Twin Peaks substation. With the addition of the Valencia to CAP Black Mountain 115-kV Line, and the Marana-Thornydale-Saguaro Interconnect project, this project would no longer be necessary, but the same route may still be used as part of the Marana-Thornydale-Saguaro Interconnect, AEPCO said.


In its Jan. 30 filing, Southline noted that the Southline Transmission Project is comprised of a new build section of about 249 miles of 345-kV double-circuit transmission line and associated facilities (183 miles in New Mexico and 67 miles in Arizona); and an upgrade section of about 121 miles of existing 115-kV WAPA transmission line that will be upgraded to double-circuit 230-kV, along with about five miles of new non-WAPA-owned 138-kV and 230-kV transmission lines and associated facilities needed to interconnect the upgraded WAPA lines to four existing substations owned and operated by other Arizona load-serving utilities.

The new build section connects the existing El Paso Electric Company Afton substation, south of Las Cruces, N.M., to a new substation to be owned by Southline near the existing AEPCO Apache substation, south of Willcox, Ariz. The company also said that the upgrade section is located entirely within Arizona.

The Arizona Power Plant and Transmission Line Siting Committee in December 2016 issued a certificate of environmental compatibility for the project, which will provide about 1,000 MW of bidirectional transmission capacity in southern New Mexico and southern Arizona.

Southline said that it currently anticipates operations to be phased into service beginning in 2019.

Among other things, the company said that the project will improve reliability of the regional grid, mitigate existing congestion, facilitate renewable generation development, and increase the region’s ability to meet demand growth, the company said.


Buckeye Generation Center, LLC (BGC Power), in a Jan. 20 filing submitted by Cogentrix to the ACC, noted that the Buckeye Generation Center Power Project is a contemplated natural gas-fired, 630-MW electric generation peaking facility currently planned for a site within southwestern Arizona in an unincorporated portion of Maricopa County.

The project will include a 230-kV electric transmission line that will connect the electric generation facility to a contemplated 69/230-kV substation to be built, owned and operated by APS. It is currently anticipated that the 230-kV “gen tie line” will be about one mile long, and the precise location or alignment of that line has not been finalized yet, the company added.

The purpose of the generation station is to provide peaking power to Arizona electric utilities and to the interstate electrical grid, BGC Power said.

Among other things, the company said that the currently estimated in-service date for the gen tie line is 2019.

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.