Boot Hill Transformer Project to Increase Electric Reliability in Southeastern Arizona

Transformer and other improvements create a “loop feed” to help eliminate outages

Barry Brown, executive director of engineering and transmission maintenance, watches as the new transformer is lowered in to place at the Boot Hill Substation east of Tombstone.

BENSON – Arizona G&T Cooperatives has installed a new transformer that will increase reliability for a large area in southeastern Arizona. The transformer and related enhancements are at AzGT’s new Boot Hill Substation, located on Gleeson Road about three miles east of Tombstone.

“The area where the transformer was installed is a whole new substation for AzGT,” said Claudia Aster, electrical engineer for Arizona Electric Power Cooperative (AEPCO), which operates under the AzGT banner.  “It adjoins another utility’s substation, the APS Boot Hill Substation.”

Completion of AzGT’s portion of the project is expected in July. Sulphur Springs Valley Electric Cooperative, one of AzGT’s six distribution cooperative Members, is building a line to distribute the power to their system, to be completed later this summer.

As Aster explained, the transformer will be part of a “loop feed” that will improve reliability in SSVEC’s service area. The loop feed will replace a radial feed, where just one line extends into the service area; when a fault de-energizes a radial feed line, all service to that area stops. “With a loop feed, we’re able to lose one side or the other of that loop and still maintain service to that area,” she said.

For Aster, one of the project’s highlights was seeing a huge crane lift the 150,000-pound transformer off the delivery flatbed and onto the substation pad.

The project represents another step forward in AzGT’s ongoing effort to enhance service and reliability.


About Arizona G&T Cooperatives

Arizona Electric Power Cooperative (AEPCO) and Sierra Southwest (Sierra) together comprise Arizona G&T Cooperatives ( AEPCO owns and operates the 625-megawatt (combined gross) Apache Generating Station, located at Cochise, east of Benson. AEPCO also owns, operates and maintains 866 miles of electric power transmission line—including line owned in part with other utilities—and 36 substations to provide wholesale electric power from Apache to six Member distribution cooperatives in southern Arizona, western New Mexico, northwestern Arizona and California.

Sierra is the vehicle to develop new ways to serve the renewable energy needs of AzGT Member cooperatives and customers, and helps maximize solar and other renewable tax credits. Sierra has initiated two utility-scale solar projects. AEPCO’s 20 MW Apache Solar project is located on AEPCO property adjacent to and northeast of Apache Generating Station. The second project includes SunAnza Phase I, a 2 MW solar array, as well as SunAnza Phase II, which includes an additional 1.4 MW solar array and a battery storage system, all on property owned by Anza Electric Cooperative adjacent to its headquarters in Anza, California.

Combined, the distribution cooperatives that receive AEPCO’s wholesale power serve more than 161,000 meters representing more than 420,000 individual residential, commercial, agricultural, and industrial member/consumers.

The Class A Member cooperatives that receive wholesale power from AEPCO include Duncan Valley Electric Cooperative, Duncan; Graham County Electric Cooperative, Pima; Mohave Electric Cooperative, Bullhead City; Sulphur Springs Valley Electric Cooperative, Willcox; Trico Electric Cooperative, Marana; and a California member, Anza Electric Cooperative, Anza.

These Member cooperatives own AzGT and, by extension, AzGT’s Member distribution cooperatives are owned by their members—the people at the end of the line who use the power.

AEPCO also serves five Class D energy services Members which are scheduling and trading customers and which include the Central Arizona Water Conservation District, Phoenix, AZ; Lincoln County Power District #1, Pioche, NV; Metropolitan Water District of Southern California, Los Angeles, CA; Southwest Public Power Agency, Maricopa, AZ; and Valley Electric Association, Pahrump, NV.

AEPCO is also a Member/owner of ACES, a nationwide energy management company ( that helps its Members and customers buy, sell, and manage energy more efficiently and with less risk. The AEPCO/AzGT Benson campus hosts the ACES West Regional Trading Center (WRTC), which benefits AEPCO/AzGT Members and customers.