Schieffelin Substation Increases Electric Reliability in Tombstone Area

New substation expands AzGT’s network

For Immediate Release
September 3, 2021

Contacts: Geoff Oldfather, (520) 586-5465, C: (520) 444-3473,
J.D. Wallace, (520) 586-5157, C: (520) 235-4203,

BENSON – Arizona G&T Cooperatives is constructing a new substation near Tombstone that will increase electric reliability by providing a new path for Sulphur Springs Valley Electric Cooperative (SSVEC) to serve its territory around the historic city. The Schieffelin Substation is scheduled to be energized in October. SSVEC is one of six electric distribution cooperative Members of AzGT.


“The new substation shows our commitment to meeting our Members’ needs,” says Claudia Aster, AzGT electrical engineer. “We have a lot of confidence in the future of the area.”

The Great Recession of 2008 slowed growth and the urgency to build new transmission infrastructure, Aster adds. The construction of Schieffelin Substation shows that is changing.

Aster explains that radial lines serve much of the Tombstone area. A radial, like a spoke from a wheel, provides one way out; there is no alternative. In the case of electric transmission, if a radial line falls out of service, everything beyond the fault’s location has no alternative service until the line is repaired. Schieffelin Substation is part of the solution for the area.

The substation is named after Ed Schieffelin, a prospector who discovered silver in the area, leading to the founding of Tombstone. Ed Schieffelin is buried at Boot Hill, which is the name of another substation AzGT is building that will connect to Schieffelin Substation. The expansion will provide a second way to serve the area and increase reliability.

Schieffelin Substation is along AzGT’s San Rafael-Butterfield 230 kV line, which runs east of the San Pedro River and state route 80. The substation, which is north of Tombstone, has a transformer that will take 230 kV down to 69 kV for used by SSVEC. A contractor installed the transformer in June.

About Arizona G&T Cooperatives

Arizona Electric Power Cooperative (AEPCO) and Sierra Southwest (Sierra) together comprise the Arizona G&T Cooperatives. AEPCO owns and operates the 605-megawatt (combined gross) Apache Generating Station, located at Cochise, east of Benson. AEPCO also owns, operates and maintains 841 miles of electric power transmission line—including line owned in part with other utilities—and 33 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; the 20 MW Apache Solar project on AEPCO property adjacent to and northeast of Apache Generating Station, and 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 of which is on property owned by the 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, California.

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.