Enhancing Reliability

AzGT upgrades transmission poles and transformers to benefit electric consumers at the end of the line


Geoff Oldfather, (520) 586-5465, C: (520) 444-3473, goldfather@azgt.coop

J.D. Wallace, (520) 586-5157, C: (520) 235-4203, jdwallace@azgt.coop

BENSON – Arizona G&T Cooperatives (AzGT) upgrades its transmission system on an ongoing basis.  In recent months, AzGT reached two significant goals that enhanced electric reliability.

  • In November, for the third time in 2020, AzGT’s transmission line crew replaced a wooden three-pole structure with a stronger, single metal pole. The latest pole was replaced east of Willcox, while the other two were near Tucson.
  • Also in November 2020, the transmission maintenance and operations crew replaced an existing transformer with a new, larger-capacity transformer at the Valencia Substation west of Tucson. The changout meets the growing needs of Trico Electric Cooperative, an AzGT Member.

Transformer Changeouts Benefit Electric Consumers West of Tucson

Replacing the transformer was no small feat. The new transformer measures 18 feet high and weighs more than 54 tons. This 56 megavolt-ampere (MVA) unit’s output is more than double that of the transformer it replaced. The older transformer—one of similar size that weighed over 32 tons—was moved to AzGT’s Three Points Substation, also west of Tucson, where it was installed alongside an existing transformer to enhance capacity there.

“There’s a lot of work ahead of time to moving these huge transformers,” said Brian O’Toole, AzGT manager of transmission maintenance and operations. “You don’t just show up and start opening switches.”

AzGT engineers started planning the moves in 2019, and AzGT’s transmission maintenance crew spent a month preparing. AzGT hired a crane company to move the transformers, and the AzGT crew took about a week to complete putting the equipment into service.

The Valencia Substation is maintained and operated by AzGT, and the transformers belong to Trico EC. Gary Kelly, Trico’s manager of engineering, said the new, larger-capacity transformer will meet Trico’s growing residential needs for years to come, and will also provide power to one of Trico’s largest customer-members, Casino del Sol.

Stronger Steel Poles Improve Electric Reliability

The pole projects involved changing out three-pole wooden structures with stronger, single-pole, self-supporting steel structures.  The wooden structures use guy wires that run from the pole to the ground for support. Sometimes, those guy wires come out of the ground and allow the wooden poles to fall.

Barry Jackson, AzGT transmission line working foreman, said changing out transmission poles requires a lot of planning.  “We’re working to make sure electricity is reliable to all our Members,” he said.

Planning began in 2019. Each pole replacement required months of design and purchasing by AzGT engineers. Then, each project took three or four months of careful preparation by engineers and line crews. The 230-kilovolt lines supported by the poles were taken out of service for about a week during installation, but electric service was not interrupted. Line crews used huge bucket trucks to perform the changeouts.

About Arizona G&T Cooperatives

Arizona Electric Power Cooperative (AEPCO) and Sierra Southwest (Sierra) together comprise the Arizona G&T Cooperatives (www.azgt.coop). 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, the 2 MW solar array adjacent to the Anza EC 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.