LIBBY, Montana -- A major rehabilitation project, to continue providing electricity to 500,000 homes, begins July 28 at Libby Dam.
The Generator Step-Up Transformer No.1 rehabilitation project signals a milestone in the U.S. Army Corps of Engineers (USACE) Seattle District’s continued efforts to enhance overall efficiency, reliability and performance of the dam’s hydropower-generating infrastructure.
The $3,940,000 rehabilitation project, which involves replacing all seals, low side bushings, protective devices (pressure gauges, gas relay, pressure relays, etc.) and conservator bladders, is anticipated to be completed September 2025.
“GSU transformers convert low-voltage, high-current AC power from the generator into high-voltage, low-current AC power,” said Libby Dam Electrical Engineer Robert Reeves. “They’re critical to our power system, as they allow power to be transported over long distances. For this reason, they require regular maintenance to prevent outages.”
Transformer No. 1 has been in service since 1975. The combination of significant physical deterioration and frequent repairs requiring intensive labor have led to full rehabilitation. Additionally, an oil analysis conducted in 2013 revealed that, for seven years prior, “hot spot” gas production in the transformer has been increasing.
““Hot gas” – methane gas content – is increasing and turning to ethane, eventually becoming ethylene,” said Reeves. “This full progression is a clear indication that the hot spot temperature is rising.”
While USACE officials do not currently detect acetylene, the current trend in gas production lends itself to the likelihood of an arcing fault (a high-power electrical discharge between two or more conductors) occurring in the future. Refurbishment, to include internal inspection and oil reconditioning, is required now to prevent this inevitable event.
For the duration of the project, Generating Units 1 and 2 will be offline for power generation. This will affect normal operations but not disrupt power service to the public.
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USACE began construction of Libby Dam in 1966 and completed the structure in 1972, with the first commercial power coming on-line on August 29, 1975. By March 1976, three more units were put on-line, and the fifth unit was finished in 1984. The powerhouse was originally designed to accommodate eight generators.
On Aug. 23, 2025, USACE Seattle District will recognize Libby Dam’s 50 years of operations, providing flood risk management, hydropower, recreation, navigation and environmental stewardship, with a Memorial unveiling and Open House.