The company said the plant will provide peaking power during periods of high demand, typically when weather is very hot or cold.
NorthWestern vice president of energy supply John Hines said that the project has been completed on-time and under budget.
"We’re ready to meet our customers’ demand for power with this efficient, scalable new plant that complements and enhances our generation fleet," Hines added.
Electrical upgrades to existing substation, transmission and natural gas pipelines to serve the plant have already been completed.
The $55m generating unit joins an existing peaking unit and the expanded site features a water storage tank, operations and maintenance facility and a 60MW Pratt & Whitney gas turbine generator.
