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July 2013

Walsh Completes Expansion of PPL Montana Rainbow Hydroelectric Dam

Last Wednesday, PPL held a dedication ceremony for the $245 million upgrade to the Rainbow Dam Powerhouse, which nearly doubles Rainbow's power generating capacity. It was the biggest power generation construction project in Montana in 30 years.

Walsh began construction of the new facility in October 2009 and work was completed earlier this year. The project required the removal of more than 500,000 cubic yards of earth and rock. More than 65,000 cubic yards of concrete were poured, and 7 million pounds of rebar went into the new powerhouse.

The new powerhouse has a single turbine about four stories tall that generates as much as 60 megawatts of electricity when the Missouri River rises. The original powerhouse was built northeast of Great Falls in 1910 and had eight smaller turbines that generated a capacity of 35 megawatts.

More than 300 power poles and 23 miles of cable were required in the three and-a-half year project. There was also sensitivity to the proximity of the Lewis and Clark Trail. The project forged a partnership with the Lewis and Clark Trail Heritage Foundation along with the labor unions, suppliers, contractors and state and local government. The idea was to build the powerhouse without interrupting the structure of historic land.

In addition to the new powerhouse, the redevelopment project included the replacement of 23 miles of 100-kilovolt power lines, substation upgrades at PPL Montana's five Great Falls hydroelectric plants, and installation of a new Crooked Falls switchyard. The enhancements will strengthen the reliability and efficiency of electrical systems connecting PPL Montana's Great Falls facilities to NorthWestern Energy's grid.

The dedication ceremony drew a host of state and local officials and celebrated the successful completion of the project. The new powerhouse opened the same day the old powerhouse was shut down. The original powerhouse saw a long, useful life, dating back to 1910.



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