On June 15, the Public Service Commission of Wisconsin approved a March 31 application from Wisconsin Public Service Corp. (WPSC) for a Certificate of Authority to replace two aging wood stave penstocks with two coated steel penstocks at its existing Grandfather Falls Hydroelectric Power Plant, located in the town of Rock Falls, Lincoln County, Wisconsin, at an estimated total cost of $15 million.
Grandfather Falls is located on the Wisconsin River, approximately 12 miles north of Merrill, Wisconsin. The hydroelectric plant was built in 1906. It currently is one of eight hydroelectric facilities that are owned and operated by WPSC on the Wisconsin River or its tributaries.
The reservoir is 5.5 miles long and covers about 340 acres. The original channel of the river has been diverted into large, wooden tubes called penstocks. The penstocks funnel and concentrate 2,500 cubic feet of water per second into the generating turbines of the plant. The facility consists of two turbines with a total generation capacity of approximately 17.24 MW.
The redwood staves installed by WPSC in 1938 were replaced by the existing treated yellow pine wood stave penstocks in 1975. The existing wood stave penstocks are nearing the end of their useful lives. WPSC’s proposal to remove the existing wood stave penstocks and replace them with steel penstocks at Grandfather Falls is the subject of this approved application. This project would help boost power generation at the site, since some of the water that would be used to push the turbines is escaping through holes in the penstocks.
Said the June 15 order: “WPSC estimates that the end of the useful life for the existing Grandfather Falls penstocks is no later than 2019. WPSC has been monitoring leakage since 1999. The historical average wood stave penstock leakage has been approximately 1,400 gallons per minute (gpm) which equates to approximately 50 kilowatts (kW) in lost generating capacity. The recent report indicates that the leakage has increased significantly to 6,000 gpm since inspections in 2012 and 2015.”
WPSC would begin construction of the proposed project in the first quarter of 2017, with completion expected by end of December 2017.