Saturday, April 28, 2012
Penstocks of the Past, and Future
Having spent most of mid-April dealing with the high style design issues of the Holly Theatre, this past week has seen a return to the more typical aspects of report writing, including covered bridges and compliance documentation. Staring back at me from my computer screen at the moment is PGE’s Faraday Powerhouse, on the Clackamas River.
“Penstocks” are the feeder tubes that connect a reservoir to the turbines that spin a generator to create electricity. They are usually large concrete or steel pipes that drop significantly in elevation to create “head,” increasing the force of the water and spinning the turbines efficiently. In more recent projects (post-WWII) penstocks are typically underwater, at the bottom of a dam, and so unseen. But in an early hydro project, like that at Faraday (which was built in 1907-1909), the penstocks are exposed and become highly visible features, dropping from the crest of the dam, down an embankment, to the powerhouse. Faraday's penstocks are typical, in that these early powerhouses tend to have multiple, smaller, generation units rather than one or two large ones, and so the penstock lines can be pretty dramatic through repetition. At Faraday there are six penstocks, five built by 1909 and one, Unit No. 6 (the larger one, at the extreme right above), that was added in 1956.
Faraday’s original penstocks are of riveted steel, between eight and nine feet in diameter, and are supported by multiple concrete piers with small semi-circular “saddles” where they meet the steel penstock itself. This has worked well for over a century, but where the concrete and the steel meet, water is trapped. Steel and water are a bad mix, and one thing you surely do not want is a weak, rusted, spot in steel tube carrying 1/6 of the Clackamas River at high pressure.
PGE has creatively developed a solution to repair the damaged spots and then modify the top of the concrete piers to re-seat the penstocks with a steel-to-steel connection. This will reduce the potential for damage and allow the Faraday penstocks to continue to operate into their second century.
People tend to glaze over when I talk about my interest in hydroelectric generation, penstocks, flow lines and the like and many of these early projects are criticized as unnecessary and un-green. That's another rant. Last night I was amused, while watching NBC's filmed-in-Portland fantasy-drama show Grimm, to see that PGE's now-decommissioned Bull Run Powerhouse (built prior to WWI) played a major role. It’s a shame, and an interesting comment on how our society has changed, that only few people still see the postcard potential in engineering marvels like these early, small scale, powerhouse projects. Think about that during the next power outage, or when you drive through a sea of wind turbines.