A PROFITABLE PRIVATE MICROHYDROELECTRIC PLANT

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Once friction losses in the 8"-diameter pipe were calculated, the designers found that they had 145 feet of head to work with. And since any figure over 60 feet is considered to be within the efficient range of a Pelton wheel, that popular and widely available turbine was the obvious choice. The 15 "-hydraulic-diameter runner (which was supplied by Canyon Industries in Deming, Washington) looks much like a thick plate with a number of oddly shaped spoons attached to its periphery. Water shoots at the buckets from two 2"-diameter nozzles to spin the manganese bronze casting. The shape of the cups splits the jets and ushers the water out to the sides of the housing . . . where it falls (having given up its energy) and exits through a drain in the floor.

This rather primitive-sounding device spins at 720 revolutions per minute (RPM)—under the force of the roughly 156 pounds per second of H 2 0, moving at just short of 65 MPH, that strikes it—and the net result of all this action is the generation of about 30 horsepower at the 1-5/8" shaft. The turbine is linked to the generator by a pair of V-belts that run on adjustable pulleys sized to provide a speed increase of 2.54:1.

The generator itself is actually a 50-HP, three-phase induction motor that—since only two of its "legs" are used—is run as a 30-HP, single-phase generator. It was purchased used, but entirely rebuilt, for only $500 . . . a price that represents a saving of about a thousand dollars when compared with that of a new synchronous generator.

Besides its low cost, the induction generator has another very useful property. When operated as a motor, it receives power from the grid and spins somewhat slower than the standard synchronous speed of 1,800 RPM (this difference is known as its slip speed). But if the induction motor is driven to the slip speed above 1,800 RPM, it begins to generate power. Furthermore, at that point the utility line's signal still regulates the voltage and frequency of the power being delivered (a process called grid excitation), so no complicated and expensive speed control is needed to insure that generator and utility stay in phase.

There are, however, a number of protective circuits needed to make the two-way hydro/utility hookup safe. The Laurel Creek control panel—the design for which was donated by an electrical engineer, Richard Suhre—includes over—and undervoltage relays, a frequency relay, and a starter used for getting the system up to speed. In addition, because the generator depends on the power company's grid for voltage and frequency regulation, it was necessary to devise a way to shut down the plant in the event of utility failure. (This also protects any power company workers from being shocked by water-generated electricity when they're repairing defective utility wires.)

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