MOTHER'S ELECTRIC HYDROELECTRIC PLANT
(Page 2 of 3)
TURBINE
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One of the most expensive components in any hydroelectric plant is the sophisticated rotor that extracts power from moving water. Though the cost of casting or joining the pieces for a turbine varies with the type, the runner generally absorbs between 1/3 and 1/2 of a small installation's entire budget! To get around that "built-in" expense, Balalau combined the knowledge gained during his years of experience working with crossflow turbines in Europe with a body of information on build-it-yourself turbines assembled by the Oregon State College Engineering Department and Volunteers in Technical Assistance (VITA). The result is a Mitchell-Banki-style turbine that was built from scrap 4"-nominal mild steel pipe, 1/4" steel plate, and a 1-7/16" stainless steel shaft . . . all for under $100!
The runner itself is 12 inches in diameter and 18 inches long, has 20 blades (formed from 72° arcs of the 4" pipe), and can handle loads ranging from 1 to 10 KW. The unit's shaft rides on a pair of standard pillow-block bearings, and water is delivered through a nozzle which can be altered to accommodate a wide range of flow rates.
SPEED CONTROL
The turbine spins at between 400 and 500 RPM and is connected to an idler shaft by three-groove pulleys and Vbelts, which increase the RPM to 1,800. Though that rotational speed is perfectly suited to electrical generation, the AC system that we opted for requires precise RPM control . . . in order to maintain consistent power cycling. And, since changing loads and flow variations do tend to affect turbine speed, we were initially faced with compromising our power output (by spilling some of the flow or employing a clutch most of the time) in order to compensate for speed and load changes.
In response to the dilemma, Mr. Balalau teamed with Sweinhart Electric to come up with a completely new way of maintaining consistent speed in a small hydropower system. The control consists of a standard Lovejoy variable-width pulley arrangement, equipped with a speed sensor and a servomotor to automatically alter the effective diameters of the pulleys in response to speed changes. Thus when the turbine slows — causing the idler shaft to spin at less than 1,800 RPM — the lower pulley squeezes together (which increases its diameter) while the upper unit expands. In this way, the alternator shaft speed is held at 1,800 RPM (plus or minus 1%), in spite of increased or reduced loads and fluctuations in flow.
ALTERNATOR
Our system's power-producing package is an off-the-shelf Kamag 14 self-exciting alternator. It is designed to deal with loads up to 10 KW on a continuous basis and provides either one 240-volt or two 120-volt, 60-cycle circuits. To allow the turbine to reach operational speed without load, the unit is set up to cut in once voltage reaches 210. And similarly, the alternator is "over-speed protected" . . . by a cutout at 270 volts.
