WATER TURBINE TECHNOLOGY FOR SMALL POWER STATIONS.

Low heads are a typical feature in hydro power station construction in Finland. Most of the heads are lower than 10m (33 ft. ), with the head range of big power stations 10-25m (33 to 82 ft). In small low-head power stations, a tubular turbine with horizontal shaft is usually used. In small machines, the draft tube is bent, allowing placing of the generator outside the waterway. The turbine runner and generator are usually located above the tailwater level. This is an important safety factor and, at the same time, the maintenance of the plant is easier and construction costs are lower. A turbine usually contains a Kaplan-runner with adjustable blades. As a guide apparatus, fixed guide vanes connected to a butterfly valve operating as a shut-off device, or a distributor with adjustable wicket gates, can be used. The typical head range for such a turbine is 3-20m (10 to 65 ft. ) and discharge is 5-60m**3/s (180 to 2100 cfs). When the discharge exceeds 80-90 m**3/s (3000 cfs), a bulb-type turbine may be used.