The Kaplan turbine works because the curved blades of the rotor are optimized to turn in relation to the velocity of the water flowing through the turbine. The curved blades generate maximum force to produce the most amount of energy possible. Kaplan turbines were invented by Austrian engineer Victor Kaplan near the beginning of the 20th century.
Kaplan turbine rotors vary in size from 2 feet up to 16 feet in diameter. Output of such turbines varies from 75 kilowatts up to 1 megawatt. Kaplan turbines resemble motor boat rotors in that they have a nosecone to optimize hydrodynamic motion. Some Kaplan models have adjustable blades for various flow rates.
Guide vanes move water in a spiral motion to further optimize electrical output. Spiraling water runs faster without extra energy pushing the water through the system. Because the design is capable of being used on small and large scales, the Kaplan turbine design is one of the most widely used in the world.
The original Kaplan design features a vertical shaft and the generator inside the casing. This type of Kaplan turbine has its entire apparatus submerged in water. This variant of hydroelectric generation is based upon the Francis turbine.