ABSTRACT
Turbines are machines that extract energy from a flow and convert it into mechanical energy. The mechanical energy is converted into electrical energy which is distributed through a grid. In hydropower turbines the flow at the blades causes the turbine to rotate. The Kaplan turbine is a reaction turbine. The pressure components within the flow are only partially converted into velocity components, thereby creating a pressure gradient within the runner. The free fall of the flow exiting the machine can be influenced by constructing a diffusor to control the downstream water level as is done in the case of conventional hydropower machines. These free-flow machines are mainly propeller type turbines or derivations. The development of hydropower machines for very low fall heads was investigated in the European Union Hydropower converters for very low head differences project. Growing power demand is leading to the exploration of more small scale hydropower technologies with free surfaces for local power generation.
