A simplified low head propeller turbine for micro hydroelectric power

This thesis describes the development of a simplified propeller turbine unit to produce power in a low head micro hydroelectric power installation. To be appropriate for remote areas and developing countries, a micro hydro system needs to be simple in design. There are good turbine designs for medium to high heads but traditional designs for heads under about 10m, ie, the crossflow turbine and waterwheel, are slow running, requiring substantial speed increase to drive an AC generator. Propeller turbines have a higher running speed but are normally too complicated for micro hydro installations. In this thesis a suitable propeller turbine was developed. The effect of flat blades and optimum turbine blade and guide vane angles has been determined, as has the effect of various cones attached to the downstream end of the hub. The large hub diameter is an important compromise. A prototype turbine for installation on a New Zealand farm was developed from model tests. The turbine has a hub diameter to blade tip diameter ratio of 0.66 and 8 flat blades set at 30° to tangential (60° from axial). The best efficiency of the model turbine was 62%, with an efficiency of 57% at the best power point. Using scaling laws it is predicted that the prototype, with a blade tip diameter of 0.410m, will produce 6.0kW at 612 RPM from a head of 2.7m and a flow rate of 0.41m³/s. This gives 4.3kW output from the 50Hz 2-pole generator. This prediction is for no cone fitted on the downstream end of the hub, but model tests indicate that the power could be improved by about 5% with the addition of a straight sided cone on the hub