Fabrication and Characterization of Floating Small Hydroelectric Power Generator using Spiral Water Wheel

Abstract

For the practical application of small hydroelectric power generation, the authors designed a floating small hydroelectric power generation system equipped with a float, and fabricated and measured the system using a spiral turbine. The authors also designed and fabricated a cylinder as a mechanism to prevent water divergence. This paper describes the number of blades of the spiral turbine and the effect of the mechanism designed and fabricated by the authors on the measurement results.

A three-phase AC generator with a rated voltage of AC 220 [V], a rated power of 30 [W], a rated speed of 900 [rpm], and a winding resistance per phase of 32.5 [Ω] was used as the generator. The three-phase AC output of the generator was converted to DC by a three-phase bridge diode. The rotation of the spiral turbine is transmitted to the generator by a gear box with bevel gears and a gear ratio of 2. The float was made of SPF material, which is moderately soft and easy to process, and a two-body float was fabricated. The total length of the float was set at 1200 [mm], taking into account the buoyancy and total weight of the device. The water wheel was made from a commercially available product and one made by the authors using a 3D printer.

Based on the measurement results, firstly, the mechanism (cylinder) for preventing water divergence is considered to be effective in a state where there is little braking by the load current, that is, in a region where the load resistance is sufficiently larger than the value of the winding resistance per phase. Measurements under a flow velocity of 1.18 [m/s] and the winding resistance per phase 32.5 [Ω] of the generator used showed that the power output and efficiency were better with the cylinder attached in the region where the load resistance was 200 [Ω] or higher. Next is the number of blades. The same can be said for the number of vanes as for the choice of whether or not to install a cylinder. In the region where the load resistance is small, the rotation of the generator is braked by the large load current, so increasing the number of blades requires a larger force to rotate the generator, making it ineffective. The authors expect that determining the number of blades and the inner diameter of the cylinder from a composite point of view, according to the load current, will increase the power and efficiency. In the measurements with a winding resistance of 32.5 [Ω] per phase and a flow velocity of 1.18 [m/s], both power and efficiency peaked in the range of load resistances between 90 [Ω] and 200 [Ω], with and without cylinders. The average power and efficiency in this range were 3.3 [W] and 8.9 [%], respectively.

For the practical application of small hydroelectric power generation, the effectiveness of auxiliary mechanisms such as floats and cylinders fabricated by the authors, as well as the characteristics of the number of blades, can be utilized.