01 Jul 2020
About Pelton Turbine's Runner
The Pelton turbine is a kind of hydraulic prime mover that draws a free jet with kinetic energy by means of a special water guide mechanism and rushes to the runner bucket to rotate the runner to do work, thereby completing the conversion of hydraulic energy into mechanical energy. Impact turbines are suitable for high-head, low-flow power stations. It converts water from pressure pipes into high-speed jets through nozzles, tangentially impacts the runner, and pushes the runner to rotate, thereby driving the generator rotor to generate electricity. In the impact hydraulic turbine, according to the difference of the relative position of the working jet and the runner and the number of workmanship, it can be divided into a shear impact turbine, an oblique impact turbine and a double-click turbine.
The manufacturing process of Pelton Turbine runner blades is complicated and there are many procedures. Although the production process varies widely, it generally includes dozens of processes such as material preparation, blank manufacturing, forming, and heat treatment. Therefore, the manufacturing technology of runner blades is often used as a landmark indicator that reflects the competitiveness of manufacturers of hydraulic turbine equipment, and is highly valued by the hydropower industry in various countries around the world.
Pelton turbine runner blades are generally designed as three-dimensional twisted curved surfaces based on hydraulics. The cross-sectional shape is very complicated, and the thickness of the water inlet and outlet is very large. The traditional blade design and production and lofting are mainly realized based on the wooden model of the blade. That is, the conformal transformation method is used to draw the blades of each calculated flow surface, and the frontal axial cross-section of the blade is drawn, and then carried out by some method. The blade is thickened and the axial cut line of the back surface of the blade is drawn. Finally, the intersection point with the front and back axial cut line of the horizontal axis is obtained through a set of horizontal auxiliary cut lines, so as to obtain the blade wooden model diagram. This production method is extremely simple and suitable in the era of manual drawing design, and the modern design concept is to replace the singular points (source point, sink point and vortex point) distributed on the wing bone line in the runner grid The wing shape replaces the actual flow field of the fluid around the cascade with the superimposed flow field of the undisturbed incoming flow and the singular point series induction. At the same time, the wing shape surrounding line is a closed flow line in the superimposed flow field. The runner blade is designed based on the principle of flow superposition. As for the production and lofting of the blade, most of them are realized by computer-aided drawing software.
All water bucket turbines are evolved from the same principle model. The fundamental difference between them is the diameter ratio. Therefore, the shape of the runner, the thickness of the wheel, the number of water buckets, the position of the water bucket on the wheel, etc., all vary depending on the diameter ratio.
According to the basic principle model theory of the water bucket turbine, all the basic cross-sectional profiles of the water bucket are similar or the same. In addition, all other geometric elements of the water bucket are different. This difference or difference changes regularly with the change of the diameter ratio of the runner of the water bucket turbine. The actual use diameter ratio of the water bucket turbine is not very large, so the geometric difference between different water buckets is not large. However, in order to pursue the highest efficiency, the runner and its bucket must be individually designed.
The diameter ratio of the bucket turbine is not determined at the beginning of the design. However, the previous hydraulic turbine works and literature set the initial diameter ratio of the bucket-type water turbine as the design specification, stipulating its use range or "selecting" the diameter ratio according to the height of the design head, and so on. It is true that if the design head is high and the volume is small, the diameter of the runner is too large and the diameter of the jet is too small, so the diameter ratio of the turbine is large. This is definitely an objective rule. However, the runner diameter D1 and jet diameter d of the water bucket turbine. Each has its own design principle, so there is a diameter ratio of the bucket turbine. Therefore, it is unfounded or even wrong to specify one or other specifications and other design principles for the diameter ratio of the water supply bucket turbine.
In summary, there are mainly three methods for forming the runner blades of the hydraulic turbine: the separate casting method, the numerical control processing method, and the molding method. The separate casting method has always been a traditional process for manufacturing blades. There are two domestic casting solutions for large blades, one is horizontal casting and the other is vertical casting. Due to the large variation in the thickness and curvature of the cross section of the turbine blade, there is no obvious order of solidification, so its shrinkage is poor. Casting blades generally have many defects, large repair work, dimensional accuracy and blade shape error are difficult to control and many other issues.