The Advantages And Disadvantages Of Comparing Axial Flow Turbine With Francis Turbine
Author: source: date: 2020-04-09 10:16:09
There are many types of hydroelectric generators. Today we will introduce the axial hydroelectric generators in detail. The applications of axial-flow hydroelectric generators over the years are mainly developed like high heads and large sizes. The development speed of domestic axial flow turbines is also very fast. The two axial flow paddle turbines installed in the Gezhouba Hydropower Station, one of which has a diameter of 11.3 meters, is the largest in the world at present. . The following are the advantages and disadvantages of the axial turbine.
Advantages of axial turbine
Compared with Francis turbine, axial flow turbine has the following main advantages
1. High specific speed and good energy characteristics. Therefore, its unit speed and unit flow rate are higher than that of Francis turbine. Under the same head and output conditions, it can greatly reduce the size of the turbine generator set, reduce the weight of the unit, and save material consumption, so it is economical. high.
2. The surface shape and surface roughness of the runner blades of axial flow turbines can easily meet the requirements in manufacturing. Axial-flow paddle turbines have higher average efficiency than Francis due to the blades can rotate. When the load and head change, the efficiency does not change much.
3. The runner blade of the axial flow paddle turbine can be disassembled, which is convenient for manufacturing and transportation.
Therefore, the axial flow turbine can be kept stable in a large operating range, the vibration is small, and it has high efficiency and output. In the range of low head, it has almost replaced the Francis turbine. In recent decades, no matter in the capacity of the single machine or the use of head, there has been great development and wide application.
3. Disadvantages of axial flow turbines
However, the axial flow turbine also has disadvantages and limits its scope of application.
The main disadvantages
1. The number of blades is small, and it is cantilevered, so the strength is poor, and it cannot be used in medium and high head hydropower stations.
2. Due to the large unit flow and high unit speed, it has a smaller suction height than the Francis turbine under the same head conditions, resulting in a large excavation depth of the power plant foundation and relatively high investment.
According to the above-mentioned shortcomings of axial-flow turbines, new materials with high-strength anti-cavitation are used in the manufacture of hydraulic turbines and the stress of the blades is improved in the design, so that the application head of axial-flow turbines is constantly increasing. At present, the applied head range of the axial flow paddle turbine is 3 to 90 m, and it has entered the area of the Francis turbine. For example, the maximum single-machine output of foreign axial flow paddle turbines is 181,700 kW, the highest water head is 88m, and the diameter of the runner is 10.3m. The maximum output of the axial flow paddle turbine produced in China is 175,000 kW, the maximum head is 78m, and the maximum runner diameter is 11.3m. Axial-flow fixed-blade turbine blades are fixed and simple in structure, but they cannot adapt to hydropower stations with large changes in head and load. They are stable to the head and serve as a large base station or multi-unit power station. When the seasonal power is abundant, the economic comparison is also possible. It can be considered. Its applicable head range is 3 to 50m. Axial-flow paddle turbines generally use vertical devices. Its working process is basically the same as that of Francis turbines. The difference is that when the load is changed, it not only adjusts the rotation of the guide vanes. , While also adjusting the rotation of the runner blades to maintain high efficiency.
In hydroelectric generators, the difference between Francis turbines and axial turbines is still very large. For example, the structure of their runners is different. The blades of the Francis turbine are almost parallel to the main shaft, while the axial flow is almost perpendicular to the main shaft.