As we all know, water turbine generator set is the core and key mechanical component of hydropower station. Therefore, it is particularly important to ensure the stable operation of the whole hydraulic turbine unit. There are many factors that affect the stability of hydraulic turbine unit, which have existed since the design of the whole hydraulic turbine unit.
In the whole design of hydraulic turbine unit, the influence of hydraulic design is small. When the water turbine unit operates under normal conditions, the water flow at the runner outlet of the unit will continue to flow out, and the water flow at the runner outlet will not rotate. When the turbine is not in the optimal working state, the flow at the runner outlet will gradually form a circular flow in the turbine draft tube. When the turbine is under 40 ~ 70% partial load of low head, the flow at the runner outlet will rotate forward and gradually form a ribbon vortex, which will even cause vibration of the turbine unit.
In the operation of hydraulic turbine, the most important factor causing the vibration of hydraulic turbine unit is the pressure pulsation of draft tube, and this factor will pose a threat to the normal operation of Francis turbine. In addition, if the Karman vortex train is generated at the tail of the flow around airfoil, it will also affect the normal operation of the hydraulic turbine, because it will lead to forced vibration of the runner blade of the hydraulic turbine. When the frequency of this forced vibration forms a multiple relationship with the natural vibration frequency of the runner blade, it will lead to cracks in the runner blade of the hydraulic turbine, and even lead to blade fracture.
In addition, there is another factor that will also affect the stable operation of the turbine, that is, hydraulic factor. If the operation condition of the turbine unit deviates from the design condition of the turbine, the flow separation phenomenon will occur at the inlet and outlet of the blade. Due to the unstable frequency of the flow separation phenomenon, the degree of harm is also different. The hydraulic model of hydraulic turbine is the power source of the whole hydropower station.
Scientific and reasonable structural design, processing and manufacturing of water turbine unit can effectively improve the stability of water turbine operation, and the main factors affecting its structural design and manufacturing are as follows:
① For flow passage components, when the flow pressure in the flow passage acts on the flow passage components, it will produce stress. With the increase of stress, it will lead to elastic deformation of the components. In addition, when the flow is agitated, each component will also produce vibration. When the vibration frequency of water flow is the same as the natural frequency of components, it will also produce resonance, which will not only produce serious noise pollution, but also affect the normal operation of hydraulic turbine unit. Especially for the water turbine unit with large size and low speed, its natural frequency is very close to the hydraulic low frequency, so it is easy to be affected by resonance.
② The influence of processing technology. In the processing and manufacturing of hydraulic turbine unit, if the blade processing is not accurate, or there are errors in the welding process of components, the inlet and outlet opening values of blades will be relatively uneven, which will eventually lead to vibration problems of hydraulic turbine unit engine.
③ When the labyrinth ring is processed, the large ovality will also lead to vibration problems of the unit.
In addition, the installation quality of water turbine unit will also affect the stable operation of water turbine unit. Among the various components of the hydraulic turbine unit, if the guide bearings are not concentric with each other or the axis is not correct, it will cause hydraulic vibration and vibration of the bearing components.
Post time: Sep-22-2021
