Three Gorges Power Station Plant Structural Vibration Studies

The vibration of large-scale Francis hydraulic turbine set, which affects the safe operation of hydropower stations, is a serious and common problem. Powerhouse vibration caused by hydraulic turbine set frequently occured in many hydropower stations equipped with large-scale Francis hydraulic turbine set at home and abroad in varying degrees. Especially, engineers and scholars pay much attention to the vibration of floor above generator However, up to now thorough study on the key problem of vital importance to the normal operation of those hydropower stations hasn't been carried out for its complexity. Therefore, in the face of the problem, many hydropower stations have to limit operating water head to keep away from the unstable operating range. The large scale of Three Gorges hydropower station, as well as the single-unit capacity of it's hydraulic turbine generator set, is well known in the world, and the stable performance of hydraulic turbine ranks first in its type selection. Furthermore, there are lots of disadvantageous factors, such as diverse water heads and large-size runner of hydraulic turbine. Therefore, rational estimation to the vibration of Three Gorges powerhouse quantitatively is not only a key technique problem to the construction of Three Gorges, but also a difficult and pioneer interdisciplinary subject with every promise of further. A new research approach— Finite element method (FEM) combined with in-situ test, is adopted in the paper, and detailed and deep research on the vibration of Three Gorges powerhouse is carried out. Its primary context involves the following aspects:1. A more realistic three-dimension model of the complex powerhouse structure is made, which includes its integral flow passage, grid structure, key holes, all galleries, etc. Based on the model, the dynamic characteristic of the powerhouse has been analyzed.2. On the basis of the measured pulsating pressure data obtained from hydraulic turbine model test, a three-dimension field of pulsating pressure in the flow passage has been constructed with refrence to existing research results, and dynamic responses of the powerhouse structure has been solved under combined complex loads. The results show:(1) Among six operating water heads, the dynamic response to 89.4m water heads is more critical.(2) The displacement vibration of the powerhouse floor is caused mainly by the low-frequency vortex flow in draft tube.(3) The pulsating pressure in the area between guide vanes and runnercontributes most to the acceleration of the powerhouse floor.3. In order to verify and perfect above finite element model; in-situ test has been carried out for the 7th hydraulic turbine generator set under the water level of 135m. The test result presents:(1) The measured amplitude of vertical displacements and their distribution of powerhouse floor; as well as their frequencies; are close to the computed results. This fact verifies the three-dimension field of pulsating pressure constructed for the draft tube and the judgement of the vibration source of powerhouse floor displacement. However; the amplitude of measured displacement is less than the computed result; which means that the similitude ratio of pulsating pressure between prototype and model is less than 1.0 for Three Gorges hydraulic turbine.(2) The vertical acceleration of powerhouse floor; with a dominant frequency of 32.50Hz; has resonance phenomena in a frequency range of the first and second modes. As for the acceleration amplitude; the difference between the computed and measured result could become small if the effect of resonance and bus bar in prototype would be neglected. As far as the frequency of acceleration is concerned; the computed result is different from the test one; which means the frequency of pulsating pressure in the region between guide vanes and runner of Three Gorges prototypehydraulic turbine is different from that in the model test.4. Based on the in-situ test result; the finite element model has been improved.5. A safety evaluation on the vibration of powerhouse has been made; and some suggestions on vibration reduction measure have been provided.Some proposals to further study on this problem has been made.