Research on upper bracket resonance and air admission damping of hydroelectric unit
(1.Hangzhou Resource Power Equipment Co.,Ltd., Hangzhou, Zhejiang 311202, China; 2.College of Water Resources ＆ Civil Engineering, China Agricultural University, Beijing 100084, China; 3.State Key Laboratory of Hydroscience and Engineering ＆ Department of Thermal Engineering, Tsinghua University, Beijing 10084, China)
Abstract：The stability test research for turbine generator set of Himmetli power station showed that the vibration amplitude of upper bracket was out of limits in specific load zone. Based on the measured experimental data, the relationship between vibration signals of upper bracket and pressure pulsation signals of spiral case inlet, head cover and draft tube is analyzed. The dynamic characteristics of upper bracket and stator bracket are analyzed and the natural frequency is obtained. The results show that the frequency of turbine pressure pulsation in the load zone is close to the natural frequency of upper bracket, which leads to the resonance of structure of the upper bracket. The test of air admission for vibration reduction, adding high pressure air from head cover into runner, has also been done. The results show that, through the spectrum analysis of the pressure pulsation signals of spiral case inlet, head cover and draft tube after air admission, the frequency which causes resonance has disappeared and the vibration amplitude has been reduced greatly. Based on the actual situation of power plant, some practicable measures of air admission, that is, inserting the pressure air compensating pipe under the original natural air compensating valve side, are proposed. After putting these measures into practice, no resonance phenomenon occurs when the unit operates in that specific load zone.
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