水电站机组水力激振耦合共振风险评估

Risk Assessment of Hydraulically Excited Coupling Resonance in Hydropower Plant Units

中文关键词:水电站  混流式水轮机  水力激振  耦合共振

keywords:hydropower station  Francis turbine  hydraulic excitation  coupling resonance

中文摘要:针对老水电站机组稳定运行域窄、振动超标的问题，通过结构模态分析、水力激振频谱测试及轴系动态评估，定位振动主因并评估共振风险。测试结果表明：导叶以弯曲或扭转振型为主，顶盖与转轮呈现伞型振动及四节点变形，其固有频率均能有效避开水力激振主频；轴系临界转速及水体自振频率均满足避频要求，能排除共振风险。振动超标主因包括2点：井字形上机架刚度不足，导致转频（2.27 Hz）水平振动能量的传递；尾水管涡带诱发的0.61 Hz低频压力脉动逆向传播至蜗壳，与机械不平衡叠加，放大了下机架垂向振动及主轴摆度。所提方法揭示了多源激励耦合振动机制，为老机组振动治理提供了理论支撑与工程实践路径。

Abstract:To address the problems of a narrow stable operation range and excessive vibration in the generating units of an old hydropower plant，this paper identifies the primary causes of vibration and assesses the resonance risk via structural modal analysis，hydraulic excitation spectrum testing and shafting dynamic evaluation. The test results show that the guide vanes are dominated by bending or torsional vibration modes，the head cover and runner exhibit umbrella-shaped vibration and four-node deformation，and their natural frequencies can effectively avoid the dominant frequency of hydraulic excitation. Two primary causes account for the excessive vibration: insufficient stiffness of the grid-shaped upper frame results in the transmission of horizontal vibration energy at the rotational frequency （2.27 Hz）； the 0.61 Hz low-frequency pressure pulsation induced by the draft tube vortex rope propagates backward to the spiral case，and superimposes with mechanical unbalance，which amplifies the vertical vibration of the lower frame and the run-out of the main shaft. This paper reveals the coupling vibration mechanism induced by multi-source excitations，and provides theoretical support and an engineering practice approach for vibration control of old generating units.