基于样本熵的高水头混流式水轮机稳定性分析

Stability of High Head Francis Turbine Based on Sample Entropy

摘要:

机组的压力脉动是表征水轮机稳定性的主要参数之一，但仅基于压力脉动幅值判定水轮机的稳定性存在一定的局限性。采用多通道压力脉动同步采集系统同步采集某高水头混流式水轮机部分负荷下多部位压力脉动数据，然后综合互相关分析和互补集合经验模态分解(CEEMD)方法提取各压力脉动信号的主分量，对各压力脉动信号的主分量数据进行样本熵计算，获得不同测点在运行范围内的样本熵分布规律。结果表明：在部分负荷下，尾水管内部的空腔涡带仍然是影响高水头混流式水轮机稳定性的主要因素；可根据水轮机各部位压力脉动信号主分量的频率信息推断水轮机内部水力不稳定源的类型；关键测点处压力脉动幅值分布规律与样本熵分布规律的对比表明，压力脉动信号主分量的样本熵变化趋势能够反映水轮机内部流动状态的变化趋势。

Abstract:

Pressure fluctuation is one of the main parameters to judge turbine stability. However, there is limitation in judging turbine stability based on the amplitudes of pressure fluctuation only. By applying the multi-channel high precision pressure fluctuation test system, the pressure fluctuation in different parts of a high head Francis turbine under partial load were collected synchronously. Then the principal components of each pressure fluctuation data were extracted by cross-correlation analysis and complete ensemble empirical mode decomposition (CEEMD) method. Finally, the sample entropy of principal component data of each pressure fluctuation signal was calculated. And then the distribution of sample entropy of different monitor points in operating range was obtained. Base on the results, it can be concluded that vortex rope in draft tube was still the main factor affecting the stability of high head Francis turbine under part load condition. And the frequency information of the principal component of the pressure fluctuation at each part of the Francis turbine can be used to infer the type of the hydraulic instability source. According to the joint comparison of the pressure fluctuation amplitude distribution and the sample entropy distribution at key monitor points, it can be proved that the variation trend of the sample entropy of principal component of pressure fluctuation can reflect the stability of hydraulic turbine. Therefore, the trend analysis of the sample entropy of principal component of pressure fluctuation can be popularized as a technical method to study the variation of the inner flow state of turbine.