中文摘要：

随着中国水电机组数量及装机容量的不断增加,水电机组启动过渡过程故障问题也日趋明显,利用信号分析法对机组故障诊断得到广泛的应用。利用一种处理非线性非平稳信号自适应方法——变分模态分解（Variational Mode Decompostion,VMD）,对葛洲坝某台机组启动过渡过程振动信号分析。首先,利用VMD方法对启动过渡过程仿真振动信号进行分析,验证VMD方法处理非线性非稳态信号的有效性。然后,利用该方法对机组启动过渡过程实测振动信号进行固有模态函数（IMF）的有效分离,通过Hilbert-Huang（HHT）变换对各IMF进行瞬时频率计算,得出相应的Hilbert谱,并将结果与经验模态分解（EMD）方法进行对比。从最终的振动信号分析中可以看出,通过VMD分解后的IMF可划分为3部分：第1部分主要为信号的发展趋势;第2部分主要为信号的基础分解,出现较强的规律性的＂纺锤形＂信号,且能够反映机组开机过程的振动变化规律;第3部分主要为干扰噪音或机组故障导致的高频特征信号,信号波形图无明显规律性,对应的Hilbert谱也明显具有主频波动小,幅值稳定等优势。结果表明：经VMD分解后,机组启动过渡过程振动信号各分量频率变化与机组转速时变规律吻合良好,能够有效提取特征频率,较EMD具有更好的自适应性,分析结果更加准确有效,能够更好地揭示水电机组过渡过程信号中的振动规律。

英文摘要：

With the increase of hydropower units and installed capacity in China,the fault problem during the transient process occurs frequently. The signal analysis method is widely used to deal with the problem. The variational mode decomposition（ VMD） method,a relatively new self-adaptive method for processing non-linear and non-stationary signals,was adopted to investigate the vibration signals during the transient process of a hydropower unit in the Gezhouba power plant. The first step was to use VMD to analyze the simulated vibration signals of the transient process,and to verify the effectiveness of the VMD method in dealing with non-linear and unstable signals. The Hilbert-Huang transform（ HHT） was then used to calculate the instantaneous frequency of each intrinsic mode functions（ IMF） decomposed by VMD to obtain the corresponding Hilbert spectrum. These results were compared with those from empirical mode decomposition（ EMD） method. From the final vibration signal analysis,the IMF decomposed by VMD could be divided into three parts.The first part was the trend of signal development. The second part was the basic decomposition of the signal with a strong regularity of＂spindle＂signal reflecting the change law of the transient process. The third part was high-frequency characteristic signals mainly caused by interference noise or unit failure. The corresponding Hilbert spectrum had the characteristics of small fluctuation and stable amplitude. The results showed good consistency between the frequency change of each component and the time-dependent rule of the rotational speed. This suggested that VMD was capable of extracting characteristic frequencies to facilitate the analysis of vibration characteristics. Compared with EMD,the VMD outperformed in self-adaptivity. It provided more accurate and effective analysis results and a better representation of the vibration rule during the transient process of the hydropower unit.