【作者】 杨勇；

【导师】 孙建平；

【作者基本信息】 华中科技大学 ， 流体机械及工程， 2007， 硕士

【摘要】 近年来,由于大型水利枢纽工程的兴建,使得水力发电在整个电网中所占的比重越来越大。因此,一旦发电机组因事故停机,将造成巨大的经济损失。水轮机空化是一个很普遍的现象,其对转轮叶片和过流部件会造成严重损坏,而且空蚀的严重程度已经成为一般水电厂大修周期的决定性因素,因此有必要对机组进行空化监测,以便及时调整机组运行方式,采取补气等各种有效措施来减少空化的发生。目前国内外,水轮机空化现象常用监测方法多种多样,而空化超声波信号的监测是现在比较新的监测方法,但国内主要还停留在实验室验证阶段,缺乏实际应用。而本课题,就是将这种监测方法应用到三峡机组的实际监测中去,通过采集机组运行期间有效数据,再应用适当算法处理,将这些信号中与空化有关的信息提取出来,分析出其与空化程度的对应关系,从而通过监测这些信息达到监测空化情况的目的。本文首先对空化产生的噪声和超声波特性做了简要介绍,然后针对超声波传播特性设计了具体的试验方案。方案包括:系统的设计、试验仪器的率定、信号的采集、信号的分析几个方面。在信号分析中,从空化信号自身特点出发,通过应用频谱有效值,结合FFT变换、小波分解和小波包分解对水轮机不同补气方式下空化信号的局部和整体分别进行分析,了解了组合式补气与自然补气对空化性能的影响效果,得到了能代表空化状态的频谱段。更多还原

【Abstract】 In recent years,large-scale hydropower project make the important role in the entire electrica network on account of large percentage of the annual average electric energy production.As a result ,the accident of the hydroturbine will result in the most serious economic losses.Stability is an important condition for ensuring the safety and reliability of hydroelectricity generating units. Cavitation is one of the main factors affecting the stable operation of the generating units.Therefore it is necessary to carry out cavitation monitoring for timely adjustment of the unit operation to take effective measures to reduce the emersion of the cavitation, for example compulsory gas supply maybe is a effective method to alleviate vibration and pressure pulsation of hydroturbines.Now, there are a variety of monitoring methods in the cavitation monitoring of the hydraulic turbine, and the ultrasonic cavitation signal monitoring is now better monitoring methodology, its effectiveness has been confirmed by many experiments. The main principle of the monitoring system is:By the sensor which isinstalled on the appointed situation of the turbine,sample the special signal which is relative to the cavitation,and distinguish and process by comfortale arithmetic todistill the information about the cavitation,analyse the relationship between thedegree of the cavitation and it,so as to accomplish the purpose of monitoring thecavitation by monitoring this information.This dissertation mostly researches the noisy and ultrasonic characteristic from theory and experimental ways. The experiment includes the choice of experimental scheme,the collecting and processing of signal etc. Through wiping off noise from signal, time domain and frequency domain analysis,wavelet analysis,wavelet package analysis,the law of cavitation noise intension and frequency distributing are found.更多还原