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。
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.
引文
[1]曹洪恩.水轮发电机组状态监测与诊断技术.水电厂自动化,1995.10
[2]聂荣晟.水轮机中的空化与空蚀.水利电力出版社,1984年11月
[3]王贵.水轮机空化的超声波特性试验研究.大电机技术,2005年第二期
[4]王涛.水电机组空蚀在线监测系统的研究.大电机技术,2002.6
[5]蒲中奇,张伟,施克仁.水轮机空化在线监测系统设计.电力系统自动化,2004年11月10日
[6]宋盛义.用超声波技术监测水力机械气蚀.国外大电机,1993 (4)
[7]王永生.电了测量学.西安:西北工业大学出版社,1995
[8]武新华、王晓伟.离心泵气蚀故障声发射监测试验研究.振动工程学报,2004年8月
[9]黄继汤.空化与空蚀的原理及应用.北京:清华大学出版社,1991
[10] R. T.柯乃普等(中译本).空化与空蚀.水利电力出版社,1981
[11]曲景学.孔板泄洪洞空化初生试验及数值模拟研究.四川大学博士论文,2001
[12]何国庚.孔泡发生与运动理论及其应用.华中理工大学博士论文,2000
[13] S. L. Ceccio, and C. E. Brennen. Observation of the dynamics and acoustics of traveling bubble cavitation. Journal of Fluid Mechanical, 233, 1991, 633~660
[14] M.Cudina. Detection of cavitation phenomenon in a centrifugal pump using audible sound. Mechanical System and Signal Processing, 2003, 17(6): 1335~1347
[15] Jong-Soo Choi, D. K. Mclaughlin, D. E. Thompson. Experiments on the unsteady flow field and noise generation in a centrifugal pump impeller. Journal of Sound and Vibration 263(20032) 493~514
[16]张克危.流体机械原理(上册).北京:机械工业出版社,2000
[17]孙寿.水泵汽蚀及其防治.北京:水利水电出版社,1989
[18]张有敬.空泡机理研究进展.高压水射流,1984,(2):9~13
[19]裴拉耶夫.华中工学院水力机械教研室译.水轮机气蚀北京:机械工业出版社,1981
[20]潘森森.“空化”条.见:中国大百科全书(力学卷).北京:中国大百科全书出版社,1985 273～274
[21]常近时,寿梅华,于希哲.水轮机运行.北京:水利电力出版社,1983
[22]刘大恺主编.水轮机,北京:水利水电出版社,1997
[23]季盛林,刘国柱.水轮机(第二版).北京:水利电力出版社,1989
[24]沈东主编.水力机组故障分析.北京:水利水电出版社,1996
[25]孙寿.水泵气蚀研究的现状[J].水泵技术,1995,(3):39-46.
[26]沈建国.应用声学基础.天津大学出版社2004年9月第1版
[27] (美)奥尔特BA著,孙承平译.固体中的声场和波.北京:科学出版社,1982.
[28]冯若.超声手册.南京:南京大学出版社,1999.
[29]崔锦泰.小波分析导论.西安:西安交通大学出版社,1995
[30]冉启文,潭立英.小波分析与分数傅立叶变换及应用.北京:国防工业出版社,2002
[31]徐长发,李国宽.实用小波方法(第二版).华中科技大学出版社2005年5月
[32]飞思科技产品研发中心编著.小波分析理论与MATLAB7实现.电子工业出版社2006年5月
[33]胡广书主编.数字信号处理.北京:清华大学出版社,1997
[34] Conn A F, et al. The Fluid Dynamics of Submerged Cavitating Jet Cutting. Proc. 5th Intel. Symp.on Jet Cutting Technology, Hanover, Gennany,1980
[35]沈儫.声学测量.科学出版社,1986年
[36] B.Branko, K.Andreas.Spectrum normalization method in vibro-acoustical diagnostic measurements of hydro-turbine cavitation. Journal of Fluids Engineering, 1996, 118: 756～761
[37] [英]I.S.柏萨耳.Cavitation,汽蚀.机械工业出版社,1984年
[38] P. Bourdon,Simorieau,D. Rayanald. Accelerometer and pit counting detection ofcavitation erosion on a laboratory jet and a large francis turbine. Proceedings of XV II IAHR Symposium, Beijing, China,1994
[39] Angrisani,Daponte, D Apuzzo. Virtual Digital Signal一Processing Instrument for Measurement Superimposed Power Line Disturbances [J],Measurement, 1998, 24(1)
[40] [卢森堡] B.巴吉克.水轮机空化的多维监测革新.水利水电快报,2005年9月
[41] [德]布兰科·巴吉克.水轮机空化的智能诊断和监测.水利水电快报,2002年3月
[42] Ahhot,P.A.,1989, "Cavitation Detection Measurements on Francis a Kaplan Hydroturhines’Proceedings of the International Symposium on Caration Noise and Erosion in Fluid Systems, ASME, New York, FED-Vol. 88pp. 55-61.
[43] Ahhott, P. A., and Morton, D. W.,1991, "Hydroturhine Cavitation Detection Using Advanced Acoustic Emissions Techniques," Hydroacoustics Facilities, Instrumentation and Ecperimeutal Techniques, ASME, New York, NCA-Vol.10, pp. 75-84.
[44] P.Dupont et al, "Cavitation Erosion Prediction on Francis Turbines一Part 3, Madel Tests and Ffow Analysis", 18" IAHR Symposium Proceedings, Valencia, 1996
[45] J. F. Gulich. Diagnosis of cavitation in centrifugal pumps. World Pumps May 1992:15～20
[46] Tan Yue Can,H. R. Velkoff. A study of the measurement of cavitation inception using and electronic technique. J Fluids Engineering Trans of the ASME, 1984, 106(March)