Study On Acoustics Based Condition Monitoring Technique Of Hydro Turbines

Hydro turbine is the key device of hydro power unit. Cavitation and erosion of hydro turbine is an unavoidable destroying phenomenon and one of main factor causing hydro turbine efficiency fall, machinery destroying and life-span shortening. It can affect unit reliable running badly and it is one crucial factor of hydro turbine repair cycle. The academic and experimental research of cavitation monitoring gets extreme attentions. It is of academic and applied importance to study on the technique of hydro-turbine's cavitation and erosion monitoring and analyzing online to perform condition maintenance of hydro turbine.Based on synthesizing theoretic of cavitation and erosion, technique of cavitation monitoring, it is more detailed to analyze and discuss the characteristics of cavitation acoustic emission on time-domain and frequency-domain in auditable and ultrasonic frenquency segment and its power characteristics, some representative eigenvalues have been summarized too. The differences of cavitation acoustic signals from normal background noises are also discussed. These can be helpful for the design and development of cavitation monitoring and analyzing system.Cavitation and erosion are of microcosmic, instantaneous, at random, and multiphase complicated phenomena, which cannot be easily measured and monitored directly. To employ appropriate monitoring and characteristic extracting approaches is the key factor for successfully monitoring condition of hydro turbine. The bandwidth of cavitation acoustic signals is wide and mainly focus on high frequency-segment in spectral. Regard to the characteristic of cavitation emssion, it is adapted to monitor and analyze cavitation emssion online by means of a hybrid approach in different frequency-segment via vibratory accelerometers to sense the structure-born vibration induced by cavitation and ultrasonic absorbers to pick up the ultrasound and the measuring bandwidth is bounded. It can not only avoid analyzing error resulting from narrow-bandwidth of captured signal by means of single vibratory accelerometers or acoustics absorbers, but also increasing measuring sensitivity and capability to price ratio of monitoring system, and broadening the measuring bandwidth.Some techniques of characteristic extracting are discussed on detail, such as relativity analysis, crest factor and power spectrum density analysis. To overcome the restriction among deviation and resolution in traditional spectrum estimation based on FFT, Maximum Entropy Spectrum Estimate (MESE) is adopted in order to extract the characteristic bandwidth and characteristics in frequency-domain. One improved MESE algorithm is proposed, its evaluation model and order selection are discussed. A multiple method of power spectrum estimate combined MESE with traditional spectrum estimation is offered to improve the spectrum analyzing precision and real-time. It is listed that the characteristics of condition information in order to monitor cavitation of hydro turbine.Based on above achievements, the Noise Monitoring and Analysis System of Hydro Turbine (NMASHT ) is developed utilizing the technology of high-speed data acquisition & recording, data communication, modern signal analysis processing. NMASHT is running experimentally in one hydro power plant now, some elementary test results are given based on some measurements in laboratory and the fields. The development of this system will provide a feasible method for hydro turbine condition monitoring and maintenance.