Processing Method Of Hydraulic Turbine Cavitation Acoustic Emission Signals Based On Empirical Mode Decomposition

Hydroturbine is one of the core components of hydroelectric generating units and it is the main power equipment involved in energy conversion.But cavitation and cavitation erosion are common failure phenomena in the operation of the hydroturbine,which is the main factor that causes the flow-through parts to be damaged,the unit output is decreased and the vibration is aggravated.It is of great significance to study the cavitation state monitoring of hydroturbine and improve the safety and stability of unit efficiency and unit operation.However,due to the complexity of the cavitation phenomenon,it is difficult to achieve effective monitoring of hydroturbine cavitation.Therefore,this paper studies the cavitation state of hydroturbine by a new detection method named acoustic emission technique which is combined with Empirical Mode Decomposition(EMD)method.The main contents include:The cavitation sound emission signal and the corresponding cavitation characteristic curves of different test points under different working conditions were obtained by changing the vane opening degree,the rotational speed and the tank surface pressure in the domestic high precision turbine model test bed.Aiming at the noise interference in the collected signal,EMD thresholding noise reduction method is used to pretreat the hydroturbine acoustic emission signal.Firstly,EMD is used to decompose the hydroturbine cavitation acoustic emission signal to obtain multiple Intrinsic Modal Functions(IMF),and then the first half of the IMF is denoised with the given threshold rule.The reduced IMF and untreated IMF reconstruction,to get the noise after the sound emission signal.Simulation and experimental results show that the method can effectively remove the noise components in the signal and keep the active components of the signal.The method of combining the extreme value continuation method and the correlation coefficient method and the energy ratio method is used to improve the self defect of the EMD method in processing the signal.The simulation proves its validity.The improved EMD method can quickly and effectively identify the false component,then extract the real hydroturbine cavitation information,and obtain the characteristic parameters that characterize the cavitation state of the hydroturbine.Furthermore,the improved EMD method can be used to identify the cavitation of hydroturbine.