Fundamental Research On Monitoring Of Operating Conditions For Centrifugal Pump Based On MCSA

A centrifugal pump served as dynamic machine is widely used in various industries.Monitoring the operating condition of pump is helpful for ensuring the safety and efficiency of pump's operating.The monitoring technology based on motor stator current signal analysis is an economical,nonintrusive and reliable technique to monitor equipment driven by motor.When centrifugal pump is operating at different conditions,there are corresponding characteristics of pressure fluctuation,which could cause the hydraulic torque pulsation.The characteristics of hydraulic torque pulsation of pump would be transmitted to motor rotor by shaft,and there would be corresponding characteristics in torque of motor rotor.The characteristics of torque of motor rotor would be transmitted to motor stator current by the electromagnetic coupling effect.Therefore,there is theoretical feasibility to monitoring operating conditions of centrifugal pump by MCSA.In this thesis,the system consisting of IS-65-50-160 centrifugal pump and Y160M-2 B3 motor is researched,and the method of combined with theoretical analysis,numerical simulation and experimental tests was taken to confirm the applicability of monitoring method based on MCSA.Through the research,it can be figured out that the characteristics of stator current when pump is operating at the conditions of different flowrates and different degree of cavitation,which laid the foundation for operation conditions monitoring.The main works and innovations as following:1.The centrifugal pump was modeled by software UG NX10.0 and meshed by ANSYS ICEM 14.0.The software of CFX was used to simulate and calculate the internal flow,pressure fluctuation and hydraulic torque of pump.The hydraulic performance obtained by numerical simulation are in good agreement with experimental results.Through frequency domain analysis,the pressure fluctuation and hydraulic torque propagation law of centrifugal pump were studied.2.The characteristics of hydraulic torque would be transmitted to motor by shaft.The law of torque transmission was studied by simulating the model of shaft through the software of Workbench.The theory that the characteristics of torque would be reflected in the stator current of the motor was analyzed.3.A test rig was established.Combined the program written in LabVIEW with virtual instruments,the purposes of collecting hydraulic performance parameters of centrifugal pump and stator current of motor,and control of experimental process were realized.4.By analyzing the stator current obtained by the test,RMS of the stator current increased with increasing flowrates of centrifugal pump.The frequency domain spectrum of stator current was obtained by use the method of FFT,which shows a good agreement with the result of theoretical analysis.The amplitude of power frequency is much higher than other frequency,which makes the signal reflecting the operating conditions of the centrifugal pump submerged in the fluctuation of power current.The method of SVD was taken to eliminate the influence of power current,and result shows that the signal-noise ratio was enhanced.Shaft frequency become the main frequency and other relatively weak frequency components appeared,which is useful for further analysis.Calculating the total harmonic distortion(THD)of stator current shows that THD increases as the operating condition of the centrifugal pump deviating from the normalized flowrate.Combining the characteristics of RMS and THD of stator current,we can achieve the goal of monitoring of the flowrate of centrifugal pump.5.The analysis of shaft torque obtained by the experiment shows that the increasing of the cavitation degree will lead to the decreasing of the mean value of the torque and the increasing of the fluctuation amplitude of torque.The shaft frequency is the main frequency when centrifugal pump was operating under different cavitation degrees,and the amplitude of shaft frequency is much higher than the amplitude of other frequencies components.As the cavitation developing,the amplitude of the main frequency gradually mounting,and the high-frequency component of the torque appeared.6.When centrifugal pump was operating under cavitation condition,stator current of motor was analyzed in time domain,frequency domain,time-frequency domain.when the degree of cavitation develops to severe,more harmonic components and noise are appeared in the stator current in time domain.Before the critical cavitation,the RMS did not change too much.But the RMS changed intensely when cavitation degree changed from critical cavitation to severe cavitation.This feature can be severed as one of the monitoring indicators of cavitation degree.The kurtosis value is sensitive to the cavitation process.The kurtosis value of the stator current increased rapidly when cavitation appeared,and the kurtosis value would keep increases as the degree of cavitation developing.In the frequency domain,the SVD method was taken to eliminate the power frequency of the stator,and the shaft frequency of the stator current signal is the main frequency.With the increase of cavitation,the shaft frequency sideband noise is getting larger and larger,and the high frequency current component is mounting.The stator current is decomposed by ‘db9' wavelet packet and 16 wavelet packet nodes are obtained.The amplitude of lowfrequency wavelet packet is found to be higher than the amplitude of high-frequency wavelet packet in frequency domain.Eliminate the power frequency wavelet packet and calculate the proportion of the energy of the remaining wavelet packets.It can be seen that as the degree of cavitation increases,the energy of the stator current gradually shifts to the high frequency.