Research On Broken Rotor Bars Fault Diagnosis For Squirrel Cage Induction Motors Based On Running States

Squirrel cage induction motors are the main electro-mechanical energy conversion device of industry and most important energy-consuming equipment.In addition to running with low efficiency but high cost,the failure of motors can result in a total loss of the machine itself and a likely costly downtime of the whole plant.More importantly,these failures may even result in the loss of lives,which cannot be tolerated.Thus,health-monitoring and fault diagnosis techniques for squirrel cage motor are of great concern to prevent the motor failures,assure the continuity of the process,reduce the maintenance costs and energy waste in the industry and are gaining an increasing attention.Broken rotor bar is peculiar to squirrel-cage motor,which has been the hotspot in motor fault diagnosis field for long time.Although the incipient broken rotor bar will not lead to the motor out of service,the motor operating running regardless its danger will worsen its performance,enhance loss of the power,and even cause the secondary faults such as eccentric and stator scratches.If the fault is not found out timely,serious personal casualty accidents maybe happen.Supported by the Chinese academy of sciences key deployment project(KGZD-EW-302)and Liaoning science and technology plan project(2015020140),the dissertation has focused on diagnosising broken rotor bars of main-fed squirrel cage motor.According to the character of complicated operating conditions,the research mainly focuses on the theory,technology,and application of the the incipient broken rotor bar fault diagnosis problem.During the study,the dual innovations of diagnosis theory and practice are carried out based on the essence of traditional Motor Current Signature Analysis(MCSA).Five aspects content are included in this paper as following:(1)When used in the broken rotor bar fault detectionof squirrel cage motor,the classical spectrum analysis has the drawback that its diagnosis capacity depends strongly on the loads of the motor because the spectral leakage has a special adverse impact on the characteristic sideband frequencies of the fault.Aiming at this problem,a diagnosis method based on square stator current demodulation analysis is proposed with hardware circuit.The experiment results on main-fed motor under different load conditions and inverter-fed motor with different reference frequency indicate that the demodulation with hardware circuit method based on square stator current can eliminate the fundamental spectrum leakage and noise interference that restricts the diagnosis capacity,which make the spectrum intelligible and enhance the diagnose certainties.Compared with the classical MCSA,presented method could reliably detect the broken rotor bar fault even if the machine operates under lowload or no-load conditions,which make it suitable diagnosis broken rotor bars of motor operating under steady condition.(2)The diagnosis techniques based on parametric model spectral estimation with pretreated stator current are proposed for the purpose of improving the diagnostic accuracy of with broken rotor bars of motor under steady condition.Having benefited from the Hilbert mathematical transform and discrete wavelet frequency refinement,the noise interference is removed and the characteristic frequencies are transferred to low frequency band.Then,extended Prony algorithm is conducted on the obtained signal for qualitative and quantitative analysis.The experiment results on main-fed motor with different severity under viarious load conditions clearly shows the effectiveness and advantages of this method to traditional MCSA,which indicate that the result of the analysis is good even in shorter data environment.(3)Inspired by traditional MCSA suitable for steady analysis,creative solutions are proposed to resolve fault diagnosis of incipient broken rotor bars with squirrel-cage induction motor operating under time-varying conditions.The theoretical and experimental results demonstrates that the conclusion of failure or not could be drawn depending on the evolution of pattern of the characteristic frequencies due to variouble speed.An evident effect on diagnosising broken rotor bars under transient regime has been achieved by using proposed solutions.Experimental comparisons show that discrete wavelet decomposition to square Park's vector modulus obtained from the stator current has better fusion performance than some traditional methods.(4)A novelty approach based on the instantaneous frequency analysis of the left sideband harmonic from the start-up current transient is presented for the purpose of assisting the fault diagnosis performances of broken rotor bars with squirrel-cage motor operating under steady conditions.Benefiting from FIR low pass filtering and time-frequency feature extraction of D WT,the conclusion of failure or not could be drawn depending on the wavelet energy analysis and the"V" characteristic pattern evolution of the IF on the f-s plane.The proposed method,characterized by independent diagnostic resources and supplementary measure of steady MCSA,is robust and reliable,since it depends on the difference between the experimental and theoretical values of the IF at all the slips tested during the start-up and not only on aunique value of left sideband harmonic.(5)A diagnosis method based on Wigner-Ville distribution(WVD)and Discrete Wavelet Transform(DWT)is presented,which combined powerful signal preprocessing function of DWT and excellent time-frequency characteristics of WVD.DWT is conducted to square Park's vector modulus obtained from the stator current for the purpose of filtering harmonic interference,WVD is used to characterize the 'energy-slip' evolution tendency based on which energy calculation is performed and diagnosis decision-making is obtained.The theory and experiments show that the diagnosis method based on combination of pattern comparison and energy calculation have the obvious advantage over other kinds of developers.The presented methods contribute to research of broken rotor bars for main-fed drived motors operating under transient regime,which are the most significant breakthroughs in this dissertation.