Research On Electrical-Magnetic-Vibration-Thermal Characteristics And Diagnosis Methods Of Squirrel-Cage Induction Motors With Inter-Turn Short Circuit Fault

Induction motors have been widely used in various industrial production and applications of daily life due to their simple structure,durability,and other advantages.The insulation of the stator winding will deteriorate,and the inter-turn short circuit(ITSC)fault will easily occur considering the complex operating conditions and environment of the motor.If the fault is not diagnosed and eliminated in time,the fault degree will deepen,which will affect the safety of production and cause economic losses.Therefore,for ensuring the motor operation reliability and economic benefits of production,the fault characteristics analysis and diagnosis method research of ITSC fault in induction motors are significant.Considering the influence of ITSC fault on multiple physical quantities of the motor,this dissertation analyzes the changes in electrical signal,magnetic field,electromagnetic vibration,thermal and thermal stress of the motor with different fault degrees under no-load,light load,and rated load conditions,extracts the fault characteristics,and studies the corresponding diagnosis methods.The most intuitive quantity after ITSC fault in the motor is the change of the electrical signal.In this dissertation,ITSC fault is realized by rewiring the stator winding of the prototype.The influence of different load conditions and fault degrees of the motor on the faulty phase,non-faulty phase,and short circuit current is analyzed.Besides,the variations of the motor current under fault are summarized.The correctness of the relevant analysis is verified by comparing the experimental results with the simulation ones.A fault diagnosis method of ITSC fault based on the complex component of stator current is proposed.The complex component represents the change of current,and the fault diagnosis and location can be realized by judging the trajectory of the complex component and the direction of the long axis.The magnetic field of the motor shows the corresponding fault characteristics with the change of electrical quantities.Considering the dual attributes in space and time of the air-gap magnetic field(AGMF),the expression of the air-gap flux density(AGFD)before and after the fault is deduced,and then the change of the space and time harmonic components of AGMF after the fault is clarified.The space distribution of AGFD is simulated,and the space harmonics of AGFD are analyzed based on the Fourier decomposition results.In addition,the influence of the fault on the space distribution of AGFD and harmonic distortion rate is obtained.The detection wire method is used to measure the AGMF directly,and the corresponding measured time harmonic results are entirely consistent with the derivation to verify the correctness of the correlation analysis.Then an apparent time harmonic fault characteristic quantity is obtained.Using detection coils to measure the radial and axial leakage magnetic flux(LMF)signals of the motor,and the time harmonic fault characteristics of the AGMF also appeared in the LMF signal spectrum,indicating that the time-frequency fault components in AGMF and LMF of the motor can be used to achieve effective fault diagnosis under different load conditions.Based on the research results of space-time harmonic characteristics of AGMF before and after fault,the space and time distribution characteristics of electromagnetic force wave(EFW)of normal and faulty motors are analyzed,and the fault characteristic component of time harmonic in EFW is determined.The modal analysis of the stator and the whole motor is carried out,and the risk of resonance caused by the additional EFW induced by the fault is evaluated.The variation of vibration displacement at the top of the motor housing is studied using harmonic response analysis and electromagnetic vibration experiment.The apparent fault characteristic value appeared in the corresponding frequency band of each load condition,which verifies the correctness of the deduced results of the EFW and the rationality of the proposed fault component.The change of the electromagnetic noise sound pressure level(SPL)before and after the fault is analyzed,and the apparent fault component also appears in the SPL spectrum in the sound domain,which indicates that the fault diagnosis can be achieved through the monitoring and spectrum analysis of the electromagnetic vibration and noise.Considering the actual heat dissipation form of the totally enclosed fan cooled(TEFC)motor,a three-dimensional whole domain transient thermal field simulation model is established through reasonable assumptions and equivalence,and the influence of the fault on the thermal field distribution under different load conditions of the motor is obtained.The temperature rise measurement of key temperature measuring points is realized by embedding temperature measuring elements in the motor.Combined with the simulation results under various load conditions,the time and space variation features of motor fault temperature rise characteristics are analyzed.The characteristic of winding temperature difference after fault is the most significant.A winding temperature monitoring method is proposed according to the characteristic of winding temperature change,which can provide a reference for fault diagnosis based on thermal characteristics.The thermal stress field distribution of the rotor before and after the fault is obtained through the thermal-structure coupling calculation,revealing the influence of ITSC fault on the thermal characteristics of the rotor.