Research On Detection Method For Motor Bearing Fault Based On Stray Flux

Bearing fault occupies a high proportion in various induction motor faults.Vibration analysis and stator current law these two diagnostic methods are widely studied,but they all have their own limitations.Bearing fault detection method based on stray flux has aroused the attention of researchers in recent years because of its advantages,such as better amplitude characteristic,lots of fault frequencies,and so on.At present,researchers generally use radial stray flux to detect bearing fault.There is no in-depth study of axial stray flux.The amplitude of the radial and axial stray flux fault frequency is out of study,too.This thesis references Schoen and Blodt two scholars' idea for deriving the stator current law and derives the frequency characteristics in stray flux of motor bearing fault from two ways-the air gap change and the torque vibration.Then,based on the magnetic circuit model,derives the normal frequency characteristics in axial and radial stray flux.Taking care of the air gap change and torque vibration at the same time,derives the bearing fault frequency characteristics in axial and radial stray flux.This thesis carried out research on the amplitude of fault frequency in radial and axial stray flux.Finding that the amplitude of fault frequency in radial stray flux is attenuating rapidly with vibration frequency multiplication increase while the amplitude of fault frequency in axial stray flux is almost unchanged with vibration frequency multiplication increase.Obtains the conclusion that axial stray flux is more effective than radial stray flux in bearing fault diagnosis.This thesis carried on experiments about induction motor with bearing fault and simulating bearing fault,with a stray flux signal acquisition system designed by myself to take the work of obtaining data.Using MATLAB takes the work of power spectrum analysis with the data,we can observe the characteristic frequency of bearing fault and do comparing research about the amplitude of fault frequency in radial and axial stray flux.The results verify the correctness of theoretical analysis,and proved the feasibility of the motor bearing fault detection method based on stray flux.