Research On The Bearing Fault Features For Induction Motors With Mixed Eccentricity

Induction motors are widely used in all kinds of national production fields because of the high performance, low cost and easy-controlled, once the induction motors have some faults, the operation efficiency for all systems will be reduced and the economic losses will be caused. The bearing is one of important part for induction motor and it is also a part which is always failed. Due to the downtime caused by bearing fault takes up a high ratio in all kind faults for induction motor, the bearing fault detection is the key to guarantee the whole system running safely and reliably.Nowadays, the bearing fault feature for motor with mixed eccentricity is rarely concerned. Based on amplitude modulation, the paper analyzes the impact on stator current when the air-gap length changes caused by bearing fault for induction motor with mixed eccentricity. Based on phase modulation, the paper analyzes the impact on stator current when the torque vibration occurs caused by bearing fault for induction motor with mixed eccentricity. According to the view of author Schoen, the induction motor inductance will change periodically when the bearing fault happens. Combining induction motor multi-loop theory, the paper calculates the induction inductance in three cases, namely, when bearing fault occurs for induction motor without mixed eccentricity, when the motor is with mixed eccentricity, when bearing fault occurs for induction motor with mixed eccentricity. MATLAB is used to do some simulation, by changing the inductance in motor model to simulate the situation that the bearing fault can cause the air-gap length change, by adding the torque pulse to simulate the situation that the bearing fault can cause torque vibration. Finally, data collected in induction motor simulation bearing fault detection platform, artificially-set bearing fault detection platform, are used to verify the analysis results and simulation results.According to the analysis, it is found that if mixed eccentricity is considered when the bearing fault occurs, the stator current spectrum is richer than the stator current spectrum when the bearing fault occurs without considering the mixed eccentricity. The reason is that there is an intermodultaion between the bearing fault signal, mixed eccentricity signal and power supply signal. It is also found that during the modulation style for bearing fault, the phase modulation is more important than the amplitude modulation. The simulation results and laboratory experiment verify correctness of the theoretical analysis for the paper.