Simulation And Characteristic Analysis Of Bearing Faults In Induction Motors

Induction motor is widely used in numerous fields, such as military, industrial production, and on vessel; its normal operation is of great importance. The motor bearing faults are the main fault accounting for30%to40%of all induction motor fault types. Hence, this thesis mainly studies on the induction motor bearing faults. At present, Motor Current Signature Analysis (MSCA) becomes one of the main methods of bearing faults diagnosis. However, the stator current contains background colored noise coming from grid and relatively high harmonics, while the amplitude of the fault characteristic frequency is small. For these reasons, this thesis is dedicated to the simulation of bearing faults in order to analyze the characteristics of the stator current more accurately.This thesis uses additional load torque variations to simulate bearing faults. By setting the switching frequency of the power switch, the load torque and current of the DC generator alter based on the switching frequency. According to the parameters of the used motors, characteristics of bearing faults and the constructional design of the system, the control circuit is designed. The trigger signal of the power switch is generated and controlled by using the STC12C5A60S2SCM and AD9850chip. The frequency, duty cycle, phases and amplitude of the trigger signal are set in the human-computer interface. In order to protect the control circuit not to be affected by the main circuit, the isolated circuit is established. A snubber circuit is also established to protect the power switch.Current sensors and vibration transducer are used to measure experiment data. Via data acquisition card NI PXIe-6356and the programmed LabVIEW program, the experiment data is collected. The collected data is analyzed in time/frequency domain on MATLAB.This paper designs and establishes the bearing fault simulation experimental platform, which single-point defects can be simulated. The experiment results not only prove the feasibility and validity of using additional load torque variations to simulate bearing faults; but also verify the phase modulation between the load torque variation caused by bearing faults and the motor stator current. The relationship between modulation index and fault-related characteristic frequencies is summarized. Furthermore, by changing the duty cycle of the trigger signal, the change of single-pointed defects’ width can be simulated, which simulates the severity of defects; by changing the amplitude of the load torque variation, the change of single-pointed defects’ depth can be simulated, which also simulates the severity of defects.