Study On The Vibration And Noise Variation Laws Of Asynchronous Motor Operating With Broken Bars

Squirrel-cage induction motor has the advantages of simple structure, reliable operation and low cost, which is widely used in industrial and agricultural production and daily life. Because of the harsh working and frequent starting conditions, it is difficult to avoid the faults of motor, and the rotor broken bars is one of the common faults. Sudden failure of the motor will cause certain economic losses, and may cause harm to people. Hence, the research on the fault diagnosis of induction motor has certain practical significance. Starting with the electromagnetic field, this paper studies the variation law of the vibration and noise of the motor before and after the rotor broken bar, and finds out the fault features.Taking a skewed induction motor Y802-2 as example, the finite element models are established for cases of a healthy rotor, a broken bar and two broken bars according to the prototype parameters, and skewed rotor is fully taken into consideration. The transient magnetic fields on the three cases are calculated respectively, and the effect of the broken bars on the electromagnetic field and the air gap flux density is analyzed. Meanwhile, by the detecting coil, the air gap flux density is measured to confirm the validity of the simulated magnetic fields.Based on air gap flux density extracted in the transient magnetic field,electromagnetic forces in the air gap of the health and fault motors are calculated by the Maxwell stress equations. Taking electromagnetic forces as the load condition,the electromagnetic vibration is calculated according to the finite element model of the motor. Vibration curves of motors are achieved, and the magnitudes and frequencies of the vibration are calculated utilizing the methods of spectral analysis and Fast Fourier Transform(FFT). By comparing the vibration spectrum of the healthy and faulty motor, the fault characteristic quantity of rotor broken bars is found out. Meanwhile, it is proved that the conclusion is correct by analytical method and vibration test.The acoustic boundary element method is used to study the electromagnetic noise,and the acoustic grid and filed point grid of motor are established, the vibration dataon the surface of the motor is used as the load condition, and the electromagnetic noise of the motor is calculated in time and frequency domain. In the time domain,acoustic pressure distributions at each time and sound pressure level curves of motor field point are got. In the frequency domain, acoustic pressure distributions at each frequency and frequency response curves of the motor field point are also got.Electromagnetic noise are compared and analyzed on the case of a healthy rotor, a broken bar and two broken bars, and the variation law of electromagnetic noise of the motor before and after the broken bars is obtained, and the characteristic frequency of the vibration spectrum is also reflected in the noise.