Help: What causes the second and third harmonics to appear when testing the motor individually?
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I don’t know much about motors. During a single-test run of one motor today, I noticed that the amplitude of the second harmonic was quite high. If a coupling is connected, it might be due to poor alignment; but why did this second harmonic appear during this single test?
First, disconnect the coupling and conduct a single test on the motor. Measure the effective values of vibration velocity in the horizontal, vertical, and axial directions at the bearing housings on both sides of the motor (in mm/s rms), as well as the amplitude of vibration peak energy (GSE) and its spectrum; measure the peak-to-peak vibration displacement values (in μm p-p) at the motor’s foot bolts, the foundation, various points on the plate adjacent to the foundation, and various points on the support columns beneath the plate; measure the vibration phase angles at the horizontal and vertical directions at the bearing housings on both sides of the motor at the power frequency (1×n). Power off the motor, and collect the vibration spectrum waterfall plots of the motor before and after the power-off moment.
Possible causes of the second harmonic: 1. Problems with the motor base or platform, leading to deformation of the motor; 2. Axial bending of the motor rotor or misalignment of the front and rear bearing housings; 3. Defects in the rolling elements of deep groove ball bearings. The third harmonic may be caused by pitting or scars on the raceways of the outer ring of the bearings