Use of the stator current for condition monitoring of bearings in induction motors

The aim of this paper is to verify the effectiveness of the stator current analysis for the detection of bearing problems. The paper reports the experimental results on four different types of bearing faults. The cyclic faults in the outer ring cause evident effects in the current spectrum, even if these effects are different from what is commonly reported the literature: i) at no-load, there are small changes at the expected frequencies, a component excited at about 1100 Hz and the considerable increase of the 3rd and 7th harmonics; ii) at load, there are no changes at the expected frequencies and the increase of odd harmonics at high frequency. The deformation of the protective shield, a cyclic fault that does not produce any eccentricity of the rotor, shows a little increase of some odd harmonics and a component excited at about 1100 Hz, but only at no-load. A non-cyclic fault like the corrosion arouses only a slight increase of some odd harmonics at high frequencies, more pronounced at fullload. So, for the cyclic fault in the outer ring the stator current analysis seems to be effective for the condition monitoring of the bearings. In the other cases, this method needs to be supported by other signals analysis. Future work could be consider more sophisticated techniques for the current processing, the measurement of vibration to find predictable frequencies for the new faults here analyzed and the extension of the results obtained for the faults related to the outer ring to all the cyclic faults, especially to those related to the inner ring.