Experimental Study on the Impact of MMF Spatial Harmonics in the Mechanical Vibration of a Three-Phase Induction Motor

In this paper, an experimental study on the influence of the air-gap magnetomotive force spatial harmonic content on an induction motor, is presented. In the experimental tests, a 4-kW, 4-pole, 36-slot, 400-V, 50-Hz, three-phase, squirrel-cage, induction motor with reconfigurable double-layer windings was used, allowing changing the coil pitch. Three different coil pitches were tested, namely, 9/9, 8/9, and 7/9, and the motor air-gap flux and radial vibration were measured. A Fast-Fourier Transformer was then used to build the flux and vibration spectra to be analyzed for harmonics. The coil pitch of 7/9 (77.8% short pitch) led to the best results in reducing the harmonic distortion and mechanical vibration. The conducted experiments and results are thus presented on this paper.