Kunalw, <br><br>I would modify your idea "harmonic waveform superimposes itself on the main waveform" as follows:<br><br>As you rightly pointed out, the non-sinusoidal armature supply itself is a cause of harmonics (probably, the supply is obtained from inverters to enable variable freq operation). When such a case arises, there's a principal component (which you call as the 'main waveform') and various harmonics- some of them cancel each other; others circulate within the windings if it's delta-connected. In any case, we do have torque produced by these harmonic currents. These won't be aiding the main torque, in most cases.<br><br>I'm not clear on what you meant by "Hence these harmonic fields act as small motors."<br><br>Regards<br><br><A HREF="mailto:umn@ieee.org">umn@ieee.org</A>