Derating of induction motors due to waveform distortion

Derating of induction motors due to harmonic distortion is discussed. It is found that a restriction for the second harmonic should be included in the harmonic distortion limits established by IEEE Standard 519-1981 and derating in some cases should be considered for less than 5% harmonic distortion. Drip-proof machines are found to be less affected by harmonic distortion than totally enclosed machines. Efficiency plays a very important role in the degree of derating; less efficient machines would require a higher derating. Smaller machines (less than 5 HP) are affected more by the harmonics than the larger machines