Polyphase Induction Motor Noise and Its Control

A plethora of sources have arisen over the years that have made noise control desirable and mandatory. The growing national concern of “the environment” has culminated in many studies in the acoustical arena dealing with noise‐related hearing loss, worker inefficiency, and many other physiological and psychological areas. The result of this noise awareness has been to effectuate a wealth of noise limitations. These range from federal, state, and local municipal ordinances to those found in the specifications of the motor buyer. The motor manufacturer has not been immune from this onslaught of noise restrictions. Whether the motivating agent is to meet a specification or simply remain competitive, the motor supplier has had to suddenly add a third dimension to motor design. Where previously only electrical and mechanical parameters were considered, sonance properties must now also be deliberated. In this paper, the gravitation towards the quiet motor will be presented. Of all the possible motor noise sources, only two have been found to have a major impact on the motor's airborne noise level, these being air movement (fan and ventilation passages) and magnetic (slot combination) in nature. While abatement of the former is possible by source, enclosure and/or acoustical treatment, magnetic noise is controllable solely through source diminishment. In summary, motor noise sources are enumerated, distinction as to whether peculiar to high‐ or low‐speed machinery is explained, and means of abatement are discussed. Both calculations and test data are also presented to verify the assertions made. Finally, it is suggested that reforms necessary to reduce motor airborne noise levels were not as debilitating as first imagined. Some related areas of further investigation are delineated at the conclusion of the paper.