Analysis on the Noise of Induction Motors With Loading

According to the noise measure standard of electric motors, the noise of induction motors is normally measured in the state of nonload and steady operation. In some motors, however, the variation of noise under load and nonload conditions is quite big， especially in the motors powered by the frequency converters, the sound power level can reach a maximum exceeding 3～22　dB(A). Yet electric machines are always run under load condition, so the noise level of induction motors under such condition will be more accurate. The effects of load on the electromagnetic noise of induction motors were analyzed through those on the vibration modal behaviours of the electric machinery system. The paper also analyzed the data gathered from the experiments. When working frequency is 50 Hz, the variation of the load noise is insignificant, often about ±3.0 dB(A), for the resonant frequency of motor and the frequency of exciting force are far apart. But when the motor is powered under frequency converter condition, the frequency of exciting force changes greatly, the variation of the load noise in some circumstances may be significant.