The Audio Noise of Transformers

When transformers arc installed near inhabited districts, their noise must be limited to unobjectionable values. Consequently, means of predetermining noise levels from the desin constants of the transformer and means of noise reduction become necessary. It has been determined that the audio noise of transformers originates in the change in dimensions (magnetostriction) produced in the core steel by the alternating magnetic flux. The vibration caused by the change in dimensions is transmitted to the air through the tank walls. The basic noise may be increased due to the resonant vibration of mechanical parts. Theoretical relations for the sound produced have been derived. These relations are checked by tests on commercial transformers.