The audio noise of transformers

When transformers are installed near inhabited districts, their noise must be limited to unobjectionable values. Consequently, means of predetermining noise levels from the design 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. Introduction When power transformers are installed in locations remote from residences or other buildings used constantly by human beings, audio noise created by them is not a problem. However, as loads increase it becomes desirable to place larger transformers closer to inhabited districts. Large transformers can create sufficient noise as to make their presence in inhabited districts objectionable. In addition, the public is becoming more noise conscious and insistent on the elimination of objectionable noise of any kind. Consequently, the calculation of the noise of a transformer from its design constants in order to predict the amount of the noise and a study of means of noise reduction becomes a practical necessity.