The source of transformer noise mainly comes from the iron core. The iron core noise is the vibration of the iron core caused by the magnetic distortion and magnetic attraction of the silicon steel sheet. The size of the magnetic distortion is related to the silicon steel sheet material/iron core compactness. The higher the magnetic flux density of the iron core, the greater the magnetic distortion of the silicon steel sheet. The condition of the stacking joints of the transformer core will affect the flow of magnetic flux, causing the core to produce different degrees of noise. If the AC power supply contains harmonic components, it will cause the noise to expand. The core noise is the fundamental wave of 2 times the power frequency, and the noise with various frequencies that are integral multiples of it. In addition, the electromagnetic force between the winding conductors or between the coils can also cause vibration and noise. Several countermeasures to suppress noise are provided below:

Reduce the magnetic flux density of the iron core: Although reducing the magnetic flux density of the iron core can reduce the noise of the transformer, it is necessary to increase the cross-sectional area of the iron core, which leads to an increase in the weight of the transformer, which offsets the effect of noise reduction, and also increases the cost of the transformer. The reduction of the magnetic flux density of the iron core is limited to an 80% reduction.

Use silicon steel sheet with small magnetic distortion: Use high-permeability silicon steel sheet, the noise can be reduced by about 2~4dB; if the high-direction silicon steel sheet processed by laser is used, the noise can be reduced more greatly.

Equalize the binding force of the iron core: In the process of assembling the iron core, do not subject the iron core to local stress and cause deterioration of its characteristics. When using the binding belt to tighten the iron core, it is advisable to make the binding force of each part uniform.

Improve iron core joints and assembly methods: minimize the joints of the iron cores and reduce the thickness of the joints; changing the core stacking method to lap joints has a great effect on improving the noise of the transformer.

Vacuum impregnation with adhesive: The best way to reduce noise for small transformers is to put the entire transformer into a Fanli sink for vacuum impregnation after assembly.