Two Reasons Affecting Transformer Noise

1. Factors affecting transformer noise

The noise generated by the iron core is mainly due to the small change in the size of the silicon steel sheet under the action of the alternating magnetic field. Since the change period of magnetostriction is half of the power frequency, the vibration of the transformer body caused by magnetostriction is based on twice the power frequency, so the vibration of the silicon steel sheet is mainly caused by the magnetostrictive properties of the ferromagnetic material.

The magnetostriction ratio is related to the material of the silicon steel sheet. The higher the magnetostriction, the higher the noise. When the magnetic field strength is the same, the magnetostriction of the silicon steel sheet made of good material is also very small, so the noise is also very small. Magnetostriction is also related to the strength of the magnetic field. The stronger the magnetic field, the louder the noise.

The magnetostriction rate is also related to whether the surface of the silicon steel sheet is coated and annealed, because the coating has adhesion to the silicon steel sheet and can prevent the deformation of the silicon steel sheet. The magnetostriction of the annealed silicon steel sheet under the same magnetic field strength is much smaller than that of the unannealed silicon steel sheet, which is due to the fact that the magnetostriction can be reduced exponentially by selecting a good annealing process.

The no-load noise of the transformer is not only related to its own material, but also to the joint condition.

2. Other factors affecting audio transformer noise

(1) The influence of the core structure. The noise is related to the diameter of the core and yoke, the height of the core window, the width of the core window and the mass of the core.

(2) The frequency of no-load noise is twice the power frequency. In addition to the fundamental magnetic flux, there is also a high-frequency magnetic flux in the core, so there are also high-frequency waves that are more than twice the no-load noise frequency. When the natural frequency of the core tank is close to the noise frequency, the noise will resonate to increase the noise. Therefore, the natural frequencies of the transformer core and tank should avoid some high frequency waves.

(3) In order to prevent the iron core from resonating, the natural frequency of the iron core should also be considered when designing a low-noise transformer.