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Factors Affecting Transformer Noise
May 09, 2018

1. Factors Affecting No-load Noise


   The reason that the iron core produces noise is mainly that under the alternating magnetic field, the silicon steel sheet size will change slightly. Since the magnetostrictive variation period is half the period of the power supply frequency, the magnetostrictive vibration of the transformer body is based on twice the power frequency. Therefore, the vibration of the silicon steel sheet is mainly caused by the ferromagnetic material. Caused by the stretching feature.


    Magnetostriction is related to the material of the silicon steel sheet. The greater the magnetostriction, the greater the noise. When the magnetic field strength is the same, the silicon steel sheet made of a good material has a small magnetostriction, so the noise is also small.


    The magnetostriction is also related to the strength of the magnetic field. The stronger the magnetic field is, the larger ε is.


   The magnetostriction is also related to whether the surface of the silicon steel sheet is painted or annealed because the coating has adhesion to the silicon steel sheet and can prevent deformation of the silicon steel sheet. The silicon steel sheet annealed at the same magnetic field strength has much smaller magnetostriction than the unannealed silicon steel sheet. This is due to the fact that by selecting the optimum annealing process, the magnetostriction can be reduced several times.


   Transformer no-load noise in addition to its own material, etc., but also related to the joints.


2. Other factors affecting no-load noise


   (1) The influence of core structure. The noise is related to the diameter of the stem and the yoke, the height of the core window, the width of the core window, and the quality of the core. For every 1t reduction in core quality, noise can be reduced by 1/3dB(A). When the ratio of the core window height to the core diameter is decreased by 0.1, the transformer noise is reduced by 2-3 dB.


   (2) The frequency of no-load noise is its fundamental frequency at twice the power frequency. In addition to the fundamental frequency magnetic flux in the iron core, there are high-frequency magnetic fluxes, so the frequency of the no-load noise also has more than two high frequency waves. When the core tank's natural frequency is close to the noise frequency, noise resonance will occur and the noise will increase. Therefore, the natural frequency of the transformer core and tank must avoid some high-frequency waves.


   (3) In order to prevent core resonance, when designing a low noise transformer, the core's natural frequency must also be considered. When the rated frequency of the transformer is 50Hz, the core's natural frequency should avoid the following frequency bands: 75-125Hz, 165-235Hz, 275-325Hz, 375-425Hz. If the resonant frequency is away from the resonance frequency band, the core will not generate resonance.