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I. Factors affecting no-load noise

The main reason for the noise generated by the transformer core is that under the action of an alternating magnetic field, the size of the silicon steel sheet will change slightly. Since the change period of the magnetostriction is a half period of the power frequency, the vibration of the transformer body caused by magnetostriction is based on twice the power frequency. Therefore, the vibration of the silicon steel sheet is mainly caused by the Caused by telescopic properties.

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

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, which can prevent the silicon steel sheet from deforming. The silicon steel sheet annealed at the same magnetic field strength is much smaller than the non-annealed silicon steel sheet. This is because the best annealing process can be selected to reduce the magnetostriction by a factor of two.

Transformer no-load noise is not only related to its material, but also to the situation of the joints.

Second, other factors affecting no-load noise

(1) The influence of core structure. The noise is related to the diameter of the core and the yoke, the height of the core window, the width of the core window, and the mass of the core. For each 1t reduction in core mass, noise can be reduced by 1 / 3db (a). Every time the ratio of the core window height to the core diameter decreases by 0.1, the transformer noise will decrease by 2-3db.

(2) The frequency of no-load noise is based on twice the power supply frequency. In addition to the fundamental frequency magnetic flux, there is also a high-frequency magnetic flux in the core, so there are more than two high-frequency frequency waves at the no-load noise frequency. When the natural frequency of the core fuel tank is close to the noise frequency, a noise resonance phenomenon will occur, which will increase the noise. Therefore, the natural frequencies of the transformer core and fuel tank should 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 natural frequency of the core should avoid the following frequency bands: 75-125hz, 165-235hz, 275-325hz, 375-425hz. If the natural frequency avoids the resonance frequency band, the core will not generate resonance.

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