1. Factors affecting no-load noise
The main reason for the noise in the iron core is that the size of the silicon steel sheet will change slightly under the effect of the alternating magnetic field. Because the change cycle of magnetoelasticity is half the cycle of the power supply frequency, the vibration of the transformer body caused by magnetoelasticity is based on twice the power supply frequency, so the vibration of the silicon steel sheet is mainly caused by the magnetism of the ferromagnetic material. Caused by elastic properties.
The magnitude of the magneto-elasticity is related to the raw material of the silicon steel sheet. The greater the magnetoelasticity, the greater the noise. When the magnetic field strength is the same, the magnetoelasticity of the silicon steel sheet with good raw materials is also small, so the noise is also small. The magnetoelasticity is also related to the strength of the magnetic field. The stronger the magnetic field, the greater the noise.
The magneto-elasticity is also related to whether the surface of the silicon steel sheet is painted and annealed, because the coating has adhesion to the silicon steel sheet and can prevent the silicon steel sheet from deforming. The magnetoelasticity of silicon steel sheets annealed under the same magnetic field strength is much smaller than that of non-annealed silicon steel sheets. This is because the best annealing process can reduce the magnetoelasticity exponentially.
The no-load noise of the transformer is not only related to its own raw materials, 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 core column and the iron yoke, the height of the iron core window, the width of the iron core window, and the quality of the iron core. Every time the iron core quality is reduced by 1t, the noise can be reduced by 1/3db(a) value. Every time the ratio of the core window height to the core diameter decreases by 0.1, the transformer noise will be reduced 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 high frequency magnetic flux in the core, so no-load noise frequency also has a high frequency of more than two times. When the natural frequency of the iron core fuel tank is close to the noise frequency, a noise resonance phenomenon will occur, which will increase the noise. Therefore, the natural frequency of the transformer core and the fuel tank should avoid some high and repeated waves.
(3) In order to prevent core resonance, the natural frequency of the core should also be considered when designing a low-noise transformer. 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 resonate.