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            FAQ
            The initial magnetization curve of the transformer core
            浏览次数:1352次 发布日期:2017-10-11
                Next, we continue to analyze the magnetization process of transformer core in detail. Figure 2-3 is a curve diagram of the corresponding changes in the input pulse voltage and the flux density B or magnetic flux in the transformer core when multiple DC pulse voltages are continuously added to the primary coils of the transformer a and B. Figure 2-3-a) the phase diagram of each DC pulse for the input voltage, figure 2-3-b) is a curve diagram of the flux density B in the transformer core or the magnetic flux diameter corresponding to the change of each input DC pulse voltage. Fig. 2-3-c) the curve of the magnetic field intensity H corresponding to the flux density B or the magnetic flux density and the DC pulse voltage in the transformer core.

                From figure 2-3-a) and figure 2-3-b) it can be seen that the flux density B or magnetic flux in the core of the transformer is linearly increased and descended once per input of a DC pulse voltage (for a pure resistance load, the decrease of flux density is not linear). When the DC pulse voltage is started, the increase of magnetic flux density B or magnetic flux is larger than that of falling.

                Figure 2-3 the curves of the input pulse voltage and the flux density B or magnetic flux in the transformer core are continuously added to the two ends of the primary coil A and B of the transformer.

                This is because, when the magnetic field is magnetized, the magnetic flux density or magnetic coercive force is not close to saturation when the magnetic field is magnetized at the beginning of the work. After a number of processes, the amplitude and the amplitude of the magnetic flux density B or magnetic flux diameter increase will be very large, which indicates the magnetic flux in the transformer core. The coercive force has basically reached saturation. This process is very similar to that of the energy storage filter capacitor at the beginning of charging.

                It is also seen from figure 2-3-c that the amplitude of the magnetic field intensity change is relatively small when the DC pulse voltage is just input, and the amplitude of the change is also increasing with the number of direct current pulses increasing, but the flux density Delta Delta B is basically unchanged until the magnetic flux density reaches the maximum value of Bm. After that, the amplitude of the magnetic field intensity is basically stable; this indicates that the amplitude of the excitation current is also relatively small when the amplitude of the excitation current begins, and the amplitude of the change of the excitation current will increase with the increase of the intensity of the magnetic field.

                When the magnetic field of the transformer core is first produced by the DC pulse voltage, the intensity of the magnetic field and the amplitude of the excitation current have to pass through a transition process, and then it is basically stable, and the amplitude of the magnetic field intensity and the excitation current change from small to large; this is mainly because the core of the transformer is open. At the beginning, the permeability is relatively large, and then the permeability gradually decreases. Fig. 2-4 is a graph of the change of magnetic flux density and magnetic flux density of transformer core.。

                In Fig. 2-4, the curve B is the relation curve of magnetic flux density corresponding to the variation of magnetic field intensity, and the curve is a relation curve of magnetic conductivity corresponding to the variation of magnetic field intensity. Since we take the magnetic field strength as the independent variable and the flux density and the iron core conductivity are all dependent variables, we can also refer to the curve B and the curve Mu as the magnetization curve of the transformer core.

                Because of the magnetization curve shown in Figure 2-4, only the switch transformer iron core has never been magnetized by any magnetic field, only when it is first polarized by the magnetic field; when the switching transformer works normally, this initial state will be destroyed and no longer exist; therefore, we call the magnetization curve shown in Figure 2-4 as the magnetization curve. Initial magnetization curve. Although in practical application, we seldom encounter the initial magnetization curve of magnetic flux density corresponding to magnetic field intensity, as shown in Figure 2-4, but in practical applications, people are used to use it to analyze the magnetization process of the transformer core or to calculate the parameters of the transformer. Therefore, the initial magnetization curve is also made by people. It is called the basic magnetization curve.

                From figure 2-4, it can be seen that the maximum magnetic conductivity of the transformer core is neither the beginning of the magnetization curve nor the end of the magnetization curve, but at the left in the middle of the magnetization curve. When the magnetic field intensity H continues to increase, the flux density B will appear saturated; at this time, the increment of the flux density Delta B will drop to 0, and the value of the magnetic conductivity will also fall to close to 0. Therefore, when designing a single excitation switch transformer, it is intended to reserve a certain air gap in the core of the transformer.

                Because the magnetic conductivity of the air is thousands of times different from the magnetic conductivity of the iron core, so long as the air gap length of one percent or a few hundred points in the magnetic loop is left, the magnetoresistance or the magnetomotive force will be largely reduced to the air gap, so the magnetic core is also difficult to saturate. For example, when the air gap length reaches one percent of the total magnetic circuit length, the ratio of Br to Bm of the transformer core will be less than ten percent, and the maximum conductivity of the core of the transformer will decrease from more than 5000 to only a few hundred to several hundred.

                However, 0 of the magnetic conductivity of the transformer core has a special application in some control circuits, for example, the magnetic amplifier or magnetic modulator works by the principle that the magnetic conductivity of the magnetic material is influenced by the magnetic conductivity of the magnetic material. At present, a large number of 50 week high power regulated power supplies are basically using magnetic amplifiers to stabilize the output voltage.

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