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Principle of the power transformer core looseness fault monitoring method ( On)

by:Transmart     2021-01-16
Principle of the power transformer core looseness fault monitoring method ( On) 2019 - 03 - 30 15:06:10 1, core mechanism of vibration of the vibration of the iron core is due to the magnetostriction and electromagnetic force. Magnetostrictive refers to its mechanical sizes in the magnetization of the magnetic material in magnetic field changes along different direction. Magnetic material in the direction of the magnetic domain with the change of the direction of magnetization is causes of magnetostriction phenomenon. In addition to the magnetostriction, silicon steel sheet in sinusoidal magnetic hysteresis phenomenon still exist in the changing magnetic field, the magnetization M and the changes of magnetic field intensity H constitute a single value of the hysteresis loop. Set for silicon steel sheet length change & lambda; , the relationship with the magnetization M can be approximated as & lambda; ( M) = a1M2 + a2M4, a1 and a2 is constant. If H is 50 hz ( China power grid frequency) Sine wave, because of the nonlinear relationship between the M and H and hysteresis loop of the origin of symmetry, M contains 50 hz odd item fundamental wave and high order harmonic. According to the above & lambda; - - - - - - M, hysteresis expansion caused by mechanical vibration is the fundamental frequency with 100 hz, and higher harmonic containing 100 hz. Magnetostrictive generally divided into two processes, respectively is the magnetic domain 90 & deg; Bloch wall movement and the rotation of the magnetic domain. The rotation of the magnetic domain in magnetic field close to the saturation stage, greater vibration. In order to reduce the eddy current loss, iron core, generally composed of silicon steel sheet pile, pile into the iron core with a clamping piece. Heart column and the conjugate laminated iron connection generally takes the form of more inclined seam, in order to reduce such as single inclined seam the additional noise. The mechanical structure of iron core of this kind of pile type vibration can produce bigger impact, with more inclined seam structure as an example analysis of core vibration conditions. There are three kinds of electromagnetic force between silicon steel sheet: 1) Caused by a layer of magnetic flux in the repulsive force between the layers; 2) Seams in silicon steel sheet tail layer within or between column and iron the conjugate electromagnetic attraction; 3) Seams in silicon steel sheet tail attraction between the layers. 2) And 3) Respectively by the magnetic flux inside the layer under the condition of saturated magnetic flux through the layer of air gap and the normal flux (at the end of the silicon steel sheet See figure 1) . Method to the flux can cause the location of the magnetostrictive increases. In addition, the tiny the irregularity of silicon steel sheet and the friction between silicon steel sheet will affect the vibration characteristics of iron core. Seams under the condition of the magnetic field is close to saturation, the magnetic field distribution of complex ( Seams in the air gap flux only in strong magnetic field) , producing all kinds of complicated electromagnetic force. Figure 1 represents the flux Bz juncture place method, air gap magnetic flux Bg and irregularity of silicon steel sheet. These factors result in an increase in the core vibration and the complexity of vibration. Core clamping force change on core vibration impact is mainly manifested in two aspects. One is the pressure force influence on hysteresis loop, the main reason is the compression force of magnetic domain wall pinning effect. Core clamping way for silicon steel sheet produced by stress is tensile stress, Considering the main vibration direction of the core) , the test results show that the tensile stress result in the M - H curve slope and remanent magnetization are less, but this has little effect, can be ignored. 2 it is the change of the mechanical structure characteristics of the influence of vibration of iron core. Smaller compaction force which resulted in increased clearance between the core layer, vibration damping is reduced, the magnetic field distribution is more complex, the electromagnetic force is easy to stimulate the inherent vibration modal of silicon steel sheet, intensified the rubbing between the silicon steel sheet, the impact of the core vibration feature enhancements.
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