Dynamics Effects on Magnetostriction Under Rotational Magnetization (original) (raw)
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IEEE Transactions on Magnetics, 2012
The ac magnetostriction in electrical steel is commonly characterized in the time domain (e.g., the peak-to-peak, zero-to-peak amplitude) and also in the frequency domain (e.g., a harmonic analysis). However, due to the dynamical coupling of the test sample with the experimental setup , the characterization of the magnetostriction (especially the one in the frequency domain) can give the wrong result. This research focuses on an experimental frequency characterization of magnetostriction and gives the theoretical background of the test sample's dynamical coupling with the experimental setup. The discussed natural dynamics of the test sample from the point of view of the different boundary conditions that can be used at the experiment gives a clear picture of the dynamical coupling. Besides the theoretical background, a detailed experimental approach is presented. This research theoretically and experimentally showed that the dynamical coupling of the sample can result in incorrect characterization of the magnetostriction. However, with the theoretical guidelines presented, the dynamical coupling can be completely avoided, which results in an accurate characterization of the magnetostriction.
Contribution of magnetostriction to transformer noise
An important source of transformer noise is magnetostrictive vibration of the magnetic core. This paper outlines some important effects of mechanical building stress on magnetostriction. Harmonic analysis of magnetostriction is necessary to quantify its influence on acoustic noise but it implied here that the most important magnetostrictive parameter has not yet been identified. A route is proposed for obtaining a definite, quantified relationship between defined magnetostrictive characteristics of core laminations and noise by systematically assessing noise and vibration modes of simple, small transformer cores.
Comparison of magnetostriction models for use in calculations of vibrations in magnetic cores
2008
In this paper, the vibrations of the magnetic cores of power transformers due to magnetostriction are studied. To achieve this, a magnetostriction model based on magnetostriction measurements is needed. Two different magnetostriction models are compared, and their advantages and drawbacks are discussed. The first model is easy to implement, but does not include the hysteresis and the frequency dependency of the magnetostriction. To include these effects, a second model has been developed. This model is more difficult to implement and requires more magnetostriction measurements. As an application, the vibrations of a small power transformer are calculated using both models. By comparing the results, it is shown that the inclusion of hysteresis in the magnetostriction model has a significant impact on the calculated results for the vibrations of the transformer.
Magnetostrictively induced mechanical resonance of electrical steel strips
2007
Extensive research has been carried out over the years to reduce the acoustic noise resulting from vibration of electromagnetic cores mainly caused by magnetostriction. This project presents the results of a basic experimental study of magnetostriction in strips of magnetic materials commonly used in electromagnetic cores which gives an important new understanding of the phenomenon. The presence of mechanical resonance in the laminations is highlighted here for the first time. A standard magnetising system was built and a new method of measuring magnetostriction was used. A single point laser vibrometer was used to measure magnetostrictive vibration of the samples. The magnetostriction of grain-oriented materials cut at various angles to the rolling direction, non-oriented samples with different silicon content and nickel iron strips was measured over a wide range of magnetising frequencies and at peak flux densities up to 1.O Tesla. Magnetostriction measurement results were used to...
IEEE Transactions on Magnetics, 2018
The noise generated by rotating machines and electrical transformers is harmful and its reduction has been the subject of several studies. Such systems are likely to come into resonance and become noisier. This resonance may come from mechanical or magnetic forces. The phenomenon of resonance is usually studied only if the frequency and the known spatial distribution of the excitation force are consistent with the natural frequency and the shape of the corresponding mode of the structure. We demonstrate in this paper that magnetostriction can induce resonance without, however, knowing its spatial distribution. A ferromagnetic frame made of a stack of non-oriented electrical steel (e.g., low-power transformers for railway applications) is used to confirm that mechanical resonance can be induced by magnetostrictive strain at a very low magnitude in in-plane and out-of-plane directions. Finite-element calculations are performed with laminated model and vibratory measurements are presented. A numerical model based on homogenization technique is also detailed. Then, experimental and computation results are analyzed and compared. Finally, results of resonance under magnetization when double the magnetizing frequency matches the resonance frequency of the ferromagnetic frame are described as well as the corresponding spectrum.
Rakenteiden Mekaniikka, 2018
The magnetostriction in electrical steel under rotational magnetization is usually measured with cross-shaped samples. However, the inhomogeneity of the magnetization and stress in the sample might hinder the measured results. In this paper, we investigate this phenomenon by using a magneto-mechanically coupled energy-based model to simulate the sample in a single sheet tester measurement setup, and compare the simulations and measurements. The results show that some anomalies in the measured magnetostriction can be explained by the inhomogeneous magnetization in the sample and the form effect, which result in inhomogeneous stresses and thus affect the observed quantities. The validity of the model as well as the presented statements are ascertained through experiments on the single sheet tester. The backgrounds of the used modelization technique are also detailed.
Magnetostriction Anisotropy and Rotational Magnetostriction of a Nonoriented Electrical Steel
IEEE Transactions on Magnetics, 2000
Magnetostriction in nonoriented (NO) electrical steel is a possible source of vibration and acoustic noise in electrical machines. The anisotropy of the magnetostriction of NO steel can be far greater than that of its specific power loss which is often quoted. Also magnetostriction under rotational magnetization can be much higher than under alternating magnetization. This paper shows the relevance of magnetostrictive anisotropy to the rotational magnetostriction of a NO steel. An investigation of the effect of anisotropy in magnetostriction was carried out, followed by rotational magnetostriction measurements. A model based on an analogy of mechanical elasticity was used to describe the effect of magnetostrictive anisotropy on the rotational magnetostriction. Results show that a high value in rotational magnetostriction is mainly driven by its high magnetostriction in the transverse direction. The phenomenon is shown to be a source of asymmetrical deformation in the back iron of electrical machine cores where rotational flux predominates.
Journal of Magnetism and Magnetic Materials, 2016
The correlation between magnetoacoustic emission signal envelopes and magnetostriction curves is investigated. Two sets of samples are being considered: tempered martensitic steel and plastically deformed ferritic steel. It is shown that even though some general relations may be observed, as was demonstrated in the literature, the correlation is not always present. One may not expect to change both quantities in the same way if a serious modification of microstructure takes place, as for instance in the case of plastically deformed samples for which the dislocation cell structure is formed once a certain level (1.5-2%) of deformation is reached. Being so, any relation not taking into account statistical properties of domain structure and pinning sites distribution may not yield a general solution of the problem.
2013
Transformer noise is of increasing environmental concern so continued efforts are being made by electrical steel and transformer producers to satisfy users by reducing the noise. Magnetostriction and magnetic forces are the main causes of transformer core noise and vibration. Understanding of the relationship from the core material to core structure and core vibration to core noise can help the design of low noise transformer cores. The most appropriate parameter for investigating the relationship between noise and vibration is sound pressure (in the unit of Pascals) in the frequency domain because it is not A-weighted. In this study, the side surfaces of transformer cores were found to emit higher noise than front and top surfaces at low magnetic induction. When the magnetic induction was increased, the effect of magnetic force increased and caused the front surfaces to emit higher noise. For three phase three limb transformer cores, the front surface of the middle limb generated h...
MAGNETOSTRICTION DISTRIBUTION IN A MODEL TRANSFORMER CORE Georgi Shilyashki * −
2011
The primary aim of this work is to study the distribution of magnetostriction-caused strain in different regions of a model transformer core. A technique of measuring the peak-to-peak strain ε with a high number of well averaging strain-gauges is presented. The results indicate very high variations of ε. In rolling direction, limbs and yokes show values of ε below 1 ppm, close to catalogue values of magnetostriction (MS). Corners exhibit values up to 2.5 ppm, probably with strong contributions of magnetostatic forces. T-joints show values up to 3 ppm due to high MS as being typical for rotational magnetization apart from contributions from forces. Generally, much lower values were found for the transverse direction. As a main conclusion, a major contribution for vibrations can be expected for the axial direction of yokes.