Tom Hilgert

Comparison of Magnetostriction Models for Use in Calculations of Vibrations in Magnetic Cores

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.

Magnetostriction Measurement by Using Dual Heterodyne Laser Interferometers

Electrical machines and transformers have a core built out of laminations of ferromagnetic materials. A portion of the vibrations and noise of these devices is due to magnetic forces and magnetostriction arising from the magnetic core. Magnetic forces are well known, and analytical methods are extensively used to calculate them. Magnetostriction can be defined as the deformation of the ferromagnetic material in the presence of a magnetic field. Unlike magnetic forces, magnetostriction shows a rather complex behavior. It varies for every material, and it depends on the applied magnetic field and external pressure. Therefore, magnetostrictive behavior of every material needs to be determined experimentally by means of strain measurements. Strain gauge measurement techniques have been used before at the Electrical Energy Laboratory (EELAB), Ghent University, Ghent, Belgium. In this paper, a new measurement method using dual heterodyne laser interferometers is proposed to overcome the drawbacks of the old method. The proposed measurement setup and the working principles are explained. The possibility to apply both techniques on one and the same sample can also reveal some interesting results about the quality of both techniques.

Application of magnetostriction measurements for the computation of deformation in electrical steel

In this paper, a method is presented to calculate the deformation of electrical steel due to magnetic forces and magnetostriction by using the finite element method. The magnetostrictive properties of the steel are determined experimentally in a small single-sheet tester with strain gauges fitted on the sheet. This method is applied to an inductor with a small airgap. The results from the computations are verified with measurements on the test object.

Influence of ordering phenomena on the magnetostriction of high Si alloys for electrical applications

The present work attempts to assess the influence of order phenomena on the magnetostriction of high Fe–Si alloys for electrical applications. The magnetostriction of high silicon electrical steels in the range of 4to6wt.% Si was studied regarding the effect of processing and thermal treatment. In addition, power losses and saturation magnetization measurements were performed and Fe57 Mossbauer spectroscopy was used to evaluate and quantify the degree of order.