Multiaxial Magneto-Mechanical Interactions in Electrical Steel Sheets

Abstract

This thesis studies multiaxial magneto-mechanical interactions in electrical steel sheets with particular attention to non-oriented electrical steel sheets. Commonly, during the magneto-elastic analysis of electromagnetic applications only uniaxial stress models are used where the effect of multiaxial stress is often neglected.

A new rotational single sheet tester (RSST) that is capable of applying arbitrary in-plane magneto-mechanical loading to steel sheets is designed and manufactured. Experiments on a non-oriented electrical steel sheet are performed for analyzing the effect of multiaxial stress on magnetic properties and iron losses in the material. Performed experiments reveal that the effect of multiaxial stress on magnetic properties and iron losses can be much more significant than that of uniaxial stress.

A simplified multiscale (SM) and a macroscopic Helmholtz energy based (HE) model are used to model the multiaxial magneto-mechanical behavior of non-oriented electrical steel sheets and their prediction capabilities are compared when limited measurement data is available for identification. The models were studied for modeling both anhysteretic and hysteretic behavior of three different materials that were characterized by different measurement setups. Comparison of the modeling results to the measured results shows that the SM model is accurate for certain cases, whereas the HE model is successful for all three materials.

In order to predict the effect of multiaxial stress on hysteresis and excess losses, a stress dependent iron loss model is developed utilizing statistical loss theory. The model is verified with measurements obtained from the manufactured RSST. For validation purposes, both the HE model and the developed loss model is implemented to a 2D finite element model of a transformer that is under mechanical stress. The applicability of the models is proven by comparing the modeling results to the measurements. It is concluded that if mechanical stresses are present in an application, using conventional methods to calculate the losses can lead to inaccurate results.