Static and dynamic energy losses along different directions in GO steel sheets

Grain-oriented (GO) Fe-Si sheets are often preferred to non-oriented steels in large rotating machines, where the material response along directions different from the rolling one (RD) matters, both in terms of magnetisation curve and energy losses. The experiments show that the material properties depend in a complex fashion on the angle θ made by the applied field with respect to RD in the lamination plane, an effect that can be quantitatively interpreted in terms of evolution of the domain wall processes. It was shown that the pre-emptive knowledge of the material behaviour along RD (θ=0°) and the transverse direction TD (θ=90°) allows one to predict, under quasi-static excitation, the normal magnetisation curve, the hysteresis loop shape, and the energy loss dependence on θ in high-permeability GO sheets. The evolution of the quasi-static magnetic properties with θ has an obvious counterpart in the dynamic behaviour. In the present work we have therefore investigated, from the experimental and theoretical viewpoint, the behaviour of the magnetic energy loss W(f,Jp) versus frequency 1Hz⩽f⩽200Hz and peak polarisation (0.15T⩽Jp⩽1.6T) in high-permeability 0.29 mm thick GO Epstein samples, cut at 15° steps between RD and TD. We show that the predicting method developed for the quasi-static loss can be made general through loss decomposition and applied, in particular, to the determination of the excess loss term. This leads to a general description of W(f,Jp) as a function of the sheet cutting angle, without using arbitrary parameters.