Effective versus standard Epstein loss figure in Fe-Si sheets

The magnetic power losses have been measured at 50 Hz and different peak polarization values on different types of non-oriented and grain-oriented Fe-Si sheets using the Epstein frame, according to the current standards. The very same measurements have then been repeated by measuring polarization and tangential magnetic field by means of localized windings, centrally placed on the strips inside the Epstein frame windings, thereby retrieving the effective field and the true power loss figure. It is obtained that the ratio of the standard P to the effective P loss figure, which can be interpreted in terms of ratio of effective l to conventional (lm= 0.94 m) magnetic path length, evolves with the peak polarization Jp, showing, in general, a monotonic increase with increasing Jp. The deviation of P from P is observed to range from about -3% in the non-oriented alloys at low inductions to about +5% in the grain-oriented alloys at Jp= 1.8 T. This behavior finds a rationale in the existence of a polarization profile Jp⁢(x) measured along the strip length and in the dependence of P on Jp, showing a power law P⁢(Jp)∝Jpn, with n>1 and increasing with Jp. The so calculated effective path length le⁢f⁢f=lm⋅P/P consistently shows a monotonic increase with Jp, which is more relevant in the GO alloys.