Effective versus standard Epstein loss figure in Fe-Si sheets

Abstract

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 $P_{\text{𝑒𝑝𝑠𝑡}}$ to the effective $P_{\text{𝑒𝑓𝑓}}$ loss figure, which can be interpreted in terms of ratio of effective $l_{\text{𝑒𝑓𝑓}}$ to conventional ( $l_m=$ 0.94 m) magnetic path length, evolves with the peak polarization $J_p$ , showing, in general, a monotonic increase with increasing $J_p$ . The deviation of $P_{\text{𝑒𝑝𝑠𝑡}}$ from $P_{\text{𝑒𝑓𝑓}}$ is observed to range from about $-$ 3% in the non-oriented alloys at low inductions to about $+$ 5% in the grain-oriented alloys at $J_p=$ 1.8 T. This behavior finds a rationale in the existence of a polarization profile $J_p(x)$ measured along the strip length and in the dependence of $P_{\text{𝑒𝑓𝑓}}$ on $J_p$ , showing a power law $P_{\text{𝑒𝑓𝑓}}(J_p)\propto J_p^n$ , with $n>$ 1 and increasing with $J_p$ . The so calculated effective path length $l_{eff}=l_m\cdot P_{\text{𝑒𝑝𝑠𝑡}}$ / $P_{\text{𝑒𝑓𝑓}}$ consistently shows a monotonic increase with $J_p$ , which is more relevant in the GO alloys.