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H. Pfützner, G. Shilyashki, E. Huber:
"Physical Assessment of the Magnetic Path Length of Energy Loss Testers";
IEEE Transactions on Magnetics, Vol.56 (2020), No. 12.

Magnetic energy losses of SiFe sheets are determined by the standardized methods of single sheet tester (SST) or Epstein tester(ET). According to IEC standards, the total power consumption is measured in Watt-metric ways, and the portion that concerns the homogeneously magnetized region(s) is estimated on a nominal value l_m of the so-called conventional effective magnetic path length
(PL). A clear definitin of PL is lacking-a suggestion being provided here. Standards express l_m through the dependence between the magnetic fild strength H and the magnetization current. However, they apply the same value l_m also for the determinationof losses P. From the viewpoint of physics, two PL quantities l_m,H and l_m,P would be preferable. The problematic is enhanced by the fact that the flu distribution within the magnetic circuit of a tester may change dynamically during the period of time, with induction changes B(t). This means that the physical PL L is a function of time, according to a PL function L[B(t)]. Finally, dynamic changes in flu distributions prove to be distinctly influnced by hysteretic mechanisms which means that L[B(t)] exhibits loop character. The resulting complexity indicates that the concept of PL is not promising, if high accuracy of testing is demanded.
However, for purposes of material comparisons, optimum PL values L_OPT may be suitable that are determined for individual material families. Analyses of instantaneous loss power values p(t) indicate that energy dissipation is weak during high induction.
Thus, determinations of L_OPT should be focussed on moderate induction. The ET is characterized by strong modifiations of 3-D
flu distributions which means that individual values L_OPT would be needed. On the other hand, the SST shows a clear design.For moderate induction, some energy dissipation is expected to occur within the yoke region. This indicates that L_OPT exceeds the conventional value of 450 mm, in weak ways.

Epstein tester (ET), magnetic losses, magnetic path length (PL), silicon iron, single sheet tester (SST)

http://dx.doi.org/10.1109/TMAG.2020.3025041