Concept for more correct magnetic power loss measurements considering path length dynamics

Abstract

In principle, single sheet testers (SSTs) or Epstein testers (ETs) determine iron losses p through the time integral over the field H and the time derivative of the induction B. Both quantities should be determined in equivalent ways, i.e. considering an identical quasi-homogeneously magnetized sample section. Partly, this condition is fulfilled by H-coil methods. However, the so far used very small coils do not meet the demand of equivalence. At least outside of Japan, most labs prefer apparatuses where H is assumed to be proportional to the magnetization current i. But exact proportionality does not exist due to the periphery -the yoke of SST and the corners of ET, respectively. Usually, the periphery is considered through a constant effective magnetic path length lM based on the peak induction Bp. But in fact, lM varies during the period, i.e. it is a function of B(t) and thus also of time. Our novel "PLC method" is characterized by path length consideration. We consider dynamics of length through a "path length function" Λ(B) which is determined for each grade of material in a calibration process by means of a large, rigid H-coil. Considering Λ[B(t)] by software, routine measurements on similar materials can be based on the "corrected" current i(t)/Λ(t). First results are presented for HGO SiFe investigated in an ET. Here, Λ proves to be above 1 for low B and below 1 for very high B. As a final target, application of the method for both ETs and SSTs should yield almost identical loss values that are close to "true" ones.

Analysis of the Magnetic Flux Distribution in a New Shifted Non-Segmented Grain Oriented AC Motor Magnetic Circuit

“…This structure seems very simple to analyze at first glance. Nevertheless, contrary to a classical NO steel sheet stack in which the magnetic flux density is homogeneous and identical in every single sheet, the latter, in this particular stack, follow rather the lamination whose RD is the most adapted to its circulation -minimizating the magnetic energy -and, depending on the reluctance of the air-gaps, crosses the latters [7].…”

A new approach to the critical induction in transformer cores

“…2). The ones related to the RD and the TD were obtained via standardized single sheet tester method [24,25], whereas the one related to the ND is obtained by using a specific test bench [26].…”

“…In both cases, the most critical areas are the corner joints where the magnetic flux distribution presents a high degree of heterogeneity [6,7]. It is the consequence of various parameters such as the geometry of the magnetic core [8], the anisotropy level of the electrical steel [9] and a critical induction B C [4,10,11]. In particular, the latter parameter, which is the average induction level for which there is enough energy in the core to generate domains in the Transverse Direction (TD), significantly modifies the ratio between the in-plane and out of plane magnetic flux density.…”

Magnetic measurement of nanocrystalline alloy based on a single sheet tester

“…However, neither a detailed analysis of oscillation produced mechanism nor the effect of the oscillation on measurement has been illustrated, so that it is difficult to provide an appropriate scheme for acquiring field intensity under this condition. Alternatively, MC method to obtain the magnetic field intensity H originated from the Ampere Law relies on the accurate determination of MC length l m , and some investigations about the influence factor of l m have been carried out for electrical steel [10][11][12][13][14][15]. It has been revealed that the MC length is not a constant in the Epstein frame, but varied with magnetic flux density [10].…”