Methods for hysteresis losses determinations at non-standard ring core geometries equivalent to Epstein measurements

The iron losses in electrical machines differ significantly from those of measurements using the standardized measurement method, i.e. by use of an Epstein frame. In order to obtain a better approximation of the losses in an electrical machine, several toroidal geometries were examined more closely. In the first step, according to the standardized method, a ring-geometry was chosen, which corresponds to the magnetic path length of the Epstein frame. Starting from this reference ring and by gradual reduction of the diameter, further ring cores were measured. Within this framework, different methods were used, in which e.g. the influence of axial height, length of the cutting edge relative to the area or the ratio of outer and inner diameter was investigated. In addition to the measurements, numerical calculations were performed. Here, the focus lies on the exploration of the field density distribution over the ring width with respect to the various methods. Taking into account for those processing effects with the highest impact, the smallest geometries of each method and the largest ring, acting as a reference, were studied in detail. The investigations on the toroidal cores of the methods were carried out at a frequency of 400 Hz and a target minimum polarization of 1.0 T. As a final outcome, a recalculation of an existing machine with the new parameters of a selected ring nucleus was done.