The single sheet tester. Its acceptance, reproducibility, and application issues on grain-oriented steel

Abstract
Different systematic error characterictics of the Epstein and the Single Sheet Tester (SST) method (according to IEC publ. 404-3 (1992)) cause differences of up to 10 % between the specific total power loss values provided by the two methods, resulting in inconsistent values of core loss building factors in transformers. In addition, the older SST version, SST(1982), being calibrated to the Epstein tester which uses annealed samples, has been found to yield questionable results for some rnaterials. Moreover, the calibration to the Epstein tester tends to decrease the reproducibility. This unclear situation made ABB initiate an international Round-Robin Test of corresponding measurements of grain-oriented materials including the comparison of SST(92) and SST(82). The results of this study are presented in this paper along with the presentation of the application issues. The results underline the need for further activities in this field. These activities should aim at arriving at the most reproducible and reasonably simple method which delivers power loss values acceptable to manufacturers and consumers. The paper concludes with suggestions for future work.