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All fields of activity using electric energy are more than ever challenged for efficiency and versatility of energy flow at reasonable costs. The emergence of electronic components with high voltage and current capabilities enables to cope with those challenges. The paper deals with assessments on Medium Frequency (MF) high-power Solid State Transformer (SST). A good technical-economic balance can be achieved by assembling suitable high power SST cells made with mature technologies for power electronics, magnetic cores and simple and reliable control strategies. In this framework, the study and design of a SST based on elementary cells involving a Grain Oriented Electrical Steel (GOES) core is addressed.

Medium-frequency transformers are used in high power electronic dc/dc converters. In case of the three-phase dual active bridge topology (DAB3), a six-step voltage is applied to the transformer. In this study, a 200 kVA three phase power transformer prototype is using 0.18 mm thick high permeability Grain Oriented Electrical Steel (GOES) at B = 1.5 T and f = 1000 Hz. The prototype has been designed and built in link with a transformer manufacturer. In this paper, a complete test bench is set up to validate GOES as a suitable material for medium-frequency transformers. The efficiency of the components is evaluated at different operating points.

We discuss the results of an international comparison regarding the measurement of magnetic power loss and apparent power between 20 Hz and 100 Hz at magnetic polarization values ranging between 1.3 T and 1.8 T in grain-oriented steel (GO) sheets using the Single Sheet Testing (SST) and Epstein methods. This exercise, carried out in the framework of the activity of Joint Working Group IEC 68/WG1-ISO/TC17/WG16, was aimed at a solid assessment of the degree of reproducibility of the SST method, under its prospective adoption in the industrial practice as a reference method for the specifications of grain-oriented alloys. Five different types of Fe-Si GO alloys were circulated among eleven different laboratories of metrological institutes and industry. The statistical analysis of the results shows close reproducibility properties of the SST and Epstein methods. It is obtained, in particular, that the power loss figures, measured by the participants at 50 Hz and the aforementioned peak polarization values are distributed around their reference value with relative standard deviation σ (P)SST = 0.88% and σ (P)Epst = 0.82% for SST and Epstein, respectively. It is obtained σ (S)SST = 2.20% and σ (S)Epst = 2.15% for the apparent power. For the industrially relevant case of polarization Jp = 1.7 T in the high-permeability P-type grades, these quantities amount to σ (P)SST = 0.48%, σ (P)Epst = 0.80%. By restricting the comparison to the European metrological laboratories (INRIM, NPL, PTB), the overall distributions narrow to σ (P)SST = 0.42%, σ (P)Epst = 0.55%, σ (S)SST = 1.19%, and σ (S)Epst = 0.82%. A qualitative interpretation of the main physical mechanisms and the measuring features underlying the lab-to-lab dispersion of the SST and Epstein results is discussed in this paper. It is concluded that the combination of good reproducibility and simple practical implementation make the SST method totally appropriate as a reference method for the definition of the material quality in the specification standards

Since 1996. a new release of European standard EN 10-107. concerning the rated properties for grain oriented electrical steels indicates that their magnetic properties can be established using either classical Epstein (IEC 404-2) or S.S.T.(IEC 404-3) tests. Consequences arising from these two different ways of assessing the steel are pointed out and discussed.

During the building process of an electrical machine, stamping operations induce stresses in electrical steels so that it affects their magnetic properties. This detrimental effect is hereafter quantified for different grades of electrical steels with attention to size effects and stamping tool configurations.

In this work systematic experiments were carried out to attempt the identification of microstructural effects (texture, grain size) on the polarization dependence of internal coercive field V/sub 0/ and hysteresis loss P/sub hys/, determined by statistical power loss model (SPLM). Experiments were performed on 0.35 mm thick 3.2 wt% SiFe non-oriented (NO) electrical steel, with different grain size and almost the same crystallographic texture. From each material Epstein samples were cut at different angles to the rolling direction (RD). Loss separation and fitting process was carried out, according to the SPLM, for determining V/sub 0/ and P/sub hys/ as a function of the polarization. Three synthetic parameters were proposed in the 0.3 T-1.2 T polarization range, where the model was found to be valid: two coefficients P/sup 0//sub (hya/) and n(1) to represent the hysteresis loss according to an exponential law and an average value of the internal coercive field V/sup (avg/)/sub 0/ over the investigated polarization range. The dependence of V/sup (avg/)/sub 0/, P/sup 0//sub (hys/) and n(1) on the grain size and texture has been clearly identified, resulting in a single texture dependent behavior for both quasistatic and dynamic properties. All the results obtained from fitted P/sub hys/ values were confirmed by quasi-static measurements. A theoretical model, based on the measured orientation distribution function (ODF) has been proposed to reproduce the obtained texture dependence.