Core Shape, Ribbon Shearing and Ribbon Width Influence on Magnetic Properties of Nanocrystalline Tape Wound Cores.

Nanocrystalline materials have very low losses compared to standard iron-silicium, amorphous materials and can work at higher inductions than ferrite materials. It makes them a good candidate for high power medium frequency transformer applications. However, manufacturing processes such as impregnation or cut significantly increase magnetic losses, as shown previous studies. Some other manufacturing processes of nanocrystalline cores can also impact magnetic properties. The core shape (toroidal, oval, C-core), the ribbon width and the ribbon shearing impact on magnetic properties will all be studied. For each of these cases, magnetic properties will be evaluated before and after impregnation and cut because these manufacturing processes have a huge impact on magnetic properties and can be coupled to the new manufacturing processes we want to study in this paper. The objectives of this study are to, firstly, be able to make a better choice of nanocrystalline cores and secondly, know how to build efficient high power medium frequency transformers with such materials. Some results in terms of losses are available on Fig. 1. These results concern cores made of sheared or unsheared nanocrystalline ribbon. Three cores of each (total of 6) have been tested. The Fig. 1 represents the average of losses density versus frequency for three induction levels. In each case, sheared cores seems to have slightly higher losses (average 11% and 21% maximum). Complex permeability versus frequency results are shown in Fig. 2. In this case, all curves of all cores are presented. Measurements have shown that the shearing of the nanocrystalline ribbons increase the losses and the permeability, while reducing the scattering between samples. The extended article will present details of how the results are obtained and some other results. One can cite the ribbon width (8 mm, 15 mm, 25 mm) and the core shape (toroidal, rectangular and oval) influence on magnetic properties.