The manufacturing processes of electrical machines may lead to significant degradation of magnetic core properties and therefore of the machine performance.Laminations are usually stacked and pressed which affects the magnetic properties and the iron losses. However, the influence of this step must be still investigated when large generators are considered. Indeed, in that case, the stator and rotor stacking process consists in assembling several stacks of electrical steel sheets separated by airvents. The surface of the airvent spacers represents about ten percent of the lamination surface of the magnetic circuit, implying, during the compaction process, an inhomogeneous stress distribution with significant local stresses. The present work deals with the experimental characterization of a lamination stack, including airvents, under compressive stress in the thickness direction. A mock-up has been designed and built-up to study magnetic properties of lamination stacks under pressing conditions corresponding to the industrial process.
This paper deals with the experimental investigation of the effect of impregnation process on the normal magnetization curve and iron losses of electrical steels. To address this issue, several laminated toroidal magnetic circuits have been designed to characterize the magnetic properties with the flux metric method. The first configuration considers magnetic circuits wrapped with adhesive tape so that the dielectric resin will be deposited only on the outer surface of the magnetic circuit. In the second configuration, the magnetic circuits are unwrapped, which will allow the resin to diffuse within the inter-laminar spaces of the magnetic circuit. The obtained experimental results show significant effects on the magnetic properties in both cases. However, depending on the considered configuration, the resin diffusion also has an influence on the changes in magnetic properties.
The manufacturing processes of electrical machines may lead to significant degradation of the magnetic properties of their magnetic core (stator, rotor) performances and, as a consequence, to a decrease of their energy efficiency. While the effects of some processes (cutting, welding …) are widely discussed in the literature, this is not the case with the compaction process although it is systematically used to maintain the assembly of electrical steel sheets that compose the magnetic circuits. In addition to the conventional one, a specific compaction process exists for high-power electrical machines. After an introduction, the paper firstly deals with the two studied processes (conventional, specific). Then, an experimental mock-up to study the impact of the two configurations on the magnetic properties (iron losses, normal magnetization curve) is presented. This mock-up is the first, in the literature, that allows to study the effect of a controlled compaction mechanical stress on magnetic properties. Obtained results in both configurations highlight a magneto-mechanical effect that is not reported in the literature where these effects are commonly considered following in-plane mechanical stresses. This paper presents a magneto-mechanical model, taking into account the compaction stress effect, as well as a modelling protocol to model the effect of 3D mechanical stress on magnetic properties, which has never been done in the literature.
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