Pierre Faverolle

Characterization of the Local Incremental Permeability of a Ferromagnetic Plate Based on a Four Needles Technique

The performances of electrical machines depend highly on the behavior of ferromagnetic materials. In some applications, these materials operate under dc polarization, i.e., when the magnetic field oscillates around a dc bias. In that condition, it is required to know the incremental permeability, which characterizes the magnetic behavior of the material around the operating point. In this paper, a non-destructive approach, involving a combination of experiment and finite-element (FE) technique, is presented in order to determine the incremental permeability. The proposed sensor is based on the four-needle method. With this sensor, Bowler et al. have proposed a method to determine the initial permeability of homogeneous metal plates based on an analytical model. Here, we propose to use the same kind of sensor to determine the incremental permeability. The measurement process is analyzed using a FE model. It is shown that the analytical approach reaches its limits if the permeability of the plate and its thickness become too high. A combination between the measurements and an FE model is introduced to overcome this difficulty to determine the incremental permeability. The study of two magnetic steel samples illustrates the interest of this method.

Characterization of the local electrical properties of electrical machine parts with non-trivial geometry

In electrical machines, knowing the electrical conductivity is of importance for the eddy current calculation, especially when massive iron parts are involved. Generally the conductivity is measured on samples of raw materials with simple geometries. Indeed, a simple geometry is suitable for applying an analytical approach to deduce the electrical conductivity from the measured electrical quantities. Nevertheless, when a non destructive measurement is required, the measurement of the electrical conductivity can become rather difficult on parts with complex geometry. To that end, with the help of the Finite Element Modeling approach (FEM), a strategy is developed to characterize the local electrical properties of parts with a non-trivial geometry.

Slinky stator: The impact of manufacturing process on the magnetic properties

The manufacturing of a slinky stator core is the result of a sequence of difference processes: straightening, punching, rolling It has been shown in the literature that manufacturing processes lead to a degradation of the magnetic properties. However, it is really difficult from the state of art to classify them a priori from the most influent to the less. In order to determine the most influent processes, it is necessary the evaluate quantitatively the impact of impact of each process. In this paper, a campaign of magnetic characterization is carried out on FeSi 1.3% specimens extracted after each process on the manufacturing line of a slinky stator. Samples have different shapes, so different characterization methods were used to determine the normal curves and total losses. Results show that the dispersion in raw material is quite important and depends on the level of induction. Straightening and training processes deteriorate the magnetic material properties and dispersion after both processes is higher than the raw material one. The effect of rolling and cutting are the most harmful compared to the other manufacturing processes, while the compacting process shows a benefic effect.

Methodology for the analysis of the impact of the forging parameters on metallurgy and mechanical properties in case of solid electromagnetic manufactured parts

For electromagnetic applications the microstructure and the final mechanical state are key parameters. These can be obtained by a judicious choice of the material, a particular design like laminated steels but also through the determination and the mastering of the fabrication process. This present paper contains a brief introduction to electromagnetics and the qualification of a “good” electromagnetic quality. Then the article highlights, based on literature, first the influence of the process parameters on microstructure, mechanical state and secondly the impact these properties themselves on magnetic properties. Eventually, a methodology is proposed in order to predict the functional behavior of a part in its final system, taking into account its manufacturing process. The academic study case presented here can illustrate such a methodology. This kind of methodology includes in particular experimental tests, physical analysis and numerical modeling.