Experimental characterization of magnetic materials for electrical machine applications

Most of the volume in classical electrical machines is occupied by magnetic materials for creating an as good as possible magnetic path. In machines with planar flux paths (2D geometries) the material is laminated to reduce eddy current losses in the core. Manufacturers typically supply reference values from Epstein frame measurements as a material performance specification and an easy way for comparison. However, the magnetic flux path in electrical machines is more complex due to rotating magnetic fields passing through the stator (with or without teeth), the rotor, and the airgap. Therefore, other material characterization methods, such as ring core measurements, are more suitable to characterize the magnetic materials for electrical machines. This paper gives a short introduction on different methods to characterize magnetic materials and a detailed description of building up a measurement system for characterizing ring core samples or electrical machine stator cores. The system is developed with regard to the IEC standard for measurements on magnetic ring core samples and can easily be build up in any lab with a power amplifier and a standard industrial control system equipped with analog input/output interfaces. Finally, reference measurements demonstrate the performance of the system.