Magnetic Characterization of Ferromagnetic Alloys for High-Speed Electric Machines

Abstract

High-speed electric machines operate at tens of thousands of revolutions per minute. The rotor and stator cores experience high-frequency electromagnetic fields. While the magnetic characteristics are available at 50/60 Hz, magnetic characteristics are required over a wide range of frequency due to variable speed operation of high speed motor. In this article, tests are carried out on ferromagnetic alloys over a frequency range of 1 Hz to 5 kHz and flux densities ranging from 0.1 to 2 T. The materials considered include the widely used M36 and 65C600 laminations. In applications where the rotor speed and shaft temperature are high, solid core rotors are more viable than laminated ones. Furthermore, the application requires that the shaft and active magnetic parts of the rotor be made of a single material. Hence, EN353 and EN8 are the prospective rotor materials considered. An extensive experimental study on the magnetic characteristics of these materials over a wide frequency range is reported in this article. The flux density variation over the core length at different frequencies is analyzed using finite element analysis. The results include B-H curves, static magnetisation curves, and power loss curves. The loss curves are useful to evaluate the loss density in the magnetic material at different frequencies and for various values of peak flux densities. These experimental data are essential for the analysis, design, and performance evaluation of high-speed electric machines.