Iron Loss Characterization in Laminated Cores at Room and Liquid Nitrogen Temperature

This paper presents the characterization of the magnetic properties of laminated cores for electrical machines at ambient and cryogenic temperature. Silicon-iron stator cores of different steel grades are characterized experimentally at room temperature and when immersed in a liquid nitrogen atmosphere. The magnetic characterizations involve the measurement of the normal magnetization curve, and the core losses in a wide range of frequencies and magnetic flux densities. The separation of the losses into their physical components is carried out with an energy based approach aiming at a thorough analysis of each loss contribution. The results show that the cryogenic temperature does not significantly impact the magnetization characteristic of the material, regardless the tested steel grade. The core losses generally increase at cryogenic temperature. The separation of the losses into components shows that the hysteresis contribution is not much affected by the cryogenic temperature; the global dynamic losses increase at a rate that depends on the steel grade instead, at least in the examined frequency and flux density ranges.