The minor hysteresis loop under rotating magnetic fields in machine laminations

In rotating AC machines, the saturated flux density waveforms contain harmonics, which create minor hysteresis loops. The minor hysteresis loop in machine laminations causes a serious challenge in core loss estimation, especially under rotating magnetic fields. This paper highlights the problem of harmonics in rotating field and its effect on the core loss estimation. In addition, the behavior of minor loops under rotating fields is compared with the minor loops under pulsating fields. Measurements were carried out on a non oriented silicon steel sample of M36G29 with different fundamental frequencies of interest to the industry, 60 Hz and 400 Hz, with consideration of the third harmonic at each frequency. A novel design of magnetizing test fixture based on an electromagnetic Halbach array is used to perform these measurements. Results are presented and discussed.