Magnetic Properties Measurement and Core Loss Modeling of Fe-Si Steel Sheet Using an Improved RSST

Rotational magnetization has been widely observed in the T-joints of three-phase transformers and in motor stators. The resulting rotational losses are significantly higher than those measured under alternating magnetization conditions. To enable more accurate electromagnetic design and hotspot detection in electrical apparatus, an improved round rotational single sheet tester (RSST) with a large sensing area and large size samples is developed, providing a more representative characterization of the material’s global magnetic anisotropy. In this paper, non-oriented (NO) silicon steel B25AV1300 and grain-oriented (GO) silicon steel B30P100 are measured under both alternating and rotating magnetic fields. Their magnetic field trajectories and loss characteristics under circular and elliptical excitations are analyzed and compared. Two core loss models are then proposed. The first model addresses one-dimensional alternating magnetization by predicting losses across flux densities and magnetization angles, whereas the second model characterizes two-dimensional rotational magnetization by predicting losses for flux densities over a defined ellipticity range. The accuracy of both models is validated experimentally.