Numerical Analysis of the Impact of Elliptical Fields on Magnetization Losses

AC losses need to be accurately estimated in order to develop more accurate thermal models for fully superconducting machines. In the framework of the development of a high-fidelity sizing tool for superconducting rotating machine for NASA, simulations showed that the classical models for ac losses, taking into account a purely alternating field, would not provide accurate estimations for the magnetization losses. Indeed, superconducting stators usually exhibit a large electrical loading and therefore are subjected to both alternating and rotating fields. As preliminary analysis, a numerical 2-D model is developed to calculate the magnetization losses generated by an elliptical magnetic field in a filament or round mono-core wire. The simulations are based on the H-formulation and executed using a commercial finite element analysis solver. The elliptical magnetic field applied to the superconducting wire is produced by a linear combination of both alternating and rotating fields. The load angle of the rotating machine, creating an angular shift between the alternating and rotating fields, has an impact on the losses and is taken into account. At this point of the study, no transport current is considered. We focus on the ratio between the effective losses and the losses created by a purely alternating field, which are considered known. The investigation leads to a fit formula of the ratio, which has been implemented in a high-fidelity superconducting machine model.