Presentation Information
[WBP2-21]Hybrid Method for Evaluating System-level AC Losses in a DC HTS Linear Machine
*Emma Gottardi1, Dave C. J. Krop1, Elena A. Lomonova1 (1. Eindhoven University of Technology (Netherlands))
Keywords:
AC losses analysis,DC HTS linear machine,Eddy currents losses,Hybrid method,T-A formulation,Harmonic modelling technique,Integral method
In linear machines, DC HTS coils within the stator cryostat experience AC losses due to non-uniform and time-varying magnetic field generated by moving AC armature-coils, while carrying a transport current. These AC losses arise mainly from two physical phenomena. First, the interaction between the external, alternating magnetic field and the DC transport current in the HTS tapes causes magnetization losses within superconducting layers. Second, the spatially non-uniform and time-varying magnetic field not only directly induces eddy currents in nearby conductive materials, such as the cryostat, but these eddy currents themselves generate secondary magnetic fields. These fields interact with the superconducting coils, creating a feedback loop where the eddy currents and the varying magnetic fields influence each other.
This work presents an innovative one-stage hybrid method to evaluate AC losses in the superconductors due to the combined effects of internal DC current, external AC magnetic field, and eddy currents induced in the surrounding conductive layers. The contribution of eddy currents arising from the interaction between conductive layers and DC superconducting coils is neglected, as these losses are expected to be significantly smaller compared to those induced directly by the external AC field. By incorporating the influence of conductive layers, this method provides a detailed quantification and characterization of their electromagnetic impact on the superconducting system, which is essential for estimating the resulting thermal load on the cryogenic environment due to eddy current losses. The proposed hybrid technique combines the harmonic modeling technique, a semi-analytical approach to model external magnetic field and reaction field caused by eddy currents, with the integral method to calculate AC losses in superconducting tapes.
The hybrid method is then compared and validated through numerical simulations based on T-A formulation in COMSOL, which also include the coupled interactions between conductive layers and superconducting coils. This comparison evaluates both computational efficiency and accuracy, with the aim of determining whether the differences between hybrid and numerical models are sufficiently small to justify neglecting the interaction between the fields generated by the superconductors and the conductive layers.
Most importantly, it demonstrates that the proposed hybrid model offers a computationally efficient alternative to fully numerical simulations, making it well-suited for design applications in realistic operating scenarios.
This work presents an innovative one-stage hybrid method to evaluate AC losses in the superconductors due to the combined effects of internal DC current, external AC magnetic field, and eddy currents induced in the surrounding conductive layers. The contribution of eddy currents arising from the interaction between conductive layers and DC superconducting coils is neglected, as these losses are expected to be significantly smaller compared to those induced directly by the external AC field. By incorporating the influence of conductive layers, this method provides a detailed quantification and characterization of their electromagnetic impact on the superconducting system, which is essential for estimating the resulting thermal load on the cryogenic environment due to eddy current losses. The proposed hybrid technique combines the harmonic modeling technique, a semi-analytical approach to model external magnetic field and reaction field caused by eddy currents, with the integral method to calculate AC losses in superconducting tapes.
The hybrid method is then compared and validated through numerical simulations based on T-A formulation in COMSOL, which also include the coupled interactions between conductive layers and superconducting coils. This comparison evaluates both computational efficiency and accuracy, with the aim of determining whether the differences between hybrid and numerical models are sufficiently small to justify neglecting the interaction between the fields generated by the superconductors and the conductive layers.
Most importantly, it demonstrates that the proposed hybrid model offers a computationally efficient alternative to fully numerical simulations, making it well-suited for design applications in realistic operating scenarios.