Estimation of hysteretic losses for MgB2 tapes under the operating conditions of a generator

TL;DR

This study estimates hysteretic losses in MgB2 superconducting tapes used in a 500 kW generator, employing advanced finite element modeling to analyze different geometries and operational conditions, including flux ripples and current ramping.

Contribution

It introduces a multi-model finite element approach to accurately predict hysteretic losses in MgB2 tapes considering various geometries and filament transpositions under operational conditions.

Findings

Simplified elliptical model validated against analytical solutions.

Losses vary with filament transposition and operational regimes.

Operational regimes significantly influence hysteretic loss levels.

Abstract

Hysteretic losses in MgB2 wound superconducting coils of a 500 kW synchronous hybrid generator were estimated as part of the European project SUPRAPOWER led by the Spanish company Tecnalia Research and Innovation. Particular interest was given to the losses found in tapes in the superconducting rotor caused by the magnetic flux ripples originating from the conventional stator during nominal operation. To compute the losses, a 2D Finite Element Method was applied to solve the H-formulation of Maxwell's equations considering the nonlinear properties of both the superconducting material and its surrounding Ni matrix. To be able to model all the different turns composing the winding of the superconducting rotor coils, three geometrical models of single tape cross section of decreasing complexity were studied: 1) the first model reproduced closely the actual cross section obtained from micrographs, 2) the second model was obtained from the computed elastoplastic deformation of a round Ni wire, 3) the last model was based on a simplified elliptic cross section. The last geometry allowed validating the modeling technique by comparing numerical losses with results from well-established analytical expressions. Additionally, the following cases of filament transpositions were studied: no, partial and full transposition. Finally, choosing the right level of geometrical details to predict the expected behavior of individual superconducting tapes in the rotor, the following operational regimes were studied: Bias-DC current, ramping current under ramping background field, and magnetic flux ripples under DC background current and field.