  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.
