Estimation of hysteretic losses for MgB₂tapes under the operating conditions of a generator

Abstract

Hysteretic losses in MgB 2 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.

Iterative multi-scale method for estimation of hysteresis losses and current density in large-scale HTS systems

“…The shape of the unitary cell in figure 2 applies to systems wound with (RE)BCO coated conductors, and the dimensions could depend on the wounding process. For different systems with different conductors, like the MgB2 coil in [19], other unitary cells with different shapes are required. The system is simulated for one period of a sinusoidal transport current.…”

“…In the context of large-scale systems, where the main problem is the large number of turns, a detailed comparison of three models for the estimation of hysteresis losses can be found in [16]. In that publication, a particular attention was paid to the homogenization method [17] and to the further development of the multi-scale method [18,19]. Recently, an efficient FEM model based on the T-A formulation of Maxwell's equations has been discussed in [20,21] for its use in large-scale systems as well.…”

Comparison of 2D simulation models to estimate the critical current of a coated superconducting coil

“…(8) can be rewritten as Eq. (13). The x and y component of the magnetic flux density are calculated by Eq.…”

“…C.R. Vargas-Llanos et al [13] used it for estimating the critical current of multi-filamentary MgB2 tapes and D. Liu et al [14] used this model to estimate the critical current of Bi-2223 cables and coils.…”

“…Readers should note that 'in the P-model the true dynamics behind the voltage drop at current density values that are far from the critical value are not considered' and detailed explanation can be found in [6]. Vargas-Llanos et al [14] used it for estimating the critical current of multi-filamentary MgB 2 tapes and Liu et al [15] used this model to estimate the critical current of Bi-2223 cables and coils.…”