Coupling currents and hysteresis losses in MgB₂superconductors

Abstract

MgB 2 multi-filamentary superconductors are widely considered for use in dc applications. To expand the possible application range to ac apparatuses, the development of a low ac loss wire is needed. This development involves several steps, and a solid understanding of the loss mechanisms is important to optimize that process as well as for evaluating dc wires exposed to current or magnetic field ripple. In this study we discuss the coupling currents and their influence on hysteresis loss as well as on coupling current loss. We give a phenomenological explanation of the origin and behaviour of the coupling currents and describe the loss patterns for hysteresis loss and coupling current loss separately. Finally, we interpret measured AC losses in an MgB 2 wire cut into different lengths representing different twist pitches. Under certain circumstances short sample lengths are shown to give inaccurate measurement results. On the other hand, short sample lengths of non-twisted wires can be used to estimate the twist pitch necessary to electromagnetically decouple the superconducting filaments.

AC losses of single-core MgB2 wires with different metallic sheaths

“…Magnusson et.al. have shown the coupling current and hysteresis losses in Ti sheathed MgB 2 superconductors and described the coupling currents by phenomenological approach [12].The main aim of the present study is to demonstrate the effect of applied metallic sheaths on AC losses in single-core MgB 2 wires without contribution of coupling currents. …”

“…Magnusson et.al. have shown the coupling current and hysteresis losses in Ti sheathed MgB 2 superconductors and described the coupling currents by phenomenological approach [12].…”

“…Decoupling effect in twisted wires and transposed cables [10] and AC losses of high current density MgB 2 wires made by IMD process have been also presented [11]. Magnusson et.al. have shown the coupling current and hysteresis losses in Ti sheathed MgB 2 superconductors and described the coupling currents by phenomenological approach [12].…”

Design of a 20-MW Fully Superconducting Wind Turbine Generator to Minimize the Levelized Cost of Energy

“…In the first estimation, the conduction losses are assumed equal to 1 W per winding [3], and the current lead losses are estimated as 46 W/kA per current lead [12]. 1) AC losses in the stator winding: Due to the fact that the hysteresis losses in the filaments contribute significantly to the total AC losses [13], [14], the coupling losses are neglected. The hysteresis losses per unit volume per cycle of a round filament perpendicularly placed to a magnetic field of an amplitude B m are expressed as (2) [13, p. 1, eq.…”

Magnetization AC losses in MgB2wires made by IMD process

“…A strong coupling effect was found in non-twisted filamentary wire and in cable made from non-twisted wires [7]. The calorimetric method was used for AC loss measurements of filamentary Ti sheathed MgB 2 wire at 32.5 K [10]. A simplified treatment of the hysteresis losses due to ripple magnetic fields in MgB 2 conductors was used, which is an important issue for wind turbine generator coils [11][12].…”