Hysteresis loss and the voltage-current relation in BSCCO tape superconductors

Hysteresis loss is an important factor when the performance of superconducting electric power devices is evaluated. The non-ideal voltage–current relation in Bi2Sr2Ca2Cu3Ox/Ag conductors is one of the reasons that critical state based loss relations do not accurately predict the AC loss in these conductors. In this paper the influence of the magnetic field dependent voltage–current relation on the hysteresis loss is discussed. An analytical high-field approach is used to demonstrate the effect of the finite steepness of the voltage–current relation on the induced current. Besides, a numerical technique is used to calculate also for applied magnetic fields below the penetration field the influence of both a field dependent critical current density and a field dependent steepness of the voltage–current relation. Both the magnitude of the hysteresis loss and the field dependence of the loss are influenced by the voltage–current relation. Especially for small applied fields the field dependence of the loss deviates from the cubic dependence that is predicted by the critical state model based relations. Results of calculations are compared with measured data. An intrinsic critical current density vs. magnetic field relation is determined in order to obtain agreement between measurements and calculations.