Frequency dependence of A.c. loss in Bi(2223)Ag sheathed tapes
The a.c. self-field loss in Bi(2223)Ag sheathed tapes with different number of filaments has been measured between 59 and 2500 Hz by means of a dual lock-in amplifier. Due to the wide frequency range of the measurements we have been able to dissociate quantitatively the different self-field loss contributions: hysteretic, eddy current and resistive loss (near Ic). This is an important advantage compared to single frequency measurements where such loss dissociation is only qualitative. The hysteresis losses of the different tapes fall between Norris’ predictions for elliptical and strip cross section. The relative weight of eddy current loss is found to be inversely proportional to the current ratio – the higher i, the less is their contribution. Frequency independent resistive loss due to flux creep is observed for high currents at low frequencies; this loss becomes quickly negligible with the increasing frequency.