An analysis of the transport losses measured on HTSC single-phase conductor prototypes

Abstract

An analysis was made of published results of transport losses measured on state of the art HTSC single-phase conductor prototypes. Fitting the data to simple existing models was attempted and the agreement is reasonably acceptable for cable design purposes. The measured and estimated losses agree within a factor of two, in a range of peak transport current between 0.3 and 1.0 of the conductor DC critical current. The model used in this current range is one that considers the conductor as a solid SC tube in its own (purely tangential) self-field. The eddy losses are estimated as in a standard procedure for non-magnetic helical multilayer reinforcements and armours, and turn out to be negligible for this geometry. Losses higher than predicted are measured on two or more layer conductors in the low-current range, being typically for a peak transport current below 0.3 of the DC transport current of the conductor. In order to explain this, it is suggested that there might be a dephasing in the AC threshold voltages of the tapes, due to the variation of the in-field critical currents of the tapes across the conductor layers. Problems that are common to this type of measurement are discussed too. The simple model is not directly applicable to the more practical case of a non-coaxial trefoil configuration, because in this case a transverse field is also present, produced on each of the three conductors by the two others. Therefore, the losses need to be measured and modelled also on the trefoil configuration, to obtain reliable data in this practical case too.