Advanced ac loss measurement methods for high-temperature superconducting tapes

Abstract

Advanced ac loss measurement methods for superconducting tapes are described in detail and demonstrated on BSCCO/Ag (Bi2Sr2Ca2Cu3Ox with a Ag matrix) tapes in liquid nitrogen at 77 K. The aim of the measurements is to simulate the situation of a tape conductor in an electric power application like a transformer coil or a power cable. In this class of devices the conductor is fed with an alternating transport current and simultaneously exposed to an alternating magnetic field. In many devices the magnetic field vector points in a single direction but in some devices such as three-phase power cables and motors the magnetic field rotates around the conductor. In all cases described above an electromagnetic approach with pick-up coils and voltage taps is used to measure the ac loss. This method enables a separate study of magnetization loss and transport current loss when both the magnetic field and transport current are present simultaneously. The magnetization loss measurement setup for unidirectional and rotating magnetic field is described. The transport current loss measurement setup is described, focusing on the suppression of cross effects of ac transport current and ac magnetic field that disturb accurate measurements. Finally several relevant examples of the results obtained are shown.