AC Loss Measurement of YBCO Cable Model

AC transport loss of the cable model constructed from YBCO coated tapes has been investigated. The single layer model 0.5 m long consists of 14 tapes placed on the surface of the epoxy-fiberglass tube of outer diameter 2 cm in one layer with 15$^{\circ}$ lay angle. In the center of the model the Cu rope with cross section 45 ${\rm mm}^{2}$ connected in parallel with the tapes was placed as an over critical current protection. The coaxial brass tube was utilized as a return wire. The critical current of the individual tape was 75 A. Two procedures for determination of the cable AC transport loss were utilized. In the first one 14 measurement loops of the length 0.36 m with taps soldered to the individual tapes and lifted 1 cm above the cable were symmetrically placed around the cable. After measurement of the individual tape voltages their average was used for calculation of the cable AC transport loss. Second one was the so-called secondary voltage method. This method is based on the fact that the cable is energized through a power transformer. The voltage from resistive parts of the secondary was subtracted from the total secondary voltage measured by contact-less loop embracing the transformer core. Afterwards, this difference was taken to calculate the cable AC transport loss. Due to non-stabilized YBCO tapes the visualization of the individual tape transition to the normal state within the period of the transport current was possible.