Impact of contact resistance on current distribution and performance of model CORC® cables with physical defects

This work investigates current redistribution around defects in conductor on round core (CORC®) cables. Special two tape CORC® cables were constructed containing just one tape per layer with a 100% I c dropout in the outer conductor. Three different cable types were measured to investigate the impact of contact resistance between tapes, R c, on current redistribution around local defects. An array of z-axis Hall sensors, which could be positioned at any location along the cable, monitored changes in the self-field due to current redistribution. A clear shift in Hall polarity occurs at the defect location, with Hall sensors producing a positive voltage upstream of the defect and a negative voltage downstream of the defect. As the current transfers around the defect, the ‘good’ tape is overloaded, initiating a normal zone. In cables with high R c, voltage taps reveal that the normal zone is confined to the ‘good’ tape, while the ‘bad’ tape remains superconducting. This normal zone can remain stable even at currents above I c and can cause significant power dissipation, 590 mW at 60 A. As R c decreases, facilitating better current sharing, the normal zone spreads to both tapes. These experiments have demonstrated that R c can have a significant impact on power dissipation and that current sharing is essential for robust cable performance.