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

Abstract

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% Ic dropout in the outer conductor. Three different cable types were measured to investigate the impact of contact resistance between tapes, Rc, 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 Rc, 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 Ic and can cause significant power dissipation, 590 mW at 60 A. As Rc decreases, facilitating better current sharing, the normal zone spreads to both tapes. These experiments have demonstrated that Rc can have a significant impact on power dissipation and that current sharing is essential for robust cable performance.