Current redistribution and stability of superconducting triplex cable without electrical insulation carrying non-uniform current

When a small normal zone is produced in a strand in a superconducting cable by a local disturbance, current redistribution occurs and can help the recovery of its superconducting state. This effect of the current redistribution depends on the initial current distribution. In this paper, the initial current distribution in a triplex cable is controlled artificially to study its influence on the stability against local disturbances. A heat pulse is applied to a strand by a carbon paste heater to initiate the quench. Transient current distributions during quench or recovery process are measured by sets of Hall sensors placed at several locations along the cable axis. When the transport current is less than a threshold value, the stability is improved by the current redistribution from the heated strand to the others, even if the initial current distribution is not uniform. This threshold is related to the current margin of the heated strand, rather than to the current margin of the whole cable. Above this threshold current, the MQE against local disturbances is smaller in the cable with the non-uniform current distribution than in the cable with the uniform current distribution, when the total transport current is identical. If the current of the heated strand is identical and above the threshold, the MQE against local disturbances does not depend on the current distribution and agrees with the MQE of the single isolated strand. It means that the quench of one strand leads to the quench of the cable, and that the stability of one strand in the cable is not influenced by interaction with the others. (C) 2003 Elsevier Science Ltd. All rights reserved.