Normal zone propagation process accompanied by current redistribution in superconducting triplex cables

Abstract

The normal zone propagation process in multi-strand superconducting cables is often accompanied by current redistribution between strands. This current redistribution possibly influences the mode of normal zone propagation and stability of superconducting cables. In this paper, details of the normal zone propagation accompanied by the current redistribution between strands are revealed in two types of superconducting triplex cables; the strands of one cable have bare-copper surface, and those of the other cable are plated with chrome. Instrumentation includes voltage taps to follow normal zone propagation in each strand and Hall sensors to measure strand currents. The contact resistances measured in situ in the setups for quench experiments are 1.7 and 20 μΩ for 1 m in the cable with bare-copper strands and in the cable with chrome-plated strands, respectively. In the recovery process assisted by the current redistribution, the current transfers from the heated strand to the others to improve the stability against local disturbance. In the quench process, it transfers from the strands carrying more current initially to the strands carrying less current. The contact resistance between strands influences the mode of current redistribution and normal zone propagation. In superconducting cables made with chrome-plated strands, the current transfers in the large region along the cable, while it transfers near the normal front in superconducting cables made with bare strands. The current redistribution preceding the normal zone propagation in a superconducting cable made with chrome-plated strands is a possible reason for the increase in the normal zone propagation velocity.