Quench characteristics and current distribution of multi-strand AC superconducting cables

When AC transport current is supplied to an imperfectly transposed AC superconducting cables, the current distribution among strands becomes nonuniform because of the inductance imbalance. The influence of the nonuniform current distribution on the AC quench characteristics of seven-strand cables was experimentally investigated. It was observed that the center strand carries the inverse current as compared to the total transport current. The influence of the current distribution on the quench current is discussed. The AC quench currents of the following three cases are compared: a seven-strand cable with small series impedance, a seven-strand cable with large series impedance, and a six-strand cable. The quench current of the second case was the largest, and that of the first case was the smallest. It can be qualitatively explained by the current distribution among strands, but the difference between their quench currents was smaller than expected. In a seven-strand cable with small series impedance, the magnitude of the inverse current in the center strand was smaller than the theoretical value. Its peak was eliminated when the total transport current became large.<
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