Non-homogeneous quench of the superconducting secondary of an inductive fault current limiter: implications for current limitation

In this work, we have studied the performance of an inductive fault current limiter having biphase (Bi-2223 and Bi-2212) superconducting rings as the secondaries of the transformer. We have paid special attention to the role played by the inhomogeneous transition of the superconducting cylinder and rings. For that, we have measured the variations of the voltage and the temperature of several parts of these rings during current faults by using metallic contacts and thermocouples attached at different points along their perimeter. Our results show that the limiter response during a fault is governed by the overheating of a small part of the superconducting element. These measurements also show that the temperature and resistance evolution of this dissipative zone is in turn mainly determined by the progress of the resistance of the Bi-2212 minority phase. This behaviour reduces the current limitation in devices based on this kind of superconducting material because it provokes a smooth impedance increment during the faults.