Fault current characteristics in a technical high Tc superconductor

A Bi-2223 tape has been developed for low-field power applications such as power cables or transformers working at liquid nitrogen temperature. For such applications it is required to understand fault current characteristics of the technical high temperature (T_c) superconductor. In this paper, we prepared two types of the samples with similar insulation structures to power cables and transformers: the straight sample and the pancake sample. Then we examined the normal transition characteristics for a sinusoidal steady current and the fault current characteristics for a sinusoidal pulse current. It is found that temperatures slightly higher than critical one of the technical high T_c superconductor make normal transition easily. However over-critical currents can´t make it normal state completely up to ∼5 I_c if the superconductor´s temperature remains bath one. The fault current tests show that the temperatures and resistances measured in both the insulated straight sample and the pancake sample with conductor insulation are similar to each other, while the pancake sample with layer insulation is significantly different from the two samples above. This means that from damage point of view under the grid´s fault conditions, the pancake sample with layer insulation has better characteristic in comparison with conductor insulation.