Over critical-current behaviour of Bi-2223 tapes

We have tested the response of Bi-2223 tapes in over-critical current conditions with a view to exploring this material's prospects for fault current limiter applications. Silver and silver-alloy dad multifilamentary tapes have been put in series with a transformer and a resistor. Currents exceeding I-c were allow ed to now through the samples when the resistor was short-circuited, AC peak currents up to 100 I-c (about 2000 A) have thus been applied to the samples for up to 50 ms. We measured the samples' resistivity and electric field as a function of the applied current. Samples had a resistivity of 0.6 micro-ohm,cm for peak currents up to several tens I-c and no sample degradation was observed, However, a resistivity of nearly 10 micro-ohm.cm was measured for peak currents over 2000 ii and samples were damaged by heating effects. The electric field was 2.2 V/m for a current of 400 A. Therefore, controlling a 400 A fault current (about 20 I-c) would require 0.45 km of tape for a 1 kV fault current limiter.