Over critical-current behaviour of Bi-2223 tapes [for fault current limiters]

The authors 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 clad multifilamentary tapes have been put in series with a transformer and a resistor. Currents exceeding I/sub c/ were allowed to flow through the samples when the resistor was short-circuited. AC peak currents up to 100 I/sub c/ (about 2000 A) have thus been applied to the samples for up to 50 ms. The authors measured the samples´ resistivity and electric field as a function of the applied current. Samples had a resistivity of 0.6 /spl mu/ohmcm for peak currents up to several tens I/sub c/ and no sample degradation was observed. However, a resistivity of nearly 10 /spl mu/ohmcm was measured for peak currents over 2000 A 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/sub c/) would require 0.45 km of tape for a 1 kV fault current limiter.