SQUID-NDE of wire breakage in aluminium transmission line

SQUID-NDE technique was applied to detection of wire breakage in aluminium transmission line, and aluminium clamp composed of compressed conductor joint. Hard aluminium transmission lines twisted from 19 aluminium wires with or without a wire breakage were prepared. While applying ac current of 2.6 mA at 200 Hz to the line, distributions of magnetic field gradient above the transmission lines were measured by a SQUID-NDE system using a HTS SQUID gradiometer. A periodic pattern was detected along the locus of broken wire in the distribution of the field gradient generated from the line with wire breakage, while such pattern was not observed in the normal line without wire breakage. Numerical simulation of distribution of field gradient from the aluminium transmission line was also carried out to compare it with the experimental results.