Inspection of Wire Breakage in Aluminum Transmission Lines using an HTS SQUID

A nondestructive inspection method to detect wire breakage in power transmission lines using an HTS SQUID gradiometer was examined. Hard-aluminum transmission lines composed of 19 twisted Al wires, with or without wire breakage, were prepared as specimens. While applying AC voltage to the specimens to induce the equivalent current in each wire, distributions of magnetic field gradient above the transmission lines were scanned by the gradiometer. A periodic pattern in the gradient distribution due to wire breakage was observed in the results of the line with wire breakage, while such pattern was not observed in that of the line without wire breakage. The effect of wire breakage in the transmission line appearing in field gradient generated by the line with current was also investigated by computer simulation, and the result was in approximate agreement with the experimental results.