Detection of wire element breakage in power transmission line using HTS-SQUID

We have proposed the application of nondestructive evaluation (NDE) using HTS-SQUID gradiometer to detect wire breakage in compressive conductor joints in overhead transmission line. In this study, we prepare an aluminum conductor steel reinforced (ACSR) transmission line with a broken wire. The ends of the ACSR cable were compressed with Al sleeves. An AC current was injected toward into the cable axis by applying AC voltage across the both ends of the sleeves. Then the two-dimensional distribution of magnetic field gradient above the cable was measured by a HTS-SQUID gradiometer. In the case of the compressed ACSR with a wire breakage, the field gradient changed periodically along the spiral of the broken wire. In contrast, such changes did not appear above the ACSR cable without defects. These results suggested the possibility to detect the wire breakage in the compressive conductor joints by this method. We also conducted electromagnetic field simulation to verify the experimental results.