Multiple-electrode probe assemblies and nondestructive testing of high-capacity joints

A technique for measuring electrical resistance with planes of multiple electrodes was experimentally used to detect off-centering of sleeves of overhead transmission lines. Very accurate and highly reproducible results were obtained with multiple-electrode probe assemblies and a micro-ohmmeter specially developed for the purpose. Tests with the technique showed a clear correlation between electrical resistance measurements and sleeve off-centering. With the multiple-electrode technique, the distribution of the measuring current can be finely controlled and a mean value for potential distribution between given planes can be obtained. The measurements reflect both the mechanical strength and the electrical quality of the joints tested. The joints have also been nondestructively tested by a magnetic method. With a suitable magnetic circuit and proper differential treatment of the signal, off-centering of the sleeve could be measured with average precision of 6 mm. This method like the multiple-electrode technique, lends itself well to systematic joint inspection