An ultrasonic guided wave approach for the inspection of overhead transmission line cables

Inspection of overhead transmission line cables is performed using various non-destructive testing techniques, such as visual, temperature, and eddy current-based inspection; yet each of these techniques have their respective shortcomings and safety concerns. The use of ultrasonic guided waves as a nondestructive testing technique is well established for simple geometries such as plates, pipes, and rods. However, its application for multi-wire cables is still in development. In this study, ultrasonic guided waves excited by a shear mode transducer collar are utilised as a defect detection technique for untensioned aluminium conductor steel reinforced cable specimens. The identification and analysis of wave propagation for a broad range of frequencies is performed using a laser scanning vibrometer, and the effect of defect size on wave propagation is studied. Signal processing algorithms, such as wavelet denoising and time scaling, are then deployed for inspection quality enhancement and analysis under noisy conditions. Results yield an extended range of defect detection coverage in pulse echo configuration; with successful detection of defects that correspond to a 4.5% reduction in the cable’s cross-sectional area; and up to 24% improvement of signal-to-noise ratio.