Ultrasonic guided wave-based detection of composite insulator debonding

Based on the theory of ultrasonic guided wave propagation, a simplified model of bilayer composite insulator was constructed, and the dispersion curves of longitudinal (L) and torsional (T) guided wave modes were obtained. To address the problem of composite insulator debonding, the propagation velocity and energy decay of longitudinal and torsional ultrasonic guided waves in the insulator bilayer model were studied, and a method for detecting the axial and circumferential debonding of composite insulator was proposed based on the ultrasonic guided wave attenuation characteristics. On the basis of the theoretical analysis, experiments were conducted to detect the debonding of composite insulator. The experimental results showed that: the same guided wave modes propagated at the same speed on the silicone rubber and rod, but differed in energy distribution; as the guided waves attenuated excessively during propagation in the silicone rubber, only segmented detection was possible for long composite insulator; when there was debonding within the detection range, the energy attenuation of guided waves would increase. Debonding size would also influence the attenuation coefficient, therefore, we could determine whether there was debonding defects as well as the size of defects by detecting the propagation attenuation coefficient of guided waves. L-mode guided waves could detect whether there was debonding defects, but could not determine the size of debonding. T mode guided waves could be used to estimate the size of debonding defects.