Aging and Reliability of Porcelain Longrod Insulators: Insights from Statistical Modeling and Acoustic Analysis

This research project investigates impulse-excited acoustic resonance testing as a nondestructive alternative to conventional destructive methods for assessing the residual strength of aged ceramic high-voltage insulators. Traditional CIGRE TB 306 guidelines rely on breaking force tests that destroy components and require complex setups, whereas acoustic testing using a MK7 device offers rapid execution, cost-effectiveness, and whole-component evaluation without prior knowledge of defect locations. This work provides the first statistically robust full-scale assessment of IET feasibility on long rod porcelain insulators. The study evaluated aged and new long-rod insulators through acoustic resonance testing followed by mechanical strength testing. Frequency measurements demonstrated excellent repeatability and negligible operator dependence, while attenuation measurements showed higher variability. The selection of a suitable hammer for the stimulation of vibration also proved to be relevant to balance frequency range and specimen safety.

Despite technical robustness, statistical analysis revealed no meaningful correlation between acoustic parameters and residual mechanical strength of insulators. Even substantial variations in mechanical properties between material batches were not reliably reflected in acoustic signatures. This disconnect stems from fundamental limitations: resonance frequencies seem to reflect bulk elastic properties, while breaking strength depends on microscopic defects too small to influence measured resonance modes.

These findings establish that impulse-excited resonance testing, though effective for detecting material variations and manufacturing defects, cannot reliably predict residual strength in ceramic insulators. Future research should explore advanced techniques as nonlinear acoustics, machine learning analysis, or localized ultrasonics to better capture defect populations responsible for mechanical failure in aged ceramic insulators.