The service life of a composite insulator involves both electrical and mechanical aspects. Electrical aging involves damage from erosion or tracking due to the thermal or chemical effects of discharge occurring when the insulation material is polluted or wet, and may even result in flashover.

Composite insulator predicting service life

Mechanical aging includes long-term drop in the strength of the core material or in the holding force of the end-fittings, as well as brittle fractures of the core material, and can on occasion result in breakage of the insulator string. A drop in core strength or holding force of end-fitting can be countered by adopting an appropriate safety factor and using a reliable method of compression. Brittle fractures, on the other hand, occur mostly near the interface between the insulation material and the end-fitting, and provided this area has been properly manufactured, the probability of their occurrence will be lower than that of electrical aging.

To estimate service life from the electrical aspect, actual- scale composite insulators were exposed to electrical stress, and were subjected to an exposure test under a natural environment. A test chamber simulating environmental stress was also constructed, and accelerated tests were carried out according to international standards (IEC 61109 Annex C). Further, by comparing leakage current waveform and cumulative charge, which may be characterized as electrical aging, evaluation of composite insulator service life was carried out.

Furthermore, since in Taiwan, a drop in insulation performance due to rapid pollution during typhoons is a familiar phenomenon, an investigation was made based on the characteristics of leakage current obtained during a typhoon into the effect of rapid pollution on electrical aging in composite insulators.

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