Prediction of surface degradation of composite insulators using PD measurement in cold fog

In this paper, surface degradation detection and analysis was investigated for composite insulators under cold fog. A composite insulator was tested with different contamination levels under various environmental stresses. The surface degradation stresses considered were cold fog, surface resistance, contamination levels, as well as interior and exterior temperatures on insulator surface. Characteristics of partial discharge and discharge current of surface discharge were studied to determine the effects of dense cold fog on the surface degradation of composite insulators for different contamination levels. AC high voltage was used for the tests. Wavelet transform analysis at different decomposition levels was carried out to recover the discharge signals from surface leakage current signals. The internal temperature of the insulator is directly related to the severity of electric discharges on its surface. The interior temperature was measured by heat propagation tests. Thermal imaging camera was used to determine the exterior temperature of the insulator. The results showed that the surface discharge signals are strongly correlated with the contamination level, water conductivity and significant damage on the insulator surface caused by some of the imposed degradation stresses.