Thermal Diffusivity of Fresh Silicone Rubber Composite Insulators Determined by Photothermal Radiometry

Thermal diffusivity was confirmed to be a useful parameter for evaluating the aging degree of silicone rubber composite insulators widely used in high-voltage–power systems. However, the aging induced thermal diffusivity change of composite insulators not only is related to the initial thermal diffusivity of fresh silicone rubber, but also could be within a certain range for fresh composite insulators due to composition differences of base polymer and fillers and additives, makes the direct correlation of thermal diffusivity of aged composite insulator to aging degree difficult. In this work, thermal diffusivities of fresh composite insulators with different voltage grades, different mechanical load grades, and manufactured by different vendors are determined with photothermal radiometry (PTR) by fitting experimental frequency dependences of PTR amplitude and phase to an appropriate theoretical model. The thermal diffusivities of composite insulators from two vendors are approximately 3.70 × 10−7 m2·s−1 to 3.76 × 10−7 m2·s−1 and 4.87 × 10−7 m2·s−1 to 4.94 × 10−7 m2·s−1, respectively, showing significant difference, due to composition difference. The thermal diffusivities of composite insulators with voltage grades 35 kV, 110 kV, and 220 kV, and with mechanical load grades 70 KN, 100 KN, and 120 KN are also measured and found to be only slightly divergent, due to the same composition. In addition, the thermal diffusivity uncertainties of two vendors are quite different, indicating sample homogeneity discrepancy. This variation is useful information for evaluating aging process of silicone rubber composite insulators from the thermal diffusivity measurements of aged composite insulators.