The deterioration at the sheath-rod interface of composite insulator is a crucial problem, which can lead to fracture fault. However, the study on the interfacial delamination failure of the composite insulator is just at the preliminary stage both inland and abroad. Therefore, it is urgent to analyze the effect of sheath-rod interfacial delamination failure on decay-fracture of the composite insulator. The thesis focuses on the sheath-rod interface performances of the composite insulator in operation. We obtain valid parameters through water diffusion test and dye penetration test, in order to describe the interface performances quantitively, including interfacial leakage current and deterioration area ratio. In this paper, we also innovatively adopt image processing method to analyze the degree of deterioration, which can provide more precise and objective information, compared to traditional manual visual observation methods. Moreover, this paper researches the effect of sheath-rod interfacial delamination failure on decay-fracture of the composite insulator through finite-element simulation and hydrothermal aging test, with regard to water content and non-uniform electric field. And the results showed that the air gap defects can make the local electric field distortion rate up to 186.4%, and the temperature rise to 1.8K. As the moisture absorption rate increases from 0% to 100%, the electric field distortion rate increases from 73% to 160%, the temperature value increases from 1.4K to 19.8K. These results are consistent with the physical and chemical property analysis of typical decay-fracture composite insulator. It has been found that strong external electric field near high-voltage side of the insulator and water infiltration have impacts on material deterioration and interface defects. The interface defects can cause partial discharge, which leads to the infiltration of the acidic liquid into the interface and acceleration of the interface degradation. The research results can provide some reference for daily operation and maintenance of composite insulators in hot and humid rain-fed areas in southern China.

composite insulator, interface defects, electric field simulation, decay fracture