Influence of Sheath-core Interface Defects on the Decay-fracture of Composite Insulators

The deterioration at the sheath-core interface of composite insulator is a crucial problem, which can lead to fracture fault. However, the study on the sheath-core interface delamination failure of the composite insulator is just at the preliminary stage both inland and abroad. The thesis focuses on the sheath-core interface performances of the composite insulator in operation. In addition, the key parameters are put forward through water diffusion test and dye penetration test, to describe the interface performances quantitively, including interfacial leakage current and deterioration area ratio. Moreover, this paper also researches the effect of sheath-core interface defects on decay-fracture of the composite insulator through finite-element simulation, with regard to water content and non-uniform electric field. It has been found that the existence of the air gap defects can make the local electric field distortion rate up to 186.4%, and the temperature rise is 1.8K. As the moisture absorption rate increases from 0% to 100%, the electric field distortion rate increases from 73% to 160%, the temperature increments increased from 1.4K to 19.8K. These results are consistent with the physical and chemical properties analyses of typical decay-fracture composite insulator. The research suggests that strong external electric field near high-voltage side of the insulator and water permeation process have impacts on material deterioration and interface defects. The interface defects can cause partial discharge, which lead to the permeation of the acidic liquid into the interface and acceleration of the interfacial degradation. The research results can provide some references to operation and maintenance of composite insulators for hot and humid rain-fed areas in southern China.