Study on interface between core and sheath of composite insulator based on leakage current

Due to the increasing number of abnormal temperature rise and fracture accident in composite insulators, the interface between the core and sheath has become one of the research hotspots in external insulation. The 30mm samples in this paper are taken from some short insulators whose core surface are treated by different methods including nonwovens, 180 mesh grinding wheel and 400 mesh sandpaper. The influence of copper foil attached to both ends of the sample on the leakage current in the water diffusion test according to national standard is studied at first and then the change process of leakage current is analyzed in detail. The results show that the copper foil on both ends of the sample will reduce the water sbsorption because the water molecules only can diffuse into the interface through the side of sheath; the interfacial performance of first sample and third sample are poorer than the second sample, probably because the rough surface can provide a larger contact area for the adhesive and core; as the boiling time increases, the amplitude of leakage current tends to increase near the S-curve and the phase angle difference between voltage and current decreases, which complementary angle (dielectric loss angle) can also be fitted by S-curve; the growth coefficient of S-curve decreases with the increase of the thickness of silicone rubber sheath.