Long-term ageing test results of various kinds of semi-conducting glaze insulators

Semi-conducting glaze porcelain insulators show better contamination flashover voltages compared with normal porcelain insulators due to surface drying effect by the leakage current flowing in the glaze together with improved voltage distribution even at the dry bands by parallel surface glaze resistance. However, ageing deterioration of semi-conducting glaze is not avoidable. We have conducted accelerated ageing test and outdoor exposure test under the continuous voltage of 160kV (line to ground for 275kV system voltage) on various types of semi-conducting glaze insulators. After 1100 cycles of accelerated ageing test and 6 years of outdoor exposure test, we examined the surface deterioration among various types of insulators, such as cap and pin type, long-rod type, station post type and bushing shell, all 275-kV class full scale insulators. The degrees of surface deteriorations are quite different among different types of insulators.