Shed parameters optimization of composite post insulators for UHV DC flashover voltages at high altitudes

DC artificial pollution tests were carried out on 26 insulators with various shed parameters in high altitude areas to investigate the influence of shed parameters on the flashover performance of composite post insulators. The parameters tested included shed overhang, shed spacing and the core diameter for type A insulators with alternating single large and small sheds and type B insulators with alternating single large and dual small sheds. Ultraviolet photons emitted during partial discharge phenomena in the tests were characterized with an ultraviolet camera, and the arc development paths along the insulator surfaces were observed using a high-speed camera. The results show that the partial discharge phenomena become increasingly intense and arc bridging between the sheds becomes more serious with increasing shed overhang, but these phenomena become weaker with increasing shed spacing. The flashover voltage decreases with increasing core diameter, but increases initially and then decreases with increasing average shed overhang or large shed spacing. An optimal value for the ratio of large shed overhang to large shed spacing must therefore exist and is recommended based on the test results.