Effect of Internal Electrodes on Ageing Deterioration of Polymer Bushing Shells

Polymer insulators are widely used all over the world due to their superior performances such as light weight, better contamination flashover voltage performance, higher resistances against vandalism and earthquake, and so on. However, polymer insulators are made of organic materials and so ageing deterioration is concerned about and extensive investigations have been conducted all over the world on this subject, but mostly for transmission or distribution line applications. Polymer insulators are, however, applied also for apparatus in power stations. When a polymer bushing shell is used for apparatus, ageing deterioration is determined not only by the design of the shell itself but also by the internal design of the apparatus. Specifically, voltage distribution along the polymer bushing shell is influenced by the internal design and so ageing deterioration of polymer shell surface could be influenced by the internal design. We started comparative ageing tests in our 275 kV accelerated ageing test chamber and in our outdoor exposure test station on the same polymer bushing shells with and without internal electrodes. As of 90 cycles of accelerated ageing test and 90 days of outdoor exposure test, any significant effects of internal electrodes on the ageing of polymer bushing shell surfaces cannot be identified. The details of investigation results including comparative voltage distributions and contamination flashover voltage test results on these specimens are presented in this paper.