NGK Insulators (Germany)

This paper shows a novel approach to reduce the aging of silicone elastomers for outdoor insulators by using different filler surface treatments and inert fillers such as barium sulphate (BaSO4). Silicone rubber composite insulators are used in overhead transmission lines (OHTL) since many years, however under specific environmental conditions, they can show a reduction of mechanical properties, embrittlement and the formation of superficial cracks. Besides other factors, these aging effects can be attributed to strong acids, which can be generated by high electrical field stresses and acidic pollution on the insulator surface. In this study, silicone elastomers used for outdoor insulation, were equipped with aluminum hydroxide with various surface treatments and inert fillers, which provokes a significant improvement of aging performance. Silicone elastomer compounds equipped with barium sulphate show improved aging resistance under acidic environment, like a reduced mass loss when immersed in concentrated nitric acid, decreased crack formation and enhanced stability of mechanical properties with comparable erosion resistance.

Composite insulators with silicone rubber housing have been applied since more than 40 years successfully under various climatic and pollution stress conditions. Since the service experience was not available in the introduction phase (Generation I and II) of this insulator technology in the early 1970ies, the life-expectation for composite insulators has always been lower than that for conventional insulators made of porcelain and glass. With growing experience and knowledge gained with this technology in the last 3 decades, this view has drastically changed and led to today's opinion that the service life-time of composite and conventional insulators are comparable even under severe application conditions. But, to obtain such insulators, the product design, material selection and quality of production must fulfil much more than the minimum requirements given by the current international standards.