Development of Smart Silicone Rubber Insulating Materials for HVDC Transmission Systems

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Silicone rubber insulators have shown excellent pollution performance and thus have been replacing the conventional insulators made from porcelain or toughened glass in alternating current (AC) overhead power transmission systems. These insulators are also recommended for use in high voltage direct current (HVDC) transmission line systems, with a few changes made in the geometry but with no consideration given to the housing material design. Modifying the geometry by increasing the creepage distance may ensure an acceptable flashover performance over the short term, but aging remains an issue of a great concern. In the light of the increased application of HVDC links in the electricity grid, this concern has driven an interest in developing reliable silicone rubber insulation housing materials for HVDC systems. Conventional silicone rubber housing materials have been developed based on more than 50 years of industry experience in AC insulators. But, this experience-based approach cannot be applied in the development of DC insulators as experience is limited in insulator aging under DC voltages. This research program proposes the development of reliable, cost-effective, and thus smart, silicone rubber housing materials for DC outdoor insulation applications in a mechanistic-based framework. The following projects are executed under the proposed research program. (1) Erosion Mechanisms: erosion of silicone rubber insulators as a result of dry-band arcing induced on the surface of the housing material is a critical aging mechanism leading to insulation failure in polluted service condition. The dynamic nature of the DC as compared to the AC dry-band arcing is studied in order to develop an electro-thermal model for the dry-band arcing as a heat source, impinging the surface and causing heat ablation. (2) The Role of Inorganic Fillers: Traditionally, housing material composites are loaded as much as possible with inorganic fillers. Inorganic fillers, as flame retardants, suppress the formation of carbonaceous tracks as a result of dry-band arcing causing decomposition of the surface. However, silicone rubber is tracking-resistant and thus erosion is of a concern. In this project, the erosion suppression effects of inorganic fillers are investigated. Emphasis will also be given to understand role of interface as nano-sized fillers are employed. Accordingly, a thermal model is developed to predict the erosion performance of composites formulated for DC outdoor insulation using inorganic fillers. (3) Material Screening Methods: In response to a great demand raised by insulator manufacturers and utilities, a material screening method for the qualification of erosion resistance of DC outdoor insulating materials is developed to provide reproducible outcomes that correlate with the actual performance in service.