DOW CORNING SILICONE MOULDING COMPOUNDS FOR HIGH-VOLTAGE APPLICATIONS
29 November 2002 - Dow Corning - Rubber Fabrication Industry

A new generation of silicone rubber compounds has been developed for moulding high-voltage insulators, surge arresters, weather sheds and other HV components. All are high-consistency rubber (HCR) products in the Dow Corning 1600 series, designed to deliver outstanding tracking resistance over a wide voltage range, superior wet electrical performance, hydrophobic transfer and recovery, as well as good mould release and other processing characteristics.

Dow Corning HV 1650-50 Silicone Rubber (Type ASTM D 1418 VMQ) is a 50-durometer material designed with low modulus, primarily for moulding surge arresters. Sister products, Dow Corning HV 1660-65, Dow Corning HV 1666-65 and Dow Corning HV 1660-75 Silicone Rubbers, are 65- and 75-durometer formulations which were specifically developed for moulding high-voltage insulators and weather sheds.

All feature good processing characteristics for easy moulding with injection, transfer or compression methods.

Because of its ability to manage surface leakage currents, silicone is frequently specified for coastal locations and areas with airborne pollutants, in which ceramic materials and organic composites experience high levels of flashover activity. Particularly effective in difficult access areas, durable silicone composite components have been shown to significantly reduce maintenance costs and help eliminate power interruptions.

The Dow Corning HV 1600 series HCRs deliver excellent electrical properties, including a dielectric strength greater than 17kV/mm (440 volts/mil) per IEC 243 and a dielectric constant up to 3.67 at 100 Hz (IEC 250). These products are supplied as one-part, fully compounded, ready-to-run materials to help moulders achieve faster processing and eliminate the need for mixing. The Dow Corning 1660 series materials exhibit excellent arc tracking performance and erosion resistance over a wide voltage range (between 3.5kV and 6.0kV), and they are extremely stable in difficult environments.

The ability to prevent film formation is a key property in resisting leakage current and insulator flashover activity. EPDM polymers start out with good hydrophobicity, but over time contaminants and weathering quickly cause these materials to lose their water-repellent properties, causing rapid deterioration of electrical performance. The process is accelerated after a flashover, which can leave carbon deposits and surface roughness that contributes to further loss of dielectric properties.

In sharp contrast, the surface characteristics of the Dow Corning HV 1600 series materials deliver excellent recovery and transfer of hydrophobic properties after periods of high surface electrical activity. The result is better electrical performance and management of surface leakage currents, which helps avoid electrical flashovers, reduce maintenance and extend service life.

The growing market for improved materials in high-voltage components is driven largely by a need to reduce overall operating costs and improve system reliability. “The cost advantages of silicone insulators are especially evident in situations where long-term reliability and maintenance-free performance is a concern, such as coastal regions and high-contamination environments,” said Dow Corning Electrical Global Marketing Manager Vittorio Salvatori.. “Additional benefits are seen in areas subject to vandalism,” he added.

Supplied as a high-consistency elastomer (either preformed or in bulk), these silicone formulations cure to a lightweight, shatter-resistant composite that helps suppress leakage current and arc tracking. The materials resist erosion and extend service life, especially in severe operating environments. Silicone insulators also resist the weathering effects of ultraviolet light, ozone and extreme temperatures, and have vastly superior mechanical shock properties when compared to ceramics, glass, epoxy or other rigid materials.

Reduced breakage during transportation and installation of silicone composites also helps utilities cut costs and inventory requirements. These lightweight, elastomeric designs allow easy power upgrades on existing ceramic insulated lines and significantly reduce installation costs on new lines.

Recent advancements in manufacturing technology have helped reduce material costs for silicone insulators, which has closed the price gap between silicone and porcelain components to the point where the purchase costs are similar. The utility demand has escalated so dramatically that virtually every major supplier of HV insulators now offers one or more silicone designs. The new silicone materials from Dow Corning exhibit easier mould flow, faster cure and less fouling than earlier generation materials, all of which have served to further reduce manufacturing costs.

Dow Corning HV 1650-50, 1660-65, 1666-65 and 1660-75 Silicone Rubbers are available in 1100-lb (500-kg) boxes, either preformed or in bulk. When stored at or below 50C (122F) in the original, unopened containers, the products have a usable life of 12 months from the date of manufacture.

http://www.dowcorning.com/rubber

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