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Editor's note: The following article is Part III of a threepart series on the use of polymer insulation material:; in outdoor insulation applications. While usage has been steadily iwlcreasing over time, polymer insulating materials do not have the same level of standardization as porcelain. As with any technology that is not well standardized, misunderstanding and confusion result, which can influence user selection and application. The objective of this series is to review for users the benefits of polymer insulating materials. Material science, design, and processing considerations all influence performance and must be considered. Part III explores some ofthe material science aspects of silicone elastomer miaterials by using a unique hybrid insulator design as a case.T h e industry perception that polymer materials are generic or somehow similar in performance only on the basis of the claimed base polymer is incorrect. PART 111 INTRODUCTIONn previous parts of this series, general considerations for polymer materials were discussed. In Part 111, greater de-I tails of materials science will be presented, using :silicone elastomer and a hybrid line post insulator as the case study. This highly protected creepage, double-bell hybrid line post insulator is specially designed for very severe contamination application, and several leakage current monitoring studies have been conducted to confirm the efficiency of the design and materials.Electrical insulating polymeric formulations first introduced over 25 years ago have been proven to have excellent long-term physical and electrical properties [l]. Some early materials were originally designed for field application by heat shrinking and are based on radiation-crosslinked, semicrystalline polyolefin copolymers. When their excellent weatherability and moisture-sealing properties were demonstrated in cable accessories, the use of these materials was expanded to such applications as surge arresters, insulators, insulation enhancement, and bushings. Whereas polyolefin copolymer-based formulations have definite advantages, other developmental materials research has taken place over many years in order to fully exploit the properties achievable with elastomer-based insulation materials.At Raychem, materials development is recognized as a complex formulation process in which the entire package is optimized, considering each of the steps involved in producing the final product. The base polymer grade and various additives that are used, combined with compounding procedures, material processing, product design, and assembly, all contribute to the overall product performance. The industry perception that polymer materials are generic or somehow similar in performance only on the basis of the claimed base polymer is incorrect. Performance is based on the specific characteristics of a unique formulation, utilizing a specific design produced under a defined set of process conditions. Products need to be individually evaluated by users. Consideration needs to be given to the reput...

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