26/01/2014
Polymer insulator
The most acceptable &applicable standard for polymer insulators is IEC 61109 which stipulates design, type, sample and routine tests. But actually speaking, the existing standards have been tailored from tests specified for porcelain (hydrophilic surface) that have not shown good correlation with actual service experience when applied to composite materials (hydrophobic surface) and therefore results from the tests are often misinterpreted. In particular, it has proven very difficult to develop test conditions that accurately duplicate material degradation which occurs during long term service. Further problem of existing laboratory tests is that they are long time consuming tests. However, EPRI, Research Center in the USA has set up Accelerated Aging Chamber in which a specific insulator design can be subjected to electrical, mechanical, and environmental stresses that closely resemble the actual service environment. A computer-controlled environmental system simulates predefined climatic conditions inside the chamber by varying temperature, clean fog, salt fog, clean rain, UV radiation, humidity and pollution. The computer-controlled accelerated multi-stress aging test allows simulating thirty years of aging in three years or so thus allowing to evaluate different types and designs of polymer insulators.
Polymeric transmission line insulators offer significant advantages of better leakage distance, light in weight, low power loss (1/10th of the conventional) etc over porcelain insulators. With due care to the formulation; product manufacture and design; polymer insulators will perform exceedingly well even in heavily-contaminated regions. But the word of caution is that the term silicone elastomer or rubber comprises a large family of synthetic rubbers which may have different properties depending on chemical composition, vulcanization process, filler material, filler content and additives. The growing market for alternative materials in high-voltage insulation components is spurred largely by a need to reduce overall costs. Therefore, standards are required to be evolved to specify the dielectric properties, physical properties, and processing characteristics of the compounded silicon material. The crux is that the refinement of test apparatus and procedures specifically for polymeric materials remains an area of focus for utilities, manufacturers and research organizations.
