Hybrid outdoor insulators

Attempts to reduce outdoor insulator problems caused by exposure to wetting, weathering, contamination, and vandalism are examined. Three main approaches are discussed: (1) improving the insulator´s shape, both to get longer creepage distance and to improve pollution catch and wetting characteristics; (2) changing the nature of the surface so as to defeat contamination and wetting; and (3) reducing the insulator´s brittleness, i.e. susceptibility to fracture, by changing the material. A hybrid insulator consisting of a cylindrical ceramic interior, elastomeric sheath, and sealant is described that meets the requirements. The first commercial application, a 25-kV railroad insulator consisting of a 75-mm diameter porcelain rod, a finned sheath applied by heat-shrinking, and a mastic sealant has proved highly satisfactory both indoor tests and at naturally polluted stations. The impact resistance results showed that the hybrid insulator resist a shotgun blast.<>