GB949509A - Improvements in insulators - Google Patents

Abstract

949,509. Insulators. COMPAGNIE GENERALE D'ELECTRO-CERAMIQUE. Feb. 14, 1961 [Feb. 24, 1960], No. 5432/61. Drawings to Specification. Heading H2C. An insulator has two end caps with a hollowone-piece insulating envelope extending between them, the internal surface of the envelope being formed to provide an internal leakage path longer than the external leakage path such that the internal surface has a flashover voltage in damp atmosphere greater than the flashover voltage of the external surface under dry conditions. The insulators particularly described each have a strong insulating core made, for example, of bonded glass fibre and cemented to the end caps. The desired result is achieved by providing annular fins or one or more helical fins on the inner surface of the envelope. Fins may also be provided on the core to ensure that arcing will occur across the outside of the envelope in preference to across the core leakage path, this result alternatively being achieved by filling the space between the core and envelope with an insulating filler. The filler may be a fluid such as a silicone grease or may be a solid such as a filled or unfilled resin or filled or unfilled sulphur. Because of differences in thermal expansion coefficients of the various materials a solid filler which adheres strongly to the core may pull away slightly from the flat portions between the fins on the inner surface of the envelope, or if instead the filler adheres strongly to the envelope it may pull away from the core in which case it is again desirable to form the core so as to increase its surface leakage path.