GB929579A - Improvements relating to high-voltage insulating lead-in bushings and their manufacture - Google Patents

Abstract

929,579. Insulators. A. REYROLLE & CO. Ltd. Oct. 6; 1961 [July 7, 1960], No. 23827/60. Class 36. A high-voltage lead-in bushing insulator comprises a rigid cellular structure of foamed synthetic resin e.g. thermosetting casting resin where the individual sealed cells are filled with gas of high dielectric strength at a superatmospheric pressure. As shown, the bushing includes tapered insulating shells 10A and 10B, preferably of porcelain and solid cast resin respectively, their open ends being secured to opposite sides of a metal sleeve 11 which is mounted on a support 12. A conductor 13 extends through the centre of the bushing and the space around the conductor within the shells and the sleeve 11 is filled with a rigid cellular structure of foamed synthetic resin preferably an epoxy resin, a polyurethane resin or a poly; carbonate resin containing an electronegative gas e.g. CCl 3 F under a pressure of about 2 atmospheres the resin being stress-graded by cylindrical metal inserts 17. The method of forming the bushing comprises first fixing a dome to the sleeve 11, in the position of shell 10A, acting as a temporary support for the metal inserts 17 which are disposed around the conductor 13, liquid foamed resin then being poured in to occupy the lower third of the enclosure and prevented from increasing in volume by introducing an electronegative gas at high pressure above the level of the resin, the resin being subsequently cured. The temporary support is then removed, the resin providing support for the metal inserts, the shell 10A replaced and the rest of the volume around the conductor filled with a second batch of foamed resin, which is then cured. Specification 838,824 is referred to.