GB660668A - Improvements in or relating to electric transformers - Google Patents

Abstract

660,668. Transformers. DOW CORNING, Ltd., and KUHLMAN ELECTRIC CO. March 11, 1949, No. 6781/49. Class 38 (ii). An air-cooled distribution transformer for outside use has a coil assembly comprising a high-voltage primary winding 36 disposed between two low-voltage secondary windings 43, 53, the primary winding being completely encased and sealed in a sheath of silicone rubber 38 and preferably with a sheath 40 of the silicone rubber between the coil layers. Specification 609,956, relating to the preparation and fabrication of the silicone rubber, is referred to. The secondary winding may be covered with an inorganic insulating material and preferably with either a resinous or rubbery silicone. Glass cloth may be used in conjunction with the silicone both as a coating for the conductors, between the coil layers and surrounding the whole coil assembly 45 which is impregnated and sealed with a silicone varnish. The coaxial windings may be disposed concentrically as shown or axially (Fig. 5, not shown) and the end turns of the primary winding may be separated by a cord 42 to prevent arcing under high voltage impulses. Beads 41 may be provided along the edge of the rubber sheets used between the coil layers to prevent the conductors slipping off the sheet during winding. The coil assembly on its strip core (Fig. 1, not shown) may be secured in a cradle extending across a cylindrical casing having perforations in its lower end and a cover spaced from the upper edge of the container. The high and low voltage terminals may respectively be carried by the cover and perforated end.