GB1087594A - Electrical apparatus - Google Patents

Abstract

1,087,594. Transformers. WESTINGHOUSE ELECTRIC CORPORATION. Oct. 7, 1965 [Oct. 23, 1964], No. 42606/65. Heading H1T. A dry, air-cooled transformer, Fig. 6, has concentric high-voltage and low-voltage windings 18 and 20 carried by laminated core sections 16 (14, Fig. 1), each winding comprising copper or aluminium strip or foil 30, 42. The turns 30 are insulated by an enamel coating 40, e.g. epoxy resin, disposed on the strip, are wound on a plastics tube 32, and are encapsulated in cast solid insulating thermosetting material 34 e.g. epoxy resin with a filler of beryllium aluminium silicate, said material 34 having the same coefficient of thermal expansion as the strip 30. The turns 42 are insulated by an enamel coating or insulating sheets 44. A glass tape 48 surrounds the winding 20, or, if the transformer is to be fluid-cooled or disposed under ground, the winding 20 may also be encapsulated with the same material. A casing (54, Figs. 1, 2) may have a corrugated base, and aluminium cooling ducts (60, Figs. 5, 3) may be provided in the windings. To reduce voltage stress the encapsulated winding 18 is coated with a conductive varnish (70) and a stress grading paint (72, Fig. 4) containing silicon carbide. In another embodiment (Figs. 7 -11) the low-voltage winding (90) is wound on a tube (92) and is encapsulated in cast insulation (100), and the high-voltage winding (102) is wound on the insulation (100) and further insulation (110) is cast around the winding (102). A conductive shield is embedded in the insulation (100) and a waterproof coating (111), e.g. unfilled epoxy resin, may be applied to the insulation (110). The transformer may be disposed in a metal casing (88) containing coolant (89), e.g. a gas SF6, or askaral, oil, water with a rust inhibitor. Alternatively, in the latter case, the core may contain a waterproof coating. If liquid cooled, the outer surface of the encapsulated winding (120) may be roughened to create nucleate boiling. In a further embodiment (Fig. 12) a dry transformer having encapsulated high- and low-voltage windings has its insulated high- and low-voltage leads (148, 142) provided with bayonet connectors (155, 157) for connecting to the primary and secondary circuits. The transformer is mounted on a carriage (136) supported by guide rails (140). In a still further embodiment (Fig. 13) a dry transformer having both windings encapsulated is buried in the earth. Its insulated high-voltage and lowvoltage leads (166, 168) and (170, 172) are connected to primary and secondary power leads (204, 206) and (171, 173) through insulating waterproof connectors (202, 200). The transformer is cooled by a surrounding heat sink comprising a rubber or polyethylene bag (182) filled with sand or gravel, and water.