Patent GB-415414-A (GB)
Title: Improvements in and relating to insulation particularly suitable for use in electric transformers
IPC: H01F27/32
Filed: 1932-12-21
Abstract: 415,414. Electric transformers ; electric insulation; paper tubes. INTERNATIONAL GENERAL ELECTRIC CO., Inc., 120, Broadway, New York, U.S.A.- (Assignees of Allgemeine Elektricitõts-Ges.; 2, Friedrich Karl-Ufer, Berlin.) Dec. 21, 1932, No. 36236. Convention date, Dec. 21, 1931. [Class 38 (ii).] In a composite insulating body particularly suitable for separating the primary and secondary windings of a high tension electric transformer, comprising layers of paper or other material impregnatable with an insulating compound or oil and other layers of a stiffer insulating material, such as hard paper, serving as a mechanical support therefor, layers of conductive material are interspersed with the impregnated layers to modify the electric field. Fig. 1 shows high and low potential concentric transformer windings a, c respectively separated by an insulating cylinder d comprising layers of uncemented paper between cylinders e<1>, e<2> of hard paper made by cementing together by heat layers of varnished paper, and the cylinder d is provided with external metallic layers f<1> and f<3> and internal metallic layers f<2>-f<4>. The layer f is connected to the middle of the winding a which is earthed at its ends and the layer f<5> to the middle of the winding c. An additional cylinder of hard paper is advantageously provided between the cylinder d and the winding c. The impregnation may be effected before or after the assembling of the transformer. Fig. 2 shows a modified constrution in which the ends of the cylinder d are bent outwards across the ends of the winding a, the end portions e<3>, e<4> of the hard paper casings being separate from the central portions e<1>, e<2> and applied subsequently to the bending. The bent-over portions are also provided with annular discs e<5>, e<6> of hard paper. The superposed and interspersed metallic layers f<1>-f<4> are arranged about the two ends of the winding a, the layer f<1> being in each case connected to the adjacent end of the winding, and the layer f extending over the length of the cylinder d between the bends is connected the winding c. Impregnation may be facilitated by providing the hard paper layers with longitudinal and transverse grooves adjacent to the layers to be impregnated, by providing absorbent pieces or wicks to conduct the impregnating medium to the middle portions of such layers and by replacing the air around the layers by carbonic acid prior to the impregnation. The impregnated layers may be maintained under pressure, e.g. that of a column of cooling oil. Specifications 246,790, [Class 36], and 360,848, [Group XXXVI], are referred to. The Specification as open to inspection under Sect. 91 comprises also (1) a modified construction in which an insulating cylinder d, without the metallic layers, is placed between the windings a and c and hard paper rings of a right-angle cross-section are arranged near the ends of the cylinders d and around the end coils of the winding a, such end coils being narrower than the other coils of the winding ; (2) a similar construction comprising two of the cylinders d, the ring of right-angle cross-section adjacent the inner cylinder being of composite material similar to that of the cylinders d. This subjectmatter does not appear in the Specification as accepted.