GB603721A - Improvements in and relating to the insulation of transformer end coils - Google Patents

Abstract

603,721. Transformers. MICAFIL, Ltd. Aug. 17, 1945, No. 21082. Convention date, Aug. 31, 1944. [Class 38 (ii)] In a method of insulating the end coils or end-coil groups of a liquid-immersed transformer with a cylindrical winding, the outermost end coil is first bound with a tape-like binding of insulating material and then superposed on the next or second coil and the two bound together in a similar manner, these being next superposed on the third coil and all three bound together, this process being repeated until the required number " n " of end coils are thus bound, thereby forming a graduated insulation which increases towards the end of the winding, after which the insulating coverings are cut along their circumferences in a plane perpendicular to the axis of the coils and bent upwardly to form a screen. Fig. 1 shows an arrangement wherein a core 17, surrounded by a cylindrical insulating sleeve 8 has applied to it a coil 1 associated with a protective metal ring 16 in a binding 9, these bound members being placed on the coil 2 and covered by an annular wooden former 18 to receive an enclosing binding 10. In a similar manner these members are associated with the coil 3 and annular wooden former 19 in a binding 11, and then associated with coil 4 and former 20 in a binding 12. The bindings 9-12 are then cut successively along the lower outer edges of the associated coils, commencing with the binding 12, and bent outwardly, as shown in Fig. 2, the wooden formers 20, 19, 18 being removed in succession and replaced by blocks 15, 14, and 13. The binding 9 around coil 1 may be cut open or left closed, as shown. The flanges 10-12 formed by the upturned insulation may be secured together either completely or at intervals by an adhesive, or they may be baked together with the aid of a polymerisible material. The cutting and bending may be done either before or after the end coils are fitted on the insulating cylinder. The arrangement may be employed for concentric sets of coils which are separated by cylindrical insulating screens, and in one example, Fig. 4 (not shown), a high-voltage winding consisting of two groups of coils is located between inner and outer low-voltage windings. The insulating material for the coils may consist of paper, presspahn, fibre layers soaked in synthetic materials, or foil made of thermoplastic material.