GB376828A - Improvements in or relating to high voltage electric switchgear - Google Patents

Abstract

376,828. Electric switchgear. REYROLLE & CO., Ltd., A., Hebburn-on-Tyne, and CHRISTIE, J., 4, Sidecliff Road, Sunderland. April 17, 1931, Nos. 11426 and 20530. [Class 38 (v).] The potential transformer fuses in H.T. switchgear structures are mounted within insulating tubes, each of which is surrounded by a metal tube constituting the innermost layer of a condenser type bushing insulator which supports the whole of the fuse unit in the cover of the potential transformer tank. As shown in Fig. 1, the fuse G is mounted within an insulating tube K and is provided with spring contacts G1 at its upper end bearing against a metal tube K<2> which is connected to the bearing K4 of the blade L of an insulating switch which normally engages a contact B<1> connected to the feeder B. The lower contact of the fuse G normally bears, as shown in Fig. 2, on a metal cap H<1> which is connected to one of the terminals of the potential transformer, the cap H<1> being screwed into a metal tube H which surrounds the lower part of the insulating tube K and which forms the innermost member of a condenser bushing F passing through the cover E<1> of the transformer tank E, the outermost member of the bushing F being in contact with the short earthed trunk E<2> connecting the transformer tank E with a depending portion of the structure. To grade the electric stresses in the insulating tube K when the fuse has blown and to prevent corona discharge from the thin fuse wire during normal working a number of short overlapping metal sheets K<3> are interleaved with the paper layers of the tube K, these condenser layers thus grading the stress between the lower end of the metal tube K<2> and the upper end of the metal tube H, which is at the same potential as the lower contact of the fuse. The fuse is provided with an insulating handle G<2> by which it may be withdrawn through the upper end of the insulating tube K. The upper end of the tube is provided with a pivoted flap J<1> which is interlocked with the operating mechanism of the isolating switch blade L so that the flaps may be raised only when the blade L is engaging an earthed terminal L<1>. Separate isolating switch blades D are provided for connecting the feeder terminals B<1> to the circuit-breaker terminals or for earthing the latter. A limiting resistance may be mounted above the fuse, especially when the fuse is of the liquid-filled type, so as to be connected in series with the fuse and to be removable with the fuse-holder. The various casings, including the insulating tube K, are oil-filled.