GB556491A - Improvements in and relating to impulse-protected electric fuses - Google Patents

Abstract

556,491. Protective arrangements. BRITISH THOMSON-HOUSTON CO., Ltd. April 23, 1942, No. 5447. Convention date, April 24, 1941. [Class 38 (iv)] [Also in Group XXXVI] A fuse having protection against disruption by impulses or lightning discharge currents (and which may be used in series with a lightning arrester) comprises a conductor having in series a fusible portion 106, Fig. 5, an electrode portion 110 and a flexible conduction portion 107, and is associated with means to increase the inductance of the fusible portion to impulse currents, and with a byepass circuit around the fusible portion including a spark gap of which the electrode 110 forms part. Three embodiments are described in which the conductor is subject to spring tension to withdraw the electrode on fusion and is housed in an insulating tube 109, closed at one end by a button head 105, connected to the fusible portion and open at the other. This combination forms a replacement element in an expulsion type fuse for overhead systems. Fig. 3 shows an insulating tube 41 carrying terminals 43, 44 for engagement with spring-clip circuit terminals in a cut-out box, a screw cap end terminal 53 to clamp the fuse head and a nut 51 to clamp the flexible conductor or pigtail 50. A ring 61 of magnetic material is arranged around the upper portion of the tube and a conductor 62 connects the terminal 53 with the terminal 43. The fuse tube 45 is perforated at 54 and a pin retained by a flange 56 and spring 57 on the terminal 43 constitutes, with the electrode 52, a spark gap in a shunt circuit round the fusible member 47. In other embodiments (Figs. 2 and 4) an inductance coil 29, 91 in series with the fuse member replaces the magnetic material. Fig. 4 shows a terminal 95 for clamping to an overhead line and an indicating arm 83 retained in place by the pigtail. The Figures show differing arrangements for providing the spark gap.