Patent GB-740670-A (GB)
Title: Electric blown fuse indicator
IPC: H02H3/04
Filed: 1953-12-30
Abstract: 740,670. Fusible cut-outs. CHASE-SHAWMUT CO. Dec. 30, 1953 [Jan. 2, 1953], No. 36194/53. Class 38 (1). In a blown fuse indicator, the high-frequency component inherent in the arc produced on blowing of the fuse is resonated in an oscillatory circuit to initiate the striking of a glow lamp. In Fig. 1, the fuse 2 is shunted by condensers 4<SP>1</SP>, 4<SP>11</SP> and the primary 51 of an air-cored step-up transformer 5. The secondary 5<SP>11</SP> is connected between earth and a control electrode 6<SP>111</SP> on the outside of a glow lamp 6, the internal electrodes 6<SP>1</SP>, 6<SP>11</SP> of which have a D.C. voltage continuously applied to them of a value between the firing voltage and the extinguishing voltage. On blowing of the fuse, the high-frequency component raises the intensity of the field between electrodes 61, 6<SP>11</SP> sufficiently to ignite the glow lamp which continues to glow until a switch 19 is opened. The transformer 5 may have a core (Fig. 2, not shown) to reduce its dimensions and the secondary may be connected directly to the electrodes 61, 6<SP>11</SP>, thus dispensing with the control electrode. In this embodiment, the D.C. voltage is fed through the secondary winding from a potentiometer with a change-over switch to provide a higher voltage for testing the glow lamp. Fig. 3 shows a similarly connected transformer and glow lamp 6 but the D.C. voltage is supplied through a rectifier 12 with a stabilizer 13. In this arrangement the primary 5<SP>1</SP> is connected to each of three parallel connected distribution lines 1<SP>1</SP>, 1<SP>11</SP>, 1<SP>111</SP>, containing fuses 21, 2<SP>11</SP>, 2<SP>111</SP>, through condensers 4, 4<SP>1</SP>, 4<SP>11</SP>, 4<SP>111</SP>. Two groups of fuses are shown and an indicator may be provided for each group. In a polyphase system (Fig. 4, not shown) a fuse in each phase is provided with an indicator lamp having an individual air-cored transformer and condensers. In Fig. 5 a further embodiment is shown wherein lines 1<SP>1</SP>, 1<SP>11</SP> are each provided with condensers 4<SP>1</SP>, 4<SP>11</SP>, a transformer 5 and a glow lamp 6, the lamps upon ignition operating electromagnetic relays 21, 22 to energize incandescent lamps 24, 25 to give a clearer indication of the blowing of one or both fuses. Fig. 6 shows a glow lamp 6, transformer 5 and lenticular-shaped condensers 41, 4<SP>11</SP> housed in a casing 30 to form a self-contained unit. The condensers may be separate (Fig. 7, not shown) and the lamp and transformer enclosed in a casting of . transparent plastic. To limit the distributed capacity of the transformer secondary, the winding may be made up of a number of separate serially-connected sections (Figs. 8 and 9, not shown). Where it is desired to operate two lamps 6 in parallel, a transformer having two secondaries 5<SP>11</SP>, Fig. 10, is employed connected as shown to the two lamps. These windings operate as H.F. chokes to accommodate slight differences in the firing voltages of the lamps. Fig. 11 shows a similar circuit for three lamps 6 except that each lamp is associated with a section 5<SP>11</SP> of the transformer secondary which is connected in -parallel with the other two sections.