Patent GB-438190-A (GB)
Title: Improvements in or relating to mercurial electrical cut-outs
IPC: H01H87/00
Filed: 1934-02-09
Abstract: 438,190. Mercury switches. JENKINS, F. T., and SPARKS, S. D., 43, St. Stephen's House, Westminster. Feb. 9, 1934, Nos. 4395 and 7563. [Class 38 (v)] A mercurial cut-out containing alternative mercurial paths for the current is so arranged that on the rupture of the mercurial fuse through one path the expelled mercury automatically directly or indirectly renders an alternative mercurial path available, an expansion space being provided between the fuses. As shown in Fig. 1, two tubes 2, 3 of ceramic material which may be externally ribbed or corrugated, enter opposite ends of a conducting cylinder 1 forming a mercury reservoir. The bore of each tube communicates with a small chamber 4 in an insulating block 5 having an inclined passage 6 leading into the cylinder 1. Either the chamber 4 or the passage 6 is lined with conducting material. A plunger 7 is located between the passages 6 and is impelled towards the opposite end of the cylinder 1 when mercury is ejected from one of the passages 6 due to rupture of the mercury column in one of the tubes 2, 3. Mercury is thus forced through the passage 6 in the opposite block 5 and hence into the corresponding ceramic tube so as to complete the mercury column therein. The lower ends of the tubes 2, 3 fit into conducting blocks 8 having pin connections 9. The ends of the cylinder 1 are closed by plugs 10, one of which has a pin connection 11. The whole apparatus is enclosed in a moulding 12 of insulating material. The pin terminals 9 are connected to a two-way switch 13, which may be incorporated with the moulding 12. Each of the mercury columns may be associated with a neon tube indicator 14, of the type described in Specification 397,105, for indicating which column is complete. The ceramic tubes 2, 3 may alternatively be coaxial with the cylinder 1 and fitted into its ends. In another construction, Fig. 6, the tubes 2, 3 are in planes parallel to the cylinder 1, their axes and that of the cylinder being disposed at the angles of a triangle as shown in Fig. 4. In a modification, Fig. 7, the two ceramic tubes are combined-into a single tube 16 in which rupture takes place, the alternative paths being provided by branches 17, 18 lined with conducting material. The plunger 7 is of conducting material and has three heads so spaced that when the plunger is in either of its extreme positions the central head occludes one of the branches 17, 18. The cylinder 1 is provided with conducting sleeves 19 separated by insulating sections 20, the length of the central sleeve 19 being such that the central head of the plunger 7 is always in contact with it. When the plunger is in the position shown, the circuit is completed through the right-hand pin terminal 9, right-hand sleeve 19, plunger 7, central sleeve 19, and mercury 17, On rupture of the mercury in the ceramic tube 16, mercury is expelled from the branch 17 and moves the plunger 7 to its left-hand position so as to make contact with the left-hand sleeve 19 and uncover the branch 18, into which mercury is swept by the motion of the plunger. Circuit through the branch 18 is completed when the switch 13 is moved to the left. The cylinder and plunger may be rifled to prevent rebounding of the plunger. In the construction shown in Fig. 9, the two ceramic tubes 2, 3 are attached to an insulating cylinder 1 by means of conducting blocks 21, 22 having insulating sleeves 23, 24 in which slide pistons 25, 26 suspended from a rocking lever 27. The piston 25, in the position shown, is in contact with the block 21, but when driven outwards owing to rupture of the mercury column in the tube 2 it bears only on the insulating sleeve 23, thus forming a supplementary point at which the circuit is broken. At the same time the piston 26 descends, makes contact with the block 22 and forces mercury into the tube 3. In a further modification, Fig. 10, the ceramic tubes 2, 3 communicate with chambers 30, 31 having metallic liners connected with the terminal 11 by a plate 32. Inclined passages 33, 34 and cross passages 35, 36 connect the chambers 30, 31 so that mercury ejected from one of the tubes 2, 3 reaches and fills the other tube. Two cut-outs may be arranged as branch lines, the mercury column of one being of greater current-carrying capacity than that of the other. A two-way switch may be provided for connecting either column in circuit and arrange to restore the cut-out of smaller capacity a given time after that of larger capacity has been switched in. The interior of the cut-out may be exhausted of air or filled with non-oxidizing gas. The mercury may be replaced by other liquids such as mercury amalgams. Means may be provided for temporarily bridging the terminals of the cut-out to which the switching means is normally connected, so that the alternative mercurial path becomes immediately available.