Patent GB-190823515-A (GB)
Title: Improvements in and relating to Electric Switch Arrangements.
Filed: 1908-11-03
Granted: 1909-10-28
Abstract: 23,515. Field, M. B., and Ferranti, Ltd. Nov. 3. Cut - outs ; switches.- Automatic switches for single-phase or polyphase alternating currents, in which transformers are utilized to supply current for the automatic operation, are provided with power-reducing means associated with the trip device. As shown in Fig. 1, which shows a switch in the closed position, the tripping action is brought about by the energization of a coil c from a transformer a<1>, a<2>, and the consequent rise of a plunger e. A trigger-lever i is turned to the right on being struck by the plunger, and a cam j, which it previously locked, is free to rotate. A strained spring q, acting through gearwheels on a pinion on the axle of the cam in such a manner that the force applied at the holding point is considerably reduced, produces the rotation of the cam and its associated parts. That part immediately attached to the spring q has a slot s, into which, while the switch remains closed, fits a pin and roller p carried by the switch handle a. The slotted part turning under the influence of the spring towards a position indicated by dotted lines frees the pin p, and the switch is opened by springs (not shown), or by the weight of its parts. After the pin has escaped, the slotted member is prevented from moving too far by means of a stop r, and lies ready, when the switch is closed, to be moved back with the pin and held by the trigger i falling behind the tooth of the cam. For a threephase switch, three tripping-magnets are provided, one energized from each phase, and are arranged so that any one will produce the tripping-movement. In the high-tension oil-switch shown in Fig. 7, the transformers 39 are of ring form, placed around the leading-in insulators 38. The central straight conductors constitute the primaries ; the secondaries are wound, as shown in Fig. 6, on a core of annular stampings. In a switch to operate on reverse current, the trip-coil c, Fig. 12, is in two sections, respectively energized by shunt and series transformers. The series transformer is similar to those described in connexion with Fig. 7, and has a core designed to be saturated before it becomes powerful enough, on the occurrence of an abnormal current, to furnish a current capable of working the trip without the co-operation of, or in opposition to, the current furnished by the potential transformer. On a low-voltage circuit, a potential winding, connected directly across the mains without the intervention of a transformer, is combined with a separate coil energized from the series transformer. In a free-handle switch, Fig. 9, the trigger, cam, gearing, spring, and slotted member are all enclosed in a dustproof box attached to the handle. The pin 12, which comes into temporary engagement with the slotted member 13, is carried by a bar linked to the switch contact frame and pivoted independently of the handle. The coils for working the striker a are enclosed in a dust-proof case 8. A thermally-released switch, Figs. 13 and 14, has a modified form of trigger lever i. actuated by the longitudinal movement of a spindle x, which is attached to a coiled spring z and to hot wires y in such a manner that extension of the wires is taken up by the spring. The hot wires are connected to series transformers in the respective phases of the circuit by clamps 3, on flexible conductors 2. The position of the clamps is altered to adjust for sensitiveness. The sensitiveness may also be adjusted by resistances. To cause hot wires to act as no-voltage release devices, they are energized from potential transformers, and the straightening or shortening of the wires is transmitted to the trigger-piece.