GB193136A - Improvements in and relating to electric switches - Google Patents

Abstract

193,136. British Thomson - Houston Co., Ltd., (General Electric Co.). Nov. 16. 1921. Oil switches of the kind in which the high pressure of oil produced in an explosion chamber is employed to extinguish the arc, are arranged so that the circuit is broken in two stages, the pressure produced at the first break being utilized to extinguish the arc at the subsequent and final break. In the form shown in Fig. 1, a subsidiary contact rod 25 engages a fixed contact 14 within an explosion chamber supported from the lid of the oil tank. The lower end of the contact rod 25 carries a contact 24 with which the contact rod 15 engages. The rod 15 is carried by the operating member 18 and the circuit between the external terminals 11 is through the contacts 14, 25, 24, 15, bridging-bar 17 and the similar contacts on the other half of the switch, all in series. When the operating rod moves downwards, the rod 25 moves downwards with the rod 15 under the action of the spring 29. Circuit is 'thereby broken between the contacts 14, 25, and, immediately afterwards, the contact 24 reaches a series of insulating plates 23 and its movement is arrested so that further movement separates the second contacts 24, 15. The second arc is extinguished by a cool flow of oil passing between the plates 23 and resulting from the pressure produced by the first arc. The rod 15 may be tubular, open at its upper end and at a point near the member 17 so that oil may be ejected across the arc and through the tube. In a modified construction shown in Fig. 2, the second contact 34 is fixed and forms part of a hollow electrode 31 mounted centrally in the explosion chamber. When the rod 15 leaves the upper contact and enters the electrode, the arc is transferred thereto, and, when the rod leaves the electrode, a ball 36 carries the orifice. When, finally, the contact rod leaves the second contact, the arc is extinguished by the pressure of oil produced by the first arc escaping through the passage 38. In the upper part of the explosion chamber a hood 40 is arranged to retain a portion of the gases to act as a cushion and prevent undue shock. In a modification of the arrangement shown in Fig. 1, the lower contact is arranged within a bushing and the lower contact rod controls oil passages between the explosion chamber and the tanks to direct, the oil at the right moment across the arc.